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E S Chen

Publications and source records attributed to E S Chen.

12 recordsLinked to original sources
PubMed2004

Molecular electron affinities and the calculation of the temperature dependence of the electron-capture detector response.

The use of the electron-capture detector (ECD) to measure molecular electron affinities and kinetic parameters for reactions of thermal electrons is reviewed. The advances of the past decade are emphasized and include the multistate electron-capture detector model and the use of semi-empirical self-consistent field quantum mechanical calculations and half wave reduction potential values to support gas phase experimental results. A procedure for the evaluation of the adiabatic electron affinities of the main group elements and the homonuclear diatomic molecules is presented. Potential excited states are identified for the magnetron (MGN) values for quinones, thermal charge transfer (TCT) values for CS2, C6F6, SF6 and photoelectron spectroscopy (PES) values for O2, NO, nitromethane, and the nucleic acids. Literature electron affinities are then evaluated. The temperature dependence of the electron-capture detector can be calculated using values for kinetic rate constants and electron affinities to optimize response and temperature sensitivity in analytical procedures. The temperature dependence for adenine, guanine, thymine and cytosine are predicted for reactions with thermal electrons. Using the recent advances, the new adiabatic electron affinities are: all in electron volts (eV), 4-F-benzaldehyde (0.57 +/- 0.05) and acetophenones (APs) 4-F-AP (0.52 +/- 0.05); 2-CF3-AP (0.79 +/- 0.05); 3-CF3-AP (0.79 +/- 0.05); 4-CF3-AP (0.89 +/- 0.05); 3-CI-AP (0.67 +/- 0.05); and 4-Cl-AP (0.64 +/- 0.05). The adiabatic electron affinities of chloro and fluorobenzenes range from 0.17 to 1.15 eV and 0.13 to 0.86 eV.

Chemical Phenomena↗
PubMed2001

The negative ion states of molecules: adenine and guanine.

Anions of cytosine and thymine predominate in radiation-damaged DNA. This is in contrast to the experimental order of adiabatic electron affinities: A, 0.95; G, 1.51; >T, 0.79, U, 0.80; C, 0.56 (+/-0.05 eV). Excited negative-ion states of adenine (A) and guanine (G) are identified using semiempirical AM1-MCCI quantum mechanical calculations. A planar G(-) has an excited state adiabatic electron affinity, AEA*, of 0.3 +/- 0.05 eV. This state and the unique Watson-Crick structure are responsible for the preponderance of charge on C(-) in radiation-damaged DNA. By analogy to the value for cytosine, the dipole-bound EA of G is estimated as 0.25 eV. New AEA values from literature reduction potentials for the ribose nucleotides are rC, 0.6; rU, 0.8; and rT, 0.8 (+/-0.1 eV). From literature photoelectron spectroscopy, AEA* vales for U are 0.15, 0.3, 0.5, and 0.6 eV. In GC(-2), stacked [GC:GC](-3), and [GC:GC:GC](-4), the charge moves to G. In [GC:GC:GC](-2 to -4), the charge moves from GC(1) to GC(3) through space without a bridge or bond. This is important to electron conduction, radiation damage and repair, and nanoscale devices.

Adenine↗
PubMed2001

Human collagenase (matrix metalloproteinase-1) expression in the lungs of patients with emphysema.

Pulmonary emphysema is believed to result from an imbalance between proteolytic enzymes and their inhibitors. Multiple studies have examined the presence of various proteases within the bronchoalveolar lavage fluid from patients with chronic obstructive pulmonary disease (COPD). However, to date extensive examination of the lung parenchyma for the expression of destructive enzymes has not yet been determined. The following study examines the lung parenchyma of 23 patients with emphysema and 8 normal control samples for the expression of matrix matalloproteinase-1 (MMP-1), MMP-12, and MMP-9. We report here that interstitial collagenase (MMP-1) RNA, protein, and activity are present in the lung parenchyma of patients with emphysema and not in the lung of normal control subjects. In contrast, metalloelastase (MMP-12) expression is absent in these samples. Immunohistochemistry studies localized MMP-1 to the Type II pneumocyte in patients with emphysema and not normal control subjects or smokers without emphysema. This observation demonstrates that the lung is altered in emphysema such that the Type II pneumocyte secretes MMP-1 and suggests that MMP-1 may be an important enzyme involved in the destruction of the lung in the human disease. In addition, the induction of a proteolytic enzyme within the Type II pneumocyte suggests that the cells within the lung itself are capable of producing degradative enzymes in this disease process.

Adult↗
PubMed2001

Attenuation of lung inflammation and fibrosis in interferon-gamma-deficient mice after intratracheal bleomycin.

Because mouse strains susceptible to bleomycin, such as C57BL/ 6J, tend to produce T helper type 1 (Th1) cytokines in response to immune activation, we hypothesized that the inflammatory response to bleomycin is mediated, in part, by local production of the Th1 cytokine interferon-gamma (IFN-gamma). Consistent with this hypothesis, fibrosis-prone C57BL/6J and A/J mice demonstrated significantly elevated expression of IFN-gamma protein (by enzyme-linked immunosorbent assay) in bronchoalveolar lavage fluid at 24 h, and subsequently increased lung inflammation, weight loss, and mortality 10 d after intratracheal bleomycin administration compared with fibrosis-resistant BALB/c mice or saline control mice. To directly determine a role for IFN-gamma in bleomycin toxicity, we exposed C57BL/6J mice with a homozygous null mutation of the IFN-gamma gene (IFN-gamma[-/-]) and wild-type C57BL/6J mice to intratracheal bleomycin. IFN-gamma(-/-) mice demonstrated significantly lower parenchymal inflammation, weight loss, and mortality 10 d after 5 U/kg intratracheal bleomycin administration compared with control mice. At 3 wk after 1.5 U/kg bleomycin exposure, single lung collagen determined by hydroxyproline assay was significantly lower in IFN-gamma(-/-) mice compared with wild-type C57BL/6J mice. Together, these results suggest that IFN-gamma mediates, in part, bleomycin-induced pulmonary inflammation and fibrosis.

Animals↗
PubMed2000

Requirement of Mis6 centromere connector for localizing a CENP-A-like protein in fission yeast.

Mammalian kinetochores contain the centromere-specific histone H3 variant CENP-A, whose incorporation into limited chromosomal regions may be important for centromere function and chromosome segregation during mitosis. However, regulation of CENP-A localization and its role have not been clear. Here we report that the fission yeast homolog SpCENP-A is essential for establishing centromere chromatin associated with equal chromosome segregation. SpCENP-A binding to the nonrepetitious inner centromeres depended on Mis6, an essential centromere connector protein acting during G1-S phase of the cell cycle. Mis6 is likely required for recruiting SpCENP-A to form proper connection of sister centromeres.

Amino Acid Sequence↗
PubMed2000

Arbor 3D: an interactive environment for examining phylogenetic and taxonomic trees in multiple dimensions.

UNLABELLED: This paper examines a new technique for the visualization of and the interaction with trees, objects frequently used to convey hierarchical relationships in biological data. Motivated by the quality of 2D tree interaction, we adapt the planar tree-of-life metaphor to a virtual, semi-immersive 3D environment. A 3D environment extends the utility of this metaphor by allowing the user to view an entire data set in a single screen. Interrogation of the tree is implemented using 3D input devices. This real-time interrogation of the tree itself provides a quick means by which to qualitatively analyse the hierarchical data. In this paper, we describe the techniques underlying the implementation of such an environment. We conclude by considering the utility of tree metaphors as a basis for the representation of highly dimensional data sets. AVAILABILITY: Arbor3D (source code, a binary executable for SGI IRIX 6.4, Perl parsers, and sample Newick data files) are available via the Internet (http://xian.tamu.edu/Arbor3D/). Arbor3D can be displayed in "CAVE simulator" mode on an SGI workstation screen, or as an interactive virtual environment on a projection workbench. CONTACT: druths@rice.edu; echen@cs.rice.edu; leland@xian.tamu.edu

Classification↗
PubMed1999

Classification of organic molecules to obtain electron affinities from half-wave reduction potentials: cytosine, uracil, thymine, guanine and adenine.

A procedure for obtaining the adiabatic electron affinities (AEA) of organic molecules from half-wave reduction potentials in aprotic solvents is presented. Molecules are placed into groups according to their structure. Each group has a different solution energy difference. Calculations of AEA and charge distributions with AM1-multiconfiguration configuration interaction are used to support the intuitive classification of the molecules. The procedure is illustrated for Vitamins A and E, riboflavin, the azines, polyenes, hydroxy-pyrimidine, oxo-guanine, the hydrogen bonded cytosine-oxo-guanine as well as the AEA, and vertical EA (VEA) of Cytosine (C), Uracil (U), Thymine (T), Guanine (G) and Adenine (A). The latter values are: (VEA) G, 0.10; A, -0.49; U, 0.33; T, 0.31; C, -1.48 and (AEA) G, 1.51 +/- 0.05; A, 0.95 +/- 0.05; U, 0.80 +/- 0.05; T, 0.79 +/- 0.05; C, 0.56 +/- 0.05 in eV.

Adenine↗
PubMed1998

The electron affinities of the radicals formed by the loss of an aromatic hydrogen atom from adenine, guanine, cytosine, uracil, and thymine.

The major ion formed in Negative Ion Chemical Ionization Mass Spectrometry of Adenine, Guanine, Cytosine, Uracil and Thymine is the dehydrogenated anion. The CURES EC procedure for optimizing Austin Model-1 Multiconfigurational Configuration Interaction semi-empirical calculations is applied to the electron affinities of the corresponding dehydrogenated bases and N-H bond dissociation energies. These calculated values will be compared with literature values of the gas phase acidities of the purines and pyrimidines. The N-H bond dissociation energies are about 3.95 eV for Guanine, Adenine, and Thymine and 4.08 eV for Cytosine and Uracil. The electron affinities of the radicals are AMinH = 3.50 eV, GMinH = 3.46 eV, CMinH = 3.38 eV, UMinH = 3.48 eV, TMinH = 3.46 eV.

Adenine↗
PubMed1991

The determination of absolute electron affinities of the purines and pyrimidines in DNA and RNA from reversible reduction potentials.

We report the reversible reduction potentials of the purines and pyrimidines of DNA and RNA. These were determined in dimethylsulfoxide using cyclic voltammetry. The absolute electron affinities have been determined from these reduction potentials by calibration with the absolute electron affinities for acridine and anthracene measured in the gas phase. These are the first experimentally determined values of the electron affinities of these purines and pyrimidines and are: Guanine = 1.51 eV, Adenine = 0.95 eV, Uracil = 0.80 eV, Thymine = 0.79 eV and Cytosine = 0.56 eV.

Adenine↗
PubMed1990

The role of electron donors and acceptors in base stacking in DNA and RNA.

The role of donor-acceptor interactions in base pair stacking in DNA and RNA has been minimized because of the perceived low or negative electron affinities of the purines and pyrimidines. The use of the electron capture detector was among the first methods for measuring electron affinities in the gas phase. Recently, the experimental determination of electron affinities has been extended and improved. Now, there are data for similar compounds in the literature which enable us to estimate electron affinities for purines and pyrimidines. These values are significant, and positive, such that donor-acceptor interactions can, and indeed should play a role in the stacking of bases in nucleic acids.

Chemical Phenomena↗