THE ANAEROBIC PHOTOLYSIS OF LENS α-CRYSTALLIN: EVIDENCE FOR TRIPLET STATE MEDIATED PHOTODAMAGE

Anaerobic solutions of lens alpha-crystallin were subjected to near-UV (greater than 295 nm) irradiation, and the photoproducts were analyzed by fluorescence and room-temperature phosphorescence spectroscopy. The principal photoproduct was excited maximally at 340 nm, fluoresced maximally at 430 nm, and phosphoresced with an emission maximum at 510 nm. The phosphorescence intensity decay of this species was well fit by a sum of two exponentials with lifetimes of 9.2 ms (78%) and 61 ms (22%); this report is the first demonstration of a long-lived triplet state associated with a protein photolysis product. As reported previously, 3trp* is also long-lived in deoxygenated alpha-crystallin solution at room-temperature (Berger and Vanderkooi, 1989, Biochemistry 28, 5501-5508), hence both tryptophan and photoproduct triplet states are good candidates to mediate photodamage. Photolysis experiments in the presence of agents known to alter the tryptophan triplet yield provide evidence for the importance of triplet-state-mediated photodamage of lens crystallins in anaerobic solution. In 30 mM acrylamide where 3trp*, but not 1trp*, is efficiently quenched, anaerobic solutions exhibited marked resistance to protein photodamage, whereas the photoprotection in aerobic solution was minimal. In D2O, where photoionization is suppressed but triplet states are longer-lived, photodamage was accelerated in anaerobic solution but reduced in aerobic solutions. Finally, the anaerobic photodestruction rate was increased in 500 mM Cs+ solution where the triplet yield is increased by a heavy atom effect.     

Matrix isolation study of the photochemical reaction of cyclohexane and cyclohexene with CrCl2O2

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of cyclohexane and cyclohexene with CrCl₂O₂. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of λ > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between cyclic alcohol derivatives and CrCl₂O, although complexes between ring expansion products and CrCl₂O could not be ruled out. This latter result could arise from C-C bond activation and oxygen atom insertion into a C-C bond. For the cyclohexene system, the cyclohexanone-CrCl₂O complex was also observed. The identification of the complexes was further supported by isotopic labeling (²H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level.     

THE QUENCHING OF TYROSINE AND TRYPTOPHAN FLUORESCENCE BY H2O AND D2O*

Abstract— The quantum yields and lifetimes of the fluorescence of tyrosine and tryptophan were determined in D₂O-H₂O and glycerol-H₂O solvent mixtures of varying composition from 10 vol.% to 100% H₂O at 15°C. Forboth amino acids the ratio of the quantum yields in D₂O and H₂O (i.e., q_D/q_H) was smaller than the ratio of the corresponding lifetimes (_D/_H). For tyrosine the ratio of the quantum yields in glycerol and H₂O (q_G/q_H) was also smaller than the corresponding _G/_H ratio, but for tryptophan q_G/g_HG/_H. The proximity of the q vs. plots for tyrosine in the two solvent mixtures indicates that at 15°C neither D₂O nor glycerol, in the pure state or when diluted with H₂O, quench tyrosine significantly. However, H₂O quenches tyrosine by a dynamic process, which increases both the radiative and the nonradiative rate constant. The quenching action is attributed to a tyrosine-H₂O exciplex, whose formation is independent of bulk viscosity and dielectric constant. Unlike tyrosine, tryptophan is quenched weakly by D₂O by a static process at 15°C (i.e., involving no change in), but H₂O quenches tryptophan much more efficiently by a dynamic process, which involves the nonradiative rate constant, but not the radiative constant. These results are explained on the basis of electrostatic complexation of the ammonium group to the carbon atom adjacent to the ring nitrogen with a lifetime which is longer thanin D₂O but shorter thanin H₂O, with solvent reorientation possibly also being an important factor in the quenching. This explanation is consistent with the fact that concentrated (8 M) urea increases q andof aqueous tryptophan ? 15–20%, while guanidine hydrochloride (6.4 M) has the opposite effect, i.e., it decreases q and t of tryptophan ? 15–20%, and with the fact that neither 8 M urea nor 6.4 M guanidine hydrochloride affects any fluorescence parameter of tyrosine at all.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS-XIV. THE SPIN TRAPPING OF FREE RADICALS FORMED DURING THE PHOTOLYSIS OF HALOGENATED SALICYLANILIDE ANTIBACTERIAL AGENTS

Several antibacterial halogenated salicylanilides, including 3,3',4',5-tetrachlorosalicylanilide (TCSA) and 3,4',5-tribromosalicylanilide (TBSA) are known to cause photoallergy. We have carried out photochemical and spin trapping studies to determine whether free radicals may be involved in the photoallergic response. Irradiation (lambda greater than 300 nm) of TCSA in buffered (pH 7.4) 50% ethanol resulted in the rapid loss of the 3-chloro atom, followed by the much slower release of 5- and then the 4'-chloro atoms to give 3'-chlorosalicylanilide as a stable photoproduct. Under the same conditions TBSA successively lost the 3-, 5- and 4'-bromine atoms to give salicylanilide. When TCSA or TBSA were irradiated (lambda = 356 nm) in buffered (pH 7.4) 50% ethanol containing 2-methyl-2-nitrosopropane (MNP) only solvent-derived free radicals were detected. However, irradiation (lambda = 356 nm) of TCSA and MNP in 0.1 N NaOH generated an ESR spectrum consisting of a broad triplet (aN = 15.6 G). This spectrum was attributed to the adduct formed by the reaction of MNP with the aryl radical generated by the loss of a chlorine atom from the sterically hindered 3-(or 4'-)-position. Under the same conditions TBSA initially generated a broad triplet (aN = 15.5 G) similar to that observed for TCSA. However, upon further irradiation a 21-line spectrum (aN = 14.4 G, a2H = 2.0 G and a2H = 0.9 G) appeared.(ABSTRACT TRUNCATED AT 250 WORDS)     

RADIATION DEGRADATION OF CHITOSAN IN THE PRESENCE OF H2O2

INTRODUCTIONChitosan, poly-β-(1 -?4)-D-glucosamine, can be obtained from chitin by deacetylation with alkali. It is soluble indilute acidic medium due to the presence of amino groups. The use of chitosan in many areas, such as foodprocessing, biochemistry, Pharmaceuticals, medicine, and agriculture has been developed over the pastdecades[1,2].In recent years, it has been reported that many properties of chitosan depend on the molecular weight[3]. Thechitosan oligomers possess better fun…     

Photooxidation of lens proteins with xanthurenic acid: a putative chromophore for cataractogenesis.

The tryptophan metabolite, xanthurenic acid (Xan), is produced through a transamination reaction in high concentrations in human lenses with age and has been isolated from aged human cataractous lenses. It has appreciable absorption between 300 and 400 nm (lambda max = 334 nm), the range absorbed by the human lens. Our recent studies have shown that unlike most tryptophan metabolites in the eye, Xan is photochemically active, producing both superoxide and singlet oxygen. To determine if Xan could act as a photosensitizer and photooxidize cytosolic lens proteins, alpha-, beta- and gamma-crystallins were irradiated (lambda > 300 nm, 12 mW/cm2) in the presence and absence of Xan. Upon irradiation and in the presence of Xan, lens proteins polymerized in the order alpha > beta > gamma as assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Further analysis of the photolyzed alpha-crystallin by mass spectrometry indicated that histidine, tryptophan and methionine residues were oxidized at specific positions in a dose-dependent (irradiation time) manner. In alpha A-crystallin two forms of oxidized histidine 154 were observed, 2-imidazolone and 2-oxohistidine. Our results suggest that naturally occurring Xan is a chromophore capable of photosensitization and photooxidation of lens proteins. Furthermore, this compound could play a role in age-related cataractogenesis.     

[Pb2(TNR)2(CHZ)2(H2O)2]4H2O的结构及热分解机理

The coordination compound of [Pb 2(TNR) 2(CHZ) 2(H 2O) 2]•4H 2O was prepared by using the aqueous solution of carbohydrazide, lead nitrate and sodium styphnate. The molecular structure of [Pb 2(TNR) 2(CHZ) 2(H 2O) 2]•4H 2O(C 7H 13 N 7O 12 Pb, Mr=594.43) was determined by using a single crystal diffraction analysis .The thermal decomposition mechanism of the title compound was studied by TGDTG, DSC and IR techniques. The crystal belongs to monoclinic with space group P2 1/n.The unit cell parameters are as follows: a=0.64700(10)nm, b=1.6074(3)nm, c=1.4883(3)nm,β=97.42(2)°,V=1.5349(5)nm3, Z=2, DC=2.572g•cm -3 ,μ(Mo, Kα)=11.080cm -1 , F(000)=1128. R=0.0422, Rw=0.0735. The binuclear lead coordination compound is bridged by two carbohydrazide molecules. The molecule has a symmetrical center. TNR 2- ,CHZ and H 2O coordinate with the central ions simultaneously.     

Stoichiometric water splitting into H2 and O2 using a mixture of two different photocatalysts and an IO3-/I- shuttle redox mediator under visible light irradiation

The stoichiometric splitting of water into H2 and O2 (H2/O2 = 2) under visible light irradiation (lambda > 420 nm) took place for the first time using a mixture of Pt-WO3 and Pt-SrTiO3 (Cr-Ta-doped) photocatalysts and an IO3-/I- shuttle redox mediator.     

二维层状结构十钒酸盐[K(H2O)2Ni(H2O)6]2[V10O28]的合成及性质(英)

A novel heteropoly compound, containing two kinds of coordinated cations, [K(H₂O)₂Ni(H₂O)₆]₂[V₁₀O₂₈], has been synthesized through routine process and characterized by elemental analyses, IR, ⁵¹V NMR and single crystal X-ray diffraction. It crystallizes in the triclinic system, space group P1 with a=0.87382(17) nm, b=1.075 4(2) nm, c=1.111 1(2) nm, α=65.10(3)°, β=75.01(3)°, γ=70.63(3)°, V=0.884 8(3) nm³ and Z=1. The X-ray analysis reveals that the two kinds of coordinated cations are linked by three shared coordinated water molecules, and K⁺ cations coordinate with ten oxygen atoms: five of which come from V₁₀O₂₈^6- anion, the other five from water molecules. The title compound exhibits extended 2D array building up of V₁₀O₂₈^6- groups connected by ten-coordinated K⁺ cations. The hexahydrated nickel cations Ni(H₂O)₆²⁺ lie in neat apposition to three adjacent V₁₀O₂₈^6- clusters. CSD: 413271.     

THE RATES OF PHOTOLYSIS OF THE FOUR INDIVIDUAL TRYPTOPHAN RESIDUES IN UV EXPOSED CALF γ-II CRYSTALLIN

Aqueous buffer solutions of the lens protein bovine gamma-II crystallin were irradiated at 295 nm in the presence of dithiothreitol to determine the individual photolysis susceptibilities of the four tryptophan residues. Reverse-phase high performance liquid chromatography was utilized to compare the tryptic peptide maps before and after irradiation. Sequence analysis of collected tryptic peptides showed that the four tryptophans in calf gamma-II crystallin. TRP-42, TRP-68, TRP-131, and TRP-157 appeared in four distinct tryptic peptides. Fluorescence and absorption (diode array) monitoring of the eluting peptides allowed assessment of the changes in peptide absorbance and fluorescence following irradiation. Tryptophan fluorescence losses of (40 +/- 15)%, (17 +/- 4)%, (35 +/- 5)% and (15 +/- 4)% were observed for the peptides containing TRP-42, TRP-68, TRP-131 and TRP-157, respectively. Thus the four tryptophans in calf gamma-II crystallin did not all photolyze at the same rate. The rate differences are presumably related to the microenvironments of the individual tryptophan residues, and this is discussed in terms of the known crystal structure of calf gamma-II crystallin.     

Matrix isolation investigation of the photochemical reaction of methyl-substituted benzenes with CrCl2O2

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of toluene, m-, o-, and p-xylene, mesitylene, and hexamethylbenzene with CrCl2O2. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of lambda > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between methylcyclohexadienone derivatives and CrCl2O. With the xylenes and mesitylene, di- and trimethylphenols, complexed to CrCl2O, were also observed, respectively. This latter result arises from C-H bond activation and oxygen atom insertion into a C-H bond. The identification of the complexes was further supported by isotopic labeling (2H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level. Product distributions were rationalized by an analysis of the electron density distribution.     

THE PHOTOREACTIONS OF 8-METHOXYPSORALEN WITH TRYPTOPHAN AND LENS PROTEINS*

Abstract— We have previously demonstrated that 8-methoxypsoralen (8-MOP) can be found in the lenses of rats injected (i.p.) with this drug, and that its presence can lead to a photosensitized enhancement of lenticular fluorescence. The cutaneous photosensitizing properties of psoralens are thought to be mediated via their excited triplet states, resulting in photoaddition cyclobutane products between pyri-midine bases and 8-MOP. We have now investigated the possibility that similar types of photoadducts could be generated between 8-MOP and the aromatic amino acid residues in lens proteins. Our experiments involved in vitro irradiation (at 360 nm) of aqueous solutions of 0.1 mM 8-MOP plus purified alpha, beta, or gamma crystallins from calf or normal human (under 20 years of age) lenses. UV absorption and fluorescence emission spectra were measured before and after radiation, and aliquots from all experiments were frozen and kept in the dark for subsequent phosphorescence and EPR spectroscopy. Similar experiments were performed with irradiated aqueous solutions of tryptophan or thymine plus 8-MOP. All controls consisted of solutions kept in the dark. NMR spectra demonstrated that the hydrogen atoms at the 3,4 and 4',5' positions of the 8-MOP molecule were lost following irradiation, suggesting that these two sites were involved in the photoproduct formed between tryptophan and 8-MOP. These studies strongly suggest that 8-MOP is capable of forming photoaddition products with tryptophan and with lens proteins as well as DNA in vivo, resulting in its permanent retention within the ocular lens.     

Synthesis and study of Bi2Ti2O7/TiO2 composites as efficient visible-light-active photocatalysts in the reduction of aqueous Cr(VI)

In this work, Bi_2Ti_2O_7/TiO_2 composites were synthesized and studied as potential visible-light-activated photocatalysts in the reduction of aqueous Cr(VI). Bi_2Ti_2O_7/TiO_2 composites with tunable compositions were synthesized via a solvothermal-calcination two-step method, simply by changing the molar ratios of Bi(NO_3)_3·5H_2O to tetrabutyl titanate in the reactants. The compositions, structures and optical properties of the as-synthesized Bi_2Ti_2O_7/TiO_2 composites were characterized by X-ray diffraction, field emission scanning electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized Bi_2Ti_2O_7/TiO_2 composites was tested in the reduction of aqueous Cr(VI)under visible-light(λ420 nm) irradiation, and compared with that of TiO_2 nanoparticles. It was observed that the as-synthesized Bi_2Ti_2O_7/TiO_2 composites exhibited much higher photocatalytic activity than TiO_2 nanoparticles, and the most efficient composite(300 mg) can achieve the complete reduction of Cr(VI) in 300 mL of 50 mg/L K_2Cr_2O_7 aqueous solution under visible-light(λ420 nm)irradiation in 90 min.     

UV photolysis of C4N2 in water ices: new possible route of synthesis of ammonium bicarbonate and ammonium formate

Laboratory experiments involving ultraviolet (UV) irradiation of dicyanoacetylene (C(4)N(2)) trapped in water ice at 10 K have been conducted and monitored by infrared spectroscopy (FTIR). By the support of isotopic experiments and theoretical calculations, the irradiation of a DCA/H(2)O ice mixture at lambda > 230 nm has been found to be a possible source of NH(4)(+)HCO(3)(-) (ammonium bicarbonate) and NH(4)(+)HCOO(-) (ammonium formate). These latter compounds can arise from a proton-transfer reaction between H(2)O and the CN radical, which is issued from photolyzed C(4)N(2).     

CH2+O2反应的反应机理

The mechanisms of the CH2＋ O2→ H2O＋ CO and CH2＋ O2→ H2＋ CO2 reactions have been studied by performing ab initio CAS(8,8)/6-31G(d,p) calculations, and five intermediates(IMn) and eight transitions(TSn) have been located along the reaction paths. The predicted path for the CH2＋ O2→ H2O＋ CO is: CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS5→ H2O＋ CO. For the CH2＋ O2→ H2＋ CO2 reaction, there are two paths: (i) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS6→ H2＋ CO2 and (ii) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS7→ IM4b→ TS8→ H2＋ CO2, with the latter path more favorable energetically.     

ULTRAVIOLET RADIATION-INDUCED PHOSPHOLIPASE A2 ACTIVATION OCCURS IN MAMMALIAN CELL MEMBRANE PREPARATIONS

Ultraviolet erythema in human skin is mediated in part by membrane derivatives of arachidonic acid (AA). UVA (320–400nm) and UVB (290–320nm) have been shown to induce release of AA from intact mammalian cells in culture. In order to investigate the mechanism of this release we examined the effect of UVA and UVB on release of [³H] AA from membrane preparations of murine fibroblasts. C3H 10T1/2 cells were prelabelled for 24 h with [³H] AA. The membrane fractions of the cells were separated after lysis by differential centrifugation. The membranes were irradiated in suspension and the [³H] AA released from the membranes was determined by scintillation spectroscopy of supernatants3–4 h after irradiation. Both UVA and UVB induced release of AA from the membrane preparations. The response to UVB was small but significant, reaching levels approximately 150% of control release at doses of 1,200-4,000 J/m². The response to UVA was larger; doses of 2.5-5.0 J/cm² induced release equal to twice control (200%) levels, while doses of10–20 J/cm² induced maximal release at levels approximately 400% of control. Time course studies with UVB and UVA showed maximal release at 4 h after irradiation. When the membrane preparations were incubated with a polyclonal anti-phospholipase A₂ antibody the UV induced release of [³H] AA was completely inhibited in both UVB (1200 J/m²) and UVA (10 J/cm²) treated cells. These data suggest that activation of phospholipase A₂ is responsible for the UV induced release of AA in mammalian cells and that the mechanism of this activation is due, in part at least, to direct photon-membrane interaction.     

THE PHOTOCHEMISTRY OF p-AMINOBENZOIC ACID

We have studied the photoreactions occurring when p-aminobenzoic acid (PABA), a component of some sunscreens, is irradiated in aqueous solution. These studies were carried out in the presence and absence of oxygen, using light of lambda = 254 nm as well as light of wavelengths greater than 290 nm. In deoxygenated solution between pH 7.5 and 11.0, we found two photoproducts that were identified as 4-(4'-aminophenyl)aminobenzoic acid (I) and 4-(2'-amino-5'-carboxyphenyl)aminobenzoic acid (V); we used 1H and 13C NMR, electron impact mass spectrometry and synthesis by an independent route to identify each of these compounds. Rapid discoloration of the photolyzed sample was observed when PABA was irradiated in aerated solution. Although a number of products were detected under these conditions, the three most abundant stable compounds have been isolated and identified as 4-amino-3-hydroxybenzoic acid, 4-aminophenol and 4-(4'-hydroxyphenyl)aminobenzoic acid (IV). The latter compound was shown to result from rapid photo-induced oxidation of I in the presence of oxygen. Even in the presence of trace amounts of oxygen, the yield of I was significantly reduced in favor of IV. Studies of the thermal oxidation of I, coupled with evidence gathered from studies of the photochemistry of incompletely deoxygenated PABA solutions, indicate that 4-(2,5-cyclohexadien-4-one)iminobenzoic acid (III) is an intermediate on the pathway between I and IV. Qualitatively, we found that the photochemical reactions resulting from irradiation of PABA solutions with lambda = 254 nm light and light with lambda greater than 290 nm were the same. The quantum yields for formation of I and V are highly pH dependent, both being less than 10(-4) at pH 7 and rising steadily to values greater than 10(-3) at pH 11. The detailed pH dependence suggests that the deprotonated PABA radical cation may be an important intermediate entering into the reactions forming I and IV.     

Matrix isolation investigation of the photochemical reaction of benzene with CrCl2O2 and OVCl3

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of benzene with CrCl(2)O(2) and OVCl(3). While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of lambda > 300 nm. Wavelength dependence studies determined that light of lambda < 590 nm led to reaction and oxygen atom transfer, forming an eta(1)-complex between 2,4-cyclohexadienone and CrCl(2)O. The identification of the complex was further supported by isotopic labeling ((13)C and (2)H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level. Merged-jet experiments in which thermal reactions are examined were also conducted, at temperatures as high as 150 degrees C. No products were observed.     

Photocatalytic overall water splitting under visible light by TaON and WO3 with an IO3-/I- shuttle redox mediator

Photocatalytic water splitting into H2 and O2 under visible-light irradiation (lambda > 420 nm) is demonstrated using the oxynitride Pt-TaON for H2 evolution and a Pt-WO3 catalyst for O2 evolution in an IO3-/I- shuttle redox-mediated system.     

LASER PHOTOLYSIS OF THE PURPLE MEMBRANE OF Halobacterium halobium IN THE PHOTOSTATIONARY STATE: THE PHOTOBRANCHING PROCESS FROM THE O640 INTERMEDIATE

Abstract The photobranching process from the O₆₄₀ intermediate (O) in the photocycle of bacteriorhodopsin was studied. The O form accumulated with continuous wave visible light (390–800 nm) irradiation of the acidic (pH 3.9–6.0) purple membrane of Halobacterium halobium at 22°C. The photocycle of O via an L-like (or N-like) intermediate was driven by 630 nm pulsed light. The newly found intermediate has an absorption band in the 450–560 nm region. The "green-light"-absorbing pigment, tentatively called G₅₂₀, was converted to O with a time constant of (1.2 ± 0.2) ms. No M-like species was found in the cycle. The quantum yield of the cycle was estimated to be 0.30 ± 0.15.