Car-Parrinello molecular dynamics of QMAP-DMSO microsolvation: first-shell structure and solvent-induced polarization.

CONTEXT: Directional solute-solvent contacts can influence the electrostatic response of donor-acceptor chromophores, although such local effects are often represented only as averaged contributions in continuum solvent models. Quinolinylaminophenol (QMAP) in dimethyl sulfoxide (DMSO) was examined as an explicit first-shell microsolvation model to clarify how local solvent organization couples to QMAP conformation and dipolar response. The Car-Parrinello molecular dynamics trajectory indicates a geometric reorganization around 12-13 ps, accompanied by changes in the first-shell DMSO dipolar arrangement. Within the limitations of the finite microsolvated model, these results suggest that transient first-shell solvent organization contributes to the modulation of the local electrostatic environment of QMAP, rather than acting only as a static dielectric background. METHODS: The gas-phase QMAP geometry was optimized at the CAM-B3LYP/6-311 + + G(d,p) level using Gaussian 16. The explicit QMAP-DMSO model contained one QMAP molecule and 21 DMSO molecules in a periodic cubic cell and was propagated by Car-Parrinello molecular dynamics using the CPMD code. The production trajectory was obtained with the PBE exchange-correlation functional, Troullier-Martins norm-conserving pseudopotentials, a plane-wave basis set, NVT equilibration at 300 K, and a restarted thermostatted CPMD production protocol, with a total analyzed trajectory length of approximately 32 ps. Structural, hydrogen-bond, dipole-moment, IR-like, and orientational-correlation analyses were carried out using in-house Python scripts.