Pulse- and X-radiolysis of 2-mercaptoethanol in Aqueous Solution

Can. J. Chem. 62, 580 (1984). Spectral changes and rates of reaction of flavins and several radical species have been investigated at pH 7, 9, and 10 in the presence and absence of P-mercaptoethanol. The radicals .C02-, e,,-, and LS;-reacted with FAD at pH 10 to give a spectrum of FAD .FI-with rate constants of 7 ? 1 x 10' and 4 ? 1 x IOX M ' s ' for . C O i and LS;-respectively. At pH 7 only .FIH was observed and at pH 9 a mixture of .FIH and .FI-.Interactions between flavin radicals and sulphydryl at M concentration did not cause perturbations in the uv-visible spectra until either the radical and/or the sulphydryl were ionized. With FAD at pH 9 or 10 and LFI at pH 10 the 370 nm peak of .FI-was enhanced by about 15% and a second larger growth occurred near 450 nm in the presence of to M sulphydryl. We attribute this to the formation of labile intermediate RSHFl .-, which must also be involved in the reduction of F1 by RSSR-at pH 9 or 10. The second order rate constant k13 for reaction of RSSR-with FAD at pH 9 and 10 was found to be 4.2 2 0.5 x lo%-' s-' and 2.0 +-0.4 X 10' M -' s-' respectively. The rate constant for the reaction between RSSR-and LFI at pH 10 was slightly faster, 7 * 1 X

Section: Fad At Ph I0mentioning

confidence: 99%

Section: Fad At Ph I0mentioning

confidence: 99%

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Formation and spectra of flavin radicals in the presence of β-mercaptoethanol at pH 9 and 10

Surdhar¹,

Ahmad²

1984

“…While this was observed with the sulphydryl molecules noted above, the values of G(H2S) and G(RH) from 2-mercaptoethanol, although equal, were reported to be only half of g,iq (10 Intuitively this seems to require the existence of a relatively long-lived RSH-ion:…”

Section: Introductionmentioning

confidence: 74%

The radiation chemistry of 2-mercaptoethanol

Lal¹

1985

MANOHAR LAL and DAVID A. ARMSTRONG.' Can. J. Chem. 63, 30 ( 1 985). Hydrogen, hydrogen sulphide, mercaptoethanol disulphide, and ethanol yields from the radiolysis of 2-mercaptoethanol are consistent with the same mechanism postulated for other sulphydryl-containing molecules. In all cases studied g,, in neutral solution appears to be enhanced ( g H = 0.7-0.9 molecule per 100 eV). However, there is no basis for attributing this to reaction [lo] which was postulated in earlier work:but is not supported by independent data from H atom studies.MANOHAR LAL et DAVID A. ARMSTRONG. Can. J. Chem. 63, 30 (1985). Les rendements en hydrogkne, en sulfure d'hydrogkne, en disulfure de mercaptoCthanol et en Cthanol, obtenus lors de la radiolyse du mercapto-2 Cthanol, sont en accord avec le mecanisme postulC pour d'autres moltcules contenant des groupes sulfhydryles. Dans tous les cas CtudiCs, il semble que la valeur de gH en solution neutre soit augmentCe (gH = 0,7-0,9 molCcule par 100 eV). Toutefois, il n'y a aucune donnCe experimentale qui puisse permettre d'attribuer ce rksultat a la reaction [lo]

“…It is simpler than cysteine in that ionisation of the -SH group is the only process which leads to changes in net charge of the molecule with pH. The pKi and the magnitude of K, are known to be 10.0 and 1.8 X 10"-' , respectively (14,15). The disulphydryl lipoamide L(SH), was also used.…”

Section: Introductionmentioning

confidence: 99%

The dependence of the photochemically induced reduction of lumiflavin on pH, light intensity, and concentration of sulphydryl compounds

Surdhar¹

1985

Can. J. Chem. 63, 341 1 (1985). The spectral changes which occur on photolysis of flavin solutions containing P-mercaptoethanol (RSH) and lipoamide (L(SH),) are in accord with the formation of dihydroflavin, except at pH values below 3 for RSH. Here an oxygen-stable product is formed, which has X , , , 360 nm and is probably a C-4a substituted dihydroflavin. ' The fraction of flavin present when FlH2 reaches a photostationary state f(F1H2),, is dependent on pH and on the absorbed light intensity I,. At certain pH values the actual photostationary concentration of FlH2 is linear in the concentration of RSH, but for the lipoamide system shows a more complex dependence on concentration. The initial quantum yields are independent of absorbed light intensity in the pH range 7 to 10 for RSH, and increase strongly with pH in the region 7 to 9 for both sulphydryl compounds. In the pH range 5-6 they are linear in sulphydryl concentration. For RSH the results can be explained by a mechanism in which flavin triplet abstracts a hydrogen atom from RSH to form RS. and .FIH radicals, These radicals undergo back reaction to RSH and F1 or form RSSR and FlH2 by one of two mechanisms: (a) formation of RSSR--. which electron transfers to F1 or .FIH or (b) reaction of RS. with .FIH--RSH complexes. The results with L(SH), can be explained similarly. PARMINDER S. SURDHAR et DAVID A. ARMSTRONG. Can. J. Chem. 63, 34 1 1 (1 985). Les changements spectraux qui se produisent lors de la photolyse de solutions de flavines contenant du P-mercaptoCthano1 (RSH) et de la lipoamide (L(SH),) pourraient Ctre expliques par la formation de la dihydroflavine, i I'exception des pH inftrieurs i 3 dans le cas du RSH. Dans ces cas, il y a formation d'un produit qui est stable vis-i-vis de I'oxygtne, qui prtsente un X, , , , i 360 nm et qui est probablement une dihydroflavine substitute en position C-4a. La fraction de flavine qui est prtsente quand la FIH, atteint un Ctat photostationnaire, f(FIH,),,, qui depend du pH et de l'intensitk de la Lumikre absorbte, I,. A certains pH, la concentration photostationnaire reelle de la FlH, varie d'une f a~o n lintaire avec la concentration en RSH; dans le cas du systtme de la lipoamide, on note toutefois une relation plus complexe avec la concentration. Dans le cas du systtme du RSH et i d e s pH allant de 7 a 10, les rendements quantiques initiaux ne dkpendent pas de I'intensitk de la lumikre absorbCe; toutefois, pour chacun des composes sulfurCs et i des pH allant de 7 2 9, ces rendements augmentent rapidement. Aux pH allant de 5 i 6, ils sont IinCaires avec les concentrations en sulfhydryles. Pour le systkme RSH, les rtsultats peuvent Ctre expliquCs par un mecanisme dans lequel 1'Ctat triplet d'une flavine enlkve une hydrogtne du RSH pour former des radicaux RS et . FIH.Ces radicaux subissent des reactions de retpur vers le RSH et la F1 ou ils forment du RSSR et de la FIH, par I'un des deux mtcanismes suivants: (a) formation de RSSR-qui donne des reactions de transferts d'electron conduisant i la F1 ou au .FIH ...