THE ELECTROPHOTOLUMINESCENCE OF CHLOROPLASTS

Abstract— Delayed light emission emanating from preilluminated chloroplasts can be perturbed with pulsed DC electric fields (200–4000 V cm^-1), The perturbation produces a strong stimulation of chlorophyll luminescence. During the field perturbation the stimulated emission rises to a maximum, typically within 100μs. and then decays. Two kinetic components, R (rapid) and S (slow)†, are distinguished on the basis of their rise and decay times and their field-dependence. The R component increases exponentially at high fields, decays within 100–300μs during the field pulse and collapses with t _1/2= 15 μs at the end of the field pulse. The S component occurs at low fields, exhibits near saturation at 500 V cm^-1, decays with t _1/2 about 3 ms during the field pulse, and collapses with t _1/2= 38μs at the end of the field pulse. Studies using inhibitors, ionophores, electron donors and electron acceptors associate the R component with ion transport processes. The relation to electron transport associated with Photosystem II is discussed.     

THE PHOTOCHEMICAL INTERACTION BETWEEN THE TRIPLET STATE OF 8-METHOXYPSORALEN AND THE MELANIN PRECURSORL–3, 4 DIHYDROXYPHENYLALANINE

Abstract— The photochemical interaction between 8-methoxypsoralen (8-MOP) and the melanin precursorL–3,4-dihydroxyphenylalanine(dopaH₂) has been studied using laser flash photolysis. Triplet excited 8-MOP was thus found to abstract electrons from dopaH₂ ( k ∼ 2 × 10⁹ dm³ mol^-1 s^-1) to form semireduced 8-MOP and semioxidised dopaH₂.The technique of pulse radiolysis was used to establish separately the spectra of (a) the semi-reduced form of 8-MOP at pH 6.5 and (b) the semioxidised forms of dopaH₂ at pH 6.5, 5.8, 4.6 and 3.3. The corresponding λ_max and extinction coefficients found were: for 8-MOP at pH 6.5, λ_max= 350 nm (= 9050 dm³ mol^-1 cm^-1); for dopa at pH 6.5, λ_max= 305 nm (ε= 12000 dm³ mol^-1 cm^-1) and for dopaH at pH 3.3, λ= 305 nm (ε= 5900 dm³ mol^-1 cm^-1).     

THE CHARACTERISATION OF THE TRIPLET STATE OF CROCETIN, A WATER SOLUBLE CAROTENOID, BY NANOSECOND LASER FLASH PHOTOLYSES

Abstract— The triplet state of crocetin, which is a water soluble carotenoid, has been sensitized by psoralen. The triplet extinction coefficient, ε_T (73000 dm³ mol^-1 cm^-1 at 470 nm), the triplet-triplet spectrum and the quantum yield of triplet formation, φ_T (less than 1%) are reported in aqueous solution.
In order to calculate the extinction coefficient of crocetin it was necessary to obtain ε_T for psoralen in water (10000dm³ mol^-1 cm^-1 at 450 nm). This latter value was obtained using the complete conversion technique and is reported with the triplet-triplet spectrum.     

NECROSIS OF MURINE TAIL SKIN FOLLOWING PHOTODYNAMIC TREATMENT WITH meso-tetra-(p-SULPHOPHENYL) PORPHINE (TPPS)

Abstract. Albino mice were injected intravenously with 2 mg of meso-tefra-(p -sulphophenyl) porphine (TPPS) and subsequently their tails were exposed to a range of doses of full-spectrum visible light. At a power density of 75 mW cm^-2, a 50% incidence of gross necrosis of the tail skin (ED₅₀) occurred at a light dose of 130 J cm^-2. For haematoporphyrin derivative at the same administered dose, the ED₅₀ was 33 J cm^-2. Increasing the interval between TPPS and light from 1 to 34 days did not spare the tail skin, in terms of an increase in ED₅₀. The slopes of curves of incidence of tail necrosis vs light dose were steep: 1/slope ranged between 20 and 50 J cm^-2.     

基于纳米CdS对尿酸的光催化氧化和铜(Ⅱ)配合物对氧的电催化还原的燃料电池性能

以纳米硫化镉薄膜修饰的铟锡氧化物电极(CdS/ITO)作光阳极, 铜(Ⅱ)配合物[Cu(phen)(L-Trp)·(H₂O)]⁺(phen=1,10-菲啰啉, L-Trp=L-色氨酸)修饰单壁碳纳米管(SWCNTs)电极作阴极, 构建了光催化尿酸(UA)燃料电池, 并研究了其性能及热处理温度的影响. 结果表明, 在40 ℃以下获得的纳米CdS修饰电极在320~550 nm波长区间显现明显的吸收和光伏响应, 在可见光辐射下能光催化氧化UA; 较高温度的热处理(200~300 ℃)却降低了纳米CdS对UA的光催化氧化活性. [Cu(phen)(L-Trp)(H₂O)]⁺/SWCNTs电极在-0.131 V电位下呈现一对准可逆的氧化还原峰, 并能电催化还原O₂和H₂O₂. 此外, 基于UA在CdS/ITO电极上的光催化氧化及O₂在[Cu(phen)(L-Trp)(H₂O)]⁺/SWCNTs电极上的电催化还原, 组装了UA(0.2 mmol/L)燃料电池, 其在可见光照射(0.18 mW/cm²)下产生0.52 V开路电压, 13.08 μA/cm²短路光电流, 在0.41 V下呈现的最大功率密度为4.10 μW/cm².     

ULTRAVIOLET RESONANCE RAMAN STUDY ON PURPLE AND BLUE MEMBRANES OF Halobacterium halobium

Abstract— Two hundred and forty and 213 nm excited resonance Raman spectra of purple membrane (PM) and blue membrane (BM) of Halobacterium halobiurn were studied. Generally intense Trp scattering and a strong relative intensity of the W3 band at 1553 cm^-1 in the 240 nm spectrum of PM indicate red-shifted B_b absorptions of some Trp sidechains. A high intensity ratio of Trp doublet at 1360 and 1340 cm^-1 suggests interactions with highly hydrophobic Trp environments. These Trp are not strongly H-bonded and their N₁ sites are located in positions easily reached by solvent water molecules. Tyrosines are also in very hydrophobic environments and H-bonded. The mainchain consists of normal and distorted α-helices whose amide NH are hardly deuterated in D₂O suspension, and some NH exchangeable irregular segments on the membrane surface. Upon acidification, the ratio of Trp doublet with 240 nm excitation decreases concomitant with increase in retinal absorbance at 600 nm, and the W3 relative intensity and overall Trp scattering also decrease. These observations strongly indicate that the counterpart of Trp interactions in PM is the retinal and that the interactions partly diminish upon acidification. The Tyr environment also changes with the color. Although the 240 nm amide I intensity is greater in acid BM than in PM, the change is not related to the color change because the amide I intensity of deionized BM is practically the same as that of PM. The amide I intensity increase in acid BM is ascribable to a structural change of the surface peptides due to acid induced aggregation.     

THE QUANTUM EFFICIENCY FOR THE INTERPHOTOCONVERSION OF THE BLUE and PINK FORMS OF PURPLE MEMBRANE

When the cations bound to purple membrane are removed it turns blue, and when this blue membrane is irradiated its color changes to pink. Irradiation of pink membrane leads to the reformation of blue membrane. We have determined that the quantum efficiency for the formation of pink membrane from deionized blue membrane is 1.6 ± 0.6 ± 10 ⁴ at 0^oC, pH 5.0. We also found that the quantum efficiency for the back photoconversion, i.e. the formation of blue membrane from pink membrane, is 8.8 ± 1.6 ± 10^-3 at 0^oC, 55 times greater than that of the forward photoconversion reaction. The extinction coefficients of the pink membrane and blue membrane were determined to be 44 500 ± 670 cm^-1 M^-1 at 491 nm and 54 760 ± 830 cm^-1 M ^-1 at 603 nm, respectively, assuming light-adapted purple membrane is 63 000 cm^-1 M ^-1 at 568 nm. The quantum efficiency for forming pink membrane from blue membrane is much lower than that for forming the photointermediate of the blue membrane's photocycle. Their relationship is similar to that of light-adaptation and photocycle of the dark-adapted purple membrane.     

REEVALUATION OF THE SPECTRAL AND KINETIC PROPERTIES OF HO2 AND O2- FREE RADICALS

Abstract— The spectra and molar absorbances of the HO₂ and O₂^- free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by ⁶⁰Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are ²²⁵= 1400 ± 80 M ^-1 cm^-1 and ²²⁵= 2350 ± 120 M ^-1 cm^-1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO₂ and O₂^-: K _Ho2+HO2= (8.60 ± 0.62) × 10⁵ M ^-1 s^-1; K _Ho2+O2-= (1.02 ± 0.49) × 10⁸ M ^-1 s^-1; K _Ho2+O2- < 0.35 M ^-1 s^-1. For the equilibrium HO₂→ O₂^-+ H⁺ the dissociation constant is K _Ho2= (2.05 ± 0.39) × 10^-5 M or p K _HO2= 4.69 ± 0.08. G (O₂^-) has been evaluated as a function of formate concentration.     

ELECTRIC LINEAR DICHROISM OF P700 CHLOROPHYLL U-PROTEIN COMPLEXES

Abstract— The P₇₀₀ chlorophyll a -protein complex (CPI) isolated from green plants was oriented in aqueous solutions using pulsed electric fields of up to 6700 V cm^-1. The electric linear dichroism spectrum is reported in the range of 400–720nm. Positive peaks in the linear dichroism Δ A = A _I - A ₁ (where A_I and A₁ are the absorbance components in which the polarizer orientation is parallel and perpendicular with respect to the electric field. respectively) are observed at 443 and 686 nm. The ΔA signal at 686 nm is discussed in terms of either a specialized chlorophyll form absorbing at 686 nm. or due to an exciton component absorbing at the same wavelength.     

AN FMN-PHOTOSYSTEM I PHOTOVOLTAIC CELL

Abstract— We have made a photovoltaic cell using Photosystem I subchloroplast particles isolated according to the method of Shiozawa et al. (1974). The particles were placed on a filter between two compartments one of which contained the electron donor, K₄Fe(CN)₆ and the other the electron acceptor, FMN. Upon illumination with white light ( I = 80 W/m²) a potential of 300 mV was observed across a 3000 Ω load resistance. Both Photosystem I photochemistry and direct photoreactions of FMN contribute to the process. A power output of 20 μW was observed for a 2 cm² filter containing 60 μg chlorophyll. This corresponds to 0.1 W/m². The power efficiency was 0.13%. The short circuit current was 108 μA.     

PICOSECOND LASER SPECTROSCOPY AND OPTICALLY DETECTED MAGNETIC RESONANCE ON A MODEL PHOTOSYNTHETIC SYSTEM

Fluorescence-detected magnetic resonance of triplets in zero magnetic field (FDMR), fluorescence fading (FF) due to triplet-formation, both at 4.2 K, and prompt fluorescence decay kinetics (FDK) at room temperature have been measured for free pheophorbide- a (f-Pheo) and bound (b-Pheo) to a synthetic polypeptide (L-L ys -L-A la -L-A la )_n, dissolved in dimethylformamide (DMF). Fluorescence decay kinetics measurements of f-Pheo in DMF yielded 1-5 ns lifetimes, for b-Pheo in DMF a ~ 50 ps decay-component was found emitting at 730–750 nm. Zero-field splitting parameters |D| and |E| of the lowest triplet state T₁ were determined from FDMR spectra as (337 and 24) 10^-4 cm^-1 for f-Pheo and (359 and 25) 10^-4 cm^-1 for b-Pheo, both in DMF. Decay rate constants of the three spin levels of T¹ of b-Pheo ( K _x= 1200 50 s^-1, k _y= 440 25 s^-1, k _z= 80 5 s^-1) and relative steady-state populations (N_x= 28 2%, N_y= 47 2%, N_z= 26 2%) determined from FF curves predict a fluorescence decrease at the D–E and D + E FDMR transitions, whereas experimentally a fluorescence increase is observed. The FDMR sign-inversion results from singlet-singlet energy transfer from b-Pheo monomers to their aggregates, followed by fast intersystem crossing to T₁. These results indicate that aggregates are formed by two or more b-Pheo molecules at different positions on the folded polypeptide chain. This situation resembles that in chlorophyll-proteins, containing low-lying traps, resulting from interaction of chromophores with other chromophores and with the protein environment.     

ACTINOMETRY IN MONOCHROMATIC FLASH PHOTOLYSIS: THE EXTINCTION COEFFICIENT OF TRIPLET BENZOPHENONE AND QUANTUM YIELD OF TRIPLET ZINC TETRAPHENYL PORPHYRIN

Abstract— The extinction coefficient ε_T, of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, Δ D ⁰_T, under demonstrably linear conditions where incident excitation energy, E ₀, and ground state absorbance, A ₀, are both extrapolated to zero. The result, 7220 ± 320 M ^-1 cm^-1 at 530 nm, validates and slightly corrects many measurements relative to benzophenone of triplet extinction coefficients made by the energy transfer technique, and of triplet yields obtained by the comparative method.
As E ₀ and A ₀ both decrease, Δ D ⁰_T becomes proportional to their product. In this situation, the ratio R = (1/ A ₀)(dΔ D ⁰_T/d E ₀) = (ε_T - ε_G)φ_T. Measurements of R , referred to benzophenone, give (ε_T - ε_G)φ_T for any substance, without necessity for absolute energy calibration.
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (ε_T - ε_G at 470 nm = 7.3 × 10⁴ M ^-1 cm^-1) give φ_T= 0.83 ± 0.04.     

PHOTOELECTRIC EFFECTS IN BILAYER LIPID MEMBRANE CONTAINING METALLO-PORPHYRINS and DYES

The bilayer lipid membrane (BLM) system containing metallo-porphyrins (M-TPP) and dyes as photosensitizers and electron mediators was studied. Cyclic voltammetry was used to determine photoconductivity and photo-emf of the system. The largest photoconductivity was observed for the Mg-TPP containing BLM with methyl viologen (MV²⁺) and iodine (I₂) present in the aqueous solution. Photoactive dyes, due to their redox ability caused photovoltage up to 30 mV to develop, but no conductance change was observed under illumination in absence of Mg-TPP. The relevance of cyclic voltammetry to the photoconductance and the photo-emf observed in the BLM is discussed.     

POTENTIAL PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY—II. PHOTOPHYSICAL PROPERTIES OF [26] PORPHYRIN

Abstract— –Photophysical properties of [26] porphyrin (26 P) were investigated in chloroform. The quantum yields of fluorescence, of S₁→ T₁ intersystem crossing and singlet oxygen formation were measured. The purity, stability, the strong absorption in the red (δ_max= 783 nm; ε_max= 28 000 M ¹ cm^-1) and the ability of singlet oxygen formation recommend 26 P as potential photosensitizer for tumor therapy.     

CdS/CdSe/TiO2多级空心微球光阳极中量子点覆盖度的提高

TiO₂多级空心微球(THHSs)具有高的比表面积、强的光散射效应以及良好的电子传输性质,以此作为光阳极材料,可以显著提升CdS/CdSe敏化太阳能电池(QDSSCs)的性能。但基于化学浴沉积方法获得的这一类电池中量子点在光阳极表面的覆盖度通常不高(50%左右),本文发展了一种基于表面选择性吸附原理的多步沉积方法,选取特定分子(正十二硫醇)限制已有量子点的生长,通过二次沉积成功提高了CdS/CdSe在TiO₂多级空壳微球表面的覆盖度。使用此方法最终得到高达85.4%的覆盖度。结果表明,量子点覆盖度的增加有效提高了电池对太阳光的利用率,使得光电流获得了明显的增加。同时,二氧化钛空白表面积的减小还可以抑制电子和空穴的复合。优化后的电池光电流密度为15.69 mA·cm^-2,填充因子为0.583,电压为0.605 V,最高光电转换效率为5.30%。     

A HIGHLY REACTIVE HETEROATOM ANALOG OF RETINAL AND ITS INTERACTION WITH BACTERIORHODOPSIN

Abstract— C₁₈ formate ester (5) [2-(6-methyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3E,5E,7E-octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (t_l/2= 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm^-1) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C₁₈ alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester-treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV-visible absorption, suggesting that a covalent bond between the C₁₈ moiety and a nucleophilic group of the protein has probably formed.     

CHEMICAL FILTERS FOR NARROW BAND U.V. IRRADIATION BETWEEN 235 AND 300 nm

Abstract— Six chemical filters are described. Bands of 10–20 nm half width are isolated at the following wavelengths: 235–240–252–260–277–294 nm. The filters transmit at the center of their band pass between 1.5 and 30 per cent of the incident radiation. Average photon fluence rates of 15–150 ergs mm^-2 sec^-1 (0.3 × 10^-3 to 3.5 × 10^-3μE cm^-2 sec^-1) are obtained with a 500 W high pressure mercury arc focussed on a 10 cm^-2 area. Under these conditions, the flux transmitted in the near i.r., visible and near u.v. does not exceed 1 per cent of the total flux transmitted. The flux transmitted outside a 40 nm band centered at the maximum does not exceed 1 per cent of the total transmitted flux for four of the filters, this flux goes up to 4 per cent of the total for the 294 nm filter and to 10 per cent for the 235 nm filter.     

PROPERTIES OF THE CHLOROPLAST FILM ELECTRODE IMMOBILIZED ON AN SnO2-COATED GLASS PLATE

Abstract— Type C chloroplasts were deposited on the surface of an SnO₂ optically transparent electrode glass plate with polyvinyl alcohol plus bovine serum albumin as immobilizing supports. This electrode, on illumination of 250 J/m² in an electrolyte solution, generated anodic photo current more than 150 nA per 10 μg chlorophyll/cm² of the SnO₂ glass plate at a potentiostatic condition of + 0.5 V against a saturated calomel electrode, and gave rise to an open circuit potential up to 300 mV. The photocurrent output was enhanced as high as 60-fold under the short circuit condition by the addition of an artificial electron carrier, l-methoxy-5-methylphenazinium methyl sulfate, to the electrolyte solution. With the electrode poised at +0.5 V against a saturated calomel electrode, the enhancement effect was exhibited as high as 13-fold in the presence of 2,6-dichlorophenol indophenol. A photocurrent spectrum coincides well with an absorption spectrum of the chloroplast film electrode. Effects of heat-treatment, photosynthetic inhibitors, and electrolyte's pH on the magnitude of the photocurrent were studied in detail. Water molecule, a primary electron donor in the chloroplast photosystems, contributes to the large majority of photocurrent generation. A minor output was observed with the electrode coated with completely inactivated chloroplasts, probably due to the chlorophyll photosensitization.     

RESONANCE RAMAN SPECTRA OF THE II-CATION RADICALS OF COPPER, COBALT, AND NICKEL METHYLOCTAETHYLCHLORINS: VIBRATIONAL CHARACTERISTICS OF CHLOROPHYLL MODELS

Abstract— By using excitation at 363.8 nm, resonance Raman (RR) spectra were obtained for Cu(II), Co(II), and Ni(II) complexes of methyloctaethylchlorin (MeOEC) and their ir-cation radicals. Additionally, the Raman spectra of the Cu(II) derivatives of (rarcs-octaethylchlorin (r-OEC) were included for comparison. The alkyl-substituted CuMeOEC exhibits a Raman spectrum that is nearly identical to that of the simpler (-CuOEC in both the neutral and oxidized states. Unlike the latter species, the cation radical of CuMeOEC is immune to oxidative dehydrogenation to porphyrin, and this has facilitated vibrational characterization of the ring-oxidized species. This study aims to compare the vibrational characteristics in the 1450 to 1700 cm^-t region of the metallochlorin ir-cation radicals to those of the corresponding oxidized metalloporphyrins. We focus on two modes in the1500–1520 cm^-1 and1620–1650 cm^-1 region that are analogous to the v₃ and v₁₀ vibrations, respectively, in the metalloporphyrin analogs. These vibrational modes are clearly defined in all species and exhibit a strong core-size dependency in the porphyrin complexes. The core-size study as well as the frequency changes upon oxidation support the conclusion that the v₃-like vibration in the chlorin species features substantial C_bC_b in addition to C_aC_m stretching character. The v,₀-like mode of the chlorin macrocycle, on the other hand, displays characteristics that closely resembles that of the porphyrin analog; consequently, these vibrations are of predominantly C_aC_m stretching character in both cases.     

SOLVENT EFFECTS ON TRIPLET-STATE BACTERIOCHLOROPHYLL a AS DETECTED BY TRANSIENT RAMAN SPECTROSCOPY AND THE ENVIRONMENT OF BACTERIOCHLOROPHYLL a IN THE LIGHT-HARVESTING COMPLEX OF Rhodobacter sphaeroides R26

The frequency of BChl that was bound to the light-harvesting complex (LHC) of Rhodobacter sphaeroides R26 was found to be 1598 cm^-1, a result which suggests that a pair of BChl molecules form a dimer in the LHC in the T₁ state.