Free and total para-aminobenzoic acid analysis in plants with high-performance liquid chromatography/tandem mass spectrometry

para-Aminobenzoic acid (PABA), a precursor in the synthesis of folates in plants, is determined by liquid chromatography/tandem mass spectrometry (LC/MS/MS). In plants PABA can be converted into its beta-D-glucopyranosyl ester (PABA-Glc) and can also exist in its free form. In this work, we developed and validated a quantitative method to study free and total PABA in plants. The total PABA (free PABA plus PABA-Glc) can be evaluated after acid hydrolysis at 80 degrees C for 2 hours. The plant material is homogenized and the PABA content is quantified using the standard addition procedure. The validated method is selective, sensitive, simple, accurate, has a recovery between 99.6 to 102.5%, is reproducible (RSD between 1.4 and 4.4%), and is linear between 2.5 and 1538 ng/mL. Free and total PABA determinations in five vegetables showed that different plant species had different amounts of free and total PABA, and that the ratios of total versus free PABA were also variable. This new method could be valuable for studies of folate synthesis in plants.     

Polymers containing anthraquinone units: Polymers from 1,5-diaminoanthraquinone and aralkyldiketones

Schiff's-base polymers have been formed by the condensation of 1,5-diaminoanthraquinone with 1,4- and 1,3-diacetylbenzene and 2,6-diacetylpyridine. These polymers were soluble in methanesulfonic and concentrated sulfuric acids (1,4-diacetylbenzene polymer) or N,N-dimethylacetamide. The polymer formed from 1,4-diacetylbenzene was ring-closed in polyphosphoric acid to yield a thermally stable polymer soluble in concentrated sulfuric acid which lost only 10% of its weight at 900°C in a TGA test.     

Determination of paramethoxyamphetamine and other amphetamine-related designer drugs by liquid chromatography/sonic spray ionization mass spectrometry

Paramethoxyamphetamine (PMA) is an amphetamine-like designer drug that has emerged recently on the European illicit drug market. This drug has a wicked reputation, as a number of lethal intoxications have occurred. A method using high-performance liquid chromatography coupled to ion trap based mass spectrometry (LC/MS) is described for the determination of this compound together with 3,4-methylenedioxymethamphetamine (XTC or MDMA), amphetamine and 3,4-methylenedioxyamphetamine (MDA) in human matrices. A liquid/liquid extraction (LLE) was applied to whole blood, urine and postmortem tissues. Reversed-phase liquid chromatography was performed on a narrow-bore phenyl-type column at a flow rate of 0.3 mL/min. A switch box allowed disposal of early-eluting irrelevant material to waste, protecting the mass spectrometer from contamination. The column effluent was directed into an ion trap mass spectrometer by a sonic spray ionization (SSI) interface. The method was validated for all three matrices, proving the applicability of SSI even when dealing with complex biological matrices. The within-and between-day precisions were less than 17.5% and accuracy was below 16.2%. Weighted (1/x) quadratic calibration curves were generated ranging from 10 to 1000 ng/mL (blood and urine) or 20 to 2000 ng/g (tissue) and correlation coefficients (r(2)) always exceeded 0.995. In addition, the mass spectrum of PMA is given together with a proposed fragmentation pattern for the obtained LC/MS spectrum. This information can be useful for future identification of PMA with LC/MS in biological matrices as well as in confiscated powders or tablets.     

Fluoride materials for optical applications: Single crystals, ceramics, glasses, and glass–ceramics

Fluoride compounds have compelling advantages for many optical applications due to their unique combination of low phonon energy, high UV absorption edge energy, and relatively weak crystal field. In this article, we offer a concise review of the current state of the art in fluoride single crystals, ceramics, glasses, and glass–ceramics for optical applications.     

An Improved Synthesis of 3-Substituted 1,2,4-Triazolo[4,3-a]pyridines and 1,2,4-Triazolo[4,3-b]pyridazines

The preliminary results of a simple and versatile one-pot procedure for the preparation of 3-substituted 1,2,4-triazolo[4,3-a] pyridines and 1,2,4-triazolo[4,3-b]pyridazines are described. Intramolecular cyclization of nitrile imine ylides are carried out by treatment of 2-pyridyl- and 3-pyridazinylhydrazones with chloramine T.     

Reaction of Triethyl Phosphite with Boron Tribromide

Summary.  Reaction of boron tribromide with triethyl phosphite led to the formation of triethyl tribromoborophosphate 1, a complex bearing a P→B bond. Received November 19, 1999. Accepted (revised) January 21, 2000     

Reaction of Triethyl Phosphite with Boron Tribromide

 Reaction of boron tribromide with triethyl phosphite led to the formation of triethyl tribromoborophosphate 1, a complex bearing a P→B bond.     

A New Synthesis of 3-Deoxy-D-arabino-hexose and its Tautomeric Equilibrium

Abstract

The title compound was synthesized in four steps from D-glucono-1,5-lactone. Reduction of 2,4,6-tri-O-benzoyl-3-deoxy-D-arabino-hexono-1,5-lactone (1) with disiamylborane afforded 2,5,6-tri-O-benzoyl-3-deoxy-D-arabino-hexopyranoae (2) which, on debenzoylation, gave 3-deoxy-D-arabino-hexoae (3). Tautomeric equilibrium of 3 was studied by ¹H and ¹³C NMR spectroscopy.     

Prediction of Euclidean distances with discrete and continuous outcomes

The objective of this paper is first to predict generalized Euclidean distances in the context of discrete and quantitative variables and then to derive their statistical properties. We first consider the simultaneous modelling of discrete and continuous random variables with covariates and obtain the likelihood. We derive an important property useful for its practical maximization. We then study the prediction of any Euclidean distances and its statistical proprieties, especially for the Mahalanobis distance. The quality of distance estimation is analyzed through simulations. This results are applied to our motivating example: the official distinction procedure of rapeseed varieties.     

Kinetic-diffusion asymptotic-preserving Monte Carlo algorithms for plasma edge neutral simulation

We developed novel Monte Carlo simulation strategies for the neutral model in plasma edge simulations where both low-collisional and high-collisional regimes are present. To maintain accuracy and reduce simulation costs in high-collisional regimes, we use hybridized particles that exhibit both kinetic and diffusive behaviour depending on the local collisionality. The method maintains an asymptotically correct distribution and a correct mean, variance, and time correlation for all values of the collisionality. We apply this scheme to a fusion case with a strongly heterogeneous background, prompting the inclusion of a diffusion-induced drift. Our numerical results show a large increase in efficiency at the expense of a minor bias.