Decoherence optimized tilted-angle cross polarization: A novel concept for sensitivity-enhanced solid-state NMR using ultra-fast magic angle spinning

Abstract

Ultra-fast magic-angle spinning (UFMAS) at a MAS rate (ω_R/2π) of 60 kHz or higher has dramatically improved the resolution and sensitivity of solid-state NMR (SSNMR). However, limited polarization transfer efficiency using cross-polarization (CP) between ¹H and rare spins such as ¹³C still restricts the sensitivity and multi-dimensional applications of SSNMR using UFMAS. We propose a novel approach, which we call decoherence-optimized tilted-angle CP (DOTA CP), to improve CP efficiency with prolonged lifetime of ¹H coherence in the spin-locked condition and efficient band-selective polarization transfer by incorporating off-resonance irradiation to ¹H spins. ¹³C CP-MAS at ω_R/2π of 70-90 kHz suggested that DOTA CP notably outperformed traditional adiabatic CP, a de-facto-standard CP scheme over the past decade, in sensitivity for the aliphatic-region spectra of ¹³C-labeled GB1 protein and N-formyl-Met-Leu-Phe samples by up to 1.4- and 1.2-fold, respectively. ¹H-detected 2D ¹H/¹³C SSNMR for the GB1 sample indicated the effectiveness of this approach in various multidimensional applications.

Keywords: (1)H-detected solid-state NMR; Biomolecular NMR; CP; Multi-dimensional solid-state NMR; Solid state NMR; Ultra-fast MAS.