Biomedical subjects

J G Chen

Publications and source records attributed to J G Chen.

At least 19 recordsLinked to original sources

PubMed2006

Correlating electronic properties of bimetallic surfaces with reaction pathways of C2 hydrocarbons.

The rate and selectivity of chemical reactions on transition-metal surfaces can be controlled by using different bimetallic combinations. The interaction of bimetallic components leads to a change in the electronic properties of the surface, which in turn produces a change in chemical reactivity. In the current paper, we illustrate the correlation of the electronic properties of bimetallic surfaces with the reaction pathways of C2 hydrocarbons. Density functional theory (DFT) was used to study the binding of hydrogen, ethylene, acetylene, ethyl, and vinyl on monometallic and bimetallic transition-metal surfaces. The binding energies of these species were found to correlate with the d-band centers of these surfaces. The binding energies for hydrogen atoms on bimetallic surfaces were lower than for those on the corresponding parent metal surfaces. This trend was consistent for ethylene and acetylene binding. Comparative studies between acetylene and ethylene revealed that acetylene was more strongly bonded to the monometallic and the bimetallic surfaces than was ethylene. Bond order conservation (BOC) theory was used to calculate the activation barriers for ethyl dehydrogenation to ethylene and vinyl dehydrogenation to acetylene. The activation barriers for these reactions were correlated with the surface d-band center of the substrates.

Journal Article↗

PubMed2005

Different signaling and cell death roles of heterotrimeric G protein alpha and beta subunits in the Arabidopsis oxidative stress response to ozone.

Arabidopsis thaliana plants with null mutations in the genes encoding the alpha and beta subunits of the single heterotrimeric G protein are less and more sensitive, respectively, to O3 damage than wild-type Columbia-0 plants. The first peak of the bimodal oxidative burst elicited by O3 in wild-type plants is almost entirely missing in both mutants. The late peak is normal in plants lacking the Gbeta protein but missing in plants lacking the Galpha protein. Endogenous reactive oxygen species (ROS) are first detectable in chloroplasts of leaf epidermal guard cells. ROS production in adjacent cells is triggered by extracellular ROS signals produced by guard cell membrane-associated NADPH oxidases encoded by the AtrbohD and AtrbohF genes. The late, tissue damage-associated component of the oxidative burst requires only the Galpha protein and arises from multiple cellular sources. The early component of the oxidative burst, arising primarily from chloroplasts, requires signaling through the heterotrimer (or the Gbetagamma complex) and is separable from Galpha-mediated activation of membrane-bound NADPH oxidases necessary for both intercellular signaling and cell death.

Arabidopsis↗

PubMed2004

Role of strain and ligand effects in the modification of the electronic and chemical properties of bimetallic surfaces.

Periodic density functional calculations are used to illustrate how the combination of strain and ligand effects modify the electronic and surface chemical properties of Ni, Pd, and Pt monolayers supported on other transition metals. Strain and the ligand effects are shown to change the width of the surface d band, which subsequently moves up or down in energy to maintain a constant band filling. Chemical properties such as the dissociative adsorption energy of hydrogen are controlled by changes induced in the average energy of the d band by modification of the d-band width.

Journal Article↗

PubMed2004

Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals.

The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts.

Journal Article↗

PubMed2001

Oxygen-containing functional groups on single-wall carbon nanotubes: NEXAFS and vibrational spectroscopic studies.

Single-walled nanotubes (SWNTs) produced by plasma laser vaporization (PLV) and containing oxidized surface functional groups have been studied for the first time with NEXAFS. Comparisons are made to SWNTs made by catalytic synthesis over Fe particles in high-pressure CO, called HiPco material. The results indicate that the acid purification and cutting of single-walled nanotubes with either HNO3/H2SO4 or H2O2/H2SO4 mixtures produces the oxidized groups (O/C = 5.5-6.7%), which exhibit both pi*(CO) and sigma*(CO) C K-edge NEXAFS resonances. This indicates that both carbonyl (C=O) and ether C-O-C functionalities are present. Upon heating in a vacuum to 500-600 K, the pi*(CO) resonances are observed to decrease in intensity; on heating to 1073 K, the sigma*(CO) resonances disappear as the C-O-C functional groups are decomposed. Raman spectral measurements indicate that the basic tubular structure of the SWNTs is not perturbed by heating to 1073 K, based on the invariance of the ring breathing modes upon heating. The NEXAFS studies agree well with infrared studies which show that carboxylic acid groups are thermally destroyed first, followed by the more difficult destruction of ether and quinone groups. Single-walled nanotubes produced by the HiPco process, and not treated with oxidizing acids, exhibit an O/C ratio of 1.9% and do not exhibit either pi*(CO) or sigma*(CO) resonances at the detection limit of NEXAFS. It is shown that heating (to 1073 K) of the PLV-SWNTs containing the functional groups produces C K-edge NEXAFS spectra very similar to those seen for the HiPco material. The NEXAFS spectra are calibrated against spectra measured for a number of fused-ring aromatic hydrocarbon molecules containing various types of oxidized functional groups present on the oxidized SWNTs.

Anthracenes↗

PubMed2001

Treatment of isolated systolic hypertension is most effective in older patients with high-risk profile.

BACKGROUND: Although present guidelines suggest that treatment of hypertension is more effective in patients with multiple risk factors and higher risk of cardiovascular events, this hypothesis was never verified in older patients with systolic hypertension. METHODS AND RESULTS: Using data from the Systolic Hypertension in the Elderly Program, we calculated the global cardiovascular risk score according to the American Heart Association Multiple Risk Factor Assessment Equation in 4,189 participants free of cardiovascular disease (CVD) and in 264 participants with CVD at baseline. In the placebo group, rates of cardiovascular events over 4.5 years were progressively higher according to higher quartiles of CVD risk. The protection conferred by treatment was similar across quartiles of risk. However, the numbers needed to treat (NNTs) to prevent one cardiovascular event were progressively smaller according to higher cardiovascular risk quartiles. In participants with baseline CVD, the NNTs to prevent one cardiovascular event were similar to those estimated for CVD-free participants in the highest-risk quartile. CONCLUSIONS: Treatment of systolic hypertension is most effective in older patients who, because of additional risk factors or prevalent CVD, are at higher risk of developing a cardiovascular event. These patients are prime candidates for antihypertensive treatment.

Age Factors↗

PubMed2001

Modulation of cell proliferation by heterotrimeric G protein in Arabidopsis.

The alpha subunit of a prototypical heterotrimeric GTP-binding protein (G protein), which is encoded by a single gene (GPA1) in Arabidopsis, is a modulator of plant cell proliferation. gpa1 null mutants have reduced cell division in aerial tissues throughout development. Inducible overexpression of GPA1 in Arabidopsis confers inducible ectopic cell division. GPA1 overexpression in synchronized BY-2 cells causes premature advance of the nuclear cycle and the premature appearance of a division wall. Results from loss of function and ectopic expression and activation of GPA1 indicate that this subunit is a positive modulator of cell division in plants.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2001

A lithium-induced conformational change in serotonin transporter alters cocaine binding, ion conductance, and reactivity of Cys-109.

Inactivation of serotonin transporter (SERT) expressed in HeLa cells by [2-(trimethylammonium)ethyl]methanethiosulfonate (MTSET) occurred much more readily when Na(+) in the reaction medium was replaced with Li(+). This did not result from a protective effect of Na(+) but rather from a Li(+)-specific increase in the reactivity of Cys-109 in the first external loop of the transporter. Li(+) alone of the alkali cations caused this increase in reactivity. Replacing Na(+) with N-methyl-d-glucamine (NMDG(+)) did not reduce the affinity of cocaine for SERT, as measured by displacement of a high affinity cocaine analog, but replacement of Na(+) with Li(+) led to a 2-fold increase in the K(D) for cocaine. The addition of either cocaine or serotonin (5-HT) protected SERT against MTSET inactivation. When SERT was expressed in Xenopus oocytes, inward currents were elicited by superfusing the cell with 5-HT (in the presence of Na(+)) or by replacing Na(+) with Li(+) but not NMDG(+). MTSET treatment of oocytes in Li(+) but not in Na(+) decreased both 5-HT and Li(+) induced currents, although 5-HT-induced currents were inhibited to a greater extent. Na(+) antagonized the effects of Li(+) on both inactivation and current. These results are consistent with Li(+) inducing a conformational change that exposes Cys-109, decreases cocaine affinity, and increases the uncoupled inward current.

Animals↗

PubMed2001

Investigation of pharmaceutical high-performance liquid chromatography assay bias using experimental design.

This article presents a systematic approach to investigate, document, and eliminate pharmaceutical HPLC assay bias using experimental design. This is the first article to describe the application of experimental design in the area of assay bias. It is found that both formulation and analytical variables can contribute to pharmaceutical HPLC assay bias using model compounds and formulations.

Chromatography, High Pressure Liquid↗

PubMed2001

Primary study of vascular endothelial growth factor immunohistochemical staining in the diagnosis of early acute myocardial ischemia.

The expression of vascular endothelial growth factor (VEGF) in the model of rat early acute myocardial ischemia was studied by Strept-Avidin-Biotin-Peroxidase Complex (SABC) immunohistochemical staining. After ligating the anterior descending branch of the left coronary artery, an initial rapid (30min) positive expression of VEGF in myocardial ischemic areas was observed, the intensity of positive expression of VEGF increased with the continuation of myocardial ischemia. After 5h infarction, the strongly positive myocytes of SABC-VEGF staining were predominantly limited to perimyocardial infarction areas. No positive expression of VEGF was found in the control group. These findings suggested that SABC-VEGF method could give a sensitive, specific, simple and objective morphologic evidence to the diagnosis of sudden cardiac death caused by acute early myocardial ischemia.

Animals↗

PubMed2001

ABP1 is required for organized cell elongation and division in Arabidopsis embryogenesis.

To directly address the function of a putative auxin receptor designated ABP1, a reverse genetic approach was taken to identify and characterize ABP1 mutant alleles in Arabidopsis. A homozygous null mutation in ABP1 confers embryo lethality. Null mutant embryos develop normally until the early stages of the globular embryo but are unable to make the transition to a bilaterally symmetrical structure because cells fail to elongate. Cell division was also aberrant both in the suspensor and embryo proper. Antisense suppression of ABP1 in tobacco cells causes slow proliferation and eliminates auxin-induced cell elongation and reduces cell division. The complete lack of auxin-inducible elongation in individual cells confirms the results observed in embryos, indicates a cell autonomous function, and, taken together with biochemical evidence that ABP1 binds auxins, suggests that ABP1 mediates auxin-induced cell elongation and, directly or indirectly, cell division.

Alleles↗

PubMed2001

Solvent effects on the absorption and fluorescence characteristics of tin(IV) mesoporphyrin.

The absorption and fluorescence characteristics of tin(IV) mesoporphyrin (SnMP) and its analog tin(IV) protoporphyrin (SnPP) were studied in a series of organic solvents. Fluorescence quantum yields were calculated using the Strickler-Berg equation. Good correlation was found between calculated values and measured relative values. Fluorescence lifetime, radiative lifetime and non-radiative lifetime were also calculated. The parameters showed variation depending on ligation as well as H-bonding. Unusual long lifetime and high quantum yields were found in alcohol solvents. This finding might contribute to elucidation of the nature of tin porphyrins to inhibit heme oxygenase.

Enzyme Inhibitors↗

PubMed2001

The role of auxin-binding protein 1 in the expansion of tobacco leaf cells.

Tobacco leaf was used to investigate the mechanism of action of auxin-binding protein 1 (ABP1). The distributions of free auxin, ABP1, percentage of leaf nuclei in G2 and the amount of auxin-inducible growth were each determined in control tobacco leaves and leaves over-expressing Arabidopsis ABP1. These parameters were compared with growth of tobacco leaves, measured both spatially and temporally throughout the entire expansion phase. Within a defined window of leaf development, juvenile leaf cells that inducibly expressed Arabidopsis ABP1 prematurely advanced nuclei to the G2 phase. The ABP1-induced increase in cell expansion occured before the advance to the G2 phase, indicating that the ABP1-induced G2 phase advance is an indirect effect of cell expansion. The level of ABP1 was highest at the position of maximum cell expansion, maximum auxin-inducible growth and where the free auxin level was the lowest. In contrast, the position of maximum cell division correlated with higher auxin levels and lower ABP1 levels. Consistent with the correlations observed in leaves, tobacco cells (BY-2) in culture displayed two dose-dependent responses to auxin. At a low auxin concentration, cells expanded, while at a relatively higher concentration, cells divided and incorporated [3H]-thymidine. Antisense suppression of ABP1 in these cells dramatically reduced cell expansion with negligible effect on cell division. Taken together, the data suggest that ABP1 acts at a relatively low level of auxin to mediate cell expansion, whereas high auxin levels stimulate cell division via an unidentified receptor.

Arabidopsis↗

PubMed2001

Cost of nonmelanoma skin cancer treatment in the United States.

BACKGROUND: Despite being the most prevalent form of cancer, the economic impact of nonmelanoma skin cancer (NMSC) in the United States has not been assessed. OBJECTIVE: To determine the overall cost and to estimate the cost per episode of NMSC care in the United States in physicians' offices, outpatient surgery centers, and inpatient settings. METHODS: Data from the Medicare Current Beneficiary Study 1992-1995 were analyzed to obtain the total cost of NMSC and the cost in different settings. To normalize these data on a per episode basis, the cost in each setting was divided by the number of procedures performed in each setting obtained from the National Hospital Discharge Survey (NHDS, 1992-1997), the National Survey of Ambulatory Surgery (NSAS, 1994-1996), and the National Ambulatory Medical Care Survey (NAMCS, 1995). RESULTS: The total cost of NMSC care in the United States in the Medicare population is $426 million/year. Physician office-based procedures for NMSC accounted for the greatest percentage of money spent to treat NMSC and the greatest percentage of procedures. The average cost per episode of NMSC when performed in a physician's office setting was found to be $492. The cost per episode of care in inpatient and outpatient settings were $5537 and $1043, respectively. CONCLUSION: Compared to other cancers, the relative magnitude of NMSC treatment costs is currently small because NMSC is managed efficiently and effectively, primarily in office-based settings. Legislative or regulatory measures that discourage office treatment of NMSC will lead to increased cost.

Ambulatory Surgical Procedures↗

PubMed2001

Implications of a utility model for ultraviolet exposure behavior.

Over the past several decades, the incidence of skin cancer has reached epidemic proportions. Despite numerous efforts to increase public awareness of the risks associated with solar radiation, people continue to sunbathe, use indoor tanning facilities, avoid photoprotective clothing, and fail to use sunscreen. We propose using an economic model, the utility model, to better understand how to reduce tanning behaviors. This model has been widely applied in financial decision-making as well as in analysis of risk-taking behaviors such as smoking. The model takes into account both the current perceived benefits of tanning and the future long-term risks. People tend to discount the future; they tend to weigh current benefits more heavily than future risks. As predicted by the model, past prevention efforts that have focused on long-term benefits gained by sun-protective behavior have been largely ineffective. In the current social environment, we cannot expect tanning reduction measures based solely on health education to be very effective. Only by changing public perceptions of a tan will efforts to decrease ultraviolet exposure behavior likely be successful.

Decision Making↗

PubMed2001

Admission base deficit in pediatric trauma: a study using the National Trauma Data Bank.

BACKGROUND: The base deficit, an important indicator of physiologic derangement after severe injury in adults, has not been specifically examined in the pediatric trauma population. The purpose of this study was to assess the ability of the admission base deficit to predict injury severity and outcome in the pediatric trauma population. METHODS: The study group included all patients in the National Trauma Data Bank over a 2-year period aged 0 to 12 years with a base deficit (0 to -30 mEq/L) recorded from the emergency department. Age, presence of a severe closed head injury, and base deficit were analyzed with respect to mortality and other indicators of injury severity. RESULTS: A total of 515 patients constituted the study group. Base deficit less than -4 mEq/L (p < 0.001) and the presence of a closed head injury (odds ratio, 3.8; p < 0.05) were predictors of mortality. For the group, an admission base deficit of -8 mEq/L corresponded to a probability of mortality of 25%. Significant correlations were found between base deficit and emergency department systolic blood pressure, Injury Severity Score, and Revised Trauma Score. There was no relationship between age and mortality. CONCLUSION: In injured children, the admission base deficit reflects injury severity and predicts mortality. The probability of mortality increases precipitously in children with a base deficit less than -8 mEq/L, and should alert the clinician to the presence of potentially lethal injuries or uncompensated shock.

Child↗

PubMed2001

[Production and cytogenetics of intergeneric hybrids between Ogura CMS Brassica campestris var. purpuraria and Raphanus sativus].

Crosses between Ogura CMS Brassica campestris var. purpuraria (AA, 2n = 20) and Raphanus sativus (RR, 2n = 18) were made and many intergeneric hybrids were produced. The F1 seedlings did not show chlorosis at low temperature. When red Raphanus sativus varieties were used as male parent, the leaf petiole and leaf vein of F1 plants were purple, and when white Raphanus sativus varieties were used as male parent, the leaf petiole and leaf vein of F1 plants were not purple. All the F1 plants had white flowers and normal honey glands. Male gametes of the F1 were highly sterile and female gametes of the F1 were partly fertile. Cytological studies indicated that chromosome number of the F1 was 2n = 19 as expected, the mean chromosome pairing pattern was 15.53 I + 1.34 II + 0.25 III + 0.01 IV. Most chromosomes exsistet as univalents, but there also exsisted some bivalents, trivalents and even tetravalents, suggesting that chromosome set A was partly homologous with chromosome set R.

Brassica↗

PubMed2001

[A study of the magnification of mandible pantomography image].

OBJECTIVE: To study the degree of magnification of mandible pantomography image. METHODS: The pantomography of 50 mandible specimens marked with lead pellets were taken by TROPHY XL-90C. The distances between each markers on film and in specimen were measured. RESULTS: The mean magnification(MM) of mandible pantomography image with TROPHY XL-90C was 1.22. MM of horizontal axle was 1.14. MM of vertical axle was 1.29. MM of horizontal axle was greatest (1.24) in the body of mandible,and lest (1.08) in genion. MM of vertical axle is similar among each regions. MM of vertical axle was greater than that of horizontal axle in all regions. CONCLUSION: The MM parameters of mandible pantomography image were useful to estimate the size of mandible lesions and provided a basis for dental implant more exactly.

English Abstract↗