“One-Shot” Measurement of Residual Chemical Shift Anisotropy Using Poly-γ-benzyl-l-glutamate as an Alignment Medium

Abstract

A method for the measurement of residual chemical shift anisotropy in one experiment using a biphasic isotropic/anisotropic lyotropic liquid crystalline medium based on poly-γ-benzyl-l-glutamate as the alignment medium is presented. This approach is demonstrated on the model compound strychnine and neotricone, a depsidone natural product with a questionable structural assignment based on comparison with the closely related excelsione and in-depth density functional theory calculations.

Residual‐Chemical‐Shift‐Anisotropy‐Based Enantiodifferentiation in Lyotropic Liquid Crystalline Phases Based on Helically Chiral Polyacetylenes

“…In essence, the sample contains two well separated phases: one with the PLA concentration below and the other with a polymer concentration well above the critical concentration (Figure S1 in supplement). As reported in similar findings for PBLG liquid crystal [25] and gel, [7b] this observation leads to the fact that RCSAs are measurable from a single 1D 13 CÀ { 1 H} spectrum provided both isotropic and anisotropic signals are present with sufficient signal-to-noise ratios and chemical shift separation. As expected, Figure 1b shows that the 1D 13 CÀ { 1 H} spectrum contains two sets of signals for each carbon resonance.…”

“…[13b] Biphasic behaviour of liquid crystals of PBLG was observed previously and used to measure 13 C RCSAs in a single carbon NMR experiment for configuration determination problems. [25] Given the fact that this biphasic behaviour also occurs for polyacetylenes, we expected that the simultaneous determination of isotropic and anisotropic data should be possible with the polyacetylenes as well. The enantiodiscriminating properties of a polyacetylene liquid crystal bearing valine-derived sidechains (PLA) has been already studied for eleven different analytes belonging to five different compound classes including hydrocarbons by comparing experimentally distinguishable RDC values as well as intertensor angles between the RDC-derived alignment tensors.…”

Single experiment measurement of residual dipolar couplings in aqueous solution using a biphasic bisperylene imide chromonic liquid crystal

“…During the submission process of this work, Martin and Wiliamson presented a similar concept successfully applied to the measurement of RCSAs using the organic solvent compatible PBLG aligning medium. [ 51 ] No doubt, the stronger aligning power of PBLG as compared to our BPI system allowed for the successful extraction of RCSAs in their case. Other aqueous compatible chromonic systems, which could be better suited for RCSA extraction, are being investigated in our laboratory.…”

Self‐Assembly of Helical Polymers and Oligomers to Create Liquid Crystalline Alignment for Anisotropic NMR Parameters

“…[ 26 ] Interestingly, a similar biphasic isotropic/anisotropic lyotropic LC medium has been also innovated for RDCs and RCSAs, respectively. [ 27 ] After submission of this Mini‐Review similar results have also been published using the annealed valine (Val) derived PPI as enantiodifferentiating alignment media. Despite the identical absolute configuration of the sidechain stereogenic centers, after thermal annealing, the L‐Ala derived PPI forms a left‐handed whereas the polyisocyanide with L‐Val derived sidechain forms a right‐handed helix.…”