Effect of Salt on the Micellization of Partially Fluorinated Octylesters and Hydrogenated Dodecylesters in Water

Abstract

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...

Synthesis, Surface Properties, and Antibacterial Activity of Novel Ester‐Containing Cationic Silicone Surfactants and Their Utilization as Fabric‐Finishing Agents

“…and ], which reflects the arrangement of surfactant molecules at the air/solution interface (Cao et al, ). An increase in A min or a decrease in Γ max means a denser arrangement of surfactant molecules at the surface of the solution (Gao et al, ; Olutaş and Acımış, ; Shi et al, ). The Gibbs adsorption isotherm equations are shown as follows: where N A is the Avogadro constant (6.02 × 10 23 mol −1 ), γ denotes the surface tension, R is the ideal gas constant (8.31 J·mol −1 K −1 ), T is the absolute temperature (298.15 K), C is the concentration of surfactants in μmol·L −1 , ( ∂γ /∂lg C ) is the slope of the linear fit of the data below the CMC in the surface tension plots, and n is a constant that depends on the number of species constituting the surfactant that is adsorbed at the interface and the value of n in this study is considered to be 2 assuming that there exist only silicone quaternary ammonium salts in the absence of any other solutes.…”

“…1 and 2], which reflects the arrangement of surfactant molecules at the air/solution interface (Cao et al, 2015). An increase in A min or a decrease in Γ max means a denser arrangement of surfactant molecules at the surface of the solution (Gao et al, 2016;Olutas ¸and Acımıs ¸, 2014;Shi et al, 2011). The Gibbs adsorption isotherm equations are shown as follows:…”

Self-assembly of amphiphilic amino acid derivatives for biomedical applications

“…1a and Table 1, entry 2). 38 Indeed, alanine and serine derivatives coupled to n -dodecanol by esterification formed polydisperse spherical micelles in water with a small size (2.5 nm for alanine derivatives and 2.6 nm for serine derivatives). Sodium chloride played a key role to control the size of the micelles owing to electrostatic repulsion of the cationic amino groups in a saline environment.…”

“…For instance, heating the hydrogels led to a reversible gel-sol transition, and Fig. 1 Various nanostructures obtained from the self-assembly of different amphiphilic amino acid derivatives: (a) spherical micelles, 38 (b) microfibers, 39 (c) spherical vesicles, 44 (d) nanoparticles, 45 (e) nanofibers (hydrogel), 58 (f) nanotubes, 59 (g) nanorods, 65 (h) flower-liked structures, 65 (i) spiral-liked structures, 65 (j) artichoke-liked structures, 65 (k) hollow spherical vesicles, 66 (l) rosette nanotubes. 73 Reproduced with permission.…”

“…73 Reproduced with permission. 38 Copyright 2014, American Chemical Society. Reproduced with permission.…”