Interaction of cisplatin with 5′-dgmp: a combined irmpd and theoretical study

IR multiple photon dissociation (IRMPD) spectroscopy of cis-[Pt(NH3)2(5′-dGMP-H)]+ and cis-[PtCl(NH3)2(5′-dGMP)]+ ions (where 5′-dGMP is 2′-deoxyguanosine-5′-monophosphate), generated in the gas phase by electrospray ionization, was performed in two spectral regions, namely, 700-1900 cm-1 and 2800-3800 cm-1. For structural assignment, experimental IRMPD spectra were compared to IR spectra computed at the B3LYP/LACV3P/6-311G∗∗ level of theory. In agreement with computational results, the vibrational spectroscopic characterization of the cis-[Pt(NH3)2(5′-dGMP-H)]+ ion points to macrochelate species resulting from the simultaneous interaction of the metal with both the N7 atom of the guanine residue and an O atom of the phosphate group, structures that bear features in common with those characterized in solution by NMR spectroscopy. Concerning the cis-[PtCl(NH3)2(5′-dGMP)]+ ion, our study points to a monodentate complex involving exclusively the N7 position of guanine, as observed in solution. Also this species exhibits a compact form due to the formation of two hydrogen bonds involving the same ammonia ligand. For both complexes, IRMPD experiments show that a strong intramolecular hydrogen bond is established between one ammonia hydrogen and the carbonyl group of guanine. The strength of this particular interaction can be qualitatively estimated by looking at the redshift of the CO vibration with respect to an unperturbed C=O stretching mode in the fingerprint region. This point is also highlighted in the X-H (X = N, O) stretch region, by the shift of the N-H stretch frequency as a function of the number of hydrogen bonds involving the ammonia ligand.