title: Accurate NMR determination of C-H or N-H distances for unlabeled molecules.
abstract: Cross-Polarization with Variable Contact-time (CP-VC) is very efficient at ultra-fast MAS (νR ≥ 60 kHz) to measure accurately the dipolar interactions corresponding to C-H or N-H short distances, which are very useful for resonance assignment and for analysis of dynamics. Here, we demonstrate the CP-VC experiment with (1)H detection. In the case of C-H distances, we compare the CP-VC signals with direct ((13)C) and indirect ((1)H) detection and find that the latter allows a S/N gain of ca. 2.5, which means a gain of ca. 6 in experimental time. The main powerful characteristics of CP-VC methods are related to the ultra-fast spinning speed and to the fact that most of the time only the value of the dipolar peak separation has to be used to obtain the information. As a result, CP-VC methods are: (i) easy to set up and to use, and robust with respect to (ii) rf-inhomogeneity thus allowing the use of full rotor samples, (iii) rf mismatch, and (iv) offsets and chemical shift anisotropies. It must be noted that the CP-VC 2D method with indirect (1)H detection requires the proton resolution and is thus mainly applicable to small or perdeuterated molecules. We also show that an analysis of the dynamics can even be performed, with a reasonable experimental time, on unlabeled samples with (13)C or even (15)N natural abundance.
authors.affiliation: JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan; RIKEN CLST-JEOL Collaboration Center, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Nishiyama
authors.affiliation: JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan; RIKEN CLST-JEOL Collaboration Center, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Malon
authors.affiliation: Polish Academy of Sciences, Centre of Molecular and Macromolecular Studies, 90-363 Lodz, Poland.
authors.forename: M J
authors.initials: MJ
authors.lastname: Potrzebowski
authors.affiliation: Polish Academy of Sciences, Centre of Molecular and Macromolecular Studies, 90-363 Lodz, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Paluch
authors.affiliation: Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China; UCCS, University Lille North of France, Villeneuve d'Ascq 59652, France. Electronic address: jean-paul.amoureux@univ-lille1.fr.
authors.forename: J P
authors.initials: JP
authors.lastname: Amoureux
keywords: Distances; Dynamics; Natural abundance; Solid-state NMR