Previtamin D conformations and the wavelength-dependent photoconversions of previtamin D

Dmitrenko, Olga; Frederick, John H.; Reischl, Wolfgang

doi:10.1016/s1010-6030(00)00425-1

Cited by 17 publications

(22 citation statements)

References 35 publications

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“…The photochemistry of the ring-opening product, Pre, has been the subject of various theoretical 32,33 and experimental studies. 34,35 By changing the excitation wavelength the composition of the reaction products can be controlled.…”

Section: Introductionmentioning

confidence: 99%

Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations

Tapavicza

Meyer

Furche

2011

Phys. Chem. Chem. Phys.

174

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We investigate the photodynamics of vitamin D derivatives by a fully analytical implementation of the linear response time-dependent density functional theory surface hopping method (LR-TDDFT-SH). Our study elucidates the dynamics of the processes involved in vitamin D formation at the molecular level and with femtosecond resolution. We explain the major experimental findings and provide new insights that cannot directly be obtained from experiments: firstly, we investigate the dynamics of the photoinduced ring-opening of provitamin D (Pro) and cyclohexadiene (CHD) and the subsequent rotational isomerization. In agreement with recent experiments and CC2 calculations, only the bright S(1) state is involved in the ring-opening reaction. Our calculations confirm the experimentally reported 5 : 1 ratio between the excited state lifetimes of Pro and CHD. The longer lifetimes of Pro are attributed to steric constraints of the steroid skeleton and to temperature effects, both emerging directly from our simulations. For CHD and Pro, we present an explanation of the biexponential decay recently reported by Sension and coworkers [Tang et al., J. Phys. Chem., 2011, 134, 104503]: our calculations suggest that the fast and slow components arise from a reactive and an unreactive reaction pathway, respectively. Secondly, we assess the wavelength dependent photochemistry of previtamin D (Pre). Using replica exchange molecular dynamics we sample the Pre conformers present at thermal equilibrium. Based on this ensemble we explain the conformation dependent absorption and the essential features of Pre photochemistry. Consistent with the experiments, we find ring-closure to occur mostly after excitation of the cZc conformers and at lower energies, whereas Z/E isomerization of the central double bond preferably occurs after excitation at higher energies. For the isomerization we provide the first theoretical evidence of the proposed hula-twist mechanism. Our results show that LR-TDDFT-SH is a highly valuable tool for studying the photochemistry of moderately large systems, even though challenges remain in the vicinity of conical intersections.

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Section: Introductionmentioning

confidence: 99%

Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations

Tapavicza

Meyer

Furche

2011

Phys. Chem. Chem. Phys.

174

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“…52 the sudden change was ascribed to a barrier for Z-E isomerization, whereas the ring closure is (nearly) barrierless; only the smooth part of the wavelength dependence was attributed to conformer control. These ideas are supported by calculation of the conformer spectra, 9,11,41,53 which showed no sudden change of absorption cross sections. The group in Leiden pointed out already in 1981 that also the wavelength dependence of vitamin D Z-E isomerization (where the conformer distribution is much simpler than in Pre) cannot be understood by conformer control alone.…”

Section: Barriers Pretwist Conformer Control and The Neer Principlementioning

confidence: 74%

“…Furthermore, the OH group of the cyclohexene A ring can be equatorial or axial, which also has some influence on the torsions in the chromophores. By various quantum chemical methods Dmitrenko and coworkers [9][10][11][12] calculated for these conformers of Pre and Tachy the relative energies and conformer equilibria at room temperature, structures (in particular twist angles), UV and CD spectra, mainly in the gas phase. The energy differences are small, so that solvent interactions may be more important to control which conformer dominates.…”

Section: Previous Experiments On Pre Photoisomerizationmentioning

confidence: 99%

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Previtamin D:Z–Ephotoisomerizationviaa Hula-twist conical intersection

Fuß¹

2019

Phys. Chem. Chem. Phys.

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On photoisomerization of previtamin D -a steroid Z-triene -produced in situ by ring opening of 7-dehydrocholesterol in a cold matrix, it was found in A. M. Müller et al. [Angew. Chem., Int. Ed., 1998, 37, 505-507] that the product (tachysterol) had rotated not only its central double bond but also an adjacent single bond. This is called a Hula twist (HT) due to the alternative description, in which it is just one central CH group that rotates. It was pointed out that the results directly support the calculated molecular structure at a conical intersection, which mediates the Z-E isomerization of polyenes. With a more sophisticated technique, Saltiel et al. (J. Phys. Chem. Lett., 2013, 4, 716-721) confirmed this tachysterol rotamer as the main product but found two additional conformers. They believed to have seen also three previtamin D conformers, suggested to be a result of hot-ground-state reactions from the primary rotamer, and interpreted all tachysterol products to be a result of a double-bond twist (DBT), not a HT. On the basis of published circular dichroism data and consideration of other reactions, it is here shown that under these conditions hot-ground-state reactions are unimportant or even negligible and that there is practically only a single conformer of previtamin D after ring opening. All products can be easily understood on the basis of an HT-type conical intersection, which is thus further supported. Invoking a published pretwist model even rationalizes product ratios. The two twists in HT are concerted. Furthermore HT is fully consistent with the NEER principle (nonequilibration of excited rotamers) and even offers additional possibilities for conformer control.Scheme 1 Structures of 7-dehydrocholesterol (Dehy), lumisterol (Lumi), previtamin D (Pre) and tachysterol (Tachy). c and t denote s-cis and s-trans arrangement around the 5-6 and 7-8 single bonds. Obviously the molecules are not planar; the chromophores in Dehy and its primary ring-opening product cZc-Pre form a left-handed screw ((À)cZ(À)c-Pre), whereas in Lumi and its cZc-Pre product ((+)cZ(+)c-Pre) they correspond to a right-handed screw.Perspective PCCP

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“…1) [2][3][4]. The dependence of photochemistry of this process on the spectral characteristics of UV radiation is well-known [4][5][6][7][8], however, the reaction medium is also of significant impact.…”

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confidence: 99%

Effect of the vitamin D photosynthesis products on thermodynamic parameters of model lipid membranes

et al. 2012

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Aim. To compare effects of vitamin D (VitD), provitamin D (ProD) and its photo- and thermoisomerization products on thermodynamical parameters of hydrated dipalmitoylphoshpatidylcholine (DPPC) multilayers. Methods. Differential scanning calorimetry, UV spectroscopy. Results. A regular decrease was established in the melting temperature accompanied with the pronounced broadening of the appropriate peaks for DPPC multilayers doped with the sterols in the order ProD3 < < ProD3 + UV < ProD3 + UV + dark storage < VitD3. Conclusions. The destabilizing effect of VitD3 on the membrane appeared to be stronger than that of ProD3 and its photoisomerization products. This can facilitate VitD3 withdrawal from the membrane into intercellular space under its biosinthesis in vivo. A possible molecular mechanism of the phenomena observed is related to the higher conformational flexibility and anisometry of VitD3 as compared to ProD3

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Previtamin D conformations and the wavelength-dependent photoconversions of previtamin D

Cited by 17 publications

References 35 publications

Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations

Unravelling the details of vitamin D photosynthesis by non-adiabatic molecular dynamics simulations

Previtamin D:Z–Ephotoisomerizationviaa Hula-twist conical intersection

Effect of the vitamin D photosynthesis products on thermodynamic parameters of model lipid membranes

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