Raman spectroscopic study of tripler-like complexes of polyuridylic acid with the isopolar, non-isosteric phosphonate analogues of diadenosine monophosphate

The formation of poly(rU) complexes with diadenosine monophosphate (3'-5') and its four isopolar, non-isosteric phosphonate analogues was studied by m eans of Raman spectroscopic titration. A set of mixed samples containing th e diadenosine monophosphate or monophosphonate and the poly(rU) at various concentration ratios was prepared. The room temperature spectra of mixed so lutions were treated by factor analysis and decomposition of the Raman mark er bands. For all the species studied, the results revealed an exclusive pr esence of the triplex-like complexes, i.e. complexes with a 1 : 2 stoichiom etric ratio of the adenosine to uridine units, the Raman spectra of which e xhibit all the features typical of the poly(ru).poly(rA).poly(rU) triple-he lical structure. The individual molar fractions of the free ApA dimer, the free poly(rU) and the triplex-like complex do not fit classical equilibrium equation, because the binding ability of the adenosine dimers to poly(rU) falls significantly for small ApA molar fractions. This tendency is stronge st for the natural diadenosine phosphate (3'-5') and weakest for two analog ues in which the -CH2- group in the modified internucleotide linkage is sit uated closer to the 5'-position. Copyright (C) 1999 John Wiley & Sons, Ltd.