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951.
Toon Verstraelen Bartłomiej M. Szyja David Lesthaeghe Reinout Declerck Veronique Van Speybroeck Michel Waroquier Antonius P. J. Jansen Alexander Aerts Lana R. A. Follens Johan A. Martens Christine E. A. Kirschhock Rutger A. van Santen 《Topics in Catalysis》2009,52(9):1261-1271
Zeolite synthesis is driven by structure-directing agents, such as tetrapropyl ammonium ions (TPA+) for Silicalite-1 and ZSM-5. However, the guiding role of these organic templates in the complex assembly to highly ordered
frameworks remains unclear, limiting the prospects for advanced material synthesis. In this work, both static ab initio and
dynamic classical modeling techniques are employed to provide insight into the interactions between TPA+ and Silicalite-1 precursors. We find that as soon as the typical straight 10-ring channel of Silicalite-1 or ZSM-5 is formed
from smaller oligomers, the TPA+ template is partially squeezed out of the resulting cavity. Partial retention of the template in the cavity is, however,
indispensable to prevent collapse of the channel and subsequent hydrolysis.
相似文献
Rutger A. van Santen (Corresponding author)Email: |
952.
Transformation of Free and Dipeptide‐Bound Glycated Amino Acids by Two Strains of Saccharomyces cerevisiae
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Dr. Michael Hellwig Marie Börner Falco Beer Prof. Dr. Karl‐Heinz van Pée Prof. Dr. Thomas Henle 《Chembiochem : a European journal of chemical biology》2017,18(3):266-275
The yeast Saccharomyces cerevisiae transforms branched‐chain and aromatic amino acids into higher alcohols in the Ehrlich pathway. During microbiological culturing and industrial fermentations, this yeast is confronted with amino acids modified by reducing sugars in the Maillard reaction (glycation). In order to gain some preliminary insight into the physiological “handling” of glycated amino acids by yeasts, individual Maillard reaction products (MRPs: fructosyllysine, carboxymethyllysine, pyrraline, formyline, maltosine, methylglyoxal‐derived hydroimidazolone) were administered to two strains of S. cerevisiae in a rich medium. Only formyline was converted into the corresponding α‐hydroxy acid, to a small extent (10 %). Dipeptide‐bound pyrraline and maltosine were removed from the medium with concomitant emergence of several metabolites. Pyrraline was mainly converted into the corresponding Ehrlich alcohol (20–60 %) and maltosine into the corresponding α‐hydroxy acid (40–60 %). Five specific metabolites of glycated amino acids were synthesized and characterized. We show for the first time that S. cerevisiae can use glycated amino acids as a nitrogen source and transform them into new metabolites, provided that the substances can be transported across the cell membrane. 相似文献
953.
954.
The removal of cadmium by anion exchange from 55 w% H3PO4 (black acid from a Nissan H process) at 90°C in the presence of small amounts of halides (Cl-, Br-, I-) was investigated. Cadmium distribution coefficients, [CD]resin/[CD]acid (concentrations in mol/1), larger than 250 were obtained with HBr equilibrium concentrations of more than 0.10 w% in the phosphoric acid solution or with HI concentrations of more than 150 ppm. The regeneration of the Cd loaded resin was performed with a very dilute phosphoric acid solution (< 1 w% H3PO4). The excess of iodide in the phosphoric acid solution could also be- removed by anion exchange. A value of about 90 was obtained for the iodide distribution coefficient of a weakly basic resin. This resin could be regenerated with an 1 M NH3 solution at 50°C. The rate of adsorption and desorption of both cadmium and iodide were mainly determined by the diffusion in the resin|particle. Effective diffusivities of about 3*10-13 mZ/s and 1.3*10-11mZ/s were obtained for the adsorption of cadmium in the presence of HI and for the adsorption of iodide respectively. 相似文献
955.
The mechanism of damage occurring in NaCl contaminated materials has not been clarified yet. Apart from crystallization pressure, other hypotheses have been proposed to explain the cause of decay. Irreversible dilation has been observed in a few cases but has never been studied in a more systematic way. The aim of the research is to contribute to the modeling of this phenomenon.In the present paper the effect of NaCl on the hydric and hygric behavior of a lime-cement mortar is extensively studied. The results indicate that NaCl influences the hydric and hygric dilation behavior of the material. The material contaminated with NaCl shrinks during dissolution and dilates during crystallization of the salt. This dilation is irreversible and sufficient to damage the material after few dissolution/crystallization cycles. This behavior is not restricted to NaCl, but is observed in the presence of other salts as well (NaNO3 and KCl). Outcomes of electron microscopy studies suggest that salts causing irreversible dilation tend to crystallize as layers on the pore wall. 相似文献
956.
957.
J. van de Loosdrecht A. M. van der Kraan A. J. van Dillen J. W. Geus 《Catalysis Letters》1996,41(1-2):27-34
The influence of the titania support and metal particle size on the performance of nickel-iron catalysts in the Fischer-Tropsch synthesis has been studied by varying the nickel-iron loading and, consequently, varying the nickel-iron particle size. Low-loaded titania-supported nickel-iron catalysts (2 wt%) turned out to be more selective towards higher hydrocarbons than high-loaded nickel-iron catalysts (20 wt%), which produce much more methane. From temperature-programmed hydrogenation experiments, magnetic measurements and Mössbauer spectroscopy it followed that different types of carbon are present on the catalysts depending on the metal loading. These types of carbon could be related to the selectivity in Fischer-Tropsch synthesis and to the deactivation of the catalysts with time on stream. These differences in catalytic behaviour are most likely due to the presence of TiO
x
species on the surface of the active phase, which species decrease the CO and H2 adsorption properties of the catalyst, but increase the dissociation of CO. 相似文献
958.
Quantitative Fourier transform infrared analysis for anisidine value and aldehydes in thermally stressed oils 总被引:5,自引:0,他引:5
J. Dubois F. R. van de Voort J. Sedman A. A. Ismail H. R. Ramaswamy 《Journal of the American Oil Chemists' Society》1996,73(6):787-794
A Fourier transform infrared (FTIR) transmission-based spectroscopic method was investigated for the simultaneous monitoring
of aldehyde formation and the determination of anisidine value (AV) in thermally stressed oils. Synthetic calibration standards
were prepared by adding known amounts of hexanal,t-2-hexenal andt,t-2,4-decadienal to canola oil (these compounds considered representative of aldehydic compounds formed during oxidation) plus
random amounts of other compounds representative of oxidation by-products. The standards were analyzed for their chemical
AV. With the partial least squares (PLS) technique, an FTIR spectrometer was calibrated to predict both the concentrations
of individual aldehyde types and AV, with the individual aldehyde contributions being related to the chemical AV by multiple
linear regression to derive “apparent” AV values. The predictive capability of the PLS calibrations was assessed by analyzing
canola oils that were thermally stressed at 120, 155, and 200°C. The apparent AV, predicted for these samples, matched the
chemical AV values within ±1.65 AV units. A PLS calibration also was derived by using thermally stressed samples as calibration
standards. This approach provided similar predictive accuracy as the use of synthetic calibration standards. As such, quantitative
determination of AV by FTIR spectroscopy was shown to be feasible, and the synthetic calibration approach provided additional
information on the aldehyde types present in a sample and allowed the use of a simple gravimetric approach for calibrating
an FTIR spectrometer. This study provides the basis for the development of a rapid, automated FTIR method for the direct analysis
for AV of thermally stressed fats and oils in their neat form without the use of chemical reagents. The implementation of
such a method as a quality control tool would eliminate the use and disposal of hazardous solvents and reagents, required
by the conventional chemical method, and drastically reduce analysis time (∼2 min/sample). Possible applications include monitoring
of the oxidative state of frying oils or evaluation of oxidative stability of biodegradable lubricants. 相似文献
959.
F. R. van de Voort J. Sedman G. Emo A. A. Ismail 《Journal of the American Oil Chemists' Society》1992,69(11):1118-1123
A simple, rapid and reproducible method of determining the iodine value (IV) and saponification number (SN) for fats and oils
was developed with an attenuated total reflectance/Fourier transform infrared spectrometer and commercially available triglycerides
as calibration standards. Partial least squares was used to determine the spectral regions correlating with the known chemical
IV and SN values, and the calibration set was augmented with additional standards generated by spectral co-adding techniques.
The calibration model obtained was used to analyze commercially available fats and oils with a wide range of IV and SN values,
and the results were compared to the values obtained by American Oil Chemists’ Society methods. With the spectrometer calibrated
and programmed, IV and SN results could be obtained within 2–3 min per sample, a major improvement over conventional wet chemical
methods. 相似文献
960.
I.D. Gunbas M.E.L. Wouters R.A.T.M. van Benthem C.E. Koning B.A.J. Noordover 《Progress in Organic Coatings》2013
In this work, two series of PDMS-modified poly(styrene-alt-maleic anhydride)s (PSMA) were prepared by the partial imidization of their anhydride groups with mono-functional, amine-terminated polydimethyl siloxanes (PDMS-NH2) with two different molecular weights. Subsequently, surfactant-free artificial latexes were prepared and characterized and applied onto cotton fabric. The water contact angle values of the coated cotton fabric indicate the formation of hydrophobic surfaces, with static contact angles varying from 119° to 142° depending on the PDMS loading and PDMS molecular weight. Coatings of the prepared copolymers on cotton fabric are highly durable, as shown by washing studies with a standard soap solution. The properties of these water-based surfactant-free latexes can be tuned easily by changing the composition of the polymers, i.e. mol% of imidization, ammonolysis and cross-linking. 相似文献