Ultraviolet light

About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.

The emergence and prospects of deep-ultraviolet light-emitting diode technologies

Abstract: By alloying GaN with AlN the emission of AlGaN light-emitting diodes can be tuned to cover almost the entire ultraviolet spectral range (210–400 nm), making ultraviolet light-emitting diodes perfectly suited to applications across a wide number of fields, whether biological, environmental, industrial or medical. However, technical developments notwithstanding, deep-ultraviolet light-emitting diodes still exhibit relatively low external quantum efficiencies because of properties intrinsic to aluminium-rich group III nitride materials. Here, we review recent progress in the development of AlGaN-based deep-ultraviolet light-emitting devices. We also describe the key obstacles to enhancing their efficiency and how to improve their performance in terms of defect density, carrier-injection efficiency, light extraction efficiency and heat dissipation. This Review covers recent progress in AlGaN-based deep-ultraviolet light-emitting devices. The key technologies of how to improve their performance, carrier-injection efficiency, light extraction efficiency and heat dissipation are discussed.

Release of ultraviolet light-induced thymine dimers from dna in e. coli k-12

Abstract: The fate of thymine dimers in DNA during incubation after uv light irradiation was studied in two strains of E. coli K-12. One was a multiply auxotrophic strain, AB1157, and the other was a uv-sensitive mutant, AB1886, derived from it. Strain AB1886 is unable to reactivate uv-irradiated Tl phage and is known to have a mutation at the uvrA locus. Cells were labeled in their DNA by growth with H/sup 3/thymidine, exposed to uv light, incubated in enriched minimal medium, and extracted with cold trichloroacetic acid. The acid precipitate and soluble fractions were hydrolyzed in hot acid, and the products were separated by paper chromatography. Thymine dimers were identified in the acid-insoluble fractions from both strains before incubation. During incubation thymine dimers were released into the acid-soluble fraction in the parental strain, AB1157, but not in the uv-sensitive strain AB1886. It is concluded that thymine dimers are excised from the DNA during the reactivation process in the uvr/sup +/ strain and that the sensitive uvr/sup -/ strain cannot do this. These findings suggest that the enzymatic removal of injured bases, including thymine dimers, and the reconstruction of the DNA from information on the complementary strand may be an important biologicalmore » mechanism for the preservation of DNA. (auth)« less

Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism

Abstract: A minimal cell can be thought of as comprising informational, compartment-forming and metabolic subsystems. To imagine the abiotic assembly of such an overall system, however, places great demands on hypothetical prebiotic chemistry. The perceived differences and incompatibilities between these subsystems have led to the widely held assumption that one or other subsystem must have preceded the others. Here we experimentally investigate the validity of this assumption by examining the assembly of various biomolecular building blocks from prebiotically plausible intermediates and one-carbon feedstock molecules. We show that precursors of ribonucleotides, amino acids and lipids can all be derived by the reductive homologation of hydrogen cyanide and some of its derivatives, and thus that all the cellular subsystems could have arisen simultaneously through common chemistry. The key reaction steps are driven by ultraviolet light, use hydrogen sulfide as the reductant and can be accelerated by Cu(I)–Cu(II) photoredox cycling. A minimal cell — one that has all the minimum requirements for life — is still a complex entity comprising informational, compartment-forming and metabolic subsystems. Here it is shown that, contrary to previous assumptions, a common prebiotically plausible chemistry can give rise to building blocks for all the subsystems.

Crystalline desoxyribonuclease: i. isolation and general properties spectrophotometric method for the measurement of desoxyribonuclease activity

Abstract: A crystalline enzyme capable of digesting thymus nucleic acid (desoxyribonucleic acid) has been isolated from fresh beef pancreas. The enzyme called "desoxyribonuclease" is a protein of the albumin type. Its molecular weight is about 60,000 and its isoelectric point is near pH 5.0. It contains about 8 per cent tyrosine and 2 per cent tryptophane. It is readily denatured by heat. The denaturation is reversible if heated in dilute acid at pH about 3.0. The digestion of thymus nucleic acid by crystalline desoxyribonuclease is accompanied by a gradual increase in the specific absorption of ultraviolet light by the acid. The spectrophotometric measurement of the rate of increase in the light absorption can be conveniently used as a general method for estimating desoxyribonuclease activity. Details are given of the method for isolation of crystalline desoxyribonuclease and of the spectrophotometric procedure for the measurement of desoxyribonuclease activity.

Studies on finely divided wood. Part 1. Extraction of lignin with neutral solvents

Abstract: Previous work on extraction of lignin and cellulose from wood, ground in various ways, and other attempts to isolate 'native lignins' are reviewed. Present opinions about the state of lignin in wood are summarized. Possible methods of disintegration and suitable neutral solvents for extraction of lignin are discussed in connection with experience gathered in the present investigation. It was found that by grinding wood, dispersed in a non-swelling liquid, in a vibrational ball mill it is possible to extract 50per thousand or more of the lignin from spruce ( Picea excelsa ), providing the charge to the mill is small enough. A 'standard method' is presented: Wood is reduced to pass a 20 mesh screen, pre-extracted to remove resins etc., ground 48 hrs. in a Lampen mill (12 g. charge) and 48 hrs. in a vibrational ball mill (6 g. charge), using toluene for dispersion, and extracted with aqueous dioxane. After evaporation of the solvent, the lignin is dissolved in aqueous acetic acid, precipitated into water, dried, dissolved in C 2 H 4 Cl 2 -EtOH (2 + 1 by volume), precipitated into ethyl ether, washed, and dried. A faintly cream-colored, ash-free powder, 'milled wood lignin' (M.W.L.), is obtained. The molecular weight of M.W.L. from spruce is about 11000 (weight average) or about 60 phenyl-propane units. Lignincarbohydrate complexes, extractable from milled wood with dimethylformamide, are slightly soluble in dioxane and contaminate M. W.L., which contains a small amount of sugars. These sugars are the same as in hemicellulose and occur in the same proportions. Determinations of the contents of phenolic hydroxyl groups and ultraviolet light absorption studies indicate similar structures of M.W.L., and lignin derivatives isolated under mild conditions. Determination of p -hydroxy-benzyl alcohol groups gave a value half of that of Brauns' native lignin but double that of wood, and it is concluded that the value of M.W.L. is equal, or close to, that of proto-lignin. It is suggested that M.W.L. is a very useful material for lignin chemists.