MAHMUT ACIMIS and LEONARD W. REEVES. Can. J. Chem. 58, 1533(1980. The lyotropic liquid crystals formed by optically active detergents, water, and electrolyte have been investigated near and above the water-rich limit of the lamellar mesophase by using nuclear magnetic resonance, relative density observations, and polarized microscopy. The racemic mixture ofa-alanine decyl ester forms a lamellar phase, adisc-micelle type I1 phase (which may co-exist in equilibrium), followed by an isotropic material as the water content increases. The resolved d or 1 detergent also forms a lamellar mesophase which may coexist with a type I1 disc-micelle system; however, as water content increases a transition occurs to a cholesteric lyotropic mesophase which itself passes over to an isotropic phase at the highest water contents studied. The range of existence, as a function of water content, for these intermediate type I1 DM and cholesteric phases is very narrow. The screw axis of the cholesteric mesophase aligns parallel to the magnetic field. A tentative structure of the cholesteric phase based on disc micelles distorted into a partial helix is suggested.M A H M U~ ACIMIS et LEONARD W. REEVES. Can. J. Chem. 58, 1533Chem. 58, (1980. Operant dans la zone situee tout pres et au-dessus de la limite riche en eau de la mesophase lamellaire et faisant appel a la rmn, a des observations de densite relative et a la microscopic polansee, on a etudie les cristaux liquides lyotropesformes par les detergents optiquement actifs, I'eau et un electrolyte. Le melange racemique de I'ester decyclique de l'a alanine forme une phase lamellaire, une phase disque-micelle de type I1 (qui peut coexister en equilibre) qui est suivie d'un produit isotrope lorsque la teneur en eau augmente. Le detergent resolu (d ou I ) forme egalement une mesophase lamellaire qui peut coexister avec un systkme disque-micelle de type 11; cependant lorsque la teneur en eau augmente, il se produit une transition en une mesophase cholesterique lyotrope qui elle-mSme se transforme en une phase isotrope pour la plus haute teneur en eau etudike. Le domaine d'existence, en fonction de la teneur en eau, de ces intermediaires de type I1 DM et des phases cholestCriques est tres etroit. L'axe sans fin de la mesophase cholesterique s'aligne parallelement au champ magnetique. On suggkre une structure non definitive pour la phase cholesterique basee sur les disques micellaires deformes en une helice partielle.[Traduit par le journal]

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The effect of added salt, NaCl, on micellization and structural properties of four enantiomeric/racemic surfactant pairs obtained from partially fluorinated octylesters (PFOEs) and hydrogenated dodecylesters (DDEs) of alanine and serine were investigated by electrical conductivity, surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The Krafft temperatures, the critical micelle concentrations, the degree of counter−ion ionization, and the Gibbs free energy of micellization were determined. The Gibbs free energy of adsorption of the esters at the air/solution interface was greater than that of micellization. The hydrodynamic radius (R H ) increased with salt concentration, and the polydispersity index exhibited a shift from monodisperse to polydisperse aggregates. The PFOEs of serine could incorporate only a minimum amount of salt, but it exhibited the largest R H (37.9 nm). DLS and TEM results indicated that the esters formed micelles of spherical shapes. Neither of the methods could detect an appreciable difference in the micelle sizes of the L-and DL-amphiphiles. The DDEs exhibited greater antibacterial activity against some gram−positive bacteria than the reference antibiotic, tetracycline, but the PFOEs did not show any activity. ■ INTRODUCTIONSurfactants, (amphiphilic molecules) owing to the delicate balance of their hydrophilic and hydrophobic moieties, selfassociate in water to form aggregates called micelles. The micelle formation first occurs at a certain minimum concentration called critical micelle concentration (cmc). This is of paramount importance because the application of surfactants in technology and science is based on the formation of a micelle structure that is able to solubilize a large number of ionic, polar, or neutral materials.The structure of micelles of chiral amphiphilic molecules, because their properties related to chiral recognition may be of importance, then the most biologically active compounds vital to life are chiral. Therefore, in the foregoing paper we studied the micellization process in aqueous solution of a new class of enantiomeric and racemic amphiphilic esters (surfactants) obtained from esterification of the amino acids, alanine (A), and serine (S) with partially fluorinated n-octyl alcohol and hydrogenated dodecyl alcohol, respectively. 1 As a result, we found that the cmc values, the thermodynamic functions (ΔG mic°, ΔH mic°, ΔS mic°) , the adsorption parameters at the air/ water interface (the surface excess concentration, Γ max , the minimum area per headgroup of the molecule, A min , and the surface tension at the cmc, γ cmc ) and the volumetric parameters (the changes in the molal volumes, ΔV φ mic ) of the partially fluorinated esters were strikingly different from those of the hydrogenated ones.Among the adsorption parameters, the quantities, Γ max and A min , for the partially fluorinated octylesters PFOEs of serine were particularly different from all of the studied systems. For comparison and space saving purposes onl...

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