Dynamics of Formation of Vesicles Studied by Highly Time-resolved Stopped-flow Experiments

Abstract

Phase behaviour and static structure of surfactant systems have been studied in much detail, but this applies much less so to their dynamic properties. Structural transitions in amphiphilic systems can be triggered by mixing different amphiphiles. Employing the stopped-flow technique we have studied the kinetics of formation of multilamellar vesicles starting from a micellar solution and a microemulsion containing a semipolar oil. This process has been investigated for various starting conditions and as a function of the charging of the amphiphilic system. The formation process is the faster the closer the starting solution is in composition to the final state and can be slowed down by the presence of ionic surfactant.

Formation Kinetics of Oil-Rich, Nonionic Microemulsions

“…Employing a larger amount of surfactantand thereby covering the complete interface between polar and nonpolar substancethermodynamically stable, nanostructured microemulsions may form. − Although their equilibrium properties like phase behavior, − low oil/water interfacial tension, , and multifarious nanostructure − have been studied in great detail for the past quarter of a century, far less is known about their formation kinetics and the formation of the internal interface in particular. In older related studies the pressure- and temperature-induced micelle formation was investigated in (pseudo)­binary water/surfactant mixtures − as well as the transformation of spherical micelles to elongated ones. , For these transitions similar studies have also been conducted using block copolymers. − Beyond that, most of the other related experiments deal with the kinetics of structural transformations, e.g., the well-studied micelle-to-vesicle transition ,− induced mainly by changes in the composition (using the stopped-flow technique) − or the lamellar-to-sponge (L 3 ) transition due to changes in temperature or pressure . Kinetic experiments on microemulsions concentrate on the exchange kinetics of prestructured inverse w/o microemulsions − or most recently on the pressure-induced sphere-to-cylinder transitions of CO 2 -swollen micelles .…”

The Influence of Arginine on the Response of Enamel Matrix Derivative (EMD) Proteins to Thermal Stress: Towards Improving the Stability of EMD-Based Products

“…(Indeed at the concentrations of interest here, the absorption in the vicinity of the peak exceeded the instrument detection limit of 7 absorption units.) This may have reflected increased exposure to the solvent of tyrosine and tryptophan present in the hydrophobic core of the EMD proteins, and hence conformational rearrangements during heating, as has been extensively discussed elsewhere in the literature for a range of protein structures [ 38 – 44 ]. It was not possible to use circular dichroism in the present case to confirm exposure of aromatic residues because acetic acid was used as the buffer, as in the manufacture of the EMD-based products that were the focus of this work, and the signal from the acetic acid masked that of the proteins.…”