CSSF-CLIP-HSQMBC: measurement of heteronuclear coupling constants in severely crowded spectral regions.

Aitor Moreno,Kine Østnes Hansen,Johan Isaksson

doi:10.1039/c9ra04118d

Abstract

A new pulse program development, a chemical shift selective filtration clean in-phase HSQMBC (CSSF-CLIP-HSQMBC), is presented for the user-friendly measurement of long-range heteronuclear coupling constants in severely crowded spectral regions. The introduction of the chemical shift selective filter makes the experiment extremely efficient at resolving overlapped multiplets and produces a clean selective CLIP-HSQMBC spectrum, in which the desired coupling constants can easily be measured as an extra proton–carbon splitting in f2. The pulse sequence is also provided as a real-time homonuclear decoupled version in which the heteronuclear coupling constant can be directly measured as the peak splitting in f2. The same principle is readily applicable to IPAP and AP versions of the same sequence as well as the optional TOCSY transfer, or in principle to any other selective heteronuclear experiment that relies on a clean 1H multiplet.

Highlights

Long-range heteronuclear scalar couplings contain important information about molecular relative con guration, structure identity and structural conformation.[1,2,3,4] The size of these couplings are in the same range as proton–proton scalar couplings, 0–15 Hz, but are generally more complicated to measure accurately
There is a large number of different pulse sequences available for the measurement of long range heteronuclear scalar couplings, mainly divided into TOCSY basedand HMBC/HSQMBC-based methods
We present a development that enables the measurement of long-range heteronuclear coupling constants in severely crowded spectral regions by using a chemical shi selective lter as means to eliminate any offresonance signals in the original CLIP-HSQMBC pulse sequence

Summary

Introduction

Long-range heteronuclear scalar couplings contain important information about molecular relative con guration, structure identity and structural conformation.[1,2,3,4] The size of these couplings are in the same range as proton–proton scalar couplings, 0–15 Hz, but are generally more complicated to measure accurately. In the case where there is no spectral overlap, a PSYCHE version of HSQMBC to achieve spectrum-wide homonuclear decoupling has been reported.[12] In order to achieve homodecoupling in the CSSF-CLIP-HSQMBC experiment, a version with real-time band-selective homodecoupling (bshd) during acquisition has been prepared.[13,14] We demonstrate that even though coupling constant measurement in the direct dimension of homodecoupled spectra can be treacherous, the heteronuclear coupling constants can be reliably measured directly as the splitting of the doublet in f2.

Results

Conclusion