COMPUTER SIMULATION OF EXCITON JUMPING STATISTICS AND ENERGY FLOW IN C-PHYCOCYANIN OF ALGAE Agmenellum quadruplicatum IN THE PRESENCE OF TRAPS

Abstract—Energy migration has been studied in C-phycocyanin (C-PC) rods with traps located in the terminal trimer disc, using the Monte Carlo method and the system of differential equations. It has been found that jump time statistics can be described by the function F = C(t/0>)exp(-t/ < t_o>), where C is the constant, t and < t₀ > are, respectively, the exciton jump time and its averaged value for chromophores of the corresponding spectral types (α 84 , β84 or β155). The values < t₀ > were calculated for the cases of C-PC monomers, trimers and higher associates.
The C-PC model, which consists of three hexamers with traps located in the β84 chromophores of the peripheral trimer, was examined. It was found that the total efficiency of excitation capturing, ø_tr, exceeds 90%, provided "local" quantum yield of energy trapping ø₀ > 10%. The ø₀ value influences both the excitation lifetime (τ) and the mean number of excitation jumps (N_iump) before its conversion. For the ø₀ = 100% and 10%, the corresponding lifetimes and numbers of jumps were calculated to be τ= 75 and 155 ps and N_jump= 105 and 222 jumps, respectively.
The dynamics of excitation redistribution along the C-PC rods and the fluorescence kinetics for various ø₀ values were calculated for C-PC chromophores excited by a +, and the correlation between these processes and ø ₀ , was disclosed. The transient processes of excitation redistribution were shown to proceed within a time period t < 30 ps.     

ENERGY TRANSFER AMONG THE CHROMOPHORES OF C-PHYCOCYANIN FROM Anabaena variabilis USING STEADY STATE AND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY

Abstract We have investigated the model of energy transfer between sensitizing (s) and fluorescing (f) chromophores for the αβ monomer and for the separated α and β subunits of C-phycocyanin from Anabaena variabilis using fluorescence emission spectroscopy, fluorescence excitation polarization, and picosecond-resolved fluorescence decay kinetics. The fluorescence emission maximum occurs at 640 nm for all samples. The fluorescence excitation polarization is constant ( P = 0.40) across the absorption hand for the α subunit, but it increases across the absorption band towards longer wavelength for the β subunit and the αβ monomer. The fluorescence decay kinetics exhibit two exponential lifetimes of 1.3-1.5 ns and 340-500 ps for the αβ monomer and for the α and β subunit preparations.
We attribute the change in polarization across the absorption band to energy transfer among the three chromophores in the αβ monomer and among the two chromophores in the separated β subunit. The constant, relatively high polarization in the separated a subunit, having only one chromophore, is consistent with the absence of both energy transfer and chromophore rotation. The concentration of the α subunit did not affect the decay kinetics, suggesting that the short lifetime component does not arise from aggregation of the α subunits. The biexponential decay kinetics of the α subunit cannot be explained using the sensitizing-fluorescing model. The possibility of conformational interactions is under investigation.     

ON THE LUMINESCENCE OF α-DIKETONES OF THE STEROID SERIES

Abstract—The absorption and luminescent properties of two steroids [16-ketoestrone (I), 5α-androstane-3β-ol-16,17-dione (II)] are compared. The behaviour of these compounds which differ only in their A-ring is significantly different with regard to solvent dependence. The transfer of excitation energy in compound (I) from the phenolic to the diketonic chromophore is studied and compared with data from analogous estrogens. The results obtained in this study indicate a significant long range (presumably conformational) influence of the steroid A and D rings on each other.     

EXCITATION OF CHLOROPHYLL DURING THE PEROXIDASE-CATALYZED OXIDATION OF ETHYL α-FORMYLPHENYLACETATE

Abstract When micelle-solubilyzed chlorophyll is present during the horseradish peroxidase catalyzed aerobic oxidation of ethyl α-formylphenylacetate its fluorescence is observed. The excitation of chlorophyll may occur via energy transfer from the enzyme-generated triplet ethyl benzoylformate. These results imply that excited states may be generated in the roots of Datura innoxia .     

THE PHOTOPHYSICAL PROPERTIES OF SOME C15 LUPINE ALKALOIDS:

Abstract Sparteine, the tetracyclic saturated amine alkaloid, is highly fluorescent in n-hexane solution (Φ_f= 0.64; ζ= 63 ns) and has a large Stokes shift [λ_max (abs) = 203 nm; λ_max (fluor) = 325 nm]. Its isomer, α-isosparteine, has similar properties: Φ_f= 0.55; ζ_f= 50 ns; λ_max (fluor) = 338 nm. Oxidized derivatives, such as lupanine, thermopsine, and α-diplospartyrine, are weakly fluorescent. Based on a comparison with spectroscopic and photophysical properties of the monoamine, quinolizidine, it is concluded that the excitation energy is delocalized over the two N-atoms in starteine and a-isosparteine. The self quenching rate constant for sparteine, ca. 1 times 10⁷M^-1 s^-1, is about 100 times smaller than that for quinolizidine, consistent with excited state derealization. The significant fluorescence quenching in lupanine is rationalized by the fact that N-methyl-2-piperidone mfe/molecularly quenches the fluorescence of quinolizidine at nearly the diffusion controlled rate in -hexane. Comparisons are made with the fluorescence properties of other diamines such as N, N'-dimethylbispidine and N, N'-disubstituted piperazines.     

THE OXIDATION OF CHOLESTEROL BY HYDROXYL RADICAL

Abstract— The oxidation of chblesterol by hydroxyl radical generated by ⁶⁰Co y-radiolysis of aqueous cholesterol dispersions or of dispersions saturated with N₂O ave in low yields the products 38-hydroxy-cholest-5-en-7-one. the epimeric cholest-5-ene-3β,7-diols, 5,6α-epoxy-5α-cholestan-3β-ol, 5.6β-epoxy-5β-cholestan-3,β-ol, and 5α-cholestane-38,5,6β-triol. Sterol hydroperoxides were not detected except in the radiolysis of dispersions saturated with oxygen.     

ON THE DISTRIBUTION OF EXCITATION ENERGY TO TWO PHOTOREACTIONS OF PHOTOSYNTHESIS

Abstract— From kinetic analysis of the Z-scheme we have derived expressions for fractions of open reaction centers and throughput quantum yield. The fraction of absorbed quanta available to photoreaction II has been treated by the wavelength dependent function, α. However, for purposes of analysis in terms of throughput electron flow it is necessary to introduce a related function, α', for actual processing of excitations by photoreaction II; α' differs from α if the individual quantum yields of the two photoreactions are not equal. 'Included in our findings are the following. As a close approximation quantum yield is maximum at α'= 0.5 and a symmetrical function of α' around the line α' =0.5. As previously noted, lowering of the apparent equilibrium constant between the photoreactions flattens dependence of quantum yield on α' near α' = 0.5 but also lowers the attainable quantum yield. For any given equilibrium constant the effective fractions of open reaction centers are equal at α' = 0.5 and mirror images of each other around the line α' = 0.5. Slow changes in quantum yield following changes in wavelength (the State 1-State 2 phenomenon) are explainable in terms of changes in α' which also have the effect of flattening dependence of quantum yield on wavelength. We have used these changes to estimate the neutral wavelength for α' = 0.5 as 681–682 nm in Chlorella .     

THERMODYNAMICS OF THE PRIMARY REACTIONS OF PHOTOSYNTHESIS

Abstract. It appears to be widely believed that fundamental thermodynamic limitations prevent the products of the primary electron transfer reactions of photosynthesis from exceeding the reactants in energy by more than about 0.7 hv ₀ where v ₀ is the frequency of the lowest energy absorption band of the reaction center. Specifically, in photosynthetic bacteria, where hv ₀ 1.34 eV, it is often said that the midpoint redox potentials of the primary electron donor and acceptor cannot differ by more than about 0.9 eV. This is incorrect. A simple expression is developed for δμ, the increase in the partial molecular free energy of an absorber under illumination. The magnitude of δμ gives one no information about the nature of the photochemical reactions that can result from excitation of the absorber. It puts no limits on the midpoint redox potentials of the reactants. However, knowing δμ does allow one to calculate the concentrations of the products if the system comes to equilibrium during illumination.     

ANTIVIRAL ACTIVITY OF THE PHOTOACTIVE THIOPHENE α-TERTHIENYL

The naturally occurring thiophene, α-terthienyl, was investigated for phototoxicity against several viruses and a line of mouse cells. The compound was extremely phototoxic to the two-membrane-containing animal viruses, murine cytomegalovirus (MCMV) and Sindbis virus (SV). Antiviral activity was detected at 10⁵μg/m in the presence of UVA. However, no effect was seen in the absence of UV-A, even at 0.1 μg/m of αT. Mouse cells were much more resistant to αT, as was the bacterial virus T4, which does not contain a membrane. Murine CMV, which had been inactivated by αT and UVA, penetrated mouse cells efficiently; but the viral DNA could not replicate, and late viral proteins were not made. Thus viral gene expression was inhibited in the photoinactivated virus. In order to account for all these data we suggest that αT may interact with viral proteins in addition to membrane lipids.     

ON THE QUENCHING OF SINGLET OXYGEN BY α-TOCOPHEROL

Abstract —D-α-tocopherol was found to be an effective quencher of ¹O₂ molecules ( k = 2.5 times 10⁸→mol^-1 s^-1 in pyridine) by measuring its effect on the autosensitized photooxidation of rubrene. The quenching process was shown to be almost entirely 'physical', that is, α-tocopherol deactivated about 120 ¹O₂ molecules before being destroyed. The results suggest that this process may be a mechanism for the protective effect of α - tocopherol in photodynamic action.     

QUANTIFICATION OF THE SOLVENT EFFECTS ON THE TRIPLET QUANTUM YIELD OF PSORALEN BY THE "LINEAR SOLVATION ENERGY RELATIONSHIP"

Triplet formation quantum yields (Φ_τ) of psoralen in a set of 17 pure solvents ranging from n -hexane to water and in dioxane: water mixtures were obtained by nanosecond laser flash photolysis. The triplet yield increases with solvent polarity. The extremum values are 0.009 and 0.545 in n -hexane and water, respectively. Good correlations of the experimental Φ_τ values with empirical "polarity" scales (Dimroth/Reichardt's E_T [30], Kamlet/Taft's solva-tochromic parameters β, and α, and Swains acity/basity A_S/B_S) were obtained: Ln(φ_T^-1 - 1) = 8.86 - 0.143E_T(30) Ln(φ_T^-1 - 1) = 4.40 - 2.34_τ - 1.70α Ln(φ_T^-1 - 1) = 4.65 - 3.72A_s - 1.12B_s The results are discussed in terms of the sensitivity of psoralen triplet quantum yield to solvent polarity and hydrogen-bonding abilities.     

INHIBITION OF THE ATPase ACTIVITY OF P-GLYCOPROTEIN BY PORPHYRIN PHOTOSENSITIZATION OF MULTIDRUG-RESISTANT CELLS in vitro

Abstract— The effectiveness of photodynamic therapy against P-glycoprotein ATPase activity in multidrug-resistant cells was studied. Chinese hamster ovary AUXB1 (drug-sensitive) and CR1R12 (multidrug-resistant) cell lines were compared with respect to uptake of ¹⁴C-polyhematoporphyrin and porphyrin photosensitization. Phototoxicity of Photofrin® was similar in both cell lines, and no major differences in uptake or efflux of ¹⁴C-polyhematoporphyrin were observed. Porphyrin photosensitization in vitro of CR1R12 cells or isolated plasma membranes from these cells caused inhibition of P-glycoprotein ATPase activity. Application of porphyrin photosensitization at a sublethal level to CR1R12 cells resulted in a small but significant increase in adriamycin-induced cytotoxicity. The hydrophobic "picket-fence" porphyrin, meso -tetrakis-( o -propionamidophenyl)porphyrin,α,α,α,β-isomer, was more inhibitory toward P-glycoprotein ATPase activity than the two less hydrophobic porphyrins tetraphenylporphine tetrasulfonate and Photofrin®.     

THE ANTI-HIV ACTIVITIES OF PHOTOACTIVE TERTHIOPHENES

Abstract— Various synthetic analogues of the naturally occurring terthiophene, α-terthienyl (αT), were evaluated for anti-human immunodeficiency virus (HIV) activity. The compounds were incubated individually with a known amount of the virus, with or without UVA radiation (long-wavelength ultraviolet) and residual virus was monitored for its ability to produce cytopathic effects in cell culture and the production of virus-specific protein (p24). The basic terthiophene structure was essential for good anti-HIV activity, although various side chains, such as alcohols, bromo, methyl, thiomethyl and trimethylsilyl groups, permitted retention of maximum activity. Under optimum conditions, as little as 12 ng/mL of these compounds ( i.e approximately 3 × 10⁻⁸ M ) could inactivate 10³ infectious virions. None of the compounds however were more active than αT itself. In all cases, UVA radiation was essential. Several side chains decreased the antiviral efficacy, and some side chains abrogated the activity.     

FLUORESCENCE OF THYMINE IN AQUEOUS SOLUTION AT 300° K

Abstract— –Fluorescence of thymine in neutral aqueous solution at room temperature has been detected using the multiscaling operation of a multichannel analyzer. The emission maximum (2.96 μm^-1) and 0-0 transition energy (3.37-3.45 μm^-1) are close to those determined at liquid nitrogen temperature in mixed solvents. The quantum efficiency of fluorescence excited at 3.77 μm^-1 is calculated to be 1.04 × 10^-4.
The corrected relative excitation spectrum shows significant differences from the absorption spectrum when both are determined under identical conditions of concentration and spectral bandwidth on the same instrument. The quantum yield of fluorescence decreases about 2-fold as the energy of excitation is increased beyond the 0-0' transition and follows the relation 1/φ°α E _excit..
This behavior is discussed in terms of (a) n π* and ππ* states, (b) emission from a minor tautomer and (c) kinetics of competing deactivation processes.     

CHEMILUMINESCENCE IN THE PROCESS OF OXIDATIVE RING-OPENING OF PURPUROGALLINQUINONES

Abstract— The oxidation of purpurogalline (PPG) by alkaline solution of H₂O₂ pH 9–11 at 298°K is accompanied by chemiluminescence (CL) in the spectral range 400–600 nm with the maximum at 500 nm and quantum yield about 10^-6. The optimal concentrations of reactants with respect to maximal intensity are: 2 × 10^-4 M PPG, 10^-2 M NaOH, 1 M H₂O₂. Activation energy calculated from the maximum intensity of CL is 8.1×0.4 kcal/mole. Light emission occurs only when OH-groups of the phenolic ring of PPG undergo oxidation and the blue anion of o -PPG-quinone is formed. The rate that determines step in the reaction associated with luminescence is the nucleophilic attack of OOH^- ion on the blue anion of o -PPG-quinone. In this exergonic step (-ΔH = 63 to 230kcal/mole) the o - and/or p -quinone ring is opened and carbonyl derivatives of α-tropolone are produced. They display fluorescence in the region 400–600 nm. The fluorescence spectrum of the reaction mixture after oxidation of PPG is very close to that of CL. It is likely that carbonyl derivatives of α-tropolone are emitters of CL.     

RESOLUTION OF THE FLUORESCENCE EXCITATION SPECTRUM OF INDOLE INTO THE 1La AND 1Lb EXCITATION BANDS*

Abstract— The fluorescence excitation spectrum and the excitation polarization spectrum of indole in propylene glycol were measured at — 58°C, after selecting by optical filters the emission originating from the ¹L_a electronic level. From the analysis of these spectra, the excitation spectrum was resolved into the ¹L_a and ¹L_a excitation bands. A similar resolution of the excitation spectrum of tryptophan is given. This method can also be applied to the resolution of the emission spectrum in cases of dual emission.     

PRODUCTS AND RELATIVE REACTION RATES OF THE OXIDATION OF TOCOPHEROLS WITH SINGLET MOLECULAR OXYGEN

Abstract— The relative reactivity of singlet molecular oxygen, 0₂(¹Δ_g), α-,β-,Γ-and δ with -tocopherol (vitamin E) was investigated using microwave discharge generation as a uniquely clean source of singlet oxygen and using a hydrocarbon solvent to approximate the membrane environment. The relative efficiencies of the tocopherols for O₂(¹Δg) were found to decrease in the order: D-α-tocopherol > D-β-tocopheroI > D–Γ-tocopherol > D-δ-tocopherol. The reaction products in all cases were found to be mixtures of quinone and quinone epoxides apparently resulting from decomposition of the primary product, the hydroperoxydienone.     

STEROL METABOLISM. XLII. ON THE INTERCEPTION OF SINGLET MOLECULAR OXYGEN BY STEROLS

Abstract— The use of cyclic 1,3-dienes and polycyclic aromatic hydrocarbons as xenobiotic substrates for the interception of electronically excited (singlet) molecular oxygen (¹O₂) in biological systems is reviewed and criticized, and the possibility of utilization of reactive endogenous substrates for ¹O₂ interception is considered. The common sterols, cholesterol, 5α-cholest-7-en-3β-ol, and 5α-lanost-8-en-3β-ol each give oxidation products with ¹O₂ different from those with ground-state molecular oxygen that can be distinguished from one another by simple chromatographic means.     

COMPARISON OF THE PHOTOTOXICITY OF α-TERTHIENYL WITH THAT OF A SELENIUM AND OF AN OXYGEN ANALOGUE

Abstract— Two analogues of α-terthienyl, namely 2, 5di(2'-thienyl) selenophene and 2, 5di(2'-thienyl) furan have been prepared and their phototoxicities toward several microorganisms have been compared. Dose response studies with Escherichia coli indicate that α-terthienyl is more active than these analogues. α-Terthienyl was shown to be the most effective of the three compounds in the photoinactivation of yeast alcohol dehydrogenase. Diagnostic tests showed the participation of singlet oxygen in the photosensitization to different extents by these three thiophenes.     

单线态分子氧的产生和体外叶绿素α的结构状态

叶绿素α(Chl α)是光合作用光量子的接受器和光能最初传递体。早期研究表明,在光合器官中,Chlα长波主吸收带位于红区。1969年Krasnovsky指出,Chlα受光照射时有可过氧化还原反应。