Study on ternary complexes of some heavy metal ions with biologically important ligands

Abstract

Ternary complexes are known to provide models for mctalloenzymcs and several other biological processes involving metal ions. The principles of coordination chemistry will thus allow an increasing under:;landing of the structure and dynamic fealures involved in biochemical processes. Ternary metal complexes oftypc [MAL], where M=Cu(ll), Ni(II), & Zn(lI), A=Aspertic Acid(Asp), 1,10 Phenanthrolinc (1,10 ph) and L= Ethylenediamine (en),a-alanine( a-ala), Glyeine(gly), Phenylalanine(ph-ala), Tyrosine(tyro) have been investigated potentiometrically at 2S"C and at ionic strength of a.2M (NaCI04). The stability constants have been determined using SCOGS (Stability Constant of Generalized Species) computer program. The stabilities in ternary complexes have been discussed in terms of Iigandligand interaction, steric interaction, basicity of the ligands, nature of donur sites and charge neutralization factor:;. The stabilization is expressed in terms of L'!.logK.Thc L'!.logKvalues and percentage species computcd gave parallel evidencc for the stabilization of tcmary eomplcxes. The stabililies of ternary complexes have been quantitatively compared 'Witheach othcr. It is observed that for the ternary complexes of ellen), 6.1ogK values are more negative than eorrcsponding Ni(ll) ternary complexes. This is due ,J the absence of Jahn- Teller distortion in Ni (ll) complcxes. It is also observed that &Iog K values are positive when phenylalanine and tyrosine are coordinated with c<:ntral metal ion. This is due to the intramolecular intcriigand interaction ben,vecn non-coordinaled side groups. •••• Another reason of extra stabilization of tyrosine is due to intramolecular interligand hydrogen bonding and stacking intcration of phenylalanine and tyrosine with metal ion. Additional stabilization in the eomplcxs can o<.:eur due to the noneovalent hydrophobic interaction between non-coordinated side group phenyl and hydroxyphenyl of phenylalanine and tyrosine respectively with A(Asp, 1,10 ph). Hence, in the present investigation, the orders of the stability of the ternary complexes is as follows- (Zo(A)(Ll] > [N;(A)(Ll] > [Cu(A)(L)) The formation of the complexes also has been confirmed by Cyclic Voltamrnogram.