High-pressure NMR spectroscopy in studies of the conformational composition of small molecules in supercritical carbon dioxide

Abstract

high-pressure NMR 2D NOESY supercritical fluid molecular structure conformers MD simulation A B S T R A C TAn experimental approach in conducting NMR measurements at supercritical parameters of state is discussed. A novel design of the high-pressure NMR cell was developed which allowed eliminating the field inhomogeneity and, thus, increasing the sensitivity of the experiment at the supercritical state.Analysis of the MD simulations and NMR data showed that two conformers of ibuprofen dominate in the solution in supercritical CO2 along the critical isochore 1.3 ρcr(CO2). Conformer populations calculated from MD simulations and from NMR spectra agree with each other

Refined high-pressure tube design for improved resolution in high-pressure NMR spectroscopy

“…While such material imperfections may not affect other analytical techniques, they lead to distortions and lower sensitivity in NMR spectra and, hence, should be avoided for optimal NMR signal. 19,28,29,32…”

“…smaller than the commercially available sapphire tubes leading to a reduction of signal-tonoise ratio (SNR). 15,[20][21][22]24,25,[27][28][29][30] Too short NMR tubes effectively prohibit their employment in benchtop NMR devices due to the compact magnet design and small opening. On the downside, the very high hardness of 9 on the Mohs hardness scale, with diamond being 10, and the brittle nature of sapphire make this material barely machinable.…”

“…While such material imperfections may not affect other analytical techniques, they lead to distortions and lower sensitivity in NMR spectra and, hence, should be avoided for optimal NMR signal. 19,28,29,32 In a recent publication, a simple and highly versatile HP system for benchtop NMR was introduced, which allows the examination of pressurized gases and their interactions with liquids and solids up to a pressure of 200 bar. 19 Despite the spectral distortions induced by the used HP sapphire NMR tube, this HP benchtop NMR setup combined with chemometrics could successfully quantify the composition of complex hydrocarbon gas mixtures with less than 0.5% disparities from dedicated gas chromatography (GC) analysis.…”

Nuclear Spin Relaxation of Longitudinal and Singlet Order in Liquid-CO2 Solutions

“…The use of CO 2 as a solvent in NMR is not new (Lamb et al, 1989;Bai et al, 1997;Gaemers et al, 1999;Gaemers and Elsevier, 2000;Yonker, 2000;Khodov et al, 2020) but our contribution is the first report in which the properties of this solvent are investigated in the context of enhancing the lifetime of long-lived spin order.…”

High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

“…It may, at times, be desirable to examine materials under conditions that are relatively harsh for NMR rotors. A number of efforts have successfully adapted liquid-state NMR technologies to conduct high-temperature, high-pressure NMR 4,5,6,7 ; however, commercial rotor caps used for solid-state MAS NMR may be expelled from the rotor at high pressures, causing significant damage to the equipment. Such effects may be compounded by examining a decomposition reaction that greatly increases the pressure in the sample holder.…”