David D. Laws

Solid-state NMR spectroscopic methods in chemistry

Over the last decades, NMR spectroscopy has grown into an indispensable tool for chemical analysis, structure determination, and the study of dynamics in organic, inorganic, and biological systems. It is commonly used for a wide range of applications from the characterization of synthetic products to the study of molecular structures of systems such as catalysts, polymers, and proteins. Although most NMR experiments are performed on liquid-state samples, solid-state NMR is rapidly emerging as a powerful method for the study of solid samples and materials. This Review outlines some of the developments of solid-state NMR spectroscopy, including techniques such as cross-polarization, magic-angle spinning, multiple-pulse sequences, homo- and heteronuclear decoupling and recoupling techniques, multiple-quantum spectroscopy, and dynamic angle spinning, as well as their applications to structure determination. Modern solid-state NMR spectroscopic techniques not only produce spectra with a resolution close to that of liquid-state spectra, but also capitalize on anisotropic interactions, which are often unavailable for liquid samples. With this background, the future of solid-state NMR spectroscopy in chemistry appears to be promising, indeed.

Solid-state NMR studies of the secondary structure of a mutant prion protein fragment of 55 residues that induces neurodegeneration

The secondary structure of a 55-residue fragment of the mouse prion protein, MoPrP(89–143), was studied in randomly aggregated (dried from water) and fibrillar (precipitated from water/acetonitrile) forms by 13C solid-state NMR. Recent studies have shown that the fibrillar form of the P101L mutant of MoPrP(89–143) is capable of inducing prion disease in transgenic mice, whereas unaggregated or randomly aggregated samples do not provoke disease. Through analysis of 13C chemical shifts, we have determined that both wild-type and mutant sequence MoPrP(89–143) form a mixture of β-sheet and α-helical conformations in the randomly aggregated state although the β-sheet content in MoPrP(89–143, P101L) is significantly higher than in the wild-type peptide. In a fibrillar state, MoPrP(89–143, P101L) is completely converted into β-sheet, suggesting that the formation of a specific β-sheet structure may be required for the peptide to induce disease. Studies of an analogous peptide from Syrian hamster PrP verify that sequence alterations in residues 101–117 affect the conformation of aggregated forms of the peptides.

NMR chemical shifts and structure refinement in proteins

SummaryComputation of the 13Cα chemical shifts (or shieldings) of glycine, alanine and valine residues in bovine and Drosophila calmodulins and Staphylococcal nuclease, and comparison with experimental values, is reported using a gauge-including atomic orbital quantum-chemical approach. The full ≈24 ppm shielding range is reproduced (overall r.m.s.d.=1.4 ppm) using ‘optimized’ protein structures, corrected for bond-length/bond-angle errors, and rovibrational effects.

NMR of supercritical laser-polarized xenon

Abstract The feasibility of producing supercritical laser-polarized xenon for nuclear magnetic resonance (NMR) investigations was studied. Using a high-pressure capillary tube, a supercritical xenon sample (52°C, 65 atm) was produced with a 129 Xe polarization approximately 140 times the equilibrium value. The polarization was observed to last for hundreds of seconds, in agreement with previous studies. These preliminary results suggest that supercritical laser-polarized xenon may be used as a polarizing solvent for numerous NMR applications.

Methoden der Festkrper-NMR-Spektroskopie in der Chemie

In den vergangenen Jahrzehnten hat sich die NMR-Spektroskopie zu einem unverzichtbaren Werkzeug fur die chemische Analyse, Strukturaufklarung und Untersuchung dynamischer Prozesse in organischen, anorganischen und biologischen Systemen entwickelt. Sie ist die Methode der Wahl fur eine Vielzahl von Anwendungen, von der Charakterisierung von Syntheseprodukten bis hin zur Untersuchung der molekularen Struktur von Katalysatoren, Polymeren und Proteinen. Speziell die NMR-Spektroskopie an Festkorpern hat sich dabei zu einer leistungsfahigen Methode zur Untersuchung fester Proben und Materialien entwickelt. Dieser Aufsatz beschreibt einige der Konzepte und Methoden der Festkorper-NMR-Spektroskopie wie Kreuzpolarisation, Magic-Angle-Spinning, Multipulssequenzen, homo- und heteronucleare Ent- und Wiedereinkopplung, Mehrquantenspektroskopie und Dynamic-Angle-Spinning sowie deren Anwendung in der Strukturaufklarung. Moderne Festkorper-NMR-Techniken ermoglichen nicht nur die Aufnahme von Spektren mit „flussigkeitsahnlicher“ Auflosung, sie nutzen daruber hinaus anisotrope Wechselwirkungen, die bei Proben in flussiger Phase nicht zur Verfugung stehen. Vor diesem Hintergrund soll hier die gegenwartige und zukunftige Bedeutung der Festkorper-NMR-Spektroskopie fur die Chemie unterstrichen werden.