ABSTRACT
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.
ABSTRACT
In our previous work we were able to prove that gelled bicontinuous microemulsions are a novel type of orthogonal self-assembled system. The study at hand aims at complementing our previous work by answering the question of whether gelled lyotropic liquid crystals are also orthogonal self-assembled systems. For this purpose we studied the same system, namely, water-n-decane/12-hydroxyoctadecanoic acid (12-HOA)-n-decyl tetraoxyethylene glycol ether (C10E4). The phase boundaries of the nongelled and the gelled lyotropic liquid crystals were determined visually and with (2)H NMR spectroscopy. Oscillating shear measurements revealed that the absolute values of the storage and loss moduli of the gelled liquid crystalline (LC) phases do not differ very much from those of the binary organogel. While both the phase behavior and the rheological properties of the LC phases support the hypothesis that gelled lyotropic liquid crystals are orthogonal self-assembled systems, freeze-fracture electron microscopy (FFEM) seems to indicate an influence of the gel network on the structure of the Lα phase and vice versa.
ABSTRACT
An orthogonal self-assembled system consists of different structures which coexist independently. Furthermore, the characteristic properties of the respective "base systems", i.e. of the systems which contain only one of the structures, are retained in the orthogonal self-assembled system. We have identified gelled bicontinuous microemulsions as orthogonal self-assembled systems and reported in a preceding paper (Soft Matter, 2013, 9, 3661) that their phase behaviour and rheological properties are in perfect agreement with those of the two base systems, namely a non-gelled bicontinuous microemulsion and a binary gel. In the paper at hand we present the results of structural investigations. With FT-PGSE (1)H-NMR measurements we verified the bicontinuity of our gelled model system H2O-n-decane/12-hydroxyoctadecanoic acid (12-HOA)-tetraethylene glycol monodecyl ether (C10E4) at appropriate temperatures. Apart from that, we proved the coexistence of the bicontinuous microemulsion domains with the gelator network in a small angle neutron scattering (SANS) study. A qualitative comparison between the SANS data of the gelled bicontinuous microemulsion and those of its base systems reveals that the characteristic scattering features of both base systems are present. Moreover, we were able to quantitatively describe and interpret the SANS data, yielding at the same time the structural parameters of the bicontinuous microemulsion and the gelator network.