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Influence of the pH on the photodynamic effect in lysozyme A comparative kinetic study with the sensitized photooxidation of isolated amino acids (1995)

Soltermann, A. T. ; Biasutti, M. A. ; Senz, A. ; [et al.]

Springer

Amino acids 9 (1995), S. 123-134

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ISSN: 1438-2199

Keywords: Amino acids ; Eosin ; Lysozyme ; Photodynamic effect ; Photooxidation ; Singlet oxygen

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Summary The kinetics of the eosin-sensitized photooxidation ([O2(1Δg)]-mediated) of the protein lysozyme (Lyso) was investigated under two different pH conditions (pH 7 and pH 11). Rates of oxygen consumption and the fade in the protein fluorescence spectrum upon sensitized irradiation were monitored. Parallel studies on both denatured Lyso (absence of the four-S-S- bridges in the protein) and different mixtures of the photooxidizable amino acids of Lyso were also carried out. The mixtures maintained the same molar ratio as in the native protein, and were selected just in order to throw into relief the preferential amino acids that were being photooxidized at both pH values. Under work conditions Lyso was only photooxidizable at pH 7, whereas the opposite accounted for the denatured protein: only measurable oxygen consumption was detected at pH 11. Nevertheless, Lyso at pH 11, evidenced an important physical quenching of O2(1Δg) due to the Tyr and Trp residues. The results for the native protein were interpreted on the basis of a previously described dark complex Eosin-Lyso, which selectively favours the photooxidation of the bounded protein. The Trp residues were the main reactive entities in the native protein. The photodinamic effect in denatured Lyso was characterized by the prevalence of Tyr residues as photooxidizable targets. In the discussion of the results, a comparisson with the photooxidation kinetics of the mixtures of free amino acids was made.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00805833

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Yield of ions produced in the luminescence quenching of tris (2,2′-bipyridine)ruthenium(II) by dichlorophenolate ions (1995)

Senz, A. ; Gsponer, H. E.

Chichester : Wiley-Blackwell

Journal of Physical Organic Chemistry 8 (1995), S. 706-712

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ISSN: 0894-3230

Keywords: Organic Chemistry ; Physical Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The electron-transfer quenching of Ru(bpy)32+ (tris(2,2′-bipyridine)ruthenium(II) excited state by 2,4-dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP) and 2,6-dichlorophenol (2,6-DCP), in their anionic forms, was studied in de-aerated solutions of neat methanol and 25, 50 and 75% v/v aqueous methanol at 30°C. The quenching rate constants (kq) were determined and their values range from 1 × 107 to 8 × 109 M-1 s-1. In all the mixtures methanol : water the kq values for 2,5-DCP were lower than for 2,4-DCP and 2,6-DCP. This result was discussed in terms of the effect of chloro atom on the quencher oxidation reaction. The photoredox product Ru(bpy)3+ was observed by laser flash photolysis and its quantum yield (ΦRu(+)) calculated by using a comparative method with the formation of zinctetraphenylporphyrin triplet state. The yields of cage escape (Yce) for the different methanol/water mixtures were calculated from the obtained values of ΦRu(+)). Yce increases from 0·1-0·2 in 25% v/v aqueous methanol to 0·5-0·6 in neat methanol. This change of Yce with the solvent composition was discussed in terms of combined effects of viscosity and solvent cage on the rate constant of cage escape (k-d) and the rate constant for back electron-transfer to the ground state from geminate pair (kbc), respectively. The constants k-d were calculated with the Eigen equation. The constants kbc were estimated from Yce and k-d by applying a simplified reaction scheme. The kbc kbc values range from 3·2 × 109 to 1·3 × 1010 s-1.

Additional Material: 3 Ill.