Synthesis and spectroscopy of clay intercalated Cu(II) bio-monomer complexes: coordination of Cu(II) with purines and nucleotides

Abstract

The spectroscopic properties of Cu(bio-monomer)_n^m+ complexes [BM=bio-monomer (purine, adenine, guanine, hypoxanthine, 5′-ADP and 5′-GMP)] in saponite clays have been investigated by diffuse reflectance spectroscopy (DRS) in the UV-Vis-NIR region and electron paramagnetic resonance (EPR) at X-band. Mono- and/or bis complexes of Cu(purine), Cu(adenine), Cu(5′-ADP) and Cu(5′-GMP) have been intercalated between the layers of saponite by a simple cation exchange procedure from aqueous solutions of pre-formed Cu(BM)_n^m+ complexes. Successful immobilisation was obtained with a BM:Cu²⁺ ratio of 5, but the exact coordination geometry of the intercalated complexes was determined by the overall Cu-loading, the pH of the initial exchange solution and the type of BM. Mono Cu(adenine) and Cu(purine) complexes with a NNOO coordination dominate at low Cu-loadings, or at an exchange solution pH between 3 and 4, whereas bis Cu(adenine)₂²⁺ and Cu(purine)₂²⁺ complexes with a NNNN coordination are exclusively present at higher Cu-loadingswithanexchangesolutionpHbetween5and8.Ontheotherhand, clay-intercalated Cu(5′-ADP)⁺ and Cu(5′-GMP)⁺ are always present as mono-complexes, most probably in a NOOO coordination.