Photolyse de l'iodure de vinyle pur et en solution dans le tétrachlorure de carbone. II. Rendements quantiques

1967 ◽  
Vol 45 (12) ◽  
pp. 1361-1367 ◽  
Author(s):  
Pierre C. Roberge ◽  
Jan A. Herman
Keyword(s):  
Rate Constants ◽  
Molecular Iodine ◽  
Reaction Scheme ◽  
Quantum Yields ◽  
Controlled Processes ◽  
Diffusion Controlled ◽  
Vinyl Radicals ◽  
Vinyl Iodide

The quantum yields of acetylene and molecular iodine from the photolysis of pure vinyl iodide are 0.22 and 0.07 respectively. The disproportionation/recombination ratio for vinyl radicals with iodine atoms in diffusion-controlled processes is 0.34, as established from the quantum yields. A reaction scheme is proposed and several ratios of rate constants are calculated.

Oxidation scheme of symmetrically disulphonated naphthidines with cerium(IV) sulphate

1981 ◽  
Vol 46 (3) ◽  
pp. 561-572 ◽  
Author(s):  
Karel Komers
Keyword(s):  
Sulphuric Acid ◽  
Rate Constants ◽  
Oxidation Product ◽  
Side Reaction ◽  
Reaction Scheme ◽  
Second Order ◽  
Intermediate Products ◽  
Stable Intermediate ◽  
Starting Compound ◽  
Oxidation Agent

The author derived theoretical dependences of preasymptotic slopes of the currentless E-t curves (potential of an indicator redox electrode against time) on the number of equivalents, n, of added oxidation agent, assuming a reaction scheme of two consecutive concurrent second-order reactions involving the formation of intermediate products ( a side reaction of the starting compound with the final oxidation product leading to an adduct, which undergoes consecutive bimolecular oxidations leading again to the final product). The dependences enable to determine the type of the relatively stable intermediate products and the ratios of the rate constants. The theory was applied to the oxidation of four symmetrically disulphonated naphthidines with cerium(IV) sulphate in aqueous sulphuric acid and the results were substantiated spectrophotometrically

Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)

1983 ◽  
Vol 61 (5) ◽  
pp. 801-808 ◽  
Author(s):  
Yuan L. Chow ◽  
Gonzalo E. Buono-Core ◽  
Bronislaw Marciniak ◽  
Carol Beddard
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Decay Rates ◽  
Polynuclear Aromatic Hydrocarbons ◽  
Aromatic Ketone ◽  
Quantum Yields ◽  
Triplet States ◽  
Quenching Rate ◽  
Triplet Energy

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.

Wavelength controlled production of SO4- radicals in the ultraviolet photolysis of ceric sulfate solutions

1984 ◽  
Vol 37 (3) ◽  
pp. 475 ◽  
Author(s):  
RW Matthews
Keyword(s):  
Rate Constants ◽  
Photochemical Reaction ◽  
Transfer Reaction ◽  
Quantum Yields ◽  
Oh Radical ◽  
Transfer Energy ◽  
Fluorescence Measurements ◽  
Sulfate Solutions ◽  
Ultraviolet Photolysis ◽  
Primary Photochemical Reaction

Solutions of cerium(III)/(IV) and formic acid in 0.4 M sulfuric acid have been photolysed under 254 nm and 365 nm light. Marked differences in the reaction kinetics and quantum yields are observed at the two different wavelengths. At 365 nm, the reactions leading to cerium(IV) reduction are caused almost exclusively by the SO4- radical. The ratio of rate constants, k(SO4- + CeIII)/ k(SO4- + HCOOH), is 116 � 11 and the quantum yield of sulfate radicals, ф(SO4-), is 0.023 � 0.002. At 254 nm, the reactions leading to cerium(IV) reduction are caused mainly by the OH radical, but approximately 35% of the oxidizing radicals formed in the primary photochemical reaction are SO4-. Cerium(III) species, excited at 254 nm, transfer energy to cerium(IV) and this results in an additional yield of OH and SO4- radicals. Fluorescence measurements confirmed the efficiency of the energy transfer reaction. The ratio of rate constants, k(OH+CeIII)/k(OH+HCOOH), is 2.22 � 0.18 and ф(CeIV*) and ф(CelIII*) giving oxidizing radicals are 0.116 � 0.010 and 0.0083 � 0.0008 respectively. Thus about 5 times more total oxidizing radicals are produced from excited cerium(IV) species at 254 nm than at 365 nm.

The photochemistry of EDA complexes in micellar solutions. II. The stilbene–methylviologen system in the presence of oxygen

1991 ◽  
Vol 69 (1) ◽  
pp. 146-150 ◽  
Author(s):  
M. Hamity ◽  
R. H. Lema
Keyword(s):  
Sodium Dodecyl Sulfate ◽  
Key Words ◽  
Methyl Viologen ◽  
Sodium Dodecyl ◽  
Cation Radical ◽  
Reaction Scheme ◽  
Quantum Yields ◽  
Micellar Solutions ◽  
Trans Stilbene ◽  
Donor Acceptor

The photolyses of electron donor–acceptor (EDA) complexes formed between both cis-stilbene (cS) and trans-stilbene (tS) as donors and mefhylviologen (MV+2) as acceptor have been carried out in homogeneous ethanolic and in micellar sodium dodecyl sulfate (SDS) solutions, in the presence of oxygen. The stilbene loss quantum yields (Φ−S) have been determined in both media. Quantum yields were observed to be dependent upon methylviologen concentration and the acidity of media. A reaction scheme is proposed, which accounts for experimental results and can be related to the photochemistry of MV+2 and its cation radical MV•+. Key words: EDA complexes, micelles, methyl viologen, stilbene.

scholarly journals Contribution of the intra- and intermolecular routes in autocatalytic zymogen activation: application to pepsinogen activation.

2006 ◽  
Vol 53 (2) ◽  
pp. 407-420 ◽  
Author(s):  
Ramón Varón ◽  
Matilde E Fuentes ◽  
Manuela García-Moreno ◽  
Francisco Garcìa-Sevilla ◽  
Enrique Arias ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Rate Constants ◽  
Time Course ◽  
Initial Conditions ◽  
Reaction Scheme ◽  
Complete Analysis ◽  
Zymogen Activation ◽  
Relative Contribution ◽  
Starting Point ◽  
Definition Of

Taking as the starting point a recently suggested reaction scheme for zymogen activation involving intra- and intermolecular routes and the enzyme-zymogen complex, we carry out a complete analysis of the relative contribution of both routes in the process. This analysis suggests the definition of new dimensionless parameters allowing the elaboration, from the values of the rate constants and initial conditions, of the time course of the contribution of the two routes. The procedure mentioned above related to a concrete reaction scheme is extrapolated to any other model of autocatalytic zymogen activation involving intra- and intermolecular routes. Finally, we discuss the contribution of both of the activating routes in pepsinogen activation into pepsin using the values of the kinetic parameters given in the literature.

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