Deuterium NMR in Chiral Polymer-Based Bimesophasic Lyotropic Mixtures: From the Demixing Process to Analytical Applications

Abstract

Among the order-sensitive (anisotropic) nuclear magnetic resonance (NMR) interactions, the residual ²H quadrupolar couplings measured at the level of natural abundance or on deuterated compounds dissolved in (chiral) oriented solvents, is a unique and relevant source of molecular information (isotopy, chirality, structure, configuration, etc.). Until now, the aligned media used as NMR solvents (lyotropic or not) have generally been monophasic, although isotropic-anisotropic biphasic systems have recently been exploited. As a promising possibility, herein, the potential of lyotropic bimesophasic samples is examined based on a mixture of immiscible helical polymers, which result in two demixed chiral nematic domains (stable over time), each with its own orientation properties. The extraction of two independent and nonlinearly related sets of anisotropic NMR data is achieved with spatially resolved ²H nD experiments. First applied to small achiral, prochiral and chiral deuterated compounds, the approach is extended to investigate nonenriched molecules by natural abundance deuterium 2D NMR. Here lyotropic bimesophasic chiral systems combining a polypeptide (PBLG) and a polyacetylene polymer (PLA or l-MSP) in organic solvents are examined in depth, in relation with several applications. The dynamic behavior of these systems (polymer demixing and exchange process) is studied by analyzing ²H EXSY, ²H relaxation and ²H DOSY data.