Improved column-switching liquid chromatographic method for the determination of the enantiomers of mefloquine

A liquid chromatographic method for the determination of the enantiomers of mefloquine has been improved. The chromatography involved two columns: an achiral cyanopropyl stationary phase for the quantification of (+/-)-mefloquine and a chiral naphthyl-urea stationary phase for the determination of the enantiomeric ratio. Compared with the previous method, which needed two detectors, this one used one detector-integrator to which the two columns are connected alternately by an automated column-switching system. The method is suitable for the quantification (0.05 microgram/ml) of mefloquine and the determination of enantiomeric ratios from 500-microliters plasma samples with ultraviolet detection.     

A perceptual analysis of viscosity

The perception of viscosity was studied using the contralateral limb-matching procedure in which subjects adjusted the viscosity of a motor connected to the wrist of one (matching) arm until it was perceived to be the same as that of the motor attached to the other (reference) arm. Two servo-controlled electromagnetic linear motors with computer-controlled viscosity were used to present viscosities ranging in amplitude from 2 to 1024 N.s/m to 11 subjects. Ten different viscosities were matched by subjects, and there were ten repetitions of each stimulus amplitude. The psychophysical function relating the reference to matching viscosity was linear (99% variance accounted for), and the accuracy with which the viscosities were matched (slope of 0.88) paralleled that reported previously for force, limb position and stiffness. The Weber fraction for viscosity was 0.34, which is 50% larger than that measured for stiffness and over twice that reported for force. An analysis of the movements and forces generated to perceive the reference viscosity revealed that subjects did not vary the amplitude of the movements and typically made very small excursions of the forearm, but that both the velocity of the movements and force changed significantly as a function of the reference viscosity. These findings were interpreted as indicating that the human proprioceptive system is capable of integrating information regarding force and movement velocity so as to perceive the viscosity of a mechanical system connected to the limbs, but that its sensitivity to changes in viscosity is much less than would be predicted from its capacity to detect variations in muscle force and limb movement.     

Highly potent irreversible inhibitors of neutrophil elastase generated by selection from a randomized DNA-valine phosphonate library

We incorporated a phosphonate irreversible inhibitor of neutrophil elastase into a randomized DNA library and, using the SELEX process, iteratively selected these assemblies for the most potent elastase inhibitors. The inhibitors were selected against purified elastase and against secreted elastase in the presence of activated neutrophils. Very active aptamer inhibitors were obtained by both methods, with second-order rate constants for inactivation of human neutrophil elastase ranging (1-3) x 10(8) M(-1) min(-1). These rates exceed those of any reported irreversible inhibitor of elastase and exceed the previous best phosphonate inhibitors by 80-fold. The selected inhibitors are also significantly more potent than alpha-1 proteinase inhibitor in blocking degradation of elastin by activated neutrophils. In contrast to a previous experiment [Smith et al. (1995) Chem. Biol. 2, 741-750], a single-enantiomer form of the valyl phosphonate was used rather than a racemic mixture. Our analysis shows that this use of a chirally resolved valyl phosphonate results in selection of much more potent inhibitors and that these inhibitors specifically potentiate a single enantiomeric form of the phosphonate.     

Conversion of phenolics to lignans: Sinapic acid to thomasidioic acid

Changes in sinapic acid when exposed to aqueous alkaline conditions were elucidated. Sinapic acid was exposed to a volatile buffer (pH 8.5) for 24 h, lyophilized, acidified, extracted, and characterized using nuclear magnetic resonance and mass spectroscopy. The product obtained was identified as the lignan thomasidioic acid. This identification was confirmed by comparison with a synthesized authentic sample of thomasidioic acid. Conversion of sinapic acid to thomasidioic acid under alkaline conditions previously has not been reported. Thomasidioic acid was present after exposure of sinapic acid to pH 8.5 for as few as 6 h. Thomasidioic acid also was formed at pH 7.     

Diel periodicity and influence of age and mating on sex pheromone titer in gypsy moth,Lymantria dispar (L.)

The diel periodicity of sex pheromone titer from pheromone glands of femaleLymantria dispar is described. On the day of emergence (day 0), pheromone titer was generally low; means ranged from 1 to 4 ngcis- 7,8-epoxy-2-methyloctadecane during photophase and gradually increased to 8.4 ng over the course of scotophase. For day-1, -2, and -3 females, the diel fluctuations of titer were more pronounced. Lowest titers (5–9 ng) occurred 0–4 hr after lights-on, and peak titers (19–32 ng) were found 0–4 hr before lights-off. Comparison of the average daily titer among the different age groups (data pooled over six time points at 4-hr intervals) indicated that significantly less pheromone was extracted from glands of day-0 (4.5 ng) than day-1 (12.4 ng), day-2 (15.4 ng), or day-3 females (13.5 ng). No significant differences were found among the three older ages. Femalesin copula exhibited a rapid reduction in titer within the first 0.5 hr of mating initiation (7.6 ng vs. 19.5 ng from virgin females of similar age). After the second 0.5 hr, the reduction in titer was not nearly as marked, falling only to 4.5 ng. Twenty-four hours after mating, titer fell below the limits of detection (0.5 ng). All extracts from pheromone glands of virgin or mated females contained < 1.0 ng of the putative pheromone precursor, 2-methyl-cis-7-octadecene.     

Multivariate discrimination of wines with respect to their grape varieties and vintages

The primary focus of the European Union funded project entitled “Establishing a WINE Data Bank for analytical parameters for wines from Third Countries” (WINE-DB project, G6RD-CT-2001-00646-WINE-DB) was the discrimination of wine samples with respect to their geographical origin using only a few chemical parameters. Taking a step further, we have investigated the possibility of discriminating the wines in the data bank according to their harvesting seasons and grape varieties. Several chemometric methods were carefully selected and evaluated for this purpose. These were discriminant partial least squares, classification and regression trees, uninformative variable elimination discriminant partial least squares and neuro-fuzzy systems. With classification and regression trees, it was possible to identify a few chemical parameters including isotopic ratios (e.g. δ¹⁸O), biogenic amines and rare earth elements that discriminate between vintages and some grape varieties for wines produced in a particular country such as Czech Republic, Hungary, Romania or South Africa. These parameters can be used in evaluating the authenticity of wines.     

Temporal patterns of sex pheromone titers and release rates inHolomelina lamae (Lepidoptera: Arctiidae)

Six hydrocarbon components (2-methylhexadecane,n-heptadecane, 2-methylheptadecane, 2-methyloctadecane,n-nonadecane, and 2-methylnonadecane) were identified in sex-pheromone gland extracts and in airborne collections ofHolomelina lamae. Low variability in the ratio of components among individuals indicates tight regulation of blend composition. Minor changes were evident in the quantity and ratio of the blend as a function of time of day. Based on gland extracts, the total quantity of the six components increased from day 1 (X = 6299 ng) to day 4 (X = 7498 ng) and subsequently decreased. No significant correlations were found between total gland contents and wet or dry weights of moths. Emission rates ofH. lamae females were determined from pheromone adsorbed onto Porapak Q. Quantities released peaked shortly after the onset of calling and decreased rapidly as calling continued. Peak release rates ranged from 13 to 350 ng/10 min, and from 37 to 835 ng/60 min. Noncalling females did not emit detectable quantities of pheromone. Based on release rates and the rate of pulsation of the abdominal tip, the average amount released per pulse is not constant. The mean ratio of components released (0.787.45 84.802.842.591.53) was not very different from the ratio of components in gland extracts of 2-day-old females (0.704.1990.12 1.651.911.42). We propose that the blend is atomized rather than volatilized from the gland, thus retaining nearly the same ratios in the female's effluvium as in her gland.