Browsing by Subject "synthesis"
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Item Connecting the role of school superintendents to teaching and learning in schools: a research synthesis of three educational administration peer reviewed research journals between 1983-2006(Texas A&M University, 2008-10-10) Shidemantle, Steven PaulThis exploratory synthesis of research was the product of three years of dissertation research efforts that systematically reviewed 23 years of empirical articles between 1983 (or its inception) and 2006 from three of the most highly regarded educational administration journals. Specifically designed to collect investigative data and information from primary research contained within Educational Administration Quarterly, the Journal of School Leadership, and the Journal of Educational Administration; this research synthesis drew upon various research methods to propose pragmatic insights and proffer an empirically founded response to: What has the educational administration profession learned from the research efforts that were independently conducted, presented, and published about the overall connections between school superintendents and education's technical core -teaching and learning in schools? Results from employing meta-analysis, descriptive synthesis, and thematic synthesis techniques to appropriately collect and analyze relevant data indicate that school superintendents remain directly connected to the technical core; however, these connections have evolved from the traditional connections presently maintained by campus administrators and to new connections that meet the increased responsibilities and complexities of the superintendents' role. The thematic synthesis, reinforced by descriptive syntheses, indicated 15 separate superintendent - technical core constructs that promote new areas for investigation; however, the extent and strength of these constructs have yet to be determined. The impact from the next step suggestions for future research indicate that effects could range from educational administration knowledge base contributions to refining in-practice standards and professional development programs. The possible knowledge base contributions, coupled with specific in-practice elements that demonstrate superintendents' direct impact on the technical core, may be the necessary raw materials from which a foundational framework that clearly redefines the superintendent - technical core connections may be forged by scholars and implemented by district leaders to improve teaching and learning in schools.Item Designing phase selective soluble polymers for applications in organic chemistry(Texas A&M University, 2004-09-30) Li, ChunmeiSoluble polymers as supports are gaining more attention now. Developing new polymers, new reagents and catalysts, new separation systems are thus of great interest as these sorts of materials' applications in synthesis and catalysis increase. The work described in the succeeding chapters describes my efforts to synthesize new catalysts that can be attached to polymer supports, to study their catalytic activity and to study separation efficiency. Most of the work focus is on polyacrylamide polymers. Both organometallic catalysts and organic catalysts have been studied. Liquid/liquid separation was the technique mainly investigated. In addition, a new separation scheme called latent biphasic system which is a new liquid/liquid separation method is described. Finally, studies with the Cremer group where the LCST behavior of polyacrylamides was studied using dark field methods are also discussed.Item Fast interconnect optimization(Texas A&M University, 2006-04-12) Li, ZhuoAs the continuous trend of Very Large Scale Integration (VLSI) circuits technology scaling and frequency increases, delay optimization techniques for interconnect are increasingly important for achieving timing closure of high performance designs. For the gigahertz microprocessor and multi-million gate ASIC designs it is crucial to have fast algorithms in the design automation tools for many classical problems in the field to shorten time to market of the VLSI chip. This research presents algorithmic techniques and constructive models for two such problems: (1) Fast buffer insertion for delay optimization, (2) Wire sizing for delay optimization and variation minimization on non-tree networks. For the buffer insertion problem, this dissertation proposes several innovative speedup techniques for different problem formulations and the realistic requirement. For the basic buffer insertion problem, an O(n log2 n) optimal algorithm that runs much faster than the previous classical van Ginneken??s O(n2) algorithm is proposed, where n is the number of buffer positions. For modern design libraries that contain hundreds of buffers, this research also proposes an optimal algorithm in O(bn2) time for b buffer types, a significant improvement over the previous O(b2n2) algorithm by Lillis, Cheng and Lin. For nets with small numbers of sinks and large numbers of buffer positions, a simple O(mn) optimal algorithm is proposed, where m is the number of sinks. For the buffer insertion with minimum cost problem, the problem is first proved to be NP-complete. Then several optimal and approximation techniques are proposed to further speed up the buffer insertion algorithm with resource control for big industrial designs. For the wire sizing problem, we propose a systematic method to size the wires of general non-tree RC networks. The new method can be used for delay optimization and variation reduction.Item A general scaffold for the synthesis of cysiherbaine and its analogues(2008-12-03) Chang Won Kang; Scott R. Gilbertson; Vincent J. Hilser; Joel Gallagher; Geoffrey T. Swanson; Amarnath NatarajanDysiherbaine 1 and a select number of structurally related compounds have been shown to have selective effects on ionotropic glutamate receptors (iGluRs). iGluRs are essential components in the central nervous system (CNS); playing an important role in memory and learning. They also play a role in a number of neurological disorders, including schizophrenia, epilepsy, Rasmussen¡¯s encephalitis and stroke; along with neurodegenerative disorders such as Alzheimer¡¯s, Parkinson¡¯s and Huntington¡¯s diseases. This dissertation describes the synthesis of key molecule 4 and future directions for its use. The molecule will serve as the branch point for the synthesis of other analogues. We designed a 12 step route to this molecule that utilizes highly stereo- and regioselective reactions. The molecule 4 will provide dysiherbaine and a series of analogues without having to design a new total synthesis for each analogue. While there are a number of syntheses of dysiherbaine reported, they are not appropriate for the easy variation of the important C8-amino C9-alcohol pharmacophore. The molecule 4 has a double bond between the C8 and C9 position as the key reactive functional group. The principal reactivity that will be used to synthesize derivatives of this molecule involves the double bond. Addition reactions of electrophilic reagents to the double bond are the most typical, and include hydroxylation, hydrogenation, halogenation, alkylation, amination, etc. This will be a unique and simple way to make dysiherbaine and analogues with just few steps from molecule 4. Finally, this work will provide unique molecules that will enhance the understanding of the structure and function of ionotropic Glu receptors in the CNS.Item Methods for the syntheses of compositionally diverse dendrimers(Texas A&M University, 2005-11-01) Steffensen, Mackay BagleyDendrimers are a unique class of macromolecules that present perfect branching on a molecular scale. The pattern of branching at the atomic scale is compared to the branching of trees, from whence dendrimers get their name. Dendrimers have been attractive synthetic targets for the past twenty years. The methods and building blocks used in the synthesis of dendrimers vary, but molecules of this class of polymeric materials all possess symmetrical branching emanating from the core. At each branch point the number of groups increases exponentially. Efforts directed toward the synthesis of dendrimers presenting multiple functional groups at the surface and within the dendrimer structure are described. Methods are described which provide access to dendrimers in a one-pot per generation fashion, with triazines as the common moiety. Chemoselective routes utilize the temperature dependant substitution of cyanuric chloride to construct dendrimers, obviating the use of protected monomers or the need to manipulate functional groups during the synthesis. These methods are atom economical, as the only by-products are HCl and a base to scavenge it. The methods are efficient, with typical isolated yields of product in the middle to high ninety percent range, often on a multi-gram scale. Methods are described for conducting three separate reactions in a single pot. Specific emphasis is placed on structural control of the interior and surface groups of the dendrimers. The synthesis of a G3 dendrimer of layered composition is described. The use of a different difunctional linkage group for each generation of dendrimer growth produced a G3 dendrimer with layered composition without the use of protecting groups or functional group interconversions. A G3 dendrimer was synthesized presenting five different functionalities at the periphery on a 10 gram scale, resulting in approximately 70% overall yield. The peripheral groups are composed of orthogonal functionality, which can be independently and selectively unmasked or manipulated in the presence of the other functionality. The syntheses of dendrimers incorporating the short linker hydrazine produce materials with interesting physical properties as well as a low ratio of carbon to nitrogen. The use of dendrimers in the construction of novel macromolecular constructs is also described.Item Studies of Platinum Polyynyl Complexes: Elaboration of Novel "Click" Cycloadducts and Fluorous and Polygon Based Platinum Polyyndiyl Systems(2012-11-13) Clough, Melissa Catherine 1985-The major directions of this dissertation involve (1) the syntheses and characterization of molecular polygons incorporating sp1hybridized carbon linkers and L2Pt corners (L2 = cis-1,3-diphosphine), (2) the development of protected carbon chain complexes featuring fluorous phosphine ligands and (3) click reactions of metal terminal polyynyl complexes and further metallations of the resulting triazole rings. A brief overview is provided in Chapter I. Chapter II details the syntheses of molecular squares containing bidendate diphosphine ligands of the formula R2C(CH2PPh2)2 where R = Me, Et, n-Bu, n-Dec, Bn, and p-tolCH2 (general designation dppp*), in which the R2 groups are intended to circumvent the solubility issues encountered by others. Their syntheses involve double substitutions of the dimesylate compounds R2C(CH2OMs)2 using KPPh2. Building blocks of the formulae (dppp*)PtCl2 and (dppp*)Pt((C?C)2H)2 are synthesized and characterized, including one crystal structure of the latter. The target complexes are accessed by reactions of (dppp*)PtCl2 with (dppp*)Pt((C?C)2H)2 under Sonogashira type conditions. Six new squares of the formula [(R2C(CH2PPh2)2)Pt(C?C)2]4 are characterized including two crystal structures. Further topics include approaches to higher homologues and cyclocarbon synthesis. Chapter III focuses on carbon chain complexes bearing fluorous phosphine ligands of the formula P((CH2)mRfn)3 (Rfn = (CF2)n-1CF3; m/n = 2/8, 3/8, and 3/10). Precursors of the formula trans-(C6F5)((Rfn(CH2)m)3P)2PtCl are synthesized and characterized, including one crystal structure, which reveals phase separation of the fluorous and non-fluorous domains. Reactions with butadiyne give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C?C)2H. Oxidative homocouplings afford the target complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C?C)4(C6F5)(P((CH2)mRfn)3)2Pt. Cyclic voltammetry indicates irreversible oxidations of the title compounds, in contrast to partially reversible oxidations of non-fluorous analogues. Chapter IV focuses on multimetallic complexes achieved by click reactions in metal coordination spheres. The copper catalyzed click reaction between trans-(C6F5)(p-tol3P)2Pt(C?C)2H (1) and (?5-C5H4N3)Re(CO)3 affords the bimetallic 1,2,3-triazole trans-C6F5)(p1tol3P)2PtC?CC=CHN((?51C5H4)Re(CO)3)N=N. Further reactions with Re(CO)5OTf and Re(CO)5Br give trimetallated adducts, which represent the first species of this type. An alternative route to a trimetallic complex involves the twofold cycloaddition of the diazide (?5-C5H4N3)2Fe and 1, giving (?5-C5H4NN=N-C(trans-(C?C)Pt(Pp-tol3)2(C6F5)=CH)2Fe. The crystal structures of the di and trimetallic complexes are compared, but attempts to achieve a fourth metallation involving the =CH groups are unsuccessful. However, when the triazolium salt [trans-(C6F5)(p-tol3P)2PtC?CC=CHN(CH2C6H5)N=N(Me)]+ I? is treated with Ag2O and [Rh(COD)Cl]2, a =CRh adduct is obtained. The success of =CH metallation is correlated to the 1H NMR chemical shift, indicative of an electronic effect.Item Synthesis, reactivity, and coordination chemistry relevant to the copolymerization of CO2 and epoxides by first row transition metal schiff base complexes(2009-05-15) Frantz, Eric BenjaminExcepting agricultural based products, which themselves require a great deal of energy to produce, our supply of natural resources such as minerals, metal ore, fresh water, coal, oil and natural gas are all limited in supply. The depletion of these substances is imminent and this knowledge weighs heavily on humankind. The utilization of CO2 for the production of polycarbonates is one attempt at exploiting a profoundly abundant and renewable resource. The importance of research in this and similar fields justifies the detailed study of the chemicals and procedures involved with this chemistry. This current work concentrates on the fundamental study of transition metal Schiff base complexes that have shown a great deal of promise in their ability to catalyze the copolymerization of CO2 and epoxide to form aliphatic polycarbonates. A new chromium(III) Schiff base complex has been synthesized and evaluated for its ability to catalyze the formation of polymer. The ligand employed bears an N2O2 coordination sphere identical to the widely utilized chromium(III) and cobalt(III) salen catalysts. This complex was shown to be active towards the copolymerization of CO2 and cyclohexene oxide. Although the activity was less than that seen with chromium(III) salen complex, the study demonstrates that new ligand systems are available beyond salen and deserve further attention. A class of manganese(III) Schiff base complexes was also synthesized and evaluated as catalysts. Although crystallographic data has shown that these complexes are structural analogs to chromium(III) salens, the difference in metal center leads to a nearly complete elimination of catalytic activity. Such a marked difference has been taken advantage of by using this very low activity to study the ring-opening of epoxide in the initial step of the copolymerization both mechanistically and kinetically. It has also been utilized in an evaluation of the coordination chemistry of the polymerization process. This has led to some valuable conclusions about the nature and role of the metal center that previously have not been studied. Manganese(III) salen complexes were also synthesized and evaluated in an effort to compare these important ligands to other Schiff bases and confirm the findings mentioned above.Item Synthetic studies toward palau?ne and enantioselective total synthesis of biogenetically related (+)-phakellin and (+)-monobromophakellin(2009-05-15) Wang, ShaohuiOroidin alkaloids, also known as pyrrole-imidazole alkaloids, have become a hot area of chemical and biological research due to their diverse and intriguing structural features and biological activities. Palau'amine (i), one of the hexacyclic oroidin-derived secondary metabolites, contains a fully substituted chloro-cyclopentane ring, a piperazinone moiety and two cyclic guanidines. With the uniqueness and complexity of its structure, palau?amine has been a synthetic challenge and has not yet succumbed to total synthesis. The overall objective of this work was to explore synthetic pathways toward palau?amine and biogenetically related congeners. Most of the work was focused on developing a synthetic pathway for the palau?amine structure proposed in its isolation report dated back to 1993. Starting from a Diels-Alder adduct (iii), oxidation/chlorination followed by phakellin (ii) annulation afforded an advanced pentacyclic intermediate possessing all the carbon framework and all but one ring system of palau?amine. Recently, however, a series of reports questioned the originally proposed palau?amine structure and called for a revision of the stereochemistry of two carbon centers (iv). Now palau?amine has an identical chlorocyclopentane core with axinellamine (vi). With the target changed, we devised a new biomimetic pathway toward both natural products via a common intermediate (v), which was synthesized in 12 steps from the Diels-Alder adduct (iii).