Application of microdialysis for study of caffeine distribution into brain and cerebrospinal fluid in rats.

The usefulness of microdialysis was examined for the chronological determination of caffeine concentration in the brain and cerebrospinal fluids (CSF) following intravenous administration of caffeine in rats. The recovery percent of caffeine by microdialysis, the concentration ratio of caffeine in the dialysate against that in the brain tissue or CSF was determined. The recovery percent was proved to be constant at 5 different steady-state plasma concentrations of caffeine (0.1-280 nmol/ml) and in different collecting periods of dialysate ranging from 30 s to 10 min. The mean recovery percent in the brain and CSF were 10.9 and 13.1%, respectively. Thus, microdialysis was proved useful for determination of drug concentration in the tissue and biological fluids with time resolution of more than 30 s. The microdialysis method was then applied for the chronological determination of caffeine concentration in the brain and CSF following intravenous bolus administration. The estimated caffeine concentration in the brain and CSF was the same as those obtained by direct determination in isolated brain and CSF, respectively. Transfer of caffeine from plasma to brain and CSF were further pharmacokinetically analyzed using a modified 2-compartment model. In this kinetic model, the transfer of caffeine between the CSF and brain was neglected, since the mutual transfer of caffeine was not detected in in vivo experiments. Calculated curves were well fitted on observed caffeine concentrations in the plasma, brain and CSF.     

Thermal lens spectrophotometry of nitrogen dioxide using an excimer-laser-pumped dye laser

A thermal lens spectrophotometer based on a pulsed dye laser pumped by an excimer laser was constructed. A thermal lens spectrum was measured for nitrogen dioxide by scanning the dye laser wavelength, which was well correlated with an absorption spectrum. A linear calibration graph was obtained in the nl 1^?1 range, the detection limit being 4 nl 1^?1, which is similar to the best value achieved by other laser spectrometric methods. The enhancement factor achieved was 16, which is much smaller than the theoretical value of 292 calculated by assuming an exciting laser with a single transverse mode (beam waist radius 0.12 mm). However, the observed enhancement factor agrees fairly well with the theoretical value of 17 calculated from the observed beam radius (0.5 mm) at the waist. Hence the observed small enhancement factor is ascribed to poor beam quality of the dye laser used. Pulsed thermal lens spectrophotometry is shown to be useful especially for the analysis of gaseous samples at elevated temperatures.     

Humidity-responsive thermal conduction properties of bacterial cellulose films

Cellulose - High hygroscopicity is an unavoidable feature of cellulose materials, and it is important for clarifying the humidity dependence of the target function toward precise utilization....     

Identification of conjugation positions of urinary glucuronidated vitamin D3 metabolites by LC/ESI–MS/MS after conversion to MS/MS‐fragmentable derivatives

A liquid chromatography/electrospray ionization–tandem mass spectrometry‐based method was developed for the identification of the conjugation positions of the monoglucuronides of 25‐hydroxyvitamin D₃ [25(OH)D₃] and 24,25‐dihydroxyvitamin D₃ [24,25(OH)₂D₃] in human urine. The method employed derivatization with 4‐(4‐dimethylaminophenyl)‐1,2,4‐triazoline‐3,5‐dione to convert the glucuronides into fragmentable derivatives, which provided useful product ions for identifying the conjugation positions during the MS/MS. The derivatization also enhanced the assay sensitivity and specificity for urine sample analysis. The positional isomeric monoglucuronides, 25(OH)D₃‐3‐ and ‐25‐glucuronides, or 24,25(OH)₂D₃‐3‐, ‐24‐ and ‐25‐glucuronides, were completely separated from each other under the optimized LC conditions. Using this method, the conjugation positions were successfully determined to be the C3 and C24 positions for the glucuronidated 25(OH)D₃ and 24,25(OH)₂D₃, respectively. The 3‐glucuronide was not present for 24,25(OH)₂D₃, unlike 25(OH)D₃, thus we found that selective glucuronidation occurs at the C24‐hydroxy group for 24,25(OH)₂D₃.     

Direct polycondensation of hydroxybenzoic acids with thionyl chloride in pyridine

The reaction promoted by thionyl chloride and pyridine could selectively activate carboxyl groups of hydroxybenzoic acids to give polyesters of high inherent viscosities up to 3.8. Favorable conditions were studied in terms of the temperatures for the initial reaction with the acids and subsequent aging at room temperature. Copolymers of several combinations of hydroxybenzoic acids with high molecular weights were obtained in quantitative yield by carrying out the polycondensation at 80°C for 3 h. The reaction could also produce high molecular polyesters in a simpler process without the initial activation of dicarboxylic acids by adding a mixture of these monomers to the condensing agent, and a tough film- and fiberforming polymer was obtained from 4,4′-dihydroxyphenylsulfone of low nucleophilicity whose polymer of high molecular weight is difficult to obtain. The process was also successfully applied to the direct copolycondensations of hydroxybenzoic acids, aromatic dicarboxylic acids, and bisphenols to produce polyesters of η_inh up to 5.6.     

Determination of 24,25-dihydroxyvitamin D(3) in human plasma using liquid chromatography-mass spectrometry after derivatization with a Cookson-type reagent

A practical LC-MS method for determination of (24R)-24,25-dihydroxyvitamin D(3) [24,25(OH)(2)D(3)] in human plasma has been developed using derivatization with a Cookson-type reagent, 4-[4-(6-methoxy-2-benzoxazolyl)phenyl]-1,2,4-triazoline-3,5-dione (MBOTAD). The derivatization with MBOTAD significantly improved the ionization efficiency of the analyte with a detection limit of 18 fmol [equivalent to 7.5 pg of 24,25(OH)(2)D(3)] per injection. The method employed protein precipitation with acetonitrile, purification with OASIS HLB cartridge and silica gel column, derivatization with MBOTAD and atmospheric pressure chemical ionization MS detection. The mass spectrometer was operated in the positive-ion mode of mass chromatography and [26,26,26,27,27,27-(2)H(6)]-24,25(OH)(2)D(3) was used as an internal standard. The intra- and inter-assay coefficients of variation were below 3.4 and 2.5%, respectively, and the analytical recovery of 24,25(OH)(2)D(3) was quantitative. Assay linearity was obtained in the range of 0.05-1.2 ng per tube and the limit of quantitation was 0.23 ng/mL for a 0.3 mL plasma aliquot. The developed method was applied to plasma samples obtained from volunteers and gave satisfactory results.     

Gas chromatography and high-performance liquid chromatography of natural steroids.

This review article underlines the importance of gas chromatography (GC), high-performance liquid chromatography (HPLC) and their hyphenated techniques using mass spectrometry (MS) for the determination of natural steroids, especially in human biological fluids. Steroids are divided into eight categories based on their structures and functions, and recent references using the above methodologies for the analysis of these steroids are cited. GC and GC-MS are commonly used for the determination of volatile steroids. Although HPLC is a widely used analytical method for the determination of steroids including the conjugated type in biological fluids, LC-MS is considered to be the most promising one for this purpose because of its sensitivity, specificity and versatility.     

Regioselectivity Control in Lipase‐Catalyzed Polymerization of Divinyl Sebacate and Triols

Lipase‐catalyzed regioselective polymerization of divinyl sebacate and triols has been performed in bulk. NMR analysis of the product obtained by the polymerization of divinyl sebacate and glycerol using Candida antarctica lipase at 60°C showed that 1,3‐diglyceride was a main unit and a small amount of the branching unit (triglyceride) was contained. The polymerization of divinyl sebacate with 1,2,4‐butanetriol or 1,2,6‐hexanetriol at 60°C produced a branched polymer. In polymerization at a lower temperature, the regioselectivity was perfectly controlled to give a linear polymer consisting of the α,ω‐disubstituted unit exclusively. The lipase origin and feed ratio of monomers greatly affected the microstructure of the polymer; under selected conditions, regiospecific polymerization was achieved.     

High-molecular-weight poly(p-phenyleneterephthalamide) by the direct polycondensation reaction with triphenyl phosphite

Poly(p-phenyleneterephthalamide) of high molecular weight was obtained when the polycondensation of terephthalic acid and p-phenylenediamine was carried out in N-methylpyrrolidone (NMP) that contained dissolved CaCl₂ and LiCl in the presence of pyridine. The molecular weight of the polymer obtained varied with the amount of pyridine relative to the metal salts and with the molar ratios of CaCl₂ to LiCl, the maximum η_inh value of 4.5 being obtained under the conditions Py/(CaCl₂ + LiCl) ≈ 2.5 (mol/mol), CaCl₂/LiCl ≈ 1.2 (mol/mol), and LiCl + CaCl₂ ≈ 4 g. Among the solvents tested, NMP was significantly effective for the reaction. Polycondensations of several combinations of other dicarboxylic acids and diamines were carried out with limited success.