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Novel Dodecaarylporphyrins: Synthesis and Variable Temperature NMR Studies

Description: An investigation of the synthesis of novel dodecaarylporphyrins using the Suzuki coupling reaction of arylboronic acids with octabromotetraarylporphyrins is reported. Studies of the dynamic properties of these new porphyrins using variable temperature (VT) <SUP>1</SUP>H NMR spectroscopy and molecular mechanics provide interesting insights into their dynamic properties, including the first determination of {beta} aryl rotation in a porphyrin system.
Date: May 5, 1999
Creator: Cancilla, Mark; Lebrilla, Carlito; Ma, Jian-Guo; Medforth, Craig J.; Muzzi, Cinzia M.; Shelnutt, John A. et al.
Partner: UNT Libraries Government Documents Department


Description: The interactions of 4-nitroquinoline-1-oxide (NQO) with the four 5{prime}-deoxyribonucleotides were probed using absorption spectra of the charge transfer bands and {sup 1}H and {sup 13}C NMR spectra of nucleotide-NQO mixtures. Applying a Benesi-Hildebrand type equation to the spectral data yielded equilibrium constants (K(dpG:NQO) = 16 M{sup -1} K(dpA:NQO) = 12 M{sup -1}, K(dpT:NQO) = K(dpC:NQO) = 4 M{sup -1}) which suggest the preference of NQO for the guanine residue in a DNA. From {sup 13}C and {sup 1}H NMR data, a structure for the dpG:NQO complex is proposed.
Date: September 1, 1977
Creator: Winkle, S.A. & Tinoco Jr, I.
Partner: UNT Libraries Government Documents Department

NMR studies of DNA oligomers and their interactions with minor groove binding ligands

Description: The cationic peptide ligands distamycin and netropsin bind noncovalently to the minor groove of DNA. The binding site, orientation, stoichiometry, and qualitative affinity of distamycin binding to several short DNA oligomers were investigated by NMR spectroscopy. The oligomers studied contain A,T-rich or I,C-rich binding sites, where I = 2-desaminodeoxyguanosine. I{center_dot}C base pairs are functional analogs of A{center_dot}T base pairs in the minor groove. The different behaviors exhibited by distamycin and netropsin binding to various DNA sequences suggested that these ligands are sensitive probes of DNA structure. For sites of five or more base pairs, distamycin can form 1:1 or 2:1 ligand:DNA complexes. Cooperativity in distamycin binding is low in sites such as AAAAA which has narrow minor grooves, and is higher in sites with wider minor grooves such as ATATAT. The distamycin binding and base pair opening lifetimes of I,C-containing DNA oligomers suggest that the I,C minor groove is structurally different from the A,T minor groove. Molecules which direct chemistry to a specific DNA sequence could be used as antiviral compounds, diagnostic probes, or molecular biology tools. The author studied two ligands in which reactive groups were tethered to a distamycin to increase the sequence specificity of the reactive agent.
Date: May 1, 1996
Creator: Fagan, P.A.
Partner: UNT Libraries Government Documents Department

Preconversion catalytic deoxygenation of phenolic functional groups. Quarterly technical progress report, July 1, 1995--September 30, 1995

Description: Compared to alkoxy complexes, the chemistry of late transition metal aryloxy complexes is expected to reflect somewhat weaker M-O bonds since aryloxides are weaker nucleophiles than alkoxides. To understand the chemistry of the phenoxides, several thiophenoxide derivatives were synthesized. Pt(II) thiolate complexes are obtained either by reaction of Pt(II) chlorides with RSH in presence of base or the reaction of Pt(0) with dialkyl disulfides. NMR was used to study the structure.
Date: December 31, 1995
Creator: Kubiak, C.P.
Partner: UNT Libraries Government Documents Department

Reaction chemistry of cerium

Description: It is truly ironic that a synthetic organic chemist likely has far greater knowledge of the reaction chemistry of cerium(IV) than an inorganic colleague. Cerium(IV) reagents have long since been employed as oxidants in effecting a wide variety of organic transformations. Conversely, prior to the late 1980s, the number of well characterized cerium(IV) complexes did not extend past a handful of known species. Though in many other areas, interest in the molecular chemistry of the 4f-elements has undergone an explosive growth over the last twenty years, the chemistry of cerium(IV) has for the most part been overlooked. This report describes reactions of cerium complexes and structure.
Date: January 1, 1997
Partner: UNT Libraries Government Documents Department

Probing oxidative degradation in polymers using {sup 17}O NMR spectroscopy

Description: Understanding the mechanism of oxidative degradation remains an important goal in being able to predict the aging process in polymer materials. Nuclear magnetic resonance (NMR) spectroscopy has previously been utilized to investigate polymer degradation, including both proton ({sup 1}H) and carbon ({sup 13}C) studies. These previous NMR studies, as well as other spectroscopic investigations, are complicated by the almost overwhelming signal arising from the native undegraded polymer. This makes the identification and quantification of degradation species at small concentrations difficult. In this note we discuss recent investigation into the use of oxygen ({sup 17}O) NMR spectroscopy to probe the oxidative degradation process in polymers at a molecular level. Due to the low natural abundance (0.037%) and a nuclear spin of I=5/2 possessing an appreciable quadrupolar moment, the use of {sup 17}O NMR in polymer investigations has been limited. By utilizing synthetically enriched oxygen gas during the accelerated aging process, both the difficulties of low natural abundance and background interference signals are eliminated. For enriched samples {sup 17}O NMR spectra now provide a unique probe since all of the observed NMR resonances are the direct result of oxidative degradation.
Date: September 1, 1997
Creator: Alam, T.M.; Click, C.A. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

Nuclear magnetic resonance of laser-polarized noble gases in molecules, materials and organisms

Description: Conventional nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are fundamentally challenged by the insensitivity that stems from the ordinarily low spin polarization achievable in even the strongest NMR magnets. However, by transferring angular momentum from laser light to electronic and nuclear spins, optical pumping methods can increase the nuclear spin polarization of noble gases by several orders of magnitude, thereby greatly enhancing their NMR sensitivity. This dissertation is primarily concerned with the principles and practice of optically pumped nuclear magnetic resonance (OPNMR). The enormous sensitivity enhancement afforded by optical pumping noble gases can be exploited to permit a variety of novel NMR experiments across many disciplines. Many such experiments are reviewed, including the void-space imaging of organisms and materials, NMR and MRI of living tissues, probing structure and dynamics of molecules in solution and on surfaces, and zero-field NMR and MRI.
Date: December 1, 1999
Creator: Goodson, Boyd M.
Partner: UNT Libraries Government Documents Department

NMR studies of bond arrangements in alkali phosphate glasses

Description: Solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has become a powerful tool for the investigation of local structure and medium range order in glasses. Previous {sup 31}P MAS NMR studies have detailed the local structure for a series of phosphate glasses. Phosphate tetrahedra within the glass network are commonly described using the Q{sup n} notation, where n = 0, 1, 2, 3 and represents the number of bridging oxygens attached to the phosphate. Using {sup 31}P MAS NMR different phosphate environments are readily identified and quantified. In this paper, the authors present a brief description of recent one dimensional (1D) {sup 6}Li, {sup 7}Li and {sup 31}P MAS experiments along with two-dimensional (2D) {sup 31}P exchange NMR experiments for a series of lithium ultraphosphate glasses. From the 2D exchange experiments the connectivities between different Q{sup n} phosphate tetrahedra were directly measured, while the 1D experiments provided a measure of the P-O-P bond angle distribution and lithium coordination number as a function of Li{sub 2}O concentration.
Date: January 1, 1998
Creator: Alam, T.M. & Brow, R.K.
Partner: UNT Libraries Government Documents Department

Nuclear magnetic resonance: Its role as a microscopic probe of the electronic and magnetic properties of High-{Tc} superconductors and related materials

Description: NMR experiments are reported for Sr{sub 2}CuO{sub 2}Cl{sub 2}, HgBa{sub 2}CuO{sub 4+d}, YNi{sub 2}B{sub 2}C and YBa{sub 2}Cu{sub 3}O{sub 7}. NMR studies typify three different aspects of microscopic properties of HTSC. In non-superconducting antiferromagnetic (AF) prototype Sr{sub 2}CuO{sub 2}Cl{sub 2}, we used NMR to investigate Cu{sup 2+} correlated spin dynamics and AF phase transition in CuO2 layers. In the superconductors, we used NMR both to investigate the electronic properties of the Fermi-liquid in normal and superconducting states and to investigate flux lattice and flux-line dynamics in the superconducting state in presence of magnetic field. A summary of each study is given: {sup 35}Cl NMR was measured in Sr{sub 2}CuO{sub 2}Cl{sub 2} single crystals with T{sub N}=257K. {sub 35}Cl NMR relaxation rates showed crossover of Cu{sup 2+} spin dynamics from Heisenberg to XY-like correlation at 290 K well above T{sub N}. A field-dependent T{sub N} for H{perpendicular}c was observed and explained by a field-induced Ising-like anisotropy in ab plane. {sup 199}Hg NMR was measured in HgBa{sub 2}CuO{sub 4+d}. Properties of the Fermi-liquid are characterized by a single-spin fluid picture and opening of a spin pseudo-gap at q=0 above {Tc}. Below {Tc}, spin component of Knight shift decreases rapidly in agreement with prediction for d-wave pairing scheme. {sup 11}B and {sup 89}Y NMR/magnetization were measured in YNi{sub 2}B{sub 2}C. Temperature dependence of {sup 11}B Knight shift and of the NSLR gave a normal state which agrees with the Korringa relation, indicating that the AF fluctuations on the Ni sublattice are negligible. Opening of the superconducting gap obeys BCS. A NMR approach to investigate vortex thermal motion in HTSC is presented, based on contribution of thermal flux-lines motion to both T{sub 2}{sup {minus}1} and T{sub 1}{sup {minus}1}. Effects are demonstrated in YBa{sub 2}Cu{sub 3}O{sub 7} and HgBa{sub 2}CuO{sub 4+d}.
Date: December 27, 1995
Creator: Suh, Byoung Jin
Partner: UNT Libraries Government Documents Department

Development of experimental techniques to study protein and nucleic acid structures

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This research project sought to develop experimental tools for structural biology, specifically those applicable to three-dimensional, biomolecular-structure analysis. Most biological systems function in solution environments, and the ability to study proteins and polynucleotides under physiologically relevant conditions is of paramount importance. The authors have therefore adopted a three-pronged approach which involves crystallographic and nuclear magnetic resonance (NMR) spectroscopic methods to study protein and DNA structures at high (atomic) resolution as well as neutron and x-ray scattering techniques to study the complexes they form in solution. Both the NMR and neutron methods benefit from isotope labeling strategies, and all provide experimental data that benefit from the computational and theoretical tools being developed. The authors have focused on studies of protein-nucleic acid complexes and DNA hairpin structures important for understanding the regulation of gene expression, as well as the fundamental interactions that allow these complexes to form.
Date: April 1996
Creator: Trewhella, J.; Bradbury, E. M.; Gupta, G.; Imai, B.; Martinez, R. & Unkefer, C.
Partner: UNT Libraries Government Documents Department

Photo-CIDNP of Photosyntheitc Reaction Centers

Description: Studies of Photochemically Induced Dynamic Nuclear Polarization in Photosynthetic Bacterial Reaction Centers: Wavelength and Time Dependence Solid-state NMR spectra of quinone-reduced photosynthetic bacterial reaction centers (RCs) and chromatophores exhibit certain strongly enhanced lines under illumination, a result of photochemically induced dynamic nuclear polarization (photo-CIDNP). This technique offers a new method to investigate photosynthetic electronic transactions while retaining the NMR advantages of narrow linewidths and site-specific resolution. Pulsed laser illumination at 532 nm was used as the basis for time resolved photo-CIDNP experiments, a technique not previously published for solid-state photosynthetic systems. These measurements offer insight about the origin of the polarization effects.
Date: October 22, 2005
Creator: McDermott, Ann. E.
Partner: UNT Libraries Government Documents Department

Trivalent metallocene chemistry of some uranium, titanium, and zirconium complexes

Description: Dicyclopentadienyluranium halide dimers have been prepared and their solution behavior examined. These molecules exist as dimers in solution, and the halide ligands undergo rapid site exchange on the NMR timescale above 50 C. Analogous dicyclopentadienyluranium hydroxide dimers have also been prepared; they oxidatively eliminate hydrogen to give the corresponding oxide dimers. Mechanism of this reaction is consistent with {alpha}migration of one of the hydroxide hydrogen atoms to a uranium center followed by elimination of hydrogen. Ground state of [(Me{sub 3}Si){sub 2}C{sub 5}H{sub 3}]{sub 3}M M = Nd, U and their base adducts has been examined by variable temperature magnetic susceptibility and EPR spectroscopy. The ground state is found to be {sup 4}I{sub 9/2} with a crystal field state consisting largely of J{sub z} = 1/2 lowest, in agreement with previous studies on tris-cyclopentadienylneodymium complexes. The zirconium metallocene Cp{sub 3}Zr has been prepared, characterized crystallographically, and its reactivity studied. Its chemical behavior is controlled by presence of an electron in the non-bonding, d{sub z}2 orbital which prevents formation of base adducts Of Cp{sub 3}Zr, but allows Cp{sub 3}Zr to abstract atoms from other molecules. Electonic and EPR spectra of Cp*{sub 2}TiX complexes, where Cp* is Me{sub 5}C{sub 5} and X is a monodentate, anionic ligand such as halide, have been studied. A {pi}-bonding spectrochemical series is developed, and trends in {pi}-bonding ability are found similar to those in other inorganic complexes. The {beta}-agostic interactions in Cp*{sub 2}TiN(Me)Ph have been examined using variable temperature EPR spectroscopy, and the enthalpy/entropy of the interaction determined. In Cp*{sub 2}TiEt, enthalpy of the {beta}-agostic interaction is {minus}1.9 kcal/mol. The titanocene anion, Cp*{sub 2}TiLi(TMEDA) (TMEDA is N,N,N`,N`-tetramethylethylenediamine), has been prepared and its structure determined.
Date: May 1, 1995
Creator: Lukens, W. W., Jr.
Partner: UNT Libraries Government Documents Department

Chemometric Analysis of Two Dimensional Decay Data: Application to {sup 17}O NMR Relaxation Matrices

Description: The use of {sup 17}O NMR spectroscopy as a tool to investigate aging in polymer systems has recently been demonstrated. Because the natural abundance of {sup 17}O is extremely low (0.037%), the use of labeled {sup 17}O{sub 2} during the oxidation of polymers produces {sup 17}O NMR spectra whose signals arise entirely from the degradation species (i.e. signals from the bulk or unaged material are not observed). This selective isotopic labeling eliminates the impact of interference from the unaged material, cause (1) above. As discussed by Alam et al. spectral overlap between different degradation species as well as errors in quantification remains a major difficulty in {sup 17}O NMR spectroscopy. As a demonstration of the DECRA and CTBSA methods, relaxation matrices obtained from {sup 17}O NMR for model alcohol systems are evaluated. The benefits and limitations of these newly developed chemometric techniques are discussed.
Date: March 18, 1999
Creator: Alam, M.K. & Alam, T.M.
Partner: UNT Libraries Government Documents Department

Investigation of hydrolysis and condensation in organically modified sol-gel systems: {sup 29}Si NMR and the INEPT sequence

Description: The spectral editing properties of the {sup 29}Si NMR INEPT heteronuclear transfer experiment have been utilized for the identification and characterization of hydrolysis and initial condensation products in methyltrimethoxysilane (MTMS) sol-gel materials. {sup 29}Si NMR assignments in MTMS are complicated by a small spectral dispersion ({approximately} 0.5 ppm) and two different {sup 29}Si-{sup 1}H J couplings. By using analytical expressions for the INEPT signal response with multiple heteronuclear J couplings, unambiguous spectral assignments can be made. For this organomethoxysilane the rate of hydrolysis was found to be very rapid and significantly faster than either the water or alcohol producing condensation reactions. The hydrolysis species of both the MTMS monomer and its initial T{sup 1} condensation products follow statistical distributions that can be directly related to the extent of the hydrolysis reactions. The role of the statistical distribution of hydrolysis products on the production and synthetic control of organically modified sol-gels is discussed.
Date: June 1, 1996
Creator: Alam, T.M.; Assink, R.A. & Loy, D.A.
Partner: UNT Libraries Government Documents Department

Morphology of a blend of zinc neutralized sulfonated poly(phenylene oxide) or polystyrene and an amino silicone

Description: A polymer blend of an ionomer based on zinc neutralized sulfonated poly(phenylene oxide) or polystyrene with a silicone copolymer containing 6.45% propylamine groups in place of one of the methyl groups on a backbone silicon was prepared. Carbon-13 magic angle spinning spectra show coordination of the amine, by the zinc ions. Morphological characterization was made by NMR spectroscopy based on proton spin diffusion, by small angle x-ray scattering and by energy filtered transmission electron microscopy. All experiments show domains in the range of 1 to 1000 nm and domain size can be controlled by the extent of coordination of the amine groups by the zinc ions and by thermal history. The different lead to an apparent hierarchy of domain sizes. The NMR domains, 2 to 10 nm, where contrast is produced by differences in chain mobility. Small angle x-ray scattering indicates domains of 16 nm while electron in the range of 100 to 1000 nm. The variation of the domain size between experiments may reflect the different sources of contrast in each cam.
Date: December 31, 1996
Creator: Jones, A.A.; Inglefield, P.T.; Zhang, Changlai & Bergquist, P
Partner: UNT Libraries Government Documents Department

{sup 17}O NMR investigations of oxidative degradation in polymers

Description: We have initiated studies using both solution and solid state magic angle spinning {sup 17}O NMR for a series of oxidatively aged polymers. This short note reports the solution {sup 17}O NMR for oxidatively degraded polypropylene, ethylene-propylene-diene, polyisoprene, and nitrile rubber. Enriched O{sub 2} is used during the accelerated aging. 3 figs, 7 refs.
Date: December 31, 1996
Creator: Alam, T.M.; Celina, M.; Assink, R.A.; Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

Structural studies of the activation of the two component receiver domain NTRC by multidimensional heteronuclear NMR

Description: Multidimensional heteronuclear NMR spectroscopy was used to investigate the N-terminal domain of the transcriptional enhancer NTRC (NiTrogen Regulatory protein C). This domain belongs to the family of receiver domains of two-component regulatory systems involved in signal transduction. Phosphorylation of NTRC at D54 leads to an activated form of the molecule which stimulates transcription of genes involved in nitrogen regulation. Three and four dimensional NMR techniques were used to determine an intermediate resolution structure of the unphosphorylated, inactive form of the N-terminal domain of NTRC. The structure is comprised of five {alpha}-helices and a five-stranded {beta}-sheet in a ({beta}/{alpha}){sub 5} topology. Analysis of the backbone dynamics of NTRC indicate that helix 4 and strand 5 are significantly more flexible than the rest of the secondary structure of the protein and that the loops making up the active site are flexible. The short lifetime of phospho-NTRC hampers the study of this form. However, conditions for determining the resonance assignments and, possibly, the three dimensional structure of phosphorylated NTRC have been obtained. Tentative assignments of the phosphorylated form indicate that the majority of the changes that NTRC experiences upon phosphorylation occur in helix 3, strand 4, helix 4, strand 5, and the loop between strand 5 and helix 5 (the 3445 face of NTRC) as well as near the site of phosphorylation. In order to examine a stable, activated form of the protein, constitutively active mutants of NTRC were investigated.
Date: May 1, 1996
Creator: Nohaile, M.J.
Partner: UNT Libraries Government Documents Department

Effects of surface chemistry on the porous structure of coal. Quarterly technical progress report, July 1996--September 1996

Description: The primary objective of this project is to use {sup 129}Xe NMR to characterize the microporous structure of coals. We will use direct information on pore size, as well as indirect information from adsorption rates and evidence for intra/extraparticle diffusion, to characterize the connectivity of the micropore network. A second objective is to use {sup 129}Xe NMR to describe the effect of controlled opening of the micropores in a microporous carbon by oxygen chemi-sorption/desorption. Our experimental focus in this quarter has been the low power presaturation of the NMR signal of {sup 129}Xe adsorbed in coal. Preliminary work on this experiment was reported in the last quarter. Low power presaturation of {sup 129}Xe adsorbed in two coals produces a hole-burning effect in the adsorbed xenon NMR signals, indicating that these signals are broad due to overlap of a series of chemical shifts. Saturation transfer to the entire adsorbed xenon signal and to the extraparticle gas is observed with increasing presaturation time. Differences in timing of saturation transfer to the external gas have implications for the nature of the connectivity of the pore structures in coal.
Date: October 1, 1996
Creator: Anderson, S.A.; Hatcher, P.G. & Radovic, L.R.
Partner: UNT Libraries Government Documents Department

Solid state {sup 31}P NMR study of phosphonate binding sites in guanidine-functionalized, molecular imprinted silica xerogels

Description: Phosphonate binding sites in guanidine and ammonium surface-functionalized silica xerogels were prepared via the molecular imprinting technique and characterized using solid state {sup 31}P MAS NMR. One-point, two-point, and non-specific host-guest interactions between phenylphosphonic acid (PPA) and the functionalized gels were distinguished by characteristic chemical shifts of the observed absorption peaks. Using solid state as well as solution phase NMR analyses, absorptions observed at 15.5 ppm and 6.5 ppm were identified as resulting from the 1:1 (one-point) and 2:1 (two-point) guanidine to phosphonate interactions, respectively. Similar absorptions were observed with the ammonium functionalized gels. By examining the host-guest interactions within the gels, the efficiency of the molecular imprinting procedure with regard to the functional monomer-to-template interaction could be readily assessed. Template removal followed by substrate adsorption studies conducted on the guanidine functionalized gels provided a method to evaluate the binding characteristics of the receptor sites to a phosphonate substrate. During these experiments, {sup 29}Si and {sup 31}P MAS NMR acted as diagnostic monitors to identify structural changes occurring in the gel matrix and at the receptor site from solvent mediated processes.
Date: January 3, 2000
Creator: Sasaki, D.Y. & Alam, T.D.
Partner: UNT Libraries Government Documents Department

(sup 6)Li and (sup 7)MAS NMR and In Situ X-Ray Diffraction Studies of Lithium Manganate Cathode Materials

Description: {sup 6}Li MAS NMR spectra of lithium manganese oxides with differing manganese oxidation states (LiMn{sub 2}O{sub 4}, Li{sub 4}Mn{sub 5}O{sub 12}, Li{sub 2}Mn{sub 4}O{sub 9}, and Li{sub 2}Mn{sub 2}O{sub 4}) are presented. Improved understanding of the lithium NMR spectra of these model compounds is used to interpret the local structure of the Li{sub x}Mn{sub 2}O{sub 4} cathode materials following electrochemical Li{sup +} deintercalation to various charging levels. In situ x-ray diffraction patterns of the same material during charging are also reported for comparison. Evidence for two-phase behavior for x &lt;0.4 (Li{sub x}Mn{sub 2}O{sub 4}) is seen by both NMR and diffraction.
Date: November 30, 1998
Creator: Lee, Young Joo; Wang, Francis; Grey, Clare P.; Mukerjee, Sanjeev & McBreen, James
Partner: UNT Libraries Government Documents Department

Chemometric Analysis of Nuclear Magnetic Resonance Spectroscopy Data

Description: Chemometric analysis of nuclear magnetic resonance (NMR) spectroscopy has increased dramatically in recent years. A variety of different chemometric techniques have been applied to a wide range of problems in food, agricultural, medical, process and industrial systems. This article gives a brief review of chemometric analysis of NMR spectral data, including a summary of the types of mixtures and experiments analyzed with chemometric techniques. Common experimental problems encountered during the chemometric analysis of NMR data are also discussed.
Date: July 20, 2000
Partner: UNT Libraries Government Documents Department

The use of NMR techniques for the analysis of water in coal and the effect of different coal drying techniques on the structure and reactivity of coal. Final report

Description: Western Research Institute has conducted a study of different methods of coal drying as pretreatment steps before liquefaction. The objectives of this study were to develop a combined chemical dehydration/nuclear magnetic resonance (NMR) method for measuring the moisture content of coal, to measure the changes in coal structure that occur during drying, and to determine the effects of different drying methods on liquefaction reactivity of coals. Different methods of drying were investigated to determine whether coal drying can be accomplished without reducing the reactivity of coals toward liquefaction. Drying methods included thermal, microwave, and chemical dehydration. Coals of rank lignite to high volatile bituminous were studied. Coals that were dried or partially dried thermally and with microwaves had lower liquefaction conversions than coals containing equilibrium moisture contents. However, chemically dried coals had conversions equal to or greater than the premoisturized coals. The conversion behavior is consistent with changes in the physical structure and cross linking reactions because of drying. Thermal and microwave drying appear to cause a collapse in the pore structure, thus preventing donor solvents such as tetralin from contacting reactive sites inside the coals. Chemical dehydration does not appear to collapse the pore structure. These results are supported by the solvent swelling measurements in which the swelling ratios of thermally dried and microwave-dried coals were lower than those of premoisturized coals, indicating a greater degree of cross linking in the dried coals. The swelling ratios of the chemically dried coals were greater than those of the premoisturized coals because the pore structure remaining unchanged or increased when water was removed. These results are consistent with the NMR results, which did not show significant changes in coal chemical structure.
Date: February 1, 1995
Creator: Netzel, D.A.; Miknis, F.P.; Wallace, J.C. Jr.; Butcher, C.H.; Mitzel, J.M.; Turner, T.F. et al.
Partner: UNT Libraries Government Documents Department

Controlling porosity in bridged polysilsesquioxanes through elimination reactions

Description: The retro Diels-Alder reaction was used to modify porosity in hydrocarbon-bridged polysilsesquioxane gels. Microporous polysilsesquioxanes incorporating a thermally labile Diels-Alder adduct as the hydrocarbon bridging group were prepared by sol-gel polymerization of trans-2,3-bis(triethoxysilyl)norbornene. Upon heating the 2,3-norbornenylene-bridges polymers at temperatures above 250 C, the norbornenylene-bridging group underwent a retro Diels-Alder reaction losing cyclopentadiene and leaving behind a ethenylene-bridged polysilsesquioxane. Less than theoretical quantities of cyclopentadiene were volatilized indicating that some of the diene was either reacting with the silanol and olefinic rich material or undergoing oligomerization. Both scanning electron microscopy and nitrogen sorption porosimetry revealed net coarsening of pores (and reduction of surface area) in the materials with thermolysis.
Date: June 1, 1996
Creator: McClain, M.D.; Loy, D.A. & Prabakar, S.
Partner: UNT Libraries Government Documents Department