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W T Yap

Publications and source records attributed to W T Yap.

14 recordsLinked to original sources
PubMed1994

Thermodynamics of the hydrolysis of penicillin G and ampicillin.

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the beta-lactamase catalyzed hydrolysis of penicillin G(aq) and ampicillin(aq) to penicillinoic acid(aq) and to ampicillinoic acid(aq), respectively. High-pressure liquid-chromatography and microcalorimetry were used to perform these measurements. The results for the reference reactions at T = 298.15 K and Im = 0 are: Ko = (9.4 +/- 3.1) x 10(-7), delta rGo = (34.4 +/- 1.0)kJ mol-1, delta rHo = -(73.7 +/- 0.4)kJ mol-1, and delta rSo = -(363 +/- 4) J K-1 mol-1 for penicillin G-(aq) + H2O(1) = penicillinoic acid2-(aq) + H+(aq); Ko = (6.0 +/- 3.0) x 10(-6), delta rGo = (29.8 +/- 1.7) kJ mol-1, delta rHo = -(70.0 +/- 7.5) kJ mol-1, and delta rSo = -(335 +/- 26) J K-1 mol-1 for ampicillin-(aq)+ H2O(1) = ampicillinoic acid2-(aq)+H+(aq). Calorimetric enthalpies of reaction for the beta-lactamase catalyzed hydrolysis of cephalosporin C have also been measured but the reaction products have not been identified and the measured enthalpies cannot be assigned to a specific reaction. Acidity constants for ampicillin, penicillin G, ampicillinoic acid, and penicillinoic acid are also reported. A strain energy of 116 kJ mol-1 for the beta-lactam ring is obtained from thermochemical data.

Ampicillin↗
PubMed1994

Analysis of biochemical reactions in equilibrium: hydrolysis of penicillin and ampicillin.

A general equilibrium model for a class of biochemical reactions was formulated, using the formalism of binding polynomials for the evaluations of the various species. Thermodynamic equilibrium constant was obtained from the observed equilibrium total concentrations of reactants at specified pH and certain ligand concentrations. Results for the hydrolysis of penicillin and ampicillin were analyzed with this equilibrium model. Predicted fractions of hydrolysis products at various pH values were calculated.

Journal Article↗
PubMed1992

Cost and efficacy of extracorporeal shock wave lithotripsy versus ureteroscopy in the treatment of lower ureteral calculi.

We retrospectively reviewed the extracorporeal shock wave lithotripsy (ESWL) and ureteroscopy experience relative to cost and efficacy of a group of practitioners skilled in the use of both procedures for the treatment of lower ureteral stones. Although the initial success rate was higher with ureteroscopy, no significant difference could be found in final success or complication rates. The cost of ESWL was approximately 60% higher than that for ureteroscopy (mean $7,320.26 versus $4,568.47, p less than 0.005). Given the current restraints on resources, and the equal efficacy and morbidity of both procedures, ureteroscopy must be considered the procedure of choice in the management of lower ureteral stones.

Cost-Benefit Analysis↗
PubMed1991

Liposome flow injection immunoassay: model calculations of competitive immunoreactions involving univalent and multivalent ligands.

The use of liposomes as detectable reagents in solid-phase immunoassays has been explored in a flow injection immunoanalysis (FIIA) system. Model calculations are presented for FIIA based on the competitive binding of univalent analyte and multivalent liposomes to immobilized antibodies. Parameters such as binding constants, concentrations of liposomes and antibody, and steric hindrance are considered for their relative effects on detectable liposome signal response to analyte concentrations. Qualitative comparisons of the model with the experimental data are made.

Flow Injection Analysis↗
PubMed1982

Ureteral replacement with a new synthetic material: Gore-Tex.

There are no currently accepted synthetic ureteral substitutes. When faced with the need for ureteral replacement, the urologist must resort to pedicle grafts of intestine or bladder. Based on encouraging preliminary work in Europe, we have used a new synthetic vascular substitute, Gore-Tex, to replace segments of ureter in the dog. This material is made of expanded (microporous) polytetrafluoroethylene. In vascular surgery it is currently the preferred material due to its non-wetting and non-clotting surface when used in the arterial and venous beds. Adult mongrel dogs underwent segmental replacement of the right ureter and subtotal replacement of the left ureter with segments of 5-mm. tubed Gore-Tex. All anastomoses were performed with running 6--0 prolene. Antibiotics were given routinely perioperatively. Data on 7 dogs are available. Results indicate that Gore-Tex is well tolerated as a ureteral substitute to bridge gaps between segments of ureter. Anastomoses of Gore-Tex to bladder were not successful, resulting in infection and migration of the prosthesis. Under proper circumstances, Gore-Tex can be a useful potential addition to the urologic armamentarium.

Animals↗
PubMed1982

Organic electrochemical techniques having potential clinical application.

The Organic Electrochemistry Group at the National Bureau of Standards is pursuing several avenues of research of potential application to problems of clinical chemists. With one development, electrochemical detectors for liquid chromatography, organomercury species can be determined in biological tissues and other matrices. Spectroelectrochemistry is being used to characterize the redox behavior of metal complexes of bleomycin, an antitumor drug. Chemically modified electrodes are being developed as selective electrocatalytic sensors for organohalogen compounds and may lead to new sensors for clinically important analytes. Surface-enhanced Raman spectroscopy is helping characterize the polymer films used to modify the electrode surfaces. Another sensor is being developed for the detection of carboxylic acids: after the photocatalytic oxidation of the acids at a semiconductor electrode, the carbon dioxide produced is subsequently determined with a flow-through gas-sensing electrode. Finally, mathematical modeling may provide a better understanding of the fundamental processes involved in several of the above techniques.

Benzidines↗
PubMed1981

Further observations on the specific red cell adherence test: effects of radiation therapy.

To assess the effects of radiation therapy on the specific red cell adherence test we have evaluated 33 patients who underwent cystectomy for bladder cancer and in whom radiotherapy had been used. With this test negative tumors were found in 32 of the 33 cases. In a second series of 10 patients histologic examinations were done by biopsy before radiotherapy and by subsequent microscopic examination of the cystectomy specimen. The specific red cell adherence test results remained constant in all of these cases. These findings strongly suggest that 1) the specific red cell adherence test does remain negative after radiotherapy and 2) this test is a valuable prognosticator of the future likelihood of invasion in all patients with transitional cell carcinoma of the bladder.

Antigens, Surface↗
PubMed1981

Long term parenteral infusion in the rat: a new technique.

We developed an improved method for continuous parenteral infusion of rats with minimal animals restraint. This method is reliable, relatively inexpensive, and imposes less stress upon the animal than other methods of infusion previously described.

Animals↗
PubMed1980

Metastases from transitional cell carcinoma of the bladder masquerading as psoas abscess.

Metastases from transitional cell carcinoma of the bladder usually progress in a stepwise fashion. We report that first case of metastasis to the body of the psoas muscle. No evidence of retroperitoneal lymphatic involvement or direct extension was identified. Furthermore, the original tumor was superficial but the history was complicated by perforation of the bladder during resection.

Abscess↗