Increase In Oxidation Potential Research Articles

Detection and Mapping of Widespread Intermolecular Protein Disulfide Formation during Cardiac Oxidative Stress Using Proteomics with Diagonal Electrophoresis

Regulation of protein function by reversible cysteine-targeted oxidation can be achieved by multiple mechanisms, such as S-glutathiolation, S-nitrosylation, sulfenic acid, sulfinic acid, and sulfenyl amide formation, as well as intramolecular disulfide bonding of vicinal thiols. Another cysteine oxidation state with regulatory potential involves the formation of intermolecular protein disulfides. We utilized two-dimensional sequential non-reducing/reducing SDS-PAGE (diagonal electrophoresis) to investigate intermolecular protein disulfide formation in adult cardiac myocytes subjected to a series of interventions (hydrogen peroxide, S-nitroso-N-acetylpenicillamine, doxorubicin, simulated ischemia, or metabolic inhibition) that alter the redox status of the cell. More detailed experiments were undertaken with the thiol-specific oxidant diamide (5 mm), a concentration that induces a mild non-injurious oxidative stress. This increase in cellular oxidation potential caused global intermolecular protein disulfide formation in cytosolic, membrane, and myofilament/cytoskeletal compartments. A large number of proteins that undergo these associations were identified using liquid chromatography-mass spectrometry/mass spectrometry. These associations, which involve metabolic and antioxidant enzymes, structural proteins, signaling molecules, and molecular chaperones, were confirmed by assessing "shifts" on non-reducing immunoblots. The observation of widespread protein-protein disulfides indicates that these oxidative associations are likely to be fundamental in how cells respond to redox changes.

The molecular structures and electrochemical response of “twisted” tetra(aryl)benzidenes

The compounds N,N,N′,N′-tetra(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (4), N,N,N′,N′-tetra(4-methylphenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5a) and N,N,N′,N′-tetra(4-methylphenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6a) undergo two reversible one electron oxidations. The first oxidation potential increases in the order 4 < 5a < 6a, while the separation between the first and second oxidation decreases in the reverse order 4 (0.30 V) > 5a (0.16 V) > 6a (0.00 V), reflecting the decreasing thermodynamic stability of the radical cations [4+] > [5+] > [6a+]. Electronic spectroscopy and spectroelectrochemistry (UV-Vis-NIR) confirm expectations, and the introduction of methyl groups at the 2,2′ and 6,6′ positions of the 1,1′-biphenyl moiety electronically decouple the arylamine moieties. In contrast, N,N,N′,N′-tetra(phenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5b) and N,N,N′,N′-tetra(phenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6b) give much less kinetically stable radical cations upon oxidation, which oligomerise/polymerise through the 4 positions of the N-phenyl groups via a step-growth process. The molecular and crystal structures of 4 and 6b are also reported.

Electrochemical Reduction and Oxidation of 3,4-Disubstituted 1,2,5-Thiadiazoles

The electron-acceptor nitrogen and sulfur atoms in 3,4-disubstituted 1,2,5-thiadiazoles are responsible for much decreased reduction potentials and much increased oxidation potentials of these compounds compared with the corresponding carbocyclic derivatives. The thiadiazole ring is resistant to oxidation, and the reversible electron transfer gives rise to fairly stable radical cations. Reductive stability of the heterocycle depends on the nature of its substituents and on the medium: When nucleofuge substituents are present, two-electron transfer in aprotic media results in heteroring opening with iminonitrile formation, whereas in the presence of two readily leaving groups, the electron transfer induces cleavage of the complete heteroring into inorganic anions.

Syntheses and some reactions of complexes containing carbon chains capped by ferrocenyl and W(CO) 3Cp groups

The preparation and some reactions of W{(CC) n }(CO)Cp [ n=1–4 ( 1– 4 )] are described. For n=1 and 2, Cu(I)-catalysed reactions between Fc(CC) n H ( n=1, 2) and WCl(CO) 3Cp gave compounds 1 and 2, respectively, while Cu(I)Pd(0)-catalysed coupling between FcCCI and W(CCCCH)(CO) 3Cp gave 3. Oxidative coupling of FcCCCCH and W(CCCCH)(CO) 3Cp gave 4, together with both homo-coupled products. Electrochemical studies showed that the Fc/Fc + oxidation potential increases by about 50 mV for each CC triple bond added to the carbon chain. Reactions with Co 2(μ-dppm) m (CO) 8−2 m ( m=0, 1) gave complexes 6– 10 in which the Co 2 fragment is attached to the sterically least-hindered CC triple bond. The novel vinylidene cluster Co 2W(μ 3-CCPhFc)(μ 3-PPhCH 2PPh 2)(CO) 5Cp ( 5) was also obtained from 1 and Co 2(μ-dppm)(CO) 6. Reactions of 1 with tetracyanoethene (tcne) gave the cyclobutenyl ( 11) and buta-1,3-dien-2-yl ( 12) complexes by cycloaddition to the CC triple bond and subsequent ring-opening. In the presence of silica gel, 12 reacts with MeOH to give the chelating imino complex W{C[C(CN) 2C(OMe)NH]CFcC(CN) 2}(CO) 2Cp ( 13). With 2 and 3, addition of tcne to the CC triple bond one removed from the tungsten centre gave buta-1,3-dien-2-yl complexes 14 and 15. X-ray crystal structure determinations have been carried out on 2, 5 , 7, 8 and 10– 14.

Redox regulation in mammalian signal transduction.

DIOXYGEN AND OXYGEN METABOLITES Gene expression of any cell, be it a unicellular organism or constituent of a mammal, is regulated in response to extracellular cues. Among the many in uences to which respirating cells are exposed, oxygen and oxygen metabolites play a central role. That cells sense these components and convert the information into changes of gene expression, has been known formany years. How oxygen homeostasis is achieved, which ones the sensors are, and how gene programs are then regulated, is a matter of current study. One aspect of recent progress has been the recognition that, although the intracellular milieu is reductive, there are redox-sensitive pockets and macromolecules. Obviously, the program of gene expression is established by speciŽ c transcription factors. These are, however, not the direct targets of oxygen or oxygen metabolites. As an illustration to this point—lack of oxygen in the multicellular mammalian organism leads to enhanced angiogenesis, erythropoesis, altered metabolism, and, if persistant, to apoptosis of the most sensitive cells. Hypoxia-inducible factor (HIF) (1) seems to represent the most important responsive transcription factor affecting relevant gene expression [see review (2)]. The promoter speciŽ city determining subunit HIF ¤ is subjected to ubiquitination and degradation in normoxic conditions. During hypoxia, degradation is prevented. The sensor for dioxygen appears to be an enzyme that modiŽ es the ubiquitin conjugating enzyme (3, 4). The opposite to hypoxia, an increase of oxidative potential, results from a number of conditions. Reactive oxygen intermediates (ROI) can be normal products of oxygen consumption. Most evident is the generation of superoxide anions and ofH2O2, HOCl, and hydroxyl radicals during a respiratory burst of neutrophils. Its absence in chronic granulomatous disease results in life-threatening infections. TheROI are produced by anNADPH oxidase that is controlled by Rac2 (5). Small G protein-regulated NADPH oxidases have also been detected in other cells and it is assumed that low concentrations of ROIs can function as sec-

Changes in skeletal muscle in males and females following endurance training

Gender differences in substrate selection have been reported during endurance exercise. To date, no studies have looked at muscle enzyme adaptations following endurance exercise training in both genders. We investigated the effect of a 7-week endurance exercise training program on the activity of beta-oxidation, tricarboxylic acid cycle and electron transport chain enzymes, and fiber type distribution in males and females. Training resulted in an increase in VO2peak, for both males and females of 17% and 22%, respectively (P < 0.001). The following muscle enzyme activities increased similarly in both genders: 3-beta-hydroxyacyl CoA dehydrogenase (38%), citrate synthase (41%), succinate-cytochrome c oxidoreductase (41%), and cytochrome c oxidase (COX; 26%). The increase in COX activity was correlated (R2 = 0.52, P < 0.05) with the increase in VO2peak/fat free mass. Fiber area, size, and % area were not affected by training for either gender, however, males had larger Type II fibers (P < 0.05) and females had a greater Type I fiber % area (P < 0.05). Endurance training resulted in similar increases in skeletal muscle oxidative potential for both males and females. Training did not affect fiber type distribution or size in either gender.

Effect of short-term exercise training on angiogenic growth factor gene responses in rats.

We investigated whether 1) 5 days of exercise training would reduce the acute exercise-induced increase in skeletal muscle growth factor gene expression; and 2) reductions in the increase in growth factor gene expression in response to short-term exercise training would be coincident with increases in skeletal muscle oxidative potential. Female Wistar rats were used. Six groups (rest; exercise for 1-5 consecutive days) were used to measure the growth factor response through the early phases of an exercise training program. Vascular endothelial growth factor (VEGF), transforming growth factor-beta1 (TGF-beta1), and basic fibroblast growth factor (bFGF) mRNA were analyzed from the left gastrocnemius by quantitative Northern blot. Citrate synthase activity was analyzed from the right gastrocnemius. VEGF and TGF-beta1 mRNA increased after each of 5 days of exercise training, whereas exercise on any day did not increase bFGF mRNA. On day 1, the VEGF mRNA response was significantly greater than on days 2-5. However, the reduced increase in VEGF mRNA observed on days 2-5 was not coincident with increases in citrate synthase activity. These findings suggest that, in skeletal muscle, 1) VEGF and TGF-beta1 mRNA are increased through 5 days of exercise training and 2) the reduced exercise-induced increase in VEGF mRNA responses on days 2-5 does not result from increases in oxidative potential.

Synthesis and characterization of novel regioregular polythiophenes

Three novel regioregular polythiophenes with side chain substituents resulting in increased oxidation potentials relative to poly(3-dodecylthiophene) have been synthesized using the McCullough polymerization protocol. All polymers have >95% head-to-tail couplings as evidenced from 1 H-NMR and are furthermore characterized by SEC, solution and solid-state UV-vis spectroscopy, and cyclic voltammetry, By varying the nature of the side chains the redox properties could he altered: the first oxidation potentials vary between 0.75 V and 1.25 V and the first reduction potentials between -1.40 V and -1.85 V. The optical properties of the polymers in solution and as thin solid films were much less affected by the different substituents.

Age-Associated Changes of Superoxide Dismutase and Catalase Activities in the Rat Brain

Oxygen free radicals have been proposed to be involved in the process of aging. Superoxide dismutase (SOD) and catalase are important for antioxidative defense. In this study, profiles of SOD, catalase, and their mRNA levels were investigated in the frontal, parietal, temporal and occipital lobes, subcortex and cerebellum of male Wistar rats at ages 1–21 months. The total SOD and Mn SOD activities increased with age and exhibited higher levels at 6 and 12 months but decreased thereafter. Activity of catalase showed a similar trend and notably peaked at 12 months. The mRNA levels of Cu/Zn SOD, Mn SOD, and catalase remained constant in all areas tested (frontal, parietal, temporal and occipital lobes, and subcortex) except the cerebellum. Post-transcriptional regulation was involved in modulating the enzymes’ activities during aging. Furthermore, the rate of mitochondrial generation of the superoxide anion (O₂^–·) increased gradually with aging. Taken together, the results suggest that the increase of oxidative potential and the loss of proper antioxidant defense in the rats appear to be highly involved in the aging process of the brain.

Age-associated changes of superoxide dismutase and catalase activities in the rat brain.

Oxygen free radicals have been proposed to be involved in the process of aging. Superoxide dismutase (SOD) and catalase are important for antioxidative defense. In this study, profiles of SOD, catalase, and their mRNA levels were investigated in the frontal, parietal, temporal and occipital lobes, subcortex and cerebellum of male Wistar rats at ages 1-21 months. The total SOD and Mn SOD activities increased with age and exhibited higher levels at 6 and 12 months but decreased thereafter. Activity of catalase showed a similar trend and notably peaked at 12 months. The mRNA levels of Cu/Zn SOD, Mn SOD, and catalase remained constant in all areas tested (frontal, parietal, temporal and occipital lobes, and subcortex) except the cerebellum. Post-transcriptional regulation was involved in modulating the enzymes' activities during aging. Furthermore, the rate of mitochondrial generation of the superoxide anion (O(2)(-).) increased gradually with aging. Taken together, the results suggest that the increase of oxidative potential and the loss of proper antioxidant defense in the rats appear to be highly involved in the aging process of the brain.

Adaptations in skeletal muscle exercise metabolism to a sustained session of heavy intermittent exercise.

The purpose of this study was to investigate the hypothesis that a single, extended session of heavy exercise would be effective in inducing adaptations in energy metabolism during exercise in the absence of increases in oxidative potential. Ten healthy males [maximal aerobic power (VO(2 peak)) = 43.4 +/- 2.2 (SE) ml x kg(-1) x min(-1)] participated in a 16-h training session involving cycling for 6 min each hour at approximately 90% of maximal oxygen consumption. Measurements of metabolic changes were made on tissue extracted from the vastus lateralis during a two-stage standardized submaximal cycle protocol before (Pre) and 36-48 h after (Post) the training session. At Pre, creatine phosphate (PCr) declined (P < 0.05) by 32% from 0 to 3 min and then remained stable until 20 min of exercise at 60% VO(2 peak) before declining (P < 0.05) by a further 35% during 20 min of exercise at 75% VO(2 peak). Muscle lactate (mmol/kg dry wt) progressively increased (P < 0.05) from 4.59 +/- 0.64 at 0 min to 17.8 +/- 2.7 and 30.9 +/- 5.3 at 3 and 40 min, respectively, whereas muscle glycogen (mmol glucosyl units/kg dry wt) declined (P < 0.05) from a rest value of 360 +/- 24 to 276 +/- 31 and 178 +/- 36 at similar time points. During exercise after the training session, PCr and glycogen were not as depressed (P < 0.05), and increases in muscle lactate were blunted (P < 0.05). All of these changes occurred in the absence of increases in oxidative potential as measured by the maximal activities of citrate synthase and malate dehydrogenase. These findings are consistent with other studies, namely, that muscle metabolic adaptations to regular exercise are an early adaptive event that occurs before increases in oxidative potential.

XPS analysis of an electrochemically modified electrode surface of natural enargite

A natural enargite (Cu 3 AsS 4 ) electrode has been studied by cyclic voltammetry (CV) and XPS. Cyclic voltammetry was carried out in a preparation chamber filled with Ar gas and coupled to the spectrometer in order to analyse by XPS, quasi-in situ, the electrochemically modified electrode surface. By CV, different potentials of oxidation and reduction were applied to the electrode in a disodium tetraborate decahydrate electrolyte solution of pH 9.2 at room temperature. Cycling in the anodic direction, XPS analysis has shown that at +500 mV the electrode surface is oxidized to CuO, CuSO 4 and As 2 O x (x = 3; 5) and the corresponding hydroxides and polysulphide are formed, whereas at lower oxidation potentials the Cu 2p and As 3d photoelectron peaks do not alter. However, with increasing oxidation potential up to +200 mV a new contribution in the S 2p signal and Cu loss indicate the formation of non-stoichiometric (metal-deficient) enargite and polysulphides in the electrode surface. Cycling then from +500 mV in the cathodic direction until -800 mV, we observe with increasing reduction potential a reverse process in the S 2p signal and Cu concentration. Furthermore, even at +200 mV the reduction from Cu(II) to Cu(I) occurs and no sulphate species are observed any more. These observations indicate that the copper concentration at the electrode surface is a sweep-direction-independent function of applied potential and that the oxide species formed at the electrode surface are only stable by application of high oxidation potentials. For comparison, the surfaces of the fractured mineral and the original polished electrode surface were also studied.

Photoinduced reactions of chloranil with 1,1-diarylethenes and product photochemistry-intramolecular

Photoinduced reactions of chloranil (CA) with 1,1-diarylethenes 1 [(p-X-Ph)(2)C=CH(2), X = F, Cl, H, Me] in benzene afforded products 4-14, respectively, with the bicyclo[4.2.0]oct-3-ene-2,5-diones 4, the 6-diarylethenylcyclohexa-2,5-diene-1,4-diones 5, and 2,3,5, 6-tetrachlorohydroquinone 13 as the major primary products. The cyclobutane products 4 are formed via a triplet diradical intermediate without involvement of single electron transfer (SET) between the two reactants, while 5 is derived from a reaction sequence with initial SET interaction between (3)CA and the alkene. The 9-arylphenanthrene-1,4-diones 6 and its 10-hydroxy-derivatives 7 are secondary photochemical products derived from 5. The isomeric cage products 9-11 are formed from 4 via intramolecular benzene-alkene [2 + 2] (ortho-)photocycloadditions induced by the triplet excited enedione moiety. The relative amount of the two groups of products (4 and its secondary products 9-11 via non-SET route vs 5 and its secondary products 6, 7, 8, 12, and 14 via SET route) shows a rather regular change, with the ratio of non-SET route products gradually increasing with the increase in oxidation potential of the alkenes and in the positive free energy change for electron transfer (DeltaG(ET)) between (3)CA and the alkene, at the expense of the ratio of the products from the SET route. The competition between the SET and non-SET routes was also found to be drastically influenced by solvent polarity, with the SET pathways more favored in polar solvent. Photo-CIDNP investigations suggest the intermediacy of exciplexes or contact ion radical pairs in these reactions in benzene, while in acetonitrile, SET process led to the formation of CA(*)(-) and cation radical of the alkene in the form of solvent separated ion radical pairs and free ions.

Muscular and metabolic responses to moderate-intensity short-term training.

The objectives of this study were to determine the effects of 10 consecutive days of moderate-intensity training on 1) the muscular metabolic response to exercise at 100% of the pre-training maximum rate of oxygen consumption (VO2max); and 2) mitochondrial enzyme markers (citrate synthase, CS; succinate dehydrogenase, SDH; 3-hydroxy-acyl-CoA dehydrogenase, HAD) of oxidative capacity in middle gluteal muscle. Six mature, unfit Thoroughbred horses completed both incremental (for determination of VO2max) and high-intensity exercise protocols before (HI1) and after (HI2) training. Training consisted of 10 consecutive days of running at 55% VO2max for 60 min per day (13-14 km/day). For the HI, horses completed a 10 min warm-up, followed by exercise at 100% of pre-training VO2max (mean speed 9.8 m/s) until fatigue. Training resulted in an 8.9% increases in VO2max (Pre: 142 +/- 4 ml/kg bwt/min; Post: 155 +/- 4 ml/kg bwt/min) and a 24% increase in run time to fatigue during HI. Whereas VO2 during HI was not altered by training, peak values for VCO2 and R were significantly lower following training. Compared to HI1, there was a 45% reduction in the net rate of muscle glycogenolysis during HI2. Peak (end exercise) values for plasma and muscle lactate concentrations decreased by 22 and 23%, respectively, after training. Training also attenuated the exercise-associated increase in plasma norepinephrine, but there was no effect on plasma epinephrine concentrations. Maximal activities of CS, SDH, and HAD were unaltered by training. We conclude that 10 days of moderate-intensity exercise results in decreases in muscle glycogenolysis and anaerobic metabolism during high-intensity exercise at the same absolute workload. Furthermore, development of measurable increases in mitochondrial oxidative potential may not be required for expression of these metabolic adaptations in early training.

Mechanism of Quenching of Triplet States by Oxygen: Biphenyl Derivatives in Acetonitrile

The rate constants, , for oxygen quenching in acetonitrile of the triplet states of biphenyl and nine of its derivatives and the efficiencies of formation thereby of singlet oxygen, , have been measured as have the oxidation potentials of these derivatives. The rate constants decrease from 12.6 × 109 to 0.88 × 109 dm3 mol-1 s-1 as the oxidation potentials of the biphenyls rise from 1.30 to 2.11 V vs SCE while varies in the opposite direction rising from 0.31 to 0.84 with increasing oxidation potential. The mechanism of quenching via singlet and triplet complexes is discussed. The energy of the charge-transfer state, involving electron transfer to oxygen, relative to the energy of the locally excited triplet state, is established as important in determining and . The free energy of activation for charge-transfer-assisted quenching by oxygen via singlet and triplet channels is shown to have a linear dependence on the free energy change for full charge transfer, but the indications are that quenching is via singlet and triplet charge-transfer complexes with only partial (about 13.5%) charge-transfer character.

Overproduction of Ascorbate Peroxidase in the Tobacco Chloroplast Does Not Provide Protection against Ozone.

Transgenic tobacco (Nicotiana tabacum cv Bel W3) plants were used to test the hypothesis that protection from O3 injury could be conferred by overproduction of ascorbate peroxidase (APX) in the chloroplast. The 10-fold increase in soluble APX activity in the chloroplast was expected to alleviate an implied increase in oxidative potential and prevent damage caused by O3. Three different O3 exposure experiments (one acute and two chronic) with two replicates each were conducted. APX activity in nontransgenic plants increased in response to chronic O3 exposure. However, most responses to O3 were similar between transgenic and nontransgenic plants. These included reductions in net photosynthesis and stomatal conductance, increases in ethylene emission and visible injury, and a decline in the level of the small subunit of ribulose-1,5-biphosphate carboxylase/oxygenase mRNA transcripts observed in response to the air pollutant in the acute and/or chronic experiments. No O3-induced effect on ribulose-1,5-biphosphate carboxylase/oxygenase quantity was observed in the chronic experiments. O3 did not induce acceleration of senescence, as expected from studies with most other species; rather, the tobacco plants rapidly developed necrotic lesions. Thus, overproduction of APX in the chloroplast did not protect this cultivar of tobacco from O3.

The fluorescence quenching of 5,6-benzoquinoline and its conjugate acid by Cl −, Br −, SCN − and I − ions

The fluorescence quenching of the free base and conjugated acid forms of 5,6-benzoquinoline (5,6-BQ) by Cl −, Br −, SCN − and I − in aqueous solution over the temperature range 25–50 °C has been investigated. Stern-Volmer plots were found to be linear for the quenching of free base 5,6-BQ by Cl − and Br − but showed upward curvature for the other quenching systems. The active sphere model was used to analyze the latter systems. As is the case in previous fluorescence quenching studies involving these ions, the rate constants were found to increase with increasing oxidation potential of the quencher. The rate constants for quenching of free base 5,6-BQ by Cl − and Br − showed little variation with temperature, while the other systems showed temperature dependences typical of diffusion-limited processes. The activation energies and frequency factors were found to increase with increasing effectiveness of the quencher. Some preliminary low temperature spectra data indicate that the quenching of these systems results in enhanced triplet-state formation.

Electrochemical, EPR and AM1 studies of acetylenic and ethylenic carotenoids

It has been shown, by cyclic voltammetry (CV) and simultaneous electrochemical and electron paramagnetic resonance (SEEPR) measurements of β-carotene (I) and 15,15′-didehydro-β-carotene (II) in dichloromethane solution, that the central triple bond increases the oxidation potentials by 237 ± 5 mV and decreases the solution EPR peak-to-peak linewidth (ΔHpp) by 1.7 G. Two synthetic carotenoids, 7,7′-diphenyl-7,7′-diapocarotene (III) and 7,7′-diphenyl-15,15′-didehydro-7,7′-diapocarotene (IV), close analogues of I and II, were also studied by CV and SEEPR methods. In contrast to compound I, two separate oxidation waves are observed for III, a feature previously found only for carotenoids containing electron-withdrawing substituents. The increase in oxidation potential of IV compared to III was similar to that of IIvs.I, but the decrease in ΔHpp(2.7 G) was considerably larger. Because the radical cation of III is adsorbed strongly on the platinum electrode in dichloromethane, complete analysis using the DigiSim® program was not possible; however, the oxidation potentials could be estimated. Structural parameters of neutral I–IV and their dications were calculated using the AM1 method, and the bond lengths and bond angles of I and II are in good agreement with crystallographic data. The magnitude of the EPR parameters, ΔHpp and the g factors, for the carotenoid radical cations of I–IV indicate a polyene π-radical cation structure with little unpaired electron density occurring near the terminal groups. The radical cation and dication deprotonate by loss of a proton from the chain methyl groups, with the former forming a polyene π-radical.

The early Precambrian atmosphere and hydrosphere; thermodynamic constraints from mineral deposits

A chemical equilibrium model for the early Precambrian atmosphere and hydrosphere is presented. Thermodynamic calculations based on observed stable minerals and mineral assemblages in banded iron-formation (BIF), pyritic, uraniferous, and auriferous quartz-pebble conglomerates, gold-bearing conglomerates of the Tarkwaian in Ghana, and red-bed sediments, yield the following conditions.Before approx 2350 Ma, the atmosphere was oxygen free (P (sub O 2 ) [leftpointingdoubleanglequotationmark] 10 (super -10) bars), consisted mainly of CO 2 (P (sub CO 2 ) 2 S) = 10 (super -7.5) bars over continents to 10 (super -9) bars over oceans) and hydrogen (P (sub H 2 ) = 10 (super -9) bars over continents to 10 (super -7.5) bars over oceans). The high CO 2 partial pressures generated acid rain and surface waters (pH > or = 3.9) and buffered the ocean water to values around pH = 6.5 to 7. In the oceans, the iron minerals of the various banded iron-formation facies (goethite, pyrite, siderite) in conjunction with the atmospheric CO 2 partial pressure acted as a mineral buffer for P (sub H 2 S) , and for the redox state (P (sub H 2 ) ). In continental weathering environments, pyrite formation from ferrous iron and atmospheric H 2 S, and oxidation of H 2 S to SO 4 (super 2-) are considered the prime redox-controlling mechanisms. River waters which previously equilibrated with pyrite precipitated banded iron-formation upon mixing with seawater, mainly due to pH changes.Between 2350 and 2100 Ma, transition from pyritic to iron oxide-bearing conglomerates indicates that photosynthetic oxygen production rates began to exceed oxygen consumption rates and that the redox buffers involving hydrogen sulfide and ferrous iron were overwhelmed. Increased oxidation potentials, and increased surface water pH due to declining atmospheric CO 2 partial pressures, led to immobilization of iron and consequently to continental red-bed formation and cessation of banded iron-formation deposition.

Synthesis and properties of diethyl 5,10-dihetera-5,10-dihydroindeno[2,1-a]indene-2,7-dicarboxylates

A series of six heterocyclic diesters 1b-6b containing all combinations of nitrogen, sulfur, and selenium has been prepared from a common precursor, diethyl 2,2'-dinitrostilbene-4,4'-dicarboxylate. Electrochemical analysis showed oxidation potential increases in the order N<Se<S, and the same trend was observed for minima of UV absorbance. Electrochemical oxidation of indoloindole 1b (but not the other members of the series) generates a persistent radical cation whine properties were investigated. Diesters containing sulfur and selenium (but not nitrogen) form S A liquid crystals. A new synthetic method leading to the indolo[1,2-b]indazole ring system has been found