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Gel/Solvent Combinations (solvent + combination)

Distribution by Scientific Domains

Chemistry	85%

Selected Abstracts

Tunable Alignment for All Polymer Gel/Solvent Combinations for the Measurement of Anisotropic NMR Parameters

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2010
Grit Kummerlöwe M.
A stretching apparatus (see figure) with arbitrary scalability of alignment strength is introduced for the measurement of anisotropic NMR parameters, which works for practically all polymer gel/solvent combinations. Its use is demonstrated in applications involving the steady incrimination of residual dipolar couplings, the distinction of enantiomers, and the conformational analysis of organic compounds. [source]

Catalytic Hydrogenation of Cyanohydrin Esters as a Novel Approach to N -Acylated ,-Amino Alcohols , Reaction Optimisation by a Design of Experiment Approach

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2006
Lars Veum
Abstract The catalytic hydrogenation of acylated cyanohydrins and subsequent intramolecular migration of the acyl group to yield pharmaceutically interesting N -acyl ,-amino alcohols is shown to be a successful one-pot preparation method. The combination of a multistep DoE approach and high-throughput methodology proved to be an effective strategy for the optimisation of the reaction. With the favoured catalyst/solvent combination of nickel on alumina in dioxane, both hydrogenation and acyl group migration proceeded smoothly, giving the N -acyl ,-amino alcohols in yields (determined by GC) of up to 90,% for aliphatic substrates and up to 50,% for benzylic ones, the latter being more prone to side reactions. No racemisation was found to occur at the chiral centre of an aliphatic molecule when an enantiopure cyanohydrin ester was used, though a minor decrease in ee was observed with a benzylic substrate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Tunable Alignment for All Polymer Gel/Solvent Combinations for the Measurement of Anisotropic NMR Parameters

Kinetics of the Solvolyses of Fluoro-Substituted Benzhydryl Derivatives: Reference Electrofuges for the Development of a Comprehensive Nucleofugality Scale

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2010
Christoph Nolte
Abstract A series of m -fluoro-substituted benzhydryl chlorides, bromides, mesylates, and tosylates 1 -X to 5 -X were prepared and subjected to solvolysis reactions in various solvents. The observed first-order rate constants ks(25 °C) were found to follow the correlation equation log,ks(25 °C) = sf(Nf + Ef), which allowed us to determine the electrofugality parameters Ef for these destabilized benzhydrylium cations and the nucleofugality parameters Nf, sf for a series of leaving group/solvent combinations. [source]

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of partially depolymerised methyl cellulose

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2003
Dane Momcilovic
Methyl cellulose (MC) was partially depolymerised and the oligomers thus obtained were studied by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS). The depolymerisation was either enzymatic or acidic. Fractions of enzymatically depolymerised MC were collected from size-exclusion chromatography and subjected to a sample preparation investigation. Several MALDI matrices and solvents were evaluated. The results showed that the solvent choice had a significant effect on the measured degree of substitution (DS). Aprotic solvents produced higher DS values, which was most likely due to poor solubility of species with low DS. The obtained signal intensity, however, did not correlate with the solubility but seemed to be more dependent on certain matrix/solvent combinations. All the matrices attempted produced mass spectra with sufficient signal intensity for accurate peak area calculation. The choice of matrix did not have any significant effect on the measured DS. Sample spots obtained from organic solvents had a more homogeneous distribution of the analyte and smaller crystals than those obtained from water. This increased both the reproducibility and peak resolution and in addition the analysis time was shorter. DS measurements were performed on two acidically depolymerised MCs with different nominal DS values. It was easy to distinguish between the two MCs, and the measured DS values agreed well with the values supplied by the manufacturers. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Safety and quality of plastic food contact materials.

PACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2003
Optimization of extraction time, based on arithmetic rules derived from mathematical description of diffusion., extraction yield
Abstract Migration of packaging constituents into food may raise concerns about food safety. This paper describes the conclusions of a EU research project (AIR 941025), aiming to facilitate the introduction of migration control into good manufacturing practice and into enforcement policies. The first part describes a re-evaluation of analytical approaches to extract and identify potential migrants released by plastic materials, viz. comparison of analytical methods, choice of extraction solvents and of fat simulants. Here we focus on the extraction time needed to achieve a given extraction yield. By correlating these parameters with simple and practical equations, it is possible to design alternative tests for control of compliance of packaging plastics. Using a reference experiment (where there is good agreement between experimental and calculated kinetic curves), it is possible to calculate the percentage of extraction which can be achieved in a given time, or the time necessary to reach a target extraction level for other polymer/solvent combinations. A global control scheme is proposed, which indicates whether and when calculation and testing should be applied. Guidelines are proposed, and can be adapted to both industrial control and to enforcement laboratories. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Purification of Fluorous Mitsunobu Reactions by Liquid-Liquid Extraction

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006
Dennis
Abstract Solvent tuning and partition coefficient measurements have identified suitable reagent and solvent combinations for the purification of fluorous Mitsunobu reaction products. The crude reaction mixtures are partitioned between 2/1 HFE-7100/FC-72 and DMF/10,% water to provide reagent (fluorous) and product (organic) fractions. [source]