Indole N—h Bond Fission During the Photolysis of Tryptophan

Pailthorpe, M.T.; Nicholls, C. H.

doi:10.1111/j.1751-1097.1971.tb06158.x

Cited by 60 publications

(41 citation statements)

References 15 publications

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“…Nicholls [25] have provided evidence that indole compounds not substituted at nitrogen undergo N-H bond rupture following excitation. The fact that methyl substitution on nitrogen does not result in N-CH, fission is suggestive that bond rupture may be the basis for the very different nitrogen yields of unsubstituted and methyl-substituted indole in our experiments in the middle pH range.…”

Section: In Epr Experiments Necessarily Carried Out At Low Temperaturmentioning

confidence: 99%

Exciplex Studies–v. Electron Ejection From Indole and Methyl‐indole Derivatives*

Hopkins

Lumry

1972

Photochem & Photobiology

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Abstract— Electron‐scavenging experiments with N2O as scavenger demonstrate at least two electron‐producing reactions of the excited singlet states of the exciplex species formed by indole or 1 ‐methyl‐indole with water. Most electrons reacting with N2O result from collision of the scavenger with a metastable state formed from the initial exciplex state but finite electron yields from indole and 1‐methyl‐indole at limiting scavenger concentrations suggest that the intermediate states also eject electrons directly into the solvent. The formation of the first metastable state from the fluorescent exciplex state has an activation energy, EM, estimated to be about 13 kcal/mole for both indole and 1 ‐methyl‐indole water exciplexes. The EM values for 1‐methyl‐indole from fluorescence and electron yields are the same, Indicating that at neutral and alkaline pH fluorescence quenching and electron extraction are both being controlled by the formation of the first metastable intermediate. Observed electron yields from indole‐water and indole‐methanol exciplexes are less than predicted using fluorescence data, although EM values of 1 kcal/mole are obtained for the indole‐methanol exciplex by both methods. At pH 12·0 and 28°C the total electron yields for indole‐water and 1 ‐methyl‐indole‐water exciplexes are 0·30 and 0·25, respectively. The residual yields attributed to outright formation of hydrated electrons from the initial exciplex excited stateare 0·11 and 0·05, respectively. Electron yields from the indole‐water exciplex are strongly pH dependent only near pH 1 where the fluorescence yields as well as the electron yields decrease rapidly with increasing acidity. The 1‐methyl‐indole‐water exciplex shows an additional pH dependence which is first‐order in hydrogen‐ion activity and has an effective pKa of about 11·5. Comparable yields for indole and 1‐methyl‐indole are found only above pH 12. High electron yields are found with indole in the exciplex‐forming solvent dioxane and in the non‐exciplex forming solvent cyclohexane. For the latter system electrons are probably derived only from the lowest excited state of indole on collision with N2O.

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Section: In Epr Experiments Necessarily Carried Out At Low Temperaturmentioning

confidence: 99%

Exciplex Studies–v. Electron Ejection From Indole and Methyl‐indole Derivatives*

Hopkins

Lumry

1972

Photochem & Photobiology

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“…Thus, differences in the force constants of the N-H bond stretching could be considered of minor importance for all the methyl-substituted indoles here considered. Furthermore, the free radical formed after the N-H bond rupture has an unpaired electron associated to the indole nitrogen, which could be stabilized by resonance leading to significant charge accumulation at C-3 [25]. This structure will be stabilized by acceptor electron groups such as -COCH3, meanwhile electron donor substituents (CH3) will reduce the stability of the resulting radical.…”

Section: Resultsmentioning

confidence: 99%

ChemInform Abstract: Reactivity of tert.‐Butoxyl Radicals Towards Substituted Indole Derivatives

et al. 1991

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Tert-butoxyl radicals react with indole and methyl substituted derivatives by hydrogen abstraction. For those compounds which are unsubstituted at the N-atom, hydrogen abstraction takes place almost exclusively at the N-H bond. The reactivity of these compounds correlates with their donor electron capacity, pointing to significant contribution of charge transfer to the transition state stability. Substitution at the N atom considerably decreases the reactivity.

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“…The major mechanism operating in the photodecomposition of tryptophan is photoejection of electrons (Grossweiner et al, 1963;Santus and Grossweiner, 1972;Pailthorpe and Nicholls, 1971). This reaction is promoted by heat and polar solvents (Feitelson,197 1).…”

Section: °Cmentioning

confidence: 99%

THE DESTRUCTION OF TRYPTOPHANYL RESIDUES IN TRYPSIN BY 280‐nm RADIATION

Volkert

Ghiron

1973

Photochem & Photobiology

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Abstract— The destruction of tryptophanyl residues in trypsin by 280‐nm radiation was studied in relation to enzyme inactivation. Quantum yields for destruction of this residue (determined using the pDAB reagent) and for the inactivation of trypsin were measured when the enzyme was exposed to different environmental perturbations. The conformational modifications of trypsin induced in 6 M guanidine‐HCl did not alter the rates of tryptophan destruction and enzyme inactivation. However, an enhanced destruction of the tryptophanyl residues was observed when trypsin solutions were irradiated at 60°C in the presence of air. The increased rate of tryptophan destruction at this temperature was not accompanied by a corresponding increase in the inactivation quantum yield. It was concluded that any photochemically induced reactions of this chromophore that are sensitive to conformational modifications or that result in the destruction of the indole ring are not important in the inactivation mechanism of trypsin.

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Indole N—h Bond Fission During the Photolysis of Tryptophan

Cited by 60 publications

References 15 publications

Exciplex Studies–v. Electron Ejection From Indole and Methyl‐indole Derivatives*

Exciplex Studies–v. Electron Ejection From Indole and Methyl‐indole Derivatives*

ChemInform Abstract: Reactivity of tert.‐Butoxyl Radicals Towards Substituted Indole Derivatives

THE DESTRUCTION OF TRYPTOPHANYL RESIDUES IN TRYPSIN BY 280‐nm RADIATION

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