Browsing by Subject "Hydrolysis"
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Item Acid hydrolysis of hemicellulose in cotton gin trash(Texas Tech University, 1984-05) Bjoraker, Robert WNot availableItem Activity and kinetics of microbial extracellular enzymes in organic-poor sands of a south Texas estuary(2009-08) Souza, Afonso Cesar Rezende de, 1968-; Gardner, Wayne Stanley, 1941-; Pease, Tamara KayeThe respective kinetics of bacterial leucine aminopeptidase and [beta]-glucosidase activities were investigated to improve understanding of factors controlling activity and hydrolytic capacity in estuarine organic-poor sands. Depth distributions of enzyme activity and bulk organic matter content were determined in sediments of Aransas Bay and Copano Bay Texas, to investigate enzyme dynamics as related to the geochemical properties of the sediment. Vertical profiles of activity in sediment showed that the enzymes were more active at the surface and that the potential hydrolysis rate of leucine aminopeptidase was higher than that of [beta]-glucosidase. Vertical patterns of enzyme activity correlated (weakly) with variations in sediment organic matter (TOC, TN, and carbohydrates) content. Enrichments of sediment samples with monomeric organic compounds and inorganic nutrients did not affect leucine aminopeptidase and [beta]-glucosidase activities in short- and long-term incubations. Enzyme activity was independent of nutrient availability and suggested that microbial communities were not nutrient-limited. Time-course assays of bacterial hydrolysis of TOC, TN, and carbohydrates provided information about how substrate limitation may affect enzyme activity. Positive correlations between bulk TOC and TN content and enzyme activity indicated enzyme dependence on polymeric substrate content. Induction of enzyme activity after sediment enrichments with specific labile compounds confirmed the importance of available organic substrate to enzyme hydrolysis efficiency. A kinetic approach established the occurrence of enzyme inhibition and its effects on enzyme hydrolytic capacity. The addition of a specific-enzyme substrate to sediment samples modified enzyme parameters and indicated that a substrate-reversible type of inhibitor could reduce enzyme hydrolytic capacity. The addition of polyphenol, as a natural inhibitor of enzyme activity, to the sediment resulted in a concomitant reduction of leucine aminopeptidase activity and ammonium regeneration rate, and thus demonstrated a close coupling between enzyme activity and sediment ammonium regeneration. These research results demonstrate the dynamic nature of the hydrolytic enzymes, provide information about the mechanisms of induction and inhibition of activity, and demonstrate some implications of reducing the hydrolytic capacity to organic matter decomposition and nutrient regeneration rates.Item Desymmetrization by changing hydrophilicity/hydrophobicity(2011-08) Mei, Zhong; Niwayama, SatomiDesymmetrization of symmetric compounds is a powerful strategy with regards to both asymmetric and nonasymmetric synthesis. When this strategy is applied to hydrolysis of symmetric diesters, the process is called monohydrolysis and half-esters can be produced. Since they are versatile building blocks in organic synthesis, various half-esters are synthesized by monohydrolysis of corresponding diesters in mainly aqueous media. However, the reason why the monohydrolysis we studied has a high selectivity is unknown. In this thesis, dynamic light scattering is employed to analyze possible intermediates of monohydrolysis. The results indicate that a “micelle-like” intermediate is likely to exist in the mainly aqueous media. Based on this mechanism, additional kinds of water-mediated desymmetric reactions are performed by changing hydrophilicity/hydrophobicity to produce “micelle-like” compounds, including mono-oxidation and mono-reduction. As water possesses many ideal characteristics as a reaction medium such as accessibility, environmental safety, and low cost, the development of organic reactions in aqueous media has been of central importance in recent organic chemistry. Since the current reaction of monohydrolysis of symmetric diesters produce racemic mixtures, attempts for enantioselective monohydrolysis is made catalyzed by chiral proline derivatives, chiral ionic liquids and cinchona alkaloids, for the purpose of producing enantiomerically enriched half-esters.Item Enzymatic hydrolysis of cellulosic biomass by using immobilized cellulase(Texas Tech University, 1982-08) Oh, SanghaNot availableItem Factors contributing to the degradation of poly(p-phenylene benzobisoxazole) (PBO) fibers under elevated temperature and humidity conditions(Texas A&M University, 2006-10-30) O'Neil, Joseph MThe moisture absorption behavior of Zylon fibers was characterized in various high temperature and high humidity conditions in a controlled environment. The results of these thermal cycling tests show that PBO fibers not only absorb, but also retain moisture (approximately 0.5-3%) when exposed to elevated temperature and humidity cycles. Also, the impurities of Zylon fibers were characterized through the use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and solid state Nuclear Magnetic Resonance (NMR). These tests demonstrated that, in addition to other impurities, PBO fibers may contain up to 0.55 weight percent phosphorus, and that this phosphorus is present in the form of phosphoric acid. It was also shown through accelerated hydrolytic degradation tests that production procedures used to neutralize the acid present in the fibers have a beneficial effect on the hydrolytic performance of the fiber. The data collected in this study was then compared and contrasted to known Kevlar studies, identifying similarities, differences, and potential trends. The results of these tests seem to indicate that there is accelerated acid catalyzed hydrolysis occurring in the fiber which is causing these fibers to degrade at an increased rate. This condition is further accelerated by heat and humidity induced permanent fiber swelling.Item Hydrolysis kinetics of gluconolactones(Texas Tech University, 1972-08) Parrott, Albert RossNot availableItem Hydrolysis of hemicellulose in cotton gin residue(Texas Tech University, 1981-08) Wang, Ta-shengNot availableItem Insights into the Serpin Inhibitory Mechanism from Structures of Mutant Serpins in the Mechaelis Complex(2008-05-13) Sul, Soon-Hee; Goldsmith, Elizabeth J.The serpins belong to a superfamily of protease inhibitors that employ a unique suicide substrate-like inhibitory mechanism. In this mechanism, target protease becomes acylated at the catalytic serine. Deacylation fails to take place, and the serpins undergo dramatic conformational changes in which the acylated protease is translocated 70Å from one pole of the serpin to the other. However, the factors causing suppression of deacylation are not fully understood. The previously solved Michaelis complex of serpin-1B with trypsin/S195A suggests that the P4 (I350) and P1' (S354) residues on the reactive center loop may be important factors in arresting the hydrolysis reaction, since these residues are involved in interactions with trypsin that are unique to serpins (unlike low molecular weight serine protease inhibitors). Inhibition assay data also show that the inhibitory activity of serpin was reduced by the introduction of a mutation either at the P4 (I350A) or at the P1' (S354A) position. The P4 (I350A) mutation nearly completely abolishes inhibitory activity of serpin-1B toward trypsin. In other words, the mutated P4 residue of serpin-1B acts as a substrate, rather than as an inhibitor. A crystallographic approach was used to understand why the serpin-1B (I350A) becomes a substrate; and, hopefully, to gain insight into the serpin inhibitory mechanism. Similarly, the formed Michaelis complex between trypsin and the serpin-1B (S354A) was also utilized to address the role of this residue in this serpin mechanism. The structural analysis shows that significant conformational changes were observed from the serpin-1B (I350A)/trypsin complex, but not from the serpin-1B (S354A)/trypsin complex. Due to these conformational changes, the special extensive interactions observed in the wild type complex were lost in the mutant complexes, the consequence being the destabilization of the mutant Michaelis complexes and, thus, perhaps destabilizing acylated covalent intermediate. Also, reduced interactions (mostly P-side of the serpin) induce a conformational change on trypsin Gln192, residue that may be important for arresting hydrolysis. Therefore, the stable and tight interactions in the Michaelis complex may be important in arresting deacylation in the serpin inhibitory mechanism.Item Interactions of nitric oxides, organic compounds, and particulate matter and their effects on air quality(2016-08) Bean, Jeffrey Kevin; Hildebrandt Ruiz, Lea; Allen, David; Corsi, Richard; McDonald-Buller, Elena; Sharma, MukulNew concerns over health effects and tightening EPA regulations are pushing policy-makers towards lower and lower levels of pollutants. In many places in the United States the EPA standards for ozone and particulate matter (PM) are difficult to meet. This concern is elevated as both standards have been tightened in recent years. Improvements to air quality are costly, and policy-makers rely on regional photo-chemical models to find the most effective methods of pollutant reduction. The accuracy of forecasted predictions of ozone and PM depends heavily on the interactions of NOx and organic compounds. An understanding of the interactions of NOx, organic compounds, and PM is necessary in three important and ongoing research areas: 1 – organic nitrate partitioning and hydrolysis, 2 – interactions between biogenic organic compounds with anthropogenic oxidants, and 3 – atmospheric impacts of hydraulic fracturing. Through environmental chamber experiments and chemical reaction modeling I quantified the gas-particle partitioning of organic nitrates as well as the hydrolysis rate of condensed organic nitrates. These interactions are important in understanding total PM levels as well as NOx recycling – the breakdown of organic nitrates to regenerate NOx that was previously removed from ozone production, which in turn is necessary for accurate forecasting of ozone levels. I collected ambient measurements near Houston, TX in September 2013 as part of DISCOVER-AQ (http://www.nasa.gov/mission_pages/discover-aq/index.html). These measurements provide valuable insight to the processes that leads to PM formation in the area. There is evidence that the interaction between biogenic organic compounds and anthropogenic oxidants has an important effect on PM levels. A diurnal cycle of increased nighttime PM concentrations suggests that reactions between terpenes and the nitrate radical significantly contribute to PM. A poorly characterized source of emissions from hydraulic fracturing activity are atmospherically vented storage tanks for flowback wastewater. Emissions of ammonia and hydrocarbons are observed as samples evaporate from 12 different wastewater samples from the Permian Basin. Through chamber experiments I tested the potential of these evaporated mixtures to produce PM in the presence of an atmospheric oxidizer, NOx and seed particles, and I observed significant formation of organic and ammonium nitrate PM.Item Intramembrane Proteolysis mediated by the gamma -Secretase Complex : Nicastrin Functions as a Substrate Receptor(2006-08-11) Shah, Sanjiv; Yu, GangThe proteolytic processing of proteins within the lipid bilayer, and release of their membrane tethered biologically active fragments, fundamentally controls a growing list of cell signaling events. The gamma -secretase, one of a small family of independently evolved proteases, performs this enigmatic hydrolysis of a peptide bond within the membrane. Remarkably atypical, gamma-secretase activity: (1) requires a complex of proteins that include presenilin, nicastrin, Aph1, and Pen-2; (2) catalyzes the intramembrane cleavage of a broad range of substrates, regulating physiology from neurodevelopment to neurodegeneration. The aim of this thesis is to elucidate the mechanism by which the gamma -secretase recognizes its substrates. I provide evidence that nicastrin, in addition to being a critical component of the complex, plays a major function in substrate recognition. The ectodomain of nicastrin binds the new amino terminus that is generated upon the prerequisite 'shedding' of substrates, thereby recruiting substrates into the gamma -secretase complex. The gamma -secretase complex has been traditionally viewed as a hub for signal transduction of substrates such as Notch and APP. The mechanism by which a broad range of substrates may be recognized and subsequently cleaved, as demonstrated in this thesis, supports a mutually inclusive function as a protease that has evolved to simply dispose transmembrane domains thus controlling the repertoire of a class of proteins present in the membrane.Item The optimal use of enhanced oil recovery polymers under hostile conditions(2009-05) Levitt, David Benjamin, 1980-; Pope, G. A.The purpose of this work is to frame the main issues one must face in the design of a mobility control process using polyacrylamide and related acrylic polymers under hostile conditions. Proper preliminary lab evaluation techniques, chemical degradation and related calcium tolerance issues, thermal degradation, and economic optimization based upon injectivity are discussed. Emphasis is placed on stability under alkaline conditions, the use of sodium dithionite to prevent thermal degradation, and the beneficial use of in-situ hydrolysis to increase injectivity. Filtration properties are a focus of screening experiments, and though it often takes several days to achieve acceptable filter ratios in the lab, experience from two field observations indicate that even high molecular weight polymers have filtration ratios on the order of 1.2 or less before they are injected, so preparation procedures that do not result in this may not yield results that scale to the field. Chemical stability issues with acrylamide polymers are addressed in two parts, the first describing the kinetics of hydrolysis under neutral and alkaline conditions and the second estimating the calcium tolerance of aged polymers using industrial and lab produced analogues. Under alkaline conditions, hydrolysis is very rapid, even at low temperatures. Though aged copolymers of acrylamide (AM) and 2-acrylamide 2-methyl propane sulfonate (AMPS) exhibit similar calcium tolerances to similarly aged polyacrylamide (PAM), viscosity loss is much higher for the latter as this limit is approached. Thermal, or "oxidative" degradation, is examined using Pourbaix diagrams for iron to understand the commonly reported relationships between pH, Eh, and stability. The beneficial effects of sodium carbonate and sodium dithionite on polymer solutions as well as some inconsistencies in the literature point towards a catalytic role played by ppb level amounts of iron in oxidative degradation mechanisms. It is put forward that addition of sodium dithionite is a conservative approach to all acrylic-backboned polymer floods, and practical issues related to this are discussed. A simple analytical model is developed to take a brief look at economic optimization of polymer viscosity, and this is used to demonstrate the benefits of in-situ hydrolysis in alkaline or high-temperature floods.Item Process design and economics of cotton gin trash prehydrolysis(Texas Tech University, 1983-08) Tso, ChengA system designed to investigate the performance of dielectrics in a multichannel surface discharge switch was built and tested. The apparatus consisted of a constant current charging supply that produced 10mA at 50 kV, a storage capacitor, a 6-ohm stripline, the surface switch, a matched 5-ohm copper sulfate water load, and diagnostics. Diagnostics to evaluate the dielectric performance included capacitive voltage probes in the stripline, a video camera to record multichannel events on videocassettes, and an optically isolated counter to record the number of events in a test run. Typical operating parameters were: 130 joules per pulse, a peak voltage of 40-50 kV, and a peak current of 7 kA. Dielectric samples were tested by placing them in the switch for 10,000 shots at a repetition rate of 1-1.2 pulses per second. The dielectrics were then compared by observing their erosion, changes in breakdown voltage, and the number of channels that occur during discharges. Further analysis to study possible chemical change in the surfaces of three of the dielectrics was performed using Electron Spectroscopy for Chemical Analysis (ESCA).Item Selected methods utilizing ozone for hydrolysis of mesquite biomass(Texas Tech University, 1982-08) Cox, Kenneth WayneNot availableItem Synthetic studies towards the total synthesis of cortistatin A synthesis of the pentacyclic core of citreamicin µ and GA-ring model studies(2016-08) Blumberg, Shawn Thomas; Martin, Stephen F.; Krische, Michael J; Anslyn, Eric V; Kerwin, Sean M; Willson, Carlton GThe route to the key bicyclic intermediate was streamlined to eight steps in 16% yield, using a TMSI promoted coupling of a furan and an enone. Additionally, methodology for the selective ozonolysis of the bicyclic intermediate was developed via ozone titration. Work on the dihydroxylation step led to the discovery and development of a new pH-neutral Sharpless-style asymmetric dihydroxylation. The synthesis of pentacyclic core of citreamicin µ was accomplished in 12 steps. New methodologies were developed, including: an ortho- selective bromination of a vanillin derivative and the use of 4-(Phenylazo)diphenylamine (PDA) as an internal indicator for the acetylide coupling. The usefulness of PDA led to its development as a general all-purpose indicator for the titration of strong bases, Lewis acids and reducing agents. The discovery of (n-Bu)4NOAc as a privileged additive led to the development of new methods for the synthesis of isocoumarins and new methodology for the condensation of amino acids using LiMe4 was developed.Item The anhydride of benzene-o-disulfinic acid-synthesis and rates of hydrolysis(Texas Tech University, 1980-12) Liao, Shih-tangNot available