Structural and Biological Behaviour of Co(II), Cu(II) and Ni(II) Metal Complexes of Some Amino Acid Derived Schiff-Bases

Biologically active tridentate amino acid (Alanine, Glycine & Tyrosine) derived Schiff-bases and their Co(II), Cu(II) & Ni(II) complexes have been synthesised and characterised on the basis of their conductance and magnetic measurements, elemental analysis and 13C-NMR, 1H-NMR, IR and electronic spectral data. These Schiff-bases and their complexes have been evaluated for their antibacterial activity against bacterial species such as Staphylococcus aureus, Escherichia coli, Klebsiella pneumonae, Proteus vulgarus and Pseudomonas aeruginosa and this activity data show the metal complexes to be more antibacterial than the Schiff-bases against one or more bacterial species.


Introduction
Transition metal chemist of virtually all naturally occurin amino acids has been studied in details-4. Almost all a_mino acids have been found to coorlinate solely through, th.e amino. and carboxylato groups tOrming a stable five membered chelate ring system with the metal ion , 6. In the present studies we have introduced an azomethine lilage which may permit a variety in their coordination behaviour and complexation role.Therefore noveI Schiffbases HLb HL and HL3 (Fig 1) were synthesised by. the reaction of amino acids e. g; tyrosine, alanine & glycine with ind.ole-3-carboxaldehyde, and their co-ordination behaviour with Co(II), Cu(II) and Ni(II) metal ions was investigated. All chemicals and solvents used were of Analar grade. All the metals were used as their chloride salts. Infrared and UV. spectra were recorded on IR 4_08. Shimadzu  H2SO were alded and this mixture was refluxed for l h. Tile reaction mixture was tlaen cpoled in an ice-bath which imm. ediately ave a p.rec.ipitated, product. The product thus obtained was filtered, washed witla ethanol 1 x 5 ml)tlaen with ether (2 x 5 ml) and dried. The crude product was crystallised from aqueous ethanol to give HL (70%), HL2 (68%) and HL3 (65%.)

Antibacterial Studies
The synthesised metal comolexes and the free Schiff bases were screened for their antibacterial activity against bacterial species Staphylococcus aureus (a), Escherichia coli (b), Klebsiella 19neumonae (c), Proteus vulyzarus -(.d) and Pseudomonas aeruginosa (e).The laper disc diffusion methode3-e5 was used for the determination of antibacterml activity Preparation of Discs A Schiff base / complex (30g) in DMF. (0.01 ml) was applied on a paper disc prepared from blottingap.er (3 mm diameter) with the help of a micropipette. The discs were left in an incubator for 8 h at 37oC and then applied on bacteria grown agar plates

Preparation of Agar Plates
Mimm.al aga_r was used for the growth of specific bacterial species. For the preparation of agar plates br Escherichia coli, MacConkey agar (50 g), olStained from Mercl Chemical Company, w. as suspended in freshly d.ist.illed .w. ater (l-L). It was allowed to soak for ! 5 minutes and then boiled on a water Oatla until the aar was completely dissolved. The mixture was autoclaved for 15 minutes at 120_C and t-hen poured into previously washed and sterilised petri dishes and stored at 40o C for inoculation.

Procedure oflnoculation
Inoculation was done with the help of a platinum wire loop which was made red hot on a flame, cooled and then used for the application of bacterial strains.

Application of Discs
A sterilised forcep was used for the application of paper disc on the already, inoculated aar p.lates. When the discs were app.lied, they were incubated at 370 C for 24 h. The zone ot" infiibition was then measured (in diameter) around the disc.
Results and discussion chiff-bases we_re prepared by. the same method as reported earlier7-9.The structural etermination or synthesised Schiff bases HL, HL and HL3 was done on the basis of their IR, H-NMR, 3C-NMR and CHN analytical data (Table 1 & 2). The IR spectra of the Schiff bases (Table 1) (Table 2)as assigned by comparin the chemica! shifts or-these molecules to those of tle known similar structures. The CHN analytical data (Table 1) also i.s found to be in agreement with the expected molecular structures orthe Schiffbases and their metal complexes (Table 3).  The metal complexes (1-9) of the title Schiff bases were prepared by reacting the metal(II) chloride and ttie Schiff base in the molar ratio M:L I:2. All the comp.lexes are stable crystalline solids which decompose without melting. The conductivity behaviour of these complexes in DMF show their low conductivity values (14-18 ohm-cruZ mol-) observed r these complexes in DMF .suggest, 12 them to be non-electrolyte.
ne magnetic susceptibility data ( It indicated that v (-C N) band in the spectra of tile Schiffases at 1625 cmdue to azomethine linkage was shifted towards lower freouencv (5-10 cm-), respectively, indicatin that the ligands are coordinated to the mtal toms through azomethine nitrogen. Also, in the spectra of the Schiff bases the bands due to v (C O) 1730 cmshiftec towards lower frequency side and the band due to v (OH) at 3465 cm disappeared which was an evidence for the coordination of these groups with the metal atqm. How.ever, the band at 3380 cmdue to v (-Nit) of indole remained unchanged indicating tlaat it is not involved in the coordination. Moreover, the new bands appearing in Volume 4, No. 5, 1997 Structural and Biological Behaviour of Co(II), Cu(II) and Ni(II) Metal Complexes of Some Amino Acid Derived Schiff-Base Ligands the spectra of the metal complexes and not observed in the spectra of the free Schiff bases within 445 450 cmand 435-440 cm-assinedl6, 17 o M O and M N modes, conclusively indicated that the ligands are coordinated to the metal ions through these groups. The electronic spectra of the metal co.rnplexes , (Table 3) show different .max va!ues with various metal(II) ions which is due to the pertur.bin influence of the central metal ato 9 n the chelate group. The shi.ft ot the band witl te change of different colours ot te comNexes however, strengthen the evidence of complex formation. In these spectra, the Co(l-I) complexes exhibit bands between 29100 3100, 17550 18215 and 8250 9850 cm-region assigned to the transitions 4Tl (F) (P) 4T2 (F)(Vl), 4TI_ (F) --> 4A2 (F)(V2) and 4T,lg.(F) ---)4Tg (P)(V3) in an octahedrgl geometry', 19. The spetra of Cu0.I) complexes exlfibit three broad bands in the region 30270-31500, 22550 23170 and 12500 13750 cm-. The lower energy band may be assigned as 10 Dq band for a distorted octahedral con.figura.tion20, 21 corresponding to the transition 2E g__, 22g The second band can. be attrib_uted to intra liand charge transfer and the highest energy, band is assigned to claarge transter transitions. The electronic spectra of N1 (II) complexes showea three ban:Is between 28350 28950 16250 17500 and 9555 10220 cmregion assignable, respectively, to the transitions 3 A), (F) 3 T 2 e (F)(V1), 3A 2e (F) 3"[' lg (F)(V2) and 3_.A2g ,(F) ---) 3T2. (P)(V3) suggest theTr oftheir octahedral geometfy:Z2, .23.
Qn ttie basis bT ttie above observations, it is, therefore, proposed tlaat al! the complexes show octa.hedral geometry in wh.ich the. two ligand.s betiavin.g as tridentate possibly accommodate themselves around the metal atom in sucla a way that a stable configuration ofa chelate ring is formed (Figure 2).  Antibacterial Studies Volume 4, No. 5, 1997 Structural and Biological Behaviour of Co(II), Cu(II) and Ni(II) Metal Complexes of Some Amino Acid Derived Schiff-Base Ligands The title Schiff bases HL l, HL2 and HL3 and their metal complexes 1-9 were tested for their antibacterialproperties against Staphylococcus aureus (a), Escherichia coli {b), Klebsiell.a pneumon.ae (c)., Proteus vulgarus (d) and Pseudomonas aeruginosa (e). All the compounds were evaluated at a concentration of 30 tg / 0.01 ml in DMF solution using the paper disc diffusion methodZ4 6. These studies (Table 4) show that all the free Schiff bases are biologi.cally active and their metal complexes show more significant activity against one or more bacterial species than the uncomplexed free Schiffbases.