The role of tachysterol in vitamin D photosynthesis – a non-adiabatic molecular dynamics study

摘要: To investigate the role of tachysterol in photophysical/photochemical regulation vitamin D photosynthesis, we studied its electronic absorption properties and excited state dynamics using time-dependent density functional theory (TDDFT), second-order approximate coupled cluster (CC2), non-adiabatic surface hopping molecular gas phase. In excellent agreement with experiments, simulated spectrum shows a broad band remarkably higher extinction coefficient than other photoisomers provitamin D, lumisterol, previtamin D. The arises from spectral overlap four different ground rotamers. After photoexcitation, first singlet (S1) decays lifetime 882 fs. S1 is characterized by strong twisting central double bond. 96% all trajectories this followed unreactive relaxation to near conical intersection. double-bond chemically induces interconversion between 2.3% observed [1,5]-sigmatropic hydrogen shift forming partly deconjugated toxisterol D1. 1.4% formation via hula-twist bond isomerization. both reaction channels, find dependence photoreactivity dihedral angle conformation: only occurs cEc cEt rotamers isomerization mainly Hence, our study confirms previously formed hypothesis that are more prone isomers. addition, also observe cyclobutene-toxisterol hot 3 (0.7%). Due large mostly behavior, acts as Sun shield suppressing formation. Tachysterol stronger can thus be seen major degradation route Absorption low energy ultraviolet light rotamer lead cyclobutene-toxisterol, which possibly reacts thermally preferably at long wavelengths. These two mechanisms consistent wavelength dependent photochemistry found experiments. Our reinforces recent constitutes source when available, it case winter or morning evening hours day.