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. 2023 May 14;28(10):4086.
doi: 10.3390/molecules28104086.

Photochemistry and Photophysics of Cholesta-5,7,9(11)-trien-3β-ol in Ethanol

Jack Saltiel  1 , Sumesh B Krishnan  1 , Shipra Gupta  1 , Anjan Chakraborty  1 , Edwin F Hilinski  1 , Xinsong Lin  1
Affiliations

Photochemistry and Photophysics of Cholesta-5,7,9(11)-trien-3β-ol in Ethanol

Jack Saltiel et al. Molecules. .

Abstract

Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D3, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. We recently described the photochemistry and photophysics of CTL in degassed and air-saturated tetrahydrofuran (THF) solution, an aprotic solvent. The zwitterionic nature of the singlet excited state, 1CTL* is revealed in ethanol, a protic solvent. In ethanol, the products observed in THF are accompanied by ether photoadducts and by photoreduction of the triene moiety to four dienes, including provitamin D3. The major diene retains the conjugated s-trans-diene chromophore and the minor is unconjugated, involving 1,4-addition of H at the 7 and 11 positions. In the presence of air, peroxide formation is a major reaction channel as in THF. X-ray crystallography confirmed the identification of two of the new diene products as well as of a peroxide rearrangement product.

Keywords: cholestatrienol; fluorescence probe; photochemistry; photophysics.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Scheme 1
Scheme 1
Photochemistry of HOCTL in THF.
Scheme 2
Scheme 2
Additional photoproducts from HOCTL in ethanol.
Figure 1
Figure 1
Irradiation of [HOCTL]0 = 5.43 × 10−5 M in ethanol.
Figure 2
Figure 2
UV spectra of (a) HOD1 and (b) HOE1 in ethanol.
Scheme 3
Scheme 3
HOCTLP thermal rearrangement.
Figure 3
Figure 3
X-ray crystal structures of HOD1 (upper) and HOD2 (lower).
Figure 4
Figure 4
X-ray crystal structure of RP2, the peroxide rearrangement product.
Figure 5
Figure 5
Enlarged vinyl and methyl regions in the 1H NMR spectrum in CD3OD of the photoproduct mixture in ethanol (Figure S1).
Figure 5
Figure 5
Enlarged vinyl and methyl regions in the 1H NMR spectrum in CD3OD of the photoproduct mixture in ethanol (Figure S1).
Figure 6
Figure 6
(a) The 3HOCTL* transient. (b) Triplet decay at 395 nm.
Scheme 4
Scheme 4
Orthogonal diallyl zwitterions from Pre and Tachy.
Scheme 5
Scheme 5
Protonation of S1 of HOCTL at C5.
Scheme 6
Scheme 6
Protonation of S1 of HOCTL at C11.
Figure 7
Figure 7
Plots of the data in Table 3: (a) Stern–Volmer plot and (b) decay rates.
Figure 8
Figure 8
The effect of [HOCTL] on ϕHOCTLP accounting for variation in τΔ.
Scheme 7
Scheme 7
Possible mechanism for the rearrangement of HOCTLP to RP2.
See this image and copyright information in PMC

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