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

The spectroscopic properties of Cu(bio-monomer)(n)(m+) complexes [BM = bio- monomer (purine, adenine, guanine, hypoxanthine, 5'-ADP and 5'-GMP)] in sap onite clays have been investigated by diffuse reflectance spectroscopy (DRS ) in the UV-Vis-NIR region and electron paramagnetic resonance (EPR) at X-b and. Mono-and/or bis complexes of Cu(purine), Cu(adenine), Cu(5'-ADP) and C u(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 wa s determined by the overall Cu-loading, the pH of the initial exchange solu tion and the type of BM. Mono Cu(adenine) and Cu(purine) complexes with a N NOO coordination dominate at low Cu-loadings, or at an exchange solution pH between 3 and 4, whereas bis Cu(adenine)(2)(2+) and Cu(purine)(2)(2+) comp lexes with a NNNN coordination are exclusively present at higher Cu-loading s with an exchange solution pH between 5 and 8. On the other hand, clay-int ercalated Cu(5'-ADP)(+) and Cu(5'-GMP)(+) are always present as mono-comple xes, most probably in a NOOO coordination.