ELECTRON AND ENERGY TRANSFER IN ILLUMINATED POROUS VYCOR GLASS

Abstract— Porous Vycor glass samples containing adsorbed molecules were illuminated at 77 K by a mercury lamp jacketed by a filter cutting off wavelengths below 250 nm. Oxygen or carbon dioxide on Vycor produces an asymmetric electron paramagnetic resonance (EPR) signal best described as holes trapped in the glass. Methyl bromide produces an identical EPR signal plus four other lines due to methyl radicals. Evidence is presented that the products result from excitonic energy transfer from the Vycor to the adsorbed materials. Triphenylamine (TPA) adsorbed on Vycor can also be photoionized by similar illumination, and the cation radical TPA⁺ can be stabilized at 77 K if an electron acceptor is also adsorbed. Attachment of the photoejected electron by carbon dioxide forms CO₂^-, and that by methyl bromide leads to methyl radicals. The CH₃ radical yield is dependent on the surface separation between the electron donor (TPA) and the acceptor (CH₃Br). By monitoring the relative quantum yield of the methyl radicals as a function of distance separating the TPA and CH₃Br, it is shown that the photoelectron is capable of migrating on the Vycor glass surface.     

AN EPR STUDY OF THE SPECIES PRODUCED DURING THE UV PHOTOLYSIS OF HETEROCYCLIC COMPOUNDS IN METHYLTETRAHYDROFURAN AT 77 K

Abstract —The ultraviolet irradiation (290 nm ≤Λ≤ 390 nm) of indole, purine, indazole, acridine and quinoline in 2-methyltetrahydrofuran glass at 77 K produces trapped radicals. Two electron-paramagnetic-resonance (EPR) signals are found at 77 K during illumination, one at high magnetic field (3–25 times 10^-1 T) assigned to the matrix radical and the other at low field (1.3 times 10^-1 to 1–5 times 10^-1 T) attributed to the lowest triplet state of the heterocyclic molecule. Quantum yields for triplet production at 77 K are 0–34 for indole, 0.51 for purine, 0.55 for indazole, 0.15 for acridine, and 0.94 for quinoline. The rate of formation of matrix radicals varies as the n _R^th power of the incident light intensity, I ₀^nR, where 1.6 ≤ n _R=≤ 2. Solvent radical yields, which depend on the light intensity, have been determined. Under the experimental conditions, no signals attributable to trapped electrons or cations have been observed. The dependence of the reciprocal value of the rise lifetime of the low field EPR signal as a function of the intensity of exposure is in accordance with a biphotonic mechanism.     

PHOTOCHEMISTRY OF trans-[Rh(BIS(DIPHENYLPHOSPHINO)ETHANE)2X2][PF6]: TRANSIENT ABSORBANCE KINETIC STUDIES OF METAL-HALOGEN BOND HOMOLYSIS

Abstract— Laser flash photolysis of trans -[Rh(dppe)₂X₂][PF₆] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH₂Cl₂ or CH₃CN produces the d⁷ Rh(II) radicals, [Rh(dppe)₂X]⁺, and halogen atoms. The kinetics of the disappearance of [Rh(dppe)₂X]⁺ radicals in CH₂Cl₂ or CH₃CN were mixed order: H-atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)₂X][PF₆], and Rh/X recombination. In the poor H-atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H-atom abstraction. The hydride complexes [RhH(dppe)²X][PF₆], formed by H-atom abstraction were completely characterized by ³¹P{¹H}-NMR, ¹H-NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3-bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies.     

A PULSE RADIOLYSIS STUDY OF THE ONE-ELECTRON OXIDATION AND REDUCTION OF 5, 10-METHENYLTETRAHYDROFOLATE

Abstract— The one-electron reduction and oxidation of 5,10-methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H₀= -1 to pH = 7 using the reducing species CO^-₂ and (CH₃)₂-COH and oxidising species Br^-₂, and H₂SeO+₃. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate p K , values of 0.5 ± 0.3 being determined. Both the bridged form (5.10-methenyltetrahydrofolate) and the unbridged form (5- formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced.     

FREE RADICALS INDUCED BY PHOTOLYSIS OF FROZEN SOLUTIONS OF THYMIDINE-5'-MONOPHOSPHATE: AN ESR STUDY

Abstract— The photolysis (Δ < 220 nm) of thymidine-5'-monophosphate was studied by electron-spin resonance (ESR) in acidic and alkaline phases. In both cases, the H–addition radical at the C₆ position is detected at 77°K. At 225°K, a triplet 1:2:1 is observed, which suggests a H abstraction radical from the CH₃ group. When oxygen is present during irradiation, a peroxide–type radical is observed, which results partly from a reaction like R + O₂→ ROO and partly from an energy transfer from thymidine-5'-monophosphate to oxygen, probably in the ¹π₀ state.     

MECHANISMS OF PHOTOELIMINATION REACTIONS OF ALKYL BENZOHYDROXAMATES

Abstract— Photolysis at 254 nm of alkyl benzohydroxamates [C, H, CONHOR: R = CH₃ H₂CH₃ CH(CH₃)₂, CH₂C₆H₅ CH(CH₃)C₂H₅ CH(CH₃)- n -C₆H₁₃] in acetonitrile or hydrocarbon solvents gives benzamide. These reactions can be sensitized by benzophenone (at ca. 350 nm) and are quenched by cis-piperylene. Racemization occurred when 2-octyl (+)-benzohydroxamate was irradiated in cyclohexane. These results are consistent with a mechanism involving a triplet biradical. Photolysis of phenyl benzohydroxamate [C₆H₅CONHOC₆H₅] and benzyl N -methylbenzohydroxamate [C₆H₅CON-(CH₃)OCH₂Q₆H₅] cannot be quenched with ris-piperylene and appear to be singlet reactions.     

THE REACTION OF METHYLENE WITH HYDROGEN

Abstract— An investigation has been made of the reaction between methylene, formed by the photolysis of ketene, and hydrogen. Ethane, ethylene and methane are the major hydrocarbon products, and it has been shown that the formation of these products may be adequately described by the sequence of processes
CH₂CO + hv → CH₂+ CO (1)
CH₂+ H₂→ CH₃+H (2)
2CH₃→ C₂H₆ (3)
CH₃+ H₂+ CH₄+ H (4)
CH₂+ CH₂CO → C₂H₄+ CO (7)
In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an 'insertion' process
CH₂+ H₂→ CH₄ (6) to account for the formation of methane.
Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k₂/k₂ increases).     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—II. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE AND 4-AMINOBENZOIC ACID USING 5,5-DIMETHYL-1-PYRROLINE-1-OXIDE

Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH₃NO₂ as well as by direct electron spin resonance techniques. The NH₂ radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [¹⁵N¹]-sulfanilamide indicated that the NH₂ radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO⁻₃ radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na₂SO₃ in the absence of any spin trap yielded the SO⁻³ radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C₆H₄COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e⁻_aq were trapped by CH₃NO₂ when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.     

HO2 ELIMINATION FROM α-HYDROXYALKYLPEROXYL RADICALS IN AQUEOUS SOLUTION

Abstract— In aqueous solutions α-hydroxyalkylperoxyl radicals undergo a spontaneous and a base catalysed HO₂ elimination. From kinetic deuterium isotope effects, temperature dependence, and the influence of solvent polarity it was concluded that the spontaneous reaction occurs via an HO₂ elimination followed by the dissociation of the latter into H⁺ and O₂^-. The rate constant of the spontaneous HO₂ elimination increases with increasing methyl substitution in α-position ( k (CH₂(OH)O₂) < 10s^-1 k (CH₃CH(OH)O₂) = 52s^-1 k ((CH₃)₂C(OH)O₂) = 665 s^-1). The OH^- catalysed reaction is somewhat below diffusion controlled. The mixture of peroxyl radicals derived from polyhydric alcohols eliminate HO₂ at two different rates. Possible reasons for this behaviour are discussed. The mixture of the six peroxyl radicals derived from d -glucose are observed to eliminate HO₂ with at least three different rates. The fastest rate is attributed to the HO₂ elimination from the peroxyl radical at C-l ( k > 7000s^-1). Because of the HO₂ eliminations the peroxyl radicals derived from d -glucose do not undergo a chain reaction in contrast to peroxyl radicals not containing an α-OH group. In competition with the first order elimination reactions the α-hydroxylalkylperoxyl radicals undergo a bimolecular decay. These reactions are briefly discussed.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–III. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE ANALOGS

The photodecomposition of sulfanilamide (4-aminobenzenesulfonamide), sulfacetamide. sulfathiazole. sulfadiazine, carbutamide and tolbutamide has been studied using the spin traps 2-methyl-2-nitrosopropanc and 5,5-dimethyl-l-pyrroline-l-oxide. The following radicals were trapped during the photolysis of sulfanilamide in aqueous solution: H' and HNC₆H₄SO₂NH, (α-fission). SO₂NH₂ and C₆H₄NH₂ (δ fission). H₂NC₆H₄SO₂ and NH₂ (δ-fission). Although the C.,H₄SO₂NH₂ and the SO; radicals were also detected these were not formed directly by homolytic bond fission. Homolytic bond fission was also observed during the irradiation of sulfacetamide (α.δ), sulfadiazine (α). carbutamide (α,δ) and tolbutamide (δ). All of the analogs, with the exception of tolbutamide, generated the SO; radical. Sulfacetamide, sulfadiazine and carbutamide generated the C₆H₄SO_2;NHR radical by some process that did not involve homolytic bond fission. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.     

Spectroscopic Properties of Quercetin Derivatives, Quercetin-3-O-rhamnoside and Quercetin-3-O-rutinoside, in Hydro-organic Mixed Solvents

The characteristic fluorescence properties of quercetin-3- O -rhamnoside (QCRM) and quercetin-3- O -rutinoside (QCRT) were studied in CH₃OH–H₂O and CH₃CN–H₂O mixed solvents. Although QCRM and QCRT are known as nonfluorescent molecules, significant fluorescence emissions were discovered at 360 nm in CH₃OH and CH₃CN when they were promoted to the second excited state. The emission band is broad and structureless and the intensity decreases quickly as the H₂O composition in the solvent increases. When the amount of H₂O exceeds 60% in both mixed solvents, this emission disappears due to the formation of the distorted excited state. This state will be formed due to the strong intermolecular hydrogen bonding between the polar groups of solute and H₂O. As the composition of CH₃OH or CH₃CN in solvent becomes large, the number of molecules having several intramolecular hydrogen bonding increases. Some of these molecules will be changed to a fluorescent species during the decay process, after excitation. The theoretical calculation further supports these results. The change of the lifetimes, quantum yields, and radiative and nonradiative rate constants of molecules was also examined as a function of solvatochromic parameters for CH₃OH–H₂O and CH₃CN–H₂O.     

CATALASE INACTIVATION FOLLOWING PHOTOSENSITIZATION WITH TETRASULFONATEDMETALLOPHTHALOCYANINES

Abstract— Catalase (CAT) in solution or incorporated in erythrocytes and K562 leukemic cells is inactivated during photosensitization with tetrasulfonated metallophthalocyantnes (MePcS₄). The effect of added scavengers and D₂0 showed that both singlet oxygen and free radical species are involved in this process. Evidence was found that direct interactions of ground or excited-stated photosensitizers with CAT are not responsible for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and polyacrylamide gel electrophoresis analyses. Different primary events of photosensitized protein damage included oxidation of cysteine residues as well as other amino acids, as demonstrated by the formation of carbon-centered free radicals and the loss of absorbance at λ= 275 nm. In parallel, we detected degradation of the CAT heme groups, accompanied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradation of the protein with formation of irreversible aggregates in solution. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H₂0₂, providing an additional pathway of phototoxicity.     

PULSE RADIOLYSIS STUDIES IN MODEL LIPID SYSTEMS: FORMATION AND BEHAVIOR OF PEROXY RADICALS IN FATTY ACIDS

Abstract— Radiolytic formation and peroxidation of fatty acid radicals have been investigated by pulse radiolysis techniques in oleate, linoleate, linolenate and arachidonate systems. A strong absorption band at 280 nm associated with conjugated radicals, R_conj, formed in polyunsaturated fatty acid moieties has been used as a probe for kinetic processes occurring at doubly allylic sites in the hydrocarbon chain. Formation of R_conj by O^- has been found to be more efficient than the less selective OH radical. Peroxidation of R_conj is shown to be somewhat slower, ( k _R+ O₂˜ 3 × 10⁸ M ^-1 s^-1), than O₂ reactions with radicals in oleate ( k _R+ O₂= 1 × 10⁹ M ^-1 s^-1). Peroxy radicals generated in these reactions disappear slowly by essentially second order processes (2 k RO₁˜ 10⁷ M ^-1 s^-1). The superoxide radical, O^-₂, shows little if any reactivity towards 0.01 M linolenate or arachidonate over periods of 20 s.     

PHOTOCHEMICAL DECARBOXYLATION OF AMINO ACIDS IN THE PRESENCE OF METAL IONS

Abstract— An electron-spin-resonance study of the radicals produced by ultraviolet irradiation of amino acids in the presence of transition metal ions at low temperature has been carried out. For the monocarboxylic acids, the photosensitized irradiation resulted in loss of carbon dioxide, which led to the formation of free radicals of the type H₃ŃR₁R₂. When the amino acid contained two carboxylic groups, e.g. aspartic acid, decarboxylation took place at the position remote from the amino group. When the odd electron is localized at the carbon atom β to the amino group, e.g. β-alanine and aspartic acid, it was stable enough to be detected at room temperature.     

PHOTOLYSIS OF ETHYL CHLOROACETATE IN LIQUID PHASE AT 2537 A°R

Abstract— Results on the photolysis of ethyl chloroacetate, CICH₂COOC₂H₅, at A°≅ 254 nm in liquid phase are presented. GLC and i.r. methods revealed as products: hydrogen chloride and ethyl acetate; in smaller quantities–ethyl succinate and ethyl oxalate; in traces–ethyl malonate, CO₂, CO and CH₃CI; yet other, unidentified products with higher boiling points. Quantum yields are determined for some products. Similar studies were performed in the presence of I₂ as a radical scavenger. In the present case, ethyl iodoacetate I – CH₂COOC₂H₅ was found to arise in the system. The following primary process may be written on the basis of the experimental data:
CICH₂COOC₂H₅← CI + CH₂COOC₂H₅
Attempts to explain the production of these compounds are based mainly on the properties of the CH₂COOC₂H₅ radical.     

PHOTODYNAMIC GENERATION OF HYDROXYL RADICALS BY HEMATOPORPHYRIN DERIVATIVE AND LIGHT

In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe³⁺-EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe³⁺-EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron-catalyzed Haber-Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H₂O₂ was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H₂O₂, was not generated. Apparently a photooxidation product of tryptophan could replace H₂O₂ in the OH-generating reaction with Fe²⁺-EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber-Weiss reaction.     

INACTIVATION OF Trypanosoma cruzi TRYPOMASTIGOTE FORMS IN BLOOD COMPONENTS BY PHOTODYNAMIC TREATMENT WITH PHTHALOCYANINES

Abstract— -Three phthalocyanine dyes HOSiPcOSi(CH₃)₂(CH₂)₃N(CH₃)₂ (Pc 4), HOSiPc-OSi(CH₃)₂(CH₂)₃N+(CH₃)3I- (Pc 5) and aluminum tetrasulfophthalocyanine hydroxide (AlOHPcS₄) were evaluated for their ability to inactivate the trypomastigote form of Trypanosoma cruzi in fresh frozen plasma (FFP) and red blood cell concentrates (RBCC). The compound Pc 4 was found to be highly effective in killing T. cruzi, Pc 5 less effective and AlOHPcS₄ ineffective. With FFP as the medium, a complete loss of parasite infectivity in vitro (≥5 log₁₀) was found to occur with 2 μ M Pc 4 after irradiation with red light (>600 nm) at a fiuence of 7.5 J/cm², while with RBCC as the medium, a complete loss was found to occur at a fiuence of 15 J/cm². Even without illumination, Pc 4 at 2 μ M also killed about 3.7-4.1 log₁₀ of T. cruzi in FFP during 30 min. Observed differences in T. cruzi killing by the various phthalocyanines may relate to differences in binding; Pc 4 binds to the parasites about twice as much as Pc 5. Ultrastructural analysis of treated parasites suggests that mitochondria are a primary target of this photodynamic treatment. The data indicate that Pc 4 combined with exposure to red light could be used to eliminate bloodborne T. cruzi parasites from blood components intended for transfusion. The inactivation of T. cruzi by Pc 4 in the dark suggests a possible therapeutic application.     

A Role for Hydrogen Peroxide in the Pro-apoptotic Effects of Photodynamic Therapy

Although the first reactive oxygen species (ROS) formed during irradiation of photosensitized cells is almost invariably singlet molecular oxygen (¹O₂), other ROS have been implicated in the phototoxic effects of photodynamic therapy (PDT). Among these are superoxide anion radical (^•O₂⁻), hydrogen peroxide (H₂O₂) and hydroxyl radical (^•OH). In this study, we investigated the role of H₂O₂ in the pro-apoptotic response to PDT in murine leukemia P388 cells. A primary route for detoxification of cellular H₂O₂ involves the peroxisomal enzyme catalase. Inhibition of catalase activity by 3-amino-1,2,4-triazole led to an increased apoptotic response. PDT-induced apoptosis was impaired by addition of an exogenous recombinant catalase analog (CAT- skl) that was specifically designed to enter cells and more efficiently localize in peroxisomes. A similar effect was observed upon addition of 2,2'-bipyridine, a reagent that can chelate Fe⁺², a co-factor in the Fenton reaction that results in the conversion of H₂O₂ to ^•OH. These results provide evidence that formation of H₂O₂ during irradiation of photosensitized cells contributes to PDT efficacy.     

FREE RADICALS FROM THE PHOTODECOMPOSITION OF BLEOMYCIN

Abstract— Irradiation of bleomycin with light (λ > 320 nm) leads to a decrease in absorbance at 290 nm, which is suppressed by metal ions and by oxygen. Light-induced oxygen consumption is diminished by the enzymes superoxide dismutase and catalase, implying that toxic reduced species of oxygen (O₂ and H₂O₂) are formed during irradiation. Spin-trapping measurements with 5,5-dimethyl-1-pyrroline-1-oxide and 2-methyl-2-nitrosopropane demonstrated that hydroxyl radical and methyl radical adducts also are generated in the system. In addition, direct ESR measurements have shown that methyl radicals are produced during irradiation of bleomycin solutions at low temperatures, together with radicals probably derived from the bithiazole moiety of the bleomycin. The latter are also produced from irradiation of the model compound bithia. Radical production is diminished by complexation of bleomycin with metal ions.     

PRIMARY PRODUCTS OF LIQUID WATER PHOTOLYSIS AT 1236, 1470 AND 1849 Å

Abstract— The yield of the primary products of the liquid water photolysis at 1236 and 1470 Å is reported. It was found that besides the dissociation of the excited water molecules into H and OH radicals probably e⁻_aq is also formed. The H and OH radicals were scavenged by means of formate, and the e⁻_aq together with a part of H₂O* by adding carbon dioxide. The quantum yields determined at 1236 Å, are: Φ(H, OH) = 1.03 & 0.02, 0.06 <Φ( e⁻_aq , H₂O*) < 0.12 and at 1470 Å,: Φ(H, OH)=0.72±0.02, 0.037 < Φ( e⁻_aq , H₂O*) <0.075. The quantum yield of high purity water at 1849 Å in the absence of any scavengers is Φ(H, OH)=0.022. Previously published data by us for 1849 Å are also given: Φ(H, OH)=0.33 ± 0.01 and 0.02 < Φ ( e⁻_aq H₂O*) < 0.04. Reaction mechanisms are proposed.