COPPER(II) COMPLEXES WITH CYCLO(L-ASPARTYL-L-ASPARTYL) AND CYCLO(L-GLUTAMYL-L-GLUTAMYL) DERIVATIVES AND THEIR ANTIOXIDANT PROPERTIES

Two new functionalized cyclodipeptides have been synthesized with the aim of obtaining a good model of superoxide dismutase. Better to mimic the: active site of this metalloenzyme, these two compounds have been designed to allow a great co-ordination flexibility. Copper(II) compl exes with cyclo(-L-aspartyl-L-aspartyl-) or cyclo(-L-glutamyl-L-glutam yl-)bis(histamine) (L) have been thermodynamically and spectroscopical ly characterized and their antioxidant activity tested against enzymat ically generated O-2(-). Taking into account the Speciation of the sys tem, it has been determined that the more active species against O-2(- ) is the [CuL(2)](2+) complex. Electron spin resonance measurements su ggest for this species the presence of four imidazole nitrogen atoms i n a slightly tetrahedrally distorted co-ordination plane. The [CuLH(-2 )] complex species also possesses four-nitrogen co-ordination involvin g two deprotonated peptide nitrogen atoms. The complex [CuL(2)](2+) sh owed the highest antioxidant activity and reasons for this behaviour a re proposed on the basis of spectroscopic and voltammetric data.