Clean pure shift 2D J‐resolved spectroscopy

Abstract

2D J-resolved spectroscopy is one of the oldest and conceptually most elegant ways to separate homonuclear scalar couplings from chemical shift information. In practice, the classical experiment suffers from a number of complications that limits accuracy and resolution, including phasetwist lineshapes, strong coupling artifacts, and the need for shearing the spectrum by 45° to obtain a (J,δ)-representation. Here, a novel pure shift 2DJ experiment based on the TSE-PSYCHE experiment is reported that deals with all these issues. Previous experiments proposed z-filtration to avoid excessive artifacts caused by chunked pure shift acquisition. It will be shown that these artifacts can also easily be avoided by means of the Pell-Keeler method. As opposed to its z-filtered counterparts, the new experiment provides pure shift 2DJ spectra that are free of artifacts from pulse imperfections and minimize responses related to strong coupling. In this way, multiplet analysis becomes possible at maximal resolution and a minimum of spectral complications.

Selective diffusion spectroscopy using excitation sculpting

“…The upper part is the complete spectrum, while the lower shows a 20‐fold vertical enlargement to show the solute resonances. The solute resonances are approximately the same amplitude as theC satellites of the solvent and have half‐height linewidths of approximately 2.7 Hz. The solvent resonances are significantly broader, probably owing to radiation damping.…”

“…The selective inversion pulse was applied simultaneously to the methyl group, one phenyl methine, one triazole methine of difenoconazole (one of the two active ingredients present) and one unidentified singlet resonance at 3.3 ppm using a gaussian shape with a duration of 22 ms. Residual signal from the solvent is barely visible in the spectrum, although oneC satellite of dimethylactamide was not suppressed owing to its proximity to the difenoconazole methyl group.…”

“…A more broadly applicable solution, however, is to use suppression methods to reduce the intensity of the intense resonances from the major species. For example, radiofrequency presaturation (which can be applied at multiple frequencies) or combinations of selective pulse and PFG such as WATERGATE or Excitation Sculpting . In these methods, a non‐selective inversion pulse is combined with selective inversion pulses on solvents resonances so that they experience no net inversion.…”

“…PFG pulses surrounding the pulses then dephase solvent resonances, but rephase resonances of interest. Because these methods rely on PFG for suppression and for diffusion encoding, PFG ratios have to be chosen carefully to avoid accidental rephasing of intense resonances …”

“…This will only be a small fraction of the magnetization if radiofrequency pulses are moderately accurately calibrated and can anyway be suppressed by a two‐step phase‐cycle. Therefore, a trivial modification to the originally proposed excitation sculpting sequence gives rise to a convection compensated diffusion spectroscopy experiment, and the attenuation of signal will be given by: where Δ is the diffusion delay, δ is the gradient duration, g is the gradient intensity, D is the diffusion coefficient, γ is the gyromagnetic ratio and S 0 is the intensity in the absence of any gradient (Fig. ).…”