Correlation between the fluorescent response of microfluidity probes and the water content and viscosity of ionic liquid and water mixtures

Accurate data on transport properties such as viscosity are essential in plant and process design involving ionic liquids. In this study, we determined the absolute viscosity of the ionic liquid + water system at water mole fractions from 0 to 0.25 for three 1-alkyl-3-methylimidazolium ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide and 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide. In each case, the excimer to monomer ratio for 1,m-bis(1-pyrenyl)alkanes (m= 3 or 10) was found to increase linearly with the mole fraction of water. Of the probes studied only PRODAN and rhodamine 6G, both of which have the ability to participate in hydrogen bonding, exhibited Perrin hydrodynamic behavior in the lower viscosity bis(trifluoromethane sulfonyl)imides. As a result, these probes allow for the extrapolation of the absolute viscosity of the ionic liquid mixture from the experimental fluorescence steady-state polarization values.     

Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

Strategy of analysis for the estimation of the bioavailability of zinc in foodstuffs

After the application of simulated digestive fluids (gastric and intestinale fluid) as extraction solutions, AAS and differential pulse anodic-stripping voltammetry (DPASV) were used as analytical methods in combination with ion-exchange procedures for the determination of zinc species and total zinc contents. The ion exchange procedure and the shifting of electrochemical potentials as well as changes of the calibration slope after standard addition in the polarographic analysis allowed discriminating statements with regard to a possible resorption of zinc. On the basis of these methods, a strategy is presented for in vitro investigations of the bioavailability of zinc in foodstuffs.     

A systematic nomenclature for cascade polymers

Cascade (dendritic) polymers are discrete, highly branched, monodisperse polymers that possess branching patterns described by a mathematical progression. A systematic nomenclature that accurately represents these molecules is described. © 1993 John Wiley & Sons, Inc.     

Sequential claisen and cope rearrangement for formation of 3-(-1-methylethyl)-substituted α,β-unsaturated aldehydes

3-(1-Methylethyl)-7-methyl2,6-octadienal, was prepared from 1,1,3-triethoxy-3,4-dimethylpentane and 3-methyl-2-buten-l-ol in a one-pot procedure utilising Claisen and Cope rearrangement of an intermediate dienol-allyl ether.     

Reactive intermediates in asymmetric cross-coupling catalysed by palladium P-N chelates

The palladium dibromide complexes of (S,R)-(1,1′-bis-diphenylphosphino)-2-ferrocencylthyldimethylamine and (S,R)-(1-diphenylphosphino)-2-ferrocenylethyldimethylamine have been reduced with dilithiocyclooctatetraene to form the corresponding Pd⁰ cyclooctatetraene complexes. Their reactions with E-4-methoxy-2′-bromophenylethene, and then benzylmagnesium chloride at −60 to −30°C, provide information on the structure of intermediates in asymmetric cross-coupling.     

On the origin of optical activity in tris-diamine complexes of Co(III) and Rh(III): a simple model based on time-dependent density function theory

Time-dependent density functional theory (TD-DFT) is applied to the CD spectra of Lambda(deltadeltadelta)-(+)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Lambda(deltadeltadelta)-(+)-[Co(en)3]3+ as well as the stereoisomers Delta-((delta)n(lambda)(3-n))-(-)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Delta(deltadeltadelta)-(-)-[Co(en)3]3+. Theory is able to reproduce the major differences in the CD spectra of the species with a Lambda-configuration and their isomers with a Delta-configuration in both the d-d and ligand-to-metal CT region. It is further possible to rationalize the trend in terms of a larger azimuthal distortion away from the octahedral geometry in the Lambda-conformation compared to the Delta-configuration. Considerations were also given to the CD spectra of the lel3-isomer, Delta(lambdalambdalambda)-(-)-[Rh(R-pn)3]3+ and the ob-isomer, Lambda(lambdalambdalambda)-(+)-[Rh(S-pn)3]3+.     

Synthesis of pyranosyl amidoximes by addition of amines to pyranosyl nitrile oxides

Addition of amines to pyranosyl nitrile oxides, generated by base-induced dehydrochlorination of the corresponding hydroximoyl chloride, affords pyranosyl N-alkyl/aryl-formamide oximes (41-90%). Reaction with amino acid esters yields the corresponding amidoximes and/or 3-pyranosyl-1,2,4-oxadiazin-6-ones. The structure of N-phenyl-C-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)formamide oxime was established by X-ray crystallography.     

Conformational mobility of thianthrene-5-oxide

[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures confirm that the relative position of the conformational equilibrium of 1 is solvent-dependent, and more polar solvents favor the conformation with the sulfoxide group in the pseudoaxial position (1(')(ax)). Variable-temperature (1)H NMR spectra have established the interconversion barrier of trans-2 and confirmed that the conformational equilibrium of cis-2 is strongly displaced toward the conformation with both sulfinyl groups in the pseudoequatorial position. The (1)H NMR data support the transannular interaction of the functional groups in 1 and trans-2.     

An ultrasensitive method for the determination of thiouracil and phenylthiouracil using capillary zone electrophoresis and laser-induced fluorescence detection

This paper reports the development of a method based on capillary electrophoresis with laser-induced fluorescence detection for the simultaneous determination of thiouracil (TU) and phenylthiouracil (PhTU) with high sensitivity (nanomolar range, i.e., attomoles detected). After derivatization with 5-iodoacetamidofluorescein, the analytes were separated by capillary zone electrophoresis using 20 mM phosphate buffer (pH 10.0) and quantified by fluorescence detection. The linearity range, precision, recovery, and detection limits were determined, and the method was shown to be applicable for the determination of TU and PhTU in spiked feed samples and urine.