Irina Terenetskaya

Spectral monitoring of biologically active solar UVB radiation using an in vitro model of vitamin D synthesis

Vitamin D synthetic capacity of sunlight is the most well known beneficial effect of solar UV radiation. The article describes the new method of biological dosimetry of solar (and artificial) UV radiation based on an in vitro model of vitamin D synthesis (D-dosimeter). Particular attention is given to spectrophotometric analysis of the multicomponent mixture of vitamin D photoisomers that has been developed for the most effective use of D-dosimeter in situ.

Laboratory facilities and recommendations for the characterization of biological ultraviolet dosimeters.

A laboratory facility for characterizing biological dosimeters for the measurement of UV radiation has been built and tested. The facility is based on a solar simulator, stabilized by photofeedback, and monitored by a spectroradiometer, with a versatile filter arrangement. This enables the following characteristics of the dosimeters to be ascertained: spectral response, linearity, and reciprocity; angular acceptance and response; calibration in simulated sunlight. The system has been tested on a variety of dosimeters and has the potential to be used with other radiometers, subject currently to the size of their active surface.

Solvent effect on previtamin D conformational equilibrium and photoreactions

Abstract The effect of solvent polarity on the conformational equilibrium of previtamin D has been discussed in terms of the abundance (5) of its conformers calculated by molecular mechanics in conjunction with nuclear magnetic resonance experimental data available in the literature. It has been assumed that polar reaction media shift the conformational equilibrium towards the most non-strained cZc conformations with the OH group in pseudo-equatorial orientation. 7-Dehydrocholesterol (provitamin D) photoisomerization on irradiation at λ = 254 nm has been studied in ethanol and hexane by UV spectroscopy. A consideration of the observed differences in combination with the calculations of the reaction kinetics provides an estimation of the quantum yields of previtamin D cis-trans isomerization and additional experimental evidence for the solvent-induced changes in the conformational equilibrium of previtamin D in favour of cZc forms in polar environments.

Two methods for direct assessment of the Vitamin D synthetic capacity of sunlight and artificial UV sources

Excessive UV exposures are commonly associated with adverse health effects, but proper amounts of UV are beneficial for people and essential in the natural production of Vitamin D(3) in skin. Two methods have been developed for direct evaluation of the Vitamin D synthetic capacity of sunlight (and artificial UV sources). The first one uses an in vitro model of Vitamin D(3) synthesis (ethanol solution of 7-dehydrocholesterol, 7-DHC), and concentration of previtamin D(3) accumulated during an UV exposure is determined using specially designed spectrophotometric analysis. The second method utilizes photoisomerization of provitamin D in nematic liquid crystalline (LC) matrix, and visual estimation of accumulated previtamin D becomes possible due to special design of a LC cell. This user-friendly method is appropriate for personal UV dosimetry and may have wide application in tanning saloons, in clinical dermatology and UV therapy.

Development of Personal UV Biodosimeter Based on Vitamin D Photosynthesis

Abstract A new approach to monitoring of vitamin D synthetic capacity of UV solar/artificial radiation is described. Nematic liquid crystal (LC) was converted into cholesteric phase by chiral dopant of 7-dehydrocholesterol (provitamin D3), and the effects of UV irradiation were studied using spectral and polarized observations. Significant changes in optical characteristics of the LC films depending on UV exposure were observed as a result of UV initiated photoisomerization that changed helical twisting power of dopant molecules.

Model analysis of branching photoreactions with conformationally flexible intermediate

The principal model of multistage branching photoreaction with conformationally flexible intermediate is analyzed. The consideration is restricted to the case of ground-state conformational control. A violation of the reciprocity low as applied to the reactions with alternating photo and dark processes is emphasized. Applications to the reactions of monomolecular photoisomerization of abundant compounds with triene chromophore are discussed. In the specific case of the previtamin D photosynthesis the ways of purposeful influence on the pathway and the products yield of the reaction are exposed. In particular, opportunities connected with an influence on the conformational equilibrium and with the use of high intensity laser irradiation, as well as the possibilities of the temperature control are considered.

Ozone and solar UV‐B radiation: monitoring of the vitamin D synthetic capacity of sunlight in Kiev and Antarctica

Vitamin D synthesis is a well‐known beneficial effect of solar UV‐B radiation. Theoretical calculations showed the significant effect of the stratospheric ozone layer thickness on the vitamin D synthetic capacity of sunlight. During 2003–2004 permanent monitoring of solar UV radiation, using an in vitro model of vitamin D synthesis, was carried out in Kiev (50°23′ N, 30°32′ E) and in the Antarctic at the Vernadsky station (65°15′ S, 64°16′ W). Simultaneously, ozone layer thickness in the Antarctic was measured with a Dobson spectrometer. The results obtained confirm the known dramatic seasonal effect on the vitamin D synthetic capacity of sunlight. In addition, for the first time, a significant increase in the efficiency of vitamin D synthesis was revealed at the Vernadsky station in October under low ozone conditions.

Features of Previtamin D Cis-Trans Isomerization in the Nematic LC Matrices: Orientation and Cholesteric Order Effects

ABSTRACT For the first time 7-dehydrocholesterol (7-DHC, provitamin D3) photoisomerization was studied in nematic LC matrices (ZLI-1695, ZhK-805) in comparison with ethanol solution using UV absorption spectroscopy. Dissolution of chiral 7-DHC molecules in the nematic LCs induces cholesteric phase, and dramatic effect of the cholesteric pitch value on the spectral kinetics has been revealed. Significant increase in trans-isomer accumulation was observed as the cholesteric pitch was reduced from 2200 to 25 mkm. Noticeable effect of the LC orientation has been observed as well.

Disclination Line in θ-Cell as an Indicator of Liquid Crystal Chirality

We report a new method for the detection and measurement of the chirality of liquid crystal compounds. The method is based on the determination of an azimuth of a disclination line in a θ-cell, with the director aligning unidirectionally at one side and circularly at another one. Experimental observation of disclination rotation was performed with a composition of ZLI-4801-0000 liquid crystal and dopants of opposite-sign chirality (R-2011, S-2011, 7-dehydrocholesterol). Dynamic behavior of the disclinaton line was revealed under the influence of continuous illumination by actinic UV radiation.

Variability of solar UV-B irradiance: in situ monitoring and model calculation of the vitamin D synthetic capacity of sunlight

The prediction of the biological effects of solar radiation on human health, in particular involving terrestrial level of solar ultraviolet (UV) radiation, requires the development of an adequate methodological strategy for remote sensing. To date, it is well understood that, in appropriate doses, UV radiation is beneficial for people, specifically due to the production of vitamin D3 in the skin from its precursor 7-dehydrocholesterol. But as far as excessive UV exposure causes acute and chronic health effects, in most cases biological activity of solar UV radiation is calculated by weighting solar UV spectra with International Commission on Illumination (CIE) erythemal action spectrum. Yet the beneficial vitamin D synthetic capacity of sunlight cannot be correctly estimated in this way because of the significant difference between the erythemic and vitamin D synthesis action spectra. With due regard to the essential role of vitamin D3 for human health, in this article we examine the possibility of simplified estimation in situ of provitamin D3 photoconversion into previtamin D3 from the UV absorption spectra of an in vitro model of vitamin D synthesis upon exposure to sunlight. A large-scale linear correlation (R = 0.99) was found on a clear summer day between the concentration of accumulated previtamin D3 and maximum absorbance decline in the initial provitamin D3 absorption spectrum. However, long-term observations showed a poorer (R = 0.77) correlation, and a source of ambiguity of such indirect estimation of previtamin D3 concentration is discussed in detail. In addition, we propose a reliable algorithm for the direct calculation of previtamin D3 accumulation using solar UV spectra as input data to the reaction model of previtamin D photosynthesis and demonstrate the critical dependence of previtamin D3 accumulation on stratospheric ozone, season, latitude and cloudiness. The comparison of experimental and simulation data conforms to recent findings on Europes darker atmosphere in the UV-B and implicates the practical certainty of the presented algorithm for the calculation of the vitamin D synthetic capacity from the remotely sensed solar spectra.