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Biomedical subjects

X Ji

Publications and source records attributed to X Ji.

At least 181 records · Page 10Linked to original sources
PubMed1989

The structures of different diastereomers of bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide.

Three diastereomers of bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide were prepared by Diels-Alder [4 + 2] cycloadditions between phenyl vinyl sulfoxide and cyclopentadiene. The isomers were separated by column chromatography on silica gel and repeated recrystallizations gave the pure racemates of three of the four possible diastereomers. It proved to be impossible to assign the stereochemistry of the products from low-resolution NMR spectra. The X-ray diffraction studies of the three diastereomers showed the relative configuration at the two chiral centers and these stereochemical assignments were, subsequently, correlated with the two-dimensional NMR spectroscopic results. Compound (I), exo-(2R*,8S*)-bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide [or the exo-(2S*,8R*)-isomer], C13H14OS, Mr = 218.31, orthorhombic, P2(1)2(1)2(1), a = 10.517 (2), b = 10.914 (2), c = 9.642 (3) A, V = 1106.7 A3, Z = 4, Dx = 1.31 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 22.14 cm-1, F(000) = 464, T = 138 (2) K, R = 0.042 for 1151 data. Compound (II), exo-(2RS,8RS)-bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide, C13H14OS, Mr = 218.31, triclinic, P1, a = 8.775 (4), b = 16.353 (8), c = 7.804 (3) A, alpha = 90.67 (3), beta = 101.08 (4), gamma = 85.64 (5) degrees, V = 1095.8 A3, Z = 4, Dx = 1.32 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 2.18 cm-1, F(000) = 464, T = 138 (2) K, R = 0.062 for 3264 data. The two molecules in the asymmetric unit are crystallographically independent, but their conformations are similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Bridged Bicyclo Compounds↗
PubMedDate not supplied

Effect of enhancers on the pyridopyridazine-peroxide-HRP reaction.

4-Substituted phenyl boronic acids (e.g., 4-iodo, 4-bromo, 4-phenyl) are effective enhancers of the horseradish peroxidase (Type VIA) catalysed chemiluminescent oxidation of various pyrido[3,4-d]pyridazine-1,4(2H,3H)dione derivatives. The most effective combination was 4-biphenylboronic acid and 8-amino-5-chloro-7-phenylpyrido[3,4-d]- pyridazine-1,4(2H,3H)dione. Generally, the intensity of light emission in the presence of peroxidase was higher with the pyridopyridazines than with sodium luminol. However, the blank light emission was much lower with sodium luminol than with the pyridopyridazines. A synergistic enhancement phenomenon was demonstrated for the combination of a 4-iodophenol and a 4-biphenylboronic acid enhancer with 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4(2H,3H) dione. The combination of these two enhancers produced a light emission intensity in an assay for 5 fmol of peroxidase that was 25% higher than expected from the sum of the individual light intensities.

Boronic Acids↗
PubMedDate not supplied

Super-sensitive enzyme immunoassay for thyroid stimulating hormone using a new synergistic enhanced chemiluminescent endpoint.

The enhancers 1,1'-biphenyl-4-yl boronic acid and 4-iodophenol act synergistically in the horseradish peroxidase-catalysed oxidation of luminol. This concentration-dependent effect reduces background, increases signal and hence improves signal/background for detection of peroxidase. The same type of synergistic effect was found when 1,1'-biphenyl-4-yl boronic acid was added to a commercial enhanced chemiluminescence signal reagent (Amerlite Signal Reagent). This synergistic enhanced chemiluminescent endpoint (Amerlite Signal Reagent containing 1,1'-biphenyl-4-yl boronic acid) for a horseradish peroxidase label has been tested in the Amerlite TSH and the Amerlite TSH-30 Ultrasensitive assays. The detection limit (mean of 20 replicates of the zero standard+2SD) in the Amerlite TSH assay was 0.0029 mIU/L, and in the Amerlite TSH-30 Ultrasensitive assay the detection limit was 0.0005 mIU/L using the synergistic enhanced endpoint. Reassessment of the detection limit using a 1:40 dilution of the first standard (0.119 mIU/L) as the lowest assay standard gave a value of 0.0015 mIU/L for the Amerlite TSH-30 Ultrasensitive assay with the synergistic endpoint. A limited (n = 29) method comparison using samples from euthyroid, hyperthyroid and hypothyroid patients revealed excellent correlation between the conventional and synergistic TSH immunoassays.

Boronic Acids↗
PubMedDate not supplied

Effect of polymers on enhanced chemiluminescent assays for peroxidase and peroxidase labels.

Hydroxypropyl methylcellulose, hydroxyethyl cellulose, and hydroxybutyl methylcellulose stabilized light emission in a boronic acid-enhanced chemiluminescent assay for horseradish peroxidase. The stabilization of light emission was concentration-dependent and more effective with substituted boronic acid enhancers (e.g. 4-iodophenylboronic acid) than with substituted phenol enhancers (e.g. 4-iodophenol). Hydroxybutyl methylcellulose improved the linearity of the dose-response curve in a peroxidase-based antioxidant assay and stabilized light emission post-consumption of the antioxidant (Trolox). This polymer had no effect on the signal from a peroxidase label immobilized on a membrane (dot blot) or on the inside surface of a microwell in an enzyme immunoassay for thyrotropin.

Antioxidants↗
PubMedDate not supplied

Imaging of chemiluminescent reactions in mesoscale silicon-glass microstructures.

Chemiluminescent reactions in mesoscale analytical structures (chips) containing micrometre-sized interconnecting channels and chambers (pL-nL total volume) were imaged. The chips were fabricated by bonding Pyrex glass to etched pieces of silicon using a high-temperature diffusive bonding technique. In initial experiments light emission from an enhanced chemiluminescent horseradish peroxidase reaction and from a peroxyoxalate reaction contained in straight channels (300 microns wide x 20 mu deep; volume 70.2 nL) and open chambers (812 microns wide, 400 microns deep, 5.2 mm long) linked by channels (100 microns wide, 20 microns deep) to an exit and entry port were studied using a specially modified microplate holder and an Amerlite microplate luminometer. Light emission from more complex structures (two chambers interconnected by a branching channel 100 microns wide, 20 microns deep) filled with a solution containing alkaline phosphatase, Emerald, and CSPD was imaged using a Photometrics Star 1 CCD camera. Detailed investigation of the detection and spatial resolution of the signal was performed on a Berthold Luminograph LB 980 using both the enhanced chemiluminescent horseradish peroxidase reaction and a peroxyoxalate reaction. We successfully resolved light emission from silicon structures with dimensions 100 microns wide and 20 microns deep. These simple silicon structures served as models for more complex designs that will be used for simultaneous multi-analyte assays in which an imaging system resolves and quantitates light emission from different locations on a silicon-glass analytical device.

Glass↗
PubMedDate not supplied

4-Phenylylboronic acid: a new type of enhancer for the horseradish peroxidase catalysed chemiluminescent oxidation of luminol.

4-Phenylylboronic acid enhances the light emission from the horseradish peroxidase catalysed oxidation of luminol by hydrogen peroxide. Optimization studies showed that the greatest enhancement was obtained using micromolar concentrations of the new enhancer. The largest degree of enhancement was found with the basic isoenzyme of horseradish peroxidase (Type VIA), and lesser degrees of enhancement were obtained with Type VII and Type IX horseradish peroxidase. The enhancer was also effective in the peroxidase catalysed oxidation of isoluminol by peroxide.

Boronic Acids↗
PubMedDate not supplied

New enhancers for the chemiluminescent peroxidase catalysed chemiluminescent oxidation of pyrogallol and purpurogallin.

The effects of various boronate compounds, 4-biphenylboronic acid, 4-bromobenzene-boronic acid, trans-4-(3-propionic acid)phenylboronic acid and 4-iodophenylboronic acid, on the horseradish peroxidase (HRP) catalysed chemiluminescent oxidation of pyrogallol and purpurogallin by peroxide were investigated. trans-4-(3-Propionic acid)phenylboronic acid produced a 13.7-fold enhancement in the peak light emission from the chemiluminescent HRP catalysed pyrogallol reaction (detection limit for HRP < 1.25 fmol). At low enhancer concentration a single peak of light emission was observed and as the enhancer concentration increased the time to peak light emission became progressively longer. The chemiluminescence showed two peaks at higher concentrations (> 54.3 mumol/L) and the individual peak times depended upon the concentration of the enhancer. All of the boronates enhanced peak light emission in the chemiluminescent HRP catalysed purpurogallin reaction. 4-Biphenylboronic acid was the most effective and it enhanced peak light emission 314-fold. The practical detection limit for HRP (Type VIA) using this enhancer was 4.18 pmol (peak emission at 20 minutes). This compound also enhanced peak light emission 232-fold from a chemiluminescent HRP-purpurogallin reaction in which molecular oxygen replaced peroxide as the oxidant.

Antioxidants↗