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Thiosemicarbazones is an important class of compounds obtained by condensing thiosemicarbazide with suitable aldehydes or ketones [1]. The active group for chelation is Sulphur [2]. In most of the complexes, the thiosemicarbazones coordinate to the metal ion as a bidentate ligand bonding through the sulphur atom and the hydrazino nitrogen atom. In a few cases they behave as unidentate ligands by bonding only through the sulphur atom. In certain cases thiosemicarbazones also act as multidentate ligands if donor groups are also present in the parent aldehyde or ketone moiety [3]. Ligands with N,N- and N,S-donor atoms and their complexes with first transition series metals have remarkable chemical and biological properties [4]. Active sites of various metallobiomolecules are coordinated by N and S atoms which is very important for biological aspects of these complexes. [5]. Interest in metal complexes with thiosemicabazone ligands has been stimulated because biological activities are often enhanced on complexation [6]. Thiosemicarbazones and their metal complexes have received considerable attention because of their antibacterial, antifungal, antitumor, antiamoebic, antimalarial, antiviral, radioprotective, trypanocidal and anti-inflammatory activities [7-22]. With the growing interest of thiosemicarbazones the present work was undertaken in order to investigate the ligational behaviour of the thiosemicarbazone towards metal ion as well as their biological activity in inhibiting the growth of some pathogenic bacteria [23].

All the chemicals and solvents used in the synthesis of ligands and transition metal complexes were of AR grade used as received. Thin layer chromatography was used to check purity of prepared compounds. IR spectra are recorded between the frequency 4000-500 cm-1 using KBr disc. Magnetic susceptibility of the synthesized transition metal complexes were measured on the vibrating sample magnetometer. Microwave synthesis was carried out in domestic microwave oven specially designed for green synthesis. Double Beam UV-Visible Spectrophotometerwas used for absorption measurement. All biological activities have been carried out with horizontal laminar.

A.    Preparations of Ligands

i. The Synthesis of 3-Nitroacetophenone Thiosemicarbazone (3NAT)

a. Microwave Irradiation Synthesis

A novel method for the preparation has been developed as per the principles of green chemistry, in which, either the reaction mixture was irradiated in a domestic microwave at 600 W for 2-10 minutes on alumina bed or reaction mixture in the solvent or the slurry of reaction mixture was exposed in a microwave reactor at 600 W maintaining different time intervals with respect to occasional and or definite inspection of TLC data. For the synthesis of 3NAT in accordance this novel synthesis method, water or water alcohol mixture of thiosemicarbazide (0.01mol) and 3-Nitroacetophenone (0.01mol) has been taken in Erlen Meyer flask capped with a funnel placed in a microwave oven and irradiated at 600 watt for 2-10 minutes. The reaction was monitored by TLC. After completion the reaction, the reaction mixture was allowed to attain room temperature and solid separated was filtered. The crude product was recrystalized from redistilled ethanol and dried under vacuum after filtration and separation. Purity of compound has been checked by TLC techniques in various solvents.

b. Conventional Thermal Method for Synthesis

In conventional thermal method, a hot ethanolic solution (25 mL) of 3-Nitroacetophenone (0.01 mol) has been mixed to a hot ethanolic refluxing solution (30 mL) of thiosemicarbazide (0.01 mol) in a 1: 1 molar ratio. The reaction mixture was refluxed in a water bath  for about 6-10 hours. Thin layer chromatography was used to check the progress of the reaction. After the concentration and cooling of the reaction mixture, product in crystallized form obtained. Purity of the compound was checked by TLC after a multiple washing and filtration.

The structures of ligands are shown in (Fig.II.B.13). A comparison between the thermal method and microwave method is given in (Table II.B.1).

ii. Synthesis of 4-Hydroxyaetophenone thiosemicarbazone (4HAT)

a. Microwave irradiation synthesis

In microwave irradiation preparation, water or water alcohol mixture of thiosemicarbazide (0.01mol) and 4-Hydroxyaetophenone(0.01mol) has been taken in Erlen Meyer flask capped with a funnel placed in a microwave oven and irradiated at 200 watt for 2-5 minutes. The reaction was monitored by TLC. After completion the reaction, the reaction mixture was allowed to attain room temperature and solid separated was filtered. The crude product was recrystalized from redistilled ethanol and dried under vacuum after filtration and separation. Purity of compound has been checked by TLC techniques in various solvents.

b.  Conventional Thermal method for synthesis

In conventional thermal method, a hot ethanolic solution (25 mL) of 4-Hydroxyaetophenone (0.01 mol) has been mixed to a hot ethanolic refluxing solution (30 mL) of thiosemicarbazide (0.01 mol) in a 1: 1 molar ratio. The contents have been refluxed for about 6-10 hours in a water bath. The reaction was monitored by TLC. The reaction was monitored by TLC. After the concentration and cooling of the reaction mixture product in crystallized form obtained. Purity of the compound was checked by TLC after a multiple washing and filtration.

The structures of ligands are shown in (Fig. II.B.17). A comparison between the thermal method and microwave method is given in (Table II.B.1)

TablE I
Physico-chemical Data of Thiosemicarbazones

(C.M. = Conventional method, M.M. = Microwave method)

Compound	Colour	Reaction Period		Yield (%)
		C.M. (Hrs)	M.M. (Min.)	C.M.	C.M.
3NAT	Brown	9.0	2.00	43	56
4HAT	Light Brown	8.0	2.30	53	64

Infrared Spectra

Fig.1.  IR spectra of 3NAT and 4HAT

Structure of 3NAT and 4HAT

iv. Biological Activities

The antibacterial activity of the compounds against E.coli, S.aureusand B.subtiliswere carried out using Muller Hinton Agar media (Hi media). The activity was carried out using paper disc method is represented in Table 2 which shows that both the 4NAT and 3NBT ligands have moderate antibacterial activities against these bacteria. Among the both ligands, 3NBT ligtand has been found out to be most effective against S.aureus bacteria showing maximum clarity of zones.

Fig.3 Biological avtivities

Table 2 Biological activities of Ligands

S. No.	Ligands	Zone of inhibition (in mm)
		E. coli	S. aureus	B. subtilis
1	4NAT	0.5	0.6	0.7
2	3NBT	0.5	8.0	0.6

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