Separating the coherence transfer from chemical shift evolution in high‐resolution pure shift COSY NMR

Abstract

Recent developments in data sampling and processing techniques have made it possible to acquire 2-dimensional NMR spectra of small molecules at digital resolutions in both dimensions approaching the intrinsic limitations of the equipment and sample on a realistic timescale. These developments offer the possibility of enormously increased effective resolution (peak dispersion) and the ability to effectively study samples where peak overlap was previously a limiting factor. Examples of such spectra have been produced for a number of 2-dimensional techniques including TOCSY and HSQC. In this paper, we investigate some of the problems in applying such techniques to COSY spectra and suggest a modification to the classic experiment that alleviates some of these problems.

Coherence transfer delay optimisation in PSYCOSY experiments

“…When interpreting the proton COSY spectrum of an unknown, we work on the assumption that the majority of observed intense correlations arise from comparatively large J-couplings (mostly 2 J and 3 J plus and occasionally 4 J). Our previous work [15] showed that for the PSYCOSY sequence (as for the CT-COSY sequence), this is not necessarily the case at all values of the coherence evolution time, t ce . We therefore wish to determine what value(s) of t ce will give PSYCOSY spectra strongly favouring correlations from comparatively large J-couplings over small ones.…”

“…In all these cases, the coupling was weak at the relevant magnetic field (14.1T), and no significant second-order coupling effects were observed. Spinach computations were carried out using the methodology described previously, [15] using values for chemical shifts and coupling constants measured from spectra.…”

“…Analytical estimates were obtained using the product operator formalism methods suggested by Rance et al [17] The numerical simulations were performed using the Fokker-Planck theory module of Spinach [18] as previously described [15] and included explicit time-domain propagation through saltire pulses [16] for spin systems with explicit spatial discretisation to enable accurate treatment of spin dynamics in the presence of magnetic field gradients. Efficient parallelisation was achieved by simulating different indirect dimension slices of a two-dimensional free induction decay on different workers of the Matlab parallel pool.…”

“…[13,14] We recently proposed a COSY sequence (PSYCOSY) in which pure shift evolution in f1 is achieved using the same technique as used in the one-dimensional PSYCHE experiment. [15] The PSYCOSY pulse sequence is reproduced in Supporting Information. Because homonuclear J-coupling is refocused by the PSYCHE element in t1, there is effectively no coherence evolution during this period as a function of t1.…”

Metabolomics analysis of herb-partitioned moxibustion treatment on rats with diarrhea-predominant irritable bowel syndrome

“…Each spectrum was referenced to TSP at δ 0.00 and peaks were aligned manually to overcome peak-shift problem [23]. With the aid of 2D NMR spectroscopy including 1 H-1 H correlation spectroscopy (COSY) [24], 1 H J-Resolved and 1 H- 13 C heteronuclear single quantum correlation (HSQC) together with previous literatures [25], the major peaks in spectra were identified and assigned to specific metabolites.…”