6533b826fe1ef96bd1283e60

RESEARCH PRODUCT

N-p-Amino- and N-p-nitro-phenylsulfonyl derivatives of dipeptides, a new family of ligands for copper(II). Potentiometric and spectroscopic studies

subject

description

The co-ordination ability of four dipeptide analogues substituted on the N-terminal amino group with p-nitrophenylsulfonyl (nps-Ala-Ala and nps-Ala-His) and p-aminophenylsulfonyl (aps-Ala-Ala and aps-Ala-His) groups was studied by potentiometric and spectroscopic (UV/VIS absorption, CD and EPR) techniques. The N-terminal sulfonyl substituent drastically changes the acidity of the sulfonamide proton making nitrogen very efficient in binding to CuII. The sulfonamide nitrogen having pK between 9 and 11 does not need any anchoring binding group to form complexes with CuII. The para substituent on the phenyl ring (amino or nitro) influences very strongly the acidity of the sulfonamide proton. The nps or aps moieties change the co-ordination equilibria considerably when compared to the parent dipeptide Ala-His. Both groups enforce the formation of dimeric complexes, whereas in the case of the parent dipeptide the major species are only monomeric.