Biomedical subjects

Foo-Tim Chau

Publications and source records attributed to Foo-Tim Chau.

14 recordsLinked to original sources

PubMed2006

Plasma fatty acid metabolic profiling and biomarkers of type 2 diabetes mellitus based on GC/MS and PLS-LDA.

Metabolic profiling has increasingly been used as a probe in disease diagnosis and pharmacological analysis. Herein, plasma fatty acid metabolic profiling including non-esterified fatty acid (NEFA) and esterified fatty acid (EFA) was investigated using gas chromatography/mass spectrometry (GC/MS) followed by multivariate statistical analysis. Partial least squares-linear discrimination analysis (PLS-LDA) model was established and validated to pattern discrimination between type 2 diabetic mellitus (DM-2) patients and health controls, and to extract novel biomarker information. Furthermore, the PLS-LDA model visually represented the alterations of NEFA metabolic profiles of diabetic patients with abdominal obesity in the treated process with rosiglitazone. The GC/MS-PLS-LDA analysis allowed comprehensive detection of plasma fatty acid, enabling fatty acid metabolic characterization of DM-2 patients, which included biomarkers different from health controls and dynamic change of NEFA profiles of patients after treated with medicine. This method might be a complement or an alternative to pathogenesis and pharmacodynamics research.

Adult↗

PubMed2006

Ab initio calculations on SCl2 and low-lying cationic states of SCl2+: Franck-Condon simulation of the UV photoelectron spectrum of SCl2.

Geometry optimization calculations were carried out on the (approximate)X (1)A(1) state of SCl(2) and the (approximate)X(2)B(1), (approximate)A(2)B(2), (approximate)B(2)A(1), (approximate)C(2)A(1), (approximate)D(2)A(2), and (approximate)E (2)B(2) states of SCl(2) (+) at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the (approximate)X (1)A(1) state of SCl(2) and the low-lying states of SCl(2)(+) listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl(2), and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)aug-cc-pV(5+d)Z PEFs. Calculated FC factors with allowance for the Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron (PE) bands of SCl(2). The agreement between simulated and observed He I PE spectra reported by Colton et al. [J. Electron Spectrosc. Relat. Phenom. 3, 345 (1974)] and Solouki et al. [Chem. Phys. Lett. 26, 20 (1974)] is excellent. However, our FC spectral simulations indicate that the first observed vibrational component in the first PE band of SCl(2) is a "hot" band arising from the SCl(2)(+)(approximate)X(2)B(1)(0,0,0)<--SCl(2)(approximate)X (1)A(1)(1,0,0) ionization. Consequently, the experimental adiabatic ionization energy of SCl(2) is revised to 9.55+/-0.01 eV, in excellent agreement with results obtained from state-of-the-art ab initio calculations in this work.

Cations, Divalent↗

PubMed2006

Pretreatments of chromatographic fingerprints for quality control of herbal medicines.

Pretreatments of chromatographic fingerprints are important for quality control of herbal medicines and they include data correction and data transformation. The data correction can reduce the variations of experimental procedures, and data transformation can put different weights on the different parts of the fingerprints. In this paper, a new target peak alignment (TPA) procedure has been proposed to correct the retention time shifts, multiplicative scattering correction (MSC) has been introduced for response correction. Then the similarity of the fingerprints with mean and median fingerprints is used to evaluate the quality of herbal medicines (HMs). Furthermore, different data transformation methods with kernel principal component analysis (PCA) have been applied to the data and their effects were discussed. The proposed approaches have been demonstrated by the essential oils data set of a herbal medicine, named Houttuynia cordata (HC), containing samples from different geographic origins. The experimental results indicate that the proposed approaches may be helpful in the quality control of herbal medicines by fingerprints.

Chromatography, Gas↗

PubMed2006

An ab initio study on the ground and low-lying doublet electronic states of SbO2.

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying doublet electronic states of antimony dioxide (SbO(2)) employing a variety of ab initio methods, including the complete active space self-consistent field/multireference configuration interaction and the RCCSD(T) methods. Both large and small core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to aug-cc-pV5Z quality. Contributions from outer core correlation and off-diagonal spin-orbit interaction to relative electronic energies have been calculated. The ground electronic state of SbO(2) is determined to be the X (2)A(1) state, as is the case for dioxides of other lighter group 15 p-block (or group VA) elements. However, the A (2)B(2) and B (2)A(2) states are estimated to be only 4.1 and 10.7 kcalmole above the X (2)A(1) state, respectively, at the complete basis set limit. Reliable vertical excitation energies from the X (2)A(1) state to low-lying excited states of SbO(2) have been computed with a view to assist future spectral assignments of the absorption and/or laser-induced fluorescence spectra of SbO(2), when they become available.

Journal Article↗

PubMed2006

Orthogonal projection (OP) technique applied to pattern recognition of fingerprints of the herbal medicine houttuynia cordata Thunb. and its final injection products.

It is a crucial issue to determine the origins of herbal medicinal materials and identify the quality grades and fakes of their final products collected from different pharmaceutical corporations. Pattern recognition technique may assist the manufacturers to achieve this purpose and effectively control the quality of their products. In this work, a widely used method in chemometrics, orthogonal projection (OP) technique, was applied to discrimination analysis and identification of fingerprints of the herbal medicine houttuynia cordata Thunb. (HCT) and its final injection products. The advantages of the OP technique are clearly shown after comparing with the conventional methods such as principal component analysis (PCA), Mahalanobis distance (MD), and similarity comparison method (SCM). Three different sources of medicinal material HCT and its final injection products from six different manufacturers were studied under 'sixfold', 'threefold' and 'threefold-bis' cross-validation procedures. The good performance of the proposed method in determination and identification of unknown samples shows it could be a powerful tool for quality control in herbal medicine production and other related research fields.

Chemistry Techniques, Analytical↗

PubMed2006

Alternative moving window factor analysis for comparison analysis between complex chromatographic data.

In this investigation, a novel chemometric method is developed for the analysis of five possible relationships of components or spectral features between two correlative but different hyphenated chromatographic systems. It is very helpful for comparison study of components present in different complex systems in both chemistry and systems biology. The proposed method, named alternative moving window factor analysis (AMWFA), could be utilized to determine the number of common components between different samples and then to identify their corresponding spectra half-automatically. AMWFA can alternatively be employed to mind for the selective information hiding in anyone of the two compared data X and Y, and to self-verify the resolution results by changing the extracted target matrices in analysis. From the results of comparison of simulated hyphenated chromatographic data, volatile chemical components in drug pair rhizoma ligustici chuanxiong-radix paeoniae rubra (RLC-RPR) and its single herbal medicines, and analysis of Angelica oral solution and its plasma sample after oral intake to rabbit, powerful ability of the proposed method is shown.

Angelica↗

PubMed2005

A combined ab initio/Franck-Condon study of the A-X single-vibronic-level emission spectrum of CCl2 and the photodetachment spectrum of CCl2 -.

State-of-the-art ab initio calculations have been carried out on the X1A1, ã3B1 and A1B1 states of CCl2 and the X2B1 state of CCl2-. Franck-Condon factors including anharmonicity have been calculated, between the CCl2 states, and between the CCl2- X2B1 state and the CCl2 states. They are used to simulate the A-X single-vibronic-level (SVL) emission spectra of CCl2 determined by M.-L. Lui et al. [PCCP 2003, 5, 352] and the 364 nm laser photodetachment spectrum of CCl2- obtained by R. L. Schwartz et al. [J. Phys. Chem. A 1999, 103, 8213]. Comparison between simulated and observed spectra confirms the vibrational assignments of the X2B1 SVL emission spectra and the T0 position of the A1B1 state of CCl2. For the photodetachment spectrum of CCl2-, spectral simulation shows that the higher binding energy ã3B1(CCl2) <-- X2B1(CCl2-) band is well separated from the X1A1(CCl2) <-- X2B1(CCl2-) band. It is concluded that the observed second band, which overlaps heavily with the X1A1(CCl2) <-- X2B1(CCl2-) band in the photodetachment spectrum of CCl2- cannot be assigned to the CCl2(ã3B1) + e --> CCl2-(X2B1) detachment process. Further ab initio calculations carried out in the present investigation support the suggestion that the second band in the 364 nm photodetachment spectrum of CCl2- is due to detachment from an excited state of CCl2-, a linear quartet state, to a triplet state of CCl2. These calculations identify the anionic state to be the lowest 4Sigmag- (4Sigma-) state, which photodetaches vertically to the 3Sigmag- (3Sigma-; adiabatically ã3B1) and/or 3Pi(u) (3Pi) states of CCl2 to give the second band observed in the 364 nm photodetachment spectrum of CCl2-.

Journal Article↗

PubMed2004

Franck-Condon simulation of the single-vibronic-level emission spectra of HPCl/DPCl and the chemiluminescence spectrum of HPCl, including anharmonicity.

Restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] potential energy functions (PEFs) were calculated for the X (2)A" and A (2)A' states of HPCl employing the augmented correlation-consistent polarized-valence-quadruple-zeta (aug-cc-pVQZ) basis set. Further geometry optimization calculations were carried out on both electronic states of HPCl at the RCCSD(T) level with all electron and quasirelativistic effective core potential basis sets of better than the aug-cc-pVQZ quality, and also including some core electrons, in order to obtain more reliable geometrical parameters and relative electronic energy of the two states. Anharmonic vibrational wave functions of the two states of HPCl and DPCl, and Franck-Condon (FC) factors of the A (2)A'-X (2)A" transition were computed employing the RCCSD(T)/aug-cc-pVQZ PEFs. Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the single-vibronic-level (SVL) emission spectra of HPCl and DPCl reported by Brandon et al. [J. Chem. Phys. 119, 2037 (2003)] and the chemiluminescence spectrum reported by Bramwell et al. [Chem. Phys. Lett. 331, 483 (2000)]. Comparison between simulated and observed SVL emission spectra gives the experimentally derived equilibrium geometry of the A (2)A' state of HPCl of r(e)(PCl) = 2.0035 +/- 0.0015 A, theta(e) = 116.08 +/- 0.60 degrees, and r(e)(HP) = 1.4063+/-0.0015 A via the iterative Franck-Condon analysis procedure. Comparison between simulated and observed chemiluminescence spectra confirms that the vibrational population distribution of the A (2)A' state of HPCl is non-Boltzmann, as proposed by Baraille et al. [Chem. Phys. 289, 263 (2003)].

Journal Article↗

PubMed2004

Use of the ultraviolet absorption spectrum of CF2 to determine the spatially resolved absolute CF2 density, rotational temperature, and vibrational distribution in a plasma etching reactor.

Broadband ultraviolet absorption spectroscopy has been used to determine CF(2) densities in a plasma etch reactor used for industrial wafer processing, using the CF(2) A (1)B(1)<--X (1)A(1) absorption spectrum. Attempts to fit the experimental spectra using previously published Franck-Condon factors gave poor results, and values for the higher vibrational levels of the A state [(0,v(2),0), with v(2) (')>6] from the ground state were missing; hence new values were calculated. These were computed for transitions between low-lying vibrational levels of CF(2) X (1)A(1) to vibrational levels of CF(2) A (1)B(1) (v(1) ('),v(2) ('),0) up to high values of the vibrational quantum numbers using high level ab initio calculations combined with an anharmonic Franck Condon factor method. The Franck Condon factors were used to determine the absorption cross sections of CF(2) at selected wavelengths, which in turn were used to calculate number densities from the experimental spectra. Number densities of CF(2) have been determined in different regions of the plasma, including the center of the plasma and outside the plasma volume, and CF(2) rotational temperatures and vibrational energy distributions were estimated. For absorption spectra obtained outside the confined plasma volume, the CF(2) density was determined as (0.39+/-0.08)x10(13) molecule cm(-3) and the vibrational and rotational temperatures were determined as 303 and 350 K, respectively. In the center of the plasma reactor, the CF(2) density is estimated as (3.0+/-0.6)x10(13) molecules cm(-3) with T(rot) approximately 500 K. The fitted vibrational distribution in the CF(2) ground state corresponds to two Boltzmann distributions with T(vib) approximately 300 and T(vib) approximately 1000 K, indicating that CF(2) molecules are initially produced highly vibrationally excited, but are partially relaxed in the plasma by collision.

Journal Article↗

PubMed2004

Correction of retention time shifts for chromatographic fingerprints of herbal medicines.

In this study, the combination of chemometric resolution and cubic spline data interpolation was investigated as a method to correct the retention time shifts for chromatographic fingerprints of herbal medicines obtained by high-performance liquid chromatography-diode array detection (HPLC-DAD). With the help of the resolution approaches in chemometrics, it was easy to identify the purity of chromatographic peak clusters and then resolve the two-dimensional response matrix into chromatograms and spectra of pure chemical components so as to select multiple mark compounds involved in chromatographic fingerprints. With these mark components determined, the retention time shifts of chromatographic fingerprints might be then corrected effectively. After this correction, the cubic spline interpolation technique was then used to reconstruct new chromatographic fingerprints. The results in this work showed that, the purity identification of the chromatographic peak clusters together with the resolution of overlapping peaks into pure chromatograms and spectra by means of chemometric approaches could provide the sufficient chromatographic and spectral information for selecting multiple mark compounds to correct the retention time shifts. The cubic spline data interpolation technique was user-friendly to the reconstruction of new chromatographic fingerprints with correction. The successful application to the simulated and real chromatographic fingerprints of two Cortex cinnamomi, fifty Rhizoma chuanxiong, ten Radix angelicae and seventeen Herba menthae samples from different sources demonstrated the reliability and applicability of the approach investigated in this work. Pattern recognition based on principal component analysis for identifying inhomogenity in chromatographic fingerprints from real herbal medicines could further interpret it.

Chromatography, High Pressure Liquid↗

PubMed2004

Franck-Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity.

Potential energy functions (PEFs) of the X (1)A(') and A (1)A(") states of HSiF have been computed using the coupled-cluster single-double plus perturbative triple excitations and complete-active-space self-consistent-field multireference internally contracted configuration interaction methods, respectively, employing augmented correlation-consistent polarized-valence quadruple-zeta basis sets. For both electronic states of HSiF and DSiF, anharmonic vibrational wavefunctions and energies of all three modes have been calculated variationally with the ab initio PEFs and using Watson's Hamiltonian for nonlinear molecules. Franck-Condon factors between the two electronic states, allowing for Duschinsky rotation, were computed using the calculated anharmonic vibrational wavefunctions. These Franck-Condon factors were used to simulate the single vibronic level (SVL) emission spectra recently reported by Hostutler et al. in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the A (1)A(")(1,0,0)-->X (1)A(') SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the A (1)A(")(0,1,0) and (1,1,0) SVL emissions of HSiF have been found. These are most likely, partly due to experimental deficiencies and, partly to inadequacies in the ab initio levels of theory employed in the calculation of the PEFs. Based on the computed Franck-Condon factors, minor revisions of previous vibrational assignments are suggested. The calculated anharmonic wave functions of higher vibrational levels of the X (1)A(') state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching.

Journal Article↗

PubMed2003

Information theory applied to chromatographic fingerprint of herbal medicine for quality control.

At present, the construction of chromatographic fingerprints plays an important role in the quality control of complex herbal medicines. In this work, information theory was applied to obtain chromatographic fingerprints with good performance. Moreover, according to the characteristics of the chromatographic fingerprints obtained, some modifications of the calculation of the information content were conducted. In comparison with the information content from several chromatographic fingerprints obtained, reliable chromatographic fingerprints with a high separation degree and uniform concentration distribution of chemical components could be determined. The successful application of information theory with modification to simulated chromatographic fingerprints together with real herbal medicines such as Rhizoma chuanxiong and Ginkgo biloba from different sources demonstrated clearly that the proposed method to determine chromatographic fingerprints was reasonable and reliable and it was user-friendly. Chromatographic fingerprints determined with high separation degrees and uniform concentration distribution of chemical ingredients might also chemically represent characteristic components of herbal medicines for quality control.

Chromatography↗

PubMed2003

Wavelet: a new trend in chemistry.

Since 1989, wavelet transform (WT) has attracted much interest of chemists working on signal and image processing, and the WT-based techniques have been successfully applied to the chemical signal processing. This approach has been demonstrated as fast in computation with localization and having quick decay properties, in contrast to the popular methods existing, especially to the fast Fourier transform. More than 370 papers have been published up to the year 2002 which covered applications of WT in various fields of chemistry, including analytical chemistry, chemical physics, and quantum chemistry. In this paper, we report on applications of WT to data compression, data smoothing and denoising, baseline and background correction, resolution of multicomponent overlapping signals, regression and classification, and analytical images processing in analytical chemistry. Through this report we wish to induce greater interest of chemists in WT and to obtain greater benefits from using the WT-based techniques.

Journal Article↗

PubMedDate not supplied

Analysis of volatile fractions of Schisandra chinensis (Turcz.) Baill. using GC-MS and chemometric resolution.

The two-dimensional data obtained from GC-MS has been used qualitatively and quantitatively to determine the components of the volatile fractions of Schisandra chinensis obtained by six different extraction methods. Sub-window factor analysis (SFA) was employed to confirm the identities of components determined in different samples. With the help of SFA, and other chemometric techniques, peak purity in the chromatograms was determined, and overlapping peaks were resolved to yield a pure chromatographic profile and mass spectrum for each component. It is demonstrated that the accuracy of qualitative and quantitative analysis may be greatly enhanced using chemometric resolution methods, such methods being particularly valuable with respect to the analysis of complex samples such as traditional Chinese medicines. It is further demonstrated that different extraction methods give rise to volatile fractions of S. chinensis which differ qualitatively and quantitatively in their composition.

Gas Chromatography-Mass Spectrometry↗