NMR artifacts caused by decoupling of multiple-spin coherences: improved SLAP experiment

Abstract

Contrary to common expectations, multiple-spin coherences containing products of proton and heteronucleus operators (e.g. Hu Cx , u = x, y, z) can produce not only sidebands but also noticeable centerband NMR signals of the heteronucleus during acquisition under 1H broadband decoupling. Such centerband signals of low abundant heteronuclei can be sources of relatively strong unexpected artifacts in NMR experiments that aim to detect very weak signals from much less-abundant isotopomers, e.g. 13C-13C ones. These findings lead to a new design of Sign Labeled Polarization Transfer (SLAP) pulse sequence (MSS-SLAP) with improved suppression of centerband peaks that are because of singly, e.g. 13C, labeled molecules (parent peaks). The MSS-SLAP experiment and its MSS-BIRD-SLAP variant are compared with a few older SLAP versions.

Multiple solvent signal presaturation in <sup>13</sup>C NMR

“…Resonance saturation in NMR occurs when an RF field is continuously applied at a frequency equal to the resonance frequency of a nucleus. The magnetization dynamics of a collection of many identical isolated spins that constitutes a macroscopic sample is governed by the Bloch equations (Bloch, 1946). The components M x , M y , and M z of the macroscopic magnetization M , when observed in the rotating frame of reference, evolve as follows,…”

“…Miscalibration may cause decoupling artifacts around the intense solvent signals, at a point their intensity is comparable to the one of the signals of interest (Blechta and Schraml, 2015). Analytically misleading decoupling artifacts were observed during the analysis by 13 C NMR of chromatographic fractions containing glycerol.…”

Multiple solvent signal presaturation and decoupling artifact removal in <sup>13</sup>C{<sup>1</sup>H} nuclear magnetic resonance

“…The optimal power of the decoupling pulses depend on probe tuning quality and on the nature of the analytes. Decoupler power miscalibration may cause decoupling artifacts around the intense solvent signals, and at a point their intensity is comparable to the one of the signals of interest .…”