AN A-FORM OF POLY[D(A-C)]CENTER-DOT-POLY[D(G-T)] INDUCED BY MERCURY(II) AS STUDIED BY UV AND FTIR SPECTROSCOPIES

The conformational changes of poly[d(A-C)].poly[d(G-T)] induced by Hg( CIO4)(2) in aqueous solution have been studied using UV absorption and fourth derivative spectrophotometries, and FTIR spectroscopy. The UV absorption and fourth derivative spectra reflect changes in the polynu cleotide stacking interactions as a result of the metal-polynucleotide interaction. The fourth derivative spectra do not indicate a Z-form e ither at low or at high metal-to-polynucleotide ratios. Furthermore, t he infrared spectrum at high metal-to-polynucleotide ratio (r = 1.2; r = [Hg(CIO4)(2)]/[nucleotide] molar ratio) has the main features of an A-form, in contrast with previous CD studies which proposed that the polynucleotide adopts a Z-form under these conditions. The nature of a different conformation of the polynucleotide induced at low r-ratios (r less than or equal to 0.2) is discussed.