Studies on transition-metal–peptide complexes. Part 9. Copper(II) complexes of tripeptides containing histidine

Abstract

Copper(II) complexes of the histidine-containing tripeptides glyclyl-L-histidylglycine (GlyHisGly), glycylglycyl-L-histidine (GlyGlyHis), and L-pyroglutamyl-L-histidyl-L-prolinamide (trf), and the dipeptide L-pyroglutamyl-L-histidine methyl ester (pghme), have been studied by pH-metric and spectrophotometric methods. It was found that, similarly as for glycyl-L-histidine (GlyHis), GlyHisGly forms a complex [CuAH_–1], but bis complexes are also formed in low concentration. For GlyGlyHis, only the highly stable species [CuAH_–2]^– is formed. A complex [CuAH_–2]^– is also formed with trf and pghme which indicates that the prolinamide side-chain in trf does not take part in the co-ordination. The sequence of deprotonation of the N¹H group of the imidazole side-chain is as follows: GlyHisGly > GlyHis > pghme > trf > GlyGlyHis.