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Tesi sul tema "Solid NMR"
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1
Smith, P. W. R. "NMR investigations of solid polyolefins". Thesis, University of East Anglia, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373108.
Testo completo
2
Heitjans, Paul, Sylvio Indris e Martin Wilkening. "Solid-state diffusion and NMR". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195770.
Testo completoAbstract (sommario):
Diffusion in solids, which requires the presence of crystal defects or disorder, has both microscopic and macroscopic aspects.
Nuclear magnetic resonance techniques provide access to microscopic diffusion parameters like atomic jump rates and activation
energies as well as to the tracer diffusion coefficient for macroscopic transport. Microscopic NMR methods include spin-lattice relaxation spectroscopy of stable and beta-radioactive nuclei, spin-spin relaxation or linewidth and spin alignment decay measurements, whereas macroscopic NMR methods are represented by the techniques of static and pulsed field gradient NMR. We recall some basic principles of the mentioned techniques and review case studies for their application to various solids like glassy and crystalline aluminosilicates, nanocrystalline composites, an intercalation compound and a simple bcc metal. Taken together, jump rates in solids are covered over about 10 decades by the microscopic, and diffusion coefficients over 3 decades by the macroscopic NMR methods.
3
Heitjans, Paul, Sylvio Indris e Martin Wilkening. "Solid-state diffusion and NMR". Diffusion fundamentals 2 (2005) 45, S. 1-20, 2005. https://ul.qucosa.de/id/qucosa%3A14378.
Testo completoAbstract (sommario):
Diffusion in solids, which requires the presence of crystal defects or disorder, has both microscopic and macroscopic aspects.
Nuclear magnetic resonance techniques provide access to microscopic diffusion parameters like atomic jump rates and activation
energies as well as to the tracer diffusion coefficient for macroscopic transport. Microscopic NMR methods include spin-lattice relaxation spectroscopy of stable and beta-radioactive nuclei, spin-spin relaxation or linewidth and spin alignment decay measurements, whereas macroscopic NMR methods are represented by the techniques of static and pulsed field gradient NMR. We recall some basic principles of the mentioned techniques and review case studies for their application to various solids like glassy and crystalline aluminosilicates, nanocrystalline composites, an intercalation compound and a simple bcc metal. Taken together, jump rates in solids are covered over about 10 decades by the microscopic, and diffusion coefficients over 3 decades by the macroscopic NMR methods.
4
Kirby, Christopher William. "Solid-state NMR studies of cobalamins". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60546.pdf.
Testo completo
5
Jackson, P. "Dipolar coupling in solid-state NMR". Thesis, Durham University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379058.
Testo completo
6
Crowe, Lindsey Alexandra. "NMR of solid phosphorus-containing compounds". Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4502/.
Testo completoAbstract (sommario):
Solid-state NMR techniques have been applied to the structure and dynamic characterisation of a range of phosphorus-containing compounds. Comparisons have been made within several series of compounds as well as studies of individual molecules with interesting NMR properties, whether dynamic, structural or magnetic. Spectral features such as shielding anisotropy, the high sensitivity of phosphorus and its large chemical shift range are extensively utilised in this work. Triple-channel, fluorine-observe and variable-temperature spectrometer facilities at different magnetic field strengths have been explored to give as much complementary information as possible. For both chlorinated and fluorinated diazadiphosphetidines, motional properties have been examined and the indirect spin-spin and dipolar interactions, together with shielding have been studied. Spectra from the NMR-active nuclei in these cyclic dimers have been used to compare effects of differing substituents on NMR properties. The bowl-shaped' molecules, calix[4] resorcinols with phosphorus functionality modifying the upper rim, constitute the other major group of compounds studied. These are of interest in inclusion chemistry. As well as simple one-dimensional NMR characterisation of solid-state calix[4]resorcinol compounds, interesting two-dimensional correlation results have helped with the assignment and conformational conclusions. A qualitative and quantitative study of a co-crystal of triphenylphosphine oxide and phenol was made to establish the nature of the disorder observed, but undefined, in an X-ray structural investigation of the hydrogen-bonded network. Complementary NMR techniques were used to extend the temperature range over which the rate of any motion can be characterised. Bandshape analysis, Tip measurement and selective polarisation inversion experiments have proved to be accurate in different regions of a variable temperature study. Other compounds explored were those which showed interesting solid-state NMR results, for example, the complexities of cross-polarisation dynamics between two abundant spins in inorganic phosphates, and compounds with potential solid-state applications. These include (i) phosphorus-containing compounds with chlorine and fluorinated aromatic substituents and (ii) complexes with transition metals. Comparison with single-crystal and powder X-ray diffraction has also been exploited. In some cases, data have been produced, and in others the applicability of a theoretical approach has led to other conclusions.
7
Heindrichs, Axel Stefan Dirk. "New methodologies in solid state NMR". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342111.
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8
Crockford, Charles. "New methodologies in solid state NMR". Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289481.
Testo completo
9
Blackband, S. J. "NMR imaging of liquid-solid systems". Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356019.
Testo completo
10
Stein, Robin Stephanie. "Structural studies using solid-state NMR". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612912.
Testo completo
11
Portieri, Alessia. "Solid state NMR of sulfa-drugs". Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3781/.
Testo completoAbstract (sommario):
This work has been a study of systems, mostly of sulfa-drugs, showing polymorphic behaviour. Using different means as solid state NMR, X-ray analysis, and theoretical calculations, we have seen how it is possible to understand results obtained from the different techniques, proving how the study of polymorphic systems needs cooperative advice from the different techniques that are able to detect polymorphic differences. Within the sulfa-drugs I have been mostly concentrating on sulfanilamide, studying (^13)C and (^15)N solid state NMR spectra of the different polymorphs. The NMR parameters that have been most interesting to study, have been the relaxation times that have revealed complicated motion of the molecule despite it being a small molecule. In order to obtain detailed information from (^15)N spectra it has been necessary to enrich the samples and this has enabled a study of the shielding tensors of the nitrogens in the molecule. (^13)C spectra were also recorded of systems studied sulfathiazole solvates that proved to show some of the same solid state effects in the NMR spectra as sulfanilamide. Shielding calculations have proved to be still limited in order to obtain reliable information on the shielding of both and (^13)C (^15)N nuclei but considering hydrogen-bonded molecules, as opposed to isolated molecules, seemed to have improved the calculations quite a lot, so that some idea of intermolecular effects could be deducted. Exact positions of the hydrogen has proved to be essential as well in order to improve the calculations. Finally a case study for the REDOR pulse sequence has been carried out. Different attempts to understand the effects influencing this particular experiment have been carried out on 20% and 99% doubly enriched glycine, as well as on a particular sample, doubly enriched BRL55834, but the internuclear distances measured with this technique still displayed some uncertainties that made results not thoroughly reliable.
12
Likovec, Wayne Robert. "Solid state NMR studies of elastomers". Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058875640.
Testo completo
13
Bennett, David Alexander. "Structural methods in solid-state NMR". Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13242/.
Testo completoAbstract (sommario):
New solid-state NMR experiments for measuring internuclear distances are designed using symmetry principles. The “recoupling” sequences described here are intended to reintroduce the MAS-averaged heteronuclear dipole-dipole coupling between a spin-1/2 nucleus (e.g. 1H) and a half-integer quadrupolar nucleus (e.g. 17O, I = 5/2). The magnitude of the dipolar interaction depends on the separation between the coupled nuclei, so the evolution of the spin system under the recoupled Hamiltonian can be used to measure the internuclear distance. Simulations of the spin dynamics are used initially to select candidate sequences and these are subsequently employed to measure both long-range and direct O–H distances in powdered L-Tyrosine.HCl (isotopically enriched with 17O at 20%to 30% at the O$^\eta$ site). Improvements to existing methods for the data analysis for this type of NMR experiment are also discussed, including the restriction and/or removal of certain fit parameters and the explicit inclusion of inhomogeneous radio-frequency fields as part of the fitting procedure. The effects of processing on the uncertainty of experimentally determined distances are considered, and a new analysis method which circumvents several of these effects is presented. Similar recoupling sequences can be used to measure the anisotropy of proton chemical shifts, and some preliminary results are also presented for this application. A systematic method for the assignment of congested spin-1/2 spectra resulting from molecules with large numbers of chemically similar sites is also described. This makes use of a comparison between the chemical shift tensor measured as usual by the 2D-PASS experiment and its principal components calculated from first principles using the density functional theory package CASTEP. The initial peak assignment is generated randomly and then varied using a steepest-ascent hill climbing algorithm with the square sum of the difference between the experimental and calculated principal values of the chemical shift tensor as the target function. The new method is tested on the 13C spectrum of the anti-inflammatory drug flufenamic acid and found to be superior to simple assignments using only the isotropic chemical shift.
14
Louie, Elizabeth April. "Solid-State NMR : investigations of biomolecular structure /". Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/8488.
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15
Saalwächter, Kay. "Heteronuclear recoupling methods in solid state NMR". [S.l. : s.n.], 2000. http://ArchiMeD.uni-mainz.de/pub/2000/0070/diss.pdf.
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16
Buda, Alina Reghina. "Solid state NMR for advanced materials characterization". kostenfrei, 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972085459.
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17
Castro, Vasco. "Solid-state NMR characterization of lipid membranes /". Stockholm : Department of Physical, Inorganic and Structural Chemistry, Stockholm university, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7681.
Testo completo
18
Barras, Jamie. "Solid-State NMR studies of inorganic materials". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339770.
Testo completo
19
Parkinson, Matthew John. "Supramolecular interactions investigated by solid-state NMR". Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429310.
Testo completo
20
Brough, Adrian R. "Solid state NMR studies of inorganic materials". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239312.
Testo completo
21
McGeorge, Gary. "NMR studies of solid nitrogen-containing dyestuffs". Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5197/.
Testo completoAbstract (sommario):
This thesis is concerned with the structural analysis of dyestuffs in their natural solid state by the application of solid-state nuclear magnetic resonance. These dysetuffs are all derived from the phenylazobenzene group, but tautomerism can produce structural changes, which have so far been uncharacterised in the solid-state for many of the dyestuffs currently under investigation. The information obtainable from (^13)C and (^15)N chemical shifts, both isotropic and anisotropic will be applied in this structure determination. Under magic-angle spinning the anisotropic nature of solid-state interactions is partially averaged or removed. The rotational resonance technique will be presented, which reintroduces the homonuclear dipolar interaction allowing dipolar coupling constants to be measured. Second-order effects arising from the (^14)N quadrupole interaction broaden spin-1/2 lines (RDC) in such a manner that bond lengths can be determined. This RDC analysis will be applied to a series of hydrazone structures to determine the (^15)N-(^14)N bond length within the hydrazone linkage. Finally, the two-dimensional magic-angle turning experiment will be discussed and applied to both the (13)C and (^15)N nuclei for a range of dyestuffs to show that accurate shielding tensor information can be obtained from large molecules.
22
Codd, Sarah. "3DFT NMR imaging of solid-like materials". Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318105.
Testo completo
23
MariÌn, Montesinos Ildefonso. "New recoupling techniques in solid-state NMR". Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438729.
Testo completo
24
Jolly, Michael Matthew. "Method development in biological solid-state NMR". Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/422129/.
Testo completoAbstract (sommario):
Solid-state nuclear magnetic resonance (ssNMR) has proved to be a useful tool in the analysis of structural and dynamic properties of proteins. However, the inherent low sensitivity of NMR hinders further advancements of the field. This thesis focuses on improving the sensitivity of ssNMR, be this through an improvement in signal to noise or an effective improvement in sensitivity by enhancing the information content. The mixed rotational and rotary resonance (MIRROR) sequence1 was employed to facilitate protein backbone assignment under moderate spinning speeds. Through the band selective nature of MIRROR, bidirectional transfer of magnetisation from the CCO site to the adjacent Cα and to the Cα of the next amino acid is possible. When applied to a 3D-NCOCA experiment this may be used to double the information content, providing correlations from CCO(i-1) to both Cα(i-1) and Cα(i). The MIRROR recoupling of CCO to Cα, is inherently low-power, allowing MIRROR to be utilised in a low-power experiment. Through this, greater enhancements in sensitivity per unit time can be realised. The longitudinal relaxation time (T1) limits the sensitivity per unit time at both room and cryogenic temperatures. To develop the use of relaxation agents for cryogenic NMR experiments, the room temperature relaxation properties and dynamics of the model protein, GB3, were explored. Site-specific relaxation measurements were used to understand the relaxation of residues in the protein and gain understanding into how this relates to the dynamics of the protein. In addition, low-temperature NMR measurements were used to investigate the effect temperature has on relaxation. The ongoing development of polarisation enhancement methods and machinery have made great progress in recent years particularly on the application towards biomolecules. However, arguably the most promising polarisation enhancement technique, dynamic nuclear polarisation (DNP) suffers from a variety of problems. Namely, line broadening effects as a result of the low-temperatures required and through doping with paramagnetic agents. Furthermore, the current method of sample preparation for DNP via the use of doping with exogenous radicals is not viable for all samples. Endogenous radicals for the DNP of large biomolecules may offer several advantages to their exogenous counterparts, including but not limited to, a greater understanding of quenching effects and polarisation transfer. This thesis explores the possibility of creating pseudo-biradicals bound covalently to a protein surface to elicit enhancements through the cross effect DNP mechanism. In summary, we have developed a range of methods that enhance the information content and sensitivity, which will provide new approaches for researchers investigating proteins using ssNMR.
25
McDougal, Nicola. "Solid-state NMR studies of structural proteins". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619667.
Testo completo
26
Nordon, Alison. "Solid-state NMR studies of inclusion compounds". Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4758/.
Testo completoAbstract (sommario):
The work contained within this thesis is a study of inclusion compounds using solid-state NMR. Such compounds typically exhibit static and/or dynamic disorder, which precludes the use of diffraction-based techniques to obtain detailed structural information. Hence, due to its ability to probe local environments, solid- state NMR can be used to provide information which would otherwise be inaccessible. However, the dynamic nature of the guest molecules within inclusion compounds can yield unusual results for routinely applied experiments, such as cross polarisation, heteronuclear dipolar decoupling and dipolar dephasing. Therefore, some of the more fundamental aspects of solid-state NMR have first been explored. The inclusion compounds of particular interest are those which contain urea or thiourea as the host species. The ordering of guest molecules and host dynamics have been investigated via both one- and two-dimensional (^13)C and (^1)H NMR experiments for the 2-hydroxyalkane/urea inclusion compounds. For the 1-fluorotetradecane/urea inclusion compound, an approach involving a combination of (^1)H→(^13)C and (^19)F→(^13)C cross-polarisation experiments, with both single-channel (^H) and double-channel decoupling ((^1)H,(^19)F) has been devised to assign (^13)C resonances and hence deduce guest ordering. Steady-state and transient (^19)F MAS NOE experiments have been used to probe the dynamics of the 1-fluorotetradecane/urea inclusion compound. Using the considerable sensitivity advantage of (^19)F NMR, over that of (^13)C, a detailed study of the conformational dynamics exhibited by fluorocyclohexane molecules included within thiourea has been performed via bandshape analysis, selective polarisation inversion and 2D exchange experiments. Intermolecular distance measurements have been determined for adjacent fluoroalkane molecules within urea tunnels using a series of static (^19)F NMR experiments. From the results obtained, conclusions regarding the mutual orientations of adjacent end-groups in such compounds have been made.
27
Avalle, Paolo. "Solid state NMR of tin containing compounds". Thesis, Durham University, 2001. http://etheses.dur.ac.uk/4382/.
Testo completoAbstract (sommario):
A recent development in chemical research has been concerned with molecular assemblies, and all manner of structural aggregates, leading to the relatively new area of supramolecular chemistry. The systems under study are organometallic ion exchangers where the structural motif is [(Me(_3)Sn(^IV))(_4)M(^II)(CN)(_6)]=(_oo) (M=Fe, Ru, Os...). These 3D cyanides are not simply molecular crystals, and their chemistry and topology are more reminiscent of inorganic solids. By replacing the bridging unit (Me(_3)Sn(^IV)) with guests such as (nPr)(_4)N(^+) and (nBu)(_4)N(^+), new 3D structures can be engineered, leading to new compounds. Tin units show unchanged trigonal bypyramidal coordination upon variation of metal (M), guest size, hindrance by the ligands. Changes in the metal affect mainly the isotropic and anisotropic (^119)Sn shielding parameters. The interplay of the electronic nature of the metal(s) and the bonding capacity of the ligands is studied by (^59)Co NMR. Quadrupolar coupling constants and asymmetry parameters show how the coordinative bond is sensitive to spatial reorganisation. Shielding calculations for the [Me(_3)Sn(CN)(_2)]’ model and for different X-ray structures have been performed to reproduce trends in chemical shift changes. Relativity effects have been omitted from the computations. This approach had four major aims: (a) to establish the extent to which (^119)Sn isotropic chemical shifts can be computed by DPT methods with acceptable basis sets for model molecular fragments relevant to four selected compounds; (b) the computation of the U^Sn isotropic chemical shifts for different coordination geometries of the CN ligands; (c) the attempt to correlate between computed and observed isotropic chemical shifts for four selected compounds; (d) to ascertain whether such a correlation can be used to establish the assignment of three experimental (^119)Sn shifts in a predictive fashion.
28
Merwin, Lawrence Hale. "NMR of solid phosphorus and nitrogen compounds". Thesis, Durham University, 1987. http://etheses.dur.ac.uk/1683/.
Testo completo
29
Goddard, Yanina Anatolievna. "Solid state NMR characterization of conductive polyanilines". W&M ScholarWorks, 2004. https://scholarworks.wm.edu/etd/1539623435.
Testo completoAbstract (sommario):
Different forms of ring deuterated polyaniline with different conductivity have been characterized by solid state deuteron nuclear magnetic resonance.;Quadrupole echo (QE) spectra of all forms of polyaniline consist of a superposition of lineshapes for nearly rigid aromatic rings and a small fraction of rings which undergo fast 180?? flips. The intensity of the fast flipping component is temperature dependent and different for conductive emeraldine salt (ES) and non-conductive emeraldine base (EB). This is a manifestation of the different structure and morphology of these polymers.;Simultaneous measurements of QE lineshapes and the relaxation time anisotropies allowed an accurate description of motion in polyanilines. Slow, small-angle libration in an asymmetric cone provided the best description for the "rigid" fractions of EB and ES. The broadening of deuteron QE lineshapes is consistent with the presence of a distribution of cone angles. Relaxation time measurements also reveal a relatively narrow distribution of librational rates for the EB sample. For ES, the magic angle spinning (MAS) spectra show the existence of two resolved signals with different relaxation rates, which are ascribed to microscopic domains with very different electrical properties. The unexpectedly short relaxation time found for nonconductive domains in ES can be explained by the presence of localized, unpaired electrons.;Spin count experiments proved that in highly conductive ES samples, loss of NMR signal intensity occurs not only because of high RF reflectance but also because of irreversible dephasing before signal acquisition due to interactions of nuclear spins with localized unpaired electrons.;Deuteron MAS spectra provided unique information about small frequency shifts. Compared to non-conductive EB, conductive emeraldine salts have an additional manifold of spinning sidebands, which is shifted ∼5.8 ppm towards higher frequencies. These shifted sidebands arise from quasi-metallic regions of the sample, where deuteron spins interact with delocalized electrons (Knight shift). The experimental temperature dependence of the intensity of the shifted peak can be explained using models developed for amorphous semiconductors. The observation of a Knight shift has an important consequence for the theory of electrical conduction in polyaniline: it implies that polarons are the charge carriers.
30
Laage, Ségolène. "High-resolution solid-state NMR for proteins". Lyon, Ecole normale supérieure, 2010. http://www.theses.fr/2010ENSL0583.
Testo completoAbstract (sommario):
La RMN a récemment prouvé son potentiel en biologie structurale. Cette thèse décrit les méthodes que nous avons développées pour l’étude de protéines par RMN du solide à haute résolution. Après une présentation des récents progrès du domaine, nous présentons les améliorations liées à l’utilisation de la rotation à l’angle magique à très haute vitesse, notamment les techniques de découplage hétéronucléaire et de polarisation croisée à basse puissance, appliquées aux cas de la Superoxide Dismutase (SOD) et de la protéine GB1. Nous détaillons ensuite les perspectives émergeant dans l’utilisation des couplages J, avec trois nouvelles séquences. La J-CHHC renseigne sur les distances entre protons, le bloc S3E améliore résolution et sensibilité en effectuant du découplage J, et l’INADEQUATE-S3E combine transfert de polarisation par couplage J et découplage J. Nous donnons enfin des perspectives de mesure de longues distances par l’exploitation des propriétés paramagnétiques de la Cu(II) SODSolid-state NMR recently proved its potential for structural biology. This thesis details metods we developed for high resolution NMR of nanocrystalline proteins. After an introductory presentation of the recent advances in solid-state NMR of bio-systems, we present the improvements we proposed in the ultra-fast magic-angle spinning regime, notably low-field heteronuclear decoupling and low-field cross-polarization. We demonstrate them with the study of the Superoxide Dismutase (SOD) and the protein GB1. We then focus on the perspectives arising for J-couplings in proteins by presenting three new sequences. The J-CHHC sequence probes 1H-1H distances encoded in 13C-13C correlation experiments. The S3E block improves resolution and sensitivity by performing J-decoupling, and the INADEQUATE-S3E combines J-based transfer of polarization and J-decoupling. We finally give perspectives to probe long-range structural constraints with data exploiting the paramagnetic properties of Cu(II)-SOD
31
Ferrara, Chiara. "Solid State NMR studies of functional oxides". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2014. http://tel.archives-ouvertes.fr/tel-00956577.
Testo completoAbstract (sommario):
The functional oxides are performing materials showing interestant properties. The study of the local environment respect to the average struvture is essential for the deep understanding of the correlations between structure and properties ; this investigation of short and medium range can be performed with the use of solid state NMR techniques. In particular in this thesis three different classes of materials for applications in fields of optic and energy are considered : perovskite structure LaSrAlO4, the melilite system LaSr(Ga/Al)3O7 and the family of orthosylicates Li2(Fe/Mn)SiO4.
32
Brown, Marco J. "Selective inversion in solid-state deuteron NMR". W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539623900.
Testo completoAbstract (sommario):
Deuteron NMR selective inversion (SI) is developed to study slow molecular motions in solids. Theoretical and practical aspects of selective inversion of spin-1 nuclei in solids are presented. Differences between powdered solids and liquids are considered. Double sideband modulated (DSBM) shaped pulses are shown to improve the performance of SI pulses. DSBM and DANTE selective pulses are compared for off-resonance SI applications. Common spin-{dollar}{lcub}1{rcub}\over{lcub}2{rcub}{dollar} shaped pulses are tested for suitability to solid state deuteron NMR. Simple, short pulses are shown to be most effective due to fast spin-spin relaxation and large underlying homogeneous linewidths in solids.;The power and utility of selective inversion is demonstrated by investigating the molecular dynamics of polycrystalline dimethylsulfone-{dollar}\rm d\sb6{dollar} (DMS). Quantitative information on the slow two-site jump motion in DMS is obtained. The complementary nature of selective inversion and quadrupolar echo lineshape (QELS) experiments is explored. Combination of QELS and SI extends the range of rates observed, increasing the accuracy of the information obtained. For DMS, motional rates were measured over a 80 K range (motional rates of {dollar}\rm 3\times 10\sp1{lcub}-{rcub}5\times 10\sp{lcub}4{rcub}\ s\sp{lcub}-1{rcub}),{dollar} permiting the barrier to slow rotation to be accurately characterized. SI was also used to observe the limiting homogeneous linewidth as a function of resonance offset and temperature. The temperature dependence of the homogeneous linewidth is shown to be sensitive to motion in the kilohertz range.;SI was used to quantify the molecular dynamics in some complex systems. SI and QELS experiments were performed on host urea-{dollar}d\sb4{dollar} in different urea inclusion compounds (UIC). Rotation rates about both the CO and CN bonds of urea-{dollar}d\sb4{dollar} in the UICs were determined as a function of temperature. Activation energies were obtained, and the results are discussed with respect to guest-host interactions in the UICs. Preliminary results are presented on quadrupolar echo lineshape simulations which include empirical, anisotropic homogeneous linewidth corrections. The modified simulations give significantly different best-fit motional rates than conventional QELS analysis. This allows some of the systematic errors of QELS analysis to be evaluated.;SI experiments were conducted, over a 125 K range, to study backbone motion in bisphenol-A polycarbonate. These experiments failed to detect the presence of any large angle slow motion of methyl groups in the isopropylidene moiety. This negative result suggests that cis-trans isomerization of the carbonate group is not the origin of the backbone motion.
33
Mitchell, Martin R. "Investigation of structure and disorder in inorganic solids using solid-state NMR". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3367.
Testo completoAbstract (sommario):
The use of solid-state NMR and DFT calculations to study Y₂Sn[subscript(x)]Ti[subscript(2-x)]O₇, Y₂Sn[subscript(x)]Zr[subscript(2-x)]O₇ and Y₂Ti[subscript(x)]Zr[subscript(2-x)]O₇, materials with applications for the safe encapsulation of radioactive actinides is investigated. As a result of cation or anion disorder in these materials, NMR spectra are often complex and difficult to interpret. Therefore, an investigation using a range of NMR active nuclei and measurement of a variety of NMR parameters (isotropic chemical shift, δ[subscript(iso)]; span, Ω and quadrupolar coupling, C[subscript(Q)]) were used to provide a full and detailed picture of each material. The measurement of Ω in these disordered compounds with multiple resonances in the NMR spectra, required the use of 2D CSA-amplified PASS (CAPASS) experiments to enable the separation of each of the spinning sideband manifolds. An experimental assessment of the CAPASS experiment showed that although low ν₁/Ω[subscript(Hz)] ratios (as found in ⁸⁹Y NMR) resulted in distortions in the spectra obtained, a modified fitting procedure could be utilised to compensate for this fact, which allowed the accurate measurement of Ω. Despite the difficulties in acquiring the ⁸⁹Y NMR spectra, they were found to be the most informative of the NMR-active nuclei available. ¹¹⁹Sn NMR spectra, although much easier to acquire than ⁸⁹Y, were more complex and harder to analyse, owing to the overlapping resonances. Therefore, ¹¹⁹Sn NMR could only be used to confirm or support the results obtained using ⁸⁹Y NMR. Although ¹⁷O NMR was found to be useful, a full study could not be implemented due to the lack of ¹⁷O enriched samples; an area where future investigation may prove fruitful. Finally, [superscript(47/49)]Ti and ⁹¹Zr NMR spectra were found to be the most difficult to acquire due to their low receptivities and the quadrupolar broadened lineshapes, and as a result, little additional information was obtained. As a result of this analysis, for the Y₂Sn[subscript(x)]Ti[subscript(2-x)]O₇ pyrochlore solid solution, using primarily ⁸⁹Y δ[subscript(iso)] and Ω, and additionally confirmed with ¹¹⁹Sn δ[subscript(iso)], it was found that the Sn and Ti cations were randomly ordered throughout the B-sites. Additionally, ⁸⁹Y Ω could be used to obtain approximate Y-O[subscript(48f)] and Y-O[subscript(8b)] bond lengths for each type of Y environment. The study of Y₂Sn[subscript(x)]Zr[subscript(2-x)]O₇ using ⁸⁹Y NMR showed that although the end members were single phase, pyrochlore (Y₂Sn₂O₇) or defect fluorite (Y₂Zr₂O₇), the intermediate compositions were mostly two phase mixtures, consisting of an ordered pyrochlore (with an average formula of Y₂Sn₁.₈Zr₀.₂O₇) and a disordered phase, where the proportions of the pyrochlore and disordered phases decreased and increased, respectively, with the Zr content. Additionally, although the coordination states of the Y and Sn cations were easily determined using ⁸⁹Y and ¹¹⁹Sn NMR, respectively, the coordination states of the Zr cations could not be confirmed directly by ⁹¹Zr NMR. However, using indirect analysis from results obtained with ⁸⁹Y and ¹¹⁹Sn NMR, it was determined that 6 coordinate Zr was present in each composition, and it was always present in a greater proportion than 8 coordinate Zr. Finally, although ⁸⁹Y NMR spectra of Y₂Ti[subscript(x)]Zr[subscript(2-x)]O₇ were extremely difficult to analyse, it was tentatively proposed that they could be similar to Y₂Sn[subscript(x)]Zr[subscript(2-x)]O₇ due to some similarities observed between the spectra.
34
Twyman, Jonathan Mark. "NMR studies of crystalline penicillins". Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330066.
Testo completo
35
Root, A. "NMR of phosphorus containing compounds". Thesis, University of East Anglia, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372798.
Testo completo
36
Iuga, Adriana. "Solid-state 31P NMR of nucleotide binding proteins". [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973225238.
Testo completo
37
Lim, Tang Kuan. "NMR studies of carbohydrates in the solid state". Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/27129.
Testo completoAbstract (sommario):
The work described herein entails the application of solid-state n.m.r. methods to both mono- and polysaccharide carbohydrates. Two major n.m.r. methods have been evaluated for studying these substances, namely, the carbon-13 cross-polarization-magic angle spinning method and the deuterium quadrupole echo method.
Heptakis-(2,6-di-O-methyl)- β-cyclodextrin and β-cyclodextrin peracetate were prepared and, together with α-and β-cyclodextrins as hosts, were used to encage a variety of organic guest molecules.
A number of metal sugar conjugates were prepared according to the procedures documented in this laboratory. Firstly, chelate coordination complexes were synthesized by forming salicylaldimine ligands derived from combinations of amino sugars (methyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-β-D-glucopyranoside or 1 , 3 , 4 , 6-tetra-O-acetyl-2-amino-2-deoxy-β-D-glucopyranose) and salicylaldehyde, with subsequent complexation of these to copper(II), zinc(ll), and cobalt(Il) ions. Similarly, chitosan Schiff's bases were prepared and complexed to copper(II) ion.
Application of the ¹³C-cross-polarization-magic angle spinning method in the spectral assignment of cyclodextrin inclusion complexes and metal sugar conjugates in the solid state has been demonstrated. In all cases, recourse to solution spectra was necessary for correct assignments of individual carbon resonances. The sugar resonances of cyclodextrins are relatively broad and are complicated by the substantial splittings. The rationales for such observations were drawn from comparative studies, based on closely related guest molecules. The smaller guest molecules were least affected by the cavity size of the host molecule heptakis-( 2 , 6-di-O-methyl) -β-cyclodextr in and the isotropic chemical shift values were similar to those measured for solutions. These values suggest that the guest molecules undergo anisotropic motion, which can be detected by the use of the dipolar dephasing technique. Studies of metal sugar conjugates by ¹³C n.m.r. revealed that paramagnetic ions have profound effects on the resolution obtained. The high concentrations of these ions result in broad featureless spectra. On the other hand, the diamagnetic ions proved to have little effect on the isotropic chemical shifts of the sugar chelates.
The deuterium quadrupole echo method has been used specifically to study the mobility of the guest molecules encaged in cyclodextrins. The "powder-type" spectra obtained were then compared with results reported in the literature in order to define the types of molecular motion.Science, Faculty of
Chemistry, Department of
Graduate
38
Feng, Xiaolong. "Estimating molecular conformations by solid-state NMR spectroscopy /". Stockholm : Eigenverl, 1998. http://www.gbv.de/dms/goettingen/265942721.pdf.
Testo completo
39
Simpson, W. Mark. "Solid state NMR studies of molecular crystalline materials". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362006.
Testo completo
40
Ball, Thomas James. "Development of new methods in solid-state NMR". Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/385/.
Testo completoAbstract (sommario):
Many chemically important nuclei are quadrupolar with half-integer spin (i.e., spin I = 1.5, 2.5, etc.) The presence of quadrupolar broadening for such nuclei can limit the information that may be extracted using NMR. MAS is able to remove first-order quadrupolar broadening but can only reduce the second-order contribution to the linewidth. The MQMAS and STMAS techniques have enabled high-resolution NMR spectra of half-integer quadrupolar nuclei in the solid state to be obtained by two-dimensional correlation under MAS conditions. Both of these experiments have several well-known limitations. One is that the conversion pulses in particular are very inefficient and the other is that the longer acquisition times required for two-dimensional experiments can be a limiting factor. Both of these disadvantages are addressed in this thesis. For the former case, existing composite pulse schemes designed to improve the efficiency of the conversion of multiple-quantum coherences are compared using 27Al and 87Rb MQMAS NMR of a series of crystalline and amorphous materials. In the latter case, a new experiment, named STARTMAS, is introduced that enables isotropic spectra of spin I = 1.5 spectra to be acquired in real time. The theoretical basis of the technique is explained and its applicability demonstrated using 23Na and 87Rb NMR of a wide range of solids. The nuclear Overhauser effect (NOE) is one of the most widely exploited phenomena in NMR and is now widely used for molecular structure determination in solution. NOEs in the solid state are rare and those to quadrupolar nuclei rarer still, this being due to the general absence of motion on the correct timescale and the usual efficiency of quadrupolar T1 relaxation, respectively. In this thesis, 11B{1H} transient NOE results are presented for a range of solid borane adducts. A comparison is made of the 11B NMR enhancements observed under MAS and static conditions and a rationale is proposed for the behaviour in the latter case.
41
Orr, Simon Timothy. "Multinuclear solid-state NMR of fuel cell materials". Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/35532/.
Testo completoAbstract (sommario):
This thesis describes the application of multinuclear solid-state NMR to three materials systems: first, components of polymer-based proton-exchange fuel cells including the fluoropolymer membranes (Chapter 4) and the precious metal supported catalysts (Chapter 5); secondly, the formation of a complex bismuth niobium aluminoborosilicate glass-ceramic with novel dielectric properties (Chapter 6); finally, platinum (II) dialkyldithiophosphates which belong to a class of compounds (metal dialkyldithiophosphates) some of which are used in mineral separation processing (Chapter 7). A full investigation into the effects of different conditions during sample preparation and 19F NMR experiments on fluoropolymer membranes recommended unmilled preparation, dry storage and magic angle spinning below 24 kHz for the study of structural differences between membranes. The application of 19F NMR to a range of commercial and experimental fluoropolymer membranes revealed that the equivalent weight does not affect the mobility of the polymer molecules such that can be detected by this technique. Calculations of equivalent weight from 19F NMR differed with quoted values by up to 14%. Discrepancies were smallest in the short sidechain polymers, as low as 3%. The assignment of spectra was invariant with sidechain structure apart from a change in the number of ester links. The presence or absence of oxygen affected chemical shielding even around nuclei separated by several bonds. Differences in 1H linewidths between membranes could not be interpreted without the control and comparison of manufacturing techniques. It is desirable to remove the necessity for organic solvents in membrane casting. However, membranes cast from aqueous solution do not possess the same properties as those from propanol. It had been proposed that rapid drying of water cast membranes would result in a structure more similar to those from organic solvent. 1H NMR revealed that the opposite is the case, rapid drying makes the ordinarily more inhomogeneous aqueous membranes even more so. The application of both 19F and 1H NMR revealed that the monomolecular layers of fluoropolymer deposited on the surface of fuel cell catalysts to aid proton conductivity are categorically different in nature to the same materials in the bulk state. 19F NMR suggests a polymer structure either more disordered, greatly less mobile or both. 1H NMR displayed water environments that could not be reconciled to the standard model of rapid exchange between bulk water and water associated with acid groups. Spectral differences caused by solvent and polymer loading were discussed. The first complete and quantitative Fourier transformed 195Pt NMR spectra of platinum fuel cell catalysts, acquired using a field sweeping method, are analysed for deviation from the cubooctohedral particle model and surface oxidation. A combination of 11B, 27Al and 29Si studies of the BN1 ceramic system after different temperature heat treatments confirmed much of the previous work on phase evolution. However, it was shown that kyanite does not make up a significant proportion of the material until heat treatment reaches 1000 ºC and that aluminium impurities in bismuthbiobate crystals appear to increase with treatment temperature. The nature and abundance of glassy phases in the system are explored for the first time. Field sweep 195Pt NMR was employed to characterise the 195Pt chemical shift anisotropy of five platinum (II) dialkyldithiophosphates complexes. Additionally the 31P chemical shift anisotropies of two of the complexes, previously unpublished are presented.
42
Bhattacharya, Prodipta. "Solid state NMR studies of ferroelectric relaxor materials". Thesis, University of Warwick, 2005. http://wrap.warwick.ac.uk/66666/.
Testo completoAbstract (sommario):
Multi-nuclear solid state nuclear magnetic resonance has been used to investigate the local atomic structure of the relaxor ferroelectric materials, lead magnesium niobate titanate (PMN-PT) and sodium potassium bismuth titanate (NKBT). In addition to these two series of materials, numerous precursor and model niobate compounds have also been analysed in order to gain a insight into the structures and phases present in these materials. The PMN-PT series was investigated using 93Nb, 207Pb and 170 NMR techniques. A total of 14 PMN-PT samples, from pure PMN to PMN-90PT, were investigated in order to fully understand the transitions taking place over the entire compositional range. 9~b proved to be the most informative nucleus, owing to its high sensitivity to the changes occurring at the B-site of the perovskite structure. We discovered three distinct niobium environments. We then proposed a new randomsite random-layer model explaining the distribution of the cations among two different layers ß' and ß". The high level of correlation between the theoretical predictions and the experimental results suggests that there are actually two different ways that PMN-PT behaves, one for titanium concentrations less than 25% and the other for concentrations over 25%. This was also clearly visible in our PMN-PT spectra, as a sharp line present in titanium concentrations below 25%, that disappears in the concentrations above 25%. We have also tied in our results with the existing literature on PMN-PT to identify possible links to the dielectric response and phase transitions in the material. NKBT was investigated using both 23Na and 39K MAS NMR techniques. The 23Na data proved most informative and results were obtained at different fields and different spinning speeds. We were then able to extract calculated isotropic chemical shift values and quadrupolar parameters to understand the subtle changes taking place. The preliminary results hint that there are some interesting changes taking place around the morphotropic phase boundary in the material.
43
Christopher, Elizabeth Anne. "Solid-state NMR study of polymorphism in pharmaceuticals". Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5752/.
Testo completoAbstract (sommario):
This thesis is concerned with attempts to establish solid-state NMR as a complementary technique to X-ray crystallography for providing information on crystal structure, i.e. information regarding conformation, packing and inter- or intra-molecular interactions. Methods of assigning the solid-state NMR spectrum have been used which rely upon (^1)H-(^13)C dipolar interactions and upon the shielding anisotropy experienced by the nuclei. Single pulse experiments have also been used to identify solvate molecules. Of particular importance, the anisotropy and asymmetry have been found for a number of steroids, and the values used to assign the high frequency region of the spectrum. This has enabled chemical shifts to be linked to the hydrogen bonds that are present. Thus, the mode of hydrogen bonding can be predicted in forms of cortisone acetate for which the crystal structure is not available. Chemical shifts have also been linked with the conformation of the D ring. In this way, important crystallographic information has been gleaned from the solid-state NMR spectrum. The effect of the formation of hydrogen bonds upon the shielding tensor components of carbonyl and ester carbons has been studied, and found to cause a high frequency shift in δ22, which is probably oriented along the C=0 bonds. This leads to a high frequency shift in the isotropic chemical shift. The effect of the spinning speed upon the centreband intensity of a peak as the anisotropy and asymmetry are varied has been investigated. It has been found that at low spiiming speeds, the centreband intensity does not vary in a simple fashion. Thus it is recommended that full shielding tensor analysis is performed. The effect of the spinning speed on the sample temperature has also been studied. Results show that at low spinning speeds (up to 2 kHz) there is sample cooling as the spinning speed increases (attributed to the Joule -Thompson effect). But at higher spinning speeds (above 2 kHz) then there is sample heating as the spinning speed increases. The importance of this result is discussed. The effect of quadrupolar nuclei (35C1 and (^14)N) upon the spectrum of a spin-(^1)(_2) nucleus ((^13)C) has been studied. In favourable cases, the anisotropy in the spin-spin coupling constant has been found, whilst in other cases, the sign and magnitude of the quadrupolar coupling constant have been obtained. The broadening of resonances of carbon atoms adjacent to quadrupolar nuclei has been valuable in assigning the solid-state NMR spectra. The broadening effect has also been observed at more distant sites. It has not been possible to distinguish the effects of (^37)C1 and (^35)C1 on the carbon spectra of chlorine containing steroids.
44
Gomez, Ruben. "Solid-state NMR studies of lithium nitrido-metallates". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430515.
Testo completo
45
Oliver, Sarah Louise. "Solid-state NMR studies of compatibilised polymer blends". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285638.
Testo completo
46
Ibbett, D. A. "A developmental system for solid state NMR imaging". Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380989.
Testo completo
47
Martin, David Richard. "Solid state deuterium NMR studies of some disaccharides". Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282274.
Testo completo
48
Cheng, Chi-Feng. "Solid-state NMR studies of mesoporous molecular sieves". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243004.
Testo completo
49
Vlachou, Maria C. "17O solid state NMR study of ceria systems". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/108288/.
Testo completoAbstract (sommario):
Ceria is a highly commercial, valuable material. Its diverse set of real-world applications demonstrates its far-reaching influence on modern society. Indeed, one only has to consider its extensive employment as an essential component of automotive, three-way catalysis (TWC) for reducing pollutants in vehicular exhaust gases; a technology that is used on a daily basis by millions of people, to appreciate its importance. Its popularity is partially due to its extraordinary oxygen storage capacity, i.e. its ability to release and store oxygen through redox reactions mediated by the two oxidation states of cerium (Ce3+/Ce4+). This unique ability can be heavily influenced by ceria’s particle size and shape, dopant concentration and surface chemistry, and is still a very active area of research today. Whilst there have been over 26,000 scientific publications on ceria since the 1950s, and although the bulk-ceria oxygen chemical shift (877 ppm) was first observed with 17O solid-state NMR in 1989, it is only within the past decade that solid-state NMR has been employed as a probe for ceria’s structure-function relationships. This study presents an extensive 17O solid-state NMR investigation into various ceria systems, in conjunction with complementary Raman spectroscopy (for which the literature is abundant). An alternative spectral assignment for the 17O NMR spectrum of nanoceria based on experimental deductions and DFT quantum mechanical calculations is proposed. The current working assignment for nanoceria is based on the work of Wang et al., where DFT calculations of a core-shell model are used to deconvolute the NMR data. In contrast to this model, it is suggested that the most upfield peak at δCG = 822 ppm (that is actually part of a multicomponent region centred at ~830 ppm), corresponds to oxygen species displaced from their standard sublattice positions, to occupy a Frenkel type defect site. The resonance regions observed at ~830 and 920 ppm are proposed to be bulk oxygen environments feeling the effects of the Frenkel defect and concomitant oxygen vacancy. For reduced ceria systems, a broad component is detected that spans > 1000 ppm, and is assigned to oxygen directly bonded to Ce3+, in agreement with the current working model. Finally, it is observed that the most deshielded peak at ~1030 ppm is multi-component and (one of these components) possesses an extensive spinning sideband manifold in comparison to the other 17O resonances. Variable temperature investigations show a small inverse temperature dependence of the peak positions, suggesting weak pseudocontact paramagnetic shifts are influencing the spectrum. In light of this, the peak at ~1030 ppm is assigned to oxygen in closer proximity to (but not directly bonded) to Ce3+, as is reported by current 27Al solid-state NMR studies of Ce3+ doped systems and as is reflected by the extensive sideband manifold. The novel 17O preparation treatments implemented in this work were engineered to probe oxygen environments near defects. Ceria’s defects are manipulated by exposure to certain temperature/atmospheric conditions, and when these replicate those of possible catalyst operating temperatures with 17O enriched gas, 17O is able to probe the distribution of oxygen in distinct sites that are important to the OSC process. A prereduction of ceria was therefore implemented, following 17O2 reoxidation to target these sites. This process was also able to identify a surface reorganization mechanism in which a low reoxidation temperature/ pressure of 17O2 is insufficient to reverse the onset of bulk oxygen diffusion induced by the reduction, an effect which is seen to be enhanced with the loading of Pd. Furthermore, the storage of these treated systems dictates the evolution of the 17O species, with an almost closed-system (to air) detecting the pathway of reoxidised oxygen species to more stable sites over time. Ceria zirconia systems are also investigated in this work. The 17O solid-state NMR spectra show an even greater sensitivity to the 17O2 enrichment conditions. The pre-reduction of the systems induces a greater oxygen removal compared to pure ceria, and thus an increase in Ce3+ paramagnetic centres, i.e. the broad component (> 1000 ppm) characterising the oxygen-Ce3+ bond reveals a greater relative intensity. The complication of increasing Ce3+ paramagnetic centres near the 17O adsorption sites is evidenced by the significant loss in 17O spectral resolution. These effects are exacerbated when ceria zirconia is supported with Pd, known to (stably) reduce the state of the system even further. A straight exchange of the 17O isotope in ceria zirconia helps to inhibit these effects, allowing observation of (1) the chemical shift of the bulk-ceria oxygen move to a more shielded position compared to the pure ceria material at 877 ppm (caused by the inherent contraction of the ceria zirconia lattice), and (2) a broad resonance at ~730 ppm, attributed to oxygen species bridging cerium and zirconium.
50
Lansing, Jonathan C. (Jonathan Clifford) 1974. "Solid-state NMR investigations of the bacteriorhodopsin photocycle". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8050.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2002.Vita.
Includes bibliographical references.
Bacteriorhodopsin (bR) is a heptahelical integral membrane protein with a retinylidene prosthetic group from H. salinarum. The protein creates a proton gradient across the cell membrane by harvesting light energy. Proton transfer events can be segregated into transfers between the Schiff base of the chromophore and the cytoplasmic and extracellular half-channels. Critical to pump function is the switch in accessibility between the two half-channels. Models of the accessibility switch invoke protein or chromophore structural changes. This thesis describes the application of solid-state Nuclear Magnetic Resonance (NMR) to investigate each of the competing models in the native purple membrane environment. Conformational changes of the chromophore have been characterized by correlation of 13C-1H and 5N-1H dipolar interactions to determine chromophore dihedral angles in multiple photocycle intermediates. The resting state of the protein is found to contain a pre-loaded chromophore, with distortion about the Schiff base linkage and the neighboring C15-C14 bond. Changes of the dihedral about the C15-C14 were characterized during the photocycle, although the timing of the changes precludes their direct involvement in the accessibility switch. Putative protein conformation changes at the X-Pro peptide bonds were probed via the peptide 1 N and 13C chemical shifts. Proposed roles of the X-Pro bonds discriminate between structural and dynamic roles during the photocycle.
(cont.) Analysis of the three membrane-embedded X-Pro bonds indicates only slight differences between the resting state of the protein and the two species with a deprotonated chromophore, indicating that the buried prolines serve a principally structural role. General application of the proton-dependent dihedral angle measurement techniques to protein structure determination is hampered at sites with methylene carbons due to the pair of directly bonded protons. A general method is described for the preparation of stereoselectively deuterated glycine, which can be subsequently incorporated into peptides and proteins. This stereoselectively labeled glycine is expected to enable more precise determination of protein secondary structure.
by Jonathan C. Lansing.
Ph.D.