Analytical contribution of NAD 2D‐NMR spectroscopy in polypeptide mesophases to the investigation of triglycerides

Abstract

In this work, we report and discuss on the use and limitations of the natural abundance deuterium two-dimensional NMR spectroscopy in polypeptide chiral and achiral aligning media in the studies of homogenous triglycerides at 14.1 T. As illustrative examples, two triglycerides with short and long alkyl chains were investigated: the 1,3-di(butanoyloxy)propan-2-yl butanoate or tributyrin (TB) and the 1,3-di(tetradecanoyloxy)propan-2-yl tetradecanoate or trimyristin (TM). If both flexible compounds are theoretically of C(s) symmetry on average, according to the Altmann's definition (Proc. Roy. Soc., 1967, A298, 184.), the analysis of spectral data in terms of enantiotopic and diastereotopic discriminations shows noticeable differences related to their orientational ordering behavior inside the mesophases. Although from NMR analysis viewpoint, TB behaves as a C(s) symmetry molecule as expected, the NMR results obtained for TM suggest a behavior that could be formally predicted for a C(3v) symmetry molecule on average. This conclusion was nicely supported by the comparison with the tri-n-propylorthoformate, a real C(3v) symmetry solute on average on the NMR timescale. This difference of effective orientational behavior could originate from the difference of size and shape between lateral and central alkyl chains of the solute molecule.

Synthesis and Stereochemical Assignment of Crypto‐Optically Active 2H6‐Neopentane

“…From the perspective of the CDP,t he absence of visible discriminations in this challenging example emphasizes the limits of efficiency of overall shape recognition mechanisms with this particular chiral liquid crystals. [23] Thec hallenging assignment of the absolute configuration of (S)-2 H 6 -1 thus at this time directly relies on the combination of highly sensitive vibrational spectroscopy with high-level theory.…”

Multinuclear NMR in polypeptide liquid crystals: Three fertile decades of methodological developments and analytical challenges

“…As a last frontier to be crossed, chiral ANAD NMR was used to analyse the case of homogeneous triglycerides (TGs), the last class of lipids [315].…”

“…This situation occurs because the ratio (V a,c /V b ) of the persistent molecular volume of the side chain (V a,c ) to the central chain (V b ) tends strongly towards unity. Here V a,b,ccorresponds to the 3D space explored by the moving atoms of each chain[315].…”

Synthese und stereochemische Bestimmung von krypto‐optisch‐aktivem 2H6‐Neopentan

“…[17] Die Bestimmung der absoluten Konfiguration wurde in Analogie zu unseren vorherigen Arbeiten durchgeführt. [23] Die Ermittlung der absoluten Konfiguration von (S)-2 H 6 -1 gelang nur durch Kombination von hochempfindlicher Schwingungsspektroskopie mit anspruchsvollen theoretischen Methoden. )beruht auf dem Unterschied von verbleibender Quadrupolkopplung (RQC) eines Enantiomerenpaars, Dn Q (R) ¼ 6 Dn Q (S)b ei Verwendung einer Kernsonde mit dem Kernspin I = 1(wie Deuterium).…”

“…Das Fehlen sichtbarer Unterschiede zeigt in diesem speziellen Fall die Grenzen der NMR-Strukturerkennung durch diesen chiralen Flüssigkristall auf. [23] Die Ermittlung der absoluten Konfiguration von (S)-2 H 6 -1 gelang nur durch Kombination von hochempfindlicher Schwingungsspektroskopie mit anspruchsvollen theoretischen Methoden.…”