SELECTIVE PHOTOOXIDATION OF THIOLS SENSITIZED BY AQUEOUS SUSPENSIONS OF CADMIUM SULFIDE

-Finely powdered cadmium sulfide in aqueous, air-saturated, phosphate buffered suspension sensitizes the photooxidation of cysteine to cystine with good efficiency; several additional thiols and inorganic sulfides are also photooxidized. The other amino acids (histidine, methionine, tryptophan, tyrosine) known to be rapidly photooxidized with typical organic photosensitizers are photooxidized only very slowly. The quantum yield of oxygen uptake during cysteine photooxidation is pH dependent with a maximum (0.021) at pH 9.5; the yield is not increased in D₂O and is not decreased appreciably by sodium azide, suggesting that singlet oxygen is not involved in the photooxidation process. The slow rate of photooxidation of histidine, which is known to react efficiently with singlet oxygen, also suggests that little if any singlet oxygen is produced by illuminated cadmium sulfide. Superoxide dismutase inhibits the yield of cysteine photooxidation to a maximum of approximately 50%, suggesting the partial involvement of superoxide in the reaction mechanism. The quantum yields of the photooxidation of cysteine, ethylenediaminetetraacetate and inorganic sulfides decrease as the wavelength of the exciting light is increased. Yeast alcohol dehydrogenase, a sulfhydryl enzyme, is inactivated by photodynamic treatment with cadmium sulfide; lysozyme, which has no free sulfhydryl groups, is not.     

SENSITIZED PHOTOOXIDATION OF WOOL BY FLUORESCENT WHITENING AGENTS. A DIRECT SPECTRAL STUDY

Abstract—A fluorescence spectral study has been made of the photochemical behaviour of two types of fluorescent whitening agents, a naphthotriazolylstilbene and a bistriazinylaminostilbene, in single fibres of wool. The photodecomposition of each molecule of the naphthotriazolylstilbene is accompanied initially by the photooxidation of up to 7 residues of trp in the fibre. Amino acid analyses show that his and met residues are also photooxidized. Inhibition of the photooxidation of these amino acids by sodium azide suggests that singlet oxygen is involved in the reaction.     

A COMPARATIVE STUDY OF THE PHOTOCHEMISTRY OF THE NON-STEROIDAL ANTI-INFLAMMATORY DRUGS, NAPROXEN, BENOXAPROFEN AND INDOMETHACIN

Abstract— The photochemical reactivity of the non-steroidal anti-inflammatory drugs, naproxen and indomethacin, has been studied and compared with benoxaprofen, a similar compound of known cutaneous phototoxicity. Although indomethacin shows some phosphorescence at 77 K, flash photolysis at room temperature revealed only a weak photoionization process, and no photochemical reactivity was detected in steady state photolysis. Naproxen has strong fluorescence and phosphorescence, and in laser flash photolysis showed photoionization and a triplet state species in approximately equal yield. Naproxen and benoxaprofen produced singlet oxygen with similar quantum yield, as deduced from the sensitized rates of photooxidation of 2,5-dimethylfuran. Naproxen underwent photodecarboxylation as detected by ESR-spin trap experiments with 2-methyl-2-nitrosopropane. The decarboxy-naproxen radical combined readily with oxygen in aerated solution, and l-(6-methoxy-2-napthyl)ethanol and 2-acetyl-6-methoxynaphthalene were formed as the oxidation products. In deaer-ated solution, the major product was 2-ethyI-6-methoxynaphthalene, with the alcohol also formed. In comparison, benoxaprofen also underwent decarboxylation, with much higher quantum yield, but the decarboxy-benoxaprofen radical did not add oxygen. This difference in photoreactivity between naproxen and benoxaprofen, together with the much lower molar absorptivity of naproxen are the significant factors in relating to the differences in reported levels of clinical photosensitivity responses.     

PHOTOOXIDATION OF EPINEPHRINE SENSITIZED BY METHYLENE BLUE—EVIDENCE FOR THE INVOLVEMENT OF SINGLET OXYGEN AND OF SUPEROXIDE

Abstract— The photooxidation of epinephrine, sensitized by methylene blue or by chlorophylls, excited with red light, involves the reduction of two molecules of oxygen to hydrogen peroxide per molecule of epinephrine oxidized to adrenochrome. The initial rates of these reactions are not affected by low concentrations of catalase. In 99 mol % D₂O, rates of methylene blue sensitized photooxidations are accelerated as much as 5.2 times over rates in ordinary water. Azide anion is a more effective inhibitor of this reaction in D₂O than in H₂O. Half maximal inhibitions are obtained by 1.3 mM azide in H₂O and by 0.1 mAf azide in D₂O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D₂O primarily by a singlet oxygen pathway; in H₂O, non-singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H₂O and in D₂O; about 25% at 10^-9 M SOD, and 50% at 10^-6 M SOD in H₂O. In the photooxidation in H₂O, both by non-singlet and singlet oxygen mechanisms, the amount of superoxide produced is equivalent to the amount of O₂ consumed in the photooxidation of epinephrine; the superoxide thus formed participates in the oxidation of epinephrine.     

THE PHOTOSENSITIZED OXIDATION OF TYROSINE REACTION UNDER HOMOGENEOUS CONDITIONS DERIVATIVES IN THE PRESENCE OF ALGINATE-I

Abstract —The rates of dye-sensitized photooxidation of tyrosine and tyramine to brown products were compared in the presence and the absence of the anionic polysaccharide, alginate. The polyelectrolyte did not affect the reaction when it was sensitized by monochromatic light absorbed mainly by the monomeric form of the dye. In white light, the rate of oxidation sensitized by thionine or phenosafranine was increased in the presence of alginate for tyramine, but not for tyrosine. In the thionine sensitized reaction, the ratio of brown product formation to tyramine consumption increased with decreasing wavelength of monochromatic excitation. These and other phenomena are believed related to the formation of complexes between the dyes and some of the oxidation products, and to association between some of the oxidation products and alginate. A mechanism for oxidation of phenols is proposed, based on the addition of O₂ (¹Δ9) across a double bond ortho to the phenolate oxygen. Dyes bind to alginate in monomeric and in aggregated forms; only the monomeric forms of thiazine dyes are photochemically active, but both the monomeric and the aggregated forms of crystal violet are active.     

光氧化反应研究 Ⅸ.N-叔丁基苯甲叉亚胺的光氧化反应

对于含C=C和N=N双键化合物的光化学与光物理迄今已进行了广泛的研究,而介于其间的C=N双键类亚胺(imines)的光化学与光物理的探讨,由于视黄醛等涉及亚胺C=N键光化学的进展,而于近来得到重视.已知的C=N双键的光化学大多涉及环加成、重排、异构化和还原反应等^[1],而亚胺的光氧化反应则报道较少.     

PHOTOCHEMICAL OXIDATIONS — VI. THE NATURE OF THE DONOR SITE IN THE OXYGEN-HYDROCARBON CONTACT CHARGE-TRANSFER COMPLEX

Abstract— Two sets of experiments, designed to determine whether the C—C or C—H bonds of hydrocarbons act as the donor site in the contact charge-transfer complex between oxygen and hydrocarbons, were performed. It was found that the rates of oxygen uptake during the photooxidation increase with decreasing ' s character' of the C—H bond. Also, the rates of product accumulation during the induction period were shown to increase with basicity of the C—H bond, i.e., tertiary C—H > secondary C—H > primary C—H. The conclusion from these data is that the C—H bond is the donor site.     

ON THE REACTION OF SINGLET MOLECULAR OXYGEN WITH N-ALLYLTHIOUREA IN AQUEOUS SOLUTION

Abstract— Experiments on the photooxidation of N -allylthiourea, thiourea, and N-allylurea sensitized by the dye phenosafranine show that in N -allylthiourea the thiourea group is the site of singlet oxygen attack, while the allyl moiety neither reacts with nor quenches this metastable form of O₂ (in neutral aqueous solutions). Low concentrations of N^-₃ (a known quencher of singlet oxygen) strongly reduce the photooxidation of allylthiourea by a mechanism which apparently obeys simple competition kinetics. From these results the rate constant of the reaction between allylthiourea and singlet oxygen is obtained ( k = 4 × 10⁶ M ^-1 s^-1; pH = 7.1).     

Chiral Primary Amine Catalysis for Asymmetric Mannich Reactions of Aldehydes with Ketimines: Stereoselectivity and Reactivity

The application potential of primary amine catalysts in the context of Mannich reactions of aldehydes with ketimines is exemplified by isatin‐derived ketimines and cyclic trifluoromethyl ketimines. Primary amine catalysts exhibit either unusual stereoselectivity or reactivity, which is not observable with secondary amine catalysts. Moreover, reversal of diastereofacial selectivity between primary and secondary amine catalysts is disclosed. These new reactions provide useful methods for the syntheses of chiral 3‐substituted 3‐amino‐2‐oxindoles and dihydroquinazolinones bearing a trifluoromethylated quaternary stereocenter. The synthetic utility of the reactions is demonstrated through the formal synthesis of AG‐041R and DPC 083 and the total synthesis of (−)‐psychotriasine.     

Unambiguous evidence for the participation of singlet oxygen ( 1 ) in photodynamic oxidation of amino acids

Abstract— A variety of experimental tests have been applied to the methylene-blue-sensitized photooxidation of amino acids to distinguish between singlet oxygen and non-singlet oxidation mechanisms. Conventional flash photolysis and laser photolysis were used to measure the rate constants for the quenching of excited triplet sensitizer and singlet oxygen by the amino acids histidine. tryptophan and methionine and the nucleotide guanosine-5′-monophosphate. In the case of histidine, the rate constants alone rule out an oxidation mechanism involving direct reaction with excited dye. With the other amino acids, and with guanosine monophosphate, the oxidation rates might be accounted for by either mechanism. The inhibition of the photo-oxidation of both tryptophan and methionine as well as histidine by the singlet-oxygen quenchers N₃^? and tetramethylethylene suggests that these reactions occur via a singlet-oxygen mechanism. A newly developed test of singlet oxygen reactions involving a comparison of photooxidation rates in normal and perdeuterated solvents has been used to establish that the photooxidation of tryptophan proceeds primarily by a singlet-oxygen mechanism. These experiments appear to constitute the first proof that singlet oxygen is involved in the photooxidation of the three amino acids tryptophan, methionine and histidine.     

高分子受阻胺对顺1,4-聚丁二烯溶液光敏降解过程的稳定作用

本文研究了高分子受阻胺光稳定剂苯乙烯4-(甲基丙烯酸)-2,2,6,6-四甲基哌啶醇酯共聚物在用罗丹明6G光敏氧化降解顺1,4-聚丁二烯过程中的稳定作用。它具有淬灭单线态氧、分解过氧化氢以及捕获大分子自由基的能力,对其光稳定机理也进行了初步的讨论。     

高分子受阻胺对顺1,4-聚丁二烯溶液光敏降解过程的稳定作用

 本文研究了高分子受阻胺光稳定剂苯乙烯4-(甲基丙烯酸)-2,2,6,6-四甲基哌啶醇酯共聚物在用罗丹明6G光敏氧化降解顺1,4-聚丁二烯过程中的稳定作用。它具有淬灭单线态氧、分解过氧化氢以及捕获大分子自由基的能力,对其光稳定机理也进行了初步的讨论。     

Photodynamic Crosslinking of Proteins. III. Kinetics of the FMN- and Rose Bengal-sensitized Photooxidation and Intermolecular Crosslinking of Model Tyrosine-containing N-(2-Hydroxypropyl)methacrylamide Copolymers

As part of a study on the role of Tyr residues in the photosensitized intermolecular crosslinking of proteins, we have surveyed the kinetics of the rose bengal- and flavin mononucleotide (FMN)-sensitized photooxidation and crosslinking of a water-soluble N-(2-hydroxypropyl)methacrylamide copolymer with attached 6-carbon side chains terminating in tyrosinamide groups (thus the -OH group of the Tyr is free, but both the amino and carboxyl groups are blocked, simulating the situation of a nonterminal Tyr in a protein). The intermolecular photodynamic crosslinking of the Tyr copolymer can result only from the formation of Tyr-Tyr (dityrosine) bonds, because the copolymer itself is not photooxidizable. Rose bengal, primarily a Type II (singlet oxygen) sensitizer, sensitized the rapid photooxidation of the Tyr residue in the Tyr copolymer only at high pH, where the Tyr phenolic group is ionized; crosslinking did not occur with rose bengal under any of the reaction conditions used. In contrast, FMN, which can sensitize by both Type I (free radical) and Type II processes, sensitized the photooxidation of the Tyr copolymer over the pH range 4-9.5. Also, significant photocrosslinking occurred, but only from pH 4 to 8, with a maximum rate at pH 6. Crosslinking required the presence of oxygen. Studies with inhibitors, D2O as solvent, catalase and superoxide dismutase indicated that the photooxidation and photocrosslinking of the Tyr copolymer with FMN at pH 6 were not mediated by singlet oxygen, superoxide or hydrogen peroxide. It appears that crosslinking involves the abstraction of an H atom from the Tyr phenolic group to give Tyr and FMN radicals. The Tyr radical in one Tyr copolymer can then react with a Tyr radical in another Tyr copolymer to give an intermolecular dityrosine crosslink.     

Inhibition of the mitochondrial F1-ATPase by rose bengal mediated photooxidation. Interaction of the Fe2+ chelate of bathophenanthroline with the sensitizer

Rose Bengal mediated photooxidation of mitochondrial F1-ATPase and its beta-subunit resulted in inactivation and loss of about 50 and 60% of their histidine residues, respectively. The beta-subunit was not cleaved upon photooxidation. Photooxidation of histidine probably results in changes in the conformational stability of F1-ATPase leading to its inactivation. The participation of singlet molecular oxygen during the photooxidation process is suggested by the selective loss of histidine residues, while other amino acids, also sensitive to singlet oxygen attack, were not affected. Photochemical damage of F1-ATPase was prevented by various phenanthroline compounds, the order of efficiency being bathophenanthroline-Fe chelate greater than bathophenanthroline greater than orthophenanthroline-Fe chelate greater than bathophenanthroline-sulfonate-Fe chelate. The prevention by bathophenanthroline-Fe chelate of photochemical damage is interpreted on the basis of its interaction with the photosensitizer, Rose Bengal, probably implying a chemical reaction which decreases the actual concentration of the sensitizer and, thereby, the extent of photoinactivation.     

Oxydation photochimique d'amines tertiaires et d'alcaloideS—IX: Oxydation photochimique d'alcaloides quinolizidiniques et indolizidiniques tetracycliques: sparteine et α-isosparteine,lupanine et α-isolupanine,camoensidine et tetrahydroleontidine

The influence of ring size and ring conformation on the site of photosensitized oxidation of tertiary amines was illustrated by the photooxidation of tetracyclic indolizidine and quinolizidine alkaloids. An amino radical intermediate has been supposed during photooxidation of lupanine sensitized by eosin under nitrogen atmosphere.     

Polychrome luminescence and photochromic transformations in anthrone solutions

Polychrome luminescence was observed in the UV irradiation of an aerated anthrone solution in ethanol or isopropanol: the initially blue luminescence of the solution changed to indigo blue and then to green. Simultaneously with the luminescence changes, the colorless solution became yellow. The appearance of green luminescence was preceded by a period during which the solution almost did not luminesce. It was found that the photooxidation of ethanol (isopropanol) with oxygen sensitized by anthrone (KH) occurred during irradiation. Green luminescence appeared at the time when the concentration of dissolved oxygen decreased below a critical value. The green luminescence spectrum with a maximum at 495 nm and a shoulder at ～475 nm was ascribed to the oxonium form of anthrone (KH ₂ ⁺ ). The possibility of using the oxygen quenching of the green fluorescence of anthrone solutions for analytical purposes and the use of the anthrone-sensitized photooxidation of ethanol with oxygen for the deoxygenation of solutions in laboratory practice are discussed.     

磺化酞菁类染料光敏氧化胆固醇及L-半胱氨酸的反应

本文合成了磺化酞菁、磺化酞菁镓和磺化酞菁铝,研究了它们光敏氧化胆固醇及L-半胱氨酸的反应。染料的聚集态和溶液的pH值对反应速率有不同程度的影响。D₂O加速反应而NaN₃猝灭反应的结果表明,光敏氧化反应主要通过Ⅱ型(涉及¹O₂)机制进行。     

The eosin-sensitized photooxidation of substituted phenylalanines and tyrosines.

Abstract— The eosin-sensitized photooxidation of tyrosine and a number of compounds related to tyrosine (substituted phenylalanines) was studied by steady-state kinetic and flash photolysis techniques. In particular, the role of the phenolic group and the amino and carboxyl groups of the alanyl side chain in the photooxidation mechanism was investigated in detail. Several relationships between substrate structure and susceptibility to photooxidation as well as effects of substrate structure on photooxidation mechanisms were found. For example, phenylalanine is not photooxidizable, hut substitution of electron-donating (activating) groups such as-OH (as in tyrosine) or-NH₂ (as in p-aminophenylalanine) results in rapidly photooxidized derivatives. However, substituting deactivating groups such as—C1 (as in p-chlorophenylalanine) or weakly activating groups such as - OCH₃ (as in 4-methoxyphenylalanine) result in non-photooxidiz-able derivatives. Substitution of additional activating groups to the ring of hydroxy-substituted phenylalanines results in increased rates of photooxidation, whereas additional deactivating groups result in decreased photooxidation rates. The rate-determining step in the photooxidation mechanism is shown to be dependent on the presence and position of an electron-donating substituent on the benzenoid ring. Only minor involvement of the side chain amino and carboxyl groups was found. Both singlet oxygen and hydrogen abstraction mechanisms are involved in the eosin-sensitized photooxidation of hydroxy-substituted phenylalanines (e.g. tyrosine). The hydrogen abstraction mechanism probably predominates at both pH 8 and 11.     

BIOLOGICAL ACTIVITIES OF PHTHALOCYANINES—IV. TYPE II SENSITIZED PHOTOOXIDATION OF L-TRYPTOPHAN AND CHOLESTEROL BY SULFONATED METALLO PHTHALOCYANINES

Abstract— Sulfonated phthalocyanine and a series of its metal chelates in combination with red light irradiation led to the degradation of L-tryptophan in oxygenated aqueous solution. The photoproducts and the rate of transformation of L-tryptophan are compared with hematoporphyrin and rose bengal sensitized photooxidation. In all cases the primary photoproducts are characterized as cis and trans -3a-hydroperoxy-l,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid. Support for the involvement of singlet excited oxygen is obtained from azide inhibition and the formation of the specific singlet oxygen product with cholesterol. We observed the contribution of another pathway in the case of the manganese complex.     

PHOTOOXIDATION OF CELL MEMBRANES USING EOSIN DERIVATIVES THAT LOCATE IN LIPID OR PROTEIN TO STUDY THE ROLE OF DIFFUSIBLE INTERMEDIATES

Eosin derivatives that bind primarily to lipid or protein sites in erythrocyte membranes were studied in solution and as sensitizers of erythrocyte membranes. In 50% ethanol-water mixtures eosin maleimide (EYMA) and 5-N-hexadecanoyl amino eosin (E16) had nearly identical absorption spectra. Higher ethanol concentrations did not change peak absorbances. In the presence of neutral detergent both sensitizers had equivalent absorbance at all ethanol concentrations. In water, EYMA was more effective than E16 at bleaching RNO, probably because of E16 aggregation into micelles, while in ethanol-water mixtures E16 was slightly more effective at bleaching DPBF, indicating equivalent singlet oxygen generation when the sensitizers are in monomeric form. In water with neutral detergent, azide in the 20 microM range inhibited the majority of RNO bleaching with both sensitizers; in 50% ethanol-water mixtures azide at 1 mM showed a 50% inhibition of DPBF bleaching with both sensitizers. Iodide in the 30 mM range reduced DPBF bleaching by 50% in 50% ethanol-water mixtures. When matched for amount loaded in erythrocyte membranes these sensitizers were about equally effective at sensitizing induction of cation permeability, assayed as rate of delayed photohemolysis, while E16 was slightly more effective at sensitizing loss of cholinesterase (AchE) activity. The relation of lysis rate to load was somewhat steeper for E16 than EYMA. For both sensitizers lysis rate increased at about the 1.5 power of light dose. Deoxygenation of the reaction media with argon totally blocked detectable photomodification. Ghost membranes made from sensitizer-treated cells were effective generators of singlet oxygen, assayed by RNO bleaching. However, when mixtures of EYMA-treated and untreated cells were illuminated together, only the EYMA-treated cells showed evidence of photomodification. Azide at 5 mM slowed the initial rate of AchE loss by about 75% with E16 and EYMA. Azide partially slowed photohemolysis. Azide decreased RNO bleaching by sensitizer-treated ghosts as it did in water with detergent micelles. A deuterium oxide solvent increased photohemolysis rate with E16 by 41%, but did not increase photohemolysis rate with EYMA. Deuterium oxide had a positive, but statistically insignificant effect on loss of AchE with both sensitizers. Deuterium oxide following illumination slowed lysis sensitized by both sensitizers more than 50%. Iodide exerted a modest inhibition of photohemolysis and loss of AchE sensitized by E16, but had virtually no influence on sensitization by EYMA. The results in solution indicate that EYMA and E16 have nearly identical photochemical properties when in monome