PRAWN: mixing sequences for selective heteronuclearjcross polarization

Abstract

In this work, we present a family of pulse sequences for selective heteronuclearJcross-polarization (JCP), which we have developed especially for indirect¹³C imaging usingJCP, for example in the CYCLCROP environment. The sequences are straightforward to implement and operate reliably. Results of an average Hamiltonian analysis are given for the basic sequence, which we term PRAWN (pulsed rotating frame transfer sequence with windows). It is shown experimentally that the pulse sequence, which operates efficiently with low RF duty cycles down to a few percent, has a useful tolerance range to absolute Hartmann-Hahn mismatch and generates coherence transfer spectra in close correspondence with theJCP average Hamiltonian. Computer simulation of the performance of the basic sequence on a heteronuclear spin½AX system is also presented. The mismatch compensation of PRAWN may be markedly enhanced further by issuing a ? pulse to each spin halfway through the basic PRAWN train and in phase quadrature to it. A simple analysis of this modified sequence, PRAWN-π, is given under conditions of mismatch and off-resonance irradiation.