Mixture Analysis in Viscous Solvents by NMR Spin Diffusion Spectroscopy: ViscY. Application to High- and Low-Polarity Organic Compounds Dissolved in Sulfolane/Water and Sulfolane/DMSO-d6 Blends.

The sulfolane/water and sulfolane/DMSO-d6 binary NMR solvents are reported for the individualization of mixture components by spin diffusion when molecular tumbling is slow due to solvent viscosity, thus strongly favoring magnetization transfer by dipolar cross-relaxation. All 1H nuclei resonances within the same molecule tend then to correlate in a 2D NOESY spectrum, opening the way to mixture analysis. Till now, analysis of organic compounds by NMR spin diffusion in viscous solvents involved 1H, 13C, 15N, and 19F. We offer a new way to analyze mixtures by considering 31P nuclei as chemical shift markers. We report the individualization of four polar dipeptides and of four nonpolar phosphorus-containing compounds respectively dissolved in sulfolane/water and sulfolane/DMSO-d6 solvents blends by means of homonuclear selective 1D and 2D 1H experiments and a heteronuclear 2D 1H-31P HSQC-NOESY experiment by taking advantage from spin diffusion. The name ViscY is proposed to refer to the class of all NMR spectroscopy experiments that rely on viscous solvents for mixture analysis.