Abstract  Recently, sugar polymers have been considered for use as biomaterials in medical applications. These biomaterials are already used extensively in burn dressings, artificial membranes, and contact lenses. In this study, we investigated the optimum conditions under which the enzymatic synthesis of sorbitan methacrylate can be affected using Novozym 435 in t-butanol from sorbitan and several acyl donors (ethyl methacrylate, methyl methacrylate, and vinyl methacrylate). The enzymatic synthesis of sorbitan methacrylate, catalyzed by Novozym 435 in t-butanol, reached an approx 68% conversion yield at 50 g/L of 1,4-sorbitan, 5% (w/v) of enzyme content, and a 1:5 molar ratio of sorbitan to ethyl methacrylate, with a reaction time of 36 h. Using methyl methacrylate as the acyl donor, we achieved a conversion yield of approx 78% at 50 g/L of 1,4-sorbitan, 7% (w/v) of enzyme content, at a 1:5 molar ratio, with a reaction time of 36 h. Sorbitan methacrylate synthesis using vinyl methacrylate as the acyl donor was expected to result in a superior conversion yield at 3% (w/v) of enzyme content, and at a molar ratio greater than 1:2.5. Higher molar ratios of acyl donor resulted in more rapid conversion rates. Vinyl methacrylate can be applied to obtain higher yields than are realized when using ethyl methacrylate or methyl methacrylate as acyl donors in esterification reactions catalyzed by Novozym 435 in organic solvents. Enzyme recycling resulted in a drastic reduction in conversion yields.

Abstract  A bacterium designated Pseudonocardia sp. strain ENV478 was isolated by enrichment culturing on tetrahydrofuran (THF) and was screened to determine its ability to degrade a range of ether pollutants. After growth on THF, strain ENV478 degraded THF (63 mg/h/g total suspended solids [TSS]), 1,4-dioxane (21 mg/h/g TSS), 1,3-dioxolane (19 mg/h/g TSS), bis-2-chloroethylether (BCEE) (12 mg/h/g TSS), and methyl tert-butyl ether (MTBE) (9.1 mg/h/g TSS). Although the highest rates of 1,4-dioxane degradation occurred after growth on THF, strain ENV478 also degraded 1,4-dioxane after growth on sucrose, lactate, yeast extract, 2-propanol, and propane, indicating that there was some level of constitutive degradative activity. The BCEE degradation rates were about threefold higher after growth on propane (32 mg/h/g TSS) than after growth on THF, and MTBE degradation resulted in accumulation of tert-butyl alcohol. Degradation of 1,4-dioxane resulted in accumulation of 2-hydroxyethoxyacetic acid (2HEAA). Despite its inability to grow on 1,4-dioxane, strain ENV478 degraded this compound for > 80 days in aquifer microcosms. Our results suggest that the inability of strain ENV478 and possibly other THF-degrading bacteria to grow on 1,4-dioxane is related to their inability to efficiently metabolize the 1,4-dioxane degradation product 2HEAA but that strain ENV478 may nonetheless be useful as a biocatalyst for remediating 1,4-dioxane-contaminated aquifers.

Abstract  The visible-light-induced degradation reaction of 4-chlorophenol (4-CP) was investigated in aqueous suspension of pure TiO2. Contrary to common expectations, 4-CP could be degraded under visible illumination (lambda > 420 nm), generating chlorides and CO2 concomitantly. The observed visible reactivity was not due to the presence of trace UV light since the visible-light-induced reactions exhibited behaviors distinguished from those of UV-induced reactions. Dichloroacetate could not be degraded under visible light, whereas it degraded with a much faster rate than 4-CP under UV irradiation. The addition of tert-butyl alcohol, a common OH radical scavenger, did not affect the visible reactivity of 4-CP, which indicates that OH radicals are not involved. Other phenolic compounds such as phenol and 2,4-dichlorophenol were similarly degraded under visible light. The surface complexation between phenolic compounds and TiO2 appears to be responsible for the visible light reactivity. Diffuse reflectance UV-vis spectra showed that 4-CP adsorbed on TiO2 powder induced visible light absorption. The visible light reactivity among several TiO2 samples was apparently correlated with the surface area of TiO2. The visible-light-induced photocurrents on a TiO2 electrode could be obtained only in the presence of 4-CP. It is proposed that a direct electron transfer from surface-complexed phenol to the conduction band of TiO2 upon absorbing visible light (through ligand-to-metal charge transfer) initiates the oxidative degradation of phenolic compounds. When the surface complex formation was hindered by surface fluorination, surface platinization, and high pH, the visible-light-induced degradation of 4-CP was inhibited. The evidence of visible-light-induced reactions and the experimental conditions affecting the visible reactivity were discussed in detail.

Abstract  The structure of the trimolecular liquid mixture of 2:6:1 cyclohexene, tert-butyl alcohol, and water has been investigated using hydrogen/deuterium substitution neutron scattering techniques, and a three-dimensional structural model refined to be consistent with the experimental data has been built using the technique of Empirical Potential Structure Refinement. The model shows a well-mixed solution of the three molecular components where the competing interactions between the nonpolar cyclohexene and polar water molecules are balanced in the solution leading to largely pure-alcohol-like interactions between the tert-butyl alcohol molecules. Cyclohexene molecules favor direct solvation by alcohol methyl groups while water molecules are accommodated, dispersed throughout the solution, via hydrogen bonding interactions with the alcohol molecule hydroxyl groups. Rare occurrences of direct cyclohexene-water interactions are of the classic hydrophobic hydration type and no evidence is found for microscopic heterogeneity in the trimolecular mixture in contrast to the general findings for binary alcohol-water solutions.

Abstract  Tetrakis(trimethylsiloxy)titanium (TTMST, Ti(OSiMe3)4) possesses an isolated Ti center and is a highly active homogeneous catalyst in epoxidation of various olefins. The structure of TTMST resembles that of the active sites in some heterogeneous Ti-Si epoxidation catalysts, especially silylated titania-silica mixed oxides. Water cleaves the Ti-O-Si bond and deactivates the catalyst. An alkyl hydroperoxide, TBHP (tert-butyl hydroperoxide), does not cleave the Ti-O-Si bond, but interacts via weak hydrogen-bonding as supported by NMR, DOSY, IR, and computational studies. ATR-IR spectroscopy combined with computational investigations shows that more than one, that is, up to four, TBHP can undergo hydrogen-bonding with TTMST, leading to the activation of the O-O bond of TBHP. The greater the number of TBHP molecules that form hydrogen bonds to TTMST, the more electrophilic the O-O bond becomes, and the more active the complex is for epoxidation. An allylic alcohol, 2-cyclohexen-1-ol, does not interact strongly with TTMST, but the interaction is prominent when it interacts with the TTMST-TBHP complex. On the basis of the experimental and theoretical findings, a hydrogen-bond-assisted epoxidation mechanism of TTMST is suggested.

Abstract  Methyl tert-butyl ether (MTBE) is one of the main additives in gasoline. Its degradation is known to be difficult in natural environments. In this study, significant MTBE degradation is demonstrated at a contaminated site in Leuna (eastern Germany). Since the extent of the plume appeared to be constant over the last 5 years, an extended study was performed to elucidate the degradation processes. Special attention was paid to the production, accumulation and degradation of metabolites and by-products. Groundwater samples from 105 monitoring wells were used to measure 20 different substances. During the degradation process, several intermediates such as tert-butyl alcohol (TBA), tert-butyl formate, formate and lactate were produced. However, the potentially carcinogenic by-product methacrylate was not detected in several hundred samples. At the Leuna site, MTBE degradation occurred under microaerobic conditions. In contrast to hydrocarbons and BTEX, there was no evidence for anaerobic MTBE degradation. Among the degradation products, TBA was found to be a useful intermediate to identify MTBE degradation, at least under microaerobic conditions. TBA accumulation was strongly correlated to MTBE degradation according to the kinetic properties of both degradation processes. Since maximum degradation rates (v(max)) and k(m) values were higher for MTBE (v(max)=2.3 mg/l/d and k(m)=3.2 mg/l) than for TBA (v(max)=1.35 mg/l/d and k(m)=0.05 mg/l), TBA significantly accumulated as an intermediate by-product. The field results were supported by bench scale model aquifer experiments.

Abstract  The influence of three variables, i.e. the concentrations of benzyl alcohol (BA), butylated hydroxytoluene (BHT) and tert-butyl-4-hydroxyanisol (BHA), on the preservative efficacy and antioxidant activity of an oily veterinary formulation was investigated using quantitative experimental designs and applying pharmacopoeial methods as part of the robustness-evaluation. Preservative Efficacy Tests (PETs) were performed using the validated European Pharmacpoeia (EP) methodology with 7 test-organisms over one month on lab-scale test-formulations. These were independently prepared according to a Box-Behnken experimental design with a triplicate central point at 0.75% m/V BA, 0.05% mN BHT and 0.05% m/V BHA, and with an additional control-point outside the Box-Behnken cube containing no preservative ingredient. The preservative efficacies were evaluated against the USP and EP criteria for formulations for oral use, as well as by the statistical comparison of the slopes obtained by linear regression of the log of CFU/g versus time. The peroxide values were determined after two months storage at 50 degrees C, using the EP titrimetric method. No interactions between the preservatives were observed for any of the seven tested micro-organisms in the PETs. BA had a very significant preservative effect against several of the tested microorganisms, while no antimicrobial effect for BHT and BHA was observed. Aspergillus niger was the most preservative-resistant micro-organism, while Staphylococcus aureus was the most sensitive test-germ. Compliance with USP-PET criteria was found for all formulations tested, even those without preservatives, while the EP-PET criteria showed compliance for those formulations with the highest BA concentration only. Stored in glass vials, a statistically significant antioxidant effect was demonstrated for BA only, although all tested formulations showed acceptable anti-oxidative properties. No significant antioxidant effects were shown for BHT or BHA.

Abstract  The mechanisms involved in the effect of ethanol on Ca2+ entry and aggregability have been investigated in human platelets in order to shed new light on the pathogenesis of alcohol consumption. Ethanol (50 mM) induced H2O2 production in platelets by Ca2+-dependent and independent mechanisms. Ca2+ entry induced by ethanol was impaired by catalase. Ethanol reduced SOCE mediated by depletion of the 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-sensitive acidic stores but enhances SOCE regulated by the dense tubular system. This effect was abolished by treatment with catalase or the sulphydryl group reducing agent dithiotreitol (DTT). Similarly, the anti-aggregant effect of ethanol was prevented by platelet treatment with catalase or DTT. In conclusion we provide considerable evidence that ethanol alters Ca2+ entry and reduces thrombin-induced aggregation as a result of the generation of H2O2 and the oxidation of sulphydryl groups in human platelets.

Abstract  This study characterizes the ozonation of the azo dye Cationic Red X-GRL in the presence of TBA (tert-butyl alcohol), a scavenger of hydroxyl radical, in a bubble column reactor. Effects of oxygen flow rate, temperature, initial dye concentration, and pH were investigated through a series of batch tests. Generally, enhancing oxygen flow rate enhanced the removal of dye. However, there was a minimum removal of dye at temperature 298 K. Increasing or decreasing temperature enhanced the degradation of dye. Increasing the initial dye concentration decreased the removal of dye while the ozonation rate increased. The rate constants and the kinetic regime of the reaction between ozone and dye were obtained by fitting the experimental data to a kinetics model based on a second order overall reaction, first order with respect to both ozone and dye. The Hatta numbers of the reactions were between 0.039 and 0.083, which indicated that the reaction occurred in the liquid bulk. The direct oxidation rate constant k(D) was correlated with temperature by a modified Arrhenius Equation with an activation energy E(a) of 15.538 kJ mol(-1).

Abstract  Standard molecular dynamics simulations have been carried out on pure alcohols and alcohol/water mixtures. A simple atom-atom force field consisting of Lennard-Jones potentials plus coulombic terms over atomic point charges, but without explicit polarization terms, has been specifically fitted to reproduce several experimental properties of the pure alcohols, and has been used for mixtures by developing combination rules with the TIP3P water model. Densities, enthalpies of vaporization, radial distribution functions, self-diffusion coefficients, and rotational correlation functions of the pure alcohols are well reproduced and compare favorably with those from more sophisticated force fields. Some key aspects of the phase behaviour are correctly reproduced by the molecular dynamics simulation, showing a distinct demixing process for the n-butanol/water mixture as opposed to the stability of the t-butanol/water mixtures. The results demonstrate the ability of a molecular dynamics simulation, even in its standard form and with easily accessible time ranges, but with a carefully optimized force field, to simulate and, to a certain extent, predict the properties of binary mixtures.

Abstract  Contamination of groundwater with the gasoline additive methyl tert-butyl ether (MTBE) is often accompanied by many aromatic components such as benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene (BTEX). In this study, a laboratory-scale biotrickling filter for groundwater treatment inoculated with a microbial consortium degrading MTBE was studied. Individual or mixtures of BTEX compounds were transiently loaded in combination with MTBE. The results indicated that single BTEX compound or BTEX mixtures inhibited MTBE degradation to varying degrees, but none of them completely repressed the metabolic degradation in the biotrickling filter. Tert-butyl alcohol (TBA), a frequent co-contaminant of MTBE had no inhibitory effect on MTBE degradation. The bacterial consortium was stable and showed promising capabilities to remove TBA, ethylbenzene and toluene, and partially degraded benzene and xylenes without significant lag time. The study suggests that it is feasible to deploy a mixed bacterial consortia to degrade MTBE, BTEX and TBA at the same time.

Abstract  The purpose of this prospective study was to evaluate the clinical performance of a new restorative material (Ceram.X) in combination with a new primer-adhesive (K-0127). One operator placed two Class I or II restorations in molars of 43 patients. One molar was restored with Ceram.X/K-0127, the other one with Tetric Ceram/Syntac Classic. At baseline, after 1 and 2 years, the restorations were evaluated by one evaluator using modified Ryge's criteria. After 2 years, 31 patients were examined. One Ceram.X-restoration had to be removed for root canal treatment due to pulpitis. Thus, failure rate of Ceram.X was 3.2% and of Tetric Ceram, 0%. In both groups, no sensitivity, no recurrent caries, and no changes in surface texture were recorded after 2 years. One restoration in each group showed slight changes in color stability (score B). Marginal discoloration (score B) was found concerning three Ceram.X-restorations (10.0%) and two Tetric Ceram-restoration (6.5%). Marginal integrity was score B for four Ceram.X-restorations (13.3%) and for four Tetric Ceram-restorations (12.9%). No statistically significant differences were found (p>0.05). After 2 years of clinical service, 96.8% of Ceram.X/K-0127 and 100% of Tetric Ceram/Syntac Classic restorations were in place and performed clinically well.

Abstract  DFT calculations suggest that the catalytic epoxidation of olefins by Mo(vi) complexes, modeled by MoO2Br2(MeN=C(H)-C(H)=NMe), in the presence of MeOOH, the model for tert-butyl hydroperoxide, starts with a hydrogen transfer from the peroxide to one of the terminal Mo=O oxygen atoms and the remaining MeOO anion binds as a seventh ligand, forming a five-membered Mo-O(alpha)-O(beta)(Me)...H-O-Mo ring held together by a hydrogen bond. In the second step, a concerted approach of ethylene to the Mo-O(alpha) bond gives rise to an intermediate containing a seven-membered Mo-C-C-O(alpha)-O(beta)(Me)...H-O-Mo ring. In the final step, decomposition of the intermediate leads to the starting complex, alcohol and the epoxide. The activation energy for the addition of the olefin (second step) is the highest one, in agreement with available kinetic studies showing that the catalyst formation is not always a rate-limiting step. DFT calculations also show that the alcohol by-product (MeOH) can react with the starting complex, competing with ROOH and hence leading to the progressive catalyst poisoning, which has been observed experimentally.

Abstract  A series of model theoretical calculations are described that suggest a new mechanism for the oxidation step in enzymatic cytochrome P450 hydroxylation of saturated hydrocarbons. A new class of metastable metal hydroperoxides is described that involves the rearrangement of the ground-state metal hydroperoxide to its inverted isomeric form with a hydroxyl radical hydrogen bonded to the metal oxide (MO-OH --> MO....HO). The activation energy for this somersault motion of the FeO-OH group is 20.3 kcal/mol for the P450 model porphyrin iron(III) hydroperoxide [Por(SH)Fe(III)-OOH(-)] to produce the isomeric ferryl oxygen hydrogen bonded to an *OH radical [Por(SH)Fe(III)-O....HO(-)]. This isomeric metastable hydroperoxide, the proposed primary oxidant in the P450 hydroxylation reaction, is calculated to be 17.8 kcal/mol higher in energy than the ground-state iron(III) hydroperoxide Cpd 0. The first step of the proposed mechanism for isobutane oxidation is abstraction of a hydrogen atom from the C-H bond of isobutane by the hydrogen-bonded hydroxyl radical to produce a water molecule strongly hydrogen bonded to anionic Cpd II. The hydroxylation step involves a concerted but nonsynchronous transfer of a hydrogen atom from this newly formed, bound, water molecule to the ferryl oxygen with a concomitant rebound of the incipient *OH radical to the carbon radical of isobutane to produce the C-O bond of the final product, tert-butyl alcohol. The TS for the oxygen rebound step is 2 kcal/mol lower in energy than the hydrogen abstraction TS (DeltaE() = 19.5 kcal/mol). The overall proposed new mechanism is consistent with a lot of the ancillary experimental data for this enzymatic hydroxylation reaction.

Abstract  The development of a new hybrid (QM/MM) method, where the QM part is treated by ab initio valence bond (VB) theory is presented. This VB/MM method has the advantages of empirical VB (EVB) methodology but does not rely on empirical parameterization for the quantum part. The method implements embedding of the quantum region of each diabatic state separately, by treating the electrostatic interactions between QM and MM regions classically. Additionally, it assumes that changes of the off diagonal matrix element due to different environments are such that the overall resonance integral does not change. These assumptions are discussed in detail and the validity of the method is shown to be successful in three different bond dissociation processes, where bond dissociation as well as solvation energies compare very well with the experimental data.

Abstract  The relaxation of electronic spins S of paramagnetic species is studied by the field-dependence of the longitudinal, transverse, and longitudinal in the rotating frame relaxation rates R1, R2, and R1rho of nuclear spins I carried by dissolved probe solutes. The method rests on the model-independent low-frequency dispersions of the outer-sphere (OS) paramagnetic relaxation enhancement (PRE) of these rates due to the three-dimensional relative diffusion of the complex with respect to the probe solute. We propose simple analytical formulas to calculate these enhancements in terms of the relative diffusion coefficient D, the longitudinal electronic relaxation time T1e, and the time integral of the time correlation function of the I-S dipolar magnetic interaction. In the domain of vanishing magnetic field, these parameters can be derived from the low-frequency dispersion of R1 thanks to sensitivity improvements of fast field-cycling nuclear relaxometers. At medium field, we present various approaches to obtain these parameters by combining the rates R1, R2, and R1rho. The method is illustrated by a careful study of the proton PREs of deuterated water HOD, methanol CH3OD, and tert-butyl alcohol (CH3)3COD in heavy water in the presence of a recently reported nonacoordinate Gd(III) complex. The exceptionally slow electronic relaxation of the Gd(III) spin in this complex is confirmed and used to test the accuracy of the method through the self-consistency of the low- and medium-field results. The study of molecular diffusion at a few nanometer scale and of the electronic spin relaxation of other complexed metal ions is discussed.

Abstract  Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.

Abstract  The purpose of this work is to investigate the freezing properties of tertiary butyl alcohol (TBA)/sucrose/water ternary system. Differential scanning calorimetry (DSC) is employed to determine the glass transition temperature of the maximally freeze-concentrated solution Tg' and the crystallization (or devitrification) temperature Tr. DSC measurements show that the presence of sucrose hinders the crystallization of TBA during cooling. The residual TBA in the glassy state will cause a decrease in Tg' and will crystallize during heating. An increase in the cooling rate causes a decrease in Tg'. For 10% TBA/10% sucrose/water ternary system, the critical heating rate is approximately 250 degrees C/min. Annealing treatment at temperatures below Tg' causes the crystallization of TBA, which indicates that TBA molecules still have appreciable mobility even at temperatures below Tg'. When the ratio of TBA to sucrose is less than 0.2, TBA cannot crystallize during cooling.

Abstract  ANG II stimulates phospholipase D (PLD) activity and growth of vascular smooth muscle cells (VSMC). The atypical protein kinase C-zeta (PKCzeta) plays a central role in the regulation of cell survival and proliferation. This study was conducted to determine the relationship between ANG II-induced activation of PKCzeta and PLD and their implication in VSMC adhesion, spreading, and hypertrophy. ANG II stimulated PKCzeta activity with maximal activation at 30 s followed by a decline in its activity to 45% above basal at 5 min. Inhibition of PKCzeta activity with a myristoylated pseudosubstrate peptide or overexpression of a kinase-inactive form of PKCzeta decreased ANG II-induced PLD activity. Moreover, depletion of PKCzeta with selective antisense oligonucleotides also decreased ANG II-induced PLD activity. Interaction between PLD2 and PKCzeta in VSMC was detected by coimmunoprecipitation. ANG II-induced PLD activity was inhibited by the primary alcohol n-butanol but not the tertiary alcohol t-butanol. The functional significance of PKCzeta and PLD2 in VSMC adhesion, spreading, and hypertrophy was investigated. Inhibition of PKCzeta and PLD2 activity or expression attenuated VSMC adhesion to collagen I and ANG II-induced cell spreading and hypertrophy. These results demonstrate that ANG II-induced PLD activation is regulated by PKCzeta and suggest a crucial role of PKCzeta-dependent PLD2 in VSMC functions such as adhesion, spreading, and hypertrophy, which are associated with the pathogenesis of atherosclerosis and malignant hypertension.

Abstract  A new Mycobacterium austroafricanum strain, IFP 2015, growing on methyl tert-butyl ether (MTBE) as a sole carbon source was isolated from an MTBE-degrading microcosm inoculated with drain water of an MTBE-supplemented gasoline storage tank. M. austroafricanum IFP 2015 was able to grow on tert-butyl formate, tert-butyl alcohol (TBA) and alpha-hydroxyisobutyrate. 2-Methyl-1,2-propanediol was identified as the TBA oxidation product in M. austroafricanum IFP 2015 and in the previously isolated M. austroafricanum IFP 2012. M. austroafricanum IFP 2015 also degraded ethyl tert-butyl ether more rapidly than M. austroafricanum IFP 2012. Specific primers designed to monitor the presence of M. austroafricanum strains could be used as molecular tools to detect similar strains in MTBE-contaminated environment.

Abstract  Methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was chemically regenerated utilizing the Fenton mechanism. Two successive GAC regeneration cycles were performed involving iterative adsorption and oxidation processes: MTBE was adsorbed to the GAC, oxidized, re-adsorbed, oxidized, and finally re-adsorbed. Oxidant solutions comprised of hydrogen peroxide (H2O2) (1.7-2.0%) and FeSO4 x 7H2O (3 g/L) (pH 2.5), were recirculated through the GAC column (30% bed expansion). The regeneration efficiency after two full cycles of treatment was calculated to be 91%. The cost of H2O2 was 0.59 dollars/kg GAC (0.27 dollars/lb) per regeneration cycle. There was no loss of sorptive capacity. Small reductions in carbon surface area and pore volume were measured. The lack of carbon deterioration under aggressive oxidative conditions was attributed to the oxidation of the target contaminants relative to the oxidation of carbon surfaces. The reaction byproducts from MTBE oxidation, tertiary butanol and acetone, were also degraded and did not accumulate significantly on the GAC. Excessive accumulation of Fe on the GAC and consequent interference with MTBE sorption and carbon regeneration was controlled by monitoring and adjusting Fe in the oxidative solution.

Abstract  The effect of pH on MnO(x)/GAC heterogeneous catalytic ozonation was investigated. Nitrobenzene was used as a model refractory organic pollutant. It was found that in MnO(x)/GAC catalytic ozonation, the degradation efficiency of nitrobenzene was higher under low pH conditions (pH 2.74-3.52) than that under high pH conditions (pH 6.72-9.61). This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of nitrobenzene due to the formation of hydroxyl radical. In the presence of MnO(x)/GAC catalyst, ozone decomposition was accelerated, and higher pH condition favored ozone decomposition. It was assumed that hydroxyl radicals might not be the dominating active species in the catalytic oxidation, for the presence of t-butanol did not have any influence on MnO(x)/GAC heterogeneous catalytic ozonation. Adsorption of organic micropollutants on MnO(x)/GAC catalyst was an important step and would have direct influence on the effectiveness of catalytic oxidation. It was assumed that the organic pollutants might be further decomposed on the surface of catalyst.

Abstract  BACKGROUND: Ethanol inhibits proliferation in astrocytes, an effect that was recently linked to the suppression of phosphatidic acid (PA) formation by phospholipase D (PLD). The present study investigates ethanol's effect on the induction of apoptosis in astrocytes and the formation of ceramide, an apoptotic signal. Evidence is presented that the formation of PA and ceramide may be reciprocally linked during ethanol exposure.

RESULTS: In cultured rat cortical astrocytes, ethanol (0.3-1 %, v/v) induced nuclear fragmentation and DNA laddering indicative of apoptosis. Concomitantly, in cells prelabeled with [3H]-serine, ethanol caused a dose-dependent, biphasic increase of the [3H]-ceramide/[3H]-sphingomyelin ratio after 1 and 18 hours of incubation. As primary alcohols such as ethanol and 1-butanol were shown to inhibit the phospholipase D (PLD)-mediated formation of PA, a mitogenic lipid messenger, we tested their effects on ceramide formation. In astrocytes prelabeled with [3H]-serine, ethanol and 1-butanol, in contrast to t-butanol, significantly increased the formation of [3H]-ceramide. Moreover, exogenous PA, added to transiently permeabilized astrocytes, suppressed ethanol-induced [3H]-ceramide formation. Vice versa, addition of C2-ceramide to astrocytes inhibited PLD activity induced by serum or phorbol ester.

CONCLUSION: We propose that the formation of ceramide in ethanol-exposed astrocytes is secondary to the disruption of phospholipase D signaling. Ethanol reduces the PA:ceramide ratio in fetal astrocytes, a mechanism which likely participates in ethanol-induced glial apoptosis during brain development.

Abstract  The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of gamma-terpinene (TH) at 50 degrees C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO* as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and tert-butyl alcohol show that chain termination involves the formal HOO. + HOO. self-reaction over a wide range of gamma-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, T., with the HOO. radical under conditions of relatively high [TH] (140-1000 mM) and low [O2] (2.0-5.5 mM). This is because the formal HOO. + HOO. reaction is comparatively slow in acetonitrile (2k approximately 8 x 10(7) M(-1) s(-1)), whereas, this reaction is almost diffusion-controlled in tert-butyl alcohol and cyclohexane, 2k approximately 6.5 x 10(8) and 1.3 x 10(9) M(-1) s(-1), respectively. Three mechanisms for the bimolecular self-reaction of HOO. radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electron-transfer between HOO. and its conjugate base, the superoxide radical anion, O2-.. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is dependent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOO. + HOO. reaction (mechanism (1)) is about 1.8 x 10(9) M(-1) s(-1) but in water at pH< or =2 where the ionization of HOO. is completely suppressed, this rate constant is only 8.6 x 10(5) M(-1) s(-1). The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham's HB acceptor parameter, beta(2)(H), for water of 0.38 and an estimated HB donor parameter, alpha(2)(H), for HOO. of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOO. + HOO. reaction in water at 25 degrees C of 1.2 x 10(6) M(-1) s(-1) in excellent agreement with experiment.