Browsing by Subject "Synthesis"
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Item A cascade approach toward indolizidine and quinolizidine alkaloids : highlighted by the total syntheses of (±)-epilupinine, (±)-tashiromine, and (-)-epimyrtine progress toward the total synthesis of (±)-meloscine(2006-05) Amorde, Shawn Marie; Martin, Stephen F.Several novel cascade processes have been designed and developed that involve sequential reactions of imines and iminium ions to form substituted quinolizidine ring systems in a single step from simple and readily available starting materials. The utility and promise of these cascades is evident from their application to extraordinarily concise syntheses of the representative quinolizidine alkaloids (±)-epilupinine, (±)-tashiromine, and (-)-epimyrtine. Within the context of a longstanding interest in aromatic heterocyclic natural product synthesis, a concise synthetic strategy incorporating new tactics for key chemical transformations, as well as novel applications of existing synthetic methods was developed constructing the natural product meloscine. Meloscine was isolated in the 1970's from the New Caledonian plant Melodinus Scandens Forst, which is used in Chinese folk medicine for the treatment of meningitis and rheumatic heart disease. In route to meloscine, a facile synthetic method was developed toward several carboline type indoles. Also, progress has been made toward the total synthesis of the natural product meloscine.Item A direct, concise and stereoselective formal synthesis of platensimycin(2011-12) Rivera, Heriberto; Magnus, Philip D.; Krische, Michael J.; Jones, Richard M.; Siegel, Dionicio R.; Kerwin, Sean M.Herein we describe the synthesis of (±) platensimycin, a potent antibiotic against gram-positive bacteria. The first chapter reviews (±) platensimycin’s isolation, biological profile and previously reported studies relevant to the area. The second chapter describes our initial efforts to synthesize (±) platensimycin. The third chapter accounts our second generation synthesis and its completion. The fourth chapter entails the experimental details of the important compounds in our synthesis.Item Elixir: synthesis of parallel irregular algorithms(2015-05) Prountzos, Dimitrios; Pingali, Keshav; Misra, Jayadev; Batory, Don; Cook, William; Sagiv, Mooly; Gulwani, SumitAlgorithms in new application areas like machine learning and data analytics usually operate on unstructured sparse graphs. Writing efficient parallel code to implement these algorithms is very challenging for a number of reasons. First, there may be many algorithms to solve a problem and each algorithm may have many implementations. Second, synchronization, which is necessary for correct parallel execution, introduces potential problems such as data-races and deadlocks. These issues interact in subtle ways, making the best solution dependent both on the parallel platform and on properties of the input graph. Consequently, implementing and selecting the best parallel solution can be a daunting task for non-experts, since we have few performance models for predicting the performance of parallel sparse graph programs on parallel hardware. This dissertation presents a synthesis methodology and a system, Elixir, that addresses these problems by (i) allowing programmers to specify solutions at a high level of abstraction, and (ii) generating many parallel implementations automatically and using search to find the best one. An Elixir specification consists of a set of operators capturing the main algorithm logic and a schedule specifying how to efficiently apply the operators. Elixir employs sophisticated automated reasoning to merge these two components, and uses techniques based on automated planning to insert synchronization and synthesize efficient parallel code. Experimental evaluation of our approach demonstrates that the performance of the Elixir generated code is competitive to, and can even outperform, hand-optimized code written by expert programmers for many interesting graph benchmarks.Item First enantioselective oxidative rearrangement of indoles to spirooxindoles, studies toward the total synthesis of IB-00208 and total synthesis of cribrostatin 6(2010-05) Knueppel, Daniel Isaiah; Martin, Stephen F.; Bielawski, Christopher W.; Krische, Michael J.; Jones, Richard A.; Whitman, Christian P.The first enantioselective oxidative rearrangement of indoles to spirooxindoles was developed. A 2,3-disubstituted indole was stereoselectively epoxidized using an in situ-generated chiral dioxirane catalyst. Rearrangement of the transient epoxide intermediate afforded the antipode of the tricyclic spirooxindole present in the marine alkaloid citrinadin A. A mild and rapid entry to 1,4-dioxygenated xanthones from benzocyclobutenones was developed. This method was applied to the construction of the highly aromatic pentacyclic core of IB-00208, a promising antitumor agent with reported nanomolar activity. The requisite angularly-fused benzocyclobutenone was accessed via a novel ring-closing metathesis approach. Lack of success in synthesizing the final ring of IB-00208 from the pentacycle led us to revise our approach and incorporate an extra ring earlier in the synthesis. After constructing a modified benzocyclobutenone, the hexacyclic core of IB-00208 was efficiently accessed using the same key chemistry. An oxidation, deprotection and glycosylation remain to complete the synthesis of the natural product. A total synthesis of antimicrobial and antineoplastic cribrostatin 6 was accomplished in only four steps in the longest linear sequence from commercially available starting materials. The key step employed a tandem 4π-electrocyclic ring opening, radical cyclization, and homolytic aromatic substitution sequence to afford the tricyclic core of the natural product, which was converted to cribrostatin 6 via a subsequent oxidation in one pot. The versatility of this reaction sequence was demonstrated by preparation of analogs of the natural product, which were tested for their anticancer activity.Item Graphene and III-V channel metal-oxide-semiconductor field-effect devices for post-Si CMOS applications(2013-12) Ramón, Michael Edward; Banerjee, Sanjay; Akinwande, Deji; Tutuc, Emanuel; Lee, Jack C; Sreenivasan, S. V.To meet the demands for continuous transistor scaling and performance improvements required by the ITRS, there has been a tremendous amount of effort related to alternative high mobility channel materials as potential Si replacements for MOSFET fabrication. Two particularly attractive material systems include III-V substrates and graphene. Thus far, the high trap density which characterizes high-κ dielectrics and the III-V/high-κ dielectric interface remains an obstacle to III-V substrate integration. In a first aspect of this work, charge traps within the gate stack of III-V MOSFETs, as well as at the III-V/dielectric interface, were examined to better understand their impact on III-V device performance. In particular, a pulsed I-V measurement technique was used to assess the impact of fast and slow transient charging effects on various III-V transistors with ALD-deposited Al2O3 gate dielectric. The charge pumping technique was also utilized to determine the density of interface traps, including their energy distribution and position profile, providing further understanding into the nature of traps in the III-V/high-κ system. Graphene has also attracted considerable interest owing to its high intrinsic mobility, large current densities, thermodynamic and mechanical stability. Yet, a primary challenge to the integration of graphene substrates is the lack of high quality, large-area graphene. Thus, in another aspect of this work, large-area graphene was synthesized by CVD of acetylene on Co thin films, and the influence of Co film thickness on graphene synthesis was studied. Resulting graphene films were characterized using Raman spectroscopy and back-gated GFETs were fabricated. Taking advantage of graphene’s intrinsic ambipolar electron-hole symmetry, GFET frequency doublers were fabricated on low-capacitance, single-crystal quartz substrates. GFETs frequency doublers were found to operate beyond their transit frequency (fT), and in the limit of vanishing device non-idealities, their maximum conversion gain was determined to approach a near lossless value. To further understand and improve GFET RF performance, the impact of parasitic resistances was experimentally examined. RF measurements as a function of temperature and modulated access resistance highlight the strong influence of RC on scaled devices, while the impact of RA becomes more evident for devices with large access regions.Item Graphite oxide and its applications in the preparation of small molecules, polymers, and high performance polymer composites(2012-05) Dreyer, Daniel Robert; Bielawski, Christopher W.; Ruoff, Rodney S.; Willets, Katherine A.; Anslyn, Eric V.; Siegel, Dionicio R.Graphite oxide (GO), a carbon material prepared in one step from low cost commercial materials, and graphene oxide have been found to catalyze a wide range of reactions including oxidations, hydrations, and dehydrations, as well as cationic or oxidative polymerizations. Applicable in both small molecule and polymer chemistry, this single, metal-free catalyst shows remarkable breadth, including the combination of the aforementioned reactions in an auto-tandem fashion to form advanced substrates, such as chalcones, from simple starting materials. Some of these reactions, such as the selective oxidation of alcohols to aldehydes, have been shown to be dependent on the presence of molecular oxygen, suggesting that this may be the terminal oxidant. Aside from its eminently valuable reactivity, the use of GO as a catalyst also presents practical advantages, such as its heterogeneous nature, which facilitates separation of the catalyst from the desired product. The use of this simple material in synthetic chemistry, as well as others like it, is distinct from other forms of catalysis in that the active species is carbon-based, heterogeneous and metal-free (as confirmed by ICP-MS and other spectroscopic techniques). This has led us to propose the term “carbocatalyst” to describe such materials. With dwindling supplies of precious metals used in many common organic reactions, the use of inexpensive and widely available carbocatalysts in their place will ensure that commercial processes of fundamental importance can continue unabated. Moreover, as we have shown with just one material, carbons are capable of facilitating a broad range of reactions.Item Logic and clock network optimization in nanometer VLSI circuits(2015-08) Roy, Subhendu; Pan, David Z.; Orshansky, Michael; Touba, Nur A; Gerstlauer, Andreas; Puri, RuchirLogic optimization and clock network optimization for power, performance and area trade-off have been imperative problems for the very large scale integrated (VLSI) circuit designers. With further technology scaling, complex designs and aggressive time-to-market targets, scalable algorithms are very much anticipated than ever before. The logic optimizations can be at pre-synthesis stage, post-synthesis stage or even cross-layer. The success of the logic optimization is determined by how much it can benefit in metrics such as power and performance after physical placement and routing. Meanwhile, building a process variation tolerant and On-Chip-Variation (OCV) aware clock network to meet the performance/power target in modern designs has become an extremely difficult job, which calls for clock tree resynthesis, i.e., restructuring of an existing clock network, to achieve better power/performance. This dissertation first focuses on a pre-synthesis logic optimization problem, high performance adder synthesis. The optimization of the prefix network, capturing the carry-computation of any adder, has been shown to be effective even after logic synthesis, placement and routing over existing adder solutions, including even hand-made custom adders designed in industrial designs. Second a post-synthesis optimization problem, a new paradigm of discrete gate sizing under multiple operating conditions, is proposed to consider both system and logic level information. Besides it helps in design space exploration by providing feedback to the system level. Our paradigm is flexible to integrate various reliability and physical design issues. Finally, a clock network optimization problem, clock tree resynthesis, is proposed to achieve multi-corner, multi-mode timing closure and dynamic power minimization on an already synthesized and routed clock tree. The clock tree resynthesis algorithms have been integrated into an industrial placement and routing tool, and validated on large-scale industrial designs.Item Low-temperature solution synthesis of alloys and intermetallic compounds as nanocrystals(2009-05-15) Vasquez, YolandaThe synthesis of solid state materials has traditionally been accomplished using rigorous heating treatments at high temperatures (1,000?C) to overcome the slow rate of diffusion between two reactants. Re-grinding and re-heating treatments improve the rate of reaction between two solids; however, the high temperatures required to overcome the diffusion barrier limit the products accessible to the most thermodynamically stable phases. In this work, nano-scale solids such as alloys and intermetallics were synthesized via solution techniques where metal compounds are reduced by NaBH4 or n-butyllithium at temperatures below 300?C. To form hollow particles, metal nanoparticles of Co, Ni, Pb were synthesized via reduction by NaBH4 in water and reacted with K2PtCl6, which resulted in the formation of alloys in the case of Co-Pt and Ni-Pt. PbPt intermetallic hollow particles were synthesized by heating a composite of PbO and hollow Pt nanoparticles in tetraethylene glycol (TEG) at 140 ?C. With n-butyllithium as a reducing agent, Au3M (M= Fe, Co, Ni) nanoparticles could be synthesized as isolatable solids in the L12 structure. PtSn and AuCu3 intermetallics were synthesized using NaBH4 and TEG. The PtSn and AuCu3 nanoparticles were characterized by transmission electron microscopy in attempts to learn about the phase diagrams of nanoscale solids. The purpose of this work was to synthesize nanoparticles via solution-mediated routes at low temperatures in compositions and morphologies not observed in the bulk, and learn about the phase diagrams of nanoparticles to understand why it is possible to access solids at temperatures significantly below those used in traditional solid state chemistry.Item Modeling and synthesis of quality-energy optimal approximate adders(2012-12) Miao, Jin; Gerstlauer, Andreas, 1970-; Orshansky, MichaelRecent interest in approximate computation is driven by its potential to achieve large energy savings. We formally demonstrate an optimal way to reduce energy via voltage over-scaling at the cost of errors due to timing starvation in addition. A fundamental trade-off between error frequency and error magnitude in a timing-starved adder has been identified. We introduce a formal model to prove that for signal processing applications using a quadratic signal-to-noise ratio error measure, reducing bit-wise error frequency is sub-optimal. Instead, energy-optimal approximate addition requires limiting maximum error magnitude. Intriguingly, due to possible error patterns, this is achieved by reducing carry chains significantly below what is allowed by the timing budget for a large fraction of sum bits, using an aligned, fixed internal-carry structure for higher significance bits. We further demonstrate that remaining approximation error is reduced by realization of conditional bounding (CB) logic for lower significance bits. A key contribution is the formalization of an approximate CB logic synthesis problem that produces a rich space of Pareto-optimal adders with a range of quality-energy trade-offs. We show how CB logic can be customized to result in over- and under-estimating approximate adders, and how a dithering adder that mixes them produces zero-centered error distributions, and, in accumulation, a reduced-variance error. This work demonstrates synthesized approximate adders with energy up to 60% smaller than that of a conventional timing-starved adder, where a 30% reduction is due to the superior synthesis of inexact CB logic. When used in a larger system implementing an image-processing algorithm, energy savings of 40% are possible.Item Process Synthesis and Optimization of Biorefinery Configurations(2012-10-19) Pham, VietThe objective of this research was to develop novel and applicable methodologies to solve systematically problems along a roadmap of constructing a globally optimum biorefinery design. The roadmap consists of the following problems: (1) synthesis of conceptual biorefinery pathways from given feedstocks and products, (2) screening of the synthesized pathways to identify the most economic pathways, (3) development of a flexible biorefinery configuration, and (4) techno-economic analysis of a detailed biorefinery design. In the synthesis problem, a systems-based "forward-backward" approach was developed. It involves forward synthesis of biomass to possible intermediates and reverse synthesis starting with desired products and identifying necessary species and pathways leading to them. Then, two activities are performed to generate complete biorefinery pathways: matching (if one of the species synthesized in the forward step is also generated by the reverse step) or interception (a task is determined to take a forward-generated species with a reverse-generated species by identifying a known process or by using reaction pathway synthesis to link to two species.) In the screening problem, the Bellman's Principle of Optimality was applied to decompose the optimization problem into sub-problems in which an optimal policy of available technologies was determined for every conversion step. Subsequently, either a linear programming formulation or dynamic programming algorithm was used to determine the optimal pathways. In the configuration design problem, a new class of design problems with flexibility was proposed to build the most profitable plants that operate only when economic efficiency is favored. A new formulation approach with proposed constraints called disjunctive operation mode was also developed to solve the design problems. In the techno-economic analysis for a detailed design of biorefinery, the process producing hydrocarbon fuels from lignocellulose via the carboxylate platform was studied. This analysis employed many state-of-the-art chemical engineering fundamentals and used extensive sources of published data and advanced computing resources to yield reliable conclusions to the analysis. Case studies of alcohol-producing pathways from lignocellulosic biomass were discussed to demonstrate the merits of the proposed approaches in the former three problems. The process was extended to produce hydrocarbon fuels in the last problem.Item Rational design and syntheis of substrate-based inhibitors of steroidogenesis(Texas Tech University, 2008-12) Liu, Jialin; Nes, William David; Shaw, Robert W.; Weber, JoachimSterol biosynthesis is crucial to all groups of life forms. Targeted inhibition of this pathway by substrate-based analogs is currently used to probe sterol function and may have therapeutic importance. In this dissertation, a series of new steroidal triperpenes with a modified lanosterol or cycloartenol frame have been designed to inhibit steroidogenesis. These compounds, along with a number of known sterol biosynthesis inhibitors with the cholestane skeleton, have been prepared and characterized in detail using GC, MS, HPLC and NMR. Notably, a series of substrate analogs constructed with a methyl, nitrogen, sulfur, bromine or fluorine atom or altered to possess a methylene cyclopropane, or elongated to contain a terminal double or triple bonds were prepared to act as mechanism-based inactivators of the sterol 24-methyl transferase enzyme. In addition, compounds with the cholestane and lanostane structures were prepared with modifications at C-7 and C-32 to be reversible and irreversible inhibitors of the ¦¤8- ¦¤7-isomerase and 14¦Á-demethylase enzymes, respectively.Item Single and Multiple Heteroatom Incorporation in MFI Zeolites(2012-11-05) Garcia Vargas, NatalyZeolites are crystalline inorganic solids that are industrially used for adsorption, ion exchange and catalysis. As catalysts, they have been particularly successful in the hydrocarbon processing industry due to their unique activities and selectivities. Zeolites are mainly used in acid catalyzed reactions, but their catalytic functionality can be diversified through the incorporation of elements that are traditionally not part of their framework. The incorporation of various elements has been studied in recent decades resulting in zeolites with potential to perform different chemistries or improve catalytic performance in existing ones. However, many of these investigations have been conducted under conditions that do not necessarily represent realistic scenarios for industrial implementation. The main objective of this dissertation was to study the single and simultaneous framework incorporation of tin, boron, germanium and aluminum in MFI zeolites under synthesis conditions that are more in line with industrial preparations. These include the use of mixtures in alkaline media with high concentration of precursor species. The interest on tin resides on its potential for Lewis acid catalysis, while boron and germanium have potential for modulating acid strength and enhancing catalytic properties respectively. Three specific systems were studied: MFI zeolites with simultaneous incorporation of germanium and aluminum (i.e. Ge-Al-MFI zeolites), MFI zeolites with simultaneous incorporation of germanium and boron (i.e. B-Ge-MFI zeolites), and MFI zeolites with single incorporation of tin (i.e. Sn-MFI zeolites). Systematic synthesis experiments were coupled with extensive analytical characterization in order to assess how element incorporation and zeolite physicochemical properties are affected by synthesis conditions. In addition, the catalytic activity of Sn-MFI zeolites for the hydroxylation of phenol was studied. The general conclusion from this work is that framework incorporation of these elements is highly influenced by pH, mixture composition and the presence of sodium cations. Sodium cations are commonly included in industrial preparations through the use of sodium hydroxide, but they were found to negatively affect framework incorporation due to a tendency to form stable extra-framework impurities with the heteroatoms, especially germanium and tin. pH and mixture composition are particularly influential in controlling germanium and boron incorporation, while the incorporation of tin, its coordination environment and catalytic performance were found to depend on synthesis conditions as well as post-synthesis treatments.Item Synthesis and Characterization of Magnesium-Silicon and Magnesium-Tin Solid Solutions for Thermoelectric Applications(2012-07-16) Hu, FangThe environmentally friendly n-type Mg2(Si, Sn) thermoelectric solid solutions have a strong potential of commercial utilization in thermoelectric (TE) energy conversion due to their availability, low density (~3.02 g/cm3), and high stability at middle temperature range (400-600 ?C) that are typically observed from waste heat dissipating systems. The bulk materials were prepared from element powders via slow cooking under vacuum condition and current-assisted hot-press sintering. Temperature vs time curves have been researched in this thesis for fully reacted magnesium-silicide & magnesium-stannide green ingots with doping materials i.e. antimony, bismuth by different doping ratios. These ingots were ground by a high energy ball miller, uniaxial cold pressed into half inch pallets and then sintered by Direct Current-assisted hot pressing. Different synthesis conditions such as ball milling, sintering time, pressure, have been compared by SEM images and XRD tests analysis to figure out optimized process parameters. Several samples? thermal conductivities (?) were plotted as a function of temperature to study different synthesis strategies and doping materials? effects on phonon scattering inside bulk thermoelectric materials.Item Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds(2009-05-15) Cable, Robert E.As devices and new technologies continue to shrink, nanocrystalline multi-metal compounds are becoming increasingly important for high efficiency and multifunctionality. However, synthetic methods to make desirable nanocrystalline multi-metallics are not yet matured. In response to this deficiency, we have developed several solution-based methods to synthesize nanocrystalline binary alloy and intermetallic compounds. This dissertation describes the processes we have developed, as well as our investigations into the use of lithographically patterned surfaces for template-directed self-assembly of solution dispersible colloids. We used a modified polyol process to synthesize nanocrystalline intermetallics of late transition and main-group metals in the M-Sn, Pt-M?, and Co-Sb systems. These compounds are known to have interesting physical properties and as nanocrystalline materials they may be useful for magnetic, thermoelectric, and catalytic applications. While the polyol method is quite general, it is limited to metals that are somewhat easy to reduce. Accordingly, we focused our synthetic efforts on intermetallics comprised of highly electropositive metals. We find that we can react single-metal nanoparticles with zero-valent organometallic Zinc reagents in hot, coordinating amine solvents via a thermal decomposition process to form several intermetallics in the M??-Zn system. Characterization of the single-metal intermediates and final intermetallic products shows a general retention of morphology throughout the reaction, and changes in optical properties are also observed. Following this principle of conversion chemistry, we can employ the high reactivity of nanocrystals to reversibly convert between intermetallic phases within the Pt-Sn system, where PtSn2 ? PtSn ? Pt3Sn. Our conversion chemistry occurs in solution at temperatures below 300 ?C and within 1 hour, highlighting the high reactivity of our nanocrystalline materials compared to the bulk. Some evidence of the generality for this process is also presented. Our nanocrystalline powders are dispersible in solution, and as such are amenable to solution-based processing techniques developed for colloidal dispersions. Accordingly, we have investigated the use of lithographically patterned surfaces to control the self-assembly of colloidal particles. We find that we can rapidly crystallize 2-dimensional building blocks, as well as use epitaxial templates to direct the formation of interesting superlattice structures comprised of a bidisperse population of particles.Item Synthesis and Electric Field-Manipulation of High Aspect Ratio Barium Titanate(2012-07-16) Li, JunjiaThe objective of this thesis is to develop high dielectric constant nanoparticle dispersion for switchable aircraft antenna systems. Two steps were designed to achieve the objective. First, obtain high dielectric, high aspect ratio nanoparticles and disperse them in dielectric oil medium. Second, manipulate the particle-oil dispersion using an external alternating current (AC) electric field to increase the effective dielectric constant. In order to obtain high dielectric dispersions, different sizes and shapes of titanium dioxide (TiO2) and barium titanate (BaTiO3) nanoparticles were purchased and measured. However, after a number of experiments detailed in the thesis, it was found that none of the commercially available nanoparticles could satisfy our requirements for a minimum effective dielectric constant. Thus, to achieve the goals above, we synthesized high aspect ratio BaTiO3 nanowires with BaC2O4 and TiO2 powders as precursors using a molten salt method. The as-synthesized BaTiO3 nanowires were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) mapping. The nanowires have a diameter ranging from 100 nm to 300 nm, and their lengths range from 1.5 micrometers to 5 micrometers. Mechanical stirring and bath sonication were used to obtain even colloidal dispersions. Different concentrations of BaTiO3 nanoparticles well dispersed in the oil medium were successfully manipulated using AC electric field. To monitor the change in microstructure of BaTiO3 nanoparticles, optical microscopy was used to observe the alignment of particles in the sample under the applied electric field. Various parameters including the magnitude, frequency, and duration of the electric field, and the concentration of BaTiO3 nanoparticles were investigated to achieve the optimal alignment of nanoparticles. The experimental results were validated by theoretical analysis using Maxwell-Garnett mixing rule. It was demonstrated that the effective dielectric constant of the colloidal dispersions would increase with the increase of the magnitude, frequency and duration of applied electric field. Synthesized BaTiO3 nanowire-based dispersions exhibit significant enhancement of the effective dielectric constant compared to other colloidal materials. The effective dielectric constant of 5 wt percent BaTiO3-oil dispersions could reach up to 10 when aligned at 1000 V/mm electric field at 1 kHz frequency for 1 hour.Item Synthesis and mobilization of carbohydrate in xylem parenchyma cells of cotton during water deficiency(2009-05) Roper, Becky Jo; Holaday, A. Scott; Payton, Paxton R.; Tissue, David T.; Zak, JohnThe aim of this study was to determine whether water deficiency affected the carbohydrate content of cotton xylem parenchyma cells and the total extractable activity of key enzymes associated with starch synthesis and mobilization and sucrose synthesis. Wild-type cotton (Gossypium hirsutum L. cv Coker 312) were subjected to well-watered, water-deficit, and re-watered treatments along with SPS+ cotton to determine whether the total sucrose phosphate synthase (SPS) activity and sucrose content of xylem parenchyma cells increased when the spinach gene for SPS is overexpressing in cotton. Cotton plants were grown to certain periods of development (seedling, flowering, or boll developing) and subjected to a gradual water deficit. Once these stages were determined and showed significant effect by water deficiency, the process was repeated on flowering cotton in the summer and autumn, and with boll developing cotton in the autumn. In these single stage experiments, half of the water deficient treated cotton were left to be re-watered for four days and sampled to determine the extent of the recovery of sink metabolism and photosynthate production. Leaf CO2-exchange measurements were conducted the day before sampling with pre-dawn leaf water status taken the day of sampling. Nodal xylem tissue with the bark removed were sampled, frozen, and stored in -85C until extraction analysis could be preformed. Activities of SPS, ADP-glucose pyrophosphorylase (AGPase), sucrose synthase (SucSyn), and amylase (fall boll only) from xylem tissue samples were determined and compared with the contents of hexose, sucrose, and starch. The results indicated that stored starch in the xylem parenchyma cells of cotton is catabolized (“mobilizedâ€) to hexose, glucose and fructose, for sucrose synthesis or other uses during water deficit stress. Water deficit stress in both types of cotton in all major stages of growth caused a decline in SucSyn and an increase in beta-amylase. This supports the hypothesis that sink carbohydrate metabolism can be downregulated and carbohydrate metabolism using stored reserves as a source of soluble sugars can be upregulated in xylem parenchyma cells during environmental stress. The information gained here will provide further insight on the possibility that starch reserves in xylem parenchyma cells can be modified to serve as sources of soluble carbohydrate for osmotic adjustment and growth of strong sinks (e.g., bolls) during water deficit stress.Item Synthesis and spectral studies of lariat ethers(Texas Tech University, 1999-05) Johnson, Russell JamesA series of highly lipophilic lariat ether esters based on 5>7w-dibenzo-16-crown-5 were synthesized for evaluation in ISFET (ion selective field effect transistor) electodes Both the substituent geminal to the functional side arm and the 0-alkyl group of the ester were varied. A series of new N-(X)sulfonyl lariat ether carboxamides and their acid precursors based on 5>7w-dibenzo-16-crown-5 were synthesized for studies of the solvent extraction of alkali metal cations and their transport across polymeric inclusion membranes. These lariat ethers contain a 1-alkynyl group of varying length geminal to the functional side arm. The N-(X)sulfonyl carboxamides contain various electron-withdrawing and electron-donating X groups to "tune" the acidity of the proton-ionizable side arm. IR and *H NMR spectra of the new jrv7w-dibenzo-16-crown-5 compounds were evaluated to obtain further information about bond characters, conformations, and chemical environments of diastereotopic methylene protons in solution.Item Synthesis of Heptakis-2-O-Sulfo-Cyclomaltoheptaose, a Single-Isomer Chiral Resolving Agent for Enantiomer Separations in Capillary Electrophoresis(2012-02-14) Tutu, EdwardSingle-isomer sulfated cyclodextrins (SISCDs) have proven to be reliable, effective, robust means for separation of enantiomers by capillary electrophoresis (CE). SISCD derivatives used as chiral resolving agents in CE can carry the sulfo groups either at the C2, C3 or C6 positions of the glucopyranose subunits which provides varied intermolecular interactions to bring about favorable enantioselectivities. The first single-isomer, sulfated ?-CD that carries the sulfo group at the C2 position, the sodium salt of heptakis(2-O-sulfo-3-O-methyl-6-Oacetyl) cyclomaltoheptaose (HAMS) has been synthesized. The purity of each synthetic intermediate and of the final product was determined by HILIC and reversed phase HPLC. The structural identity of each intermediate and the final product was verified by 1D, and 2D NMR, and MALDI-TOF mass spectrometry. HAMS has been used as chiral resolving agent for the CE separation of a set of nonionic, weak base and strong acid enantiomers in pH 2.5 background electrolytes. Rapid separations with satisfactory peak resolution values were obtained for the enantiomers of most of the nonionic and weak base analytes. Typically, low concentrations of HAMS were required to effect good enantiomer resolution. The trends in the effective mobilities and separation selectivities as a function of HAMS concentrations followed the predictions of the ionic strength-corrected charged resolving agent migration model (CHARM model). HAMS showed poor complexation with the anionic strong electrolyte enantiomers for which no peak resolution was observed. The separation patterns observed with HAMS as chiral resolving agent were compared with those of other ?-cyclodextrin analogues, including heptakis(2-O-methyl- 3-O-acetyl-6-O-sulfo)-b-cyclodextrin (HMAS), heptakis(2-O-methyl-3,6-di-O-sulfo)-b- cyclodextrin (HMdiSu), heptakis(2,3-di-O-acetyl-6-O-sulfo)-b-cyclodextrin (HDAS) and heptakis(2,3-di-O-methyl-6-O-sulfo)-b-cyclodextrin (HDMS).Item Synthesis of novel proton-ionizable calix[4]arenes(2006-05) Shen, Xin; Bartsch, Richard A.; Li, Guigen; Birney, David M.A series of p-tert-butylcalix[4]arenes was synthesized with enlongated acidic groups, 4-oxybutanoic acid, 5-oxypentanoic acid, N-(X)sulfonyl 4-oxybutanamide and N-(X)sulfonyl 5-oxypentanamide, on the lower rim as proton ionizable groups with or without tert-butyl groups on the upper rim. Calix[4]arenes with butoxy groups instead of methoxy groups, which are fixed in the cone conformation, are also prepared. An efficient synthesis route for p-benzoyl and p-benzyl-substituted calix[4]arenes is reported. Further preparation of novel proton-ionizable calix[4]arenes with four benzoyl or benzyl groups on the upper rim and two methoxy groups and two N-(X)sulfonyl carboxamide groups on the lower rim are described. Di-p-benzoyl- and di-p-benzyl substituted calix[4]arenes were synthesized to achieve individual control of the para substituent of the four aromatic rings and further preparation of proton-ionizable calix[4]arenes with two methoxy groups and two N-(X)sulfonyl carboxamide groups on the lower rim was achieved. The syntheses of di-p-nitrocalix[4]arenes was accomplished by ipso-substitution. Proton-ionizable calix[4]arenes with two tert-butyl groups and two nitro groups on the upper rim and either one methoxy group and two N-(X)sulfonyl carboxamide groups or two methoxy groups and one N-(X)sulfonyl carboxamide group on the lower rim were synthesized.Item Synthetic studies of N-heterocycles via catalytic reductive C-C bond formation and tertiary neopentyl substitution(2012-05) Grant, Christopher Donald; Krische, Michael J.; Martin, Stephen F.; Siegel, Dionicio R.; Brodbelt, Jennifer S.; Kerwin, Sean M.Whilst there are a large number of C-C bond forming reactions available for the construction of heterocycles a number of these protocols require the use of stoichiometric organometallic reagents. Since heterocycles are present in the vast majority of pharmaceutical agents the ability to forge these structures efficiently with a minimal amount of stoichiometric metallic waste is important. With this in mind we initiated a series of projects that focus on the use of [pi]-unsaturates to serve as surrogates to toxic, air and moisture sensitive nucleophilic organometallic reagents utilized in traditional C-C bond forming reactions. This has allowed us to develop catalytic couplings of vinyl azines to imines to form branched amines, to couplings of dimethylallene to isatin forming a tert-prenyl hydroxy oxindole and this neopentyl alcohol can be substituted with C-nucleophiles forming two contiguous quaternary all-carbon centers in our synthetic studies tert-prenyl indole alkaloid natural products.