Solvent-dependent structural dynamics of an azido-platinum complex revealed by linear and nonlinear infrared spectroscopy

Abstract

The vibrational and anisotropic relaxation dynamics and structural dynamics of a potential anticancer prodrug, trans,trans,trans-[Pt(N₃)₂(OH)₂(py)₂], were investigated using time-resolved infrared pump–probe spectroscopy and ultrafast two-dimensional infrared (2D IR) spectroscopy. Herein, two representative bio-friendly solvents, H₂O and DMSO, were used, in which the local structural and dynamical variations were monitored using the antisymmetric linear combination of the two N₃ stretching vibrational modes as an infrared probe. It was found that the vibrational relaxation process of the N₃ antisymmetric stretching (as) mode in H₂O is two to three times faster than that in DMSO. The anisotropic relaxation process of the anticancer prodrug was observed to be hindered in DMSO; this indicated a tighter solvent environment around the sample molecule in this solvent. The vibrational frequency time correlation of the N₃ antisymmetric stretching mode in H₂O decays with a time constant of 1.94 ps, in agreement with the hydrogen bond formation and breaking times of water. In DMSO, the frequency time correlation of the N₃ as mode decays on a much longer time scale; this further indicates its sensitivity to the out-layer DMSO structural dynamics, which are relatively static in the experimental time window.