Optimal 2H rf Pulses and 2H-13C Cross-Polarization Methods for Solid-State 2H MAS NMR of Perdeuterated Proteins

We present a novel concept for if pulses and optimal control designed cross-polarization experiments for quadrupolar nuclei. The methods are demonstrated for H-2 CP-MAS and H-2 multiple-pulse NMR of perdeuterated proteins, for which sensitivity enhancements up to an order of magnitude are presented relative to commonly used approaches. The so-called RESPIRATION rf pulses combines the concept of short broad-band pulses with generation of pulses with large flip angles through distribution of the rf pulse over several rotor echoes. This lead to close-to-ideal rf pulses, facilitating implementation of experiments relying on the ability to realize high-performance 90 and 180 degrees pulses, as, for example, in refocused INEPT and double-to-single quantum coherence experiments, or just pulses that provide a true representation of the quadrupolar powder pattern to extract information about the structure or dynamics. The optimal control H-2 -> C-13 CP-MAS method demonstrates transfer efficiencies up to around 85% while being extremely robust toward rf inhomogeneity and resonance offsets.