Sunlight-induced oxidation

A steroid very closely related structurally to cholesterol is its 7 dehydro derivative 7 Dehydrocholesterol is formed by enzymatic oxidation of cholesterol and has a conju gated diene unit m its B ring 7 Dehydrocholesterol is present m the tissues of the skin where it is transformed to vitamin D3 by a sunlight induced photochemical reaction... 

One of the main causes of cell damage, especially on skin is oxidation. In case of human skin, exposure to sunlight induces a lipid peroxidation process in human skin layer which leads to deterioration. In this matter, squalene has been reported to protect human skin from lipid peroxidation caused by either UV exposure or any other oxidative stress. 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

Zepp R. G. (1988) Sunlight-induced oxidation and reduction of organic xenobiotics in water. EPA/600/D-88/033. Athens, GA. US Environmental Protection Agency Office of Research and Development, 26p. 

T uminescence studies of commercial polymers have provided valuable -L information on the nature of some of the light absorbing chromophoric impurities believed to be responsible for sunlight-induced oxidation (1-13). The luminescence (fluorescence and phosphorescence) from commercial polyolefins has been attributed to the presence of impurity carbonyl groups (1,2,5,6,8), and recent work on polypropylene has indicated that these groups are conjugated with ethylenic unsaturations... 

Of the field and laboratory air studies that have been performed, sunlight-induced chemical oxidations and photochemical reaction pathways usually render pesticide residues less toxic, more polar, and more susceptible to being washed-out of the air mass (J1,12,13,14,15), Field and laboratory atmospheric pesticide fate studies have also reported the formation of photooxidation products that can have equal or higher toxicity and/or greater environmental persistence than the parent pesticide 16,17,18,19), Because of the limited number of atten ted atmospheric fate studies, there remains a substantial degree of uncertainty in regards to the mechanistic behavior and possible fate of many pesticide groups that can reside in the lower atmosphere. 

Sunlight-induced transformations that lead to chemical oxidation or photolysis are likely to dominate the removal of pesticides, especially in their gaseous forms, fi om the lower troposphere (10,11,12,32,33). The residence time for an airborne pesticide will depend on the rate at which it will undergo direct photo-transformation and/or chemical oxidation by tropospheric reactants such as hydroxyl/peroxy radicals, NOx radicals, or ozone. For pesticides that absorb sunlight, e loss firom direct photolysis will be a function of both the extent of sunlight absorbance and the efficiency of transformation after absorbance. 

Conventional tillage exposes the OM, which are naturally stabilized in the soil, to the action of sunlight and oxidation conditions that favor microbial activity. Consequently, only the very stable fraction of SOM generally remains. The importance of SOM functions is well known, but structural information, chemical composition, and changes induced by anthropogenic factors, such as tillage practices, are still under research. 

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