UV screening

AH latex compounds should contain at least 5 phr of zinc oxide. This is needed to absorb evolved hydrochloric acid either in the compound or finished part. A larger amount should be considered if the part contains or is in contact with acid-sensitive materials such as cotton cloth. Magnesium oxide may destabilize anionic soap systems, and is avoided for that reason. The compound should also contain two parts of an antioxidant, and consideration should be given to the need for a uv screen in light-colored products. 

The chromophores are yellow and act as uv screening agents. The reactions occur at surfaces and uv penetration is avoided. Mechanical properties are thereby protected (47). 

Quantum yields and lifetimes of emission (fluorescence) as well as other principal rates of deactivation have been measured on 2-hydroxy benzophenone and 2-hydroxyphenyl benzotriazole derivatives. Polymerizable UV screening agents have been prepared and copolymerized with acrylics in order to obtain transparent films containing nonfugitive UV screening agents. Preliminary results of studies of photodegradation on these copolymers are also reported here. 

For all phototrophic organisms exposed to UV radiation for substantial parts of their life cycles, strategies that passively screen UV radiation will contribute to preventing UV-induced direct and indirect damage to essential biomolecules. In addition, UV-screening may also save metabolic energy by reducing the need for constantly active avoidance and repair processes. 

Weather-resistant films, UV screening films for glazing panels, surface covering for PVC films, surface protection for sign industry. .. 

UV screening films, surface covering for PVC film, surface protection of signs... 

Schlumpf M., B. Cotton, M. Conscience, V. Haller, B. Steinmann, and W. Lichtensteiger (2002). In vitro and in vivo estrogenicity of UV screens. Environmental Health Perspectives 109 239-244. 

Some studies have shown no changes in flavonoid levels in response to UV. Originally, only the flavonoids were thought to serve as UV-screening pigments. It is now clear, however, that other phenolics, such as hydroxycinnamic acids and their esters, are also... 

Hoque, E. and Remus, G., Natural UV-screening mechanisms of Norway spruce (Picea abies [L.] Karst.) needles, Photochem. Photobiol, 69, 177, 1999. 

Kolb, C.A. et al., UV screening by phenolics in berries of grapevine Vitis vinifera). Fund Plant Biol, 30, 1177, 2003. 

Other compounds such as phlorotannins, sporopollenin, coumarins, tridentatols, polyphenolics, and several as yet unidentified substances (e.g., P380) have also been implicated as UV protectants that can increase UV tolerance.57-63 With the rapidly accelerating rate of research in the area of aquatic UV photobiology, it is highly likely that additional new types of UV-screening compounds will continue to be discovered. Many of these secondary metabolites probably have multiple protective functions. For example, tridentatols serve as allelopathic agents, antioxidants, and sunscreens.57,58,64... 

The location and concentration of MAAs within cells and various tissues are prime determinants of effective UV screening. If UV absorption equates to a protective function, then sunscreening compounds would provide maximum benefit if located in external surfaces of cells and organisms.175 In unicellular taxa, MAA distribution and localization are vital factors for cell survival. Since MAAs are water soluble, it is not likely that they would be an integral part of cell membranes, but it is plausible that they are dissolved in the cytoplasm. 

There is at least one report where the presence of scytonemin does not provide enhanced protection for UVB exposure. In Nostoc commune, the presence of extracellular MAAs provides substantial protection against the photobleaching of chlorophyll by UVB, but in strains that contain scytonemin and no MAAs, UVB exposure causes complete destruction of cellular chlorophyll.168 It is most probable that MAAs and scytonemin serve as complementary UV protectants and do not have sufficient overlap in their UV screening ranges to act as interchangeable filters. 

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