Methanol-Assisted Autocatalysis in Catalytic Methanol Synthesis.

Catalytic methanol synthesis is one of the major processes in the chemical industry and may grow in importance, as methanol produced from CO2 and sustainably derived H2 are envisioned to play an important role as energy carriers in a future low-CO2 -emission society. However, despite the widespread use, the reaction mechanism and the nature of the active sites are not fully understood. Here we report that methanol synthesis at commercially applied conditions using the industrial Cu/ZnO/Al2 O3 catalyst is dominated by a methanol-assisted autocatalytic reaction mechanism. We propose that the presence of methanol enables the hydrogenation of surface formate via methyl formate. Autocatalytic acceleration of the reaction is also observed for Cu supported on SiO2 although with low absolute activity, but not for Cu/Al2 O3 catalysts. The results illustrate an important example of autocatalysis in heterogeneous catalysis and pave the way for further understanding, improvements, and process optimization of industrial methanol synthesis.

Thermal Cracking of Sugars for the Production of Glycolaldehyde and Other Small Oxygenates.

Thermal cracking of sugars for production of glycolaldehyde, a potential renewable platform molecule, in yields up to 74 % with up to 95 % carbon recovered in the condensed product is demonstrated using glucose as the feed. The process involves spraying an aqueous sugar solution into a fluidized bed of glass beads. Continuous operation is carried out for more than 90 h with complete conversion and stable product selectivity. Besides glycolaldehyde, the other identified condensed products are pyruvaldehyde (9 %), formaldehyde (7 %), glyoxal (2 %), acetol (2 %), and acetic acid (1 %). The effects of temperature, glucose feed concentration, and type of sugar feedstock are investigated. Cracking the monosaccharides fructose and xylose leads to very different product distributions from glucose, but similar carbon recovery. A reaction network in agreement with the main observed products from cracking of monosaccharide sugars is proposed.

Ketene as a Reaction Intermediate in the Carbonylation of Dimethyl Ether to Methyl Acetate over Mordenite.

Unprecedented insight into the carbonylation of dimethyl ether over Mordenite is provided through the identification of ketene (CH2CO) as a reaction intermediate. The formation of ketene is predicted by detailed DFT calculations and verified experimentally by the observation of doubly deuterated acetic acid (CH2DCOOD), when D2O is introduced in the feed during the carbonylation reaction.

Cell mass and cell cycle dynamics of an asynchronous budding yeast population: experimental observations, flow cytometry data analysis, and multi-scale modeling.

Despite traditionally regarded as identical, cells in a microbial cultivation present a distribution of phenotypic traits, forming a heterogeneous cell population. Moreover, the degree of heterogeneity is notably enhanced by changes in micro-environmental conditions. A major development in experimental single-cell studies has taken place in the last decades. It has however not been fully accompanied by similar contributions within data analysis and mathematical modeling. Indeed, literature reporting, for example, quantitative analyses of experimental single-cell observations and validation of model predictions for cell property distributions against experimental data is scarce. This study focuses on the experimental and mathematical description of the dynamics of cell size and cell cycle position distributions, of a population of Saccharomyces cerevisiae, in response to the substrate consumption observed during batch cultivation. The good agreement between the proposed multi-scale model (a population balance model [PBM] coupled to an unstructured model) and experimental data (both the overall physiology and cell size and cell cycle distributions) indicates that a mechanistic model is a suitable tool for describing the microbial population dynamics in a bioreactor. This study therefore contributes towards the understanding of the development of heterogeneous populations during microbial cultivations. More generally, it consists of a step towards a paradigm change in the study and description of cell cultivations, where average cell behaviors observed experimentally now are interpreted as a potential joint result of various co-existing single-cell behaviors, rather than a unique response common to all cells in the cultivation.

Evaluation of binary solvent mixtures for efficient monoacylglycerol production by continuous enzymatic glycerolysis.

This study was aimed at evaluating different binary solvent mixtures for efficient industrial monoacylglycerol (MAG) production by enzymatic glycerolysis. Of all investigated cases, the binary mixture of tert-butanol:tert-pentanol (TB:TP) 80:20 vol % was the most suitable organic medium for continuous enzymatic glycerolysis, ensuring high MAG formation in a short time, reasonable solvent price, and easy handling during distillation/condensation processing. A minimum solvent dosage of 44-54 wt % of the reaction mixture was necessary to achieve high MAG yields of 47-56 wt %, within 20 min. The melting and boiling points of the TB:TP mixture were estimated to be 7 and 85 degrees C, respectively, using thermodynamic models. These predictions were in good agreement with experimentally determined values. In spite of the high reaction efficiency in the binary TB:TP system, the mixture of glycerol and sunflower oil (containing 97.1% triacylglycerol) yielded surprisingly a liquid/liquid phase split behavior even at high temperatures (>80 degrees C). This in contrast to thermodynamic model calculations suggested full miscibility in all proportions. These findings suggest that enhanced reaction efficiency in organic solvent also depends upon aspects other than the system homogeneity such as reduced viscosity, reduced mass transfer limitations, and the accessibility of the substrate to the active site of the enzyme.

Thermal dissociation of SO3 at 1000-1400 K.

The thermal dissociation of SO3 has been studied for the first time in the 1000-1400 K range. The experiments were conducted in a laminar flow reactor at atmospheric pressure, with nitrogen as the bath gas. On the basis of the flow reactor data, a rate constant for SO3 + N2 --> SO2 + O + N2 (R1b) of 5.7 x 10(17) exp(-40000/T) cm3/(mol s) is derived for the temperature range 1273-1348 K. The estimated uncertainty is a factor of 2. The rate constant corresponds to a value of the reverse reaction of k1 approximately 1.8 x 10(15) cm6 mol(-2) s(-1). The reaction is in the fall-off region under the investigated conditions. The temperature and pressure dependence of SO2 + O (+N2) was estimated from the extrapolation of low temperature results for the reaction, together with an estimated broadening parameter and the high-pressure limit determined recently by Naidoo, Goumri, and Marshall (Proc. Combust. Inst. 2005, 30, 1219-1225). The theoretical rate constant is in good agreement with the experimental results. The improved accuracy in k(1) allows a reassessment of the rate constant for SO3 + O --> SO2 + O2 (R2) based on the data of Smith, Tseregounis, and Wang (Int. J. Chem. Kinet. 1982, 14, 679-697), who conducted experiments on a low-pressure CO/O2/Ar flame doped with SO2. At the location in the flame where the net SO3 formation rate is zero, k2 = k1[SO2][M]/[SO3]. A value of 6.9 x 10(10) cm3 mol(-1) s(-1) is obtained for k2 at 1269 K with an uncertainty a factor of 3. A recommended rate constant k2 = 7.8 x 10(11) exp(-3065/T) cm3 mol(-1) s(-1) is consistent with other flame results as well as the present flow reactor data.

Differential reactivity of alpha- and beta-anomers of glycosyl acceptors in glycosylations. A remote consequence of the endo-anomeric effect?

When phenyl tri-O-benzyl-1-thio-beta-D-galactopyranosiduronic acid esters were coupled with a 1/1 mixture of alpha and beta 2,3 di-O-protected D-galactopyranosiduronic acid esters, the beta-anomer proved to be more reactive. Data from theoretical calculations suggested that the enhanced reactivity of this anomer compared with the alpha one would be due to a stronger hydrogen bond of the C-4 OH with the ring oxygen.

Tandem mass spectrometric analysis of aspergillus niger pectin methylesterase: mode of action on fully methyl-esterified oligogalacturonates.

The substrate specificity and the mode of action of Aspergillus niger pectin methylesterase (PME) was determined using both fully methyl-esterified oligogalacturonates with degrees of polymerization (DP) 2-6 and chemically synthesized monomethyl trigalacturonates. The enzymic activity on the different substrates and a preliminary characterization of the reaction products were performed by using high-performance anion-exchange chromatography at neutral pH. Electrospray ionization tandem MS (ESI-MS/MS) was used to localize the methyl esters on the (18)O-labelled reaction products during the course of the enzymic reaction. A. niger PME is able to hydrolyse the methyl esters of fully methyl-esterified oligogalacturonates with DP 2, and preferentially hydrolyses the methyl esters located on the internal galacturonate residues, followed by hydrolysis of the methyl esters towards the reducing end. This PME is unable to hydrolyse the methyl ester of the galacturonate moiety at the non-reducing end.

Performance of selected microbial pectinases on synthetic monomethyl-esterified di- and trigalacturonates.

Two monomethyl esters of alpha-(1-4)-linked D-galacturonic dimers and three monomethyl esters of alpha-(1-4)-linked D-galacturonic acid trimers were synthesized chemically and further used as substrates in order to establish the substrate specificity of six different endopolygalacturonases from Aspergillus niger, one exopolygalacturonase from Aspergillus tubingensis, and four selected Erwinia chrysanthemi pectinases; exopolygalacturonan hydrolase X (PehX), exopolygalacturonate lyase X (PelX), exopectate lyase W (PelW), and oligogalacturonan lyase (Ogl). All A. niger endopolygalacturonases (PGs) were unable to hydrolyze the two monomethyldigalacturonates and 2-methyltrigalacturonate, whereas 1-methyltrigalacturonate was only cleaved by PGI, PGII, and PGB albeit at an extremely low rate. The hydrolysis of 3-methyltrigalacturonate into 2-methyldigalacturonate and galacturonate by all endopolygalacturonases demonstrates that these enzymes can accommodate a methylgalacturonate at subsite -2. The A. tubingensis exopolygalacturonase hydrolyzed the monomethyl-esterified digalacturonates and trigalacturonates although at lower rates than for the corresponding oligogalacturonates. 1-Methyltrigalacturonate was hydrolyzed at the same rate as trigalacturonate which demonstrates that the presence of a methyl ester at the third galacturonic acid from the nonreducing end does not have any effect on the performance of exopolygalacturonase. Of the four E. chrysanthemi pectinases, Ogl was the only enzyme able to cleave digalacturonate, whereas all four enzymes cleaved trigalacturonate. Ogl does not cleave monomethyl-esterified digalacturonate and trigalacturonate in case the second galacturonic acid residue from the reducing end is methyl-esterified. PehX did not hydrolyze any of the monomethyl-esterified trigalacturonates. The two lyases, PelX and PelW, were both only able to cleave 1-methyltrigalacturonate into Delta4,5-unsaturated 1-methyldigalacturonate and galacturonate.

Gynaecology, forced sterilisation, and asylum in the USA.

PIP: On September 30, 1996, the US Congress enacted a law to grant asylum protection to victims of forced sterilization, forced abortion, and other forms of coerced population control and to opponents of these practices. Before this time, the US Board of Immigration Appeals judged forced sterilization insufficient grounds for political asylum unless it was performed for some discriminatory reason. The authors of this article have examined five women who claimed they were forcibly sterilized in China and were granted political asylum in the US as a result. The average age of these women was 32 years, while the average duration since forced sterilization was 8.6 years. Since asylum applications are not filed according to cause, there are no estimates of the number of women seeking asylum in the US as a result of forced sterilization. The Chinese government claims it does not authorize forced sterilization, but local officials acknowledge it sometimes occurs. In many cases, sterilization is not formally coerced but required as a condition of employment. Consistency between the woman's claim of forced sterilization and medical or psychological reports is essential to the success of asylum applications. US physicians should be prepared to play a documentary role in the evaluation of such requests.^ieng

Synthesis of the two monomethyl esters of the disaccharide 4-O-alpha-D-galacturonosyl-D-galacturonic acid and of precursors for the preparation of higher oligomers methyl uronated in definite sequences.

Methyl (alpha-D-galactopyranosyluronic acid)-(1-->4)-D-galactopyranuronate and methyl alpha-D-galactopyranosyl-uronate-(1-->4)-D-galactopyranuronic acid have been synthesized by coupling methyl (benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate (3) or benzyl (benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate (4) with benzyl (phenyl 2,3,4-tri-O-benzyl-1-thio-beta-D-galactopyranosid)uronate and methyl (phenyl 2,3,4-tri-O-benzyl-1-thio-beta-D-galactopyranosid)uronate, respectively, using N-iodosuccinimide and trifluoromethanesulphonic acid as promoters, followed by removal of the benzyl groups. The 4'-OH unprotected dimers benzyl (methyl 2,3-di-O-benzyl-alpha-D-galactopyranosyluronate)-(1-->4)-(benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate and methyl (benzyl 2,3-di-O-benzyl-alpha-D-galactopyranosyluronate)-(1-->4)-(benzyl 2,3-di-O-benzyl-beta-D-galactopyranosid)uronate were prepared from methyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-beta-D-galactopyranosid) uronate and benzyl (phenyl 2,3-di-O-benzyl-1-thio-4-O-trimethylsilyl-beta-D-galactopyranosid) uronate and acceptors 4 or 3, respectively. These compounds have been designed to serve as precursors for the preparation of higher-membered D-galacturonic acid oligomers methyl esterified in definite positions.

Optical parametric amplifiers: a discrete dynamical model of singly resonant operation leading to a novel approach to the design of systems for high-efficiency amplification.

A simple plane-wave model of pulsed, singly resonant, optical-parametric-oscillator and optical-parametric-oscillator-amplifier operation leads to a description of such systems in terms of a discrete dynamical system. The theoretical limits on conversion efficiencies derivable from this model were explored. Analysis of the model for an optical parametric oscillator-amplifier (OPOA) indicates that the effect that backconversion has in limiting efficiency can be avoided if one precisely shapes the time profile of the pump pulse and combines it with an OPOA that is Q switched. For a case of type I phase matching with ß-barium borate with a specific pump profile and a 65-mJ input pulse, under the assumption of small absorption, the following are demonstrated: (l) the theoretical possibility of amplification to a few joules at quantum efficiencies higher than 90% and (2) the possibility of amplification to approximately 1 J at an energy efficiency near 45% in a configuration satisfying realistic stress constraints. Pulse widths are in the nanosecond range, and spot sizes are in the millimeter range. Issues of implementation are discussed.

Inducing properties of analogs of 2-keto-3-deoxygluconate on the expression of pectinase genes of Erwinia chrysanthemi.

In Erwinia chrysanthemi, all the genes involved in pectin degradation are controlled by the negative regulatory gene kdgR. 2-keto-3-deoxy-gluconate (KDG) is the inducing molecule that interacts with KdgR to allow the expression of all the genes of the kdg regulon. The inducing properties on the expression of genes regulated by kdgR of various analogs and derivatives of KDG were tested. All the inducers share the common moiety COOH-CO-CH2-CHOH-C-C included in a pyranic cycle. Our results show that esterification of C1 prevents induction. Presence of a ketone function on C2 and absence of hydroxyl on C3 are necessary for induction. The nature and the configuration of substituent on C5 has no influence on induction. Two compounds have interesting properties: 5-O-methyl-KDG is a gratuitous inducer, and gluconic acid can prevent induction.

Conception and realization of artificial dyed embryos for training in in vitro fertilization and embryo transfer (IVF and ET).

An artificial embryo model is proposed for current training in in vitro fertilization and embryo transfer. It consists in resin microballs of 180 micron diameter, stained either with fluoresceinamin or methylene blue. These microspheres release, even at the maximum dye concentrations tested, very negligible amounts of dye; heat stable they can be sterilized. This model, already checked for human embryo transfer, seems to be a useful tool in other reproduction studies such as embryo transport.

Bile acid sulfates in serum bile acids determination.

Some bile acid sulfates were synthesized and characterized. The configuration of sulfate groups at C-3, C-7 and C-12 positions was confirmed by Nuclear Magnetic Resonance analysis. These sulfates were utilized in a study of their chemical behaviour in different analytical procedures currently used for serum bile acids determination. Procedures for bile acids extraction from serum with ethanol or Amberlite XAD-2 result in an important loss of the most polar sulfated bile acids. Complete separation of unsulfated from sulfated bile acids on Sephadex LH-20 is not achieved when deconjugation of the most polar bile acid sulfate is slow but does not produce artifacts. Enzymatic determination of bile acids gives positive response with some bile acid sulfates. The current procedures of serum bile acids determination are discussed in consideration of these results.