Swept-frequency two-pulse phase modulation (SWf-TPPM) sequences with linear sweep profile for heteronuclear decoupling in solid-state NMR

Recently, a pulse scheme for heteronuclear spin decoupling in solid-state NMR, called swept-frequency two-pulse phase modulation (SW(f)-TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency-sweep profile can be varied to achieve optimal efficiency for crystalline and liquid-crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SW(f)-TPPM sequences with tangential sweep profiles (SW(f) (tan)-TPPM) and linear sweep profiles (SW(f) (lin)-TPPM). Using the (13)CH(2) resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut-off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise.