A laser diffraction and nuclear magnetic resonance investigation of the cholesteric potassium N-dodecanoylalaninate mesophase system

Abstract

KEITH RADLEY and ALAN S. TRACEY. Can. J. Chem. 63, 95 (1985). Nematic and twisted nematic mesophases have been prepared from various mixtures of potassium N-dodecanoyl-I-alaninate and its racemate. The induced pitch was determined as a function of optical purity as werc nmr spectra from a variety of additives including several inorganic salts and d,l-alanine. Dipolar couplings from the CHCHl moiety of the alaninate headgroup were studied, as were quadrupole splittings from the N-D of the amido group and the DZO of the water. It was proposed that with development of cholesteric behaviour on proceeding in a stepwise fashion from the d,l to I amphiphile, the individual disk-like micelles twisted into a chiral shape, then aggregated to form domain-like structures. The major axis of these aggregates is the axis along which the helix propagates and this local axis serves as the director axis for the aggregates. The individual aggregates reorient as a unit when placed in the magnetic field of an nmr spectrometer. As a consequence of this, the diamagnetic anisotropy of the mesophase prepared from the I amphiphile is positive in sign while that of the d,l analogue is negative. Despite this observed change in diamagnetic anisotropy, the alignment of the individual micelles is not different for the chiral and racemic materials.KEITH RADLEY et ALAN S. TRACEY. Can. J . Chem. 63, 95 (1985).On a prCpart des mCsophases nCmatiques et nematiques croistes a partir de divers mtlanges de N-dodtcanoyl I-alaninate de potassium et de son rackmate. On a dktermint le pas induit en fonction de la purett optique ainsi que les spectres rmn obtenus par I'addition de divers produits incluant plusieurs sels inorganiques et la d.1-alanine. On a ktudiC les couplages dipolaires de la portion CHCH3 de I'alaninate de t&te ainsi que les couplages quadrupolaires N-D du groupe amido et du D1O de I'eau. II a ttt propost que, si on dkveloppe le caractkre cholestCrique lorsqu'on procede par Ctape de I'amphiphile d.1 vcrs le I, les micelles individuelles en forme de disques se croisent pour prendre unc forme chirale et elles s'agglutinent ensuite pour former des structures en forme de domaines. L'axe principal de ces aggrtgats est I'axe le long duquel I'htlice se propage et cet axe local sert d'axe directeur pour ces aggrtgats. Les aggrtgats individuels se rtorientent sous forme d'unite lorsqu'ils sont placts dans le champ magnCtique d'un spectromktre rmn. A cause de cette reorientation, I'anisotropie diamagnitique de la mksophase prCparte a partir du I-amphiphile est de signe positif alors que celle de I'analogue d,l est nkgative. En dipit de ce changement observt dans I'anisotropie diamagnktique, il n'y a pas de diffirence dans I'alignement des micelles individuelles des substances chirales et ractmiques.[Traduit par le journal]

NMR Spectroscopy and the Effects of Enantiomerism on the Micelle Formation of PotassiumN-n-Dodecanoylalaninate

“…moiety and is known to form cholesteric mesophases which are composed of micelles (9)(10)(11)(12). However, the structure of in the case of carbon-13 NMR spectra.…”

“…Heteronuclear broad-band and power-gated proton decoubecome chiral as the content of the L-derivative is increased (12). Enantiomerism in cybotactic systems is also of interest pled carbon-13 NMR spectra, at 30ЊC and 62.95 MHz on a Bruker AM-250 spectrometer, and at ca.…”

Liquid crystalline behaviour of N-cetyl N,N,N,-trimethyl ammonium bromide: An experimental study

“…Nematic phase samples can also be obtained by using mixed detergents with oppositely charged head groups. Most quaternary systems can be modified by leaving out the salt resulting in ternary systems which still maintain a nematic phase under a wide range of temperatures and composition variations [9]. The ideal lyotropic amphiphilic nematic phase systems from the theoretical and experimental point of view can be derived from a binary system of detergent and D 2 O only.…”

Enantiomeric discrimination of water soluble compounds using deuterium NMR in a glucopon/buffered water/n-hexanol chiral lyotropic liquid crystal

“…[10][11][12][13] Thus Tracey and Diehl discriminated the enantiomers of L L -alanine by 1 H NMR using a sodium n-decylsulfate/())-sodium decyl-2-sulfate/ sodium sulfate/decanol/water system. 10 Later, it was shown that such a discrimination could also be achieved using a potassium N-dodecanoyl-L L -alaninate/decanol/ caesium chloride/water mesophase.…”

“…10 Later, it was shown that such a discrimination could also be achieved using a potassium N-dodecanoyl-L L -alaninate/decanol/ caesium chloride/water mesophase. [11][12][13] However, this four component system appeared rather unfriendly to use due to the complexity of the phase diagram and to the instability of the mesophase when dissolving some chiral guest molecules. 14 Recently, Baczko et al reported the synthesis of new sulfonated L L -alanine and L L -phenylalanine surfactant derivatives whose association with some chlorinated Tetrahedron: Asymmetry solvents and water led to liquid crystalline systems.…”