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.
