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Biomedical subjects

X L Lu

Publications and source records attributed to X L Lu.

At least 19 recordsLinked to original sources
PubMed2006

Biodegradability and thermal stability of poly(propylene carbonate)/starch composites.

Poly(propylene carbonate)/starch (PPC/starch) composites with different starch contents were prepared by melt compounding. The biodegradability of the composites was studied by soil burial for a period of 6 months. FTIR study, thermal analysis and morphology observation indicated clearly the changes of the buried specimens. The weight loss curves and the molecular weight changes of the specimens revealed a three-stage biodegradation, corresponding to the propagation of microorganisms, the degradation of starch and the degradation of PPC. The experimental results showed that the addition of starch accelerated the degradation of PPC. Specimens with higher starch content exhibited greater weight loss in the second stage and smaller weight loss in the third stage.

Biocompatible Materials↗
PubMed2003

Correlations between cadmium and mineral nutrients in absorption and accumulation in various genotypes of rice under cadmium stress.

The absorption and accumulation of Cd2+, Fe3+, Zn2+, Mn2+, Cu2+ and Mg2+ in the roots and leaves of 20 rice cultivars (Oryza sativa L.) with different genotypes under cadmium (Cd) stress were investigated with pot experiments. The results showed that there existed significant differences among the rice cultivars in the contents of six mineral elements in both roots and leaves at both heading and ripening periods. The statistical analysis showed that, for their contents in roots, significant and positive correlations between Cd2+ and Fe3+, Cd2+ and Zn2+, Cd2+ and Mn2+, Cd2+ and Cu2+ existed, but no significant correlation between Cd2+ and Mg2+, at the two periods. In the leaves, Cd also showed significant and positive correlations with Fe3+, Zn2+ and Cu2+ at the both periods, but a significant and negative correlation with Mn2+ and no significant correlation with Mg2+ at heading, a significant and positive correlation with Mg2+ and no significant correlation with Mn2+ at ripening. These results suggested that there were cooperative absorption between Cd2+ and Fe3+, Mn2+, Cu2+, Mn2+ in rice plants. Genotypic differences in Cd uptake and translocation among the rice cultivars suggested that paddy field of some rice cultivars may be irrigated with partially treated sewage water.

Absorption↗
PubMed1999

Study of environmental biomonitoring of the Jiaozhou Bay.

The content of 34 elements was determined in tissue samples of several marine bivalve species collected from various sites in the Jiaozhou Bay. The scope of the study was to determine the most suitable bivalve species to be used for environmental biomonitoring and to evaluate the environmental status of the bay. Clams exhibited higher elemental contents than oysters and they are the major marine bivalve species in the Jiaozhou Bay; therefore, we consider clams to be more suitable than oysters as bioindicators for evaluating the environmental status of the area. Increased elemental levels in clam tissues indicate polluted sites. Also, increased elemental levels in mussels point to possible pollution from tourism development at one selected site.

Animals↗
PubMed1994

Enantiomer resolution of camazepam and its derivatives and enantioselective metabolism of camazepam by human liver microsomes.

Camazepam [3-(N,N-dimethyl)carbamoyloxy-7-chloro-1-methyl-1,3-dihydro- 5-phenyl-2H-1,4-benzodiazepin-2-one, CMZ] possesses anxiolytic, anticonvulsant, muscle relaxant, and hypnotic properties. CMZ is clinically used as a racemate. Enantiomer resolution of CMZ and 11 of its derivatives was studied by high-performance liquid chromatography (HPLC) using 5 different chiral stationary phase (CSP) columns. Enantiomers of 10 compounds were resolved by at least one of the 5 CSP's tested. Enantiomers of two other compounds, which have either one or two hydroxymethyl groups at the carbamoyl nitrogen, were either not resolved or resolved with very low efficiency. However, enantiomers of the hydroxymethyl derivatives were resolved via base-catalyzed dehydroxymethylation. In vitro metabolism of racemic CMZ by human liver microsomes was found to be enantioselective. Major metabolites were isolated by normal-phase and reversed-phase HPLC and further characterized by ultraviolet absorption and circular dichroism spectral analyses, and by chiral stationary phase HPLC analysis. Following an in vitro incubation of rac-CMZ, the unmetabolized CMZ was found to be enriched in (S)-CMZ, indicating that the R-enantiomer was enantioselectively metabolized. Metabolites were formed primarily by hydroxylation and demethylation of the methyl groups at the C3 side chain. All metabolites were found to be optically active, enriched in either the S-enantiomer or the R-enantiomer.

Adult↗
PubMed1991

N,N-dimethylcarbamyl derivatives of oxazepam.

Three N,N-dimethylcarbamyl derivatives of oxazepam (1-(N,N-dimethylcarbamyl)oxazepam, 3-O-(N,N-dimethylcarbamyl)oxazepam, and 1,3-O-bis(N,N-dimethylcarbamyl) oxazepam) and a 3-O-acyl-1-(N,N-dimethylcarbamyl)-oxazepam were synthesized from either oxazepam or demoxepam. Enantiomeric pairs of these derivatives and of camazepam were resolved by high-performance liquid chromatography on at least two of three commercially available chiral stationary phase columns employed. Absolute configurations of resolved enantiomers were established by comparing their circular dichroism spectra to those of enantiomeric oxazepams with known absolute stereochemistry. Similar to those of oxazepam, enantiomers of 1-(N,N-dimethylcarbamyl)oxazepam undergo rapid racemization (t1/2 1.9 min at 23 degrees C and 0.9 min at 37 degrees C) in an aqueous solution at pH 7.5. The (R)-enantiomer of rac-3-O-acyl-1-(N,N-dimethylcarbamyl)oxazepam was hydrolyzed approximately 4.6-fold faster than the (S)-enantiomer by esterases in rat liver microsomes, whereas the (S)-enantiomer was hydrolyzed approximately 43-fold faster than the (R)-enantiomer by esterases in rat brain S9 fraction.

Animals↗
PubMed1990

Metabolism of halazepam by rat liver microsomes: stereoselective formation and N-dealkylation of 3-hydroxyhalazepam.

Metabolism of halazepam [7-chloro-1,3-dihydro-5-phenyl-1-(2,2,2-trifluoroethyl)-2H-1,4-benzod iazepin- 2-one, HZ] was studied by incubation with liver microsomes prepared from untreated, phenobarbital (PB)-treated, and 3-methylcholanthrene (3MC)-treated male Sprague-Dawley rats. Metabolites of HZ were separated by normal-phase HPLC. Relative rates of HZ metabolism by liver microsomes prepared from untreated and treated rats were PB-treated much greater than untreated greater than 3MC-treated at low concentration of microsomal enzymes (0.25 mg protein per ml of incubation mixture) and PB-treated much greater than 3MC-treated approximately untreated at high concentration of microsomal enzymes (2 mg protein per ml of incubation mixture). The relative amounts of major metabolites were found to be 3-hydroxy-HZ (3-OH-HZ) greater than N-desalkylhalazepam (NDZ, also known as N-desmethyldiazepam and nordiazepam) much greater than oxazepam (OX) for all three rat liver microsomal preparations and the distribution of metabolites was independent of microsomal enzyme concentrations. Enantiomers of 3-OH-HZ were resolved by HPLC on a Chiralcel OC column (cellulose trisphenylcarbamate coated on silica gel, particle size 10 microns). 3-OH-HZ enantiomeres have racemization half-lives of approximately 150 min in pH 4, 7.5, and 10 aqueous solutions. 3-OH-HZ formed in the metabolism of HZ by liver microsomes prepared from untreated and treated rats were found to have 3R/3S enantiomer ratios of 37/63 (untreated), 55/45 (PB-treated), and 36/64 (3MC-treated), respectively. N-dealkylation of 3-OH-HZ by liver microsomes from PB-treated rats was substrate enantioselective; the 3R-enantiomer was N-dealkylated faster than 3S-enantiomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Improved enantiomeric separation of dihydrodiols of polycyclic aromatic hydrocarbons on chiral stationary phases by derivatization to O-methyl ethers.

K-region trans-dihydrodiol derivatives of phenanthrene, 1-methylphenanthrene, 4,5-methylenephenanthrene, pyrene, 1-bromopyrene, chrysene, benzo[c]phenanthrene, benz[a]anthracene, 1-, 4-, 6-, 7-, 11- and 12-methylbenz[a]anthracenes, 7,12-dimethylbenz[a]anthracene, 3-methylcholanthrene, and benzo[a]pyrene, and non-K-region trans-3,4-dihydrodiols of benz[a]anthracene, chrysene, and 7,12-dimethylbenz[a]anthracene are converted to O-methyl ethers. Enantiomers of these O-methyl ethers are generally more efficiently separated on Pirkle's chiral stationary phases than the enantiomers of underivatized dihydrodiols. O-Methyl ethers are substantially less polar than dihydrodiols, and O-methyl ethers are eluted with shorter retention times. Eluents of lower polarity can hence be used. This enhances chiral interactions between chiral stationary phase and solutes, allowing improved separation of enantiomers.

Chemical Phenomena↗
PubMed1989

Racemization kinetics of enantiomeric oxazepams and stereoselective hydrolysis of enantiomeric oxazepam 3-acetates in rat liver microsomes and brain homogenate.

Enantiomers of oxazepam and of 3-O-acyl, 1-N-acyl-3-O-acyl, and 3-O-methyl ether derivatives of oxazepam were resolved on HPLC columns packed with Pirkle's chiral stationary phases [CSP; (R)-N-(3,5-dinitrobenzoyl)phenylglycine or (S)-N-(3,5-dinitrobenzoyl)leucine] bonded either ionically or covalently to spherical particles of gamma-aminopropylsilanized silica, and on a column packed with poly-N-acryloyl-(S)-phenylalanine ethyl ester bonded covalently to silica gel (Chiraspher). Resolution was achieved, with several mobile phases of different solvent compositions and with varying chromatographic resolutions, on all of the chiral stationary phases tested. Resolved enantiomers of oxazepam undergo racemization, whereas enantiomers of 3-O-acyl and 3-O-methyl derivatives are stable. Racemization half-lives of oxazepam enantiomers were determined by monitoring changes in ellipticity as a function of time on a spectropolarimeter immediately (within 30 s) following resolution of enantiomers and were found to substantially vary, depending on the solvents used. Rates of hydrolysis of racemic and enantiomeric 3-O-acyl-oxazepams by esterases in liver microsomes and brain homogenate of rats were determined by a simple and sensitive CSP-HPLC method. The relative rate of hydrolysis was 3R greater than racemate much greater than 3S by rat liver microsomes and 3S greater than racemate much greater than 3R by rat brain homogenate.

Animals↗
PubMed1989

Metabolism of prazepam by rat liver microsomes: stereoselective formation and N-dealkylation of 3-hydroxyprazepam.

The metabolism of prazepam (7-chloro-1-(cyclopropylmethyl)-1,3-dihydro-2H-1, 4-benzodiazepin-2-one) (PZ) was studied using liver microsomes prepared from untreated, phenobarbital (PB)-treated, and 3-methylcholanthrene (3MC)-treated male Sprague-Dawley rats. Relative rates of PZ metabolism by liver microsomes prepared from rats were PB-treated greater than untreated greater than 3MC-treated. Metabolites of PZ were separated by normal phase high performance liquid chromatography and the relative amounts of major metabolites were found to be N-desalkylprazepam (also known as N-desmethyldiazepam and nordiazepam) greater than 3-hydroxy-PZ (3-OH-PZ) greater than oxazepam. Enantiomers of 3-OH-PZ were resolved by high performance liquid chromatography on an analytical column packed with Pirkle's chiral stationary phase, (R)-N-(3,5-dinitrobenzoyl)phenylglycine covalently bonded to spherical particles of gamma-aminopropylsilanized silica. 3-OH-PZ formed in the metabolism of PZ by liver microsomes prepared from rats was found to have 3R/3S enantiomer ratios of 84:16 (untreated), 85:15 (PB-treated), and 84:16 (3MC-treated), respectively. Relative rates of N-dealkylation of PZ by three rat liver microsomal preparations were PB-treated greater than untreated greater than 3MC-treated. N-Dealkylation of 3-OH-PZ by rat liver microsomes was substrate enantioselective; the 3S-enantiomer was N-dealkylated faster than the 3R-enantiomer. The results indicated that both C3-hydroxylation of PZ and N-dealkylation of 3-OH-PZ catalyzed by rat liver microsomes were stereoselective, resulting in the formation of a 3-OH-PZ highly enriched in the 3R-enantiomer.

Animals↗
PubMed1987

Thermal and pH stability of "beta-benzyme".

The thermal and pH stability of "beta-benzyme", an artificial chymotrypsin based on beta-cyclodextrin, has been studied and compared with the stability of real chymotrypsin. Artificial chymotrypsin is vastly superior to real chymotrypsin with regard to both temperature and pH stability. The reasons for this increased stability are discussed.

Chymotrypsin↗