[Study of primary photochemical interactions of chlorophyll pigments with electron acceptors and donors by use of impulse spectroscopy].
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Chemical Phenomena↗
Biomedical subjects
V B Evstigneev
Publications and source records attributed to V B Evstigneev.
On evolution of the photosynthetic pigments.
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Bacteria↗
[Resolution of the structure of the absorption spectrum of blue-green algae by a method of measuring the 2d derivative at -196 degrees C].
By measuring the 2nd derivative at -196 degrees C the thin structure of the absorption spectrum of intact cells, isolated in phycobilisomes and pure pigments of blue-green algae Anabaena variabilis and Aphanizomanon flos-aquae is shown. 8 absorption bands in the region 669--710 nm pertaining to chlorophyll a in different aggregation region were found. Almost the same number of bands were found in the region 550--660 nm. The latter were conditioned by the absorption of allophycocyanin, phycocyanin, and probably by phycoerythrin present in the form of different associates.
Cyanobacteria↗
[Impulse photoconductivity of solutions of chlorophyll and its analogs. II. Effect of medium polarity on the yield of ion-radicals during the photoxidation of chlorophyll a ].
The effect of the dielectric constant epsilon of the solvent on the yield delta n of ion-radicals during photooxidation of chlorophy-l a with n-benzoquinone was studied by the method of impulse photoconductivity. It was shown that in the studied range of dielectric constant valve (epsilon congruent to 5-25) delta n monotonously increased with an increase of epsilon the relationship delta n (epsilon) being of clearly pronounced S-like character with a bend in the region of epsilon congruent to 10. A half-quantitative explanation of the data obtained is presented.
1-Propanol↗
[Impulse photoconductivity of solutions of ohlorophyll and its analogs. III. Photoconductivity of hexanol solutions of chlorophyll a in the presence of n-benzoquinone. Kinetic and temperature measurements].
It is shown that an increase deltasigma of electroconductivity of chlorophyll "a" (Chlalpha) solution in hexanole in the presence of n-benzoquinone (Q) under impulse illumination of solution is proportional to flash intensity: deltasigma=1(0,99+/-0,07). Dependence deltasigma on solution temperature is of an exponential character with the activation energy Esigma=0,30+/-0,01 ev. In the temperature range studied (248--298 degrees K) the ratio between the recombination velocity constant and the mobility of ion-radicals Chlalpha+ and Q-(Kp/mu) is shown to be equal (8+/-1)X 10(-8) cm-v. The activation energy for the dissociation of coulomb pair (Chlalpha+Q-) into free ion-radicals Epiapproximately0,1 ev is evaluated. The value of total mobility of negative and positive ion-radicals is calculated from the date obtained and literature ones: mu=(1,0+/-0,2)X10(-5) cm2/v-sec.
Chlorophyll↗
[Photopotential during the photochemical reaction of chlorophyll with duroquinone].
Under the illumination of ethanol solutions of chlorophyll "alpha" and "beta" in the presence of duroquinone positive photopotential (PP) appears, the sign of which is not changed with an increase of pH. However, if duroquinone is used, which had been illuminated with white light in the absence of air, in ethanol, which results in an increase of concentration of its reduced forms, at neutral weakly alkaline pH the PP sign gets negative. This fact supports the assumption that the change of PP sign at the change of pH when parabenzoquinone is used as an oxidizer results from the change of the direction of electron transfer during photoreaction. During photoreaction of pheophytin incapable of photooxidation with duroquinone and disposed to photoreduction, PP at all pH is negative.
Chlorophyll↗
[Effect of the dielectric constant of the medium on the photooxidation of chlorophyll a by parabenzoquinone].
Spectrophotometric study was carried out of the effect of medium polarity on the parabenzoquinone photooxidation of chlorophyll "a" at lower temperature using as solvents toluene and CCl4 containing different quantities of polaric solvents, methanole, ethanole, amilic alkohol, acetone. It is shown that the photoreaction with the formation of primary photooxidized form of the pigment starts only if some amount of the polar component is in the medium. The data are in favour of the suggestion that chlorophyll and quinone in non-polar medium form an reaction complex which disintegrates under the given conditions at a definite value of medium polarity.
Acetone↗
[Photophosphorylation sensitized by chlorophyll in the adsorbed state].
Products of phosphate oxidation in a weak alkaline medium in the electrolysis and in the reaction, photosensitized by chlorophyll, are studied. It is shown that besides perphosphates, pyrophosphate can be formed under electrochemical phosphate oxidation. Phosphate was used as an electron donor and the air oxygen was an electron acceptor in the red-ox reaction, photosensitized by chlorophyll. The reaction was accompanied by the decrease of inorganic phosphate content in the reaction medium and by the phosphorylation of ADP to ATP. The mechanism of photophosphorylation is discussed on the basis of the data obtained.
Binding Sites↗
Phycobilisomes from the blue-green algae Aphanizomenon flos-aquae and Anabaena variabilis.
Phycobilisomes (PBS) were isolated from Aphanizomenon flos-aquae and Anabaena variabilis. The absorption spectra and second derivative of the absorption spectra of isolated PBS indicate the presence of phycoerythrocyanin, and allophycocyanin. The fluorescence spectra of PBS were measured at room temperature and -196 degrees C. Undamaged PBS have the principal fluorescence maximum in the region of 660 nm at room temperature and in the region of 685-690 nm at -196 degrees. When the PBS were heated from ) to 60 degrees the fluorescence at 685-690 nm disappeared and it increased in the region of 650-660 nm. This is apparently due to disruption of the structure of PBS, which results in a disturbance in the migration of energy along the chain phycoerythrocyanin leads to phycocyanin leads to allophycocyanin.
Cell Fractionation↗
[Ferredoxin reduction by polarographic methods].
The reduction of iron-sulphur protein of the higher plant ferrodoxin has been studied by polarographical methods. Ferredoxin initiates a reversible wave with E1/2=--0,61 v (N. C. E.) at pH 7. Protein absorption greatly influences the electrochemical reduction. The protons have been shown to take part in the electrode reaction. The potentiometrically obtained data about the difference between E1/2 and E0=--0.70 v and its causative factors are discussed. As a result of the experiments with modification of ferredoxin active centre it has been concluded that the active centre participates in the polarographical reduction.
Ferredoxins↗
[Mechanism of photochemical oxidation of bacterioviridin].
The mechanism of bacterioviridin photochemical oxidation has been studied by the methods of ESR, flash-photolysis and low-temperature spectrophotometry. ESR spectrum of pigment cation-radical, a singlet line with H=11 G, g = 2.0027, has been recorded. The bands with maxima at 370, 470, 525, 590, 840 nm correspond to bacterioviridin cation -- radical in the absorption spectra. When -- benzoquinone is used as an electron acceptor with excitation light 640 nm the product of bacterioviridin irreversible oxidation is formed with the absorption band maximum 760 nm and absorption between 350 and 370 nm. It is suggested that this product is of double-oxidized non-radical nature and the mechanism of its formation through oxidation of the pigment cation-radical is discussed. The regeneration reaction of double-oxidized bacterioviridin up to cation-radical form in the presence of triphenylamine as a reducing agent has been carried out. The rate constants of cation-radical decay in the dark and desactivation of triplet state have the following values: K1=(1,64+/-0,15)-10(3) sec-1, K2=(13+/-2,0)-10(3) sec-1 correspondingly. The activation energy of the radical decay in the dark is Eact =(13,2-0,5) kcal/mole.
Bacteriochlorophylls↗
[Photochemical generation of the cation-radical of bacteriochlorophyll b and the anion-radical of bacteriochlorophyll b and bacteriopheophytin b, components of the photosynthesizing bacteria Rhodopseudomonas viridis].
The mechanism of photochemical redox reaction of bacteriochlorophyll b, bacteriopheophitin b was studied. The oxidation of bacteriochlorophyll b was carried out in ethanole by means of p-benzoquinone. In ESR spectra the singlet line with delta H = 8.4 gs and g = 2.0025 corresponded to cation-radical. The changes within the region of 400-500 nm, 500-600 nm and the band with the maximum at 685 nm corresponded to cation-radical in the absorption spectra. Photoreduction of bacteriochlorophyll b and bacteriopheophitin b was carried out in triet containing phenilhydrosin. Anion-radicals of bacteriochlorophyll b and bacteriopheophitin b observed in the ESR spectra had singlet form with weak and superthin structure and correspondently with delta H = 10 gs, delta H = 12 gs. The spectrophotometric characteristics of the above pigments were obtained.
Bacteriochlorophylls↗
[Role of phycobilin pigments in photosynthesis].
Experimental data on possible role of phicobilliprotein (PhBP) in photosynthesis are analysed. It is concluded that the widely spread notion about PhBP only as the light-gathering pigments which transfer the energy to chlorophyll, turned to be insufficiently substantiated experimentally until recently. At the same time the discovered ability of PhBP for reversible redox transformations together with the new data on the nature of fluorescence of blue-green algae and PhBP localization in the cell allowed a suggestion that PhBP can independently of chlorophyll or together with it directly participate in photochemical reactions of photosynthesis. A suggestion is advanced concerning possible existence of the reaction centres of PhBP in phicobillisomes.
Hydrogen-Ion Concentration↗
[Yield of pigment cation-radicals in the reaction of quinone photooxidation of chlorophyll].
Photoinduced transfer of electrons in alkohol solutions of chlorophyll and its deuterated analog, deuterochlorophyll containing the quinoses: p-benzoquinone, chloranyl, duroquinone, 1,4-naftoquinone and ubiquinone (coenzyme Q6) is studied. It is shown that pigment cation-radical and quinone anion-radical are the primary products of photoreaction. A relationship between stationary concentrations of deuterochlorophyll and p-benzoquinone radicals and quinone concentration in solution is obtained. The reaction mechanism and causes of other authors' (G. Tollin et al.) failure in finding pigment cation-radicals which are formed in the reaction of the latter with quinoses are discussed. It is shown that optimal conditions for accumulating photoinduced cation-radicals of the pigment in pigment solutions of chlorophyll with quinones are lowered temperature, high viscosity of the solvent, low pH of the solution, careful purification of the quinone from hydroquinone admixture.
Chemical Phenomena↗
[Spectral-kinetic characteristics of the cation-radical of pheophytin a].
The photochemical generation of pheophytin a cation-radical in acidulated ethanol and aceto nitril has been studied by the method of flash-photolysis. The bands with maxima at 450, 580 and 800 nm correspond to pheophytin a cation-radical in the differential absorption spectra. The efficient rate constants of pheophytin a triplet state desactivation in ethanol, acetonitril, aceton have the following values: 1.5.10(4), 9.10(3), 8.7.10(3) sec(-1) correspondingly. The rate constant of electron transfer from pheophytin a to p-benzoqui-none in ethanol solutions is 7.8.10(9) l/m.sec. The recombination constants of pheophytin a cation-radical with Q-in acetonitril, and with quinone neutral (QH) in acidulated ethanol have the following values: 5.10(9) and 2.10(9) l/m.sec correspondingly.
Chlorophyll↗
[Comparative study of the photopotential and EPR signal arising after photooxidation of metal substituted pheophytins].
Ethanolic solutions of Zn-, Cd-Phe a and b and Chl a and b with p-benzoquinone as electron acceptor have been studied at pH 4. In all systems positive photopotentials and singlet ESR lines of the pigment cation radicals are observed. A conclusion is made that the photopotential is only partly attributable to an electrode reaction of the cation radicals, to a greater extent arising due to unknown, non-radical particles.
Chlorophyll↗
The photosensitizing action of phycobiliproteins in the adsorbed state.
In connection with the elucidation of the possibility of photochemical participation of phycobiliproteins in the primary processes of photosynthesis, the ability of a mixture of phycocyanin + allophycocyanin (PC + APC) for photosensitization of redox reactions in the adsorbed state was investigated. It was shown that adsorbates of PC + APC on Sephadexes G-200 and G-25, diethylaminoethylcellulose, carboxyethylcellulose, Bacto-agar, Lifogel, polyethylene glycol, Dowex 50Wx2, and aluminum oxide are capable of sensitizing the photoreduction of methyl red by ascorbid acid. In this case the effectiveness of the sensitizing action depends on the concentration of the adsorbate, the pigment concentration on the carrier, the pH of the medium, and the nature of the solvent. It was shown that in the case of binding to a carrier, the sensitizing ability of PC + APC increases in comparison with that for pigments in the dissolved state. It is suggested that this is promoted by an increase in the concentration and a mutual approach of the reagents after adsorption, and the possible formation of complexes of some or all the participants of the reaction on the surface of the adsorbent.
Hydrogen-Ion Concentration↗
[Photochemical reaction of chlorophyll a and pheophytin a with low concentrations of hydroquinone].
It has been shown that when illuminating chlorophyll a solution (approximately 10(-5) M) in ethanol containing small concentrations of hydroquinone at pH higher than 7, a markable negative photopotential (-PhP) is initiated. Similar picture is also observed both in the presence of 2 . 10(-5) M parabenzoquinone and when using pheophytin a instead of chlorophyll. The data obtained are in favour of the idea that when illuminating the solutions of these pigments in ethanol containing pure p-benzoquinone at pH higher than the definite value, PhP initiation is conditioned by photochemical reaction of pigments with equilibrium amounts of hydroquinones or semiquinone always present in quinone solutions.
Chemical Phenomena↗