Dynamics of w/o AOT microemulsions studied by neutron spin echo

Essential role of w/o microemulsion structure on catalytic activity of entrapped proteins studied by small-angle X-ray scattering and circular dichroism

“…Other studies showed that the proteins mostly locate in the water pools of the microemulsions and that the occlusion of the proteins induces a minor change of the microemulsion structure (Hirai et al, 2001a, b). In addition, we indicated that the bending fluctuation of the microemulsion without the proteins is significantly enhanced at the oligomeric phase (Hirai et al, 1999a) and that such a fluctuation tends to be enhanced by the protein occlusion (Hirai et al, 2003). Thus, the above previous results suggest that the characteristics of structure and dynamics of w/o microemulsions would be closely related to the enhancement of catalytic activities of proteins entrapped in w/o microemulsions.…”

Characteristics of AOT Microemulsion Structure Depending on Apolar Solvents

“…Enzymes entrapped in water in oil (w/o) microemulsions are known to show significant enhancement of enzymatic activity, so-called super-activity, which has attracted significant interest concerning not only the biophysical catalytic properties of enzymes but also the possible future practical applications such as microreactors. − Previously, by using synchrotron radiation small-angle X-ray scattering (SR-SAXS) and enzymatic activity measurements we showed that the hydrolysis of some esters catalyzed by α -chymotrypsins entrapped in water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane reversed micelles is enhanced at low water/surfactant molar ratio w 0 (= [H 2 O]/[AOT]) of 8−16 and that at this low w 0 range the appearance the oligomeric phase of the reversed micelle would play an important role for the acceleration of the metabolic turnover. , For water/AOT/hexane and water/AOT/heptane systems, our recent small-angle neutron scattering (SANS) experiments using a solvent contrast variation method clarified a change of the excluded volume of AOT molecule at low w 0 value which resulted in the increase of an apparent interfacial area of the micelles close to the enzymes . In addition, our neutron spin−echo (NSE) study of the water/AOT/heptane system showed that the effective diffusion coefficient D eff relating to bending fluctuation of the reversed micelle is significantly enhanced at low w 0 value . These previous studies suggest that the structure and dynamics of the AOT-reversed micelles would be essentially important to the appearance of super-activity of enzymes entrapped in the reversed micelles.…”

“…9 In addition, our neutron spinecho (NSE) study of the water/AOT/heptane system showed that the effective diffusion coefficient D eff relating to bending fluctuation of the reversed micelle is significantly enhanced at low w 0 value. 10 These previous studies suggest that the structure and dynamics of the AOT-reversed micelles would be essentially important to the appearance of super-activity of enzymes entrapped in the reversed micelles. We have carried out further SR-SAXS experiments to clarify and compare the structural features of the AOT-reversed micelles with four different apolar solvents depending on w 0 .…”

Microemulsions: A Potential Drug Delivery System

“…Scattering method that has been employed in the study of microemulsions include Small Angle X-ray Scattering (SAXS) [91][92][93][94][95][96][97][98][99]114], Small Angle Neutron Scattering (SANS) [100][101][102][103][104][105][106][107] and static light scattering & dynamic light scattering or Photon Correlation Spectroscopy (PCS) [108][109][110][111][112][113]. These techniques have a lower size limit of about 2 nm and an upper limit of about 100 nm for SANS and SAXS and a few microns for light scattering.…”