Evolution of CPMAS under fast magic-angle-spinning at 100 kHz and beyond

This article describes recent trends of high-field solid-state NMR (SSNMR) experiments for small organic molecules and biomolecules using (13)C and (15)N CPMAS under ultra-fast MAS at a spinning speed (νR) of 80-100kHz. First, we illustrate major differences between a modern low-power RF scheme using UFMAS in an ultra-high field and a traditional CPMAS scheme using a moderate sample spinning in a lower field. Features and sensitivity advantage of a low-power RF scheme using UFMAS and a small sample coil are summarized for CPMAS-based experiments. Our 1D (13)C CPMAS experiments for uniformly (13)C- and (15)N-labeled alanine demonstrated that the sensitivity per given sample amount obtained at νR of 100kHz and a (1)H NMR frequency (νH) of 750.1MHz is ~10 fold higher than that of a traditional CPMAS experiment obtained at νR of 20kHz and νH of 400.2MHz. A comparison of different (1)H-decoupling schemes in CPMAS at νR of 100kHz for the same sample demonstrated that low-power WALTZ-16 decoupling unexpectedly displayed superior performance over traditional low-power schemes designed for SSNMR such as TPPM and XiX in a range of decoupling field strengths of 5-20kHz. Excellent (1)H decoupling performance of WALTZ-16 was confirmed on a protein microcrystal sample of GB1 at νR of 80kHz. We also discuss the feasibility of a SSNMR microanalysis of a GB1 protein sample in a scale of 1nmol to 80nmol by (1)H-detected 2D (15)N/(1)H SSNMR by a synergetic use of a high field, a low-power RF scheme, a paramagnetic-assisted condensed data collection (PACC), and UFMAS.