Cisplatin adducts of d(CCTCTGGTCTCC)·d(GGAGACCAGAGG) in aqueous solution by vibrational circular dichroism spectroscopy

The vibrational circular dichroism (VCD) and IR absorption spectra of a dodecamer d(CCTCTGGTCTCC)·d(GGAGACCAGAGG) coordinated with cisplatin are distinct compared to those of the dodecamer without cisplatin. Although the intensity of PO2/deoxyribose absorptions (1150–850 cm−1) increases noticeably relative to those of the carbonyl and ring deformations of the bases (1750–1500 cm−1), the VCD spectra differ to a much greater extent. Overlapping positive and negative bands can be assigned relatively easily to individual vibrational modes. The effect of platination on the dodecamer duplex is expressed most prominently in VCD arising solely from the vibrations of the guanines bound to the platinum atom. The effect on the VCD features of other bases leads to minute wavenumber shifts at most. These observations are in agreement with previous NMR and X‐ray experiments on the same oligonucleotide. The assignment of the absorption and VCD bands strongly resembles those of the octamer duplex d(CCTGGTCC)·d(GGACCAGG) when coordinated with platinum. The spectra of the dodecamer did not indicate any isomerization of the complex with time, as is clearly the case for the octamer. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 490–499, 2003