Absorbing UV light

UV absorbers (UVA) act by absorbing UV light hence retarding the photolysis of hydroperoxides. Their activity is also associated with hydrogen bonding between the 2-hydroxy group and the carbonyl chromo-phore [22]. Typical examples are based on 2-hydroxy-benzophenones and 2-hydroxybenztriazoIes (e.g., Table lb, AO 23 and AOs 24-26). 

Detection is primarily based on the principle of fluorescence quenching by substances absorbing UV light. It is also possible to detect certain substances whose absorption wavelengths interfere with the uranyl cation [1]. 

C07-0015. Gaseous helium atoms absorb UV light of wavelength 53.7 nm. After absorbing a photon of this... 

C07-0088. When ozone molecules in the mesosphere absorb UV light, they fragment into oxygen atoms and oxygen molecules. Draw a molecular picture that illustrates this process. 

OV-absorbing compounds can be measured by fluorescence quenching as well as by reflectance. The fluorescence quenching technique provides a means of visualizing spots absorbing UV-light... 

Applications Chromatography is a preferred technique for additive analysis as it allows both separation of additives in a mixture and subsequent quantitation. Despite the developments in GC, this technique cannot separate many polymer additives. Even with its lower efficiency in comparison to GC, HPLC is today one of the cornerstones in a polymer additive laboratory. Judging by the number of publications in recent years, HPLC is first among analytical methods for additives (confirmation/identification/quantification). Most additives may be analysed by HPLC if they can be dissolved in an HPLC solvent and absorb UV light. Typical polymer/additive analyses are carried out using LPE followed by HPLC with UV or RI detection [605-611]. Verification of the identity of an analyte is then based on a combination of retention time, UV and RI evidence. RPLC is used most frequently for polymer/additive analysis, but normal-phase and SEC are also used. Consequently, techniques for additive analysis by HPLC are legion. 

The cycloalkylcarbamates do not absorb UV light above 220 nm and therefore can be used as the CSPs for thin-layer chromatography (TLC).191 The TLC chromatogram was readily detected by UV radiation at 254 nm and showed the resolution of racemates into each enantiomer. The TLC results can be compared with those obtained by HPLC with the same CSP. The a values in HPLC are slightly larger than those in TLC, although a good correlation is observed between these a values. The cycloalkylcarbamates can be very useful CSPs for TLC as well as for HPLC resolution. 

Of alkane chains and conjugated pi bond structures, which chemical structure do molecules that absorb UV light have ... 

Not all potential mixture components will absorb UV light. 

A structural feature that many molecules that absorb UV light have is a conjugated pi bond skeleton. 

Mycosporine-like Amino Acids (MAA) Small molecular weight organic compounds that absorb UV light and are thought to function as natural sunscreens. 

Hypericin from St. John s wort is another phenolic compound with multiple rings and multiple double bonds. This compound readily absorbs UV light and is a primary photosensitizing agent that will result in severe sunburn in species that either ingest the plant or come in contact with plant dust or leaf extracts. 

The aromatic rings in the protein absorb ultraviolet light at an absorbance maximum of 280 nm, whereas the peptide bonds absorb at around 205 nm. The unique absorbance property of proteins could be used to estimate the level of proteins. These methods are fairly accurate with the ranges from 20 p,g to 3 mg for absorbance at 280 nm, as compared with 1 to 100 p,g for 205 nm. The assay is non-destructive as the protein in most cases is not consumed and can be recovered. Secondary, tertiary and quaternary structures all affect absorbance therefore, factors such as pH, ionic strength, etc can alter the absorbance spectrum. This assay depends on the presence of a mino acids which absorb UV light (mainly tryptophan, but to a lesser extent also tyrosine). Small peptides that do not contain such a mino acids cannot be measured easily by UV. 

Photolytic. Chlordane should not undergo direct photolysis because it does not absorb UV light at wavelengths greater than 280 nm (Gore et ah, 1971). 

Photolytic. 2,4-Dimethylphenol absorbs UV light at a maximum wavelength of 277 nm (Dohnal and Fenclova, 1995). 

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