IPAP-HSQMBC: Measurement of long-range heteronuclear coupling constants from spin-state selective multiplets

A new NMR approach is proposed for the measurement of long-range heteronuclear coupling constants ((n)J(XH), n > 1) in natural abundance molecules. Two complementary in-phase (IP) and anti-phase (AP) data are separately recorded from a modified HSQMBC experiment and then added/subtracted to provide spin-state-selective alpha/beta-HSQMBC spectra. The magnitude of (n)J(XH) can be directly determined by simple analysis of the relative displacement between alpha- and beta-cross-peaks. The robustness of this IPAP-HSQMBC experiment is evaluated experimentally and by simulation using a variety of different conditions. Important aspects such as signal intensity dependence and presence of unwanted cross-talk effects are discussed and examples on the measurement of small proton-carbon ((n)J(CH)) and proton-nitrogen ((n)J(NH)) coupling constants are provided. (C) 2010 Elsevier Inc. All rights reserved.