Development and validation of a reversed‐phase HPLC method for CYP1A2 phenotyping by use of a caffeine metabolite ratio in saliva

CYP1A2 is important for metabolizing various clinically used drugs. Phenotyping of CYP1A2 may prove helpful for drug individualization therapy. Several HPLC methods have been developed for quantification of caffeine metabolites in plasma and urine. Aim of the present study was to develop a valid and simple HPLC method for evaluating CYP1A2 activity during exposure in xenobiotics by the use of human saliva. Caffeine and paraxanthine were isolated from saliva by liquid‐liquid extraction (chlorophorm/isopropanol 85/15v/v). Extracts were analyzed by reversed‐phase HPLC on a C₁₈ column with mobile phase 0.1% acetic acid/methanol/acetonitrile (80/20/2 v/v) and detected at 273nm. Caffeine and paraxanthine elution times were <13min with no interferences from impurities or caffeine metabolites. Detector response was linear (0.10–8.00µg/ml, R²>0.99), recovery was >93% and bias <4.47%. Intra‐ and inter‐day precision was <5.14% (n=6). The limit of quantitation was 0.10µg/ml and the limit of detection was 0.018±0.002µg/mL for paraxanthine and 0.032±0.002µg/ml for caffeine. Paraxanthine/caffeine ratio of 34 healthy volunteers was significantly higher in smokers (p<0.001). Saliva paraxanthine/caffeine ratios and urine metabolite ratios were highly correlated (r=0.85, p<0.001). The method can be used for the monitoring of CYP1A2 activity in clinical practice and in studies relevant to exposure to environmental and pharmacological xenobiotics. Copyright © 2015 John Wiley & Sons, Ltd.     

A correspondence principle connecting IBVPs of wave propagation and heat conduction

A wave-heat correspondence principle is established by utilizing previous operational relations of van der Pol and Bremmer. By the suggested procedure, heat conduction problems can be solved by using an auxiliary wave-propagation problem in conjunction with the correspondence principle. A check on this procedure was provided by solving a mixed BVP of transient heat flow. The present correspondence principle is particularly useful in dealing with IBVPs involving wedge-shaped domains, and characteristic lengths.     

On-line sorption preconcentration of metals based on mixed micelle cloud point extraction prior to their determination with micellar chemiluminescence: Application to the determination of chromium at ng l levels

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is modified to extract and preconcentrate metal species rapidly, avoiding the formation of hydrophobic complexes, using a mixed micellar medium. Coupling the procedure with chemiluminescence (CL) detection based on the catalytic activity of metal species on the luminol-hydrogen peroxide reaction and enhancing the signal with the presence of a micellar carrier containing bromide ions produces a powerful tool for the preconcentration and determination of metal species at ng l⁻¹ levels. As an analytical demonstration ultratrace concentrations of chromium were conveniently detected and quantified in samples with a complex matrix such as seawater and wastewater. The figures of merit for the determination of chromium were: 0.9-1.6% R.S.D. (n=5) with detection and quantification limits 0.5 and 2.0 ng l⁻¹, respectively. The calibration graph was rectilinear from 2 to 200 ng l⁻¹ (r=0.9996, n=6). Several other metal ions were determined in ideal situations, with analogous results.     

Development of 1-(2-pyridylazo)-2-naphthol-modified polymeric membranes for the effective batch pre-concentration and determination of zinc traces with flame atomic absorption spectrometry

The development of 1-(2-pyridylazo)-2-naphthol (PAN)-modified polymeric membranes for the effective batch pre-concentration and determination of zinc traces with flame atomic absorption spectrometry (FAAS) is described. The method is based on the chemical bonding of the metal species with a suitable ligand, which has been immobilized into a water-insoluble cellulose acetate (CA) membrane followed by simple rinsing of the chelating agent-metal complex with an acidified methanolic solution. The latter is directly aspirated to the nebulizer of a FAA spectrophotometer without any other treatment. As an analytical demonstration, trace concentrations of Zn(II) were successfully detected in real samples, such as seawater, river and lake water, wastewater as well as in a reference material, without any laborious and time-consuming treatment. Several working parameters were investigated. A pre-concentration factor of 100 was achieved by simple immersing of a circular piece of the CA-PAN membrane (0.6 cm diameter) in the tested samples for 30 min at room temperature. The analytical curve was rectilinear up to 30 mug l(-1) zinc with detection limit of 0.7 mug l(-1), a quantitation limit of 2.0 mug l(-1) and a relative standard deviation lower than 2%.     

Computational studies on the thermal decomposition and isomerization of CHBr2O radical

The unimolecular decomposition study of dibromomethoxy radical, CHBr₂O, and its isomeric hydroxy dibromomethyl radical, CBr₂OH, is carried out using ab initio electronic molecular structure methods. Three kinds of reaction pathways are examined, C–H and C–Br bond scissions, intramolecular three-center HBr elimination and isomerization. Based on the ab initio results, energy-specific rate coefficients k(E) and thermal rate constants k(T,P) are evaluated using RRKM theory and master equation numerical analysis. Relevance to existing experimental evidence is discussed.     

Stereoselective ring closure of 6-[[(methylamino)carbonyl]oxy]-2H-pyran-3(6H)-ones. Formation of the 5H-pyrano[3,2-d]oxazole-2,6-dione ring system

The stereospecific formation of the 5H-pyrano[3,2-d]oxazole-2,6-dione ring system from 2,2-disubstituted-6-[[(methylamino)carbonyl]oxy]-2H-pyran-3(6H)-one via an enolization at C-5 is presented. The outcome of the same reaction in the case of 2-monosubstituted 2H-pyran-3(6H)-ones is also discussed.     

Solid-phase synthesis of an oxalic acid amide library

Monoamides of oxalic acid are of interest as bioisosteric replacements for phosphate groups in the design of new enzyme inhibitors. Here, we have demonstrated the use of oxalic acid as a linker to the Wang resin to synthesize individual or libraries of phosphate biosteres. The highly reactive resin-bound acid chloride reacts with arylamines to yield resin-bound N-aryloxamic acids (oxanilic acids). This methodology is especially useful for the rapid synthesis of 2-(oxalylamino)benzoic acids (OBAs), because it can be utilized for library synthesis and eliminates the intermediate purification step necessary in solution-phase reactions. The products are cleaved off the resin with trifluoroacetic acid in dichloromethane in good yields.     

Ab initio molecular orbital and RRKM calculations of the thermal decomposition of CH2BrO radical

A theoretical study of the thermal decomposition and isomerization channels of bromomethoxy radical is carried out using ab initio molecular orbital methods and RRKM theory. Three kinds of reaction pathways are examined, bond scission, intramolecular three-center HBr elimination and isomerization. Energy-specific rate coefficients k(E) and thermal rate constants k(T,P) are evaluated using the ab initio data and RRKM theory. Relevance to existing experimental evidence is discussed.