scholarly journals Stability of carotenoids toward UV-irradiation in hexane solution

2008 ◽  
Vol 73 (1) ◽  
pp. 15-27 ◽  
Author(s):  
Dragan Cvetkovic ◽  
Dejan Markovic
Keyword(s):  
Free Radical ◽  
Uv Irradiation ◽  
First Order ◽  
Chemical Structures ◽  
First Order Kinetics ◽  
Uv C ◽  
Hexane Solution

The stabilities of four selected carotenoids dissolved in hexane, two carotenes and two xanthophylls, toward UV-irradiation of three different ranges (UV-A, UV-B and UV-C) were studied in this work. The carotenoids underwent bleaching via a probable free radical mediated mechanism following first-order kinetics. The bleaching rates were highly dependent on the input of the involved photons and, although not consistently, on the chemical structures of the investigated compounds. For the two xanthophylls, a possible role of oxygen associated with their bleaching cannot be neglected.

scholarly journals Effects of continuous UV-irradiation on the antioxidant activities of quercetin and rutin in solution in the presence of lecithin as the protective target

2011 ◽  
Vol 76 (7) ◽  
pp. 973-985 ◽  
Author(s):  
Dragan Cvetkovic ◽  
Dejan Markovic ◽  
Dragana Cvetkovic ◽  
Blaga Radovanovic
Keyword(s):  
Lipid Peroxidation ◽  
Uv Irradiation ◽  
Energy Input ◽  
Antioxidant Activities ◽  
Antioxidant Action ◽  
First Order ◽  
First Order Kinetics ◽  
Uv Photons ◽  
Uv C

The stabilities and antioxidant action of two selected flavonoids, quercetin and rutin, dissolved in methanol and water, toward continuous UV-irradiation from three different sub-ranges (UV-A, UV-B and UV-C) were studied. The flavonoids underwent degradation (bleaching) following first-order kinetics. The bleaching rates were highly dependent on the energy input of the involved UV-photons. The antioxidant activities of the two flavonoids on UV-induced lecithin lipid peroxidation were studied by the TBA-MDA test, and appeared to be also affected by the continuous UV irradiation. The energy input of the incident UV-photons again played a major governing role, but an impact of the flavonoids structures cannot be neglected.

scholarly journals A marginal contribution of selected carotenoids to the supression of UV-irradiation-induced lecithin peroxidation in hexane solution

2007 ◽  
Vol 72 (3) ◽  
pp. 235-250 ◽  
Author(s):  
Dragan Cvetkovic ◽  
Dejan Markovic
Keyword(s):  
Lipid Peroxidation ◽  
Free Radicals ◽  
Uv Irradiation ◽  
Marginal Contribution ◽  
Lipid Peroxidation Process ◽  
Uv Photons ◽  
Uv C ◽  
Hexane Solution

The aim of this work was to study the anticipated antioxidant role of four selected carotenoids in mixtures with lecithin lipoidal compounds in hexane solution, under continuous UV-irradiation in three different ranges (UV-A, UV-B and UV-C). Two carotenes (b-carotene and licopene) and two xantophylls (lutein and neoxanthin) were employed to control the lipid peroxidation process generated by UV-irradiation, by scavenging the involved free radicals. The results show that while carotenoids undergo a substantial, structural dependent destruction (bleaching), which is highly dependent on energy of the UV-photons, their contribution to the expected suppression of lecithin peroxidation is of marginal importance, not exceeding a maximum of 20%. The marginal antioxidant behaviour has been attributed to a highly unordered hexane solution, where the scavenging action of the carotenoids becomes less competitive.

scholarly journals Bleaching of chlorophylls by UV irradiation in vitro: The effects on chlorophyll organization in acetone and n-hexane

2008 ◽  
Vol 73 (3) ◽  
pp. 271-282 ◽  
Author(s):  
Jelena Zvezdanovic ◽  
Dejan Markovic
Keyword(s):  
Uv Irradiation ◽  
Photosynthetic Pigments ◽  
Energy Input ◽  
First Order ◽  
First Order Kinetics ◽  
Uv Photons ◽  
The Stability ◽  
Major Factors

The stability of chlorophylls toward UV irradiation was studied by Vis spectrophotometry in extracts containing mixtures of photosynthetic pigments in acetone and n-hexane. The chlorophylls underwent destruction (bleaching) obeying first-order kinetics. The bleaching was governed by three major factors: the energy input of the UV photons, the concentration of the chlorophylls and the polarity of the solvent, implying different molecular organizations of the chlorophylls in the two solvents.

scholarly journals The role of histidine-118 of inorganic pyrophosphatase from thermophilic bacterium PS-3

1991 ◽  
Vol 278 (2) ◽  
pp. 595-599 ◽  
Author(s):  
N Hirano ◽  
T Ichiba ◽  
A Hachimori
Keyword(s):  
Thermophilic Bacterium ◽  
Complete Loss ◽  
Inorganic Pyrophosphatase ◽  
Histidine Residue ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Lysyl Endopeptidase ◽  
First Order Kinetics ◽  
Pseudo First Order

Treatment of the inorganic pyrophosphatase from thermophilic bacterium PS-3 with diethyl pyrocarbonate resulted in the almost complete loss of its activity, which followed pseudo-first-order kinetics. The presence of Mg2+ prevented the inactivation. Enzyme inactivated with diethyl pyrocarbonate was re-activated by hydroxylamine. The inactivation parallelled the amount of modified histidine residue, and a plot of the activity remaining against the amount of modified histidine residue suggested that the modification of one of two histidine residues totally inactivated the enzyme. The site involved was found to be located in a single lysyl endopeptidase-digest peptide derived from the ethoxy[14C]carbonylated enzyme. Amino acid analysis and sequence analysis of the peptide revealed that it comprised residues 96-119 of the inorganic pyrophosphatase from thermophilic bacterium PS-3. These results, when compared with those reported for the Escherichia coli and yeast enzymes, imply that His-118 of the inorganic pyrophosphatase from thermophilic bacterium PS-3 is located near the Mg(2+)-binding site and thus affects the binding of Mg2+.

The Effects of Solvent and Oxygen Pressure on the Autoxidation of Benzoin Catalysed by Nickel Acetate

1979 ◽  
Vol 32 (2) ◽  
pp. 421 ◽  
Author(s):  
RP Chaplin ◽  
S Vorlow ◽  
MS Wainwright
Keyword(s):  
Free Radical ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxygen Pressure ◽  
Second Order ◽  
Nickel Acetate ◽  
Coordination Complex ◽  
First Order ◽  
First Order Kinetics

Kinetic results are reported for the autoxidation of benzoin, catalysed by nickel acetate in methanol and ethanol. The reaction in methanol is first order with respect to benzoin and the catalyst and is independent of the oxygen partial pressure. The reaction is non-free-radical and probably involves a coordination complex between the substrate and the catalyst. In ethanol the reaction is found to obey second-order reversible kinetics with respect to benzoin and first-order kinetics with respect to the catalyst. The oxidation is also at least 10 times faster in ethanol than in methanol at 303 K.

scholarly journals Separation of Ag and Cu from Their Aqueous Thiosulfate Complexes by UV-C Irradiation

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1178 ◽  
Author(s):  
Han ◽  
Wang ◽  
Zou ◽  
Shi
Keyword(s):  
Silver Sulfide ◽  
Recovery Ratio ◽  
Silver Recovery ◽  
First Order ◽  
First Order Kinetics ◽  
Recycle Ratio ◽  
Copper Component ◽  
Phase And Chemical Composition ◽  
Thiosulfate Leaching ◽  
Uv C

In recent years, there has been renewed interest in the use of thiosulfate as a substitute for cyanide in silver leaching. Copper thiosulfate leaching without ammonia was applied to extract silver from silver sulfide, resulting in the production of Ag–Cu polymetallic thiosulfate complexes in solutions. It is necessary to separate Ag–Cu polymetallic thiosulfate complexes with the purposes of silver recovery and copper recycling. In this paper, the feasibility study on the use of UV-C irradiation to separate Ag–Cu polymetallic thiosulfate complexes was investigated based on the different photosensitivity of silver and copper. First, a kinetic study on the photolysis of silver and copper thiosulfate complexes by UV-C was investigated, indicating that the reactions follow first-order kinetics. The rate constant reactions were calculated, and it decreased with solution concentrations. On the other hand, the photoproducts of the silver and copper thiosulfate complexes were characterized by XRD and XPS in order to confirm the phase and chemical composition. It indicated that the silver photoproducts are Ag2S, S, Ag and the copper photoproducts are Cu2S, CuS, CuO, Cu, S. Finally, the four-step continuous separation of Ag–Cu polymetallic thiosulfate complexes by UV-C irradiation was investigated. The silver component was recovered with the accumulated recovery ratio of 97%, and the copper component was recycled with the accumulated recycle ratio of 51%, which made it possible for silver recovery and copper recycling.

The catalysis of the para -hydrogen conversion by the solid free radical αα -diphenyl- β -picryl hydrazyl

1953 ◽  
Vol 220 (1140) ◽  
pp. 77-90 ◽  
Keyword(s):  
Free Radical ◽  
Adsorbed Layer ◽  
Inhomogeneous Magnetic Field ◽  
Langmuir Adsorption ◽  
First Order ◽  
Heterogeneous Catalytic ◽  
Hydrogen Molecules ◽  
First Order Kinetics ◽  
Increasing Temperature ◽  
Kinetics Of

A detailed study of the kinetics of the heterogeneous catalytic ortho - para -hydrogen conversion on the solid free radical αα -diphenyl- β -picryl hydrazyl, shows that this conversion follows the usual first-order kinetics and that the rate is independent of pressure. Examination of the rate at 90, 190 and 290° K indicates that it decreases with increasing temperature. This type of behaviour has been observed for other paramagnetic heterogeneous conversions, and the ‘negative activation energy' has been assumed to indicate that the catalysis takes place in a physically adsorbed layer of hydrogen molecules. Some evidence that this is the true explanation of the phenomenon is shown by the results of studies of the adsorption of hydrogen on the free radical. Experiments carried out at 77 and 90° K indicate that hydrogen is physically adsorbed by the free radical to form a weakly sorbed layer which obeys the Langmuir adsorption isotherm for the case when the surface is only sparsely covered. A theoretical discussion is given for a heterogeneous conversion occurring during the collision of the hydrogen molecule with the catalyst surface both in the absence, and in the presence, of a physically adsorbed layer. It is shown that only the theory based on the latter model is in agreement with experimental results, and so it is concluded that in the present case the catalysis is due to the interaction between the hydrogen molecules in a physically adsorbed layer, and the inhomogeneous magnetic field at the surface of the catalyst, which enables the otherwise forbidden ortho - para transitions to take place.

scholarly journals Quantitative analysis of proton-linked transport system. β-Galactoside exit in Escherichia coli

1980 ◽  
Vol 188 (2) ◽  
pp. 467-473 ◽  
Author(s):  
I R Booth ◽  
W A Hamilton
Keyword(s):  
Escherichia Coli ◽  
Quantitative Analysis ◽  
Transport System ◽  
Rate Constants ◽  
The Other ◽  
First Order ◽  
First Order Kinetics ◽  
Solute Accumulation ◽  
External Ph

The exit of lactose and thiomethyl-beta-D-galactoside from Escherichia coli ML308-225 has been studied to determine the role of carrier-dependent (zero-trans efflux) and carrier-independent (leak) processes. On the basis of its sensitivity to p-chloromercuribenzene sulphonate the exit of lactose was found to be almost wholly mediated by the carrier. Consistent with this conclusion was the finding that the rate of exit of this sugar was dependent on the external pH, being considerably slower at acid pH. On the other hand exit of thiomethyl-beta-D-galactoside was found to be composed of both carrier-dependent and carrier-independent processes. Both processes exhibited first-order kinetics with the rate constants for zero-trans efflux and leak being 0.137 min-1 and 0.079 min-1, respectively. The relevance of these findings for out earlier proposal for the methods of attenuation of solute accumulation is discussed [Booth, Mitchell & Hamilton (1979) Biochem. J. 182, 687–696].

Decolourization of Methylene Blue by Persulfate

2013 ◽  
Vol 634-638 ◽  
pp. 76-80
Author(s):  
Wei Hu ◽  
Shen Xin Li ◽  
Cheng Duan Wang
Keyword(s):  
Methylene Blue ◽  
Ionic Strength ◽  
Uv Irradiation ◽  
Reaction Temperature ◽  
Uv Light ◽  
Kinetics Model ◽  
Dye Wastewater ◽  
First Order ◽  
First Order Kinetics ◽  
Pseudo First Order

The decolourization of dye wastewater by persulfate was studied using methylene blue as a model dye wastewater. Effects of several parameters, such as dose of oxidant, ionic strength, pH, temperature and UV irradiation, were investigated in detail. The results showed that the decolourization reaction of methylene blue by persulfate could be fitted to a pseudo-first order kinetics model. In addition, when the oxidant amount used is 2 times of methylene blue, pH 3.43 and reaction temperature for 60°C, after uv light under the irradiation of 20 min, methylene blue decolorization rate can reach more than 98%. The results are useful for the treatment of dye wastewater.

Role of pH on Metribuzin Dissipation in Field Soils

Weed Science ◽  
1976 ◽  
Vol 24 (5) ◽  
pp. 508-511 ◽  
Author(s):  
James S. Ladlie ◽  
William F. Meggitt ◽  
Donald Penner
Keyword(s):  
Soil Ph ◽  
Half Life ◽  
Residue Analysis ◽  
Soil Samples ◽  
First Order ◽  
First Order Kinetics ◽  
Field Soils ◽  
Pseudo First Order

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] residue analysis of soil samples showed greater amounts of residue extractable at soil pH 6.7 than 4.6. Metribuzin leaching increased with increasing soil pH. Metribuzin disappearance from soil followed pseudo first-order kinetics. The half-life of metribuzin decreased as soil pH increased and increased at all soil pH levels as depth of sampling increased. The decreased activity and decreased rate of metribuzin dissipation at lower soil pH is apparently due to protonation and increased adsorption.

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