Studies on some copper(II) ternary complex systems containing amino acids

Abstract

The chemical equilibria involved in CU(II)-<img src='http://www.niscair.res.in/jinfo/small.gif' border=0>( + )-aspar-agine/<img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-aspartic acid(A)-<img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0><img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-2-aminobutyricacid (2-aba)/<img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0><img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-3-aminobutyric acid (3-aba)/4-aminobutyric acid (4-aba)/<img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0><img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-4-amino-3-hydroxybutyric acid (ahba) and Cu(II)-<img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-aspartic acid(A)- <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>( + )-asparagine(B) ternary systems have been studied by <em>p</em>H-titrimetry at 37ᵒC and <em>1</em>=0.15 NaClO₄ in aqueous perchlorate medium. In the Cu(II)-asparagine/aspartic acid(A)-4-aba(B) ternary systems and Cu(II)-aspartic acid(A)-ahba (B) system, no appreciable complex formation is revealed. In the remaining systems, CuAB type of ternary species has been detected in addition to the binary species due to ligands A and B. In the copper(II)-asparagine(A)-2-aba/3-aba/-ahba (B) systems, asparagine binds in a glycine like mode. The ahba ligand in the copper(II)-asparagine(A)-ahba (B) system appears to bind in a bidentate manner. The results on the Cu(II)-aspartic acid(A)-2-aba/3-aba/asparagine (B) systems indicate that aspartic acid functions in an ambidentate manner. The preferential formation of the Cu(II) chelates containing five-and six-membered rings has been well demonstrated from the results in the present investigation.