Tryptophan photolysis

Photochemistry within a glass gas chromatographic column Photodecomposition of sulfonamides and tetracyclines Photoreduction of methylviologen adsorbed on cellulose Radiolysis of D,L-tryptophan Photolysis of dichlorofluanid... 

Lu, C. Y. Lui, Y.Y. (2002). Electron transfer oxidation of tryptophan and tyrosine by triplet states and oxidized radicals of flavin sensitizers a laser flash photolysis study. Biochimica et Biophysica Acta (BBA) - General Subjects, Vol. 1571, No.l, (May 2002), pp. 71-76, ISSN 0304-4165... 

Figure 3.35 presents TR spectra obtained with varying time delays between the pump and probe pulses following photolysis of HbCO. The Raman band features have been attributed to tyrosine (Y) and tryptophan (W) vibrational modes as indicated at the top of Figure 3.35. These Raman bands change with time and provide information about the environment of the typrosine and tryptophan residues in the heme. Inspection of Figure 3.35 reveals that the negative difference Raman...

El-Agamey, A., M. Burke, R. Edge et al. 2005. Photolysis of carotenoids in chloroform Enhanced yields of carotenoid radical cations in the presence of a tryptophan ester. Rad. Phys. Chem. 72 341-345. 

In another study, the irradiation (X = 290-310 nm) of hexachlorobenzene in an aqueous solution gave only pentachlorobenzene and possibly pentachlorophenol as the transformation products. The photolysis rate increased with the addition of naturally occurring substances (tryptophan and pond proteins) and abiotic sensitizers (diphenylamine and skatole) (Hirsch and Hutzinger, 1989). 

B12. Bazin, M., Patterson, L. K., and Santus, R., Direct observation of monophotonic photoionization in tryptophan excited by 300-nm radiation. A laser photolysis study. J. Phys. Chem. 87, 189-190(1983). 

Work on indole, tryptophan, etc. continues because of their relevance to the complex field of protein photophysics. Creed has produced reviews of the photophysics and photochemistry of near-u.v.-absorbing amino-acids, viz. tryptophan and its simple derivatives, tyrosine and its simple derivatives, and cysteine and its simple derivatives. The nature of the fluorescent state of methylated indole derivatives has been examined in detail by Meech et al. Another investigation on indole derivatives deals particularly with solvent and temperature effects. Fluorescence quenching of indole by dimethylfor-mamide has also been examined in detail. Fluorescence excitation spectra of indoles and van der Waals complexes by supersonic jets give microscopic solvent shifts of electronic origin and prominent vibrational excitation of L(, states. Conventional flash photolysis of 1-methylindole in water shows R, e p, and a triplet state to be formed. " Changes in the steady-state fluores-... 

Luse and M(iLaren (1963) have reviewed published research on the photolysis products and quantum yields tor the destruction of amino acids and have attributed the photochemical inactivation of the enzymes chymo-trypsin, lysozyme, ribonuclease, and trypsin by UV light at 254 m i primarily to destruction of the cystyl and tryptophyl residues. The destruction of these residues in proteins was suggested to be a function of the product of the number of residues present, the molecular extinction coefficient, and the quantum yield for destruction of each residue. Cysteine and tryptamine were identified among the irradiation products from cystine and tryptophan, respectively. Tyrosine, histidine, and phenylalanine were also shown to be degraded by UV, histidine yielding histamine, urocanic acid, and other imidazole derivatives, and phenylalanine yielding tyrosine and dihydroxyphenylalanine. Destruction of these three amino acids was not considered to contribute appreciably to the enzyme inactivation. 

Mialocq has examined the formation of the solvated electron by UV photolysis of inorganic anions and neutral molecules like tryptophan in polar solvents and by the biphotonic photolysis of water. Problems of electron localization and solvation are analysed with reference to theoretical studies. 

A ns laser flash photolysis study of peptides composed of alanine (Ala) and tryptophan (Trp), modified with the (nitro)pyrenesulfonyl chromophore (Pyr and NPyr), reveals the existence of a triplet excited state local to the pyrene... 

Tryptophan can be used as an indicator amino acid for the photolysis of protein fibres, such as wool, silk or human hair. Schafer has compared different methods for the quantification of tryptophan and the interference to the colorimetric method (with dimethylaminobenzaldehyde) caused by pigments and dyes. 

Singh A, Bell MJ, Korroll GW (1984) Radiolysis and photolysis of aqueous aerated tryptophan solutions. In Bors W, Saran M, Tait D (eds) Oxygen radicals in chemistry and biology, de Gruyter, Berlin, p 491... 

In this chapter results of the picosecond laser photolysis and transient spectral studies on the photoinduced electron transfer between tryptophan or tyrosine and flavins and the relaxation of the produced ion pair state in some flavoproteins are discussed. Moreover, the dynamics of quenching of tryptophan fluorescence in proteins is discussed on the basis of the equations derived by the present authors talcing into account the internal rotation of excited tryptophan which is undergoing the charge transfer interaction with a nearby quencher or energy transfer to an acceptor in proteins. The results of such studies could also help to understand primary processes of the biological photosynthetic reactions and photoreceptors, since both the photoinduced electron transfer and energy transfer phenomena between chromophores of proteins play essential roles in these systems. 

Photolytic studies of aromatic dipeptides and tripeptides in NaC104 and NaOD glasses (50) show that r-cation radicals of phenylalanine, tyrosine, and tryptophan can undergo different reactions depending on their disposition in the molecule and the molecular conformation. (Electrons produced upon photolysis of the perchlorate system are converted to O -, for which corrections can be made). For PheAla and PheGly charge transfer from the — COO" occurs, followed by decarboxylation, as shown by reactions 8, 9, and 10 ... 

The indole singlet excited state can be quenched by proton transfer to the indole, and this can lead to deuterium exchange of the ring hydrogens [10]. In the case of tryptophan, the conjugate acid of the side-chain amine can act as the proton source [11], and an intermediate assigned as the 4-protonated indole 3 has been observed by flash photolysis [12]. 

Sensitized photolysis of indole in the presence of formaldehyde [107] and of tryptophan in the presence of acetic acid [108] has been reported to yield the fused heterocycles 101 and 102, respectively. The dye-sensitized addition of singlet oxygen to ground-state indoles has been the subject of many reports. Indoles without substituents on the nitrogen atom are converted to hydroperoxides that can be isolated, although they usually undergo further... 

The photolonlzatlon process was exhibited both by steady state ultraviolet Irradiations and flash photolysis studies (24-31). Feltelson (24) studied the electron ejection process by steady state ultraviolet irradiations at 254 nm In aqueous solutions as a function of pH and temperature. His work indicated that the hydrated electrons originated from the fluorescent state. Mlalocq et al. (31) monitored the formation of both e at 660 nm and the Indole cation radical IH at 600 nm In picosecond laser photolysis of Indole and tryptophan. They report a quantum yield of 0.21 for the formation of e and conclude that It arises primarily from a monophotonic process Involving an excited singlet state. 

Figure 11 shows the result of this experiment on a solution of 5 mM N-acetyl tryptophan and 0.2 mM 3-N-carboxy-methyl lumiflavin, hereafter simply called flavin (see Figure 10). Positive enhancements can be observed for the aromatic C-2, C-4 and C-6 protons, while the CH2 group shows emission. This polarization pattern corresponds with a tryptophyl radical in which the electron spin is delocalized over the aromatic ring. It can further be noted that almost no flavin polarization is present in the difference spectrum. Figure 11c (weak lines are present at 2.6 and 4.0 ppm). This is due to cancellation of recombination and escape polarization as will be discussed in Section 5. The mechanism of the photoreaction undoubtedly involves triplet flavin (17). Since 1-N-methyl tryptophan shows similar CIDNP effects, the primary step most probably is electron transfer to the photo-excited flavin. This is also supported by a flash photolysis study by Heelis and Phillips (18). The nature of the primary step in the photoreactions with amino acids is important in view of the interpretation of "accessibility" of an amino acid side chain in a protein as seen by the photo-CIDNP method. This question is therefore the subject of further study.

Scheme 8.3 Photolysis of proteins. Reactions involving tryptophan moieties [7].

Intermediates occurring in these mechanisms have been identified by ESR measurements and by flash photolysis studies using optical absorption detection. For example, ESR measurements on wool keratins revealed the formation of sulfur-centered radicals of the structure RCH2S, which, in this case, are assumed to result from a reaction of electronically excited tyrosine moieties with cystine residues [11]. In many proteins, cross-links are formed. In the case of keratin and collagen, the cross-links are of the tryptophan-histidine and dityrosine types [11]. Cross-links formed by the combination of R-S or R-S-S radicals, both intermolecularly and intramolecularly, with incorrect sites are considered to be an important source of photoaggregation effects [8]. ESR measurements have also yielded evidence of C-H and C-N bond ruptures [8]. 

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