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C D Tran

Publications and source records attributed to C D Tran.

At least 19 recordsLinked to original sources
PubMed2001

Near-infrared spectrometric determination of di- and tripeptides synthesized by a combinatorial solid-phase method.

A new method based on near-infrared (NIR) spectrometry and partial least-squares analysis has been developed for the noninvasive and nondestructive determination of the identity and sequences of amino acid residues in di- and tripeptides. The di- and tripeptides were synthesized from six amino acids with similar structures (Gly, Ala, Leu, Met, Phe, Val) on two different polymer beads (bead with and without a linker) using the solid-phase peptide synthetic method. The developed NIR method is capable of determining the identity of sequences of these di- and tripeptides (with and without the Fmoc protecting group) directly on the polymer beads. It can distinguish not only dipeptides from tripeptides but also peptides with very similar structures (e.g., bead-Gly-Ala-Ala, bead-Gly-Ala-Phe, bead-Gly-Ala-Leu, bead-Gly-Ala-Val, and bead-Gly-Ala-Met). More importantly, the method is capable of distinguishing di- and tripeptides with the same amino acid residues but different sequences (e.g., bead-Gly-Leu-Val from bead-Gly-Val-Leu).

Combinatorial Chemistry Techniques↗
PubMed2001

Multispectral imaging microscope with millisecond time resolution.

A new multispectral imaging microscope with micrometer spatial resolution and millisecond temporal resolution has been developed. The imaging microscope is based on the use of an acousto-optic tunable filter (AOTF) for spectral tuning and a progressive scan camera capable of snapshot operation for recording. It can operate in two modes: images are recorded as a function of time or wavelength. When operated as a function of time, the microscope is configured so that as many images as possible are recorded, grabbed, and stored per one wavelength. Upon completion, the AOTF is scanned to a new wavelength, and a new set of images are recorded. Up to 33 images/ second (i.e., 30 ms/image) can be recorded in this mode. In the other configuration, the recording wavelength is rapidly scanned (by means of the AOTF) and only one image is rapidly recorded, grabbed, and stored for each wavelength. Because additional time is needed to scan the AOTF, the maximum number of images can be grabbed in this case is 16 frames/s. Preliminary applications of the imaging microscope include measurements of photoinduced changes of a single unit cell in temperature-sensitive cholesteric liquid crystals as a function of time and wavelength. The changes were found to be varied with time and wavelength. Interestingly, the photoinduced changes of unit cells in the liquid crystal are not the same but different from cell to cell. This imaging microscope is particularly useful for measurements of small-size samples that undergo rapid chemical or biochemical reactions, e.g., activities of a single biological cell.

Cholesterol↗
PubMed2001

Development and analytical applications of multispectral imaging techniques: an overview.

A multispectral imaging spectrometer is an instrument that can simultaneously record spectral and spatial information of a sample. Chemical and physical properties of the sample can be elucidated from such images. By synergistic use of an acousto-optic tunable filter and a progressive scan camera capable of snap shot recording it was possible to develop a novel imaging spectrometer with a spatial resolution of a few microns and which can record, grab and store up to 33 images per second (at a function of time) or 16 images per second (as a function of wavelength). This overview article summarizes the instrumentation development of various imaging spectrometers and their applications including its use as the detector for the determination of identity and sequences of peptides synthesized by the combinatorial solid phase method.

Amino Acid Sequence↗
PubMed2000

Near-infrared spectrophotometric determination of tri- and tetrapeptides.

A new method based on the near infrared technique has been developed for the noninvasive and nondestructive determination of the identity and sequences of amino acid residues in small peptides. The method is capable of distinguishing not only peptides with very similar structures (e.g., Gly-Ala-Ala, Gly-Ala-Leu, Leu-Gly-Gly and Gly-Leu-Leu-Gly, Gly-Leu-Gly-Gly, Gly-Gly-Ala-Gly) but also peptides with the same amino acid residues but different sequences (e.g., Gly-Ala-Ala, Ala-Gly-Ala, Ala-Ala-Gly and Gly-Gly-Gly-Ala, Gly-Gly-Ala-Gly).

Peptides↗
PubMed1999

Investigation of solid-phase peptide synthesis by the near-infrared multispectral imaging technique: a detection method for combinatorial chemistry.

A near-infrared (NIR) multispectral imaging spectrometer was used to monitor solid-phase peptide synthesis. This imaging spectrometer has fast scanning ability and high sensitivity because it is based on an acousto-optic tunable filter and a NIR InGaAs focal plane array camera. This NIR imaging instrument possesses all the advantages of conventional NIR spectrometers; namely, it can be used for noninvasive monitoring of the reactions and identification of the products during the solid-phase peptide synthesis of glycine, alanine, and valine mediated by aminomethylstyrene resin beads. The reaction was determined by monitoring either the decrease of the band at 1529 nm, which is due to the amine group on the beads, or the increase of the amide band generated at 1483 nm. The amine band at 1529 nm was also used to determine the presence of the Fmoc protecting groups and the efficiency of its removal. More importantly, this NIR imaging spectrometer has additional features that conventional NIR spectrometers cannot offer; namely, its ability to measure spectra at different positions within a sample. This feature was utilized for the first demonstration in which reactions of three different solid-phase peptide syntheses (in a three-compartment cell) were simultaneously monitored. As expected, the kinetics obtained for three reactions are similar to those obtained when the each of the reactions was individually determined. In this study, data recorded by 16 x 16 pixels were used to calculate a spectrum for each sample. However, a relatively good spectrum can be obtained by using data recorded by a single pixel. Since the NIR camera used in this camera is equipped with 240 x 320 pixels, this NIR mutispectral imaging technique is not limited to the three-compartment cell used in this study but rather can be used as the detection method for the solid-phase peptide synthesis in combinatorial chemistry.

Chemistry, Organic↗
PubMed1999

Evidence for kinetic inhomogeneity in the curing of epoxy using the near-infrared multispectral imaging technique.

The kinetics of curing of an epoxy resin by amine was studied using a near-infrared (NIR) multispectral imaging spectrometer. This imaging spectrometer is capable of sensitively and rapidly recording NIR spectral images of a sample because it was constructed with an acousto-optic tunable filter and an InGaAs focal plane array NIR camera. The high sensitivity and fast scanning ability of the spectrometer make it suitable for kinetic determination of fast reactions. Additionally, it has features that conventional NIR spectrometers cannot offer, namely, its ability to provide kinetic information at different positions within a sample. Furthermore, the high spatial resolution and sensitivity of the InGaAs camera make it possible to determine the kinetics from data collected by a single pixel in the camera. The kinetics of curing of epoxy by amine, determined by this multispectral imaging instrument, show that the reaction rates within the sample are very inhomogeneous. Because of this kinetic inhomogeneity, differences in the degrees of cure at different positions within the sample can be as high as 37% when data from only a single pixel were used for calculation. The inhomogeneity was not be observed if an average of a large number of pixels were used.

Epoxy Compounds↗
PubMed1999

Regional distribution and localization of zinc and metallothionein in the intestine of rats fed diets differing in zinc content.

BACKGROUND: Zinc (Zn) is protective and enhances epithelial repair in gut diseases. In this study we investigate the localization and distribution of Zn and its binding protein, metallothionein (MT), in the gut of rats fed diets varying in Zn content. METHODS: Male-Sprague Dawley rats were fed low, normal, high, or excess Zn in their diets (10, 100, 400, or 1000 mg Zn/kg, respectively) and killed 7 days later. Blood, liver, and gut tissues were collected. Tissue Zn was determined with atomic absorption spectrophotometery and MT with a Cd/haem affinity assay. Zn and MT were immunohistochemically localized in the small-intestinal wall with zinquin and an anti-MT antibody. RESULTS: Most Zn in the intestinal wall was present in the mucosal scrapings, with 94% membrane-bound and 6% cytosolic, irrespective of dietary Zn. MT levels increased in all gut regions at dietary Zn levels above 100 mg Zn/kg. MT was 40% higher in the ileum than in other gut regions in rats fed low- and normal-Zn diets. The Zn content of the ileum was also 20% higher than that of other gut regions in rats fed low-, normal-, or high-Zn diets. Zn and MT were colocalized in the base of the intestinal crypts, most visibly in the ileum. CONCLUSION: Mucosal cytosolic Zn and MT concentrations are increased only at high or excessive Zn intakes in all gut regions except the ileum, which can respond to a lower Zn intake. As the cytosolic Zn pool most likely influences mucosal protection and repair mechanisms, it is proposed that an increased MT may indicate the adequacy of oral Zn therapy in gut disease.

Abdominal Muscles↗
PubMed1998

Simultaneous multispectral imaging in the visible and near-infrared region: applications in document authentication and determination of chemical inhomogeneity of copolymers.

A new multispectral imaging spectrometer capable of simultaneously recording spectral images in the visible and near-infrared has been developed. In this instrument, an acoustooptic tunable filter is used to diffract an unpolarized incident light into two diffracted beams with orthogonal polarization; one of them is detected by a silicon camera for the visible region while the other beam is detected in the near-infrared region (from 1 to 1.7 microns) with a NIR camera. The imaging spectrometer is sensitive, inexpensive, and field deployable because it is based on the recently available InGaAs focal plane arrays camera, which is low cost and can be sensitively operated at room temperature. Preliminary applications of the imaging spectrometer include measurements of the visible and NIR absorption spectra of ink used to print U.S. currency. Such results may help to characterize samples as well as to control and to ensure the quality of the samples during the production processes. More important are the results obtained on ethylene/vinyl acetate copolymers. The NIR spectral images obtained clearly indicate that these copolymers exhibit a high degree of chemical inhomogeneity. Because of the possibility of inhomogeneity, it is very important that the homogeneity of polymers or copolymers be thoroughly understood before the NIR methods, especially those based on NIR spectrometers equipped with a single-element detector, are used for measurements.

Diagnostic Imaging↗
PubMed1998

Regional distribution of metallothionein and zinc in the mouse gut: comparison with metallothionien-null mice.

Gut Zn homeostatic responses to low, replete, and excess dietary Zn (10, 150, and 400 mg Zn/kg, respectively) were compared in mice with (MT+/+) and without (MT-/-) metallothionein (MT) expression. MT concentrations decreased progressively from stomach (12.9 nmol Cd bound/g) to colon (4.6 nmol Cd bound/g). Small intestinal MT was increased in mice fed the 400-mg Zn/kg diet (+130%, duodenum; +56%, jejunum; +29%, terminal ileum), but not in the stomach, cecum and colon. Zn concentrations were much higher in the distal gut at increasing Zn intakes in MT+/+ mice but to a lesser extent in MT-/- mice. On the 10-mg Zn/kg diet, MT-/- mice had 45% more Zn in the jejunum/ileum than MT+/+ mice. In fasted (20 h) mice, Zn concentrations in all gut regions were similar to those of MT+/+ mice fed the 10-mg Zn/kg diet, irrespective of prior Zn intake or genotype. Liver MT quadrupled in mice fasted after the 10-mg Zn/kg diet but only doubled after the 400-mg Zn/kg diet, a trend also present in gut MT. Glucagon administration stimulated gut as well as liver MT, implicating it as a major component of the MT response to fasting. MT-/- mice had five times more variation than MT+/+ mice in plasma Zn over all dietary groups. Together, these findings demonstrate that without MT, there is little modification of regional gut Zn concentrations in response to extremes of dietary Zn and poorer regulation of Zn homeostasis.

Animals↗
PubMed1997

Determination of monomethylhydrazine with a high-throughput, all-fiber near-infrared spectrometer based on an integrated acoustooptic tunable filter and an erbium-doped fiber amplifier.

A novel integrated acoustooptic tunable filter (IAOTF) has been developed. This tunable filter is based on the Bragg interactions between waveguide and surface acoustic waves. Compared to (bulk) AOTF, its advantage include all-fiber construction, smaller size, narrower spectral resolution (1.7 nm), higher diffraction efficiency (37%), and lower rf power requirement (150 mW). A relatively narrow spectral tuning range (about 80 nm) is the only drawback for this integrated tunable filter. However, this disadvantage was overcome by judiciously using the filter for measurements in which its tuning range is coincident with the light source and also with absorption bands of analytes. In fact, an all-fiber, compact, high-throughput near-infrared spectrophotometer has been successfully constructed by synergistic use of this integrated AOTF and the erbium-doped fiber amplifier (EDFA), which has been shown to provide high intensity and wide spectral band-width in the near-infrared region from 1500 to 1600 nm. This spectral region is particularly useful for the determination of samples which have O-H and/or N-H groups. The all-fiber nature, compactness, high throughput, and high sensitivity of this spectrophotometer make it particularly suitable for on-line and real-time detection of trace gases in hostile environments, including leak detection of monomethylhydrazine (at a limit of detection of 191 ppm), which is often used as the hypergolic propellant for the space shuttle thruster systems.

Acoustics↗
PubMed1996

Characterization of an erbium-doped fiber amplifier as a light source and development of a near-infrared spectrophotometer based on the EDFA and an acoustooptic tunable filter.

A novel light source for the near-infrared region which has the highest intensity and widest spectral bandwidth of all near-IR light sources has been developed. The system is based on a single-mode fiber (about 18 m long) doped with Er3+ ion. The doped ion produces amplified spontaneous emission (ASE) in the near-IR region (from 1500 to 1600 nm) when it is excited by a diode laser at 980 nm. Because the diode laser is fusion-spliced directly to the doped fiber, the system is compact, all-solid-state, reliable, and stable and requires little maintenance. Its ASE output intensity was found to be comparable with those of diode lasers currently available for this near-IR region and is much higher than those of conventional halogen-tungsten lamps and the so-called (high-intensity) superluminescent light emitting diodes (SLEDs). Its spectral bandwidth is, however, much wider than those of the diode lasers and the SLEDs. Even higher intensity can be obtained from the doped fiber when a low-intensity (1 mW) light from a 1550-nm laser diode is introduced into the doped fiber. The intensity is enhanced (up to 7 times compared to the ASE) because the input light is amplified by the doped fiber. Furthermore, the output intensity of this erbium-doped fiber amplifier (EDFA) can be appropriately adjusted to provide relatively higher output intensity at any range of wavelengths (within this 1500-1600-nm region) by simply changing the temperature and/or the driven current of the input diode laser. Subsequently, an acoustooptic tunable filter was used to provide a means to spectrally tune the EDFA rapidly and to develop an all-solid-state, compact near-IR spectrophotometer which not only is very sensitive, stable, and reliable but also has a very high throughput. This spectrophotometer can detect water in ethanol at a limit of detection of 10 ppm. More importantly, the high through-put makes it possible to use the instrument to measure spectra of highly absorbing samples (e.g., absorption spectrum of 1.0 M Pr3+ aqueous solution through four sheets of paper); measurements which are currently not possible with halogen-tungsten lamp-based spectrophotometers.

Amplifiers, Electronic↗
PubMed1996

Near-infrared detection of flow injection analysis by acoustooptic tunable filter-based spectrophotometry.

The instrumentation development of a near-infrared (near-IR) spectrophotometer based on an acoustooptic tunable filter (AOTF) and its application as a detector for flow injection analysis (FIA) are reported. In addition to being compact and all solid state, this AOTF-based instrument is very sensitive, has high resolution, and can be rapidly scanned. The latter advantage make it uniquely suited as a detector for FIA, in that it can rapidly record the whole near-IR absorption spectrum of a mixture passing through the FIA flow cell. Subsequent treatment of the recorded spectra with multivariate calibration methods makes it possible to use the FIA, for the first time, for such applications as the simultaneous determination of trace amounts of water and benzene in ethanol. Because all organic compounds absorb light in the near-infrared region, this AOTF-based near-IR detector can serve as a universal detector for FIA; as a consequence, applications of the FIA techniques can be expanded to other areas which are not possible otherwise.

Benzene↗
PubMed1994

Universal spectropolarimeter based on overtone circular dichroism measurements in the near-infrared region.

A novel and highly sensitive circular dichroism spectropolarimeter for the near-infrared region has been developed. In this instrument, a solid state titanium-sapphire laser that can be spectrally tuned from 670 to 1030 nm was used as the light source. The laser beam was converted into linearly polarized light by a polarizer and into left circularly polarized light and right circularly polarized light at 42 kHz by a photoelastic modulator (PEM). A limit of detection of 1.1 x 10(-6) AU was achieved by this instrument for (+)-Co(en)3(3+) at 765 nm. Further improvement including employing double modulation (at 42 kHz by the PEM and at 85 Hz by a chopper just before the laser beam was converted to CPL), demodulating and amplifying the signal with high-performance lock-in amplifiers, was made to enable the instrument to have the required sensitivity for the measurements of the circular dichroism of overtones and combination transitions of saturated chiral compounds, e.g., (R)- and (S)-camphor, (R)- and (S)-2-octanol, and (R)- and (S)-2-amino-1-octanol. Because the measured CD spectra originate from the overtones and combination transitions of the C-H and O-H groups, the spectropolarimeter can be used to detect virtually any compounds that have O-H and/or C-H groups.

Aluminum Oxide↗
PubMed1994

Chiral detection in high-performance liquid chromatography by vibrational circular dichroism.

A novel chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents in the infrared region, i.e., vibrational circular dichroism (VCD). In this instrument, a solid-state spectral tunable (from 2.4 to 3.5 microns) F-center laser was used as the light source. The linearly polarized laser beam was converted into left circularly polarized light (LCPL) and right circularly polarized light (RCPL) at 42 kHz by means of a photoelastic modulator. The intensity of the LCPL and RCPL transmitted through the sample was measured by a liquid nitrogen cooled indium antimonide detector. Double modulation was employed to reduce the noise associated with the laser beam. Specifically, the linearly polarized laser beam, prior to being converted to CPL, was modulated at 85 Hz by a mechanical chopper. Demodulation and amplification were accomplished with the use of two lock-in amplifiers. In its present configuration, the instrument can be used to measure the VCD of O-H groups. Its sensitivity is so high that it was able, for the first time, to detect chirally (with limits of detection of micrograms) (R)- and (S)-2,2,2-trifluoro-1-(9- anthryl)ethanol and (R)- and (S)-benzoin when these compounds were chromatographically separated from the corresponding racemic mixtures by a Chiralcel-OD column. The main advantage of this chiral detector is, however, its universality; i.e., it can be used to virtually detect any chiral compounds which has O-H group (e.g, aliphatic alcohols such as 2-octanol).

Chromatography, High Pressure Liquid↗
PubMed1994

Thermal lens technique for sensitive and nonintrusive determination of isotopic purity.

A new technique in which absorption in the infrared region is sensitively monitored in the visible has been developed. This was accomplished using the visible laser to probe the thermal lens effect induced in a sample as a consequence of its absorption of radiation in the infrared. The sensitivity of the technique is much higher than that of conventional transmission measurements because, in addition to its inherent ultrasensitivity, infrared absorption is monitored in the visible region, which is relatively less noisy, and is detected by a phase-lock-detecting method. The technique is so sensitive that it can be used to determine the isotopic purity of methanol and its 13C and deuterated samples by measuring, not directly the absorption of the C-H group but rather indirectly the absorption of the O-H group. With use of the multivariate calibration method to analyze the data, this technique can be utilized for the nondestructive, noninvasive, and sensitive determination of isotopic impurity in methanol, 13CH3OH, CD3OH, CD2HOH, and CDH2OH at concentrations as low as 10(-3)% (w/w).

Carbon Isotopes↗
PubMed1993

Spectrofluorometer based on acousto-optic tunable filters for rapid scanning and multicomponent sample analyses.

Advantages of the acousto-optic tunable filter (AOTF), namely its ability for fast scanning and multiple-wavelength diffraction, were exploited to develop a novel, all solid-state, nonmoving parts spectrofluorometer. This instrument is based on the use of two AOTFs: one for excitation and the other for emission. The first AOTF was used to specifically diffract white incident light into a specific wavelength(s) for excitation. Depending on the needs, the second AOTF (i.e., the emission AOTF) can be used as either a very fast dispersive device or a polychromator. In the first configuration, the sample was excited by a single-excitation wavelength; the emitted light was analyzed by the emission AOTF, which was scanned very fast. A speed of 4.8 A was found to be the fastest speed which the AOTF can be scanned with a reasonable S/N and resolution. With this speed, a spectrum of 150 nm can be measured in 312 microseconds. Faster scanning is possible but, because of the limitation due to the speed of the acoustic wave, may undesiredly lead to degradation in the S/N and spectral resolution. In the second configuration, both AOTFs were used as a polychromator. Several different rf signals were simultaneously applied into the first AOTF to provide multiple-excitation wavelengths. The emission was simultaneously analyzed at several wavelengths by the emission AOTF. With this configuration, the fluorometer can be used for the analysis of multicomponent samples, and the maximum number of components it can analyze is, in principle, a x b, where a and b are the number of excitation and emission wavelengths, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Eosine Yellowish-(YS)↗
PubMed1992

Acousto-optic tunable filter as a polychromator and its application in multidimensional fluorescence spectrometry.

Acousto-optic tunable filter (AOTF) is an electronically driven dispersive device which operates on the principle of acousto-optic interaction in an anisotropic medium. Incident white light will be diffracted by the AOTF into a specific wavelength when a specific rf is applied to it. The diffracted light needs not be a monochromatic light. Multiwavelength light can be diffracted from the AOTF when several rf signals are simultaneously applied into the filter. Compared to conventional polychromators, advantages of this electronic AOTF polychromator include its ability to individually amplitude-modulate each wavelength of the diffracted multiwavelength light at different frequency. This is accomplished by individually and sinusoidally modulating each applied rf signal at the desired frequency. This feature makes it possible to develop a novel AOTF-based multidimensional fluorimeter in which the sample was simultaneously excited by two different wavelengths (514.5 and 488.0 nm) whose amplitudes were sinusoidally modulated at two different frequencies (100 and 66 Hz). Multicomponent samples, e.g., mixtures of rhodamine 6G and rhodamine B, were successfully analyzed using this novel fluorimeter and the developed data analysis.

Filtration↗