FORMATION-CONSTANTS AND EXTRASTABILISATION OF MIXED-LIGAND COMPLEXES OF CO2-DIPYRIDYL O-PHENANTHROLINE AND AMINO-ACIDS(, NI2+, CU2+, ZN2+ AND CD2+ WITH ALPHA,ALPHA')

Formation constants (log K(MAL)MA) of mixed ligand complexes of the ty pe [MAL] (where M = Co2+, Ni2+, Cu2+, Zn2+ or Cd2+, A = alpha, alpha'- dipyridyl (dipy) or o-phenanthroline (phen), and L = alpha-alanine (al pha-ala), glutamine (gln), asparagine (asn), aspartic acid (asp), glut amic acid (glu), ornithine (orn), arginine (arg), proline (pro) or hyd roxy-proline (hy-pro)) have been determined pH-metrically usually the Irving-Rossotti approach. There is an evidence of extrastabilisation o f these complexes with gln, asn, arg and orn. The observed stability s equence with respect to metal ions is generally Co2+ < Ni2+ < Cu2+ > Z n2+ >Cd2+ and that with respect to amino acids is (i) asn > gln, (ii) asp > glu, (iii) arg > orn and (iv) pro > hy-pro for related amino aci ds.