Small Molecule Mixture Analysis by Heteronuclear NMR under Spin Diffusion Conditions in Viscous DMSO-Water Solvent

Spin diffusion in NMR occurs for small- and medium-sized molecules when their tumbling rate reduces in solution so that magnetization exchange by longitudinal cross relaxation becomes highly efficient. Composite DMSO-water viscous solvents were used for the first time to access the individual NMR spectra of a mixture components in spin diffusion conditions. The easy handling and high dissolution power of [D-6]DMSO/H2O offers a wide range of potential applications for polar and moderately apolar mixture analysis. In addition to 2D H-1-H-1 NOESY and H-1-C-13 HSQC-NOESY, H-1-N-15 HSQC-NOESY, 1D and 2D H-1-F-19 heteronuclear NOESY (HOESY) experiments were set up to offer new ways to individualize molecules within a mixture. This article reports the analysis of a polar mixture of four dipeptides dissolved in [D-6]DMSO/H2O (7:3 v/v) and that of a medium-polarity fluorinated dinucleotide dissolved in [D-6]DMSO/H2O (8:2 v/v) by means of spin diffusion in NOESY, HOESY, and HSQC-NOESY experiments.