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Biomedical subjects

C D Tran

Publications and source records attributed to C D Tran.

28 records · Page 2Linked to original sources
PubMed1992

Multiwavelength thermal lens spectrophotometer based on an acousto-optic tunable filter.

The instrumentation development of a novel, all solid-state, nonmoving parts, fast-scanning and wide-tuning range multiwavelength thermal lens spectrophotometer based on the acousto-optic tunable filter (AOTF) is described. Initially, the essential electronic driver was developed to facilitate the systematic characterization of the paratellurite (TeO2) AOTF and to demonstrate that this filter can be successfully and uniquely used as an all solid-state, nonmoving parts dispersive device to rapidly diffract white incident light into a selected color beam, to amplitude modulate the diffracted monochromatic light, and to keep its intensity constant. The multiwavelength thermal lens instrument was subsequently constructed using this AOTF, and preliminary results on advantages of this spectrophotometer such as its ability to characterize trace chemicals and to analyze multicomponent samples are delineated.

Acoustics↗
PubMed1991

High-performance liquid chromatographic separation of racemic and diastereomeric mixtures of 2,4-pentadienoate-iron tricarbonyl derivatives.

beta-Cyclodextrin chiral stationary phase facilitates the chiral separation of the (+/-)-methyl-5-formyl-2,4-pentadienoate-iron tricarbonyl (1) racemic mixture. The separation of oxazolidine derivatives 2 and 3 diastereomers were achieved with a C18 column but the compounds underwent in-column hydrolysis to give (-)- and (+)-1, respectively. This hydrolysis was exploited for the determination of 2 and 3 by the beta-cyclodextrin column, namely 2 and 3 were initially and completely hydrolyzed in the column to give (-)- and (+)-1 and this racemic mixture was then separated by this chiral column.

Chromatography, High Pressure Liquid↗
PubMed1990

Thermal lens-circular dichroism detector for high-performance liquid chromatography.

A novel and ultrasensitive chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents by the thermal lens effect. In this instrument, the chromatographic effluent was sequentially excited by left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams were derived from the same argon ion laser whose linearly polarized output was transformed into circularly polarized light by means of a Pockels cell. The heat generated as a consequence of the sample absorption of the LCPL and RCPL was measured by the probe laser beam collinearly overlapping with the two excitation beams. A lock-in amplifier was used to measure the thermal lens-circular dichroism (TL-CD) signal which corresponds to the difference in the thermal lens signals produced by the LCPL and RCPL excitation beams. In addition to its high sensitivity, the advantages of this TL-CD chiral detector include its ability to provide, directly and in real time, information on the chirality (i.e., circular dichroism) and optical purity of chiral samples. A detection limit of 7.2 ng was achieved for (-)-tris(ethylenediamine)cobalt(III) (k' = 0.45) as well as for the (+)-tris(ethylenediamine)cobalt(III) (k' = 1.40) when these two enantiomers were chromatographically separated from the corresponding racemic mixture through the use of bis(mu-d-tartrato)diantiomonate(III) ion pair reversed-phase chromatography. This limit of detection was found by using a 10-microL flow cell and having 5-mm path length and 6-mW excitation laser beam (lambda = 514.5 nm) modulated at 2 Hz.

Chromatography, High Pressure Liquid↗
PubMed1986

A review of techniques of crown fabrication for existing removable partial dentures.

Fourteen methods for making a crown to fit an RPD have been described. The techniques have been briefly reviewed and classified to indicate whether crown pattern construction is direct, direct-indirect, or indirect, and whether the RPD is needed in the laboratory phase. The choice of a technique appears to be a matter of personal preference for the dentist.

Acrylic Resins↗
PubMed1985

Studies of the fluorescence from tryptophan in melittin.

The fluorescence lifetime and rotational correlation time of the tryptophan residue in melittin, as both a monomer and tetramer, have been measured between pH 6 and 11. The fluorescence decays are non-exponential and give lifetimes of 0.7 +/- 0.1 ns and 3.1 +/- 0.1 ns. This emission is consistent with a model in which the tryptophan residue is in slightly different environments in the protein. In a dilute solution of monomer the mean fluorescence lifetime is 2.3 +/- 0.1 ns, below pH 10, but falls to 1.7 ns at higher pH. In contrast, the melittin tetramer has a mean fluorescence lifetime of only 2.2 ns at pH 6, which falls to 1.9 ns by pH 8, and falls again above pH 10 to the same value as in monomeric melittin. The behaviour between pH 6 and 8 is explained as the quenching of the Trp residue by lysine groups, which are near to the Trp in the tetramer but in the monomer, are too distant to quench. Fluorescence anisotropy decays show that the Trp residue has considerable freedom of motion and the range of "wobbling" motion is 35 +/- 10 degrees in the tetramer.

Animals↗
PubMed1982

Secondary structure and dynamics of glucagon in solution.

A correlation between the secondary structure of glucagon determined by circular dichroism and its dynamic behaviour as obtained from picosecond fluorescence anisotropy is demonstrated. The CD data show that the percentage of alpha-helix decreases with increasing temperature, but the rotational relaxation time of the glucagon increases with temperature. These observations suggest that the protein's shape changes with temperature in such a way that its volume is larger at 38 degrees C than at 5.5 degrees C. The fluorescence anisotropy of glucagon decays biexponentially at each temperature studied and at 26 degrees C the rotation lifetimes are 1670 and 307 ps at pH 10.2 and 2147 and 517 ps at pH 2.2. It is proposed that the shorter decays are due to the restricted motion of the single tryptophan residue while rotation of the whole protein is responsible for the longer decays. The calculated rotational diffusion coefficient, Dw, of the tryptophan residue is much smaller, (ie. has a larger apparent volume) than that of a free tryptophan in solution. The hydrophobic interactions between residues Phe-22 to Leu-26 are probably responsible for the larger apparent volume in the protein compared to solution and will stabilize this part of the protein. The rotational diffusion of aggregated glucagon is also discussed.

Circular Dichroism↗