40yrs CPMAS & 25yrs REDORSolid State Nuclear Magnetic Resonance

About

Authors
Hellmut Eckert
Year
2015
DOI
10.1016/j.ssnmr.2015.10.010
Subject
Nuclear and High Energy Physics / Instrumentation / Chemistry (all) / Radiation

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into the medium-range structure of matter. It was truly this techs timely research the former two contribution is followed by the article of Amoureux, presenting a

Contents lists available at ScienceDirect .el

M

Solid State Nuclear Magnetic Resonance 72 (2015) 1–3http://dx.doi.org/10.1016/j.ssnmr.2015.10.010nique that made biological solids and complex assemblies amenable to meaningful structural analysis by solid-state NMR, as documented by the many excellent publications from his lab during the past 25 years ([13–16], to cite just the most influential new dipolar recoupling technique for indirect detection of nuclear species (such as 14N) characterized by strong anisotropic broadening effects. The issue concludes with the three papers by Goldbourt, Cegelski, and Ren and Eckert, which are devoted to distance 0926-2040/& 2015 Published by Elsevier Inc.significant applications of this method was the measurement of specific internuclear distances between selectively labeled atomic positions in a molecule or polymer, providing fundamental insights papers focus on precise measurement and interpretation of the chemical shift tensor, while the new experiments by Hong rely on dipolar recoupling and spin diffusion for spectral editing. Herdipolar interactions under the high-resolution conditions afforded by MAS, using a dipolar re-coupling approach [12]. One of the most port on the use of various re-coupling approache assignments and editing purposes. To this end,sonance (REDOR), an ingenious method to measure heteronuclear The following group of papers by Dybowski, Gan, and Hong res to aid spectralthe group landed its next major coup: rotational echo double reto biological materials [9] and intact whole cells [10,11]. In 1989 Barnes, outlining the promising perspectives of thi field.Editorial 40 yrs CPMAS & 25 yrs REDOR

This year we commemorate 40 years of cross-polarizationmagic angle spinning (CPMAS)-NMR and 25 years of rotational echo double resonance (REDOR) spectroscopy, which arguably belong to the most frequently used solid state NMR experiments worldwide. Both of them were conceived and developed in

Professor Jacob (“Jake”) Schaefer's laboratories at the Monsanto

Company and at the Chemistry Department of Washington University and have become standard methods of solid state NMR structural analysis. To celebrate this event, we dedicate this Special

Issue of Solid State Nuclear Magnetic Resonance to Professor Schaefer honoring his outstanding contributions to NMR methodology, polymer science and structural biology and the tremendous impact his work has made upon solid state NMR research in essentially every laboratory all over the world.

Jake's research in nuclear magnetic resonance started out at the

Monsanto Company, St. Louis, with classical solution-state NMR analyses of polymer samples. One of his early contributions to NMR methodology was the introduction of quadrature phase cycling for artifact removal in FT-NMR spectroscopy [1], nowadays considered a matter of course in every NMR experiment. In the early seventies, he added high-resolution solid-state NMR to his experimental portfolio, using a home-built magic-angle spinning probe [2].

Dramatic signal improvements were observed by combining MAS with proton decoupling [3], and, further, by incorporating the “cross-polarization” method [4], into his NMR strategy. The combination of those three elements, averaging of the chemical shift anisotropy by MAS, resolution enhancement by proton decoupling, and signal enhancement by 1H–13C cross-relaxation led to the decisive breakthrough of CPMAS-NMR [5], opening up an entirely new field of scientific inquiry. The subsequent years were devoted to refining the methodology (including sideband suppression [6] and double-cross-polarization [7]) and developing a wide range of applications for structural and dynamic analysis of polymers [8] and organic solids of great diversity, including the first applications journal homepage: www

Solid State Nuclearones). To the present date, Jake's research agenda has been devoted to developing ever more creative applications of REDOR and related techniques to increasingly challenging materials and chemical physics problems, both in structural biology and polymer science.

The 16 contributions assembled in this Special Issue document eloquently the enormous influence of Jake's work upon contemporary solid state NMR research. The first three contributions deal with important innovations regarding the CPMAS experiment itself. These include (a) a more accurate measurement of spinning speeds (Gullion), optimum conditions for cross-polarizing samples under ultra-fast MAS (Ishii), and an insightful discussion of radiofrequency inhomogeneity effects on CPMAS performance (Polenova and A.J. Vega). These contributions are followed by a number of articles dealing with the characterization of structural and dynamic order/disorder effects in amorphous copolymers. This topic has been one of the long standing interests of the Schaefer group, with numerous widely cited and influential publications on dynamics [8] and chain packing [17–19] in amorphous materials. In this context, the article by Afeworki presents new 13C NMR results on structural ordering in stretched polyethylene films while the contribution by Tekely introduces a new constant-time CPMAS experiment for characterizing motional dynamics. An alternative approach for the study of dynamic heterogeneities is described by

Saalwächter, who have used low-resolution spin diffusion measurements for spectral editing based on motional dynamics in nano-heterogeneous copolymers. Structural and/or dynamic disorder at surfaces and interfaces are the subject of the contributions of Schmidt-Rohr (catalytic systems) and Buntkowsky (inorganic-organic hybrids). The latter study makes also use of dynamic nuclear polarization (DNP)- enhanced CPMAS-NMR, a field in which the

Schaefer group had also done some early pioneering work [20].