Studies of Some Novel Coordination Compounds and their Application in Nanoparticle Synthesis

CONTENTS

CHAPTER-1: Introduction
Introduction
1.1. Schiff Base Complexes
1.2. Nanotechnology
1.3 Biological studies of Schiff base complexes and nanoparticles
1.4 Selection of ligand and Aim of the study
References

CHAPTER-2: Materials and methods
2.1. Materials
2.2. Analytical methods and Physical Measurements
2.3. Biological studies
References

CHAPTER-3: Synthesis, Characterization and biological activity of 1-benzylidene/ 1,4-dibenzylidenethiosemicarbazide complexes of Zn(II), Cd(II) and Hg(II): New single source precursor in pyrolytic synthesis of metal sulphide nanoparticle
Introduction
3.1. Experimental
3.2. Results and Discussion
3.3. Antibacterial screening
References

CHAPTER- 4: Synthesis, characterization and biological activity of 1,4-bis((1 H -pyrrol-2-yl)methylene)thiosemicarbazide complexes of Zn(II), Cd(II) and Hg(II): New single source precursor in metal sulphide nanoparticle synthesis
Introduction
4.1. Experimental
4.2 Results and Discussion
4.2. Antibacterial Activity
References `

CHAPTER- 5: Synthesis, Characterization and biological Tetraethylthiuram disulphide complexes of Zn(II), Cd(II) and Hg(II): New single source precursor in pyrolytic synthesis of metal sulphide nanoparticle
Introduction
5.1. Experimental
5.2. Results and Discussion
5.3. Antibacterial Screening
* References

CHAPTER I Introduction

S tarting way back from Werner’s1 theory to the most modern Ligand Field Theory or Molecular Orbital Theory, coordination chemistry has been changed entirely not only its theoretical aspects but also in its experimental dimensions and attained different shape and form. On its firm theoretical and experimental foundation, it has transformed itself from a minor section of inorganic chemistry into a vast interdisciplinary chemistry. It appeared actively developing biocoordination chemistry, homogeneous catalysis, 2 analytical, organometallic, 3 solid state chemistry and the area of advanced materials, 4 including photonics and liquid crystal materials, 5 molecular ferromagnets 6 etc. Coordination chemistry is now recognized as an independent discipline covering a wide range of areas from medicine to environment. In the recent past, there has been a great upsurge in the studies of metal complexes of bioinorganic and medicinal relevance. The discovery and basic concepts of medicinal inorganic chemistry have been recently reviewed. 7-9

The development of complexes for application in medicine is an obvious example of investigation and creativity. The remarkable example being cisplatin, cis -PtCl2(NH3)2 introduced by Barnett Rosenberg 10 in 1965, which is successfully employed worldwide as an anticancer drug. 11, 12 The antitumour activity of Cu (I) and Cu (II) complexes have also attracted much attention. 13 In-vivo antimetastatic activity of NAMI- A14-19 and cholorectal anticancer activity of KP 1019, have invited scientist to work on ruthenium sulphoxide complexes. 20-22 R. Wai-Yan Sun et al. 23 have described their work on several classes of gold(III), platinum(II), ruthenium(II, III, IV), iron(II) and vanadium(IV) complexes for anti-HIV and anticancer activity.

Nanoparticles have attracted great interest in recent years because of their unique chemical and physical properties, which are different from those of either the bulk materials or single atoms. Nanostructure materials have potential applications in ceramics, optoelectronics and catalysis. 24 Research on the synthesis of nanomaterials using metal complexes as precursors has been less reported. Application of metal complexes as precursors may be helpful to control the physical properties of metal nanoparticles. 25 In the last few years, researchers have characterized the tunable properties by altering the nanostructure size, shape, and chemical composition and have developed reproducible strategies to make nanostructures of desired properties. 26-28 It has been already proved that by controlling the size of the particle and manipulating surface structures of the semiconductor materials, the electronic, magnetic, mechanical, and chemical properties can be modified to suit a wide range of device application in many fields. 29 Synthesis and characterization of nano-structures are important for scientific and industrial applications. 30

Multidentate Schiff base ligands have played an important role in the development of coordination chemistry due to their preparative accessibility and spectral properties. Schiff bases and their complexes embrace very wide and diversified subjects such as, catalysis, 31, 32 reversible oxygen transport, 33, 34 various aspects of bioinorganic chemistry, 35-40 biological activities, 41-44 clinical 45 and analytical fields. 46-48

1.1. Schiff base complexes:

The chemistry of Schiff base and its application have received renewed attention because of their preparative accessibility, diversity and structural variability. Presently, there is a growing interest in the coordination chemistry of structurally modified bio-ligands. Transition metal complexes with potential biological activity are the focus of extensive investigations. Primary, secondary and tertiary amines can add to aldehydes and ketones to give different kinds of products. Primary amines give imines and in contrast to amines in which the nitrogen is attached to hydrogen, these imines are stable enough for isolation.

However, in some cases, especially with simple R groups, they rapidly decompose or polymerize unless there is at least one aryl group on the nitrogen or the carbon. When there is an aryl group, the compounds are quite stable. They are usually called Schiff bases, and this reaction is the best way to prepare them. The reaction is straightforward and proceeds in high yields. The initial N–substituted hemiaminals lose water to give the stable Schiff base.
Due to the easiness and simplicity in preparation of Schiff bases by the condensation between aldehydes and amines, Schiff bases are considered as privileged ligands in coordination chemistry. These ligands are able to co-ordinate with many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations as well as in many other fields. The Schiff bases contain an azomethine group and have tendency to donate the lone pair of electrons present on the nitrogen atom of the azomethine moiety (–CH=N). The donating property of the lone pair of electrons increases when a functional group such as –SH or –OH is sufficiently near to the azomethine moiety and this facilitates the formation of stable metal complexes.

So the Schiff bases derived from an amine and any aldehyde are an important class of compounds which coordinate to metal ions via the azomethine nitrogen 49 and their metal complexes play a key role in our understanding of the coordination chemistry of transition metal ions. 50 There is considerable interest in the chemistry of transition metal complexes of ligands containing oxygen, nitrogen and sulphur donor atoms due to the carcinestatic, antitumour, antiviral, antifungal and antibacterial activity and industrial uses. 51, 52

Schiff base complexes have remained an important and popular area of research due to their simple synthesis, versatility and diverse range of applications. Schiff base complexes are used as catalyst in some chemical processes, as biological models for understanding the structures of bio-molecules and to emulate the activity of proteins. 53, 54 Several azomethines were reported to possess remarkable antimicrobial, 55-57 anticancer 58 and diuretic activities. 59 Schiff bases and their complexes were recently found to have significant antitumor and biological activity. 60, 61 During the last decade, the coordination chemistry of Schiff bases derived from heterocyclic carbaldehyde has received much attention. 62-63

1.1.1. Applications of Schiff base complexes

Schiff base and its complexes are widely used in biology, medicine, catalysis 64-66 and corrosion. 67 They can not only interact with DNA, 68 but also show good biological activity such as anti-bacterial, 69 antifungal, anti-viral, anti-inflammatory, 70 sterilization, herbicidal and antitumor agents. 71-73 Many Schiff base complexes exhibit excellent catalytic activity in the reaction of ring opening, polymerization, sulfide oxidation, etc. Some aromatic Schiff bases are usually used to inhibit copper corrosion. Also, Schiff base can display different optical properties from the ligand itself and be used as a fluorescent probe. Owing to different donor sites on Schiff base, it exhibits high sensitivity and selectivity as the fluorescent probe and can recognize metal ions selectively. In Schiff base metal complexes, the environment at the coordination center can be modified by attaching different substituent to the ligand, which provides a useful range of steric and electronic properties essential for the fine-tuning of structure and reactivity. Therefore, Schiff base ligands are among the most fundamental chelating systems in coordination chemistry 74, 75 and complexes of both transition and p-block metals based on this type ligands were shown to catalyse a wide variety of reactions. 76-78

The Schiff-base ligands have also received more and more attention, mainly because of their wide application in the fields of pharmaceutical industry, polymer industry, agriculture, dyes and pigment industries and organic synthesis, 79, 80 solid phase extraction of metal ions 81 and various types of polymerization. 82 Furthermore, Schiff bases and other macrocyclic ligands as well as their complexes are widely used for the preparation of highly selective polymer membrane electrodes, 83-87 optical sensors and biological probes. 88-90 This attention is still growing and considerable research effort is still devoted to the synthesis of new Schiff-base complexes with transition 91, 92 and main group metal ions. 93-95 Some Schiff bases have also been used as analytical reagents, flocculants and inhibitors against corrosion.

The Schiff bases exhibit important properties such as antibiotic activity 96 and antimicrobial activity. 97 The Schiff bases prepared by the condensation of aldehydes and various amines have been reported to have the antitumor activity against leukemia 98 in rats. The Schiff base 2-arylidine-amino-5-aryl-1,3,4-thiadiazoles have been reported to have fungicidal 99, 100 and bactericidal activites 101 against microorganisms. Hodnett et al . 102 have reported that the carbonyl part of the Schiff bases play the key role in antitumor activity. They have also observed that antitumor activity is enhanced by the introduction of an electron withdrawing group in the benzene ring near to the azomethine group.

It has been observed that the Schiff base prepared by the condensation of arylamine and o and p–substituted benzaldehyde are potential anticancer agents. 103 Zikolova et al. 104 have observed that the Schiff base stimulates the central and peripheral system. The Schiff base pyridine–4–carboxaldehyde–isonicotinyl–hydrazone and its transition metal complexes show good antibacterial activity 105 against Klebsiella penumonia , E. coli and Staphylococcus . Some Schiff bases with a substituted amino group, like 4,5–dibromosalicylanilide have been reported to possess antituberculor activity. 106

A number of Schiff bases and their transition metal complexes have been used in dyeing and pigment industries 107 due to their colour imparting nature. The dyeing of object incorporating a water soluble group in the aldehyde part of the Schiff base or by transition metal complex formation. 108 The Schiff base in combination with other dyes have been used for dyeing hydrophobic materials 109-111 like wool, cellulose, polyacrylonitrile, polyamide, polyesters, etc.

The Schiff bases and their metal complexes have extensively been used in resin and polymer industries. The Schiff base have been used to prepare highly elastic polymers from polyvinyl chloride. 113 By incorporating the Schiff base an epoxy resin with increased durability has been prepared. The Schiff base obtained from isophthaldehyde and 4,4'–diaminodiphenyl sulphide reacts with bisphenolepichlorohydrin polymers to give a resin which is used as the coating material. 114

Several Schiff base complexes have been used as an oxidizing agent for the oxidation of phenols. 115 A novel polymeric Schiff base 116 was synthesized by the reaction of 2,4–dihydroxy benzaldehyde and aniline with acryloyl chloride and was polymerized in methyl ethyl ketone with benzoyl peroxide as a free–radical initiator. A thiosemicarbazone Schiff base 117 was introduced by Divinyl benzene (DVB)–crosslinked polystyrene and was used to prepare several chelates of Fe(III), Co(II), Ni(II), Cu(II) and Zn(II). Schiff base 2,4–dinitrophenylhydrazone and their derivatives of Cu(II), Co(II) and Ni(II) complexes have been synthesized and their antimicrobial activity was also studied. 118 Recently, some chiral Schiff base ligands 119 were also synthesized, characterized and their catalytic applications were also studied.

1.1.2. Sulphur containing Schiff base ligand

Schiff bases have often been used as chelating ligands in the field of coordination chemistry and their metal complexes are of great interest for many years. During the past few decades a great deal of interest has been centered on metal complexes of chelating agents containing mixed donor atoms such as oxygen, nitrogen and sulphur. The interest in this field has been stimulated for the following reasons :

(i). Ligand incorporating donor atoms at both medium crystal field strength (nitrogen donors) and low crystal field strength (sulphur ligands) might lead to complexes of unusual stereochemistry and with anomalous magnetic and spectroscopic properties;

(ii). Biological activities may be expected for some of these compounds. In fact, sulphur-nitrogen ligands and their metal complexes have been reported to possess antiamoebic, 120,121 antiviral, 122 antibacterial, 123 antipyretic, 124 fungicidal, 125 analgesic 126 and cancerostatic (anticancer) activities. 127-130 On a more general basis, ligands containing sulphur as one of the donor functions, and the transition metal complexes thereof, have been subject of intense research due to their biological activities. 131, 132

It is well known that the S atom plays a key role in the coordination of metals at the active sites of numerous metallobiomolecules. 133 Schiff base metal complexes have been widely studied because they have industrial, antifungal, antibacterial, anticancer and herbicidal applications. 134, 135 They serve as models for biologically important species and find applications in biomimetic catalytic reactions. Chelating ligands containing S donor atoms show broad biological activity and are of special interest because of the variety of ways in which they are bonded to metal ions. It is known that the existence of metal ions bonded to biologically active compounds may enhance their activities. 136-138 The variety of possible Schiff base metal complexes with wide choice of ligands, and coordination environments, has prompted researcher to undertake research in this area. 139 Copper complexes containing N/S ligands are of interest as models for the CuA center of cytochrome-c oxidase (CcO). 140 Research focused on this topic resulted in the design of tailored ligands including C6H4(CHNC6H4S)2, iso-abt, which has two discrete N/S donor sets connected via the m-xylene spacer for use in Cu(I) coordination chemistry. Iso-abt belongs to the group of ligands containing N/S donor functions attatched to an aromatic ring system. 141 Thiosemicarbazones are considered as an important class of nitrogen–sulfur donor ligands because of their highly interesting chemical, biological and medicinal properties. 142, 143 These ligands possess both hard nitrogen and soft sulfur donor atoms in their backbones by virtue of which they are capable of coordinating with a wide range of metal ions, forming stable and intensely coloured metal complexes, of which some have been found to exhibit interesting physicochemical properties 144 and potentially beneficial biological activities. 145-148 Although a very large number of metal complexes of thiosemicarbazones and dithiocarbazates have been reported, The biological activity of thiosemicarbazones is related to their chelating ability with transition metal ions, bonding through N, N, and S atoms 149 or O, N and S atoms. 150-152 The presence of substituent at the 4-position has been shown to affect the activity of thiosemicarbazones and their metal complexes. 153 For example, metal complexes of 2-acetylpyridine thiosemicarbazones are found to exhibit increased antineoplastic activity when the N atom in the 4-position is part of a hexamethyleneiminyl ring instead of being a propyl- or dipropyl-containing amine group. 154 Metals bound to atoms such as N, O and S and can form a chelate ring that binds the metal more tightly when compared to the non chelate form. Large biological molecules (proteins, enzymes, DNA, etc.) are electron-rich but metal ions are electron-deficient. Therefore, interactions occur between metal ions and many important biological molecules. This event has led to the use of metals or metal containing agents to modulate biological systems. 155

1.1.3. Brief overview on Schiff base complexes and ligands

In 2006, M. M. Omar et al. 156 have reported metal complexes of Schiff base derived from 2-furancarboxaldehyde and 2-aminobenzoic acid (HL). The complexes are found to have the formulae [M(HL)2](X)n·yH2O (where M = Fe(III) (X = Cl, n = 3, y = 4), Co(II) (X = Cl, n = y = 2), Ni(II) (X = Cl, n = y = 2), Cu(II) (X = Cl, n = y = 2) and Zn(II) (X = AcO, n = y = 2)) and [UO2(L)2]·2H2O. The ligand and its metal complexes have shown good biological activity against some bacterial species.

In 2007, S. Rayati et al. 157 have synthesized (Fig 1.8) new [di-μ-oxo bis[oxovanadium (V)] complex containing tridentate ligand of 1:1 condensation of 1,2-propylenediamine and 2′-hydroxy-4′-methoxyacetophenone. This complex is used as catalyst for the selective epoxidation of cyclooctene to cyclooctene oxide with tert-butylhydroperoxide (TBHP) selectively.

In the same year E. Canpolat, et al. 158 have synthesized 4-hydroxysalicylaldehyde-p-aminoacetophenoneoxime (LH) from p-aminoacetophenoneoxime and 4-hydroxysalicylaldehyde and the metal compexes have been characterized by elemental analyses, IR, 1H- and 13C-NMR spectra, magnetic susceptibility measurements and thermogravimetric analyses (TGA).

M. N. Ibrahim et al . 159 prepared Schiff bases N-(4-(N, N-Dimethyl- amino) benzylidene) naphthalen-1-amine (I), N-(4-Nitrobenzylidene)naphthalen-1-amine (II), N-(4- Chlorobenzylidene) naphthalen-1-amine (III), Sodium-4-(4-(N,N-dimethylamino)benzylideneamino)naphthalene-1-sulfonate (IV), Sodium-4-(4-nitrobenzyli-deneamino) naphthalene-1-sulfonate(V), Sodium-4-(4-chlorobenzylidene amino)-naphthalene-1-sulfonate (VI) through condensation of 1-naphthylamine and 4-amino-1-naphthalene sulfonic acid with the corresponding aldehyde derivatives (p-(N,N-dimethylamino)benzaldehyde, p-nitrobenzaldehyde, p-chlorobenzaldehyde). These Schiff bases were used as fluorimetric analytical reagents and show fluorescent properties in acid-base medium. These compounds are excellent indicators due to the colour change over a wide pH range.

Yu-Guang Li et al. 160 have synthesized six new transition metal complexes (M = Cu(II), Ni(II) and Mn(III)) of tridentate (H2L1, HL2) and/or bidentate (HL3, HL4) Schiff-base ligands, obtained from the condensation of salicylaldehyde with glycine, N-(2-aminoethyl)morpholine, 4-(2-aminoethyl)phenylic acid and 4-(2-amino ethyl)benzsulfamide, respectively, and structurally determined by X- ray analysis.

In 2008, Y. Xiao et al. 161 have reported a newly synthesized L-glutamine-containing copper complex has proteasome-inhibitory activity in human breast cancer and leukemia cells. The inhibition of the tumor proteasomal activity results in the accumulation of ubiquitinated proteins and ubiquitinated form of I-kappa, B-alpha, a natural proteasome substrate, followed by induction of apoptosis. Furthermore, this glutamine Schiff base copper complex selectively inhibits the proteasomal activity and induces cell death in cultured breast cancer cells, but not normal, immortalized breast cells. Their data suggest that glutamine Schiff base copper complexes have a potential use in cancer treatment and prevention.

In the same year N. A. Negm and M. A. Zaki 162 have synthesized novel series of nonionic Schiff bases. These Schiff bases and their complexes with Cu and Fe showed antibacterial activity against Staphylococcus aureus , Pseudomonas aureus, Candida albicans, Bacillus subtilis and Escherichia coli and their fungicidal activity against Aspcrgillus niger and Aspcrgillus flavus.

M. P. Sathisha et al. 163 have synthesized some metal complexes of Co(II). The bidentate ligand was obtained by condensation of N,N′-thiocarbohydrazide with 3-acetylcoumarin. The compounds have shown promising cytotoxic activity when screened using the in-vitro method and at the same time showed to have good activity when tested using the Ehrlich Ascites Carcinoma model.

In the same year S. Rayat et al. 164 have synthesized oxovanadium(IV) complexes of tetradentate Schiff base ligands, derived from aromatic aldehydes and aliphatic diamine (2,2′-dimethylpropandiamine) and characterized. The catalytic potential of these complexes was tested for the oxidation of cyclooctene and styrene using tert-butylhydroperoxide (TBHP) as oxidant. Excellent selectivity of epoxidation for cyclooctene and good selectivity for styrene were obtained.

K. A. Melha and J. Enzy 165 reported the Schiff base ligand, oxalic bis[(2-hydroxybenzylidene)hydrazide], H2L, derived from 2-hydroxybenzaldehyde with oxalylhydrazide and its Cu(II), Ni(II), Co(II), UO2(VI) and Fe(III) complexes were prepared and tested as antibacterial agents. These metal complexes exhibited high antibacterial activities.

N. M. Hosny et al. 166 have prepared metal complexes of Cu(II), Co(II), Ni(II), Cr(III), and Fe(III) chlorides with the tridentate Schiff base ligand (L) derived from the condensation reaction between leucine and 2-acetylpyridine.

In 2009 S. A. Shaker et al. 167 have prepared bidentate Schiff base having nitrogen and oxygen atom by the condensation of the p -amino-2,3-dimethyl-1-phenyl-3-pyrozoline-5-on with salicylaldehyde in methanol. Schiff base has been characterized using FTIR, UV-Vis spectroscopy, Elemental analyses, atomic absorption technique. The magnetic susceptibility and the conductivity have also been measured.

In the same year N. Raman et al. 168 have synthesized five novel copper(II) complexes using Schiff base ligands, synthesized by the condensation of anthranilic acid and Knoevenagel β-ketoanilide condensates (obtained by the condensation of acetoacetanilide and substituted benzaldehydes). The in-vitro antimicrobial activity of the compounds is tested against the bacteria E. coli, S. typhi, S. aureus, K. pneumoniae and P. aeruginosa and fungi A. niger, R. stolonifer, A. flavus, R. bataicola and C. albicans by well diffusion method. The complexes show stronger antimicrobial activity than the free ligands.

M. M. Omar et al. 169 have prepared novel Schiff base (HL) ligand via condensation of 4-aminoantipyrine and 2-aminobenzoic acid. The metal complexes were found more potent/antibacterial against Escherichia Coli , Pseudomonas aeruginosa , Staphylococcus Pyogones and Fungi (Candida).

H. Mihara et al. 170 have synthesized a new heterobimetallic Ga(O-iPr)3/Yb(OTf)3/Schiff base 2d complex for catalytic asymmetric α-additions of isocyanides to aldehydes. Schiff base 2d derived from o-vanillin was suitable to utilize cationic rare earth metal triflates with good Lewis acidity in bimetallic Schiff base catalysis. The Ga(O-iPr)3/Yb(OTf)3/Schiff base 2d complex promoted asymmetric α-additions of α-isocyanoacetamides to aryl, heteroaryl, alkenyl, and alkyl aldehydes in good to excellent enantioselectivity (88−98% ee).

F. Xue-song et al. 171 have synthesized four Schiff base Zinc (II) complexes with either benzo-10-aza-crown ether pendants or morpholino-pendants and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalysed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have been also examined. The rate increases with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis.

H. H. Monfared et al. 172 have prepared tridentate Schiff base ligands derived from aromatic aldehydes and benzhydrazide, and their iron complexes [Fe(L1)(HL1)], [Fe(HL1)Cl2(CH3OH)]·(CH3OH) and [Fe(HL2)Cl2(H2O)] and characterized (H2L1 = (E)-N′- (2-hydroxy-3-methoxybenzylidene)benzohydrazide, H2L2 = (E)-N′-(5-bromo-2-hydroxybenzylidene)benzohydrazide). The catalytic potential of these complexes has been tested for the epoxidation of cyclohexene, cyclooctene, norbornene, cis- and trans-stilbene using tert-butylhydroperoxide (TBHP) as oxidant.

S. Chandra et al.173 have synthesized transition metal complexes of Co(II), Ni(II) and Cu(II) metal ions with general stoichiometry [M(L)X]X and [M(L)SO4], where M = Co(II), Ni(II) and Cu(II), L = 3,3’-thiodipropionic acid bis(4-amino-5-ethylimino-2,3-dimethyl-1-phenyl-3-pyrazoline) (pentadentate ligand) and X = NO3-, Cl- and OAc-. The nickel(II) complexes were found to have octahedral geometry, whereas cobalt(II) and copper(II) complexes were of tetragonal geometry. The ligand and its complexes have been found good antifungal and antibacterial activities against fungi and bacteria.

A. D. Khalaji et al. 174 have synthesized new {[CoIII(μ-salpn)(μ1,1-N3)2]Na}n (1) complex, involving Schiff base [H2salpn= (N,N′-bis(salicylidene)-1,3-diaminopropane)] and large excess of sodium azide (NaN3) and characterized by single crystal X-ray diffraction analysis. The crystal structure shows polymeric 1D complex generated by the hexadentate Schiff base salpn2− and two crystallographically different azide ligands.

R. M. Issa et al. 175 have been synthesized Full-size image (17K) a series of metal complexes of bidentate Schiff bases derived from condensation of sulfa-guanidine with 1-benzoylacetone (H2L1), 2-hydroxybenzophenol (H2L2), dibenzoylmethane (H2L3), 5-methylisatine (H2L4), and 1-methylisatine (H2L5). All complexes were found most effective on Gram negative, Gram positive bacteria, and fungi (Escherichia coli , Bacillus subtilis, Candida albicans and Aspargillus flavas).

In 2010, S. Malik, et al. 176 have prepared sulfur-nitrogen donor monbasic bidentate ligands, thiosemicarbazones of 5-nitro-1H-indole-2,3-dione, 6-nitro-1H- indole-2, 3-dione and 5-chloro-1H- indole-2,3-dione and its copper complexes. All the ligands and their metal chelates were found active against various pathogenic bacterial and fungal strains.

In the same year S. Nagarajan et al. 177 have synthesized and characterized neutral dinuclear Cu(II) complexes of Schiff base ligands derived from D-glucose. These complexes were evaluated for their interaction with DNA, and DNA cleavage was observed even in the presence of radical inhibitors.

G. Kumar et al. 178 have synthesized complexes of the type [HLCu2Cl3], [HLCu2(O(CO)CH3)3], [HLM2Cl4(H2O)3] and [HLM2(OC(O)CH3)4(H2O)3], where M = Ni(II), Co(II); by condensation of 3-acyl-2-one indol and hydrazinecarbothioamide (2:1) in the presence of divalent metal salt in methanolic medium. Abbildung in dieser Leseprobe nicht enthaltenAbbildung in dieser Leseprobe nicht enthalten

M. Dolaz et al. 179 have prepared bidentate Schiff base ligand (L) and its metal complexes having general formula [M(L)(Cl)2] (M: Cu(II), Co(II) and Ni(II) metal ions). They studied electrochemical properties, thermal properties of the metal complexes. These complexes were found to have good catalytic activity on the cyclohexane as a substrate.

S. Nayak et al. 180 have synthesized four coordination complexes from the planar tridentate Schiff-base ligand 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH) with several transition metal ions (FeIII, CoII, and CuII). The FeIII-complex was found to be an efficient catalyst for catalytic oxidation of several alkanes and alkenes.

In 2011, B. K. Singh et al.181 have synthesized Cu(II), Co(II), Ni(II) and Mn(II) Schiff base complexes from 2-aminophenol and pyrrole-2- carbaldehyde by the coordination of N and O atoms of ligand. The authors characterize all the complexes by the physicochemical, spectroscopic method and MM2 calculations. They have been also examined the bio-efficacy of the ligand and their complexes.

In the same year R. Manikandan et al. 182 have synthesized Ruthenium(II) hydrazone Schiff base complexes of the type [RuCl(CO)(B)(L)] (were B = PPh3, AsPh3 or Py; L = hydrazone Schiff base ligands) from the reactions of hydrazone Schiff base ligand with [RuHCl(CO)(EPh3)2(B)] (where E = P or As; B = PPh3, AsPh3 or Py) in 1:1 molar ratio. They have been characterized all the complexes by FT-IR, 1H-NMR and 13C-NMR spectroscopy. They were also found to catalyze the transfer hydrogenation of aliphatic and aromatic ketones to alcohols in KOH/Isopropanol.

In 2012 Q. Zhou et al. 183 have described the synthesis and spectral characterization of a Schiff base, 2-pyridinecarbaldehyde-phenylenedihydrazone. They have established a sensitive method for ferric ion selective detection and this method was successfully applied to determination of iron in tea and milk powder.

In 2013 M. N. Islam et al. 184 have synthesized [N-salicylidene glycinato diaqua cobalt (II) dimer] (SGCo)2, [N- salicylideneglycinato-di-aqua-nickel(ll)dimer] (SGN)2, [N-salicylideneglycinato-aqua-copper(II)] (SGC) and [N-salicylidene glycinato diaqua zinc(II) dimer] (SGZ)2 from salicylaldehyde and glycine and they have characterized these compounds through a rapid, simple, and efficient methodology in excellent yield and screened for in vitro antibacterial activities against six pathogenic bacteria.

In the same year M. B. Halli et al. 185 have synthesized metal complexes of Cu(II), Co(II), Ni(II), Zn(II), Cd(II), and Hg(II) by the schiff base of benzofuran-2-carbohydrazide and 4- methyl-thiobenzaldehyde. They have characterized all the complexes on the basis of elemental analysis, magnetic moments and spectral studies. They also have been screened all the metal complexes against fungi and bacteria.

In 2014 O. B. Ibrahim et al . 186 have prepared Metal chelates derived by Schiff base and characterized them by the elemental analysis, magnetic and spectroscopic measurements such as FT-IR, XRD and SEM. The Schiff base and its metal chelates also have been screened for their in vitro antibacterial activity against four bacteria, gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and two strains of fungus (Aspergillus flavus and Candida albicans).

In the same year F. A. Al-Saif187 has synthesized Schiff bases of 2-thiophenecarboxaldehyde and 4-amioantipyrine (4APT) and their metal complexes. These Schiff bases and complexes were characterized based on elemental analyses, IR, Raman, 1H-NMR, molar conductance, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and thermal analysis (TGA).

1.2. Nanotechnology

Developments during the past decade in the scientific and engineering communities have resulted in a tremendous upsurge of interest in the properties of small particles in the field of nanoscience and nanotechnology. The unit nanometre derives its prefix nano- from the Greek word meaning “dwarf”, 188 therefore nanotechnology is the study of small structures and materials with structured features, in between those of atoms and bulk materials 189, 190 with at least one dimension in the nanometre range 1-100 nm. Nanostructures are similar in size to many biological species, which comprise a variety of basic structures (Table 1.1). To give a better idea of the length of a nanometre, the hydrogen atom is about 0.1 nm, while a virus may be approximately 100 nm and an erythrocyte 2500 nm in diameter, however, it is living cells that are the best examples of machinery that operate at the nanoscale, and currently there is no engineered mechanical, biological or chemical technology that matches the ability to perform at perfection levels seen in living cells.

1.2.1. What is nanoscience and nanotechnology?

‘Nanoscience’ is the study of phenomena exhibited by materials at atomic, molecular and macromolecular levels, of dimensions ranging from a few nanometres to less than a hundred nanometres. In chemistry, this size range has been associated with colloids, micelles, polymer molecules and similar structures. In physical and electrical engineering, nanoscience is often associated with quantum behaviour, and electron behaviour in nanoscale structures. The fields of biology and biochemistry are also associated with nanoscience as cellular components (Table 1.1), such as DNA and RNA are considered to be nanostructures. 191 Whilst nanoscience is described as the study of the properties exhibited by nanomaterials, nanotechnology is the application of science to control matter at the molecular level. At the molecular level, the properties differ significantly from that of bulk materials. Nanotechnology is thus referred to as the term for designing, characterization, production and application of structures, devices and systems by controlling shape and size at nanometre scale. 192 Rao et al. in 2004193 described nanoscience and nanotechnology as a field which focuses on (i) the development of synthetic methods and surface analytical tools for building structures and materials, (ii) to understand the change in chemical and physical properties due to miniaturization, and (iii) the use of such properties in the development of novel and functional materials and devices. The area of research in the field of nanotechnology is as diverse as physics, chemistry, material science, microbiology, biochemistry and also molecular biology. The interface of nanotechnology in combination with biotechnology and biomedical engineering has emerged with the use of nanoscale structures in diagnosis, gene sequencing, and drug delivery.

Table 1. 1: Typical biological and atomic structures in the nanometre size range (Adapted from Rao et al., 2004)

Abbildung in dieser Leseprobe nicht enthalten

1.2.2. Emergence of Nanotechnology

The “first” scientific study of nanoparticles took place in 1831, when Michael Faraday i nvestigated the red ruby colloids of gold and made public that the colour was due to the small size of metal particles. For over 2000 years gold and silver have been used in glassware usually as nanoparticles, where they have been frequently used as colourants for church windows. 194 It was only in 1959 that Nobel laureate physicist Richard Feynman thought of using atoms and molecules for fabricating devices, though it was only later in 1974 that the term nanotechnology was derived by Norio Taniguchi, a researcher at the University of Tokyo, while engineering the materials precisely at the nanometer level. The primary driving force for miniaturization at that time came from the electronics industry, which aimed to develop tools to create smaller electronic devices on silicon chips of 40–70 nm dimensions. The use of the term, nanotechnology has since grown to include a diverse range of tiny technologies, such as material sciences for designing of new materials for wide-ranging applications, electronics (memories, computers, components and semiconductors) and biotechnology (diagnostics and new drug delivery systems). 195

1.2.3. Types of nanomaterials

Based on the number of dimensions at nanoscale, nanomaterials are classified into three categories:

Nanoparticles: They have all the three dimensions at nano scale.

Nanofilms: They have two dimensions at nano scale.

Nanorods: They have only one dimension at nano scale.

The other classes of nanoparticles listed below are all very general and multi-functional, however, some of their basic properties and current known uses in biotechnology, and particularly nanomedicine are described here.

- Fullerene, Bucky balls and Carbon tubes:

Both members of the fullerene structural class, buckyballs and carbon tubes are carbon based, lattice-like, potentially porous molecules.

- Liquid Crystals:

Liquid crystal pharmaceuticals are composed of organic liquid crystal materials that mimic naturally-occuring biomolecules like proteins or lipids. They are considered a very safe method for drug delivery and can target specific areas of the body where tissues are inflammed, or where tumors are found.

- Liposomes:

Liposomes are lipid-based liquid crystals, used extensively in the pharmaceutical and cosmetic industries because of their capacity for breaking down inside cells once their delivery function has been met. Liposomes were the first engineered nanoparticles used for drug delivery, but problems such as their propensity to fuse together in aqueous environments and release their payload, have lead to replacement, or stabilization using newer alternative nanoparticles.

- Nanoshells:

Also referred to as core-shells, nanoshells are spherical cores of a particular compound surrounded by a shell or outer coating of another, which is a few nanometers thick.

- Quantum dots:

Also known as nanocrystals, quantum dots are nanosized semiconductors that, depending on their size, can emit light in all colours of the rainbow. These nanostructures confine conduction band electrons, valence band holes, or excitons in all three spatial directions. Examples of quantum dots are semiconductor nanocrystals and core-shell nanocrystals, where there is an interface between different semiconductor materials. They have been applied in biotechnology for cell labelling and imaging, particularly in cancer imaging studies.

- Superparamagnetic nanoparticles:

Superparamagnetic molecules are those that are attracted to a magnetic field but do not retain residual magnetism after the field is removed. Nanoparticles of iron oxide with diameters in the 5-100 nm range, have been used for selective magnetic bioseparations. Typical techniques involve coating the particles with antibodies to cell-specific antigens, for separation from the surrounding matrix. Used in membrane transport studies, superparamagenetic iron oxide nanoparticles (SPION) are applied for drug delivery and gene transfection. Targeted delivery of drugs, bioactive molecules or DNA vectors is dependent on the application of an external magnetic force that accelerates and directs their progress towards the target tissue. They are also useful as MRI contrast agents.

- Dendrimers:

Dendrimers are highly branched structures gaining wide use in nanomedicine because of the multiple molecular "hooks" on their surfaces that can be used to attach cell-identification tags, fluorescent dyes, enzymes and other molecules. The first dendritic molecules were produced around 1980, but interest in them has blossomed more recently as biotechnological uses are discovered.

1.2.4. Methods of Nanoparticle synthesis

Nanoparticles can be produced using two techniques, (i) the top down approach or (ii) the bottom up approach. The top down approach refers to the breakdown of larger structures by use of ultra fine grinders, lasers and vaporization followed by cooling. 196 The bottom up approach allows the rearrangement of these molecules to form complex structures with new and useful properties. 197 Both of these approaches play important roles in the nanotechnology industry however, both have their advantages and weaknesses. Nanotechnologists however, prefer to use the bottom up approach which involves the synthesis of nanostructures from the bottom, atom by atom, molecule by molecule or cluster by cluster. The various methods for the synthesis of nanoparticles by this ‘bottom up’ method are described as follows:

1.2.4.1. The Sol Process

In this approach, the reagents (metal ion solutions) are rapidly added into a reaction vessel containing a hot coordinating solvent such as alkyl phosphate, pyridine and alkylamine furan. This quick addition of reagents to the reaction vessel increases the precursor concentration, with the solution becoming supersaturated due to the high chemical reaction temperatures. 198 As a result a short nucleation burst occurs and the concentration of the metal species in solution drops below the critical point of nucleation. 199 This method produces a nano-cluster growth of metal species, and if this period of growth during the nucleation time is short enough, nano-clusters maybe uniform and mono-dispersed. There are a number of reports in the literature on nanoparticle synthesis utilizing this method, with a wide range of nanoparticles been successfully synthesized such as CdSe, 200 CdS, 201 ZnO, 202 bimetallic clusters such as CdSe/ZnS, 203 CdSe/CdS 204 and CdSe nanorods. 205

1.2.4.2. Chemical Precipitation

During this process organic molecules are utilized to control the release of the reagents and metal ions in solution during the precipitation process. The particle size is influenced by the reactant concentration, pH and temperature. By engineering these factors, CdTe 206 and HgTe 207 nanoparticles have been produced by this approach. Although the method of using precipitation to produce nanoparticles is considered to be straightforward and simple, very complicated nano-structures such as CdS/ HgS/ CdS 208 and CdS/ (HgS)2 / CdS 209 have been produced.

1.2.4.3. Reverse micellization

The use of reversed micelles in the synthesis of metal nanoparticles has been well documented in the literature, with reducing agents such as NaBH4, N2H4 and H2 being used. 210 A variety of nanoparticles such as Pt, Rh, Pd and Ir have been synthesised using this process. 211 The water content of the micelles seems to greatly affect the shape of nanoparticles and thus nano-wires such as BaCO3 and BaSO4 have been synthesized. 212

1.2.4.4. Pyrolysis or Thermal decomposition

Pyrolysis is a chemical process in which chemical precursors decompose into solid compounds and the unwanted waste evaporates away. It has been used to prepare various kinds of nanoparticles including metals, metal oxides, metal sulphides, semiconductors, and composite materials. Generally the pyrolytic synthesis of compounds leads to powders with a size distribution in the micrometer range, though to get uniform nano-sized material, revisions of the procedure need to be changed such as slowing of the reaction or decomposition in an inert solution.

1.2.5. Applications of Nanotechnology

There are many applications of nanotechnology in various fields like sunscreen, cosmetics, food products, packaging industries, surface coatings, electronic circuits and environment cleaning. Some other universal applications of the nanoparticle include:

- Optical: Nanoparticles could be engineered and used for anti-reflection product coatings, producing a refractive index for various surfaces, and also providing light based sensors for use in diagnosing cancer.
- Magnetic: Nanoparticles have the potential to increase the density of various storage media, and also when magnetized they can improve the detail and contrast of MRI images as previously alluded to.
- Thermal: Specifically engineered particles could improve the transfer of heat from the collectors of solar energy to their storage tanks. They could also enhance the coolant system currently used by transformers in these types of processes.
- Mechanical: Nanoparticles could provide improved wear and tear resistance for almost any mechanical device. They could also give these devices previously unseen anti-corrosion abilities, as well as creating entirely new composites and structural materials that are both lighter and stronger than those we use today.
- Electronics: Because of their tiny size, nanoparticles are inherently poised to aid in the production of high performance, delicate electronics; they may provide not only materials with a high rate of conductivity, but also sleeker parts for small consumer electronics like cell phones. In advertising, nanoparticle electronics can create digital displays that are more electricity-efficient, less expensive to produce, brighter in color, and also bigger.
- Energy: Nanoparticle batteries would be longer-lasting and have a higher energy density than those we use today. Metal nanoparticle clusters could also have revolutionary applications for hydrogen storage; they could also produce extremely efficient fuel cells by acting as electrocatalysts for these devices. Nanoparticles may also pave the way for practical and renewable energy; they have already demonstrated an ability to improve solar panel efficiency many times over. Not only that, but when nanoparticles are used as catalysts in combustion engines, they have shown properties that render the engine more efficient and therefore more economic.
- Biomedical: We may soon find that our wounds are dressed with antibacterial coatings of silver nanoparticles. Nanoparticles have also been used to produce “quantum dots,” which can detect diseases, as well as interactive foods and drinks that change flavor and color based on our tastes, or in some cases may even alter their nutrient content based on your state of health.

1.2.6. Nanoparticles as semiconductor quantum dots

Nanoparticles specifically focused on quantum dots (QDs) are fragments of semiconductors consisting of thousands of atoms with the bulk bonding geometry and surface states eliminated by enclosure in a material of a larger band gap. These nanoparticles are often composed of atoms from groups II-VI or III-V elements in the periodic table such as CdS (cadmium sulfide), CdSe (cadmium selenide). The dimension of these particles which is important to their optical and electronic properties is typically on a scale from 0.2 to 100 nm. QDs exhibit different properties due to two fundamental factors. They possess a high surface to volume ratio and the actual size of the particle can determine the electronic and physical properties of the material. 213 With a size reduced to a nano-scale, the electronic energy states become discrete and the surface-to-volume ratios of materials are large, which significantly changes the fundamental optical and electronic properties from the bulk material. Therefore, these features lead to a size-tunable optical property which sparks QDs with potential applications in every discipline of sciences. The most striking feature of QDs is their broad spectral tenability, over their sizes which can be controlled by the temperature, the duration and ligand molecules used in the preparation process. 214

The second important characteristic of QDs is the influence of their surface states on the optical and electronic properties. Passivation of nanoparticles with organic molecules is necessary to avoid the aggregation of nanoparticles and increase the fluorescence quantum yield. The ability to tailor the shapes of QDs results in the production of rod-shaped nanoparticles, also known as QRs. Quantum dots have been widely used in energy conversion, chemical analysis and clinical diagnosis for their rich, colourful, unbleached excited emissions with a narrow peak wavelength by controllable QDs species and sizes.

QDs have tunable band gaps and this proves to be useful in biological applications. Currently, many of them rely on using organic dyes with limited wavelengths which are sometimes in a region of the spectrum which proves inconvenient as most absorb in the same regions as biological materials with water being a major interferant. This is why two-photon excitation technology has found many applications in biology, using IR radiation instead of UV to excite conventional dyes, however, that causes the excitation of multiple organic dyes to be difficult and expensive. QDs tend to be brighter than dyes because of the compounded effects of extinction coefficients that are an order of magnitude larger than those of most dyes with comparable QYs and similar emission saturation levels. The main advantage of QDs over dyes is their resistance to bleaching over long periods of time. Dyes tend to have short lifetimes meaning that it is difficult to get sharp and well contrasted images. The increased photostability of QDs is very useful for three-dimensional optical sectioning. The new generation of QDs is far reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumour targeting and diagnostics. 215 These Qds have found applications ranging from bioanalytical assays, to live cell imaging, fixed cell and tissue labeling, biosensors and in vivo animal imaging. Qds when used in conjunction with MRI, can produce exceptional images of tumor sites. These Qds are used in vivo targeting of cells, tissues, organs and tumors in animals for diagnosis, therapy and drug testing.

Some of the most successful uses of QDs have been the immunofluorescence labelling of fixed cells and tissues and fluorescence immunocytochemical probes. QDs are photostable, have high QYs, narrow emission spectra and an apparent large Stoke’s shift meaning that they have several advantage over organic fluorophores in immunocytochemical studies of erythrocytes, for example. 216 The probes are generally used to detect antigens in tissue.

1.2.8. Brief overview on nanoparticles

In 1996 L. Qi et al. 217 have synthesized three different types of mixed CdS, ZnS semiconductor nanoparticles in reverse micelles and characterized them by optical absorption and photoluminescence (PL) spectroscopy. They explained that these nanoparticles have absorption spectra similar to those of the coated CdS/ZnS nanoparticles but show no significant luminescence activation.

In 1997 M. Kundu et al. 218 have synthesized and studied the organically capped ultra small clusters of cadmium sulphide using non-aqueous and aqueous chemical methods. They have been used thiophenol as a capping agent for non-aqueous synthesis whereas various reagents such as mercaptoethanol, hexametaphosphate, ethylene glycol and ethanol have been used as additives for an aqueous method of synthesis. They also have characterized these nanoparticles on the basis of optical absorption, X-ray diffraction, transmission electron diffraction and photoelectron spectroscopy.

In the same year Z. C. Kang and Z. L. Wang219 have synthesized monodispersive carbon spheres with a high percentage of purity. For this synthesis they have used a mixed-valent oxide-catalytic carbonization (MVOCC) process and the chemical activities of the carbon spheres are examined by dispersing Pt, CdS and WO, nanoparticles, respectively, on the carbon surfaces from the microstructure information provided by transmission electron microscopy. They studied that the carbon spheres are good candidate for catalysis applications.

In 1999, T. Tsuzuki and P. G. McCormick220 have synthesized ZnS, CdS and Ce2S3 nanoparticles by mechanochemical reaction. They showed that the resulting particles and crystallite sizes were dependent on the milling conditions, starting materials and the presence of a diluents and Structural change with decreasing particle size was observed for CdS & Ce2S3.

In 2000, A. Agostiano et al. 221 have reported a novel synthetic pathway to obtain cadmium sulphide (CdS) nanoparticles in a quaternary “water-in-oil” microemulsion formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB), pentanol, n -hexane and water. They mixed two microemulsions containing Cd(NO3)2 and Na2S, respectively in this system for the synthesis of CdS nanoparticles and the nanocrystals have been characterised by using UV–visible spectroscopy and Transmission Electron Microscopy to investigate the influence of various parameters of the particles’ formation and stability in solution.

In 2001, J. Hambrock et al . 222 have prepared TOPO capped CdSe nanoparticles by the pyrolysis of Me2Cd type complexes in a hot coordinating solvent and the resulting nanocrystals have been characterized by Electronic Spectroscopy, IR Spectroscopy, Mass Spectrometry and Transmission Electron Microscopy (TEM).

In 2002, P. S. Nair et al. 223 have synthesized CdS nanoparticles using cadmium ethylxanthate as a single source precursor and they used Tri-n-octylphosphineoxide (TOPO) as capping agent. They also confirmed the size of nanoparticles by TEM.

In the same year Le-Yu Wang et al . 224 have developed a synchronous fluorescence method for the rapid determination of DNA with functionalized CdS as a fluorescence probe, based on the synchronous fluorescence quenching of functionalized CdS in the presence of DNA and synthesized Nanometer-sized fluorescent particles. They explained that these particles have a narrow, tunable, symmetric emission spectrum and a broad, continuous excitation spectrum. These particles are also photochemically stable.

L. Wang et al. 225 have prepared CdS nanoparticles, which is modified with mercaptoacetic acid. They studied that these functionalized nanoparticles are water-soluble and biocompatible and they used as could be used as a fluorescence probe in the determination of bovine serum albumin (BSA), which was proved to be a simple, rapid and specific method.

In the same year W. Wang et al . 226 have been developed a novel and simple one-step, solid-state reaction to synthesize uniform cubic-phase h-CdS nanoparticles with an average diameter of ca. 5 nm, in the presence of a nonionic surfactant, C18H37O(CH2CH2O)10H (abbreviated as C18EO10). They also have characterized these nanoparticles using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV–VIS optical absorption spectrum and X-ray photoelectron spectrum (XPS).

Li-Piin Sung et al. 227 have reported that metal-oxide nanoparticles used to optimize UV absorption and to enhance the stiffness, toughness, and probably the service life of polymeric materials. They also recorded the characterization of the nano and microstructure dispersion of particles is necessary to optimize the structure-property relationships and dispersed in an acrylic-urethane matrix and TiO2 nanostructured films obtained through sol-gel synthesis.

S. H. Liu et al. 228 have prepared CdS nanoparticles with CS2 as the sulfur source through the hydrothermal process where Poly(vinyl pyrrolidone) (PVP) used as capping agent. The obtained nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible and fluorescence spectroscopy. They also reported these capped CdS nanoparticles showed remarkable stability and significantly enhanced luminescence property compared with that of the noncapped ones.

H. Zhang et al. 229 have used sonochemical reaction for the preparation of CdS nanoparticles coating with SrZrxTi1xO3 (x ¼ 0:27) microparticles and the prepared particles were characterized by TEM, XRD, FT-IR and other techniques and the fabrication mechanism. They also explained the photocatalytic properties of the nanoparticles by degradation of methylene blue.

In 2004 B. Yan et al. 230 have fabricated a novel nanocomposite in which CdS nanoparticles were embedded in poly(N-isopropylacrylamide) (P(N- iPAAm)) matrix. They have also characterized the nanocomposites by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV–vis absorption and fluorescence spectra (FLS) measurements and recorded the fluorescence property of CdS/P(N-iPAAm) nanocomposites.

In 2004 M. Zhang et al. 231 have developed a controlled fabrication of wire-like assemblies of cadmium sulfide (CdS) nanoparticles on the basis of template technique. They were used core-shell cylindrical polymer brushes as a single molecule templates, utilizing the coordination of cadmium ions with carboxylate groups in the core of the brush. Formation of CdS nanoparticles inside the polymer brush was carried out via the reaction of the coordinated Cd2+ ions with H2S.

In the same year M. Ghosh et al . 232 have synthesized CdO and CuO nanocrystals by the decomposition of cupferron complex in the presence of TOPO under solvothermal condition. Here TOPO used as a surfactant to determine the size of nanocrystals and the nanocrystals have been characterized by electron microscopy and absorption spectroscopy.

M. Z. Rong et al. 233 have synthesized nanometer-sized clusters of CdS in inverse-micellar solution and were studied in situ chemical derivatization of the surface of these cluster compounds. They observed that nanoparticle surface can be terminated and passivated by the addition of imidazole and thiol molecules, which allows of inhibiting the particle from agglomeration, improving particle distribution in organic solvents and polymer matrices, and blocking surface defects that cause radiation-less recombination of charge carriers and the solubility of these re-dispersible powders in different solvents and then the CdS quantum dots– polymer composites were prepared using solution mixing method.

In 2005 L. Pedone et al. 234 have been used water-in-oil microemulsions for the synthesis of CdS nanopowder capped with sodium bis(2-ethylhexyl)sulfosuccinate. They also have been characterized these transparent yellow compound by optical absorption and emission spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. They observed that the nanoparticles are homogeneously dispersed in the matrix and no change in size occur during the embedding process, even if the surface slightly changes its luminescence properties, as a consequence of the different new chemical environment.

In 2006 N. Revaprasadu et al . 235 have used metal complexes as precursor and traditional chemical vapor deposition and molecular epitaxy methods for the preparation of semiconductor nanoparticles.

In the same year M. Jayalakshmi et al. 236 have synthesized the zinc sulphide nanoparticles using zinc nitrate and thiourea in aqueous solutions and characterized these particles by TEM and XRD for electrochemical capacitor applications.

P. H. Borse et al . 237 have prepared Pb-doped Zinc sulphide nanoparticles at room temperature using a chemical method in which the particle surfaces were passivated using mercaptoethanol. They also recorded the effect of pH on photoluminescence enhancement in particles.

In 2007 Y. L. Wu et al. 238 have synthesized nano-crystalline ZnO particles using alcoholic solutions of zinc acetate dihydrate through a colloidal process and studied surface modification of particles; they also recorded Photoluminescence spectra which indicate a good surface morphology of particles with little surface defects.

In the same year M. Vafaee et al. 239 have used TEA (Triethanolamine) as surfactant for the preparation of ZnO nanoparticles by sol-gel route and they reported that the particles which prepared by this method have higher photoluminescence spectra as compared to other methods.

M. Maleki et al . 240 have synthesized CdS nanoparticals by a chemical reaction route using ethylenediamine as a complexing agent and they used XRD, SEM, UV–VIS absorption spectroscopy, and photoluminescence spectroscopy for the characterization of the nanoparticles.

B. S. Amma et al. 241 have used various organic stabilizers as capping agent and solutions of cadmium acetate and sodium sulphide as precursor for the synthesis of CdS nanoparticles. They also synthesized CdS nanoparticles in an aqueous medium with mercaptopropionic acid (MPA) as a stabilizer and in non-aqueous methods with (PVP) and thiophenol as capping agent.

In 2008 K. Manickathai et al. 242 have used ethylene glycol as capping agent to prepare CdO nanoparticles and H2S gas to prepare CdS nanoparticles. They also used UV-Vis Absorption spectroscopy and SEM to carry out structural characterization of the nanoparticles.

In the same year Z. Li et al. 243 have synthesized the monodisperse silica modified ZnS nanoparticles by sol–gel-hydrothermal method and characterized these particles by XRD, FT-IR and also proved that there existed strong interaction between the SiO2 and ZnS

S. Senthilkumaar et al. 244 have prepared the Zinc sulphide nano particles and rods by sol-gel method via ultrasonication using mercaptoethanol as capping agent. They also investigated structural and morphological characteristics of zinc sulphide by SEM and TEM studies.

In 2009 K. Kandasamy et al. 245 have synthesized CdS and CdSe nanoparticles using novel single source precursors and characterized particles by X-ray powder diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM).

In the same year M. L. Singla et al . 246 have studied and characterized optical properties of ZnO nanoparticles capped with various surfactants such as tetraethylammonium bromide (TEAB), cetyltrimethylammonium bromide (CTAB), tetraoctylammonium bromide (TOAB). They showed the presence of surfactant on the surface of zinc oxide plays a significant role in reducing defect emissions.

S. N. Mlondo et al. 247 have synthesized and characterized nano dimensional crystals of CdS, using Cadmium thiosemicarbazide complexes as precursors. They also studied the morphology of product by Transmission Electron Microscopy (TEM).

A. K. Singh et al. 248 have synthesized the ZnO nanoparticles using triethaneolamine (TEA), oleic acid and thioglycerol as capping agent and studied structural, optical and photoluminescence properties. They also reported effect of capping agent on particles

T. Mthethwa et al . 249 have reported the synthesis of hexadecylamine capped CdS nanoparticles using heterocyclic cadmium dithiocarbamates as precursors, and studied the optical property of these particles. They also reported that HDA used as capping agent, inhibits the agglomeration of particles.

N. Moloto et al. 250 have used tetramethylthiuram disulphide cadmium complex as single-source precursor and hexadecylamine (HDA), trioctylphosphine oxide (TOPO) as surfactants for the synthesis of CdS nanoparticles. They also studied the effects of precursor concentration, temperature and capping environment on the morphology and size of particles.

In 2010 Y. K. Jung et al. 251 have synthesized Zinc alkyldithiocarbamate complexes and prepared the nanoparticles of Zinc by the thermal decomposition of these complexes in the presence of alkyl amines, which used as a surfactant. They also studied the morphology of product by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM).

In 2010, M. Darbandi et al. 252 have developed a facile method for the preparation of single quantum dots in silica spheres with tunable size and optical property. They also have been used a time interval addition of silica precursor method to increase the size of the silica shell and in parallel tuning the photoluminescence property and also characterized the resulting CdSe/ZnS/SiO2 nanocomposites by transmission electron microscopy, photoluminescence spectroscopy and zeta-potential measurements.

In the same year A. Hosseinian and A. R. Mahjoub253 have synthesized [Cd(DADMBTZ)2(NO2)2], DADMBTZ = 2,20-diamino-5,50-dimethyl-4,40-bithiazole and it has been used as a single source precursor for the synthesis of CdS nanoparticles by the thermal decomposition. They also have characterized these nanoparticles by the X-ray diffraction measurements (XRD), scanning electron microscopy (SEM).

D. Saikia et al. 254 have prepared CdS/PVA nanocomposite thin films by the thermal pyrolysis of the complex precursor. They also characterized prepared films by the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), UV–vis spectroscopy, and photoluminescence (PL) spectra.

J. F. A. Oliveira et al. 255 have synthesized CdS nanoparticles were synthesized via microwave-assisted solvothermal technique. On the basis of characterization they also have recorded the presence of crystalline structures presenting single phase with different morphologies such as “nanoflowers” and nanoplates, diffuse reflectance and the influence of the different solvents on the optical properties due to structural defects generated during synthesis. They also proposed that these defects are related to sulfur vacancies, with higher concentration of defects for the sample synthesized in ethylene glycol in comparison with the one synthesized in ethylene diamine.

K. Yao et al. 256 have prepared short nanorods, quasi-nanospheres and faceted CdS nanoparticles with the thermal decomposition of cadmium diethyldithiocarbamate complexe precursors. In his work they also reported the effect of reaction temperature, monomer concentration, reaction time, and ionic liquid ratio for the shape, size and crystallinity of the products.

N. Ghows and M. H. Entezari257 have induced micro-emulsion method to synthesize Cadmium sulfide nanoparticles with a hexagonal phase in the absence of surfactant at a relatively low temperature and the product was characterized by different techniques such as UV–visible absorption spectroscopy, X-ray powder diffraction, and high resolution transmission electron microscopy (HRTEM).

Na Li et al . 258 have synthesized Oleic acid capped CdS nanoparticles via the direct reaction of Cd(CH2COO)2.2H2O with S powder in OA solvent at 230°C under nitrogen flow, which was a kind of clean and air-stable solvent. They also examined the morphologies and structures of nanoparticles by TEM, HRTEM, XRD, FTIR, PL and UV-vis spectroscopy.

In 2012 V. Ramasamy et al. 259 have synthesized ZnS and transition metal (Mn, Co, Ni, Cu, Ag and Cd) doped ZnS using chemical precipitation method in an air atmosphere. They were studied the structural and optical properties using X-ray diffraction, Electron dispersive analysis, transmission electron microscopy, scanning electron microscopy, UV-Vis and photoluminescence.

In the same year V. Safarifard and A. Morsali260 have synthesized nanoparticles of a three-dimensional supramolecular Cd(II) compound, [Cd(L)2(H2O)2] (1), (L_ = 1H-1,2,4-triazole-3-carboxylate) by a sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. they also studied the thermal stability of compound 1 in both its bulk and nano-size by thermal gravimetric (TG) and differential thermal analyses (DTA) and compared with each other. They recorded that size and morphology of nano-structured compound 1depends upon Concentration of initial reagents.

H. Hejase et al. 261 have used the co-precipitation method to synthesize Manganese zinc iron magnetic nanoparticles and reported that these nanoparticles used as hyperthermia inducing agents. They also have been characterized the structure, morphology and magnetic properties of the nanoparticles using scanning electron microscopy, X-ray diffraction, and a superconducting quantum interference device and magnetic properties being investigated include Curie temperature, saturation magnetization, remnant magnetization, coercive field, and hysteresis.

In 2013 G. Yordanov et al. 262 have synthesized etoposide based on poly(butyl cyanoacrylate) nanoparticles by controlled emulsion polymerization of butyl cyanoacrylate in aqueous medium using two different non-ionic colloidal stabilizers (pluronic F68 and polysorbate 80). They have described physicochemical characterization and cytotoxicity assessment of novel colloidal formulations of nanoparticles. They also recorded all tested etoposide formulations induced apoptosis in adenocarcinoma human epithelial (A549) cells, as evident from condensation of chromatin and fragmentation of nuclei and it was found that etoposide formulated with poly(butyl cyanoacrylate) nanoparticles and polysorbate 80 exhibited the highest cytotoxicity toward adenocarcinoma cells.

H. Mu et al. 263 have prepared Iron nanoparticle by liquid phase reduction method in microemulsion systems. They also reported A novel oxygen scavenger using iron nanoparticle was produced and evaluated as a potential oxygen scavenger and explained Successful application of the nano sized oxygen scavenger on roasted sunflower seed and walnut demonstrated its ability toinhibit lipid oxidation in lipid-containing food. Roasted nut treated with nanosised oxygen scavengerpossessed the lowest PV and AnV in all treatments after 120 days of storage. Therefore, it has the potentialfor broad application as an active packaging in a variety of oxygen-sensitive foods.

In 2013 I. A. Wani et al. 264 have used three different surfactants viz., cetyl-trimethyl ammonium bromide (CTAB), Tergitol and Triton X-100 for the synthesis of Silver nanoparticles in the inverse microemulsions. They have shown effect of the surfactants on the particle size and properties of the silver nanoparticles and microscopic studies shown the formation and size of silver nanostructures. They have been investigated the antimicrobial activity of silver nanoparticles, they were tested against the yeast, Candida albicans and the bacterium, E. coli. And they suggested very good antimicrobial activity of the silver nanoparticles against the test microbes.

In the same K. S. Lohar et al. 265 have been synthesized Ultrafine Ni–Cd ferrite nanoparticle by the citrate sol gel process and confirmed the formation of single phase cubic spinel structure by the IR and XRD.

M. Vijayakumar et al. 266 have developed a method for the synthesis of silver nanoparticles (AgNPs) from Artemisia nilagirica (Asteraceae), whereas Silver nitrate was used as the metal precursor and hydrazine hydrate as a reducing agent. They have been used scanning electron microscopy (SEM) and and energy-dispersive spectroscopy (EDX) to characterize the nanoparticles obtained from A. nilagirica.

N. M. Khalil et al. 267 have used a single-emulsion solvent-evaporation technique for the synthesis of Polylactic-co-glycolic acid (PLGA) and PLGA–polyethylene glycol (PEG) (PLGA–PEG) blend nanoparticles containing curcumin and studied that curcumin was released more slowly from the PLGA nanoparticles than from the PLGA–PEG nanoparticles. They also have been developed LC–MS/MS method and validated to quantify curcumin in rat plasma and on the basis of all these studies they reported that PLGA and, in particular, PLGA–PEG blend nanoparticles are potential carriers for the oral delivery of curcumin.

S. Raveendran et al. 268 have reported the synthesis of an extremophilic bacterial sulfated polysac-charide based nanoparticle as a stable biocompatible material for drug delivery, evaluation of anticancer efficacy and bioimaging. They also have used Mauran (MR), the sulfated exopolysaccharide for the synthesis of nanoparticles along with chitosan (CH) and MR/CH nanoparticles were synthesized by simple polyelectrolyte complexation of anionic MR and cationic CH. They also have recorded that cytotoxicity assay revealed that MR/CH nanoparticles were non-cytotoxic towards normal cells and toxic to cancer cells. They also reported the introduction of an extremophilic bacterial polysaccharide, MR, for the first time as a novel biocompatible and stable biomaterial to the world of nanotechnology, pharmaceutics and biomedical technology.

1.3. Biological studies of Schiff base complexes and nanoparticles

There are a number of chemical and biological options that control pests, like bacteria, fungi, insects, weeds and rodents. Chemical pesticides are substances that are manufactured in laboratories that, when applied to crops, reduce the vitality of pest populations while leaving crops unharmed. Chemical controls can kill pests that come in contact with the chemical (toxicants), eliminate the reproductive potential of pests (sterilants), disrupt their developmental potential (growth regulators) or influence their behavior (semiochemicals). Most of these chemical controls are fast acting and effective. Chemical controls are cheap and readily available. Chemical controls, especially toxicants, have been in use since the 1940's and have remained in popular use due to their fast acting and effective results in controlling pest populations. Many new chemicals have been developed in recent years that are even more efficient in controlling pests, maintaining the popularity of chemical control in agricultural practices. 269

Some bacteria are pathogenic and cause diseases both in animals and plants. The reason for giving special attention to bacteria, fungi and insects is obvious in view of the facts how seriously they affects the economy, plant, human and animal, health. Organisms which cause disease are called pathogens. The extent of damage caused by fungi may be realized from the facts that only one fungal species Phytopthera infestans was responsible for famine in Ireland in middle of 19th century, as a consequence of which million of people either died of malnutrition or forced to emigrate. 270

The toxic chemicals used to destroy any species of pests are termed as pesticide. Pesticide can be classified based on the practical purpose of application. 271 Thus, the pesticides used against microbial pests are microbicides, and those used against animal pests are called zoocides, and those used to destroy weeds are termed as herbicide. Microbicides consist of fungicides, bactericides, viricides and algicides, etc.

Zoocides are consisting of insecticides, acaricides (mite killers), nematodicides (nematode killer) and rodenticides (rodent killers) in it. The fungicides have more important amongst microbicides and insecticides amongst the zoocides. Most of the early used fungicides are components of the metals, copper, mercury, lead, etc. Horsfall (1956) established the following order of fungitoxicity of metals:

Abbildung in dieser Leseprobe nicht enthalten

The fungicidal action of copper and mercury compounds can be explained by their interaction with thiol groups in the organism. However, sulphur and its compounds are also well known for their fungicidal activity. Dithiocarbamates 272 constitute to most important group of fungicides for controlling plant disease since maneb, zinceb, ziram, nabam and vapam are well known commercial fungicide of this group. These dithiocarbamate probably reacts with the HS–containing enzymes and co–enzymes of the fungal cells and inhibit their activities and thereby, destroying the fungus.

The pathogen named Treponema plalladium , the causative agent of syphilis, which is much known dreaded sexually transmitted disease. 273-275 Campylobacter jejum is the most pathogenic species causes as many as cases of diarrhoea as Salomnella and Shigella . It is transmitted to human by ingestion of food or water containing faecal matter from infected animals. These microorganisms produce acute oxidative and hemorrhagic inflammation of the wall of small and large intestine. 276, 277

The species Microbacterium tuberculosis was responsible for over 90% of all cases of tuberculosis. This organism can survive and multiply within phagocyte cell such as macrophage in bacterial walls and it can disrupt the respiration of mitochondria in phagocyte and tissue cells. 278

Escherichia coli is a part of normal flora of intestine tract, certain strains can cause moderate to severe gastroenteritis in human and animal. Enteropathogenic strains colonize the jejunum and in infants up to two years of age. Entero–invasive strains invade the epithelial cells of the large intestine and cause diarrhea in older children and adults. Enterotoxigenic strains produce one, two or both of two different toxins as heat stable toxin (ST) and a heat labile toxin (LT). Both toxins cause diarrhea in adults and infants. Other strains of E. coli are usually harmless in normal habitat (the intestine) they can cause disease when they gain access to other sites or tissues. These diseases include urinary tract infection, septic infection, meningitis, pulmonary infection and abscesses of skin a wound infections.

Aspergillus fumigatus is a fungus of genus Aspergillus and is one of the most common Aspergillus species to cause disease in immune-compromised individuals. In immune-compromised individual such as transplant patients and people with AIDS or leukemia, the fungus is capable of becoming pathogenic, over–running the host weakened defenses and causing a range of diseases generally termed aspergillosis. 279

1.4. Selection of ligand and Aim of the study

Metal ion being electron deficient work as a Lewis acid, and always tend to bind with a chemical species that are electron rich in comparison to metal ion. The bonding in these metal complexes ranges in between predominantly ionic to predominantly covalent, and is dependent on nature of both the metal ion and the ligand.

Thiosemicarbazide derivatives are known to have antibacterial, antifungal, herbicidal activities 280 and supposed to be mutagenic in human cells, since it is consist of a N=C=S group. Pyrrole and its derivatives are widely used as an intermediate in synthesis of pharmaceuticals, agrochemicals, dyes, photographic chemicals, perfumes and other organic compounds. Its derivatives are used as catalysts for polymerization process, corrosion inhibitors, preservatives, and as solvents for resins and terpenes. They are used as the standard of chromatographic analysis. In pharmaceutical chemistry N -methylpyrrole is a precursor to N-methylpyrrole carboxylic acid, a building-block in pharmaceutical chemistry. 281 N-substituted pyrrole derivatives block HIV fusion 282 and exhibits different biological activities such as antibacterial, 283 antitumor, 284 analgesics, anti-tubercular, anti-inflammatory and antiallergic 285 and used in material science.

Thiophene nucleus has been established as the potential entity in the largely growing chemical world of heterocyclic compounds possessing promising pharmacological characteristics. 286 The similar compounds synthesized through different routes bear variable magnitudes of biological activities. The knowledge of various synthetic pathways and the diverse physicochemical parameters of such compounds draw the special attention of medicinal chemists to carry out exhaustive efforts in the search of lead molecules. Thiophene derivatives have been very well known for their therapeutic applications. Many thiophene derivatives have been developed as chemotherapeutic agents and are widely used.

Disulfiram is a drug used to support the treatment of chronic alcoholism by producing an acute sensitivity to alcohol and treatment for cocaine dependence, as it prevents the breakdown of dopamine (a neurotransmitter whose release is stimulated by cocaine); the excess dopamine results in increased anxiety, higher blood pressure, restlessness and other unpleasant symptoms. Several studies have reported that it has anti-protozoal activity as well. 287, 288 In order to monitor whether a drug delivered by nanoparticles is biologically active a toxic model drug, disulfiram, was chosen as a payload with micelle and liposome nanoparticles a mouse fibroblast cell L929. The toxic effect observed was most likely not due to the disulfiram delivered by the nanoparticles but rather to the amount of free disulfiram that is present in the nanoparticle preparation. 289

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Chapter 2 Materials and Methods

This chapter includes the details regarding the materials used, physical measurements, analytical procedures adopted during the course of the present investigation and antibacterial studies.

Glass apparatus fitted with interchangeable joints were used throughout the experimental work. The apparatus was well cleaned and dried, weighing tubes were used for analytical sampling of solid. Volatile fractions and solvents were removed under reduced pressure; traps of conventional design were used to prevent the back diffusion of solvent vapours into the pump or passage of moisture from the pump. All the experiments were carried out under inert atmosphere. All the chemicals and solvents were used of A.R. grade. The solvents were purified and dried before use by standard procedure 1 whenever necessary.

2.1 Materials

Mercury(II)chloride, cadmium(II)chloride, thiosemicarbazide, benzaldehyde, trioctylphosphineoxide, triethanolamine, oleic acid, methanol, ethanol, toluene (All E. Merck), hexadecylamine, (Aldrich, USA), zinc(II)chloride (CDH), pyrrole-2-carboxaldehyde and 2-thiophenecarboxaldehyde (Qualigens). Disulfiram (Sigma Aldrich) were used as received.

2.2 Analytical methods and physical measurements

2.2.1. Estimation of metals

2.2.1.1. Estimation of Zinc

Zinc was estimated as 8-hydroxyquinaldinate. 2 A known weight of the compound was decomposed by concentrated hydrochloric and nitric acid and the mass was extracted with distilled water. Dilute aqueous ammonia solution was added to the solution until a white precipitate of zinc hydroxide just appeared. Zinc hydroxide was re-dissolved with a drop of acetic acid. To this 8-hydroxyquinaldine reagent was added in a slight excess and then 2-3 drops of concentrated ammonia solution. During this process the pH was maintained at 5.5. The precipitate was digested at 60-80°C for 15 minutes, allowed to stand for 10-20 minutes and filtered through a sintered glass crucible. It was dried at 130-140°C to constant weight as Zn(C10H8ON)2.

2.2.1.2. Estimation of Cadmium

When Cadmium is present in the complex, it was estimated by mixed anthranillate method. 3 It gives a total percentage of cadmium. A known weight of the compound was decomposed by concentrated hydrochloric and nitric acid and the mass was extracted with distilled water. During this process, pH was maintained at or above 4.5. This solution was heated to boiling and added with stirring 15-20 ml of 3% sodium anthranillate solution, and continued the boiling for another 10 minutes. The solution was allowed to settle for 20 minutes and filtered on a sintered glass crucible. It was washed ice cold 0.15% sodium anthranillate solution, followed by alcohol and dried at 110-120°C to constant weight as Cd(C7H6O2N)2.

2.2.1.3. Estimation of Mercury

Mercury was estimated as mercuric sulphide. 2 A known weight of the compound was decomposed by concentrated hydrochloric acid and the mass was extracted with 100 ml of distilled water. It was saturated with hydrogen sulphide and the precipitate was allowed to settle. The precipitate was washed with carbon disulphide and dried at 110°C to weigh as HgS.

2.2.2. Analysis of constituent elements

Carbon, hydrogen, nitrogen and sulphur present in the synthesized complexes, were estimated on Elementar Vario EL III, elemental analyzer at SAIF, Central Drug Research Institute, Lucknow (U.P.)

2.2.3. Melting point determination

Melting point of synthesized complexes was determined by open-capillary method on electrical melting point apparatus.

2.2.4. Conductance measurements

Molar conductivities of the complexes were measured at 25°C in acetone/ dimethylsulfoxide/ chloroform with the help of EI-181, Conductivity Bridge with a dipping type cell (Cell constant 0.934).

2.2.5. Electronic spectral studies

A Shimadzu-1700, UV-VIS Spectrophotometer was used to carry out the optical measurements and the samples were placed in silica cuvettes (1 cm, path length), using toluene as a reference solvent.

2.2.6. Infrared spectral studies

Infrared spectra of synthesized ligands and complexes (4000-400cm-1) were recorded in KBr pellets on Shimadzu-8400 PC, FT-IR spectrophotometer at Department of Chemistry, Rani Durgawati Vishwavidyalaya, Jabalpur (M.P.) and Shimadzu-8400 S, FT-IR spectrophotometer at Department of Chemistry, Govt. Model Science College, Jabalpur (M.P.).

2.2.7. Nuclear magnetic resonance studies

1H-NMR, 13C-NMR and 2D-NMR spectra of synthesized ligands and complexes were recorded in dmso-d6 or MeOD on Bruker DRX-300/Bruker Avance-400, spectrometers at SAIF, Central Drug Research Institute, Lucknow. 1H-NMR signals were referenced to tetramethylsilane as internal and external standard.

2.2.8. Mass spectral studies

ESI/FAB-mass spectra of ligands and complexes were recorded on a Micromass Quattro II Mass Spectrometer using ESI capillary and on Jeol SX-102, Mass Spectrometer, using NBA as matrix respectively at SAIF, CDRI, Lucknow (U.P.).

2.2.9. XRD measurements

XRD measurements of metal sulphide nanoparticles were carried out using Cu-Kα radiation (λ = 1.5406 A°) with Bruker D8-Advance X-ray diffractometer and graphs were plotted using Origin software from UGC, DAE Consortium Research Center, Indore.

2.2.10. Transmission Electron Microscopy

TEM photographs of metal sulphide nanoparticles were taken on a Tecnai 20 G2 and Image J software was used for the calculation of d spacing. Pcpdfwin software was used for matching calculated d-spacing with standard values of d and hkl reflection planes from UGC, DAE, Consortium Research Center, Indore.

2.3 Biological Studies

In the present investigation, all the Schiff base ligands are of pharmacological importance and they were coupled with heavy metals, which are Lewis acid, also toxophorically more important and known to inhibit the growth of bacteria. 4

All the Schiff base ligands, synthesized complexes and their nanoparticles were screened for antibacterial activity against gram-negative bacteria Escherichia coli MTCC, 1304 using, Well Diffusion method. 5, 6

Escherichia coli is an anaerobic gram-negative bacterium belongs to the family Enterobacteriaceae. It occurs in the lower portion of the intestine of human and warm-blooded animals, where it is a part of normal flora. Escherichia coli is opportunistic pathogenic bacteria, which cause disease only in a patient whose defense mechanisms against infection have been weakened. It causes acute gastrointestinal disease, urinary tract infections, bactericemia meningitis, pulmonary infections, abscesses and skin infections. 7

2.3.1. Preparation of sub culture

Sample organisms of Escherichia coli, was received from the Department of Zoology, Govt. Model Science College, Jabalpur (M.P.), were grown in broth and incubated for 18 h, at 37±1°C. The obtained growths were introduced into the agar plate, under sterile condition7, for the bacterial culture. The broth was used for subculture; it was prepared by dissolving Nutrient broth (2.8 g) in distilled water (100mL). Sterile cotton swab dipped in this broth was streaked onto the agar plate.

2.3.2. Isolation of pure culture

‘Well diffusion method 8 was applied for antibacterial testing. Assays of test microorganisms were done on agar plate by lawn culturing from the sub culture. Agar plates were prepared, by dissolving Muller Hinton Agar (3.8g) into distilled water (100mL), in a 250mL conical flask; and the cotton swab was placed on it. Media and petriplates were sterilized by autoclave. The well were prepared on each agar plate by using a standard bore with a diameter of 5 mm, in which 50 µL solution of test sample of different concentration were filled. The agar plates were further incubated at 37±1°C, for 24-48 hours for the growth becomes appreciable. During this period the last solution diffuse and growth of inoculated microorganisms were affected.

2.3.3. Antibacterial activity

Antibacterial properties of sample were assessed, which were apparent from the circular zone of bacterial inhibition around well. The diameter of this zone of bacterial inhibition was measured in millimeters and the zone was found more than 8 mm, was taken as active inhibition zone. Antibiotic chloramphenicol was used for comparison.

References

1. A. I. Vogel, “Textbook of Practical Organic Chemistry”, 4th Edn., Longman, London, (1978).

2. A. I. Vogel, “Textbook of Quantitative Inorganic Analysis”, 3th Edn. (ELBS and Longman; Green London) 486, 495, 526, 529, 573, 574 (1964).

3. G. H. Jeffery, J. Bassett, J. Mendham, R. C. Denney, “Vogel’s Textbook of Quantitative Chemical Analysis”, 5th Edn. (ELBS and Longman; London) (1989).

4. S. N. Shukla, P. Gaur, H. Kaur, M. Prasad, J. Coord. Chem. 60(10), 1047-1055 (2007).

5. P. B. Chakrawarti, J. Ind. Chem. Soc. 78, 273 (2001).

6. N. Raman, J. Dhaveethu Raja, Ind. J. Chem. 46A, 1611-1614 (2007).

7. M. J. Pelczar, E. C. S. Chan, N. R. Krieg, “Text Book of Microbiology”, 5th Edn. McGraw-Hill Publishing Company Ltd. 138 (2001).

8. P. V. Menon, N. D. Shashikiran, V. V. S. Reddy, J. Ind. Soc. Pedodontics Prevent Dent. 133-136 (2007).

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