UV light damage

How does UV light damage polyolefin polymers How do anti-UV additives help protect polymers ... 

The mechanism by which UV light damages DNA has been extensively studied, and many pathways are responsible. One such pathway involves a thymine base of DNA absorbing UV light to give an excited state that Is capable of undergoing a [2+2] cycloaddition with a neighboring thymine base. 

Even very small amounts of transition-metal ions like cobalt, nickel, and copper cause rapid decomposition. They form reactive intermediates that can decrease the stabiUty of oxidizable compounds in the bleach solution and increase the damage to substrates. Hypochlorite is also decomposed by uv light (24,25). Acidic solutions also lose available chlorine by the reverse of equations 1 and 2. 

Ultraviolet photons have enough energy to break chemical bonds. When UV light breaks bonds in biochemical molecules, the products can undergo chemical reactions that lead to cell damage. 

Ultraviolet light is also harmful to the eyes. Although our eyes do not detect UV photons, the lens of the eye is particularly susceptible to damage by UV light. The lens focuses visible photons, but it does not absorb... 

WEI H, CAO Q AND RAHN R o (1996) Inhibition of UV light- and Fenton reaction-induced oxidative DNA damage by the soybean isoflavone genistein. Carcinogenesis. 17 (1) 73-7. 

Electron donation to nucleobases is a fundamental process exploited by nature to achieve the efficient repair of UV induced lesions in DNA [27, 28]. Nature developed to this end two enzymes, CPD photolyases and (6-4) photolyases, which both inject electrons into the UV damaged DNA bases [29, 30]. Both enzymes are, in many species, including plants, essential for the repair of the UV-light induced DNA lesions depicted in Scheme 1 [31]. 

Lycopene had a protective effect on the oxidative stress-mediated damage of the human skin after irradiation with UV light (Ribaya-Mercado and others 1995). 

So, in summary, the extent of the damage caused by these different types of UV light depend on the amount of energy per photon of light, itself a function of its wavelength. 

We have just seen that melanin is quite efficient at stopping UV light below about 370 nm. If the skin is damaged or the body cannot generate its own melanin - which is the case for an albino -then the UV will not be blocked. It is also common for young children and babies to have insufficient amounts of melanin in their skin to block the UV effectively. For this reason, babies should be protected from direct sunlight. 

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