Vibrational Energy Relaxation of Deuterium Fluoride in d-Dichloromethane: Insights from Different Potentials

Abstract

Vibrationally excited deuterium fluoride (DF) formed by fluorine atom reaction with a solvent was found (Science, 2015, 347, 530) to relax rapidly (less than 10 ps) in acetonitrile-d 3 (CD 3 CN) and dichloromethane-d 2 (CD 2 Cl 2 ). However, insights into how CD 2 Cl 2 facilitates this energy relaxation have so far been lacking, given the weak interaction between DF and a single CD 2 Cl 2 . In this work, we report the results of reactive simulations with a two-state reactive empirical valence bond (EVB) potential to study the energy deposited into nascent DF after transition-state passage and of nonequilibrium molecular dynamics simulations using multiple different potential energy functions to model the relaxation dynamics. For these second simulations, we used the standard Merck molecular force field (MMFF) potential, an MMFF-based covalent-ionic empirical valence bond (EVB) potential (EVB CI ), a newly developed potential [referred to as MMFF(rDF)] which extends upon the MMFF potential by making the DF/CD 2 Cl 2 interaction depend on the value of the DF bond stretching coordinate and by taking the anisotropic charge distribution of the solvent molecules into account, the polarizable atomic multipole optimized energetics for biomolecular applications (AMOEBA) potential, and the quantum mechanics/molecular mechanics (QM/ MM) potential. The relaxation is revealed to be highly sensitive to the potential used. Neither standard MMFF nor EVB CI reproduces the experimentally observed rapid relaxation dynamics, and they also fail to provide a good description of the interaction potential between DF and CD 2 Cl 2 as calculated using CCSD(T)-F12. This is attributed to the use of a point-charge model for the solute and to failing to model the anisotropic electrostatic properties of CD 2 Cl 2 . The MMFF(rDF), AMOEBA, and QM/MM potentials all reproduce the CCSD(T)-F12 two-body DF---CD 2 Cl 2 interaction potential rather well but only with the QM/MM approach is fast vibrational relaxation obtained (lifetimes of ∼288, ∼186, and ∼8 ps, respectively), which we attribute to differences in the solute−solvent local structure. With QM/MM, a unique "many-body" interaction pattern in which DF is in close contact with two solvent Cl atoms and more than three solvent D atoms is found, but this structure is not seen with other potentials. The QM/ MM dynamics also display enhanced solute−solvent interactions with vibrationally excited DF that induce a DF band redshift and hence a resonant overlap with solvent CD modes, which facilitate the intermolecular energy transfer. Our work also suggests that potentials used to model energy relaxation need to capture the fine structure of solute−solvent interactions and not just the twobody part.

Biodegradation of highly crystallized poly(ethylene terephthalate) through cell surface codisplay of bacterial PETase and hydrophobin

“…The structural models of PETase and GCW51 fusion protein, HFBI and GCW61 fusion protein were generated by AlphaFold2 86 . The 4PET polymer chain and the corresponding parameter files (.top and.itp) were generated following previously published procedures 87 . For the modeling of solution-state PETase, a predocked PETase/4PET or PETase-GCW51/4PET complex was solvated with TIP3P waters and ions (0.15 M NaCl, total of 164,478 atoms).…”