КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 10, с. 774-779
УДК 541.49
COORDINATION CHEMISTRY OF OXOVANADIUM(V) COMPLEXES WITH ACTIVE SCHIFF BASES: SYNTHETIC, SPECTRAL, AND ANTIMICROBIAL APPROACH
© 2007 R. Garg, N. Fahmi, and R. V. Singh
Department of Chemistry, University of Rajasthan, Jaipur 302004, India Received July 14, 2006
The Schiff bases, 3-(indolin-2-one)hydrazinecarbothioamide (LXH), 3-(indolin-2-one)hydrazinecarboxamide (L2H), 5,6-dimethyl-3-(indolin-2-one)hydrazinecarbothioamide (L3H), and 5,6-dimethyl-3-(indolin-2-one)hy-drazinecarboxamide (L4H), have been synthesized by the condensation of ^-indol^^-dione and 5,6-dimethyl-l^-indol-2,3-dione with the corresponding hydrazinecarbothioamide and hydrazinecarboxamide, respectively. The complexes of oxovanadium and ligands have been characterized by elemental analyses, melting points, conductance measurements, molecular weight determinations, and IR, XH NMR and UV spectral studies. These studies showed that the ligands coordinated to the oxovanadium in a monobasic bidentate fashion through oxygen or sulfur and the nitrogen donor system. Thus, penta- and hexacoordinated environment around the vanadium atom has been proposed. All the complexes and their parent organic moieties have been screened for their biological activity on several pathogenic fungi and bacteria and were found to possess appreciable fungicidal and bactericidal properties.
The chemistry of azomethines becomes more and more apparent and is a point of considerable attention because of their well established industrial and biological importance [1]. Metal complexes of these ligands possess a wide spectrum of medicinal properties [2]. Sulfur-containing ligands can show pronounced biological potency as antituberculosis [3], antifungal [4], and antitumor agents [5]. The biopotency, industrial, pharmacological, catalytic, and polymeric properties are also responsible for tremendous and unexpected research in this area [6]. Hydrazinecarbothioamides are known as analytical reagents [7-11]. These compounds contain an azomethine nitrogen atom, and this is responsible for their activity with a number of transition metal ions forming colored complexes [12]. Metal chelates of these reagents inhibit tumor growth and increase the activity of some drugs [12]. The oxovanadi-um(V) ions have a good affinity toward O,N-donor ligands due to its hard nature. Vanadate has been found to interact with biological molecules through various functionalities. Such chemical interactions with proteins and/or other cellular components are likely to be the key in understanding the biological effects of vanadium [13]. The interactions between vanadate and ligands in aqueous solutions are governed by the versatile coordination chemistry of vanadium(V) [13]. Enzymes play vital role in cellular metabolism of microorganisms and inactivation of these biocatalysts ulti-
mately leads to the inactivation of the microorganism [13]. Metal chelates of these reagents are used as pesticides and fungicides in agriculture [14]. In view of the versatile importance of these ligands, it was, therefore, considered worthwhile to prepare and study oxovanadi-um(V) derivatives of some biologically active hydrazi-necarboxamides and hydrazinecarthioamides.
experimental
The VOCl3 was prepared according to the literature method [15]. All the reagents were dried and distilled before use. l#-Indol-2,3-dione and 5,6-dimethyl-l#-indol-2,3-dione were purchased and used as such. All preparations were done under anhydrous conditions [15].
Synthesis of ligands. The ligands 3-(indolin-2-one)hydrazinecarbo-thioamide (L*H), 3-(indolin-2-one)hydrazine-carboxamide (L2H), 5,6-dimethyl-3-(indolin-2-one)hyd-razinecarbothioamide (L3H), and 5,6-dimethyl-3-(indolin-2-one)hydrazinecarboxamide (L4H), were prepared by the condensation of 1^-indol-2,3-dione and 5,6-dimethyl-l#-indol-2,3-dione with hydrazinecarbo-thioamide and hydrazinecarboxamide (in the presence of sodium acetate) in 1 : 1 molar ratio in ethanol. The reaction mixture was re fluxed for 3-4 h and the separated solid was removed by filtration, re-crystallized from ethanol, and dried in vacuo [16]. Structures of the ligands are the following:
Y-
N—NH— C—NH2
X
Y
"O
n—n=c-nh2
XH
O
Y = 5,6-Dimethyl; X = S (L3H) and O (L4H).
Preparation of complexes. The VOCl3 was added with sodium salt of the ligands in 1 : 1 and 1 : 2 molar ratios in dry methanol. The resulting mixture was heated under reflux for 10-12 h and filtered to remove NaCl, and the solvent was removed under reduced pressure. The product was dried in vacuo. The complexes were washed with dry n-hexane and again dried in vacuo for 3 h. The complexes are soluble in methanol, DMF, DMSO, and THF. They are monomeric and nonelectrolytes.
Preparation of sodium salt of ligand. The sodium salt of the ligand was prepared by reacting the ligand with sodium metal in the 1 : 1 molar ratio in a methanol medium.
Physical measurements and analytical methods.
The molecular weights were determined by the Rast Camphor Method. Conductivity measurements in anhydrous DMF were performed on a Systronic model 305 conductivity bridge. Infrared spectra were recorded on a Nicolet Megna FTIR-550 spectrophotometer using KBr pellets. Electronic spectra of the complexes were recorded in chloroform on a UV-160A Shimadzu spectrophotometer in the range 200-600 nm. XH NMR spectra were recorded in deuterated dimethyl sulfoxide (DMSO-d6) using tetramethylsilane (TMS) as standards on a JEOL-AL-300 FT NMR spectrometer. Vanadium was estimated as V2O5, whereas sulfur, chlorine, and nitrogen were determined by Messenger's, Volhard's, and Kjeldahl's methods. Carbon and hydrogen analyses were performed at the Central Drug Research Institute (CDRI) (Lucknow) [17] (Table 1).
Antifungal screening. The antifungal activity of the ligands and their complexes with vanadium has been estimated by the radial growth method using the composition: glucose 20 g, starch 20 g, agar-agar 20 g, and distilled water 1000 ml. Solutions of the test compounds in methanol at 50, 100, and 200 ppm concentrations were prepared and then were mixed with the medium. These Petri plates were wrapped in polythene bags containing few drops of alcohol and were placed in an incubator at 25 ± 2°C. The controls were also run, and three replicates were used in each case. The linear growth of the fungus was obtained by measuring the fungal colony diameter in Petri plates after 4 days. The percentage inhibition was calculated as 100(C - T)/C, where C and T are the diameters of the fungus colony in the control and test plates, respectively. The organisms used in these investigations included Macrophom-ina phaseolina and Fusarium oxysporum [17].
Antibacterial screening. The activity against bacteria was estimated by the paper disc plate method [18]. The nutrient agar medium having the composition peptone (5 g), beef extract (5 g), NaCl (5 g), agar-agar (20 g), and distilled water (1000 ml) was pipetted into the Petri dish. When it solidified, 5 ml of warm seeded agar was applied. The seeded agar was prepared by cooling the molten agar to 40°C, and then an amount of a bacterial suspension was added. The compounds were dissolved in methanol in 500 and 1000 ppm concentrations. Paper discs of Whatman No. l filter paper (measuring diameter of 5 mm) were soaked in these solutions of varied concentrations. The discs were dried and placed on the medium previously seeded with organisms in Petri plates at a suitable distance. The Petri plates were stored in an incubator at 28 ± 2°C for 24 h. The zone of inhibition thus formed around each disc containing the test compounds was measured accurately in mm. The organism used in these investigations included Escherichia coli and Staphylococcus aureus [18].
RESULTS AND DISCUSSION
The resulting oxovanadium complexes are dark green solids, soluble in methanol, DMF, and DMSO, and sparingly soluble in H2O. The molar conductances of 10-3 M solutions of the complexes in DMF lie in the 10-15 Ohm-1 cm2 mol-1 range, indicating that they are nonelectrolytes. Molecular weight determinations indicate their monomeric nature. The reactions of VOCl3 with sodium salts of the ligands were carried out in unimolar and bimolar ratios in methanol. The successive replacement of chloride resulted in the formation of products [VOCl2(L)] and [VOCl(L)2] as shown below.
VOCl3 + LNa
VOCl3 + 2LNa
Methanol 1 : 2
Methanol
[VOCl2(L)] + NaCl, (1) [VOCl(L)2] + 2NaCl. (2)
The reactions in a 1 : 3 molar ratio were also attempted but even on prolonged heating did not proceed beyond the replacement of two chlorine atoms by the ligand moieties, and [VOCl(L)2] type of derivatives were the end products. The complexes isolated are presented in Table 1 together with their analytical data.
UV spectra. The electronic spectra of the ligands show two maxima at ca. 274 and 316 nm due to n-n* transitions of the aromatic ring [19]. The band at ca. 336 nm due to n-n* transitions of the >C=N chro-mophore shows a bathochromic shift of 20-30 nm in the complexes. This shift is due to the coordination of
1 : 1
Table 1. Elemental analisis data and some physical characteristics of the ligands and their oxovanadium complexes
On
W O O hj M
s
ffi >
s O
ffi
ffi >
s s
1
o
(O
o o -J
Compound Empirical formula Color Melting Yield, Contents (found/calcd), % Molecular weight (found/calcd)
point, °C % V N S C1 C H
LXH C9H8N4SO Dark green solid 217 84 25.13/25.43 14.12/14.55 49.01/49.13 3.18/3.66 205/220
L2H C9H8N4O2 Grey solid 228 93 27.10/27.43 52.18/52.98 3.65/3.95 200/204
[VOa2(L1)] C9H7VN4SO2C12 Green 293 72 14.15/14.26 15.23/15.69 8.23/ 8.97 19.81/19.85 30.11/30.27 1.89/1.97 351/357
[VOCl(L1)2] C18H14VN8S2O3C1 Dim green 286 77 9.12/9.41 20.64/20.71 11.11/11.85 6.32/6.55 39.92/40.03 2.18/2.61 523/540
[VOC12(L2)] C9HvVN4O3C12 Dark green 297 81 14.54/14.93 16.22/16.42 20.33/20.79 30.99/31.79 2.01/2.0
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