Enantiodifferentiating Properties of the Alignment Media PELG and PBLG – A Comparison

Abstract

Homopolypeptide‐based alignment media can induce different orientations of enantiomers as a result of their α‐helical structures. This property enables the discrimination of enantiomers through anisotropic NMR parameters such as residual dipolar couplings (RDCs). In this paper, the enantiodiscriminating properties of two alignment media derived from polyglutamic acid derivatives – poly‐γ‐benzyl‐L‐glutamate (PBLG) and poly‐γ‐ethyl‐L‐glutamate (PELG) – are compared and discussed. The two analytes, isopinocampheol and β‐pinene, are investigated, and the role of the lateral side chain of the homopolypeptide in the orientation process is examined.

Polyaspartates as Thermoresponsive Enantiodifferentiating Helically Chiral Alignment Media for Anisotropic NMR Spectroscopy

“…We observed that the enantiodifferentiation of IPC in PPDA with β =44.3° is higher than for other known homopolypeptides like PBLG (8.1°) and PELG (29.6°) . Furthermore, we were interested to see to what extend these 5D‐angles are reproducible by comparing all enantiomorphous (e) and diastereomorphous (d) interactions of (+)‐ and (−)‐IPC in PPDA and PPLA (Figure ).…”

“…Down to 9 % (w/w) a stable liquid crystal was formed and well resolved CLIP‐HSQC spectra were obtained. Even the dipolar couplings of C10−H10a and C10−H10s have been extracted from CLIP‐HSQC spectra (Figure ), which is often quite challenging …”

Poly‐γ‐p‐Biphenylmethyl‐Glutamate as Enantiodifferentiating Alignment Medium for NMR Spectroscopy with Temperature‐Tunable Properties

“…To evaluate these, we performed a series of experiments with both enantiomers of isopinocampheol [(+)‐ and (−)‐IPC]. We chose IPC as an analyte because both enantiomers are commercially available and it has proven as a reliable test substance for new alignment media . We prepared the anisotropic samples above the critical concentration and verified the stability of the LLC‐phase by 2 H NMR spectra until no line shape change occurred.…”

Synthesis of Poly‐γ‐S‐2‐methylbutyl‐l‐glutamate and Poly‐γ‐S‐2‐methylbutyl‐d‐glutamate and Their Use as Enantiodiscriminating Alignment Media in NMR Spectroscopy

“…The LLC phases of the homochiral polyglutamic acid derivatives poly‐γ‐benzyl‐ l ‐glutamate (PBLG, 1 ) and poly‐γ‐ethyl‐ l ‐glutamate (PELG, 6 ) (Figure a) act in an enantiodifferentiating manner . We previously studied their enantiodiscriminating properties by comparing experimentally distinguishable RDC values and differences in the order tensor orientations observed for each enantiomer …”

“…Therefore, not only the type and structure of the polymer, but also the shape and polarity of the analyte significantly influence the resulting orientation. Additionally, the orientation of the polymers in the magnetic field (into a nematic or cholesteric LLC phase), influences of the homopolypeptide's side chain (its flexibility, chirality, steric demands, and potential π–π interactions) and the character of possible interactions between analyte and alignment medium (hydrogen bonding, steric interactions, electronic aspects, and dipole moments) have to be considered . The ability of 1 and 6 to discriminate between enantiomers has been studied with enantiomers of β‐pinene and isopinocampheol (IPC, 5 ) previously .…”