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Biomedical subjects

C A Chang

Publications and source records attributed to C A Chang.

32 records · Page 2Linked to original sources
PubMed1988

Diagnosis of sickle cell anemia and beta-thalassemia with enzymatically amplified DNA and nonradioactive allele-specific oligonucleotide probes.

We have developed a simple and rapid nonradioactive method for detecting genetic variation and have applied it to the diagnosis of sickle cell anemia and beta-thalassemia. The procedure involves the selective amplification of a segment of the human beta-globin gene with oligonucleotide primers and a thermostable DNA polymerase, followed by hybridization of the amplified DNA with allele-specific oligonucleotide probes covalently labeled with horseradish peroxidase. The hybridized probes were detected with a simple colorimetric assay. We demonstrated the usefulness of this method in a retrospective analysis of two pregnancies at risk for beta-thalassemia and one at risk for sickle cell anemia, as well as in an analysis of nine DNA samples simulating three family sets.

Alleles↗
PubMed1986

Mobile phase effects on the separations of substituted anilines with a beta-cyclodextrin-bonded column.

The capacity factors of several substituted anilines were measured on a beta-cyclodextrin (beta-CD)-bonded column with mobile phases varying from the classical, normal-phase condition, e.g. n-heptane-2-propanol, to the classical, reversed-phase condition, e.g. water-2-propanol. Different modifiers, such as acetonitrile, methanol, and tetrahydrofuran and a Partisil PXS-ODS column were also used for comparison. In general, it was found that the beta-CD column, having the ability to form inclusion complexes with certain substrates is better and more selective in the reversed-phase separation of many aromatic compounds than the Partisil PXS-ODS column. The normal-phase separation on beta-CD was even more efficient, owing to the presence of large number of hydroxy groups on the surface of beta-CD molecules and the more rapid mass transfer in the column. In the present case, alcohols were found to be better modifiers than aprotic solvents. The effects of organic solvents on both normal-and reversed-phase separations are also discussed. The minima observed for the log k' vs. percent organic solvent plots for a number of substituted anilines are reasoned to originate from solute-solvent competition, which interacts with the stationary phase, as well as from the "relative solubility" of solutes in the stationary and mobile phases.

Aniline Compounds↗
PubMed1986

Normal-phase high-performance liquid chromatographic separations of positional isomers of substituted benzoic acids with amine and beta-cyclodextrin bonded-phase columns.

The separation of positional isomers of several substituted benzoic acids was studied using two different columns, i.e. amine and beta-cyclodextrin bonded silicas, at appropriate normal-phase conditions. Although some other columns do separate substituted benzoic acids, particularly the octadecylsilica column in a reversed-phase mode, the present separation under simple normal-phase, isocratic conditions is unique. In particular, the retention order of these acids for the amino bonded-phase column can be roughly predicted using the pKa values of the analytes. On the other hand, due to the strong interaction between substituted benzoic acids and the beta-cyclodextrin bonded phase, a small amount of acetic acid has to be added into the mobile phase to overcome band broadening and tailing problems. Possible retention mechanisms are also discussed.

Amines↗
PubMed1985

Liquid chromatographic retention behavior of organometallic compounds and ligands with amine-, octadecylsilica- and beta-cyclodextrin-bonded phase columns.

Effects of solvent composition and ligand variation on the retention of organometallic compounds have been studied using an amino, an octadecylsilica (ODS) and a beta-cyclodextrin (beta-CD) bonded phase column in either a normal-phase or a reversed-phase mode. The retention behavior for the organometallic compounds with the amino column can be rationalized using the displacement model. The "apparent" molecular areas are greater for compounds capable of strong hydrogen bonding. The retention in the ODS column roughly follows an argument based on the expected solubility behavior while mixed retention mechanisms are involved for the solubility behavior while mixed retention mechanisms are involved for the beta-CD column, i.e. both inclusion process and solubility or solvophobic interactions are possibly operative.

Amines↗
PubMedDate not supplied

Ionic versus nonionic MR imaging contrast media: operational definitions.

An experimental rationale is provided to differentiate between the terms ionic and nonionic for magnetic resonance (MR) imaging contrast media such as gadodiamide and gadopentetate dimeglumine. Four independent types of physical measurements (electric conductivity, osmolality, electrophoresis, and ion exchange) were performed on a range of test compounds, including D-glucose, iohexol, gadopentetate dimeglumine, and gadodiamide. Iohexol, D-glucose, and gadodiamide are shown to be nonionic species at physiologic pH (7.4), not measurably dissociating in solution. A range of gadopentetate salts behave as electrolytes, dissociating into constituent charged ions in aqueous media. Operational definitions for the terms ionic and nonionic are provided, and the terms neutral and net zero charge are compared with nonionic for accuracy. The nomenclature nonionic and ionic is deemed appropriate for differentiating MR imaging contrast media.

Contrast Media↗
PubMedDate not supplied

Physiological effects of sucrose substitutes and artificial sweeteners on growth pattern and acid production of glucose-grown Streptococcus mutans strains in vitro.

The synergistic effects of four sucrose substitutes, polysorbate and five artificial sweeteners were studied in vitro on growth pattern and acid production of seven glucose-grown Streptococcus mutans strains, representing the five serological groups after Bratthall. Four distinct growth patterns during glucose fermentation were observed: high rate of growth with low acid production, moderate growth rate with moderate acid production, moderate growth rate with high acid production, and slow rate of growth with moderate acid production. Depending on the strain used, the final OD at 546 nm ranged from 0.55 to 0.99 and the final pH of the medium varied between 4.65 and 4.15. While added sucrose substitutes, with exceptions, usually enhanced growth rate, most artificial sweeteners suppressed or, at higher concentrations, even inhibited growth of S. mutans; addition of polysorbate to the medium always increased growth rate of S. mutans significantly. The presence of sucrose substitutes during glucose fermentation had no effect on final pH of the medium, but addition of artificial sweeteners, especially sodium saccharin, elevated final pH up to 1.8 units. The observed physiological patterns and differences within the several strains of S. mutans during glucose fermentation in vitro do not necessarily relate to the five serological groups of the species.

Fructose↗
PubMedDate not supplied

Congenital chylothorax managed by partial pleurodesis: report of one case.

Congenital chylothorax, a rare cause of respiratory distress in neonate, presented here with respiratory distress from two days of age. Thoracocentesis was performed at six days, revealing a clear fluid with high protein content. Thoracotomy was performed at the age of 33 days because of a profuse amount of chest tube drainage. A leak of chyle was found near the esophageal hiatus of the costophrenic angle. Partial pleurodesis was performed because of difficulty in identifying the exact leakage point. Respiratory status improved very quickly after the operation, and oral intake was well-tolerated during follow-up.

Chylothorax↗