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We use the first-principles molecular-dynamics¡@simulation method (MD), which is based on the density functional theory (DFT) with local-density approximation (LDA), to calculate the sticking property of a carbon atom on hydrogen covered C(100) surface. We focused on trajectories and kinetic energy transfer of the gas-phase C atom for four incident angles of =0, £k/8, £k/6 and £k/4. We find that the calculated trajectories and the kinetic energy transfer of the gas-phase atom, Cn, overall are not very sensitive to the change of the incident angle. The insensitivity of the sticking property on the incident angle may be due to a large chemisorption energy, which bends the trajectory of Cn toward the surface, so that Cn is confined to move within a small range.

Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. The intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic (V) and the vibronic (L) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N-N distance; we show this to be a poor approximation in many cases. The activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and L. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract the microscopic parameters. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. But this method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, as the electron transfer in most of the class-II compounds with distinct intervalence bands is too fast to observe on the ESR timescale. We show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in such compounds. Simulation of ESR spectra based on density functional theory calculation and comparison with optical data also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.

The distinct response of biological systems to the two enantiomers of a chiral chemical has led to a large market for enantiopure pharmaceuticals and raised fundamental issues about the origin of biological homochirality. It is therefore important to understand the interactions of chiral molecules with chiral environments. Chiral environments associated with solid surfaces could potentially play a useful role in chirally specific chemical processing. There are a variety of routes for creating chiral solid surfaces. Surfaces of materials whose bulk crystal structure is enantiomorphic can be used as one type of chiral solid surfaces. Metal surfaces that are intrinsically chiral due to the presence of kinked surface steps provide another route for creating chiral solid surfaces. Alternatively, we can impart chirality onto surfaces by attaching irreversibly adsorbing chiral organic species on otherwise achiral surfaces. Understanding and ultimately controlling enantiospecific interactions of molecules on this kind of surfaces requires detailed insight into the adsorption geometries and energies of these complex interfaces. To tackle these issues, we performed density functional theory (DFT) calculations that have proved to be a useful tool for quantitative prediction of these effects. Besides our main topic above, we theoretically examine the effects of K atoms as a promoter coadsorbed with small molecules on Mo2C surfaces, a promising catalyst for a range of chemicals applications. Our results in this thesis provide fundamental information about these systems and demonstrate that using DFT for this purpose can be a useful means of identifying the phenomena that control chiral surface chemistry.

The vesicle-mediated degradation of low-density lipoprotein (LDL) is an essential cellular function due to its role in cellular biosynthesis of membranes and steroids. Using multi-color single particle tracking fluorescence microscopy, the intracellular degradation of LDL was probed in live, intact cells. Unique to these experiments is the direct observation of LDL degradation using an LDL-based probe that increases fluorescence intensity upon degradation. Specifically, individual LDL particles were labeled with multiple fluorophores resulting in a quenched fluorescent signal. The characteristics of the vesicle responsible for degradation were determined and the vesicle dynamics involved in LDL degradation were quantified. Visualization of early endosomes, late endosomes and lysosomes was accomplished by fluorescently labeling vesicles with variants of GFP. Transient colocalization of LDL with specific vesicles and the intensity of the LDL particle were measured simultaneously. These studies, which are the first to directly observe the degradation of LDL within a cell, strive to completely describe the endo-lysosomal pathway and quantify the dynamics of LDL degradation in cells.

The interface of a zinc-terminated polar zinc oxide surface (0002) with a series of chemisorbed fluorinated benzylphosphonic acids has been studied using density functional theory. The calculations indicate that there is a substantial change in the binding energies and work function modification depending on the binding motif. The results also indicate that there is a pronounced difference in the magnitude and trends of the factors determining the total change in work function. The oxygen core-level binding shifts have been calculated and compared to available experimental data.

Thesis (M.U.D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 92-94).

The auroral density cavity constitutes the boundary between the cold, dense ionospheric plasma and the hot, tenuous plasma sheet plasma. The auroral density cavity is characterized by low electron density and particle populations modified by parallel electric fields. Inside the cavity the electron densities can be as much as a factor 100-1000 lower than same altitude outside the cavity.The Cluster mission's wide range of instruments, long lifetime and ability to make multi-spacecraft observations has been very successful. Over its 15 year lifespan, the Cluster satellites have gathered data on auroral density cavities over a large altitude range and throughout an entire solar cycle, providing a vast data material.The extent of the density cavity and acceleration region is large compared to the typical altitude coverage of a satellite crossing the cavity. This makes it difficult to produce a comprehensive altitude/density profile from a single crossing. In order to facilitate comparisons between data from different events, we introduce a new reference frame, pseudo altitude. Pseudo altitude describes the satellites' position relative to the acceleration region, as opposed to relative to the Earth. This pseudo altitude is constructed by dividing the parallel potential drop below the satellite with the total parallel potential drop. A pseudo altitude of 0 corresponds to the bottom of the acceleration region and a pseudo altitude of 1 to the top of the acceleration region. As expected, the pseudo altitude increases with altitude. The electron density exhibits an anti-correlation with the pseudo altitude, the density becomes lower close to the upper edge of the acceleration region. The upper edge of the acceleration region is located between a geocentric altitude of 4.375 and 5.625 RE. Above the upper edge of the acceleration region, the electron density continues to decrease for the entire range of the study, 3.0-6.5 RE. This is much further than the geocentric altitude range of 2-3 RE which is suggested by previous models. We can conclude that the auroral density cavity is not confined by the auroral acceleration region, as suggested by previous models, and may extend all the way to the plasma sheet. / <p>QC 20151102</p>

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] have been identified as an independent risk factor for vascular diseases including coronary heart disease and stroke. In the current study, we have examined the binding and degradation of recombinant forms of apolipoprotein(a) [r-apo(a)], the unique kringle-containing moiety of Lp(a), using a cultured cell model. We found that the incubation of human hepatoma (HepG2) cells with an iodinated 17 kringle-containing (17K) recombinant form of apo(a) resulted in a two-component binding system characterized by a high affinity (Kd = 12 nM), low capacity binding site, and a low affinity (Kd = 249 nM), high capacity binding site. We subsequently determined that the high affinity binding site on HepG2 cells corresponds to the LDL receptor. In the HepG2 cell model, association of apo(a) with the LDL receptor was shown to be dependent on the formation of Lp(a) particles from endogenous LDL. Using an apo(a) mutant incapable of binding to the high affinity site through its inability to form Lp(a) particles (17KΔLBS7,8), we further demonstrated that the LDL receptor does not participate in Lp(a) catabolism. The low affinity binding component observed on HepG2 cells, familial hypercholesterolemia (FH) fibroblasts and human embryonic kidney (HEK) 293 cells may correspond to a member(s) of the plasminogen receptor family, as binding to this site(s) was decreased by the addition of the lysine analogue epsilon-aminocaproic acid. The lysine-dependent nature of the low affinity binding site was further confirmed in HepG2 binding studies utilizing r-apo(a) species with impaired lysine binding ability. We observed a reduction maximum binding capacity for 17K r-apo(a) variants lacking the strong lysine binding site (LBS) in kringle IV type 10 (17KΔAsp) and the very weak LBS in kringle V (17KΔV). Degradation of Lp(a)/apo(a) was found to be mediated exclusively by the low affinity component on both HepG2 cells and FH fibroblasts. Fluorescence confocal microscopy, using the 17K r-apo(a) variant fused to green fluorescent protein, further confirmed that degradation by the low affinity component on HepG2 cells does not proceed by the activity of cellular lysosomes. Taken together, these data suggest a potentially significant route for Lp(a)/apo(a) clearance in vivo. / Thesis (Master, Biochemistry) -- Queen's University, 2009-09-26 02:15:50.754

No description available.