Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

Abstract

Antioxidants solubilized in micellar solutions can change micellar properties like the size and shape of micelles, critical micellar concentration (cmc) and viscosity. Interactions arising between antioxidants and the surfactant determine the locations of antioxidants and vice versa. The location and interaction are dependent on the type of both the antioxidant and surfactant. Influences of various antioxidants on the physical and structural properties were tested in micellar systems of cationic CTAB, non-ionic Brij 58 and anionic SDS. The antioxidants used to investigate the effects of gradually increasing lipophilicity were gallic acid (GA) and the gallate esters from methyl to octyl gallate (MG-OG). Hydroxy cinnamic acids (HCAs) like p-coumaric acid (pC), caffeic acid (CA), ferulic acid (FA) and sinapic acid (SA) were employed to observe effects of functional groups like hydroxyl and methoxy groups. Micellar size and shape determined by small angle neutron scattering (SANS), viscosity and cmc were chosen to characterize the antioxidant influence. In Brij 58 systems propyl gallate (PG) did not affect the cmc or aggregation number but decreased micellar size slightly due to an intercalation of PG into the region of the polyoxyethylene chain and the first adjacent alkyl chain methylene groups. In SDS systems the micellar size and cmc decreased in the presence of PG. This was attributed to PG residing in the Stern layer. However, in CTAB systems micelles swelled at low PG concentration and in the presence of GA, while higher PG concentrations and more lipophilic antioxidants led to a sphere-to-rod transition with a simultaneous increase in viscosity and decrease in cmc. This revealed the intercalation of antioxidants in the palisade layer of CTAB micelles entering into strong interactions of electrostatic and hydrophobic origin. It could be demonstrated that the interactions became stronger the more lipophil an antioxidant is and the more hydroxyl groups are attached to the aromatic ring. Differences in the location and interaction of antioxidant and micelles are proposed as being responsible for the effectiveness of antioxidants.

Tuning Cationic Micelle Properties with an Antioxidant Additive: A Molecular Perspective

“…The CTAB solutions with 0 to 50 mM of [PG] show a η value that is independent of the increase in shear rate, which is a characteristic feature of the Newtonian behavior. Here, as the [PG] increases, the η increases dramatically, giving a hint of plausible morphology change in CTAB micelles in the presence of antioxidants, 24 i.e., the solution with 100 mM PG shows a higher η and a shearthinning behavior in the whole range of the shear from 1 to 100 s −1 , which demonstrates the formation of a higher order of micellar geometry, probably the elongated ellipsoidal or rod-/ worm-like micelles in the examined systems. These findings are in agreement with the reported study.…”

Alkyl caffeates as antioxidants in O/W emulsions: Impact of emulsifier type and endogenous tocopherols

“…An explanation for the stronger interactions with Tween may be the molecular structure of the emulsifiers, since Tween is a larger and more bulky molecule than Citrem; however, this has to be further evaluated. Furthermore, Schwarz et al evaluated partitioning of different antioxidants in dispersed lipid systems with different emulsifiers. Significant differences were observed in partitioning of the antioxidants between phases, both as a function of pH, emulsifier type and concentration.…”

Novel pH-Responsive Nanoparticles

“…The micellar structure and properties of similar surfactants have been extensively studied earlier. [25][26][27][28][29][30][31][32][33] For all cases, a concentration of surfactant used for nanoparticles preparation was substantially above the cmc value (cmc ) 2.9 × 10 -3 %) reported for Brij 98. 34 Our surface tension measurements by Wilhelmy plate method give a lower cmc value (1.0 × 10 -3 %).…”