STRUCTURAL, BIOASSAY AND THERMAL STUDIES OF METAL COMPLEXES WITH NOVEL SCHIFF BASES

Abstract

Schiff base chemistry was elaborately studied using the anionic ligands obtained by reacting, various primary aryl amines with medicinally important salicyldehyde. Different ligands, ranging from simple non rigid bidentate/tridentate anionic Schiff base ligands to sterically free twisting ligands have been prepared. All these ligands were complexed with transition metals like cobalt, nickel, copper and zinc. The coordination complexes of square planar and distorted tetrahedral geometry were obtained for bidentate anionic Schiff base ligands and octahedral for tridentate Schiff base ligands. Characterization of all the Schiff base ligands were done using various spectroscopic and analytical methods including 1 H, 13 C{ 1 H}-NMR, infrared spectroscopic method, ES + -MS, elemental analyses and conductance studies. Apart from it Schiff base ligands like 2-[(E)-(quinolin-3-ylimino)methyl]phenol (H-QMP), [1-({[(Z)-(2-hydroxynaphthalen-1- yl)methylidene]amino}methyl)cyclohexyl]acetic acid (H-HHMAC) and 2-(2-hydroxyphenyl)-3- {[(E)-(2-hydroxyphenyl)methylidene]amino}-2,3-dihydroquinazolin-4(1H)-one (H-HHAQ) were recrystallized from concentrated THF solution in Pc, P1 and C222 1 space groups respectively. All the synthesized transition metal complexes of the representative Schiff base ligands were also characterized by elemental analyses, ES + -MS, IR and UV Visible spectroscopic studies, magnetic susceptibilities and molar conductance studies. The metal complexes like 1 and 2 were recrystallized by slow diffusion of diethyl ether into the concentrated solution of metal complexes in CH 2 Cl 2 in P2 1 /c space group having trans square planar arrangement of ligand around the metal centers. Based upon the medicinal importance of the salicyldehyde unit the Schiff base ligands and its metal complexes were studied for their In Vitro enzyme inhibitory activities against urease, α- iiichymotrypsin, acetylcholinesterase and butyrylcholinesterase in order to study their effectiveness to treat peptic ulcer and Alzheimer disease. Ligand like H-HHMAC was found active against urease α-chymotrypsin and acetylcholinesterase whereas the Schiff base ligands like CIMP and BIMP were found good inhibitors for α-chymotrypsin. It was found that metal based inhibitors for urease can be designed which include metal complexes like 7, 11, 18 and 22 respectively, similarly for α-chymotrypsin the metal based inhibitors include 18 and 19, for acetylcholinesterase are 19, 20, 23 and 24 metal complexes and for butyrylcholinesterase the inhibitors are 2, 3, 14, 18, 19, 20, 22 and 23. In all these compounds interesting results were obtained for 3 metal complex which is acting as selective inhibitor of butyrylcholinesterase and 7 and 11 which are acting as selective inhibitors for urease. Apart from it all the synthesized compounds were studied for their antimicrobial activities against pathogenic microbes including Gram positive bacteria Bacillus atrophaeus, Bacillus subtilis, Staphylococcus aureus, Gram negative bacteria Klebsiella pneumoniae, Salmonella typhus, Pseudomonas aeruginosa, Escherichia coli, Agrobacterium tumefaciens, Erwinia carotovora, fungal Strain Candida albican. These results suggest that metal complexes and Schiff base ligands are moderately active against these microbes. All the compounds were studied for their thermal degradation studies using TG-DTA analysis in the temperature range 30-1000 o C under static air at 10 o C rise/minute. The thermogravimetry (TG) and Differential thermal analysis (DTA) curves were obtained and used for kinetic and thermodynamic calculations. The activation energies and order of pyrolysis were calculated using Horowitz–Metzger method. The TG results and calculated activation energies were subsequently used for the calculations of thermodynamic parameters including change in entropy of activation, change in enthalpy of activation and change in Gibb’s free energy of activation. ivIncreasing activation energy order and also the order for stability was assigned to each studied series. Part II The synthesis of highly fluorinated zinc carboxylates [{CF 3 (CF 2 ) 5 CH 2 CH 2 CO 2 } 2 Zn], and alkoxides [{CF 3 (CF 2 ) 5 CH 2 CH 2 O} 2 Zn(OEt 2 ) 2 ] and their use as catalysts for the ring opening polymerisation of ɛ-caprolactone are described. Quenching the polymerisation reaction with fluorous acids or alcohols regenerates the catalyst, which can be recovered by fluorous solvent extractions, and the catalytic activity is retained for three cycles. The superior recyclability of the alkoxide to the carboxylate zinc compound is due to the greater partition coefficient between fluorous and organic solvents. The well-defined aryloxide compound [(ArO) 2 Zn(THF) 2 ] were also investigated, which yields very well controlled polymerisation, but cannot be recycled by quenching with a fluorous alcohol.