Comparison of micellar electrokinetic chromatography, liquid chromatography, and microbiologic assay for analysis of cephalexin in oral suspensions

Two well-accepted methodologies, based on a microbiologic assay (MA) and liquid chromatography (LC), and a novel methodology using micellar electrokinetic chromatography (MEKC), were compared for the determination of cephalexin in commercially available and simulated samples of oral suspensions. The MA, described in the Brazilian Pharmacopeia, was performed with a strain of Staphylococcus aureus ATCC 6538 as the test organism, following the cylinder-plate method. The LC analysis followed the European Pharmacopoeia, 3rd Ed., and was used with minor modifications. The MEKC analysis was based on a previous work of the group. Estimates of the repeatability relative standard deviations of the MA, LC, and MEKC methods in the analysis of a commercial sample were 0.34, 0.42, and 0.37%, respectively. The recovery obtained with LC was 99.90 +/- 1.11%; for MEKC, it was 100.09 +/- 0.56%. Although the 3 methodologies were statistically equivalent for the determination of cephalexin in oral suspensions, MA gave suitable repeatability despite being nonspecific and time-consuming. MEKC provided faster analysis and higher column efficiency, whereas LC presented superior sensitivity. The results indicated that MEKC can be used as an alternative method to MA and LC in routine quality control laboratories.     

Metabolism of a novel antiangiogenic agent KR-31831 in rats using liquid chromatography-electrospray mass spectrometry

KR-31831 ((2S,3R,4S)-4-(((1H-imidazol-2-yl)methyl)(4-chlorophenyl)amino)-6-amino-2-(dimethoxymethyl)-2-methyl-3,4-dihydro-2H-chromen-3-ol) is a novel antiangiogenic agent. In vitro and in vivo metabolism of KR-31831 in rats has been investigated using LC-MS and LC-MS/MS analysis. Incubation of rat liver microsomes and hepatocytes with KR-31831 produced three metabolites (M1-M3). M1, M2, and M3 were identified as N-((1H-imidazol-2-yl)methyl)-4-chlorobenzenamine, (2R,3R,4S)-4-(((1H-imidazol-2-yl)methyl)(4-chlorophenyl) amino)-6-amino-2-(hydroxymethyl)-2-methyl-3,4-dihydro-2H-chromen-3-ol, and N-((2S,3R,4S)-4- (((1H-imidazol-2-yl)methyl)(4-chlorophenyl)amino)-2-(dimethoxymethyl)-3-hydroxy-2-methyl-3,4-dihydro-2H-chromen-6yl)acetamide, respectively, by co-chromatography with the authentic standards and by comparison with product ion spectra of the authentic standards. Those in vitro metabolites were also detected in bile, plasma, or urine samples after an intravenous administration of KR-31831 to rats. The metabolic routes for KR-31381 included the metabolism of acetal group to hydroxymethyl group (M2), N-dealkylation to M1, and N-acetylation at the 6-amino group (M3).     

Preliminary investigation of the water-soluble polysaccharides from the leaves of the bambooSasamorpha chiisanensis

It has been shown that the water-soluble polysaccharides of the leaves of the bambooSasamorpha chiisanensis Nak., after the removal of starch, contain residues of D-galactose, D-glucose, mannose, arabinose, D-xylose, rhamnose, and glucuronic and galacturonic acids and form an involved polysaccharide complex. Eight polysaccharide fractions differing in their uronic acid contents and in the ratio of neutral sugars have been isolated with the aid of chromatography on DEAE-cellulose.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–48, January–February, 1987.     

Intramolecular, reductive cyclization of beta-ketoisothiocyanates promoted by using samarium diiodide

A novel samarium diiodide (SmI2) promoted intramolecular cyclization of beta-ketoisothiocyanate, derived from alpha,beta-unsaturated esters and ammonium thiocyanate led to alpha-hydroxythiolactams and/or thiolactams in high yields. Treatment of beta-ketoisothiocyanate with two equivalents of SmI2 gave a mixture of alpha-hydroxythiolactam and thiolactam. Four equivalents of SmI2 afforded only thiolactam in high yields. The intramolecular cyclization took place with high to complete stereoselectivity. A mechanism to explain this transformation is proposed.     

An Opportunity for Recycling Semi‐dry Scrubber Residues Directly from Municipal Solid Waste Incineration Plants without Concern of Leaching Toxicity

The leaching behaviors of heavy metals from semi‐dry scrubber (SDS) residues of municipal solid waste incineration (MSWI) plants are re‐investigated. The most leachable heavy metals in semi‐dry scrubber residues from municipal solid waste incinerators are found to be chromium ions (Cr(III) and Cr(VI)), but neither lead nor cadmium. Both of the leachabilities of Cr(III) and Cr(VI) in MSWI scrubber residue are a function of the CaO/Al₂O₃ ratio of residues. The pH‐dependent leaching behaviors are only observed in the case of Cr(III), but not for Cr(VI). Our results show that it is worth recycling SDS residues which possess a lower chemical composition ratio of CaO/Al₂O₃, in order to reduce the potential risk of toxic leaching of chromium species.     

Participation of benzene hydrogen bonding upon anion binding

A m-xylene-bridged imidazolium receptor, 1, has been designed and synthesized. The receptor 1 utilizes two imidazole (C-H)(+)- - -anion hydrogen bonds and one benzene hydrogen- - -anion hydrogen bond. The major driving force of complexation between the receptor 1 and anions comes from two imidazole (C-H)(+)- - -anion hydrogen bonds. However, both NMR experiments and ab initio calculations show that the benzene hydrogen attracts the anion guests, clearly indicating benzene (C-H)- - -anion hydrogen bonding. [reaction: see text]     

Single-walled carbon nanotube biosensors using aptamers as molecular recognition elements

We report the real-time detection of protein using SWNT-FET-based biosensors comprising DNA aptamers as molecular recognition elements. Anti-thrombin aptamers that are highly specific to serine protein thrombin were immobilized on the sidewall of a SWNT-FET using CDI-Tween linking molecules. The binding of thrombin aptamers to SWNT-FETs causes a rightward shift of the threshold gate voltages, presumably due to the negatively charged backbone of the DNA aptamers. While the addition of thrombin solution causes an abrupt decrease in the conductance of the thrombin aptamer immobilized SWNT-FET, no noticeable change was observed with elastase.     

Effective preparation of montmorillonite/polyurethane nanocomposites by introducing cationic groups into the polyurethane main chain

In this study, the effect of introducing a small amount of cationic groups into the polymer main chain on the exfoliation of montmorillonite (MMT) and the physical properties of the subsequent MMT/polymer nanocomposites were investigated. As a matrix polymer, a polyurethane cationomer (PUC) containing 3 mol% of quaternary ammonium groups was synthesized and MMT/PUC nanocomposites containing various amounts of MMT were prepared by the solution intercalation method. From the WAXS and TEM analyses, it was found that the MMT layers were completely exfoliated and dispersed in the PUC matrix. The Young’s modulus of the MMT/PUC nanocomposites significantly increased with increasing MMT content, but their elongation at break and maximum stress were maintained at a level close to that of the PU only at an MMT content of 1 wt% and decreased as the content of MMT increased above this level. The phase separation of the MMT/PUC nanocomposites was retarded with increasing content of MMT, due to the strong interactions between the PUC chains and the exfoliated MMT layers. It was found that the presence of small amounts of cationic groups in the main chain of the matrix polymer was very effective in facilitating the preparation of the MMT/polymer nanocomposites.     

A new C2-symmetric chiral bisphosphine ligand containing a bioxazole backbone: highly enantioselective hydrosilylation of ketones

C₂-Symmetric (4S,4′S)-2,2′-bis(o-diphenylphosphinophenyl)-4,4′,5,5′-tetrahydro-4,4′-bi(1,3-oxazole) (1, Phos-Biox) has been designed and synthesized as a chiral ligand for metal-catalyzed reactions. The Phos-Biox 1 was found to be an efficient ligand for rhodium(I)-catalyzed asymmetric reduction of prochiral acetophenones with diphenylsilane to give optically active secondary alcohols of up to 97% ee.     

Separation of racemic 2,4-dinitrophenyl amino acids on zirconia-immobilized quinine carbamate in reversed-phase liquid chromatography

Zirconia is known to be one of the best chromatographic support materials due to its excellent chemical, thermal, and mechanical stability. A quinine carbamate-coated zirconia was prepared as a chiral stationary phase for separation of enantiomers of DNP-amino acids in reversed-phase liquid chromatography. Retention and enantioselectivity of this phase were compared to those for quinine carbamate bonded onto silica. Most amino acids studied were separated on the quinine carbamate-zirconia CSP although retention was longer and chiral selectivity was somewhat lower than on the corresponding silica CSP. Increased retention and decreased selectivity are probably due to strong non-enantioselective Lewis acid-base interactions between the amino acid molecule and the residual Lewis acid sites on the zirconia surface.