Nonconventional lecithin gels in hydrocarbon oils

Mechanism for Transition of Reverse Cylindrical Micelles to Spherical Micelles Induced by Diverse Alcohols

Herein, the effects of various alcohols on lecithin/CaCl₂ organogels are investigated. Mixtures of lecithin and CaCl₂ form reverse cylindrical micelles, resulting in optically transparent organogels. The addition of various alcohols to a mixture of lecithin and CaCl₂ induces a decrease in viscosity through which reverse cylindrical micelles are transformed into spherical micelles (or short cylindrical micelles). Long-hydrocarbon-chain alcohols decrease the viscosity of lecithin/CaCl₂ mixtures more efficiently. Hydrogen bonding and hydrocarbon chain interactions between lecithin and alcohol play important roles in the morphological transition. More importantly, isothermal titration calorimetry was conducted to obtain thermodynamic variables such as the enthalpy, equilibrium constant, Gibbs free energy, entropy, and stoichiometry of the associated molecules observed in the transition. It was found that the transition is an entropically driven process, in which the endothermic and exothermic behaviors were observed depending on the hydrocarbon chain length in the alcohol. In addition, the enthalpy for the association of the alcohol with lecithin showed a linear relationship depending on the hydrocarbon chain length, in which the magnitude of hydrogen bonding and hydrocarbon chain interactions was obtained quantitatively. To the best of our knowledge, this is the first study reporting the thermodynamic properties of the morphological transition observed in a reverse self-assembly process.

Synergistic interactions between lecithin and fruit wax in oleogel formation

In this study, the effect of lecithin (LEC) on the crystallization and gelation of fruit wax (FW) with sunflower oil was researched. A synergistic effect on the gel strength was observed at FW : LEC ratios of 75 : 25 and 50 : 50, compared to the corresponding single component formulations (100 : 0 and 0 : 100). Even below the critical gelling concentration (C_g) of FW, the addition of lecithin enabled gel formation. Lecithin affected the thermal behavior of the structure by delaying both crystallization and gel formation. The phospholipid acted as a crystal habit modifier changing the microstructure of the oleogel, as was observed by polarized light microscopy. Cryo-scanning electron microscopy revealed a similar platelet-like arrangement for both FW as a single oleogelator and FW in combination with LEC. However, a denser structure could be observed in the FW : LEC oleogelator mixture. Both the oil-binding capacity and the thixotropic recovery were enhanced upon lecithin addition. These improvements were attributed to the hydrogen bonding between FW and LEC, as suggested by Raman spectroscopy. We hypothesized that lecithin alters the molecular assembly properties of the FW due to the interactions between the polar moieties of the oleogelators, which consequently impacts the hydrophobic tail (re)arrangement in gelator-gelator and solvent-gelator interactions. The lipid crystal engineering approach followed here offered prospects of obtaining harder self-standing structures at a lower oleogelator concentration. These synergistic interactions provide an opportunity to reduce the wax concentration and, as such, the waxy mouthfeel without compromising the oleogel properties.

The development of phytosterol-lecithin mixed micelles and organogels

We demonstrate that by mixing the phytosterol-ester oryzanol with lecithin in an organic solvent, both components may be dispersed at much higher concentrations than they may be individually. Dynamic light scattering and molecular dynamics simulations show that the mechanism for this is the formation of r ∼ 4 nm mixed micelles. Infrared spectroscopy and simulations suggest that these micelles are formed due in part to hydrogen bonding of the phosphate of the lecithin head-group, and the phenol group of the oryzanol. Rheology shows that by mixing these materials at an equimolar ratio, highly viscous suspensions are created. Furthermore, by adding water to these samples, a solid-like gel may be formed which offers mechanical properties close to those desired for a margarine type spread, whilst still solubilizing the oryzanol.

Effects of Alkali Cations and Halide Anions on the Self-Assembly of Phosphatidylcholine in Oils

The interactions between ions and phospholipids are closely associated with the structures and functions of cell membrane. Instead of conventional aqueous systems, we systematically investigated the effects of inorganic ions on the self-assembly of lecithin, a zwitterionic phosphatidylcholine, in cyclohexane. Previous studies have shown that addition of inorganic salts with specific divalent and trivalent cations can transform lecithin organosols into organogels. In this study, we focused on the effect of monovalent alkali halides. Fourier transform infrared spectroscopy was used to demonstrate that the binding strength of the alkali cations with the phosphate of lecithin is in the order Li⁺ > Na⁺ > K⁺. More importantly, the cation-phosphate interaction is affected by the paired halide anions, and the effect follows the series I^- > Br^- > Cl^-. The salts of stronger interactions with lecithin, including LiCl, LiBr, LiI, and NaI, were found to induce cylindrical micelles sufficiently long to form organogels, while others remain organosols. A mechanism based on the charge density of ions and the enthalpy change of the ion exchange between alkali halides and lecithin headgroup is provided to explain the contrasting interactions and the effectiveness of the salts to induce organogelation.

WITHDRAWN: Interfacial layers of complex-forming ionic surfactants with gelatin

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/ 10.1016/j.cis.2014.05.001. The duplicate article has therefore been withdrawn.

Molecular interactions between lecithin and bile salts/acids in oils and their effects on reverse micellization

It has been known that the addition of bile salts to lecithin organosols induces the formation of reverse wormlike micelles and that the worms are similar to long polymer chains that entangle each other to form viscoelastic solutions. In this study, we further investigated the effects of different bile salts and bile acids on the growth of lecithin reverse worms in cyclohexane and n-decane. We utilized rheological and small-angle scattering techniques to analyze the properties and structures of the reverse micelles. All of the bile salts can transform the originally spherical lecithin reverse micelles into wormlike micelles and their rheological behaviors can be described by the single-relaxation-time Maxwell model. However, their efficiencies to induce the worms are different. In contrast, before phase separation, bile acids can induce only short cylindrical micelles that are not long enough to impart viscoelasticity. We used Fourier transform infrared spectroscopy to investigate the interactions between lecithin and bile salts/acids and found that different bile salts/acids employ different functional groups to form hydrogen bonds with lecithin. Such effects determine the relative positions of the bile salts/acids in the headgroups of lecithin, thus resulting in varying efficiencies to alter the effective critical packing parameter for the formation of wormlike micelles. This work highlights the importance of intermolecular interactions in molecular self-assembly.

Phosphate vibrations probe local electric fields and hydration in biomolecules

The role of electric fields in important biological processes such as binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and show how that sensitivity can be quantified, allowing electric field measurements to be made in phosphate-containing biological systems without chemical modification.

Cylindrical-to-spherical shape transformation of lecithin reverse micelles induced by CO2

The effect of CO(2) on the microstructure of L-alpha-phosphatidylcholine (lecithin) reverse micelles was studied. The small-angle X-ray scattering (SAXS) results show that CO(2) could induce a cylindrical-to-spherical micellar shape transformation. Fourier transform infrared (FT-IR) and UV-vis techniques were also utilized to investigate intermolecular interactions and micropolarity in the reverse micelles at different CO(2) pressures. The reduction of the degree of hydrogen bonding between surfactant headgroups and water with added CO(2) was found to be the main reason for the micellar shape transformation. In the absence of CO(2), the hydrogen bonding between water and P=O of lecithin forms a linking bridge in the interfacial layer. Therefore, the free movement of the polar head of lecithin is limited and the cylindrical reverse micelles are formed. Upon adding CO(2) to the reverse micelles, the hydrogen bonds between lecithin and water in reverse micelles are destroyed, which is favorable to forming spherical micelles. Moreover, the CO(2)-combined reverse micelles were utilized in the synthesis of silica particles. Rodlike silica nanoparticles were obtained in the absence of CO(2), and ellipsoidal and spherical mesoporous silica particles were formed in the presence of CO(2). This method of tuning micellar shape has many advantages compared to traditional methods.