PHOTOCHEMICAL AND SPECTRAL PROPERTIES OF A PARTICULATE MODEL SYSTEM OF CHLOROPHYLL WITH AMPHIPHILES PREPARED FROM HISTAMINE

Abstract— In the photosynthesis model system described, chlorophyll a at an interface photosensitizes the transfer of hydrogen equivalents from a hydrocarbon phase to an aqueous phase. The hydrocarbon phase, to which chlorophyll is adsorbed, consists of polyethylene particles swollen with tetradecane. The particles are also charged positive by co-adsorption of dodecylpyridinium iodide. Furthermore, chlorophyll is ligated with the imidazole function of one of several amphiphiles derived from histamine, which may or may not contain a reducible nitroaromatic group that can serve as primary electron acceptor from photoexcited chlorophyll. The fluorescence quantum yield of chlorophyll on these particles is diminished by self-association of the pigment and by reaction with an oxidizing amphiphile; in the latter case, the quantum yield is correlated with the one-electron redox potential of the amphiphile. Fluorescence-lifetime analysis reveals that most excited singlet states of chlorophyll are quenched rather quickly, and that most of the fluorescence comes from a small fraction of chlorophyll with long lifetime. All preparations sensitize the photoreduction of 5,5′-dithiobis(2-nitrobenzoate) (DTNB) to the water-soluble thiolate by hydrazobenzene. When the amphiphile that ligates chlorophyll is not oxidizing, the quantum yield of photoreduction is unrelated to the fluorescence yield of the particles, but may be related to the degree of self-association of chlorophyll. When the amphiphile that ligates chlorophyll is oxidizing, the kinetics of photoreduction of DTNB require that the electron passes through the primary oxidant to DTNB. Quantum yields for photosensitized reducton of oxidizing amphiphiles in the absence of DTNB have a reversed correlation with redox potential, which can be rationalized in terms of the Marcus theory of electron transfer. All data are most consistently accounted for if the primary photoproduct is an ion pair of chlorophyll and primary oxidant when the latter is available, and a chlorophyll radical ion pair when it is not, both formed by electron transfer from the singlet excited state of chlorophyll.     

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NITROTHIENYL DERIVATIVES

Abstract Some 2-nitrothienyl derivatives characterized by the presence of an aryl or heteroaryl substituent in the C-5 position were synthesized by using a photochemical coupling procedure. All synthesized compounds were demonstrated to be singlet oxygen sensitizers in the trans-α,α'-dimethylstilbene photooxidation.     

PHYSICAL AND PHOTOCHEMICAL PROPERTIES OF A FLUORESCENT CHLOROPHYLL COLLOID

Abstract— A fluorescent colloid of chlorophyll a , of which some qualitative properties were noted by Krasnovsky and Brin⁽¹¹⁾, has been quantitatively characterized. The colloid is formed in neutral PO₄ buffer containing 0 1 to 8.0% Tween 20, and is stable in darkness. The extinction coefficient is 7.8 × 10⁴ 1. mole cm^-1 at the red absorption peak (668 mμ), the yield of fluorescence is ˜ 0.25, and the yield of photoautooxidative bleaching is ˜ 2 times 10^-4. The colloid sensitizes the autooxidation of paratoluenediamine with a yield of ˜0.01 to ˜0.3 depending on light intensity and substrate concentration. The yield is independent of detergent and chlorophyll concentrations. In all respects—except the dependence of yield on illumination—the colloid appears to be physically and photochemically equivalent to dissolved chlorophyll, as known in dilute solutions in organic solvents. The light dependence—the yield is inversely proportional to the cube root of absorbed intensity—could be due to a bimolecular back reaction of a chlorophyll or substrate derivative.     

PHOTOCHEMICAL PROPERTIES OF FLAVIN DERIVATIVES

Abstract— The triplet yields of 15 derivatives of riboflavin modified either in position 8 or in the ribityl side chain have been determined. The triplet yields measured range from 0.002 to 0.9. In addition, estimates for the rate constants of the photoreaction with EDTA and for the complex formation constants with EDTA at pH 7.0 are given. Evidence for an interaction in solution of at least the 2' and 5' hydroxyl groups of RF with the isoalloxazine ring is presented.     

THE PHOTOCHEMICAL PROPERTIES OF FLUOROALUMINUM PHTHALOCYANINE

Abstract Fluoride is known to inhibit the photodynamic activity of aluminum phthalocyanine in a variety of biological systems. In order to gain insight into this phenomenon, the effect of fluoride on the photophysical properties of free and albumin-bound chloroaluminum phthalocyanine sulfonate (AlPcS_n.) were studied. The association constant of NaF with AlPcS_n, in aqueous solution was measured as 500 ± 20 M^?1. This binding affects the photophysical properties of the dye: the absorption bands in the visible range are blue-shifted by 6–8 nm, and this effect is mirrored in the fluorescence emission spectrum. Human serum albumin significantly quenched the dye fluorescence independent of the presence of fluoride ion. The transient absorption spectrum of the excited dye triplet is unchanged by NaF, but the quantum yield for its generation is increased by 50%, with no decrease in its lifetime. Formation of fluoroaluminum phthalocyanine complexes was also observed in tetrabutylammonium fluoride-assisted solutions in wet acetonitrile. The fluoro-AlPcS_n, complex is a better photosensitizer for generation of singlet oxygen than the original dye-hydroxyl ion complex, as confirmed using the imidazole-N,N-dimethyl-4-nitrosoaniline method. On the other band, the fluoro-AlPcS_n. complex exhibits an intense inhibitory effect on photohemolysis of red blood cells (RBC) even after the cells are washed to remove free dye and fluoride prior to irradiation, indicating that once the dye is attached to the cellular site, the fluoride ligand is no longer prone to displacement (by hydroxyl ion, for example). Nonetheless, it is clear from the spectroscopic data that the new fluoro complex is an efficient sensitizer for photo-oxidation. Therefore, the reduced photodynamic action of the fluoro-AlPcS_n. complex on RBC (Ben-Hur et al., Photochem. Photobiol. 58 , 351–355, 1993) may result from a lowering of the efficiency of interaction of the fluorodye complex with sensitive cell target moieties.     

PHOTOCHEMICAL REACTIONS OF DIBROMOTHYMOQUINONE: STRUCTURE AND INHIBITORY PROPERTIES OF THE PHOTOPRODUCT

Abstract— The chemical structure of the major product that resulted from illumination of ethanolic solutions of dibromothymoquinone was deduced using ¹³C-and ¹H-nuclear magnetic resonance spectroscopy. The photoproduct is 2,5-dibromo-3-allyl-6-methyl- p -dihydrobenzoquinone. The inhibition of photosynthetic electron transport by the photoreduced compound was found to be roughly equivalent to inhibition by nonirradiated dibromothymoquinone.     

PHOTOCHEMICAL AND PHOTOBIOLOGICAL PROPERTIES OF KETOPROFEN ASSOCIATED WITH THE BENZOPHENONE CHROMOPHORE

Abstract Irradiation of ketoprofen in neutral aqueous medium gave rise to 3-ethylbenzophenone as the major photoproduct. Its formation is justified via protonation of a benzylic carbanion or hydrogen abstraction by a benzylic radical. Minor amounts of eight additional compounds were isolated. Four of them are derived from the benzylic radical: 3-(1-hydroperoxyethyl)benzophenone, 3-(1-hydroxyethyl)benzophenone, 3-acetylbenzophenone and 2,3-bis- (3-benzoylphenyl)butane. The other four products involve initial hydrogen abstraction by the excited benzophenone chromophore of ketoprofen: 1,2-bis-(3-ethylphenyl)-1,2-diphenyl-1,2-ethanediol, 2-(3-benzoylphenyl)-1-(3-ethylphenyl)-1 -phenylpropan-1 -01,α -(3-ethylphenyl)phenylmethanol, 1,2-bis-[3-(2-hydroxycarbonylethyl)phenyl]-1,2-di-phenyl-1,2-ethanediol. The latter process was found to mediate the photoperoxidation of linoleic acid through a type I mechanism, as evidenced by the inhibition produced by the radical scavengers butylated hydroxyanisole and reduced glutathione. The major photoproduct, which contains the benzophenone moiety but lacks the propionic acid side chain, also photosensitized linoleic acid peroxidation. Because lipid peroxidation is indicative of cell membrane lysis, the above findings are highly relevant to explain the photobiological properties of ketoprofen.     

PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF TRITON X-165 IN AQUEOUS AND METHANOLIC SOLUTIONS

Abstract Laser flash photolysis of the nonionic surfactant Triton X-165 was carried out at 248 nm in methanolic and aqueous solutions at different pHs. Cation radical, triplet, phenoxy radical and solvated electron were observed as the transient absorbing species. Various characteristics of these transient species and their decay constants are reported. Photoionization was found to be a major process and it was monophotonic. The results obtained are compared with the photolysis of a small molecule p -methoxytoluene (PMT). Fluorescence and phosphorescence properties of the surfactants Triton X-100, Triton X-165 and PMT are also studied. A suitable reaction scheme is proposed to account for the observed results.     

PHOTOCHEMICAL PROPERTIES OF ERYTHROCYTE GHOSTS CONTAINING PORPHYRIN

Abstract— Rabbit erythrocyte cell ghosts were prepared containing tetrasodium meso-tetra (4-sulfona-to-phenyl) porphine (12-hydrate), a water soluble porphyrin. Laser flash kinetic spectroscopy of the suspension revealed a difference spectrum consistent with the porphyrin T, state. The time profiles of the signal decay were bi-exponential, and oxygen quenched each of the two components differently. Triplet-triplet extinction coefficients and quantum yields were lower for the ghost suspension than for porphyrin in solution. Fluorescence lifetime studies of the suspension also showed the presence of two components. Singlet oxygen luminescence, as measured by germanium diode detection, was observed, with a lifetime of 46 (jls and a 4>A of 0.09.     

TWENTY-TWO CARBON HOMOLOGUE OF 11-CIS RETINAL. PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES

Abstract— Results concerning absorption-emission spectra and fluorescence quantum yields at 77 and 298K. triplet absorption spectra, and quantum yields of intersystem crossing and photoisomerization at 298 K, are presented for 11- cis β-apo-14'-carotenal (C₂₂-Ald), the immediate higher homologue of 11- cis retinal. The absorption spectra are characterized by two band-systems with maxima at 390–400 and 270–280 nm, respectively. Upon cooling from 298 to 77 K, the intensities of these two band-systems undergo changes in opposite directions indicating 12-s- cis: 12- s-trans conformational changes. No intermediate band-system analogous to the one located at 270–310 nm in cis retinals is observed for 11- cis C₂₂-Ald. In nonpolar hydrocarbon solvents (e. g. cyclohexane) at room temperature, quantum yields of fluorescence (0.01), intersystem crossing (0.6) and photoisomerization (0.4) are all quite pronounced. The photophysical and photochemical properties of 11- cis C₂₂-Ald are discussed in the light of similarities and dissimilarities with those of all- trans C₂₂-Ald and 11- cis retinal under comparable conditions.     

PREPARATION AND SPECTRAL PROPERTIES OF SYMMETRICAL S-ARYL ARENESULFONOTHIOATES (THIOSULFONATES)

Abstract

Arenesulfinyl chlorides (4-XC₆H₄S(O)Cl); × = H, CH₃, F, Cl, Br) react with activated zerovalent zinc in benzene at 6 to 8°C to give symmetrical S-aryl arenesulfonothioates (thiosulfonates) in good to excellent yields. 2-and 3-Substituted arenesulfinyl chlorides (X = Cl, CH₃) give a mixture of products (disulfide, thiosulfinate, and/or thiosulfonate). 2,4,6-Triisopropylbenzenesulfinyl chloride reacts with zinc in 1,2-dimethoxyethane to give S-(2,4,6-triisopropylphenyl) 2,4,6-triisopropylbenzenesulfinothioate and bis(2,4,6-triisopropylphenyl) disulfide. Possible mechanisms for the reactions, the ¹H and ¹³C NMR spectra, and the chemical ionization and electron impact mass spectra of the thiosulfonates are discussed. The para carbon substituent chemical shifts (C_p-SCS) for the thiosulfonates and for symmetrical diaryl disulfides have been subjected to several dual substituent parameter (DSP) correlations.     

ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF SOME 2-PHENYLQUINOLINES AND RELATED FUSED SYSTEMS

Abstract— A series of modified 2-phenylquinolines were synthesized and their absorption and emission spectral properties measured in order to determine the effect of structural modifications on excited states. It was hoped that modifications would sufficiently change excited-state properties so that similar structural modifications in 2-phenylquinolinemethanols would negate the phototoxicity of these compounds. The excited states of 2-( o -hydroxyphenyl)quinoline, 11 H-indeno[1,2-b]quinoline, and l,4-dimethyl-5,6-dihydrobenz[c]acridine proved to have properties different from those of normal 2-phenylquinolines, and this effect was shown to be reflected in simple photochemistry of the dihydrobenzacridine. Absorption spectra provided information on conformational preferences for several of the derivatives.     

SPECTRAL PROPERTIES OF PHYCOBILISOMES AND PHYCOBILIPROTEINS FROM THE BLUE-GREEN ALGA-NOSTOC SP.*

Abstract— An improved method for phycobilisome isolation from a blue-green alga Nostoc sp. was developed using 1% Triton X-100. The phycobilisome preparations showed little fragmentation and had structures similar in size to those observed in thin sections of the organism. Phycobiliproteins isolated from phycobilisomes and examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, had subunits with the following molecular weights: phycoerythrin (PE), 20,000 and 16,900; phycocyanin (PC), 14,700 and 16,300; and allophycocyanin (APC), 14,000. Isoelectric focusing of each phycobiliprotein resulted in major bands isoelectric at the following pH values: PE, 4.43, 4.45; PC 4.32; APC, 4.38. Absorption spectra at -196°c showed maxima at 551 and 566 nm for PE; 598 and 631 nm for PC; and 590, 600, 629 and 650 nm for APC. Concentrated vs dilute difference spectra of phycobiliproteins showed increased absorption at 574 nm (PE), 630 nm (PC) and 651 nm (APC) suggesting that spectral changes resulted from aggregation. Fluorescence analysis of each phycobiliprotein and of intact phycobilisome preparations showed that energy absorbed by phycoerythrin is transferred to allophycocyanin, possibly by a resonance transfer mechanism. These observations support a model where allophycocyanin forms the base of the phycobilisome which is attached to the photosynthetic membrane. The next layer is assumed to be phycocyanin, which in turn is followed by a phycoerythrin layer that is the outermost layer (on the stroma side) of the phycobilisome.     

INVESTIGATION OF MAGNESIUM TETRABENZPORPHYRIN-II.:REDOX AND PHOTOCHEMICAL PROPERTIES IN ORGANIC SOLVENTS AND AQUEOUS MEDIUM

Abstract Absorption and fluorescence properties of MgTBP were studied resulting from chemical oxidation and phtooxidation. The absorption spectra of the oxidised product in methanol and acetone are markedly different from those in aqueous solvents.     

ELECTRONIC PROPERTIES AND PHOTOCHEMICAL MONOMOLECULAR REACTIONS IN ORGANIC CONJUGATED COMPOUNDS: PHOTOCYCLIZATIONS, PHOTOISOMERIZATIONS AND PHOTOCHEMICAL REARRANGEMENTS—II

Abstract— Using theoretical indexes derived in Part I and Huckel and unrestricted Hartree-Fock wave-functions, the stabilizing deformation of the excited molecule is studied for a large number of planar conjugated compounds presenting monomolecular photo-reactions: it is shown that in all the cases, the potential hole of the excited state of the initial molecule is strikingly displaced from its ground state configuration towards the fundamental configuration of the photoproduct. The possible influences of others electronic, steric and vibratory factors in particular are discussed in the study of photocyclization of 1–3 cis-butadiene derivatives.     

ELECTRONIC PROPERTIES AND PHOTOCHEMICAL MONOMOLECULAR REACTIONS IN ORGANIC CONJUGATED COMPOUNDS: PHOTOCYCLIZATIONS, PHOTOISOMERIZATIONS AND PHOTOCHEMICAL REARRANGEMENTS—I

Abstract— It is assumed that quantum yields of monomolecular reactions are mainly determined by the probability of de-excitation from the excited state to the ground state of the photoproduct and that a reaction will occur only if the stable molecular configuration of the excited state is close enough the molecular configuration of the photoproduct. In order to evaluate the stabilizing deformation of the excited states, the different methods of representing the excited states wave-functions are compared. Though very different in their ability to reproduce spin densities in the triplet state, these methods appear to give very close results for the electronic repartition; particularly, unrestricted Hartree-Fock calculations seem to give nearly the same net charges and bond indices for corresponding singlet and triplet states. A simple method for a rough evaluation of the direction and of the amplitude of the stabilizing deformation is proposed. In the Hiickel scheme, the variations in bond orders may be taken as an approximate index of that deformation.     

A STUDY OF THE PHOTOCHEMICAL PROPERTIES OF SOME CINNAMATE SUNSCREENS BY STEADY STATE AND LASER FLASH PHOTOLYSIS

The E ⇄ Z photoisomerization of 4'-methoxycinnamates, used as sunscreens in cosmetics, has been studied by steady state and laser flash photolysis, in aqueous and organic solutions. Photoisomerization quantum yields are found to be fairly high (˜0.5-1), although no intermediate is detected upon laser flash photolysis. Cinnamates are not photodynamic sensitizers but are able to quench the 8-methoxy-psoralen and 5-methoxypsoralen triplets which produces E → Z isomerization.     

SPECTRAL PROPERTIES OF THE RHODOPSIN-SYSTEM OF THE CRAYFISH Astacus leptodactylus

Abstract— The absorption spectra of the membrane-bound and of the digitonin-solubilized visual pigment of crayfish Astacus leptodactylus were investigated by conventional spectrophotometry. A method was developed to isolate purified rhabdoms almost entirely free from screening pigments from a single retina. The quantity of isolated and purified rhabdoms from a single retina was sufficient to measure the absorption spectra of the visual pigment.
The absorption spectra of the chromoprotein system (R and M) show that both the membrane-bound and the digitonin-solubilized visual pigment isomers are stable at 0°C and pH 7.0. Rhodopsin and metarhodopsin are photoreversible under these conditions without any light-induced denaturation. The difference spectra for the chromoprotein isomers and those of different photostationary states yield maximal values for ΔE at 570 and 485 nm.
At neutral pH, 0°C, Λ_max of rhodopsin is 530 nm. Irradiation with light of Λ= 630 to 640 nm isomerizes rhodopsin nearly quantitatively to metarhodopsin with Λ_max, of 500 nm. The molar extinction coefficient of metarhodopsin is greater than that of rhodopsin by a factor of ˜ 1.41. each measured at its respective Λ_max Metarhodopsin can be isomerized to rhodopsin by irradiating at Λ > 630 nm. As the absorption spectra of the two chromoprotein isomers overlap, only part of the metarhodopsin can be reversed to rhodopsin. The maximal photoreversion can be achieved by irradiating at 460 nm. The stability of the digitonin-solubilized chromoprotein is remarkably dependent on temperature. Warming the digitonin extract of rhabdoms from 0 to 20 or 30°C caused a shift of the rhodopsin spectrum to shorter wavelengths (Λ_max= 485 nm) accompanied by a decrease of E_Λmax by about 30%.     

PHOTOPHYSICAL and PHOTOCHEMICAL PROPERTIES OF COUMARIN DYES IN AMPHIPHILIC MEDIA

Abstract— Photophysical properties of coumarin dyes solubilized in aqueous detergent solutions have been investigated including measurement of absorption and fluorescence emission maxima, and fluorescence quantum yields. Use of coumarin 4 as a fluorescence probe of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) solutions led to the conclusion that the sites for dye incorporation in micelles are significantly hydrogen-bonded (hydrated). The inhibition of photochemical decomposition for detergent-solubilizcd dyes has also been observed. Electron transfer from micelle-bound dye to a water soluble acceptor, methyl viologen, has been investigated by flash photolysis.