Nanoscale electrical characterization of semiconducting polymer blends by conductive atomic force microscopy (C-AFM).

For the first time local electrical characteristics of a blend of two semiconducting polymers were studied with conductive atomic force microscopy (C-AFM). The investigated mixture is potentially interesting as the active layer in plastic photovoltaic devices. Besides conventional topography analysis of morphology and phase separation, the internal structure of the active layer was investigated by observing the current distribution with nanoscale spatial resolution. Similar to force spectroscopy, current imaging spectroscopy was performed during scanning the sample surface. Different types of current-voltage (I-V) characteristics were extracted from the array of spectroscopic data obtained from each point of the scans, and local heterogeneities of the electric characteristic were determined and discussed.

Glutathione transferase mimics: micellar catalysis of an enzymic reaction.

Substances that mimic the enzyme action of glutathione transferases (which serve in detoxification) are described. These micellar catalysts enhance the reaction rate between thiols and activated halogenated nitroarenes as well as alpha,beta-unsaturated carbonyls. The nucleophilic aromatic substitution reaction is enhanced by the following surfactants in descending order: poly(dimethyldiallylammonium - co - dodecylmethyldiallylammonium) bromide (86/14) >>cetyltrimethylammonium bromide>zwittergent 3-16 (n-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulphonate)>zwittergent+ ++ 3-14 (n-tetradecyl-N,N-dimethyl - 3 - ammonio -1 - propanesulphonate) approximately N,N - dimethyl - laurylamine N-oxide>N,N-dimethyloctylamine N-oxide. The most efficient catalyst studied is a polymeric material that incorporates surfactant properties (n-dodecylmethyldiallylammonium bromide) and opens up possibilities for engineering sequences of reactions on a polymeric support. Michael addition to alpha,beta-unsaturated carbonyls is exemplified by a model substance, trans-4-phenylbut-3-en-2-one, and a toxic compound that is formed during oxidative stress, 4-hydroxy-2-undecenal. The latter compound is conjugated with the highest efficiency of those tested. Micellar catalysts can thus be viewed as simple models for the glutathione transferases highlighting the influence of a positive electrostatic field and a non-specific hydrophobic binding site, pertaining to two catalytic aspects, namely thiolate anion stabilization and solvent shielding.