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Biomedical subjects

J H Xu

Publications and source records attributed to J H Xu.

At least 19 recordsLinked to original sources
PubMed2006

Controllable preparation of monodisperse O/W and W/O emulsions in the same microfluidic device.

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants. Highly uniform droplets ranging from 50 to 400 mum with a polydispersity index (sigma) value of less than 2% were successfully prepared. With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable. Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 0.1-2.0 wt % Span 80 and an aqueous solution with 0.1-2.0 wt % Tween 20 as a continuous-phase flow, respectively. It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device.

Emulsions↗
PubMed2005

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties.

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Emulsions↗
PubMed2001

1-acetyl-3-[benzoyl(4-methoxyphenyl)methylene]-2,3-dihydro-1H-indol-2-one.

In the title compound, C25H19NO4, the indole moiety is not completely planar, the heterocyclic ring being distorted very slightly towards a half-chair conformation. The benzoyl and 4-methoxyphenyl substituents are individually almost planar and are in a bisecting and nearly perpendicular configuration, respectively, with respect to the plane of the indole moiety. The molecular and packing structures in the crystal are stabilized by intramolecular and intermolecular C-H...O interactions.

Journal Article↗
PubMed2001

Efficient preparation of (R)-alpha-monobenzoyl glycerol by lipase catalyzed asymmetric esterification: optimization and operation in packed bed reactor.

Optically active (R)-alpha-monobenzoyl glycerol (MBG) was synthesized by Candida antarctica lipase B (CHIRAZYME L-2) catalyzed asymmetric esterification of glycerol with benzoic anhydride in organic solvents. Various conditions, such as the type and composition of the organic solvent, water content of the system, reaction temperature, and concentrations of the substrates were systematically examined and optimized in screw-capped test tubes with respect to both the reaction rate and the enzyme selectivity. 1,4-Dioxane was found to be the best solvent and no additional water was needed for the system. The optimum temperature was around 30 degrees C, while the most suitable substrate concentrations were 100 mM each for glycerol and benzoic anhydride, respectively. However, when excessive anhydride (e.g., 200 mM) was used, the produced MBG could be further transformed into 1,3-dibenzoyl glycerol (DBG) by the same enzyme with a priority to (S)-MBG, resulting in a significant improvement of the product optical purity from ca. 50-70% e.e. Under optimal conditions (100 mM glycerol, 100-200 mM benzoic anhydride, dioxane, 25-30 degrees C), the enzymatic synthesis of (R)-MBG was successfully operated in a packed-bed reactor for about 1 week, with an average productivity of 0.79 g MBG/day/g biocatalyst in the case of continuous operation and 0.94 g MBG/day/g biocatalyst in the case of semicontinuous operation. After refinement and preferential crystallization of the crude product, (R)-MBG could be obtained in an almost optically pure form (>98% e.e.).

Benzoates↗
PubMed2001

Dynamics of 'Technegas' deposited in the lung.

In tomographic Technegas ventilation studies, the deposited aerosol should be stable. The aim of this study was to investigate the stability of deposited Technegas in severely obstructed patients and in healthy volunteers. Six emphysematous patients and five healthy volunteers were studied. Anterioposterior (AP) and posterioanterior (PA) dynamic images of ventilation (120 frames, 1 frame.min-1) were acquired after inhalation of 99mTc-Technegas' in the supine position. The time-activity curve of the whole lung showed two phases in the emphysematous patients as well as in the healthy volunteers. The activity decreased rapidly in the first phase, then reached almost a constant level (the second phase) after approximately 50 min. The logarithms of both the first phase and the second phase were close to straight lines. The half-time of the first phase was approximately 9 min. No systematic differences in 'Technegas' clearance rate were found between central regions and peripheral regions and between high count rate regions and normal count rate regions. Pertechnegas contamination was subsequently detected, and we conclude that the rapid first phase is probably due to clearance of Pertechnegas. When stable Technegas is required, we suggest that data acquisition should start about 50 min after inhalation.

Adult↗
PubMed2001

Isolation of an esterase-producing Trichosporon brassicae and its catalytic performance in kinetic resolution of ketoprofen.

A yeast strain CGMCC 0574, identified as Trichosporon brassicae, was selected from 92 strains for its high (S) selectivity in the hydrolysis of ketoprofen ethyl ester. The effective strains of the microorganisms were isolated from soil samples with the ester as the sole carbon source. The ethyl ester proved to be the best substrate for resolution of ketoprofen among several ketoprofen esters examined. The resting cells of CGMCC 0574 could catalyze the hydrolysis of ketoprofen ethyl ester with an enantiomeric ratio of 44.9, giving (S)-ketoprofen an enantiomeric excess of 91.5% at 42% conversion.

Esterases↗
PubMed2001

[Investigation on the excited state dynamics properties of hemicyanine molecules].

In this paper, the excited state dynamics properties of hemicynine were investigated by using time-resolved fluorescence and 3D fluorescence spectra techniques. The interaction of hemicyanine molecules caused formation of H-aggregates and a blue shift of the 3D fluorescence spectra in interleaving hemicyanine/arachidic acid multilayers. The peak of fluorescence was a red shift along with the time decay. The lifetime of the LB fluorescence was much shorter and the difference of beginning luminescence was less than that of the hemicyanine solution due to the stronger intermolecule interactions in the aggregates.

English Abstract↗
PubMed2000

Photoinduced reactions of 1-acetylisatin with phenylacetylenes.

[reaction: see text]Photoinduced reactions of 1-acetylisatin 1 with diphenylacetylenes 2a-2c afforded the corresponding 3-methylene-2-indolones 4a-4e and 5a-5e in 80-90% yields via a spirooxetene intermediate. Similar irradiation of 1 with phenylacetylene, on the other hand, resulted in efficient formation of two diastereoisomeric dispiro[3H-indole-3,2'-furan-3',3"-(3H)-indole]-2,5',2"(2H,5'H,2"H )triones 6 and 7 via a reaction sequence with initial formation of the spirooxetene intermediate. The regioselectivity in the photocycloaddition of 1 with phenylacetylene and the reaction mechanism for the formation of 6 and 7 are discussed.

Acetylene↗
PubMed2000

Distribution of ventilation-to-perfusion ratios analysed in planar scintigrams of emphysematous patients.

The aim of the present study was to develop and evaluate a method for semi-quantification of ventilation-to-perfusion ratios in small regions in planar pulmonary scintigrams using 99mTc-Technegas (Tetley Manufacturing Ltd, Sydney, Australia) and 99mTc-macro-aggregated human albumin. Eight emphysematous patients and eight healthy volunteers were investigated in the supine position. Anterio-posterior and posterio-anterior images of ventilation and ventilation-and-perfusion were acquired consecutively. Perfusion images were obtained by subtracting the corrected ventilation images from ventilation-and-perfusion images. Lung regions of interest were divided into 2.03 x 2.03 cm regions. The ratio of normalized counts of ventilation-to-perfusion (V/Q) was calculated in each square region. The log (V/Q)s of healthy volunteers were distributed symmetrically and similarly around 0, whereas the corresponding ratios in patients distributed unevenly. The standard deviations of log (V/Q)s were significantly higher in patients than in healthy volunteers. Parametric images of V/Q distribution were constructed to visualize the magnitude and location of 'waste ventilation' and 'shunt' effects. In conclusion, the present semi-quantitative method is validated by confirming the expected dispersed V/Q distribution in emphysematous patients compared to healthy volunteers.

Adult↗
PubMed1999

Plasma homocysteine distribution and its association with parental history of coronary artery disease in black and white children: the Bogalusa Heart Study.

BACKGROUND: Elevated homocysteine is associated with increased risk for coronary artery disease (CAD) in adults, but its distribution in children is not well documented. We examined the distribution of homocysteine in children and its relation to parental history of CAD. METHODS AND RESULTS: A subsample of 1137 children (53% white, 47% black) aged 5 to 17 years in 1992 to 1994 examined in the Bogalusa Heart Study (n=3135), including all with a positive parental history of CAD (n=154), had plasma homocysteine levels measured. Homocysteine correlated positively with age (r=0.16, P=0.001). No race or sex differences in homocysteine levels were observed; geometric mean (GM) levels were 5.8 micromol/L (95% CI, 5.6 to 6.1) among white males, 5.8 micromol/L (95% CI, 5.5 to 6.0) among white females, 5.6 micromol/L (95% CI, 5.4 to 5.8) among black males, and 5.6 micromol/L (95% CI, 5.4 to 5.9) among black females. Children with a positive parental history of CAD had a significantly greater age-adjusted GM homocysteine level (GM, 6.7 micromol/L; 95% CI, 6.4 to 7.1) than those without a positive history (GM, 5.6 micromol/L; 95% CI, 5.4 to 5.7); this relation was observed in each race-sex group. CONCLUSIONS: Higher homocysteine levels were observed among children with a positive family history of CAD. Additional studies should elucidate the contribution of genetic, dietary, and other factors to homocysteine levels in children.

Adolescent↗
PubMed1999

[A method for preparation of carbon fiber electrode].

Carbon fiber electrode (CFE) can be used in detection of exocytosis of single neuron or endocrine cell. A simplified method for preparation of CFE, as described in the present paper, greatly ensures the coordination and success of the preparation. Such CFEs have a low noise level. Exocytosis of rat adrenal chromaffin cells was investigated in the clarification of the effect of MPP+ on transmitter release. It is found that exocytosis was not stimulated by MPP+ and the high K+ induced secretion was not changed by MPP+. These observations suggest that the previously reported elevation of dopamine content in the surrounding histosolution of DA neuron is probably resulted from blockage of the re-uptake of DA by MPP+.

1-Methyl-4-phenylpyridinium↗
PubMed1999

[Role of M-type receptor in internal calcium release and quantal secretion in rat adrenal chromaffin cells].

In rat single adrenal chromaffin cells, the effects of methacholine (MCh) on [Ca2+]i and catecholamine secretion were studied with fura-2 fluorescence and carbon fiber electrodes. In the presence of 2 mmol/L Ca2+ in the bath, locally applying 1 mmol/L MCh, either containing or not containing Ca2+, evoked both [Ca2+]i and secretion signals. In the absence of Ca2+ in the bath, MCh could still evoke [Ca2+]i and secretion. These results suggest that MCh causes release of Ca2+ from Ca2+ stores, which is sufficient to yield the evoked secretion. The Ca2+ store can be depleted by single MCh puff in the absence of Ca2+ in the bath.

Adrenal Medulla↗
PubMed1998

Microsatellite instability is rare in the clinical course of myelodysplastic syndrome studied with DNA from fresh and paraffin-embedded tissues.

Microsatellite instability (MSI) has been reported to occur in various types of malignant neoplasms. We performed a polymerase-chain-reaction-based assay for MSI between the initial and the most recently available ("latest") samples from 23 patients with myelodysplastic syndrome (MDS). Of these patients, 15 were informative at more than three microsatellite loci. Seven patients showed an increase in leukemic cells while 8 patients did not during the interval between the two analyses. Only 1 of the patients, who had refractory anemia with excess blasts, which changed to acute myelogenous leukemia, showed microsatellite alteration at the analysis times. Among all 23 patients, two alterations were detected in the 42 informative paired samples that showed an increase in leukemic cells (4.8%), while none was detected in the 59 paired samples without such an increase. In total, therefore only two alterations were detected among 101 informative paired samples (2%). This indicates that MSI is rare in the clinical course of MDS irrespective of disease status, and is consequently not a critical genetic event for disease progression in most MDS patients.

Adult↗
PubMed1998

Inhomogeneity in planar ventilation scintigraphy of emphysematous patients.

The aim of this study was to develop and evaluate a method for the quantification of inhomogeneity in ventilation scintigraphy. Ten healthy volunteers and 10 emphysematous patients were investigated. Anteroposterior (AP) and Posteroanterior (PA) images of planar ventilation scintigraphy were acquired. Lung regions of interest (ROI) were obtained by manual delineation of the lung contours and then divided into several 10-pixel-high horizontal-stripe regions. By allowing for the statistical noise of the pixel count rate, the biological coefficient of variation (CVB) of the pixel counts in each stripe region was calculated. The apex-to-base distribution of the CVB in the emphysematous lungs dispersed largely and with higher values than the corresponding distribution in the healthy lungs. The mean values of the CVB (MCVB), the ranges of the CVB (RCVB) and the maximum values of the CVB (MAXCVB) in the stripe regions in emphysematous lungs were significantly higher than the corresponding ones in the healthy lungs (all P < 0.001). The intraobserver variations of the MCVB, RCVB and MAXCVB (calculated using the standard deviations of the differences) were less than 2.3% units, 5.2% units and 3.9% units respectively. The corresponding values for interobserver variation were 5.7% units, 6.1% units and 6.4% units. A systematic decrease in lung ROI size, i.e. inclusion of successively less of the lung edge, resulted in a linear decrease of 1.7% units in the MCVB and MAXCVB of both emphysematous and normal lungs. In conclusion, the stripe-region method is a reliable tool for the quantification of inhomogeneity in the planar ventilation scintigraphy.

Adult↗
PubMed1997

[The anti-anaphylactic action of potassium channel openers and its mechanism].

The anti-anaphylactic action of potassium channel openers was studied and reported in this paper. Minoxidil(Min) was shown to inhibit passive cutaneous anaphylaxis in rats. Diazoxide (Dia) and Min were found to inhibit antigen-induced guinea-pig ileum smooth muscle contraction in vitro. Min was shown to antagonize 5-HT-induced capillary permeability in rat skin. Dia was demonstrated to inhibit histamine release from rat peritoneal mast cells induced by A23187 and compound 48/80, but it failed to antagonize guinea-pig ileum smooth muscle contraction induced by histamine in vitro. These results provide evidence that potassium channel openers may be a new group of inhibitors of histamine release and indicate that the mechanism of its anti-anaphylactic action may be related to its potassium channel opening effect. As a result of this effect, Ca2+ influx to the mast cells decreases and Ca2+ release from calcium storage was inhibited, thus inhibiting histamine release.

Anaphylaxis↗
PubMed1997

Repair of incomplete simple syndactyly by a web flap on a subcutaneous tissue pedicle.

A new web flap on a subcutaneous tissue pedicle was developed to repair incomplete simple syndactyly. It was isolated from the top skin in syndactyly and transferred down into the depth of the web space to create a web commissure. With use of this technique, aesthetic appearance of the web and well-functioning fingers were gained. Moreover, this technique made full use of the original skin of the syndactyly, and a skin graft was not needed. We report here the operative technique, which presents another alternative for repair of incomplete simple syndactyly.

Adolescent↗