Solvent effect on previtamin D conformational equilibrium and photoreactions

Dmitrenko, Olga; Terenetskaya, I. P.; Reischl, Wolfgang

doi:10.1016/s1010-6030(97)04597-8

Cited by 21 publications

(12 citation statements)

References 16 publications

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“…[19][20][21][22] The values vary to some extent between one publication and another but, as they were obtained in a Table 1 Molar extinction coefficients, e, (in M -1 cm -1 ) in ethanol of provitamin D 3 (Pro; 7-dehydrocholesterol) from Glover et al, 15 previtamin D 2 (Pre) and derived lumisterol (Lumi) and tachysterol (Tachy) from Sternberg et al 23 in agreement with pre-D 3 and derived Lumi and Tachy in Fig. 3b of Dmitrenko et al, 24 and calculated percentages of previtamin D 3 , lumisterol and tachysterol in the photostationary state formed from an initial 100% provitamin D 3 (7- variety of solvents at temperatures varying from 0 to 37 • C and were sometimes based on ergosterol and previtamin D 2 rather than on 7-DHC and previtamin D 3 , perhaps this is not too surprising. The reaction 7-DHC → previtamin D 3 has the same quantum yield at 254 and 302.5 nm implying that the action spectrum, at least for low UV exposures, should parallel the absorption spectrum of 7-DHC, which is not the case (see Fig.…”

Section: Construction Of the Action Spectrum For The Conversion Of 7-...supporting

confidence: 57%

Is the action spectrum for the UV-induced production of previtamin D3 in human skin correct?

Norval

Björn

Gruijl

2010

Photochem Photobiol Sci

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The universally recognised action spectrum for the UV-induced conversion of 7-dehydrocholesterol to previtamin D(3) in human skin was published in 1982, and indicates a maximum at about 297 nm with essentially no production above 315 nm. This work represents a milestone in research on vitamin D, but limitations in the original data should be recognised. Various findings have arisen in recent years which cast doubts on the accuracy of the action spectrum and its application for spectral weighting in calculations of effective UV doses. In conclusion, the construction of an entirely new computational model to predict previtamin D levels is recommended.

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Section: Construction Of the Action Spectrum For The Conversion Of 7-...supporting

confidence: 57%

Is the action spectrum for the UV-induced production of previtamin D3 in human skin correct?

Norval

Björn

Gruijl

2010

Photochem Photobiol Sci

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“…As noted previously, previtamin D 3 can exist in two basic rotamers, cZc and cZt. The energies of these rotamers have been calculated to lie within a few hundred wavenumbers of each other with cZc previtamin D thought to be slightly more stable …”

Section: Discussionmentioning

confidence: 99%

Subpicosecond Ring Opening of 7-Dehydrocholesterol Studied by Ultrafast Spectroscopy

1999

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The photoinitiated electrocyclic ring opening of 7-dehydrocholesterol (DHC) to form previtamin D 3 was studied in methanol solution with femtosecond transient absorption spectroscopy. The molecules were excited at 265 nm and probed at 20 wavelengths ranging from 261 to 650 nm. A sizable absorption signal decaying on a 0.95 ( 0.10 ps time scale was seen at all probe wavelengths from 470 to 650 nm. This absorption is assigned to an S 1 f S n transition that peaks near 470 nm. Thus, the S 1 state has a lifetime of 0.95 ps, while the initially prepared S 2 state has a lifetime e 0.1 ps. Data obtained with probe wavelengths in the ultraviolet yielded a subpicosecond (0.4-1.0 ps) component corresponding to the lifetime of the S 1 state. This data set also exhibits a 1-5 ps wavelength-dependent component assigned to vibrational cooling, and a 100 ( 20 ps component assigned to rotational isomerization of the photoproduct to achieve a thermal distribution of rotamers. No further dynamics are seen for time delays of up to 1 ns. Agreement between the static difference spectrum and the absorption difference observed in the kinetic data at 300 ps indicates that there are no significant longer-time dynamics.

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“…6,[20][21][22][23] In addition the solvent environment plays a significant role in the conformational equilibrium of previtamin D 3 and on the various photochemical pathways. 24,25 The electronic absorption spectrum of DHC is located in the UV, with the lowest allowed transition peaking at 282 nm (see Fig. 2).…”

Section: Introductionmentioning

confidence: 99%

Ultrafast electrocyclic ring opening of 7-dehydrocholesterol in solution: The influence of solvent on excited state dynamics

Tang

Rury

Orozco

et al. 2011

The Journal of Chemical Physics

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Broadband UV-visible femtosecond transient absorption spectroscopy and steady-state integrated fluorescence were used to study the excited state dynamics of 7-dehydrocholesterol (provitamin D(3), DHC) in solution following excitation at 266 nm. The major results from these experiments are: (1) The excited state absorption spectrum is broad and structureless spanning the visible from 400 to 800 nm. (2) The state responsible for the excited state absorption is the initially excited state. Fluorescence from this state has a quantum yield of ∼2.5 × 10(-4) in room temperature solution. (3) The decay of the excited state absorption is biexponential, with a fast component of ∼0.4-0.65 ps and a slow component 1.0-1.8 ps depending on the solvent. The spectral profiles of the two components are similar, with the fast component redshifted with respect to the slow component. The relative amplitudes of the fast and slow components are influenced by the solvent. These data are discussed in the context of sequential and parallel models for the excited state internal conversion from the optically excited 1(1)B state. Although both models are possible, the more likely explanation is fast bifurcation between two excited state geometries leading to parallel decay channels. The relative yield of each conformation is dependent on details of the potential energy surface. Models for the temperature dependence of the excited state decay yield an intrinsic activation barrier of ∼2 kJ/mol for internal conversion and ring opening. This model for the excited state behavior of DHC suggests new experiments to further understand the photochemistry and perhaps control the excited state pathways with optical pulse shaping.

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Solvent effect on previtamin D conformational equilibrium and photoreactions

Cited by 21 publications

References 16 publications

Is the action spectrum for the UV-induced production of previtamin D3 in human skin correct?

Is the action spectrum for the UV-induced production of previtamin D3 in human skin correct?

Subpicosecond Ring Opening of 7-Dehydrocholesterol Studied by Ultrafast Spectroscopy

Ultrafast electrocyclic ring opening of 7-dehydrocholesterol in solution: The influence of solvent on excited state dynamics

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