Raman spectra and binding of CuII to purine nucleotides

Raman spectra of adenosine 5′‐monophosphate, poly(rA), guanosine 5′‐monophosphate and their CuII complexes have been obtained and analysed by referring to spectra of D‐, 15N‐ and 13C‐labelled nucleobases. The greatest spectral changes on attachment of CuII to these nucleotides are associated with changes in the five‐membered ring and suggest that the metal binds preferentially to N‐7 of nucleobases. However, in the CuII coordinated poly(rA) species, N‐1 binding sites are also present to some extent, as deduced from the comparison of the Raman spectrum of the Cu‐poly(rA) complex with that of the protonated polynucleotide. In the complexes of guanosine 5′‐monophosphate with CuII, the guanine residue is located at the anti position with respect to the ribose moiety through the glycosidic bond. In all cases, strong changes are also recorded for characteristic bands of phosphate groups, indicating their participation as ligands surrounding CuII.