Presence Of Photosensitizer Research Articles

Photoinduced graft copolymerization of dichlorodimethylsilane onto ethyl cellulose in homogeneous media

Photoinduced homogeneous graft copolymerization of dichlorodimethylsilane (DCDMS) onto ethyl cellulose (EC) was investigated in the absence and presence of photosensitizers, such as benzophenone, benzil and biacetal. The grafting process was carried out in benzene using UV radiation in the range 310–460 nm. The weight conversion, grafting percentage and grafting efficiency were determined as a function of the time of irradiation and the concentrations of monomer, EC and initiator. The structures of the photosensitizers were also considered. Various techniques were used to study the graft copolymers produced such as IR spectroscopy, nuclear magnetic resonance and thin layer chromatography. A Trommsdorf effect (accelerated grafting) was observed in certain systems. The rate of copolymerization of DCDMS onto EC was rapid ( R p = 2.1% min −1). The grafting efficiency values in the presence of the photosensitizers were found to be in the following order: benzil&>benzophenone&>biacetal. Pre-irradiation of samples increased the grafting percentage values. The mechanisms of formation of grafted chains in the absence and presence of photosensitizers are discussed.

論文特集「有機・無機の光機能材料」 ニトロ化ポリアセナフチレンの合成とその高分子増感剤としての応用

Polymers having photosensitive nitroaryl groups were synthesized by the nitration of polyacenaphthylene or by the ionic polymerization of 5-nitroacenaphthylene. The photoisomerization of trans-cinnamic acid in the presence of photosensitizers was carried out in DMF. From the results obtained, it was found that the partially nitrated polyacenaphthylene reveals an excellent photosensitizing activity compared with that having 100% photosensitizer unit and that its sensitivity depends on the content of the nitro group.

Photosensitized Oxidation of Tryptophan: Effect on Liver and Brain Tryptophan

Toxic products are formed when tryptophan is irradiated with light in the presence of photosensitizers such as riboflavin. In order to further investigate this phenomenon, solutions of tryptophan (48 mumol.mL-1) were irradiated with broad spectrum fluorescent light in the presence or absence of riboflavin (0.01 mg.mL-1). Solutions of riboflavin were similarly irradiated; control solutions were the respective solutions not exposed to light. Two-week-old suckling gerbils were then assigned to receiving 7 days of intraperitoneal injections of the light-exposed or non-light-exposed solutions. There were significant differences in the concentrations of tryptophan in serum, liver, and brain; activity of gamma-glutamyl transferase (GGT) as well as liver protein were also significantly different among the groups. Body and liver weights were also significantly different among the groups. In order to identify the photoproducts responsible for these changes, solutions of tryptophan that had been irradiated with light in the presence of riboflavin were then fractionated based on time of elution during high-pressure liquid chromatography and the fractions were then injected into the gerbils as before. GGT responses to one of the fractions was similar to that of the parent compound. Chromatographic studies indicated the presence of numerous photoadduct compounds of tryptophan and riboflavin after exposure to light. Both the presence of riboflavin and the exposure of the solutions to light alter brain concentrations of tryptophan in the developing gerbil indicating differing availability to the brain of this serotonin precursor. Clinical implications of the infusion of amino acids in the presence of photosensitizers and light must be considered.

Postcolumn formation of fluorophores from nitrogenous pesticides by UV photolysis

The ultraviolet (UV) photolysis of several classes of nitrogenous pesticides was examined with a view to photo-induced fluorescence detection in flow-injection analysis (FIA) and liquid chromatography. The solvents evaluated as typical reversed-phase mobile phases included water, methanol, and 1:1 mixtures of methanol/water and acetonitrile/water, and methanol/acetonitrilelwater mixtures. Acetone, acetophenone, the surfactant triton X-100, and the photocatalyst titanium dioxide were assessed as photosensitizers to enhance the UV photolysis and fluorescence responses. FIA and liquid chromatographic separations of several pesticides were followed by post-column UV photolysis for the fluorescence detection. Ultraviolet photolysis produces some fluorescent products. The type of photolytic solvent seems to play a significant role. The presence of photosensitizers also affects the fluorescence response of some pesticides. The photochemical transformation products of some of the pesticides are suggested. Analytical figures of merit were evaluated for determination of several pesticides in ground water. The post-column UV photolysis approach for fluorescence detection in liquid chromatography was assessed for several nitrogenous pesticides in ground water samples at ng/g concentrations.

Ultraviolet Photolysis and Ortho-Phthalaldehyde-Mercaptoethanol Derivatization of Pharmaceuticals for Enhanced Fluorescence Detection in HPLC

Abstract Several classes of nitrogenous pharmaceutical were examined for fluorescence after ultraviolet (UV) radiation induced photolysis followed by reaction with o-phthalaldehyde-2-mercaptoethanol (OPA-MERC), and after UV photolysis alone. Photolyses were examined in water, mixtures of methanol/water (1:1), and acetonitrile/water (1:1). Acetone was assessed as a photosensitizer to enhance photolysis and fluorescence response. Flow injection analysis and high-performance liquid chromatographic techniques were used for several pharmaceuticals. The analytes were subjected to UV photolysis and reaction with OPA-MERC reagent for generation of fluorophores that responded to fluorescence detection. During photolysis, solvent type as well as the presence of photosensitizers seem to play a significant role in the formation of primary amines and fluorophores. Photochemical transformation products of some of the pharmaceutical chemicals are proposed. Analytical figures of merit were determined for some analytes. T...

Structure and stability of gamma-crystallins--IV. Aggregation and structural destabilization in photosensitized reactions.

Abstract— Unlike α‐ and β‐, γ‐crystallins become turbid upon irradiation with 300 nm or white light in the presence of photosensitizers, e.g., methylene blue (MB) or riboflavin (RF). These proteins, however, do not aggregate in the presence of guanidine hydrochloride. Turbidity formation is concentration‐dependent. Except in RF‐sensitized reactions, the onset and rate of turbidity formation are faster in γ‐IV than in the other two crystallins. Labeling the thiol groups of the protein with iodoacetamide does not change the turbidity rate in case of irradiation with 300 nm light, but it does change it in case of RF‐ or MB‐sensitized reaction. The order of rate constants of the decrease in tryptophan emission under aerobic conditions upon 300 nm irradiation and MB‐ and RF‐sensitized reactions is γ‐IV > γ‐III > γ‐II. The rate constants in the absence of air and in the presence of D2O upon MB‐ and RF‐sensitized reactions also indicate that the role of singlet oxygen is significant in the former reaction. We suggest that the photoinduced structural changes occur in two steps. In the first, photooxidation of tryptophan as well as cysteine residues (including the buried cysteines) occurs, leading to small conformational changes of the protein. Conformational changes of the protein, as evident from the near‐UV CD and fluorescence lifetime measurements, subsequently result in aggregation of the protein. As suggested by X‐ray analysis, the perturbation of the cys 78 and 32 by the active species of oxygen appears to be responsible for the destabilization of the protein structure, resulting in rapid aggregation of these crystallins.

Porphyrin-sensitized photodynamic inactivation of cells: A review

When mammalian cells are exposed to light in the presence of photosensitizers, such as porphyrins, a number of reactions takes place. The most important photoproduct is singlet oxygen, which reacts with and degrades a variety of biomolecules. This species can travel only about 0.1μm in a cell during its lifetime. Therefore, the structures most exposed to photodamage are those containing high concentrations of sensitizer. For porphyrins, membranes and mitochondria are such structures. Photosensitized damage to mitochondria and membranes has been observed by several techniques. The incubation time with sensitizers is critical since the rates of accumulation of sensitizer are different at different cellular locations. Several other aspects of the action of photosensitizers are reviewed: Have sublethal doses any effect on proliferation and DNA? How can photodynamic treatment act selectively on tumour tissue? Should photodynamic cancer treatment be combined with other therapies? Does photodynamic therapy work under low oxygen concentrations?

Ultraviolet light irradiation of defined-sequence DNA under conditions of chemical photosensitization.

Abstract— The formation of cyclobutane pyrimidine dimers and UV light‐induced (6‐4) products was examined under conditions of triplet state photosensitization. DNA fragments of defined sequence were irradiated with 313 nm light in the presence of either acetone qr silver ion. UV irradiation in the presence of both silver ion and acetone enhanced the formation of TT cyclobutane dimers, yet no (6‐4) photoproducts were formed at appreciable levels. When photoproduct formation was also measured in pyrimidine dinucleotides, only cyclobutane dimers were formed when the dinucleotides were exposed to 313 nm light in the presence of photosensitizer. The relative distribution of each type of cyclobutane dimer formed was compared for DNA fragments that were irradiated with 254, 313, or 313 nm UV light in the presence of acetone. The dimer distribution for DNA irradiated with 254 and 313 nm UV light were very similar, whereas the distribution for DNA irradiated with 313 nm light in the presence of acetone favored TT dimers. Alkaline labile lesions at guanine sites were also seen when DNA was irradiated with 313 nm light in the presence of acetone.

Photosensitized oxidation of tryptophan and hepatic dysfunction in neonatal gerbils.

Hepatic dysfunction is a common metabolic complication of parenteral nutrition. Studies in animals have suggested that several amino acids, especially tryptophan, may play a role in the development of hepatic dysfunction. Further, photoirradiation of amino acids in the presence of photosensitizers, such as riboflavin, causes photooxidative changes in several amino acids. The present study was undertaken to determine the effect of tryptophan, after photoirradiation in the presence of riboflavin, on hepatic function in neonatal gerbils. Two-week-old suckling gerbils received approximately 4 mmol/kg/day of light-exposed or nonlight-exposed tryptophan or received saline intraperitoneally for 4 days. An increase in the activity of serum gamma-glutamyl transpeptidase was found in gerbils receiving both light-exposed and nonlight-exposed tryptophan compared to control. Concentrations of tryptophan were significantly higher in animals receiving saline than in the other two groups. There were no significant differences in the major tissue amino acids among the three groups of animals. Our data suggest the role of photosensitized oxidation of tryptophan in the pathogenesis of hepatic dysfunction in neonatal gerbils. It is possible that similar photooxidation occurring during infusion of parenteral amino acid solutions containing vitamins exposed to constant illumination in the newborn nursery is responsible for the observed hepatic dysfunction in parenterally fed neonates.

Damage of photoreceptor membrane lipids and proteins induced by photosensitized generation of singlet oxygen.

It has been shown that illumination of rod outer segment suspension in the presence of photosensitizers (methylene blue lambda greater than or equal to 620 nm; retinal 370 less than or equal to lambda less than or equal to 390 nm) results in chemical modification of the lipid and protein components of the photo-receptor membranes. This modification can be registered by accumulation of lipid peroxidation (LPO) products as well as oligomerization of rhodopsin and a decrease of rhodopsin thermal stability. These effects are prevented by 'O2-quenchers and free radical scavengers. It has been found that the electric activity (ERG) of isolated frog retina is inhibited due to photosensitized generation of 'O2 which can be overcome by preliminary addition of 'O2-quenchers and free radical scavengers to the incubation medium. The LPO products are accumulated in the retinae of rats exposed to high intensity light in vivo. It is concluded that 'O2 and LPO are involved in light-induced damage of the retina.

Donor-Acceptor Complexes in Copolymerization. XXXIX. Alternating Diene-Dienophile Copolymers. 6. Photosensitized Copolymerization of Conjugated Dienes and Maleic Anhydride

Abstract Equimolar, alternating copolymers are produced when solutions of conjugated dienes and maleic anhydride are subjected to 2537 A UV light in the presence of photosen-sitizers or 3000 A or higher wavelength light in the absence or presence of sensitizers. The yield of copolymer is highest when the sensitizer has ET < 74 kcal/mole. The copolymers are insoluble in polar organic solvents when the sensitizer has ET < 75.

Some properties of n-CdS-p-Cu2S film heterojunctions

Some n-CdS-p-Cu2S film heterojunctions have been obtained which differ from previously studied hetero junctions in the anomalous sign of the rectification and the presence of photo sensitivity only in the fundamental-absorption region of Cu2S. These features of the characteristic are associated with the effect of the surface states at the boundary on the energy structure of the hetero junction. The results are interpreted on the assumption that the main mechanism involved in the passage of current across the hetero junction is the tunneling of the electrons through the barrier at the boundary into the Cu2S.

The effect of heat processing, gamma radiation, and ultraviolet radiation on the anaphylactogenic properties of milk

Molecular alteration in proteins has been accomplished with extensive heat treatment, ultraviolet irradiation in the absence or presence of photosensitizer, and gamma radiation. Alteration in the anaphylactogenic properties of raw skimmed milk protein, when tested on milk-sensitized guinea pigs, was observed by all three methods. Measurements made of the contractions on excised uterine strip from milk-sensitized guinea pigs produced by a challenge with gammairradiated milk revealed that a 9.30 megarad sample produced a response which was 85 per cent of that produced by raw skimmed milk. A lower radiation dose of 5.58 megarads produced a contraction which was 93 per cent of that produced by raw skimmed milk. The mean lethal shocking doses (LD 50 values) for gamma-irradiated milk samples at radiation doses of 0.456, 2.79, 5.58, and 9.30 megarads were, respectively, 29 ± 4, 64 ± 11, 602 ± 270, and 1,157 ± 422 mcg. of protein nitrogen when injected into milk-sensitized guinea pigs. The LD 50 value for 90° C. milk heated for thirty-five minutes was 347 ± 99 mcg. protein nitrogen. The LD 50 value for ultraviolet-irradiated milk without photosensitizer (hematoporphyrin) was 228 ± 52, and with hematoporphyrin added it was 1,272 ± 299 mcg. of protein nitrogen. The LD 50 value for control or raw skimmed milk in all experiments ranged from 24 to 37 mcg. of protein nitrogen. Using treatment-response curves, 9.30 megarad gamma-irradiated milk was found to be equivalent to an 89° C. heat-treated milk. Electrophoretic patterns and viscosity measurements have been made on gamma-irradiated milk protein. The significance of the three methods of processing on the alteration of the allergenicity of milk protein has been discussed.