Solid state NMR: Methodology development and applications to novel systems

Abstract

Solid state NMR has been proven to be an efficient probe of structure and dynamics of molecules because the properties measured by NMR, such as chemical shifts and quadrupolar interactions, provide extensive information.

Resolved chemical shift spectra are obtained from nearest-neighbor perturbed nuclei in solid solutions for ²⁰⁷Pb nuclei in lead/strontium titanates. The analysis of the intensities of the lead resonances using Monte-Carlo/Metropolis calculations suggest that cations are clustered along the lattice axis directions and anti-clustered along diagonals.

The vibrational modes of the very strongly hydrogen bonded molecule, one of the shortest O-H...O hydrogen bond system, 4-cyano-2,2,6,6-tetramethyl-3,5-heptanedione and its isotopomers were studied by infrared spectroscopy and inelastic neutron scattering spectroscopy. Ab initio calculations revealed that a low barrier double well potential accounts for the low first vibrational frequency, which is consistent with the NMR temperature dependence results we found. A systematic study of a series of very short hydrogen bonded molecules was performed by variable-temperature ²H NMR, proving that NMR temperature dependence can be diagnostic of low-barrier hydrogen bonds.

Nitromalonamide is remarkable in that it possesses one of the shortest known intramolecular O-H...O hydrogen bonds. Using a combination of kinetic solution and solid-state NMR measurements, here we show that the compound also has a rich solution chemistry, with the amide and imidic acid tautomers interconverting on a time scale of seconds at room temperature.

The 2H quadrupole coupling tensors of the N2-D,N3-D, -ND₃ ⁺ and D₂O residues in a single crystal of L-histidine hydrochloride monohydrate-d₇. Although N2-D and N3-D are both in a typical imidazole ring, not only the magnitude but also the orientation of the principal values of the ²H quadrupole coupling tensors are quite different. The characterization of the effects of the strong internal hydrogen bond involving N2-D, which causes these differences, complements our studies on other strong hydrogen bonded systems.