Small-Angle Neutron Scattering Study of the Effect of Pressure on AOT−n-Octane−Water Mesophases and the Effect of α-Chymotrypsin Incorporation

Abstract

It has been demonstrated that the application of hydrostatic pressure to enzymes placed in surfactant "nanocontainers", such as reversed micelles, can bring additional advantages for both increasing the enzyme stability and modulating the enzyme activity. The effects of pressure on the structural properties of the surfactant matrices are essentially unknown, however. In this paper, small-angle neutron scattering experiments were carried out to study the effect of pressure on the structure of AOT-n-octane-water mesophases. The applied pressure range was 0.1-3000 bar. The hydration degree w0 ) cH 2 O/cAOT (mol/mol) was varied from 5 to 46, and the AOT concentration was varied from 0.1 to 1 M. Depending on the AOT concentration and hydration degree, a pressure-induced elongation of the micellar structure or a pressureinduced phase transition from a dense water-in-oil droplet structure to a bicontinuous L 3 phase or lamellar phase is observed. Incorporation of R-chymotrypsin, a water-soluble enzyme, has a significant influence on the topology of the surfactant mesophase, in particular if the radius of the water droplet inside the reversed micelle reaches the size of the protein, i.e., at hydration degree of w0 ≈ 10. Under these conditions, lipid-protein interactions lead to significant changes of the structure and phase behavior of the system, and the changes observed are enhanced with increasing pressure.

Single‐Crystal Hexagonal Disks and Rings of ZnO: Low‐Temperature, Large‐Scale Synthesis and Growth Mechanism

“…On the other hand, it was reported that the anionic surfactant NaAOT can be made to form micelles with diverse shapes by adjusting experimental parameters. [33][34][35][36] The self-assembled AOT À layers at the interface of water and oil could act as template for growing ZnO. The hydrophilic head of AOT À can form an anionic surface exposed to water, and thus Zn 2+ cations can directly attach to the negatively charged AOT À template to initiate the first layer of crystal growth [Eq.…”

“…On the other hand, it was reported that the anionic surfactant NaAOT can be made to form micelles with diverse shapes by adjusting experimental parameters. [33][34][35][36] The self-assembled AOT À layers at the interface of water and oil could act as template for growing ZnO Fast growth along h21 1 0i results in the formation of a hexagonal disk (Figure 5 a). Slight bending of the selfassembled AOT À monolayer makes it possible to accommodate local strain in the disk by formation of small-angle grain boundaries closely parallel to {21 1 0}.…”

Single‐Crystal Hexagonal Disks and Rings of ZnO: Low‐Temperature, Large‐Scale Synthesis and Growth Mechanism

“…The large polar surface is generally energetically unfavorable unless the surface charge is compensated by a passivation agent. On the other hand, it was reported that the anionic surfactant NaAOT can be made to form micelles with diverse shapes by adjusting experimental parameters 33–36. The self‐assembled AOT − layers at the interface of water and oil could act as template for growing ZnO.…”

pH-dependent Substrate Preference of Pig Heart Lipoamide Dehydrogenase Varies with Oligomeric State

“…In the case of AOT reverse micelles, the particle size distribution is narrow, i.e. uniformed micelles of equal size are formed at each surfactant hydration degree, (28,29). The inner cavity radius of the micelle, r m , expressed in Å, was shown to conform to the empirical equation (27), r m ϭ 1.5w 0 ϩ 4 (Eq.…”

“…which holds for all enzyme-containing reverse AOT micellar systems studied thus far (29). In a typical kinetic experiment, a solution of LADH, NADH, and DCPIP in 50 mM Tris-HCl buffer, pH 7.5, or in 25 mM citrate buffer, pH 5.8, was solubilized by intensive shaking in a solution of 0.1 M AOT in octane.…”