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Solid state NMR: Theoretical and experimental investigations

Paolo Rossi, University of Nebraska - Lincoln

Abstract

Solid-state NMR is a valuable tool for structural studies since it provides the means to acquire spectra that correspond to single conformations, in contrast to the conformational averages seen by solution NMR methods. In this thesis, the observables NMR properties are correlated to structure and dynamics of molecules in the solid state. The chemical shift and quadrupolar interactions are measured and calculated for the 13C, the 2H, and the 207Pb nuclei in a variety of biological and inorganic systems. ^ A correlation between the isotropic 13C chemical shift and the conformation is found in RNA nucleotides and nucleosides. The distinct effects of sugar puckering on the C1, C4, and C5 resonances of C2 endo (S type) and C3 endo (N type) furanoid conformations allow us to separate them into two groups. Further analysis of each group reveals an additional dependence of the C1 and C5 resonances on the glycosidic and C4 - C5 exocyclic torsion angles respectively. ^ The asymmetry parameters and quadrupole coupling constants of the H-bonded deuteron in sodium hydrogen bis(4-nitrophenoxide) dihydrate are analyzed as a function of temperature. The electric field gradient of the strongly hydrogen-bonded deuteron is highly unusual, with a quadrupole coupling constant of less than 100 kHz over the range 213 K and 333 K. This anomalous decrease is attributed to a shortening of the O---O distance as the temperature of the crystal is lowered, resulting in a lengthening of the nominal O-D single bond. ^ Structural changes of PbZrO3 have been monitored using the 207Pb chemical shift. The two distinct lead sites show rather different behavior as a function of temperature. The less shielded lead maintains an almost constant asymmetry parameter η = 0.2 from 173 K to 503 K while the more shielded lead resonance becomes more axially symmetric as the temperature is raised going from η = 0.199 at 173K to η = 0 at 443 K. Powder pattern singularities remain distinct near the phase transitions, and the temperature dependence of the chemical shift tensor principal values remains continuous. That is evidence that a first order transition to a higher-symmetry phase is not present. ^

Subject Area

Chemistry, Physical

Recommended Citation

Rossi, Paolo, "Solid state NMR: Theoretical and experimental investigations" (2001). ETD collection for University of Nebraska - Lincoln. AAI3022659.
http://digitalcommons.unl.edu/dissertations/AAI3022659

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