Chiral separation of bupivacaine enantiomers by capillary electrophoresis partial-filling technique with human serum albumin as chiral selector

Capillary electrophoresis (CE) is a powerful technique for enantiomer separations due to its intrinsic high separation efficiencies, speed of analysis, low reagent consumption and small sample requirements. However, some chiral selectors present strong background UV absorption providing high detection limits. The present paper deals with the application of the partial-filling technique to the separation of bupivacaine enantiomers by capillary electrophoresis using human serum albumin (HSA) as chiral selector. In this procedure the cationic surfactant cetyltrimethylammonium bromide (CTAB) was used as a dinamic capillary coating in order to reduce the electro-osmotic flow and detect both bupivacaine enantiomers out of the chiral selector plug. Several experimental conditions such as CTAB concentration, pH, HSA concentration and plug length, background electrolyte concentration, temperature and voltage were studied. Under the selected conditions it is possible to detect the separated enantiomers out of the HSA plug in less than 4 min using 50 mM Tris pH 8 as background electrolyte with 50 microM CTAB, at 30 degrees C and using a separation voltage of 25 kV. The proposed methodology was then validated for analytical purposes and applied to the analysis of pharmaceutical preparations commercially available. The results obtained with the proposed methodology were in good agreement with those declared by the manufacturers. The simplicity, sample throughput, accuracy, reproducibility and low cost of the proposed method make it suitable for the control of the enantiomeric composition of bupivacaine in pharmaceuticals.     

Self-assembly of peptides into a beta-barrel motif

We report the results of a study of the self-assembly of four minimalist peptide strands with a native beta-barrel structure. Using a soft-well potential to mimic cellular crowding, molecular dynamics simulations were performed in confining spheres of varying radii. By utilizing a previously introduced scaling factor lambda for the non-native hydrophobic interactions (0相似文献   

The use of pyridine-2-azo-p-dimethylaniline as an indicator in glacial acetic acid

Pyridine-2-azo-p-dimethylaniline is suggested as an indicator in the titration of amines (aniline, butylamine, p-phenylenediamine and ethylenediamine) with perchloric acid in glacialacetic acid medium. The precision obtainable is much better than that with crystal violet indicator. The pyridine dye can also be used satisfactorily in the titration of sodium carbonate and sodium acetate.     

Comparison of different sample preparation treatments for the analysis of wine phenolic compounds in human plasma by reversed phase high-performance liquid chromatography

Phenolic compounds are common constituents of wine. Due to their healthy properties the analysis in human fluids is interesting within bioavailability evaluation. They have been reported not to be stable in human plasma, particularly at room temperature. Most sample treatments have been reported for a single compound. Our aim in this paper is to study sample handling control conditions and improve phenolic stability in human plasma samples. We tested various sample treatments to determine whether they could be used for analysing a set of phenolic compounds usually present in wines.The compounds studied were six phenolic acids, five flavonoids, trans-resveratrol and tyrosol. The effect of the following factors was explored: temperature, pH, the addition of antioxidants and the addition of anticoagulants.The results suggest that the plasma samples should be kept at temperatures below −20 °C before analysis and that 1% ascorbic acid plus 10 μl/ml o-phosphoric acid should be added. Anticoagulants (heparin or EDTA) do not play a significant role in the stability of polyphenolic compounds.The recovery values of a number of sample treatments (solid phase extraction, extraction with methanol, deproteinization, inhibition of enzymatic plasma activity) were compared. The recovery values for most phenolic compounds were better if the enzymatic plasma activity was inhibited and acidified ethanol was used for deproteinization.     

Headspace solid-phase microextraction method for determining 3-alkyl-2-methoxypyrazines in musts by means of polydimethylsiloxane-divinylbenzene fibres

A method for determining 2-methoxypyrazine, 3-methyl-, 3-ethyl-, 3-isopropyl-, 3-sec.-butyl- and 3-isobutyl-2-methoxypyrazine in musts is described. It involves headspace solid-phase microextraction (SPME) and determination by capillary gas chromatography using nitrogen–phosphorous detection. Pyrazines were satisfactorily separated under isothermal conditions, and quantification was carried out using 3-isopropyl-2-ethoxypyrazine as the internal standard. Ionic strength, time and temperature were studied in order to make SPME as efficient as possible. The developed method enabled detection limits at the 0.1 ng l⁻¹ levels for some of the analytes. The method was successfully applied to identify and quantify different 3-alkyl-2-methoxypyrazines in experimental musts of Cabernet Sauvignon and Merlot. Their evolution during the ripening was also monitored.     

Patterns in the precision of quantitative data from multicomponent gas chromatographic or gas chromatographic-mass spectrometric analysis

The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed.     

A two-stage approach to automatic determination of 1H NMR coupling constants

(1)H NMR scalar coupling constants are a rich source of information on molecular structure, but their extraction from spectra can be less than straightforward. Previous approaches to J extraction include methods proposed by Hoye, Golotvin, and the 'modified J-doubling' method. Here we describe the ACCA method, currently implemented in the NMR package MestReC, which allows a high degree of automation in the extraction of coupling patterns even in the case of complex multiplets with sublinewidth splitting. The new approach is illustrated by application to strychnine, for which it has detected previously unreported couplings.     

Extraction of the [(C4H9)4N]3[Fe(SCN)6] ion-pair with chloroform: Spectrophotometric determination of iron

When excesses of ammonium thiocyanate and tetrabutylammonium chloride are added to an iron(III) solution, a water-insoluble ion-pair is formed. This compound is soluble in chloroform and other organic solvents. The variables affecting extraction with CHCl₃ are studied in order to obtain the optimal conditions and an extraction procedure is proposed. The separation of iron as a previous step to its spectrophotometric determination is studied.     

Ultraviolet B radiation induces upregulation of calcitonin gene-related peptide levels in human Finn chamber skin samples

One of the neuropeptides that plays a role in UVB-induced immunomodulation is calcitonin gene-related peptide (CGRP), as demonstrated in several animal studies. CGRP can be detected in human skin, but effects of UVB exposure on CGRP levels in human skin are not known. We determined CGRP levels in human Finn chamber skin samples of 15 UVB-irradiated and 10 control volunteers. Filter samples were collected prior to and immediately after a UVB exposure protocol (5 consecutive days, with one personally determined minimal erythema dose (MED(jp)) per day). CGRP levels in filter samples were determined using a commercially available radioimmunoassay kit. CGRP could be detected in the filter samples and volunteers showed statistically significantly increased levels after UVB exposure. In addition, the CGRP levels of UVB-exposed volunteers were positively correlated with the dose of UVB in J/m(2) that they received on 5 consecutive days. In other words, higher UVB doses resulted in higher CGRP levels. In summary, CGRP, a mediator in UVB-induced immunomodulation, could be detected in human Finn chamber skin samples, and was significantly increased after UVB exposure. The CGRP level appeared to depend on the amount of UVB the volunteers received.     

Parallel transformations of cyclohexene mediated by the Cp*W(NO) fragment

Hydrogenolysis of Cp*W(NO)(CH2CMe3)2 at room temperature in cyclohexene results in the formation of the intermediate 16e organometallic complex, [Cp*W(NO)(eta2-cyclohexene)]. This intermediate leads to three parallel transformations of cyclohexene, namely (a) C-H activation of cyclohexene to form an eta3-cyclohexenyl hydrido complex, (b) combination of cyclohexene and H2 to form a cyclohexyl hydrido complex, and (c) coupling of two molecules of cyclohexene with concomitant loss of two hydrogen atoms to form a complex containing a novel eta1,eta3-(cyclohexyl)cyclohexenyl ligand. Single-crystal X-ray crystallographic analyses of products resulting from transformations (b) and (c) have been effected.