Absence Of Acetic Acid Research Articles

Synthesis and Cytotoxicity of a Diazirine‐Based Photopsammaplin

AbstractThe first photoreactive derivative of the cytotoxic marine natural product psammaplin A (1) has been synthesized by appending 1‐azi‐2,2,2‐trifluoroethyl moieties at both benzene rings. Photopsammaplin 8 exhibited anticancer activity in vitro with a geomean IC50 value of 1.4 μM in a panel of 42 human cancer cell lines. Particularly sensitive cell lines were found among bladder, lung, mammary, and prostate cancer as well as melanoma (MEXF 276), with IC50 values ≤ 0.6 μM. In a COMPARE analysis, diazirine‐functionalized photopsammaplin exhibited a very similar cytotoxicity profile to that of the natural product 1. Furthermore, photopsammaplin 8 was found to be a potent HDAC inhibitor (IC50 35 nM) and can be considered as a suitable candidate for photoaffinity labeling, which may assist in the identification of new targets of psammaplin A. Irradiation experiments with a model diazirine‐functionalized α‐hydroxy iminoester in dichloromethane in the presence or absence of acetic acid and methanol revealed the stability of the oxime unit and confirmed that reactions took place solely at the carbene center. The isolation of triplet and singlet photoproducts is consistent with DFT calculations [B3LYP 6‐311G (2d,2p)] showing that, in polar solvents, the triplet‐singlet gap is very small.

Characterization of a Recombinant Flocculent Saccharomyces cerevisiae Strain That Co-Ferments Glucose and Xylose: II. Influence of pH and Acetic Acid on Ethanol Production

The inhibitory effects of pH and acetic acid on the co-fermentation of glucose and xylose in complex medium by recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated. In the absence of acetic acid, the fermentation performance of strain MA-R4 was similar between pH 4.0-6.0, but was negatively affected at pH 2.5. The addition of acetic acid to batch cultures resulted in negligible inhibition of several fermentation parameters at pH 6.0, whereas the interactive inhibition of pH and acetic acid on the maximum cell and ethanol concentrations, and rates of sugar consumption and ethanol production were observed at pH levels below 5.4. The inhibitory effect of acetic acid was particularly marked for the consumption rate of xylose, as compared with that of glucose. With increasing initial acetic acid concentration, the ethanol yield slightly increased at pH 5.4 and 6.0, but decreased at pH values lower than 4.7. Notably, ethanol production was nearly completely inhibited under low pH (4.0) and high acetic acid (150-200mM) conditions. Together, these results indicate that the inhibitory effects of acetic acid and pH on ethanol fermentation by MA-R4 are highly synergistic, although the inhibition can be reduced by increasing the medium pH.

Oxidation of sulfides to sulfones with hydrogen peroxide in the presence of acetic acid and Amberlyst 15

The oxidation of thioanisole to its sulfone with hydrogen peroxide (H2O2) in the presence of acetic acid and Amberlyst 15 was investigated and found to be a simple and effective method. Oxidation experiments in the absence of acetic acid or Amberlyst 15 confirmed the essentiality of these components for the complete oxidation of thioanisole to its sulfone with H2O2. In the two-step oxidation process of sulfide, in the oxidation of sulfide to sulfoxide, H2O2 plays a major role, whereas in the oxidation of sulfoxide to sulfone, peracetic acid formed with H2O2 in the presence of acetic acid and Amberlyst 15 plays a major role. Sulfone formation increased with an increase in H2O2, temperature and Amberlyst 15 and decreased with acetic acid. However, with a very low amount of acetic acid, sulfone formation decreased due to water in H2O2 and released in the reaction. Reutilization of Amberlyst 15 for six cycles resulted in a 6.8 % decrease in sulfone yield and 3.4 % decrease in oxygenation. Dialkyl, dibenzyl, diphenyl, alkylaryl, arylbenzyl, alkylbenzyl sulfides are completely oxidized with this oxidation system to their corresponding sulfones. The reactivity of sulfides is in the order dialkyl > dibenzyl > diphenyl sulfides, which is in line with their order of nucleophilicity.

Gluconacetobacter medellinensis sp. nov., cellulose- and non-cellulose-producing acetic acid bacteria isolated from vinegar

The phylogenetic position of a cellulose-producing acetic acid bacterium, strain ID13488, isolated from commercially available Colombian homemade fruit vinegar, was investigated. Analyses using nearly complete 16S rRNA gene sequences, nearly complete 16S-23S rRNA gene internal transcribed spacer (ITS) sequences, as well as concatenated partial sequences of the housekeeping genes dnaK, groEL and rpoB, allocated the micro-organism to the genus Gluconacetobacter, and more precisely to the Gluconacetobacter xylinus group. Moreover, the data suggested that the micro-organism belongs to a novel species in this genus, together with LMG 1693(T), a non-cellulose-producing strain isolated from vinegar by Kondo and previously classified as a strain of Gluconacetobacter xylinus. DNA-DNA hybridizations confirmed this finding, revealing a DNA-DNA relatedness value of 81 % between strains ID13488 and LMG 1693(T), and values <70 % between strain LMG 1693(T) and the type strains of the closest phylogenetic neighbours. Additionally, the classification of strains ID13488 and LMG 1693(T) into a single novel species was supported by amplified fragment length polymorphism (AFLP) and (GTG)5-PCR DNA fingerprinting data, as well as by phenotypic data. Strains ID13488 and LMG 1693(T) could be differentiated from closely related species of the genus Gluconacetobacter by their ability to produce 2- and 5-keto-d-gluconic acid from d-glucose, their ability to produce acid from sucrose, but not from 1-propanol, and their ability to grow on 3 % ethanol in the absence of acetic acid and on ethanol, d-ribose, d-xylose, sucrose, sorbitol, d-mannitol and d-gluconate as carbon sources. The DNA G+C content of strains ID13488 and LMG 1693(T) was 58.0 and 60.7 mol%, respectively. The major ubiquinone of LMG 1693(T) was Q-10. Taken together these data indicate that strains ID13488 and LMG 1693(T) represent a novel species of the genus Gluconacetobacter for which the name Gluconacetobacter medellinensis sp. nov. is proposed. The type strain is LMG 1693(T) ( = NBRC 3288(T) = Kondo 51(T)).

Cross ketonization of Cuphea sp. oil with acetic acid over a composite oxide of Fe, Ce, and Al

The objective of this work was to demonstrate the viability of the cross ketonization reaction with the triacylglycerol from Cuphea sp. and acetic acid in a fixed-bed plug-flow reactor. The seed oil from Cuphea sp. contains up to 71% decanoic acid and the reaction of this fatty acid residue with acetic acid yields the fragrance compound and insect repellent 2-undecanone. To this end, we screened several ketonization catalysts taken from the literature including CeO2, CeO2/Al2O3, CeO2/ZrO2, MnOx/Al2O3. The catalysts were characterized by N2 adsorption/desorption, H2-TPH, CO2-TPD, and XRD. Each of these catalysts affected the conversion but the highest yield was found with a new coprecipitated mixed metal oxide of empirical formula Fe0.5Ce0.2Al0.3Ox. In a flow reactor, Fe0.5Ce0.2Al0.3Ox gave 2-undecanone at 91% theoretical yield with reaction conditions of 400°C, weight hourly space velocity of 2, molar ratio of acetic acid to Cuphea oil of 23, and N2 carrier gas flow of 125ml/min at 2.4bar. This high yield is attributed to the low rate of coke formation on the mixed metal catalyst. In the absence of acetic acid, coupling of the decanoic acid residues gives 10-ketononadecane.

The effect of acetic acid on the CO 2 corrosion of grade X70 steel

The effect of acetic acid (HAc) on the CO 2 corrosion of grade X70 steel was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), polarization tests and electrochemical impedance spectroscopy (EIS). In the absence of acetic acid, a fairly dense layer of iron carbonate (FeCO 3/siderite) was formed. At 500 ppm HAc, FeCO 3 layer became more porous. In addition, anodic/cathodic polarization curves were activated with the more pronounced effect on the cathodic side. By adding 1000 ppm HAc, similar polarization behavior was obtained and FeCO 3 layer became yet more porous than previous conditions. At 2000 ppm HAc, FeCO 3 layer disappeared completely, while polarization behavior changed and the limiting diffusive current density was observed in the cathodic side. There were two major increases in the corrosion rate at 500 and 2000 ppm HAc. The EIS results reflected similar behavior for the specimens exposed to the solutions with 0–1000 ppm HAc. Under these conditions, a charge transfer controlled behavior due to the FeCO 3 layer was observed which was accelerated by increasing HAc concentration. At 2000 ppm HAc, the corrosion behavior changed considerably and the formation/adsorption of corrosion product followed by the dissolution process was observed.

CO2 corrosion of carbon steel in the presence of acetic acid at higher temperatures

The corrosion behaviour of X 65 carbon steel in the presence of acetic acid in N2- and CO2-saturated systems has been investigated using electrochemical techniques. The presence of acetic acid does not influence the anodic reaction but strongly accelerates the cathodic reaction. The cathodic reaction and consequently the corrosion rate of mild steel in the CO2-saturated system increase with increase in acetic acid concentration and temperature. From the values of the apparent activation energies, the corrosion reaction in the absence of acetic acid was found to be under mixed interfacial reaction/diffusion control while interfacial reaction control dominates in the presence of acetic acid. The reduction of adsorbed undissociated acetic acid on the metal surface is proposed as the key species primarily responsible for accelerated corrosion rate at all temperatures.

Survival of planktonic and sessile Acetobacter cerevisiae

SummaryThis study was designed to investigate the individual or combined effects of ethanol (4–12%), glucose (10–30%) and acetic acid (0–6%) on survival of planktonic and sessile cells of one strain belonging to the new species Acetobacter cerevisiae isolated from traditional balsamic vinegar. The results confirm that the planktonic cells’ survival was negatively affected by ethanol and by acetic acid; moreover, there was a positive correlation between survival and glucose concentration. On the contrary, biofilm formation was observed only in the absence of acetic acid, which was the most affecting variable on the natural ability of cells to attach and grow on surfaces. The obtained results supply new information about the physiology of a novel Acetobacter species and about its natural capability to develop biofilms so that improved control over balsamic vinegar fermentation could be implemented in the future.

Kinetics of ethylene combustion in the synthesis of vinyl acetate over a Pd/SiO 2 catalyst

The kinetic parameters of ethylene combustion in the presence of acetic acid, i.e., during the synthesis of vinyl acetate and in the absence of acetic acid, have been measured in the temperature range 413–453 K over Pd supported on a high surface area SiO 2 (600 m 2/g) at pressures ranging from 5.0 to 15.0 kPa of C 2H 4 and 1.0 to 10.0 kPa of O 2. CO 2 formation as a function of the partial pressures of C 2H 4 and O 2 exhibited a negative reaction order with respect to C 2H 4 and a positive order with respect to O 2. The kinetic parameters of ethylene combustion in the presence and absence of acetic acid were essentially the same, consistent with ethylene combustion being primarily responsible for CO 2 formation in the synthesis of vinyl acetate from ethylene and acetic acid over unpromoted Pd within the pressure regime investigated.

Performance testing of Zymomonas mobilis metabolically engineered for cofermentation of glucose, xylose, and arabinose.

IOGEN Corporation of Ottawa, Canada, has recently built a 40t/d biomass-to-ethanol demonstration plant adjacent to its enzyme production facility. It has partnered with the University of Toronto to test the C6/C5 cofermenta-tion performance characteristics of the National Renewable Energy Labora-tory's metabolically engineered Zymomonas mobilis using various biomass hydrolysates. IOGEN's feedstocks are primarily agricultural wastes such as corn stover and wheat straw. Integrated recombinant Z. mobilis strain AX101 grows on D-xylose and/or L-arabinose as the sole carbon/energy sources and ferments these pentose sugars to ethanol in high yield. Strain AX101 lacks the tetracycline resistance gene that was a common feature of other recombinant Zm constructs. Genomic integration provides reliable cofermentation performance in the absence of antibiotics, another characteristic making strain AX101 attractive for industrial cellulosic ethanol production. In this work, IOGEN's biomass hydrolysate was simulated by a pure sugar medium containing 6% (w/v) glucose, 3% xylose, and 0.35% arabinose. At a level of 3 g/L (dry solids), corn steep liquor with inorganic nitrogen (0.8 g/L of ammonium chloride or 1.2 g/L of diammonium phosphate) was a cost-effective nutritional supplement. In the absence of acetic acid, the maximum volumetric ethanol productivity of a continuous fermentation at pH 5.0 was 3.54 g/L x h. During prolonged continuous fermentation, the efficiency of sugar-to-ethanol conversion (based on total sugar load) was maintained at >85%. At a level of 0.25% (w/v) acetic acid, the productivity decreased to 1.17 g/L x h at pH 5.5. Unlike integrated, xylose-utilizing rec Zm strain C25, strain AX101 produces less lactic acid as byproduct, owing to the fact that the Escherichia coli arabinose genes are inserted into a region of the host chromosome tentatively assigned to the gene for D-lactic acid dehydrogenase. In pH-controlled batch fermentations with sugar mixtures, the order of sugar exhaustion from the medium was glucose followed by xylose and arabinose. Both the total sugar load and the sugar ratio were shown to be important determinants for efficient cofermentation. Ethanol at a level of 3% (w/v) was implicated as both inhibitory to pentose fermentation and as a potentiator of acetic acid inhibition of pentose fermentation at pH 5.5. The effect of ethanol may have been underestimated in other assessments of acetic acid sensitivity. This work underscores the importance of employing similar assay conditions in making comparative assessments of biocatalyst fermentation performance.

Synthesis of 5-N-glycosylaminopyrimidines. A new class of compounds with potential anti-aids activity

Reactions between 5,6-diaminopyrimidines 1a-c and pentoses 2a-e yield 5-N-glycosylaminopyrirnidines or 7-polyhydroxyalkylpteridines, depending on the presence or absence of acetic acid. The “in vitro” anti-HIV activity of 6-amino-2-methoxy-3-methyl-5-N-D-ribosylaminopyrimidin-4(3H)-one 3e, 6-amino-2-methoxy-3-methyl-5-N-β-D-xylopyranosylaminopyrimidin-4(3H-one 3f, and 6-amino-2-methylthio-5-N-β-L-xylopyranosylminopyrimidin-4(3H)-one 3k, appears to be promising.

Main and interaction effects of acetic acid, furfural, and p‐hydroxybenzoic acid on growth and ethanol productivity of yeasts

The influence of the factors acetic acid, furfural, and p-hydroxybenzoic acid on the ethanol yield (YEtOH) of Saccharomyces cerevisiae, bakers' yeast, S. cerevisiae ATCC 96581, and Candida shehatae NJ 23 was investigated using a 23-full factorial design with 3 centrepoints. The results indicated that acetic acid inhibited the fermentation by C. shehatae NJ 23 markedly more than by bakers' yeast, whereas no significant difference in tolerance towards the compounds was detected between the S. cerevisiae strains. Furfural (2 g L−1) and the lignin derived compound p-hydroxybenzoic acid (2 g L−1) did not affect any of the yeasts at the cell mass concentration used. The results indicated that the linear model was not adequate to describe the experimental data (the p-values of curvatures were 0.048 for NJ 23 and 0.091 for bakers' yeast). Based on the results from the 23-full factorial experiment, an extended experiment was designed based on a central composite design to investigate the influence of the factors on the specific growth rate (μ), biomass yield (Yx), volumetric ethanol productivity (QEtOH), and YEtOH. Bakers' yeast was chosen in the extended experiment due to its better tolerance towards acetic acid, which makes it a more interesting organism for use in industrial fermentations of lignocellulosic hydrolysates. The inoculum size was reduced in the extended experiment to reduce any increase in inhibitor tolerance that might be due to a large cell inoculum. By dividing the experiment in blocks containing fermentations performed with the same inoculum preparation on the same day, much of the anticipated systematic variation between the experiments was separated from the experimental error. The results of the fitted model can be summarised as follows: μ was decreased by furfural (0–3 g L−1). Furfural and acetic acid (0–10 g L−1) also interacted negatively on μ. Furfural concentrations up to 2 g L−1 stimulated Yx in the absence of acetic acid whereas higher concentrations decreased Yx. The two compounds interacted negatively on Yx and YEtOH. Acetic acid concentrations up to 9 g L−1 stimulated QEtOH, whereas furfural (0–3 g L−1) decreased QEtOH. Acetic acid in concentrations up to 10 g L−1 stimulated YEtOH in the absence of furfural, and furfural (0–2 g L−1) slightly increased YEtOH in the absence of acetic acid whereas higher concentrations caused inhibition. Acetic acid and furfural interacted negatively on YEtOH. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 46–55, 1999.

Acetic acid—friend or foe in anaerobic batch conversion of glucose to ethanol by Saccharomyces cerevisiae?

The permissible region of growth of Saccharomyces cerevisiae on glucose under anaerobic conditions was determined as a function of both pH and the concentration of added acetic acid to the medium. In the absence of acetic acid, growth was possible at a pH as low as 2.5, whereas a total acetic acid addition of 10 gl −1 increased the minimum allowable pH for growth to 4.5. The results showed that the concentration of the undissociated form of acetic acid should not exceed 5 gl −1 in the medium for growth to occur. The addition of acetic acid had a profound effect on growth energetics, thereby leading to an increased ethanol yield on glucose. At a concentration of 3.3 gl −1 of undissociated acetic acid, the ethanol yield was 20% higher than without added acetic acid. Furthermore, the biomass and glycerol yields decreased by 45 and 33%, respectively.

Optimization of seed production for a simultaneous saccharification cofermentation biomass-to-ethanol process using recombinantZymomonas

The five-carbon sugar D-xylose is a major component of hemicellulose and accounts for roughly one-third of the carbohydrate content of many lignocellulosic materials. The efficient fermentation of xylose-rich hemicellulose hydrolyzates (prehydrolyzates) represents an opportunity to improve significantly the economics of large-scale fuel ethanol production from lignocellulosic feedstocks. The National Renewable Energy Laboratory (NREL) is currently investigating a simultaneous saccharification and cofermentation (SSCF) process for ethanol production from biomass that uses a dilute-acid pretreatment and a metabolically engineered strain of Zymomonas mobilis that can coferment glucose and xylose. The objective of this study was to establish optimal conditions for cost-effective seed production that are compatible with the SSCF process design.Two-level and three-level full factorial experimental designs were employed to characterize efficiently the growth performance of recombinant Z. mobilis CP4:pZB5 as a function of nutrient level, pH, and acetic acid concentration using a synthetic hardwood hemicellulose hydrolyzate containing 4% (w/v) xylose and 0.8% (w/v) glucose. Fermentations were run batchwise and were pH-controlled at low levels of clarified corn steep liquor (cCSL, 1-2% v/v), which were used as the sole source of nutrients. For the purpose of assessing comparative fermentation performance, seed production was also carried out using a "benchmark" yeast extract-based laboratory medium. Analysis of variance (ANOVA) of experimental results was performed to determine the main effects and possible interactive effects of nutrient (cCSL) level, pH, and acetic acid concentration on the rate of xylose utilization and the extent of cell mass production. Results indicate that the concentration of acetic acid is the most significant limiting factor for the xylose utilization rate and the extent of cell mass production; nutrient level and pH exerted weaker, but statistically significant effects. At pH 6.0, in the absence of acetic acid, the final cell mass concentration was 1.4 g dry cell mass/L (g DCM/L), but decreased to 0.92 and 0.64 g DCM/L in the presence of 0.5 and 1.0% (w/v) acetic acid, respectively. At concentrations of acetic acid of 0.75 (w/v) or lower, fermentation was complete within 1.5 d. In contrast, in the presence of 1.0% (w/v) acetic acid, 25% of the xylose remained after 2 d. At a volumetric supplementation level of 1.5-2.0% (v/v), cCSL proved to be a cost-effective single-source nutritional adjunct that can support growth and fermentation performance at levels comparable to those achieved using the expensive yeast extract-based laboratory reference medium.

Oxidation of Sulfides with Electrocatalytic P-450 Model System.

Controlled potential electrolysis (CPE) of meso-tetraphenylporphyrinatomanganese (III) chloride (1 mM, 1a) at -0.4V (vs. saturated calomel electrode (SCE)) in acetonitrile containing diphenyl sulfide (100mM, 2), 1-methylimidazole (5mM), and tetrabutylammonium perchlorate (0.1 M) as supporting electrolyte with a reticulated vitreous carbon (RVC) cathode and bubbling O 2 gas, gave diphenylsulfoxide (12.6%-16.4%, 3) and diphenylsulfone (0.5%-1.5%, 4) in the presence of acetic acid/or tetramethylammonium hydroxide (5). In the absence of acetic acid or 5, compound 2 was not oxidized. The results of cyclic voltammetry and CPE at -0.4 V (vs. SCE) showed that the oxidant of 2 was an oxo-manganese (V) species which was generated from la and dissolved dioxygen by two-electron transfer and that the presence of H + was essential not only to cleave the O-O bond in the peroxo-manganese species, but also to transfer the second electron. This catalytic cycle is similar to that of P-450. The current efficiency was 79.1%. CPE of dissolved O 2 was carried out at -1.0 V in acetonitrile and superoxide ion was detected by use of an electron spin resonance spectrometer in the frozen electrolyzed solution. Addition of potassium superoxide to acetonitrile containing 1a, 1-methylimidazole and 2 gave 3 (15.6%-26.7%) and 4 (0%-2.7%) in the presence of acetic acid or 5. A similar procedure in the absence of the acid or 5 did not give 3 or 4. When the applied potential was -1.0 V, superoxide ion generated by cathodic reduction of dissolved oxygen in the electrolytic solution containing acetic acid was converted into hydrogen peroxide by the reaction with protons. The reaction of manganese (III) porphyrin with hydrogen peroxide produced an oxo-manganese (V) species, which is a strong oxidant and oxidized 2 and 3. This mechanism is similar to the shunt mechanism in the cytochrome P-450 catalytic cycle

Synthesis of 5-glycosylamino pyrimidines. A new class of compounds with potential anti-aids activity

Reaction of the diamino pyrimidine derivative, 1, with D-ribose and D-xylose produces 7-polihydroxyalkylpteridines or 5-glycosylaminopyrimidines depending on the presence or absence of acetic acid. The preliminary results in tests “i vitro” against HIV for compounds 5 and 6 seem to be promising.

The mechanisms of the reduction reactions of Cr(VI) in the radiolysis of acidic potassium and silver dichromate solutions in the presence or absence of acetic acid

The mechanisms and the kinetics of reactions in deoxygenated and oxygen-saturated aqueous solutions of potassium dichromate in the range of pH 0.4–0.8, in the presence and absence of acetic acid, were investigated by pulse and steady-state radiolysis. Computer simulation of reaction mechanisms was compared with experimental kinetics data for solutions containing silver dichromate and acetic acid. It was found that carboxymethyl reduces Cr(VI) to Cr(V) with a rate constant of 1.8 x 10 8 M -1 s -1, while carboxymethylperoxyl does not reduce Cr(VI). Hydroperoxyl reduces Cr(VI) to Cr(V), but at a much lower rate constant of <10 6 M -1 s -1. The oxidation-reduction reaction between radiolytically produced Cr(V) and Ag(II) was measured and found to have a rate constant of 1.0 x 10 8 M -1 s -1. The mechanism for the enhanced stability of Cr(VI) in the presence of Ag + was studied in the light of the kinetics and the reactivity of the Ag(II) with the intermediate free radicals occurring in this system. The present findings help elucidate the mechanisms of the dichromate dosimeter, its dose-rate independent response and its stability.

Uncoupling by Acetic Acid Limits Growth of and Acetogenesis by Clostridium thermoaceticum

When cells of the anaerobic thermophile Clostridium thermoaceticum grow in batch culture and homoferment glucose to acetic acid, the pH of the medium decreases until growth and then acid production cease, at about pH 5. We postulated that the end product of fermentation limits growth by acting as an uncoupling agent. Thus, when the pH of the medium is low, the cytoplasm of the cells becomes acidified below a tolerable pH. We have therefore measured the internal pH of growing cells and compared these values with those of nongrowing cells incubated in the absence of acetic acid. Growing cells maintained an interior about 0.6 pH units more alkaline than the exterior throughout most of batch growth (i.e., DeltapH = 0.6). We also measured the transmembrane electrical potential (DeltaPsi), which decreased from 140 mV at pH 7 at the beginning of growth to 80 mV when the medium had reached pH 5. The proton motive force, therefore, was 155 mV at pH 7, decreasing to 120 mV at pH 5. When further fermentation acidified the medium below pH 5, both the DeltapH and the DeltaPsi collapsed, indicating that these cells require an internal pH of at least 5.5 to 5.7. Cells harvested from stationary phase and suspended in citrate-phosphate buffer maintained a DeltapH of 1.5 at external pH 5.0. This DeltapH was dissipated by acetic acid (at the concentrations found in the growth medium) and other weak organic acids, as well as by ionophores and inhibitors of glycolysis and of the H-ATPase. Nongrowing cells had a DeltaPsi which ranged from about 116 mV at external pH 7 to about 55 mV at external pH 5 and which also was sensitive to ionophores. Since acetic acid, in its un-ionized form, diffuses passively across the cytoplasmic membrane, it effectively renders the membrane permeable to protons. It therefore seems unlikely that mutations at one or a few loci would result in C. thermoaceticum cells significantly more acetic acid tolerant than their parental type.

Surface band energy shifts of a p-type Si electrode in the presence of redox couples: Study of anthraquinone derivatives in the dark and under illumination

Surface band energy shifts of a p-type Si electrode have been observed, in the presence of various redox couples, in the dark and in dry acetonitrile solution. These results are reinforced by the study of the reduction of a large series of anthraquinone derivatives at the mercury electrode and at illuminated p-type Si and p-type GaAs electrodes (in acetonitrile solution and in the presence or absence of acetic acid). The two semiconducting materials exhibit the Fermi level pinning phenomenon, giving a constant photovoltage output independent of the E s 0 of the anthraquinone derivatives. Unexpectedly, the anthraquinones used in the present work do not show any trend towards sluggish kinetics in reduction, even in the presence of acetic acid and a slight amount of water. This result indicates that the choice of the best anthraquinone derivative for photoelectrochemical devices using p-type Si or p-type GaAs will be mainly dictated by stability properties of the depolarizer in the chemistry one seeks to develop.

Effect of acetic acid on subcellular structures of cocoa bean cotyledons

AbstractCharacteristic post‐mortem changes in subcellular structures are described which are caused by the penetration of acetic acid during incubation of cocoa seeds in aqueous media. In the storage cells lipid is agglomerated and separates from hydrophilic portions in proportion to the acetic acid concentration and pH. This effect is less pronounced at 50°C than at 40°C. In the absence of acetic acid or with very low concentration of undissociated acetic acid other substructural characteristics dominate in most of the cells. At 50°C Post‐mortem changes do not induce lipid agglomeration. At 40°C the intact protein vacuole swells and its matrix structure becomes spongy as a response to in‐vivo water absorption. Finally, it is shown that a concentration gradient persists in whole seeds for most of the time required for fermentation, because of the slow diffusion of acetic acid. The results are compared with temperature effects on subcellular structures and are discussed in relation to their significance for proteolysis in cocoa seeds during fermentation.