Solution structural studies of molybdate-nucleotide polyanions

The complexation of molybdate with the nucleotides adenosine-5'-monophosphate (5'-AMP), adenosine-3'-monophosphate (3'-AMP) and guanosine-5'-monophosphate (5'-GMP) has been investigated by H-1 and P-31 NMR and Mo K-edge X-ray absorption near edge (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Acidification of aqueous solutions containing molybdate and each of the nucleotides resulted in the formation of a single species characterized by H-1 resonances which are deshielded relative to those of free nucleotide. Analysis of the two-component systems indicated a Mo/nucleotide ratio of 2.5:1 for the complexation species. White compounds, characterized as Na-2[Mo5O15(HB)(2)] (B = 5'-AMP, 5'-GMP), have been isolated from the acidified molybdate/H2B solutions. Dissolution in D2O replicates the NMR spectra of the solution species observed prior to precipitation. Solution and solid state Mo K-edge XAS and EXAFS spectroscopy of Na-2[Mo5O15(HAMP),] and Na-6[Mo5O15(PO4)(2)] provide convincing evidence for the presence of a pentamolybdodiphosphate core in the molybdate-nucleotide complexes in both the solid and solution states. (C) 2002 Elsevier Science Inc. All rights reserved.