Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Muscular Fatigue Influences Motor Synergies During Push-ups(2018) Bell, Elizabeth M; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research used the push-up as an experimental paradigm for the study of adaptations in motor synergies throughout the challenge of muscular fatigue. Fatigue was expected to lead to greater synchronization of power production (greater motor synergy) by the Central Nervous System (CNS). Greater between and within-limb synergies would be necessary to overcome the reduced force production of fatigued muscles. Different changes in joint power synergies were expected for eccentric and concentric phases due to muscle properties and direction of gravity. Eleven subjects performed push-ups repetitions to self-selected failure. Subjects initially performed push-ups using positive between and within-limb joint power synergies, however synergies reduced throughout reps. Congruent with hypotheses, between and within-limb synergy reduced at a lesser rate throughout eccentric movements. The strategy used relied on bilateral elbow and shoulder joint production. The CNS was not able to adapt control strategies, but instead the dominant strategy was affected throughout fatigue.Item Early Transition Metal Studies of Dinitrogen Cleavage and Metal-Nitrogen Bond Reactivity Towards Catalytic N2 Fixation(2015) Keane, Andrew John; Sita, Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of energy efficient catalysts that provide a range of commodity chemicals derived from the fixation of N2 is a highly attractive target due to the abundance of molecular nitrogen present in Earth’s atmosphere. Studies have focused on the systematic investigation of several key components of metal-catalyzed N2 fixation that detail molecularly discrete transformations involving the activation of N2, cleavage of the strong N≡N triple bond and N-atom functionalization to provide ammonia and other organic molecules of scientific and industrial interest. To this end, an evaluation of group 5 N2 cleavage using the pentamethylcyclopentadienyl, amidinate (CPAM) ligand framework that includes extensive kinetic and mechanistic investigations detailing the N-N cleavage reaction coordinate has been undertaken. Further studies conducted within group 5 include the synthesis and reactivity of tantalum imido complexes to elucidate metal-nitrogen bond reactivity and N-N cleavage relevant to the Chatt cycle. In group 6, photolytic N-N cleavage has been further investigated. Most notably, chemistry has been discovered for N2-derived metal nitride complexes of Mo and W that gives access to imido complexes capable of participating in nitrene group transfer (NGT) to carbon monoxide and isocyanides to provide isocyanates and carbodiimides respectively. For the first time, it has been demonstrated that imido complexes that participate in NGT chemistry can be derived from N2 to provide N-C based organic products. Collectively, these results serve to establish a new platform for studying the catalytic viability of the discovered transformations.Item Kinetics of Tetrachloroethene-Respiring Dehalobacter and Dehalococcoides Strains and Their Effects on Competition for Growth Substrates(2010) Lai, Yenjung; Becker, Jennifer G; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The chlorinated solvents tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. Reductive dechlorination of PCE and TCE at contaminated sites is commonly carried out by dehalorespiring bacteria that utilize these compounds as terminal electron acceptors, but often results in the accumulation of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), rather than non-toxic ethene. This project focused on evaluating how interactions among dehalorespiring populations that may utilize the same electron acceptors, electron donors and/or carbon source may affect the extent of PCE dechlorination in situ. These interactions may be particularly important if both Dehalococcoides ethenogenes (Dhc. ethenogenes) and Dehalobacter restrictus (Dhb. restrictus) are present because these bacteria utilize the same electron donor (H2) and both respire PCE and TCE. However, unlike Dhc. ethenogenes, Dhb. restrictus cannot dechlorinate PCE beyond cDCE. Therefore, the outcome of the population interactions may determine the extent of detoxification achieved. Monod kinetic parameter estimates that describe chlorinated ethene and electron donor utilization by Dhc. ethenogenes and Dhb. restrictus at non-inhibitory substrate concentrations were obtained in batch assays. Substrate inhibition effects on both populations were also evaluated. Highly chlorinated ethenes negatively impacted dechlorination of the lesser chlorinated ethenes in both populations. In Dhc. ethenogenes, cometabolic transformation of VC was also inhibited by the presence of other chlorinated ethenes. PCE and TCE dechlorination by Dhb. restrictus was strongly inhibited by VC. The microbial interactions between Dhc. ethenogenes and Dhb. restrictus was investigated using reactors and mathematical models under engineered bioremediation and natural attenuation conditions. Under engineered bioremediation conditions, Dhc. ethenogenes became the dominant population, and the modeling predictions suggested that the inhibition of Dhb. restrictus by VC was a key factor in determining this outcome. Dechlorination rates by Dhb. restrictus appeared to be affected very little by low acetate concentrations under natural attenuation conditions, giving it an advantage over Dhc. ethenogenes, which requires relatively high acetate concentrations. This study highlighted that substrate interactions among dehalorespiring bacteria can influence their performance and contaminant fate under common bioremediation scenarios. A better understanding of the factors affecting the outcomes of these microbial interactions was achieved, which should aid in the design of successful bioremediation strategies.Item STATE-RESOLVED QUENCHING DYNAMICS IN COLLISIONS OF VIBRATIONALLY EXCITED MOLECULES(2010) Du, Juan; MULLIN, AMY S; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The collisional relaxation of highly excited molecules plays a very important role in many chemistry processes. The work presented in this thesis studies the collisional quenching dynamics of highly vibrationally excited molecules using high–resolution transient IR absorption spectroscopy. This work investigates “weak” (small energy transfer) and “strong” (large energy transfer) collisions between donor and bath molecules. The experimental results illustrate how the properties of donor molecules influence the collisional energy transfer. These properties include the molecular structure, internal energy, state density. In several weak collision studies, this thesis studies the vibration–rotation/translation pathway for pyrazine/DCl, pyrazine/CO2 with different internal energies and for three excited alkylated pyridine molecules/CO2 systems. A single–exponential rotational distribution and J–dependent translational energy distributions of scattered DCl molecules are observed. For CO2 collisions, the scattered CO2 has a biexponential rotational distribution and J–dependent translational energy distributions for all collision pairs. Recoil velocities scale with product angular momenta. The observed collision rates for these collision pairs match Lennard–Jones rates. The full energy transfer distribution for these pairs is determined by combining data for weak and strong collisions. Lowering the internal energy of donor molecules reduces the amount of rotational and translational energy transfer to CO2. Reducing the internal energy of pyrazine decreases the probabilities of strong collision and increases the probabilities of weak collision. The average energy transfer reduces by ∼ 50% when the internal energy is decreased by only 15%. The collision rates are independent on the internal energy for these systems. Methylation of donor molecules decreases the magnitude of V—RT energy transfer. The collision results are affected by the number of methyl–groups, and not by the position of the group. Increasing the number of methyl groups increases the ratio of the measured collision rate to the Lennard–Jones collision rate. In the strong collision studies, the effects of alkylation and internal energy are studied. In collisions with alkylated pyridine donors with E ∼ 39000 cm−1, CO2 molecules gain less energy from alkylpyridine than from pyridine. The alkylated donors undergo strong collisions with CO2 via a less repulsive part of the intermolecular potential compared to pyridine. For azulene/CO2 collisions with two different internal energies, scattered CO2 molecules gain double the amount of rotational and translational energy when the azulene energy is doubled. The rate of strong collisions increases four times when the internal energy is doubled.Item Kinetic and Structual Characterization of Glutamine-Dependent NAD Synthetases(2010) Resto, Melissa; Gerratana, Barbara; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Multifunctional enzymes catalyzing successive reactions have evolved several mechanisms for the transport of intermediates between active sites. One mechanism, substrate channeling, allows the transport of the intermediate without releasing it into the solvent. Members of the glutamine amidotransferase (GAT) family often utilize substrate channeling for the transport of intermediates. GAT enzymes hydrolyze glutamine to ammonia, which is transported to an acceptor domain preventing wasteful hydrolysis of glutamine and increasing the efficiency of the reaction. Many GAT enzymes utilize molecular tunnels to shuttle ammonia between active sites. Often GAT enzymes synchronize the active site through conformational changes that occur during catalysis. Glutamine-dependent NAD synthetases are GAT enzymes and catalyze the last step in the biosynthesis of NAD, utilizing nicotinic acid adenine dinucleotide (NaAD), ATP and glutamine. Steady-state kinetic characterizations and stoichiometric analysis of NAD synthetase from Mycobacterium tuberculosis (NAD synthetaseTB) revealed a substrate channeling mechanism for ammonia transport and tight coordination of the active sites resulting in an enzyme that is highly efficient in the use of glutamine. The crystal structure of NAD synthetaseTB has revealed a 40 Å tunnel that connects the active sites and is postulated to play a role in the synchronized activities. Several regions of the enzyme were identified that may be important for regulation, such as the YRE loop which contacts the glutamine active site and key regions of the tunnel. Mutations of tunnel residues, such as D656A, show that interruption of important interactions can result in compromise in transfer of ammonia or active site communication. Phylogenetic analysis revealed that glutamine-dependent NAD synthetases have different levels of regulation. Three groups of enzymes were identified represented by NAD synthetase from M. tuberculosis, S. cerevisiae (NAD synthetaseYeast) and Thermotoga maritima (NAD synthetaseTM). Steady-state kinetic characterizations and stoichiometric analysis of NAD synthetaseTM has revealed a compromised coordination of the active sites compared to the highly synchronized NAD synthetaseTB and the moderate synchronization of NAD synthetaseYeast. Sequence alignment of these groups has allowed identification of residues that line the tunnel that may be responsible for the differences observed in active site coordination and are, therefore, important for active site communication.Item Handwriting Kinetics: A Search for Synergies(2008) Hooke, Alexander W.; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this study was to investigate central nervous system strategies for controlling multi-finger forces in three-dimensional (3-D) space during a circle drawing task. In order to do this the Kinetic Pen, a pen capable of measuring the six-component force and moment of force that each of four individual contacts applies to the pen during writing, was developed. The synergistic actions of the contact forces, defined as kinetic synergy, were investigated in three orthogonal spaces: radial, tangential, and vertical to the circle edge during a circle drawing task. We employed varying directional (clockwise vs. counterclockwise) and pacing (self-paced vs. external-paced) conditions. Results showed that synergies between pen-hand contact forces existed in all components. Radial and tangential component synergies were greater than in the vertical component. Synergies in the clockwise direction were stronger than the counter-clockwise direction in the radial and vertical components. Pace was found to be insignificant in all conditions.Item Hepatic Phase I and II Biotransformation Kinetics in Fishes: A Comparative Study(2006-12-04) Gonzalez, Jaime Fernando; Kane, Andrew S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eight finfish species were selected to test the similarities and dissimilarities on their phase I and II biotransformation capabilities using microsomal and cytosolic fractions of the liver. This research had three main objectives: 1) a comparison among the kinetics of the 8 species using model substrates, 2) farm-raised and laboratory-acclimated specimens of channel catfish, rainbow trout and tilapia were compared to determine similarities and differences in the biotransformation reactions, and 3) the same latter three species were tested to compare in vitro hepatic metabolism of albendazole, a drug that undergoes metabolic biotransformation mainly through hepatic phase I reactions. The comparison among the 8 finfish species showed that some of them had higher biotransformation capabilities than others. For most of the seven phase I- II reactions that were tested; rainbow trout, tilapia, channel catfish and Atlantic salmon had higher enzymatic efficiencies than those showed by of striped bass, hybrid striped bass and bluegill. Largemouth bass shared some enzymatic capabilities with one group or the other. The comparison between lab-acclimated and farm-raised specimens of tilapia, channel catfish and rainbow trout did not show biologically significant differences among the two groups of fish for the 3 species. All the values found for the kinetics of the reactions were within the ranges of the constitutive expression that has been reported for them and far below those found in other works when inducers (e.g. pollutants) of enzymatic reactions have been used. The phase I-mediated hepatic sulfoxidation of albendazole in tilapia, channel catfish and rainbow trout showed significant differences in Vmax and Km values among the three species. However, the catalytic efficacies of the reaction (Vmax/Km) in the 3 species transforming the parent compound were similar. In addition, albendazole induced EROD activity (2.6 fold) in in vivo dosed channel catfish. The results found in the present study showed that the catalytic efficiency of hepatic phase I-II enzymatic reactions varied among finfish species. Some of them may be categorized as "more efficient metabolizers" than others. This may have important implications in drug metabolism and residue depletion patterns.