Ultraviolet light deactivators

Ultraviolet Light Deactivators. These absorb short-wavelength radiation which might otherwise generate free radicals—e.g.,... 

All herbicides degrade in soil, but at variable rates (Dawson et al, 1968 Rouchard et al, 2000). The rates of breakdown or deactivation of herbicides are related to a number of soil and environmental factors (Upchurch and Mason, 1962 Upchurch et al, 1966). Surface-applied herbicides volatilize at varying rates, dependent on their vapor pressure (Kearney et al, 1964). Some surface-applied herbicides also break down from ultraviolet light. 

If the energy-rich radiation is absorbed as visible or ultraviolet light, then the energy is immediately assimilated and the molecule is converted into the excited state. The excited molecule either dissociates into free radicals or dissipates the energy by fluorescence, phosphorescence, or thermal collision deactivation. 

It has long been known that many lanthanide ions fluoresce under ultraviolet light, the fluorescence coming from f -> f transitions some ions which do not normally fluoresce at room temperature do so when they are cooled. This fluorescence property has led to lanthanide ions being incorporated in the phosphor of domestic fluorescent tubes and in the screens of colour televisions. When an ion is in an electronically excited state there is a competition between deactivation by radiative and non-radiative processes. For an ion to be a good emitter, any non-radiative process must be a poor second in the competition. If studies are carried out using aqueous solutions, it is found that the lanthanide ions at the centre of the lanthanide series are... 

The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction which occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds and the adjacent allylic functions are the sites of this chemical activity. Oil oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (18 3) with three double bonds is more susceptible to oxidation than linoleic (18 2) with only two double bonds, which is ten or more times as susceptible as oleic (18 1) with only one double bond. Oxidative deterioration results in the formation of hydroperoxides, which decompose into carbonyls, and dimerized and polymerized gums. It is accelerated by a rise in temperature, oxygen pressure, prior oxidation, metal ions, lipoxygenases, hematin compounds, loss of natural antioxidant, absence of metal deactivators, time and ultraviolet or visible light. Extensive oxidation will eventually destroy the beneficial components contained in many fats and oils, such as the carotenoids (vitamin A), the essential fatty acids (linoleic and linolenic), and the tocopherols (vitamin E). 

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