Absence Of Electron Acceptors Research Articles

Unleashing hydrogenase activity in carbon monoxide dehydrogenase/acetyl-CoA synthase and pyruvate:ferredoxin oxidoreductase.

These results demonstrate that two well-studied metalloenzymes, carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) and pyruvate:ferredoxin oxidoreductase (PFOR), can reduce protons to H2 and, at much lower rates, oxidize H2 to protons and electrons. To our knowledge, this if the first time that PFOR has been shown to have hydrogenase activity. CODH/ACS and PFOR evolved H2 at maximum rates when CO and pyruvate were the electron donors, respectively, and when electron acceptors are absent; dithionite was a very poor substitute. PFOR, when purified to greater than 99% homogeneity, exhibited a specific activity for pyruvate-dependent H2 production of 135 nmol min-1 mg-1. The H2 evolution activity divided by the H2 uptake activity was 282:1; the highest ratio previously reported (22:1) was with the membrane-bound hydrogenase from Rhodospirillum rubrum [Fox, J.D., Kerby, R. L., Roberts, G. P., & Ludden, P. W. (1996) J. Bacteriol. 178, 1515-1524]. Highly purified samples of CODH/ACS (> 99% homogeneity) exhibited a specific activity of CO-dependent H2 evolution in the absence of electron carrier of 590 nmol min-1 mg-1. Equivalent rates of CO oxidation and H2 production were observed when determined in the absence of electron acceptor. This level of activity can account for the rate of H2 production that has been observed by growing cultures of Clostridium thermoaceticum and could solve the paradox that the highly CO-sensitive hydrogenases from acetogenic bacteria evolve H2 when grown on CO. The ratio of the rates of (H2 evolution):(H2 uptake) for purified CODH/ACS is between 20:1 and 30:1. H2 evolution and uptake by CODH/ACS were strongly inhibited by cyanide (ki = 1 microM), indicating that these reactions are catalyzed by cluster C, the site of CO oxidation. Our results extend earlier findings that the CODHs from Methanosarcina barkeri [Bhatnagar, L., Krzycki, J. A., & Zeikus, J. G. (1987) FEMS Microbiol. Lett. 41, 337-343] and Oligotropha carboxydovorans [Santiago, B., & Meyer, O. (1996) FEMS Microbiol. Lett. 136, 157-162] exhibit hydrogenase activity. Mechanistic implications of hydrogenase activity are discussed. Several physiological roles for proton reduction by CODH/ACS and PFOR are discussed, including the prevention of radical formation from reduced metal clusters when electron carriers (ferredoxin, flavodoxin, etc.) are limiting.

The role of phospholipids in regulating photosynthetic electron transport activities: Treatment of thylakoids with phospholipase C

The involvement of phospholipids in the regulation of photosynthetic electron transport activities was studied by incubating isolated pea thylakoids with phospholipase C to remove the head-group of phospholipid molecules. The treatment was effective in eliminating 40-50% of chloroplast phospholipids and resulted in a drastic decrease of photosynthetic electron transport. Measurements of whole electron transport (H2O→methylviologen) and Photosystem II activity (H2O→p-benzoquinone) demonstrated that the decrease of electron flow was due to the inactivation of Photosystem II centers. The variable part of fluorescence induction measured in the absence of electron acceptor was decreased by the progress of phospholipase C hydrolysis and part of the signal could be restored on addition of 3-(3',4'-dicholorophenyl)-1,1-dimethylurea. The B and Q bands of thermoluminescence corresponding to S2S3QB (-) and S2S3QA (-) charge recombination, respectively, was also decreased with a concomitant increase of the C band, which originated from the tyrosine D(+)QA (-) charge recombination. These results suggest that phospholipid molecules play an important role in maintaining the membrane organization and thus maintaining the electron transport activity of Photosystem II complexes.

The flash photolysis of aqueous solutions of rhodizonic and croconic acids

AbstractThe flash photolysis of aqueous solutions of rhodizonic and croconic acids has been studied in the presence and absence of electron acceptors. No transient absorption which could be identified with an excited state was observed with either anion. The rate of recovery of the ground state in the absence of additives was a first‐order process with both acids and gave rate constants for deactivation of the excited state, kD, of 2.4 × 105 s−1 for rhodizonate and 2.8 × 105 s−1 for croconate. With croconate dianion in the presence of three acceptors, 4‐nitrobenzylbromide, methylviologen, and biacetyl, a transient absorption was detected, with a maximum absorbance at 500 nm, and was tentatively identified with the monoanion radical, formed following electron transfer to the acceptor. From the rate of growth of the transient, rate constants for the rate of electron transfer to the acceptor were measured as follows: 4‐nitrobenzylbromide: 2.8 × 109 M−1 s−1; methyl viologen: 3.7 × 1010 M−1 s−1; and biacetyl: 2.0 × 108 M−1 s−1. The significance of the measurements is discussed in relation to the mechanism proposed for the photochemical reactions of these dianions. © 1994 John Wiley & Sons, Inc.

Photoinhibition affects the non-heme iron center in photosystem II

Effects on the PS II acceptor side caused by exposure to strong white light (180 W/m 2) of PS II membrane fragments (spinach) at pH 6.5 and 0°C were analyzed by measuring low temperature EPR signals and flash-induced transient changes of the flourescence quantum yield. The following results were obtained: (a) the extent of the light induced g = 1.9 EPR signal as a measure of photochemical Fe 2+Q − A formation declines with progressing photoinhibition. The half-life of this effect is independent of the absence or presence of an exogenous electron acceptor during the photoinhibitory treatment; (b) in samples photoinhibited in the absence of an electron acceptor and subsequently incubated with K 3[Fe(CN) 6] in the dark, the extent of the g = 8 EPR signal (reflecting the oxidized Fe 3+ form of the endogenous non-heme iron center) and of the flash-induced change of the flourescence yield (as a measure of fast electron transfer from Q − A to Fe 3+ after the first flash; [see (1992) Photosynth. Res. 31, 113–126] exhibits the same dependence on photoinhibition time as the g = 1.9 EPR signal; (c) in samples photoinhibited in the presence of an exogenous electron acceptor, the signals reflecting Fe 3+-formation and fast electron transfer from Q − A to Fe 3+ decline faster than the g = 1.9 EPR signal. These results provide for the first time direct evidence that the endogenous non-heme iron located between Q A and Q B is susceptible to modifications by light stress. The implications of this finding will be discussed.

The role of free radicals in photosensitized oxidation reactions induced by merocyanine 540

Abstract The formation of the anion radical of merocyanine 540 (MC − ) and its properties in methanol-aqueous media were studied using electron spin resonance (ESR), pulse radiolysis (PR) and laser flash photolysis (LFP). On illumination of MC, in the presence of ascorbate or catechol, characteristic ESR signals were observed due to ascorbyl or o -semiquinone radicals respectively. The durosemiquinone radical was detected in the illuminated samples that contained MC, reduced nicotinamide adenine dinucleotide (NADH) and duroquinone. The nature of the excited state of MC responsible for such electron transfer reactions was determined using LFP experiments. The LFP data indicated rapid quenching of the triplet excited state of MC with concurrent formation of MC − in the presence of ascorbate. In PR experiments, MC − was generated by an efficient interaction of the solvated electron with MC ( k = 6 × 10 9 M −1 s −1 ). It was found that MC − had an absorption maximum at 400 nm with ϵ = 5.9 × 10 4 M −1 cm −1 . In the absence of electron acceptors, MC − decayed probably via disproportionation. In the presence of oxygen or ferric ions (as in the complex with diethylenetriaminepentaacetic acid (DTPA)), the decay of MC − was greatly enhanced indicating efficient interaction between these species ( k = 1.7 × 10 9 M −1 s −1 and k = 6.5 × 10 8 M −1 s −1 for the reaction of MC − with O 2 and DTPA-Fe 111 respectively). Hence photoinduced electron transfer and the formation of MC − which may occur in MC-photosensitized systems could lead to the generation of oxygen radicals. The formation of hydroxyl radicals in such systems was shown indirectly by ESR spin trapping of methanol-derived radicals. It is postulated that the hydroxyl radicals are generated via a Fenton reaction driven by reducing radicals derived from photoinduced electron transfer reactions. An additional mechanism for the photodynamic efficiency of MC is proposed based on electron transfer reactions induced by light.

Phosphorylation of serine residues in endogenous proteins of thylakoids and subthylakoid particles in the dark under nonreducing conditions

Isolated thylakoids, Photosystem I and Photosystem II particles were phosphorylated with [γ- 32P]ATP at high specific radioactivity in the dark under nonreducing conditions and in the light in the absence of electron acceptor. The resulting phosphoproteins were compared by gel electrophoresis and autoradiography. Phosphorylation of thylakoids in the dark and in the light rendered distinct patterns of phosphoproteins. Some of the dark-phosphorylated proteins in thylakoids were diminished or not detected in the light-phosphorylated membranes. Phosphorylation of subthylakoid particles was insensitive to light and most of the phosphoproteins in these membranes were also observed in the dark-phosphorylated thylakoids. Dark phosphorylation rendered mostly phosphoserine in individual proteins of thylakoids, subthylakoid particles and lysine-rich histone phosphorylated by the particles. Conversely, phosphothreonine was prevalent in light-phosphorylated thylakoids. The results are consistent with the presence of a protein serine kinase activity that is distributed homogeneously within the thylakoid regions, is more active in the dark, does not require reducing conditions for activity and phosphorylates a number of endogenous substrates most of which belong to the stroma membranes.

Photochemical alterations of Photosystem II induced by two different photoinhibitory treatments in isolated chloroplasts of pea. A thermoluminescence study

Suspensions of chloroplasts were submitted to photoinhibitory treatments consisting of an illumination given either in the absence of electron acceptor, or in the presence of electron acceptor. Properties of two thermoluminescence bands: (1) the band at 32–35°C due to S 2 3 Q − B recombination and (2) the low-temperature band (near −68°C) induced by an illumination at −80°C, were studied in the two types of photoinhibited material. In both photoinhibitory treatments the 32°C band was reduced in size in photoinhibited chloroplasts in parallel with decrease of rates of O 2 evolution and kept the same shape and position in temperature. These results indicate that the PS II centers remaining active have retained quite normal properties compared to the control. However, in chloroplasts photoinhibited in the absence of acceptor, a high level of luminescence emission was observed after a large number of flashes (more than ten), compared to control chloroplasts. This difference demonstrates an increase in the reduction state of the plastoquinone pool after the photoinhibitory treatment performed when no exogenous acceptor is present. The low-temperature band was charged only by continuous light at −80°C (or in the range −100°C to −60°C) and in the literature it is known as the Z v band. The band was reduced in size in chloroplasts photoinhibited in the presence of an exogenous acceptor in parallel with the decrease of PS II activity. Conversely, in chloroplasts photoinhibited in absence of acceptor a new low-temperature band appeared which could be differentiated from the usual Z v band by its insensitivity to ethanol. This band increased with degree of PS II inhibition. This new ethanol-insensitive low-temperature band is proposed to result from recombinations of a charge pair generated in PS II centers photodamaged at the acceptor side.

Purification of NADH-ferricyanide dehydrogenase and NADH-quinone reductase from Escherichia coli membranes and their roles in the respiratory chain

The respiratory chain-linked NADH-quinone reductase (NQR) and NADH-ferricyanide dehydrogenase (NFD) were extracted from membranes of Escherichia coli by n-dodecyl octaethyleneglycol monoether detergent and purified by DEAE-Sephacel, DEAE-5PW and Bio-Gel HTP column chromatography. The purified NQR contained FAD as a cofactor, catalyzed the reduction of ubiquinone-1 (Q1) and reacted with NADH, but not with deamino-NADH (d-NADH), with an apparent Km of 48 microM. On the other hand, the purified NFD contained FMN as a cofactor, reacted with both NADH and d-NADH, and catalyzed the reduction of ferricyanide but not Q1. NFD showed a high affinity for both NADH and d-NADH with a Km of 7-9 microM. NFD was inactivated, whereas NQR was rather activated, by preincubation with an electron donor in the absence of electron acceptor. These properties were compared with those of activities observed with inverted membrane vesicles with special reference to the generation of inside-positive membrane potential (delta psi). It was found that d-NADH-reactive FMN-containing NFD is a dehydrogenase part of energy-generating NADH-quinone reductase complex. The FAD-containing NQR was very similar to that purified by Jaworowski et al. (Biochemistry (1981) 20, 2041-2047), and reduced Q1 without generating delta psi.

Influence of transport energization on the growth yield of Escherichia coli.

The growth yields of Escherichia coli on glucose, lactose, galactose, maltose, maltotriose, and maltohexaose were estimated under anaerobic conditions in the absence of electron acceptors. The yields on these substrates exhibited significant differences when measured in carbon-limited chemostats at similar growth rates and compared in terms of grams (dry weight) of cells produced per mole of hexose utilized. Maltohexaose was the most efficiently utilized substrate, and galactose was the least efficiently utilized under these conditions. All these sugars were known to be metabolized to glucose 6-phosphate and produced the same pattern of fermentation products. The differences in growth yields were ascribed to differences in energy costs for transport and phosphorylation of these sugars. A formalized treatment of these factors in determining growth yields was established and used to obtain values for the cost of transport and hence the energy-coupling stoichiometries for the transport of substrates via proton symport and binding-protein-dependent mechanisms in vivo. By this approach, the proton-lactose stoichiometry was found to be 1.1 to 1.8 H+ per lactose, equivalent to approximately 0.5 ATP used per lactose transported. The cost of transporting maltose via a binding-protein-dependent mechanism was considerably higher, being over 1 to 1.2 ATP per maltose or maltodextrin transported. The formalized treatment also permitted estimation of the net ATP yield from the metabolism of these sugars; it was calculated that the growth yield data were consistent with the production of 2.8 to 3.2 ATP in the metabolism of glucose 6-phosphate to fermentation products.

Nucleotide sequence of the pyrD gene of Escherichia coli and characterization of the flavoprotein dihydroorotate dehydrogenase.

Dihydroorotate dehydrogenase (EC 1.3.3.1) was purified to near electrophoretic homogeneity from the membranes of a strain of Escherichia coli carrying the pyrD gene on a multicopy plasmid. The preparation had a specific activity of 120 mumol min-1 mg-1 and contained flavin mononucleotide (FMN) in amounts stoichiometric to the dihydroorotate dehydrogenase subunit (Mr = 37000). The flavin group was reduced when dihydroorotate was added in the absence of electron acceptors. The complete sequence of 1357 base pairs of an EcoRI-EcoRI DNA fragment containing the pyrD gene was established. Dihydroorotate dehydrogenase is encoded by a 336-triplets open reading frame. The molecular mass (Mr = 36732), the amino acid composition and the N-terminal sequence of the predicted polypeptide agree well with the data obtained by analysis of the purified protein. A region of the amino acid sequence (residues 292-303, i.e. Ile-Ile-Gly-Val-Gly-Gly-Ile-Asp-Ser-Val-Ile-Ala) shows distinct homology to the cofactor binding site of other flavoproteins. No hydrophobic regions large enough to span the cytoplasmic membrane were observed. By the S1-nuclease technique an mRNA start was mapped 34 +/- 2 nucleotide residues upstream of the beginning of the coding frame of pyrD. The leader region contains no similarity to the attenuators of the pyrB and pyrE genes of E. coli.

Analysis of the Chl- a+II reduction kinetics with nanosecond time resolution in oxygen-evolving Photosystem II particles from Synechococcus at 680 and 824 nm

The kinetics of Chl- a + II (P-680 +) reduction have been measured under repetitive excitation with nanosecond time resolution by monitoring the time-course of the absorption changes at 680 and 824 nm. O 2-evolving Photosystem II particles from Synechococcus sp. have been used because of the following advantages: (i) small ratio of antenna chlorophylls to Chl- a II (approx. 100), (ii) low content of PS I and (iii) reduced light scattering. 1. Identical time-courses of the absorption changes at 680 and 824 nm were found in these PS II particles. 2. For the most part (approx. 70%), Chl- a + II is reduced in the nanosecond time range. The remaining Chl- a + II (approx. 30%) is reduced with half-life times in the microsecond time range. 3. The decay in the nanosecond time range is multiphasic. This multiphasic reduction can be explained quantitatively by a superposition of different reduction kinetics reported for the first single turnover flashes in dark-adapted samples (Brettel, K., Schlodder, E. and Witt, H.T. (1984) in Advances in Photosynthesis Research, Vol. 1 (Sybesma, C., ed.), pp. 295–298, Martinus Nijhoff/Dr. W. Junk Publishers, The Hague). It results a description of the nanosecond decay (approx. 70%) by three exponential phases with t 1 2 ≈ 20 ns (approx. 33%), ≈ 50 ns (approx. 19%) and 300 ns (approx 19%). 4. The nanosecond kinetics are attributed to electrons supplied by the oxygen-evolving complex via a secondary donor, D. For the microsecond kinetics, different suggestions are discussed. 5. The difference spectrum of the absorption changes decaying in the nanosecond time range resembles that attributed to Chl- a + II minus Chl- a II. 6. In the absence of electron acceptors, a fast absorption change transient ( t < 6 ns) is observed, possibly due to a charge separation and recombination between Chl- a II and pheophytin. 7. Additional absorption changes observed at supersaturating flash intensities are described.

Oxygen requirement of photosynthetic CO 2 assimilation

In the absence of electron acceptors and of oxygen a proton gradient was supported across thylakoid membranes of intact spinach chloroplasts by far-red illumination. It was decreased by red light. Inhibition by red light indicates effective control of cyclic electron flow by Photosystem II. Inhibition was released by oxygen which supported a large proton gradient. Oxygen appeared to act as electron acceptor simultaneously preventing over-reduction of electron carriers of the cyclic electron transport pathway. It thus has an important regulatory function in electron transport. Under anaerobic conditions, the inhibition of electron transport caused by red illumination could also be released and a large proton gradient could be established by oxaloacetate, nitrite and 3-phosphoglycerate, but not by bicarbonate. In the absence of oxygen, ATP levels remained low in chloroplasts illuminated with red light even when bicarbonate was present. They increased when electron acceptors were added which could release the over-reduction of the electron transport chain. Inhibition of electron transport in the presence of bicarbonate was relieved and CO 2-fixation was initiated by oxygen concentrations as low as about 10 μM. Once CO 2 fixation was initiated, very low oxygen levels were sufficient to sustain it. The results support the assumption that pseudocyclic electron transport is necessary to poise the electron transport chain so that a proper balance of linear and cyclic electron transport is established to supply ATP for CO 2 reduction.

The indispensability of phospholipid and ubiquinone in mitochondrial electron transfer from succinate to cytochrome c.

The indispensability of phospholipid and ubiquinone (Q) in mitochondrial electron transfer was studied by depleting phospholipid and Q in succinate-cytochrome c reductase and then replenishing the depleted enzyme. More than 90% of phospholipid and Q was removed by repeated ammonium sulfate-cholate fractionation. The depleted succinate-cytochrome c reductase showed no enzymatic activity for succinate leads to c or QH2 leads to c and yet retained most of the succinate leads to Q activity. All enzymatic activity was restored upon the addition of Q and phospholipid. Restoration required the addition of Q prior to the addition of phospholipid. Reversing the addition sequence or addition of a mixture of phospholipid and Q resulted only in a small restoration of activities. The conditions for restoration are given in detail. Removal of phospholipid from succinate-cytochrome c reductase resulted in reduction of cytochrome c1 in the absence of exogenous electron donor. Replenishing the preparation with phospholipid brought about the reoxidation of cytochrome c1 in the absence of electron acceptor or oxygen.

Regulation of photosynthetic electron transport and photophosphorylation in intact chloroplasts and leaves of Spinacia oleracea L.

Oxygen ist reduced by the electron transport chain of chloroplasts during CO2 reduction. The rate of electron flow to oxygen is low. Since antimycin A inhibited CO2-dependent oxygen evolution, it is concluded that cyclic photophosphorylation contributes ATP to photosynthesis in chloroplasts which cannot satisfy the ATP requirement of CO2 reduction by electron flow to NADP and to oxygen. Inhibition of photosynthesis by antimycin A was more significant at high than at low light intensities suggesting that cyclic photophosphorylation contributes to photosynthesis particularly at high intensities. Cyclic electron flow in intact chloroplasts is under the control of electron acceptors. At low light intensities or under far-red illumination it is decreased by substrates which accept electrons from photosystem I such as oxaloacetate, nitrite or oxygen. Obviously, the cyclic electron transport pathway is sensitive to electron drainage. In the absence of electron acceptors, cyclic electron flow is supported by far-red illumination and inhibited by red light. The inhibition by light exciting photosystem II demonstrated that the cyclic electron transport pathway is accessible to electrons from photosystem II. Inhibition can be relieved by oxygen which appears to prevent over-reduction of electron carriers of the cyclic pathway and thus has an important regulatory function. The data show that cyclic electron transport is under delicate redox control. Inhibition is caused both by excessive oxidation and by over-reduction of electron carriers of the pathway.

On the estimation of proton gradient and osmotic volume in chloroplast membranes

The dependence of thylakoid osmotic volume on NH4Cl uncoupling and on phosphorylation substrates is determined by the centrifuge filtration method. The values obtained are used to evaluate the transmembrane proton gradient in conjunction with either the 9-aminoacridine fluorescence quenching method or the [14C]methylamine uptake method. The DeltapH values obtained with the two methods are compared and a linear relationship is demonstrated in the DeltapH range from 1.4 to 2.7 ([14C]methylamine values). Different linear relationships are obtained depending on the presence or absence of electron acceptor. We conclude that the 9-aminoacridine method can be used for DeltapH determination after calibration with other methods.

Flexibility of coupling and stoichiometry of ATP formation in intact chloroplasts

Since coupling between phosphorylation and electron transport cannot be measured directly in intact chloroplasts capable of high rates of photosynthesis, attempts were made to determine ATP 2 e ratios from the quantum requirements of glycerate and phosphoglycerate reduction and from the extent of oxidation of added NADH via the malate shuttle during reduction of phosphoglycerate in light. These different approaches gave similar results. The quantum requirement of glycerate reduction, which needs 2 molecules of ATP per molecule of NADPH oxidized was found to be pH-dependent. 9–11 quanta were required at pH 7.6, and only about 6 at pH 7.0. The quantum requirement of phosphoglycerate reduction, which consumes ATP and NADPH in a 1 1 ratio, was about 4 both at pH 7.6 and at 7.0. ATP 2 e ratios calculated from the quantum requirements and the extent of phosphoglycerate accumulation during glycerate reduction were usually between 1.2 and 1.4, occasionally higher, but they never approached 2. Although the chloroplast envelope is impermeable to pyridine nucleotides, illuminated chloroplasts reduced added NAD via the malate shuttle in the absence of electron acceptors and also during the reduction of glycerate or CO 2. When phosphoglycerate was added as the substrate, reduction of pyridine-nucleotides was replaced by oxidation and hydrogen was shuttled into the chloroplasts to be used for phosphoglycerate reduction even under light which was rate-limiting for reduction. This indicated formation of more ATP than NADPH by the electron transport chain. From the rates of oxidation of external NADH and of phosphoglycerate reduction at very low light intensities ATP 2 e ratios were calculated to be between 1.1 and 1.4. Fully coupled chloroplasts reduced oxaloacetate in the light at rates reaching 80 and in some instances 130 μmoles · mg −1 chlorophyll · h −1 even though ATP is not consumed in this reaction. The energy transfer inhibitor phlorizin did not significantly suppress this reduction at concentrations which completely inhibited photosynthesis. Uncouplers stimulated oxaloacetate reduction by factors ranging from 1.5 to more than 10. Chloroplasts showing little uncoupler-induced stimulation of oxaloacetate reduction were highly active in photoreducing CO 2. Measurements of light intensity dependence of quantum requirements for oxaloacetate reduction gave no indication for the existence of uncoupled or basal electron flow in intact chloroplasts. Rather reduction is brought about by loosely coupled electron transport. It is concluded that coupling of phosphorylation to electron transport in intact chloroplasts is flexible, not tight. Calculated ATP 2 e ratios were obtained under conditions, where coupling should be expected to be optimal, i.e. at low phosphorylation potentials [ ATP] [ ADP] [ P i ] . Flexible coupling implies, that ATP 2 e ratios should decrease with increasing phosphorylation potentials inside the chloroplasts.

Carbanions. Electron transfer vs. proton capture. I. Base-catalyzed hydrogen-deuterium exchange of triphenylmethane in the presence and absence of electron acceptors

Carbanions. Electron transfer vs. proton capture. I. Base-catalyzed hydrogen-deuterium exchange of triphenylmethane in the presence and absence of electron acceptors

Thermoluminescence studies on photosynthetic energy conversion. I. Evidence for three types of energy storage by Photoreaction II of higher plants

Thermoluminescence was examined in isolated chloroplasts in the presence and absence of electron acceptors and inhibitors of electron transport, and in digitonin subchloroplast particles. Absence of emission from Photosystem I particles indicated that thermoluminescence originated from energy storage in Photoreaction II. Three distinct glow peaks were observed, suggesting that quantum conversion at Reaction Center II may involve three different types of energy storage with differing stabilization energies. Electron acceptors and inhibitors of electron transport had different effects on the three glow peaks. Although correlations can be drawn between the three storage states of the glow curves and components of delayed light emission at different dark times, we were unable to definitely associate any of the thermoluminescence peaks with delayed light emitted during a particular time-range of dark decay.

ChemInform Abstract: LASER PHOTOLYSIS STUDIES ON THE IONIZATION OF N‐VINYLCARBAZOLE AND N‐ETHYLCARBAZOLE IN THE PRESENCE AND ABSENCE OF ELECTRON ACCEPTORS

Chemischer InformationsdienstVolume 4, Issue 35 Preparative Organic Chemistry ChemInform Abstract: LASER PHOTOLYSIS STUDIES ON THE IONIZATION OF N-VINYLCARBAZOLE AND N-ETHYLCARBAZOLE IN THE PRESENCE AND ABSENCE OF ELECTRON ACCEPTORS YOSHIO TANIGUCHI, YOSHIO TANIGUCHISearch for more papers by this authorYASUZO NISHINA, YASUZO NISHINASearch for more papers by this authorNOBORU MATAGA, NOBORU MATAGASearch for more papers by this author YOSHIO TANIGUCHI, YOSHIO TANIGUCHISearch for more papers by this authorYASUZO NISHINA, YASUZO NISHINASearch for more papers by this authorNOBORU MATAGA, NOBORU MATAGASearch for more papers by this author First published: August 28, 1973 https://doi.org/10.1002/chin.197335150Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue35August 28, 1973 RelatedInformation

Laser Photolysis Studies on the Ionization of N-Vinylcarbazole and N-Ethylcarbazole in the Presence and Absence of Electron Acceptors

Abstract Formation of solvated ion radicals in the N-vinylcarbazole (VCZ)-and N-ethylcarbazole (ECZ)-electron acceptor systems in polar solvents has been studied by means of laser photolysis, transient photoconductivity and transient absorption measurements. Ion radical formation due to the encounter collision between an excited VCZ or ECZ and electron acceptor was confirmed directly. In the absence of electron acceptor, formation of cation radicals of carbazoles due to biphotonic process was observed in polar solvents. The Sn←S1 spectra of these molecules were observed both in polar and nonpolar solvents.