TY  - JOUR
A1  - Wellert, Stefan
A1  - Tiersch, Brigitte
A1  - Koetz, Joachim
A1  - Richardt, Andre
A1  - Lapp, Alain
A1  - Holderer, Olaf
A1  - Gaeb, Juergen
A1  - Blum, Marc-Michael
A1  - Schulreich, Christoph
A1  - Stehle, Ralf
A1  - Hellweg, Thomas
T1  - The DFPase from Loligo vulgaris in sugar surfactant-based bicontinuous microemulsions  structure, dynamics, and enzyme activity
JF  - European biophysics journal : with biophysics letters ; an international journal of biophysics
N2  - The enzyme diisopropyl fluorophosphatase (DFPase) from the squid Loligo vulgaris is of great interest because of its ability to catalyze the hydrolysis of highly toxic organophosphates. In this work, the enzyme structure in solution (native state) was studied by use of different scattering methods. The results are compared with those from hydrodynamic model calculations based on the DFPase crystal structure. Bicontinuous microemulsions made of sugar surfactants are discussed as host systems for the DFPase. The microemulsion remains stable in the presence of the enzyme, which is shown by means of scattering experiments. Moreover, activity assays reveal that the DFPase still has high activity in this complex reaction medium. To complement the scattering experiments cryo-SEM was also employed to study the microemulsion structure.
KW  - Dynamic light scattering
KW  - Neutron spin echo
KW  - Microemulsion
KW  - Enzyme catalysis
KW  - SANS
KW  - Protein structure
Y1  - 2011
U6  - https://doi.org/10.1007/s00249-011-0689-0
SN  - 0175-7571
VL  - 40
IS  - 6
SP  - 761
EP  - 774
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Lemke, Karina
A1  - Prietzel, Claudia Christina
A1  - Koetz, Joachim
T1  - Fluorescent gold clusters synthesized in a poly(ethyleneimine) modified reverse microemulsion
JF  - Journal of colloid and interface science
N2  - This paper is focused on the formation of gold clusters in a tailor-made polyelectrolyte-modified reverse microemulsion using poly(ethyleneimine) (PEI) as a cationic polyelectrolyte. PEI incorporated into a ternary w/o microemulsion consisting of water/heptanol/zwitterionic surfactant 3-(N,N-dimethyl-dodecylammonio)-propanesulfonate (SB) acts as a reducing and stabilizing agent and shows an additional template effect. The nanoparticle synthesis is performed by a simple mixing of two microemulsions, one containing the PEI and the other one containing the gold chloride precursor. UV-vis measurements in the microemulsion show two pronounced absorption maxima, one at 360 nm and the other one at 520 nm, indicating two particle fractions. The absorption maximum at 360 nm in combination to the unique fluorescence properties indicate the formation of gold clusters. After a complete solvent evaporation the redispersed nanoparticles have been characterized by using UV-vis and fluorescence spectroscopy, in combination to dynamic light scattering and transmission electron microscopy (TEM). In addition to the gold nanoparticle fraction (>5 nm) the fluorescent gold cluster fraction (<2 nm) can be redispersed without particle aggregation. By means of asymmetric flow field flow fractionation (AF-FFF) two different cluster fractions with particle diameter (<2 nm) can be identified.
KW  - Microemulsion
KW  - Gold cluster
KW  - Field flow fractionation
KW  - Polymer capped gold nanoparticles
Y1  - 2013
U6  - https://doi.org/10.1016/j.jcis.2012.11.057
SN  - 0021-9797
VL  - 394
SP  - 141
EP  - 146
PB  - Elsevier
CY  - San Diego
ER  -