The 4-carboxybenzophenone-sensitized photooxidation of sulfur-containing amino acids in alkaline aqueous solutions. Secondary photoreactions kinetics

Bobrowski, Krzysztof; Hug, Gordon L.; Marciniak, Bronisław; Kozubek, Halina

doi:10.1021/j100053a031

Cited by 59 publications

(42 citation statements)

References 7 publications

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“…The complete reaction scheme 13 indicates that the OH adducts to the sulfur and the nitrogen (symbolically SNOH in Scheme 1) can both decay, sometimes even with further OH -participation. Without any additional OH -participation, the inclusion of a k 4 for the decay of SNOH in Scheme 1 would not change eq A8 by much.…”

Section: Time Resolution Of Transientsmentioning

confidence: 99%

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation

1996

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A radical cation with an intramolecular sulfur-nitrogen bond was formed in the photoinitiated transfer of an electron from the sulfur atom of the dipeptide Met-Gly to 4-carboxybenzophenone in its triplet state. The sulfur-nitrogen coupling involved two-center, three-electron bonds. The kinetics of the reactions of these radical cations, which were initiated by a laser flash, were followed over time. The spectrum of the radical cation had to be extracted from the interference of other absorbing transients. The principal method of implementing the spectral resolutions was accomplished through a multiple linear regression technique. This spectral analysis was repeated for numerous time windows during the lifetime of the transients' decays. The resulting concentrations of the transients were consistent with an independent factor analysis. It was found that the decay of the radical cations was multiexponential and that the decay varied with pH. A simplified reaction scheme was proposed whereby the absorbing radical cations can alternatively decay by an irreversible channel or react reversibly with OH -. Rate constants for the three elementary reactions of this scheme were determined from an analysis of the decay of the concentration of the radical cations. In addition, the equilibrium constant for the reversible reaction was determined by two separate procedures. In one, the equilibrium constant was calculated from the approximate linear [OH -] dependence of the faster of the two rate constants (in the observed two-exponential decay). The second determination of the equilibrium constant was made from the preexponentials of the empirical two-exponential fits. It was shown how these preexponentials were related to the equilibrium concentrations of the species involved in the equilibrium.

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Section: Time Resolution Of Transientsmentioning

confidence: 99%

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation

1996

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“…It was concluded that the reaction proceeds through the triplet state of the DBA thereby differing from other stilbenes which undergo dimerization upon direct irradiation, that is, through the singlet excited state. [3,4] Moreover, only N-acyl derivatives, such as N-acetyl (10) and N-propionyl DBA (14) [1, 2,5] or the pharmaceutically active N-carbamoyl compound ™carbamazepine∫ (21), were found to photodimerize.…”

Section: Introductionmentioning

confidence: 99%

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

Querner

Wolff

Görner

2003

Chemistry A European J

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The photoprocesses of a series of N-substituted dibenz[b,f]azepines (iminostilbenes) were studied by absorption and emission spectroscopy, by laser flash photolysis, and by preparative irradiation with NMR analysis. In solutions, 2pi+2pi photodimers of N-cyano and N-acyl dibenzazepines are formed via the triplet state upon acetone- or benzophenone-sensitized energy transfer. T-T absorption spectra were measured and absorption coefficients were determined. The triplet energy transfer is equally efficient for N-alkyl dibenzazepines, which do not dimerize. Excited states of npi* character in the latter cases are discussed to rationalize the different reactivities. In spite of negligible intersystem crossing of 21 dibenzazepine derivatives, photodimers of N-acyl and N-cyano dibenzazepines are formed upon direct excitation in concentrated solutions (0.01-0.1 mol dm(-3)) as well as in the solid state. A selective anti-configuration of the photodimers was found throughout.

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“…Even though the picture of the processes is similar for all amino acids tested, it should be pointed out that the photooxidation of L ‐phenylalanine and D , L ‐phenylalanine salts (Figure 2(a), (b)) occur with significantly lower efficiency (only traces of BP •− are observed in transient spectra). Such behavior is predictable taking into account the fact that in neutral solution the rate constant of benzophenone triplet quenching by amino acids is in order of 10 −5 M −1 · s −1 , in contrast to sulfur containing amino acids that quench benzophenone triplet with the rates about four magnitudes higher 15. A word of caution is required for the case of N ‐benzylglycine as electron donor; This molecule quenches the benzophenone triplet in a similar fashion to sulfur containing amino acids.…”

Section: Resultsmentioning

confidence: 98%

Onium Salts of Amino Acids as Co‐Initiators in Photoinduced Free‐Radical Polymerization

Ścigalski

Kryszak

Jędrzejewska

et al. 2006

Macro Materials & Eng

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Summary: The onium salts of selected aliphatic and aromatic amino acids were investigated as electron donors in photoinduced free radical polymerization, in conjunction with either DIBF or BP as sensitizer. The laser flash photolysis experiments unmistakably documented that the free radical formation occurs via an electron transfer reaction from the amino acid salt to the chromophore triplet state. The kinetic studies clearly showed that either the DIBF or BP onium salts of selected aliphatic and aromatic sulfur‐containing amino acids exhibit a significant increase in the efficiency of free‐radical polymerization of TMPTA as compared to non‐sulfur‐containing co‐initiators and that the efficiency of all tested electron donors is only slightly dependent on the cation type coupled with co‐initiators tested.Possible mechanism for the free radical photoinitiated polymerization.magnified imagePossible mechanism for the free radical photoinitiated polymerization.

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The 4-carboxybenzophenone-sensitized photooxidation of sulfur-containing amino acids in alkaline aqueous solutions. Secondary photoreactions kinetics

Cited by 59 publications

References 7 publications

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

Onium Salts of Amino Acids as Co‐Initiators in Photoinduced Free‐Radical Polymerization

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The 4-carboxybenzophenone-sensitized photooxidation of sulfur-containing amino acids in alkaline aqueous solutions. Secondary photoreactions kinetics

Cited by 59 publications

References 7 publications

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)+ Radical Cation

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)+ Radical Cation

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

Onium Salts of Amino Acids as Co‐Initiators in Photoinduced Free‐Radical Polymerization

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Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation

Acid−Base Equilibria Involved in Secondary Reactions Following the 4-Carboxybenzophenone Sensitized Photooxidation of Methionylglycine in Aqueous Solution. Spectral and Time Resolution of the Decaying (S∴N)⁺ Radical Cation