Theoretical study of CP-VC: A simple, robust and accurate MAS NMR method for analysis of dipolar C–H interactions under rotation speeds faster than ca. 60kHz

• Published in: Journal of magnetic resonance (1997) Vol. 252; pp. 67 - 77
• Main Authors: Paluch, P., Trébosc, J., Nishiyama, Y., Potrzebowski, M.J., Malon, M., Amoureux, J.P.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.03.2015
• Subjects: Cross-Polarization; C–H distances; Dynamics; Ultra-fast MAS; C–H distances; Ultra-fast MAS; Dynamics; Cross-Polarization
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2015.01.002

Dipolar slices at δ13C=50ppm in CP-VC spectra of l-alanine, recorded versus resonance irradiation on 13C channel done at: 0 (a), 50 (b), 100 (c), and 150 (d) ppm. [Display omitted] •Robust method.•Quantitative C–H distance measurement.•Insensitive to: CSA, offsets, H–H mismatch, rf-inhomogeneity.•Requires ultra-fast MAS (νR⩾60kHz). We show that Cross-Polarization with Variable Contact-time (CP-VC) allows an accurate determination of C–H dipolar interactions, which permits an easy detailed analysis of bond lengths and local dynamics, e.g. in biomolecules. The method presents a large dipolar scaling factor of 1/√2, leading to a better determination of dipolar interactions, especially for long C–H distances, and it allows the observation of very small local details such as those related either to CH2 three spin systems, or even to hydrogen bonds. CP-VC is very simple to set up and very robust with respect to most experimental parameters, such as: rf-offsets, chemical-shift anisotropies, imperfect Hartmann–Hahn setting, and rf-inhomogeneity. The only required condition is the use of a sufficiently fast MAS spinning speed of at least ca. 60kHz.