Comprehensive stability‐indicating high‐performance liquid chromatography coupled with diode array detection method for simultaneous determination of amprolium hydrochloride and ethopabate in powder dosage form for veterinary use

This research deals with the development of a stability‐indicating high‐performance liquid chromatography method for simultaneous determination of amprolium hydrochloride and ethopabate. To the best of our knowledge, no comprehensive stability‐indicating method has been reported for analysis of this mixture. Separation was achieved using Kromasil cyano column with gradient elution of the mobile phase composed of sodium hexane sulfonate solution and methanol. Quantification was based on measuring peak areas at 266 nm. Amprolium and ethopabate peaks eluted at retention times 10.42 and 18.53 min, respectively. The proposed procedure was validated with respect to system suitability, linearity, ranges, precision, accuracy, specificity, robustness, detection, and quantification limits. Linearity ranges for amprolium and ethopabate were 1.5–240 and 1–160 μg/mL, respectively. Analytes were subjected to stress conditions of hydrolysis, oxidation and thermal degradation. The proposed method enabled resolution of drugs from their forced‐degradation products and amprolium related substance (2‐picoline). Moreover, specificity was verified by resolution of the analytes from about 22 drugs used in antimicrobial veterinary products. The validated method was successfully applied to assay of the combined veterinary powder dosage form, additionally it was implemented in the accelerated stability study of the dosage form when stored for six months at 40°C and 75% relative humidity.     

The KS-transformation revisited

We show that the Kustaanheimo-Stiefel (KS) regularizing transformation for the perturbed Kepler motion is so deeply rooted to the Keplerian orbital elements as to yield the position vector of a particle on the osculating orbit as the effect of a peculiar roto-dilatation in the physical Euclidean space. Adopting the conventional vector formulation, quaternions and spinors are also involved. A key role is played by (i): a simple hodographical approach to the integrals of the Kepler motion (angular momentum vector, Runge-Lenz vector); (ii) a polarized outlook on the attitude frame of the Kepler orbit; (iii) a simple kinematical expression for the orbital elements. The mechanical energy, the bilinear relation, the gauge transformation — fundamental in the KS-theory — are naturally arrived at, acquiring interesting kinematical interpretations.

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Sommario Si mostra come la trasformazione di Kustaanheimo e Stiefel (KS) per regolarizzare il moto kepleriano perturbato sia cosí legata agli elementi orbitali da condurre, tramite una particolare roto-omotetia nello spazio fisico euclideo, al vettore posizione di una particella sull'orbita osculatrice. Avvalendosi del consueto calcolo vettoriale, si introducono solo all'occorrenza quaternioni e spinori. Fondamentali risultano (i): l'introduzione per via odografica degli integrali primi caratteristici del moto kepleriano (momento della quantità di moto, vettore di Runge-Lenz); (ii) l'interpretazione polarizzata della terna di assi che dà la posizione dell'orbita nello spazio; (iii) le semplici espressioni cinematiche degli elementi orbitali. L'energia meccanica e la relazione bilineare, basilari nella teoria KS, acquistano interessanti interpretazioni cinematiche.

     

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

The reactions of (+)‐car‐2‐ene ( 1 ) and (+)‐car‐3‐ene ( 2 ) with aldehydes in the presence of montmorillonite clay were studied for the first time (Schemes 3 and 5). The major products of these reactions are optically active, substituted hexahydroisobenzofurans, probably formed as a result of an attack of the protonated aldehyde at the cyclopropane ring. Quite unexpectedly, the products are cis‐configured at the ring‐fusion site; the fact was established by means of quantum‐chemical calculations and NMR data. It appeared that the behavior of the 2 : 3 mixture 1 / 2 in reactions with aldehydes in the presence of K10 clay differed substantially from the reactivities of the corresponding individual monoterpenes.     

Volatile profiling reveals intracellular metabolic changes in <Emphasis Type="Italic">Aspergillus parasiticus</Emphasis>: <Emphasis Type="Italic">veA</Emphasis> regulates branched chain amino acid and ethanol metabolism

Background  

Filamentous fungi in the genus Aspergillus produce a variety of natural products, including aflatoxin, the most potent naturally occurring carcinogen known. Aflatoxin biosynthesis, one of the most highly characterized secondary metabolic pathways, offers a model system to study secondary metabolism in eukaryotes. To control or customize biosynthesis of natural products we must understand how secondary metabolism integrates into the overall cellular metabolic network. By applying a metabolomics approach we analyzed volatile compounds synthesized by Aspergillus parasiticus in an attempt to define the association of secondary metabolism with other metabolic and cellular processes.     

Analysis of cocaine and benzoylecgonine in urine by using multisyringe flow injection analysis‐gas chromatography‐mass spectrometry system

In this paper, a method was described to determine cocaine (COC) and benzoylecgonine (BZE) in human urine samples by GC‐MS detection. The extraction of analytes from urine samples was achieved in an Oasis hydrophilic–lipophilic balance column (20 mm×3.9 mm id, dp=25 μm; Waters, USA), incorporated in a multisyringe flow injection system, used for the sample treatment. Finally, to improve the volatility of the BZE, an in‐line derivatization reaction with N,O‐bis (trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane was made microwave‐assisted in order to reduce the reaction time. The results showed that the proposed method is a good alternative for the analysis of COC and BZE in urine samples because it offers advantages compared with those described in the literature, which include simplicity in the sample treatment, the sensitivity and selectivity necessary to determine the analytes of interest at low levels in the urine and high sample throughput.     

Quantifying surface coverage of colloidal silica by a cationic peptide using a combined centrifugation/time-resolved fluorescence anisotropy approach

Recent experimental studies have shown that time-resolved fluorescence anisotropy (TRFA) is a promising methodology for in situ characterization of the surface modification of aqueous silica nanocolloids. Here we provide a more fundamental insight into the principle of this approach and discuss how the adsorption parameters for a cationic peptide, Lys-Trp-Lys (denoted using the standard shortform KWK), onto Ludox nanoparticles (NPs) are linked to the rotational dynamics of rhodamine 6G (R6G) dispersed in the KWK/Ludox mixture. First, the adsorption isotherm of KWK on hydrophilic controlled pore glass (CPG-3000) was obtained using the traditional centrifugation method, which provides the total molar amount of KWK per unit surface area of the silica. Assuming that both CPG and Ludox particles possess identical surface properties when suspended in the same aqueous buffer, both materials should also have identical adsorption properties. Thus, the adsorbed amount of KWK per unit area at a given total KWK concentration, as determined by the centrifugation method, can be plotted against the fractions of R6G anisotropy decay components at the same KWK concentration to relate the anisotropy components to the absolute surface coverage. Using this approach, it was determined that the concentration of KWK at which the CPG surface was saturated corresponded to the condition g = 0 in the R6G decay, where g is the fraction of the nondecaying anisotropy component. This condition means that there is no R6G bound to the fraction of Ludox NPs with a radius R > 2.5 nm at maximum KWK coverage, consistent with the adsorbed peptide forming a continuous layer on the Ludox surface. Hence, the g value obtained from TRFA analysis can be used to assess the absolute surface coverage of monolayer coatings on colloidal nanoparticles.     

Direct monitoring of toxic compounds in air using a portable mass spectrometer

A portable tandem mass spectrometer, capable of performing atmospheric pressure chemical ionization (APCI) using a direct atmospheric inlet, is applied to the real-time monitoring of toxic compounds in air. Analytes of interest include dimethyl methylphosphonate, arsine, benzene, toluene, pyridine and vinyl acetate. The detection, identification and quantification of organic and inorganic compounds in air is demonstrated using short analysis times (<5 seconds) with detection limits in the low ppb (v/v) levels and linear dynamic ranges of several orders of magnitude. Highly specific detection and identification is achieved, even when the analyte is a trace component in a complex mixture including such interferents as fuels, lubricants, and cleaners. The effects of environmental conditions, including temperature and humidity, are delineated. Receiver operating characteristic (ROC) curves are presented to show the trade-off between false positive and false negative detection rates. Tandem mass spectrometry based both on collision-induced dissociation and on selective atmospheric pressure ion/molecule reactions is also used to increase selectivity and sensitivity.     

Preparation, characterization and in vitro dissolution studies of solid systems of valdecoxib with chitosan

In the present study, the solubilizing and amorphizing properties of Valdecoxib (a poorly water soluble anti inflammatory drug) with low molecular weight chitosan (a polymer), have been investigated. Binary systems of varying drug/polymer ratios were prepared using different techniques (physical mixing, co-grinding, kneading) and were tested for dissolution. Drug carrier interactions were investigated in both the liquid and solid state, by phase solubility analysis, differential scanning calorimetry, powder X-ray diffractrometry, FT-IR spectroscopy and scanning electron microscopy. The solubility of the drug increased with increasing polymer concentration showing A(N) type phase solubility diagram. Differential scanning calorimetry, powder X-ray diffractrometry and scanning electron microscopic studies of binary systems suggested generation of amorphous form of drug (in kneading and co ground mixtures). IR spectroscopy revealed the presence of hydrogen bonding in kneading and co ground mixtures. Drug dissolution was improved with increasing the polymer concentration in the mixture (Kneaded>co ground>physical mixture), which was attributed to the amorphonization and/or decreased drug crystallinity, size and polymer wetting effect. Enhanced dissolution combined with its direct compression feasibility and anti ulcerogenic action results in low molecular weight chitosan for developing fast release oral solid dosage forms of valdecoxib.     

New Potential Biocatalysts by Laccase Immobilization in PVA Cryogel Type Carrier

Laccases are enzymes belonging to the Oxidoreductases class. These enzymes may be good biocatalysts for different processes, at laboratory and industrial levels. A successful use at industrial scale demands a higher stability of the enzyme. As an easy way to obtain longer life biocatalysts, the immobilization process is recommended. Thus, the paper presents different ways of obtaining new biocatalysts by a laccase covalent immobilization on a macroporous carrier based on poly(vinyl alcohol) cryogel. Different procedures of covalent immobilization are described, the newly obtained biocatalysts being characterized. According to the experimental data, the stability of the immobilized enzyme increased and the pH profile changed, compared with those of the free enzyme.