ON THE KINETICS OF TYROSINE DESTRUCTION AND DOPA FORMATION BY ULTRA-VIOLET RAYS

1938 ◽  
Vol 42 (3) ◽  
pp. 415-418 ◽  
Author(s):  
L. EARLE ARNOW
Keyword(s):  
Ultra Violet ◽  
Kinetics Of ◽  
Dopa Formation

Vacuum ultra-violet flash photolysis of water vapour

1962 ◽  
Vol 266 (1325) ◽  
pp. 185-197 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Complex Formation ◽  
Hydroxyl Radical ◽  
Water Vapour ◽  
Iodine Atom ◽  
Flash Photolysis ◽  
Ultra Violet ◽  
Kinetics Of ◽  
Vacuum Ultra Violet

An apparatus for effecting flash photolysis in the vacuum ultra-violet region is described. Appreciable decompositions of water, carbon dioxide, acetylene, ethylene and methane were effected with a 2000 J flash of 30 p .s duration. A detailed study of water vapour photolysis has established that, in the primary step, at least 90 % of the dissociation leads to a hydrogen atom and a hydroxyl radical. The kinetics of the hydroxyl radical disappearance, following flash photolysis of water vapour in the presence of various third bodies, has been studied. The rate constant is faster in xenon than in helium and other similarities with the data on iodine atom recombination suggest the operation of a mechanism involving intermediate complex formation.

The photolysis of polymethylvinylketone. I. Reactions and kinetics

1955 ◽  
Vol 233 (1193) ◽  
pp. 153-172 ◽  
Keyword(s):  
Molecular Weight ◽  
Ultra Violet ◽  
Type I ◽  
Type Ii ◽  
Weight Changes ◽  
Violet Light ◽  
Aliphatic Ketones ◽  
Primary Reactions ◽  
Acetyl Radical ◽  
Kinetics Of

The photolysis of polymethylvinylketone has been studied in solution. The two primary reactions which occur upon absorption of a quantum of ultra-violet light by the carbonyl group have been shown to be similar to those which occur with simple aliphatic ketones; namely, the type I split to form a polymer radical and a free methyl or acetyl radical, and the type II split at the C—C linkage α — β to the carbonyl which results in a decrease in the molecular weight of the polymer and the formation of a double bond. The kinetics of the molecular weight changes have been followed by viscosity, osmotic pressure and ultracentrifuge measurements on the degraded polymers, and it is shown that these can be explained on the basis of a competing reaction which opposes the breakdown by type II. A mechanism is proposed for this reaction which involves a ‘repolymerization’ due to the addition of free radicals to the double bonds formed by type II.

scholarly journals The Influence of Chemical Structure and the Presence of Ascorbic Acid on Anthocyanins Stability and Spectral Properties in Purified Model Systems

Foods ◽  
2019 ◽  
Vol 8 (6) ◽  
pp. 207 ◽  
Author(s):  
Rachel Levy ◽  
Zoya Okun ◽  
Avi Shpigelman
Keyword(s):  
Ascorbic Acid ◽  
Spectral Properties ◽  
High Performance ◽  
Degradation Products ◽  
Ultra Violet ◽  
Model Systems ◽  
Degradation Rates ◽  
Kinetics Of Formation ◽  
Important Quality ◽  
Kinetics Of

The loss of color pigment is an important quality factor of food products. This work aimed to systematically study, in purified model systems, the influence of anthocyanins’ structure (by increasing the size of the conjugated sugar) and the presence of ascorbic acid on their stability and spectral properties during storage at two pH levels relevant to medium and high acid foods (6.5 and 4.5, respectively). Anthocyanins (cyanidin (Cy), cyanidin 3-O-β-glucoside (Cy3G) and cyanidin 3-O-β-rutinoside (Cy3R)) displayed first-order degradation rates, presenting higher stability in acidic medium and enhanced stability with increasing size of conjugated sugar. The addition of ascorbic acid resulted in significantly enhanced degradation. Changes in ultra violet visible (UV-VIS) spectral properties presented a decrease in typical color intensity and pointed towards formation of degradation products. Identification and kinetics of formation for cyanidin degradation products were obtained by high performance liquid chromatography system-mass spectrometry (HPLC-MS).

Investigation of the Aging Processes in Rubber. I. The Effect of Irradiation with Ultra-violet Light or the Surface Tension of Rubber Solutions

1934 ◽  
Vol 7 (2) ◽  
pp. 302-308
Author(s):  
B. Dogadkin ◽  
G. Pantschenkow
Keyword(s):  
Surface Tension ◽  
Ultra Violet ◽  
Oxidation Products ◽  
Independent Effect ◽  
Surface Tensions ◽  
Ultra Violet Light ◽  
Violet Light ◽  
Surface Active ◽  
Kinetics Of

Abstract 1. Irradiation of rubber solutions in the presence of air with ultra-violet light brings about a pronounced lowering of their surface tensions at the boundary of solution and water. This lowering is connected with the formation of oxidation products of rubber, which are surface-active. 2. The kinetics of the changes in the surface tension are similar to those of the changes in viscosity brought about by irradiation of the solutions. 3. Irradiation of solutions of purified rubber in an atmosphere of nitrogen does not bring about any change in their surface tensions, as judged by the values of the minima of their isotherms. 4. These facts show that, in the absence of oxygen, light may exert an independent effect on rubber by causing depolarization of the rubber molecules and disaggregation of the micelles, which is closely related to this depolarization. In a general way, the nature of the action of light on rubber and the conditions necessary for the light to be effective are explained by the present work. In conclusion, the authors wish to express their appreciation to Professor A. A. Seide for his kindness in furnishing the samples necessary for the work.

scholarly journals THE KINETICS OF INACTIVATION OF COMPLEMENT BY LIGHT

1920 ◽  
Vol 3 (2) ◽  
pp. 169-183
Author(s):  
S. C. Brooks
Keyword(s):  
Temperature Coefficient ◽  
Molecular Species ◽  
Wave Length ◽  
Ultra Violet ◽  
Limiting Factor ◽  
Monomolecular Reaction ◽  
Rate Of Reaction ◽  
Effective Wave ◽  
Kinetics Of ◽  
Coefficient Of Diffusion

The photoinactivation of complement has been studied with a view to determining if possible how many kinds of molecules disappeared during the reaction. It was found that: 1. The apparent course of photoinactivation is that of a monomolecular reaction. 2. Diffusion is not the limiting factor responsible for this fact, because the temperature coefficient of diffusion is much higher than that of photoinactivation (Q10 = 1.22 to 1.28, and Q10 = 1.10 respectively). 3. There is no change in the transparency of serum solutions during photoinactivation, at least for light of the effective wave-length, which is in the ultra-violet region probably at about 2530 Ångström units. It is pointed out that under these conditions only one interpretation is possible; namely, that during photoinactivation a single disappearing molecular species governs the rate of reaction. This substance must be primarily responsible for the hemolytic power of serum when it is used as complement.

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