Dynamics of proteins confined in non-ionic bicontinuous microemulsions: a FCS study

Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions

Microemulsions provide a unique opportunity to tailor the polarity and liquid confinement in asymmetric catalysis via nanoscale polar and nonpolar domains separated by a surfactant film. For chiral diene Rh complexes, the influence of counterion and surfactant film on the catalytic activity and enantioselectivity remained elusive. To explore this issue chiral norbornadiene Rh(X) complexes (X=OTf, OTs, OAc, PO2 F2 ) were synthesized and characterized by X-ray crystallography and theoretical calculations. These complexes were used in Rh-catalyzed 1,2-additions of phenylboroxine to N-tosylimine in microemulsions stabilized either exclusively by n-octyl-β-D-glucopyranoside (C8 G1 ) or a C8 G1 -film doped with anionic or cationic surfactants (AOT, SDS and DTAB). The Rh(OAc) complex showed the largest dependence on the composition of the microemulsion, yielding up to 59 % (90 %ee) for the surfactant film doped with 5 wt% of AOT as compared to 52 % (58 %ee) for neat C8 G1 at constant surfactant concentration. Larger domains, determined by SAXS analysis, enabled further increase in yield and selectivity while the reaction rate almost remained constant according to kinetic studies.

Surfactant Monolayer Bending Elasticity in Lipase Containing Bicontinuous Microemulsions

Lipase-catalyzed reactions offer many advantages among which a high degree of selectivity combined with the possibility to convert even non-natural substrates are of particular interest. A major drawback in the applicability of lipases in the conversion of synthetically interesting, non-natural substrates is the substantial insolubility of such substrates in water. The conversion of substrates, natural or non-natural, by lipases generally involves the presence of a water-oil interface. In the present paper, we exploit the fact that the presence of lipases, in particular the lipase from Candida antarctica B (CalB), changes the bending elastic properties of a surfactant monolayer in a bicontinuous microemulsion consisting of D₂O/NaCl -n-(d)-octane-pentaethylene glycol monodecyl ether (C₁₀E₅) in a similar manner as previously observed for amphiphilic block-copolymers. To determine the bending elastic constant, we have used two approaches, small angle neutron scattering (SANS) and neutron spin echo (NSE) spectroscopy. The time-averaged structure from SANS showed a slight decrease in bending elasticity, while on nanosecond time scales as probed with NSE, a stiffening has been observed, which was attributed to adsorption/desorption mechanisms of CalB at the surfactant monolayer. The results allow to derive further information on the influence of CalB on the composition and bending elasticity of the surfactant monolayer itself as well as the underlying adsorption/desorption mechanism.

Smart microgels investigated by super-resolution fluorescence microscopy: influence of the monomer structure on the particle morphology

In a recent publication [Bergmann et al. Phys. Chem. Chem. Phys., 2018, 20, 5074-5083] we presented a method which enables to investigate the morphology of microgels by superresolution fluorescence microscopy. Here, this method is applied to three microgel species, based on N-isopropylmethacrylamide (NIPMAM), N-n-propylacrylamide (NNPAM) and N-n-propylmethacrylamide (NNPMAM)) with 5, 7.5 and 10 mol% cross-linker, respectively. Super-resolution microscopy reveals differences of the network morphology of the synthesized particles showing the importance of the monomer structure.