Enantiomeric analysis in a polypeptide lyotropic liquid crystal by deuterium NMR

2H NMR Studies on Two‐Homopolypeptide Lyotropic Enantiodiscriminating Mesophases: Experimental Quantification of Solute–Fiber Affinities

“…[1][2][3] These lyotropic chiral oriented media are formed by organic solutions of polypeptide helices oriented with their long axes parallel to the static magnetic field B o of the NMR magnet (mesophase of positive magnetic susceptibility anisotropy Dc m ). Hitherto, the best enantiorecognition was obtained with poly-g-benzyl-l-glutamate (PBLG), in which the side chain is À A C H T U N G T R E N N U N G (CH 2 ) 2 CO 2 CH 2 C 6 H 5 .…”

“…Hitherto, the best enantiorecognition was obtained with poly-g-benzyl-l-glutamate (PBLG), in which the side chain is À A C H T U N G T R E N N U N G (CH 2 ) 2 CO 2 CH 2 C 6 H 5 . [1][2][3] When no spectral discrimination occurs in PBLG solutions, other polypeptides such as poly-e-carbobenzyloxy-l-lysine (PCBLL) and poly-g-ethyl-l-glutamate (PELG), in which lateral chains are ÀA C H T U N G T R E N N U N G (CH 2 ) 4 NHCO 2 CH 2 C 6 H 5 and À A C H T U N G T R E N N U N G (CH 2 ) 2 CO 2 -CH 2 CH 3 , respectively, can provide excellent results due to the chemical differences in the side chain. [4,5] The key point for NMR in polypeptide CLCs is the ability of these mesophases to interact differently with enantiomers or enantiotopic directions in prochiral molecules, and to orient them on average differently relative to B o .…”

“…[4,5] The key point for NMR in polypeptide CLCs is the ability of these mesophases to interact differently with enantiomers or enantiotopic directions in prochiral molecules, and to orient them on average differently relative to B o . [1,2,6] The orientational behavior of solutes dissolved in these CLCs can be efficiently monitored by the 2 H quadrupolar interaction H Q , which dominates proton-decoupled deuterium ( 2 H-{ 1 H}) NMR spectra. Assuming axial symmetry for the electric field gradient along the C À D bond, the quadrupolar splitting of the deuteron is simply given by Equation (1) [2,7] Abstract: The analytical potential and enantioselective properties of lyotropic mesophases made by mixing two chemically different chiral polypeptides are described.…”

“…Such a value is not common for thermotropic systems (< 2 %), but it is standard for lyotropic PBLG or PCBLL mesophases, particularly in numerous analytical applications (determination of enantiomeric purity by 13 C or 2 H NMR spectroscopy at natural abundance). [1,3] It could be argued that such a concentration of solute is not compatible with infinite dilution (see Supporting Information), because the solute-solute interactions could significantly modify the solute distribution and also the K value. This objection was overruled, since the K parameter obtained from the analysis of NMR data at low solute concentration (1.7 wt %) is identical to values obtained at 10 wt %.…”

Electrochemical Reduction in an Aprotic Medium of New Functionalized Amphiphilic Molecules Derived from Sugars: Stereoselective Pinacolization and an Example of a Glycosidic Carbon-Oxygen Bond Cleavage

“…During the past decade, a very convenient technique based on the 2 H-NMR spectroscopy in liquid crystals has been developed. [21] The solvent used for the NMR experiments is a liquid crystal obtained by dissolution of poly-γ-benzyl--glutamate (PBLG) in dichloromethane. In such a chiral medium, the two enantiomers of the studied substrate can be set out differently and in this way give two quadrupolar splittings for the 2 tion with CD 3 I in the presence of NaH.…”