Search

The accepted picture of the structure of a micelle in solution arises from the idea that the surfactant molecules self-assemble into a spherical aggregate, driven by the conflicting affinity of their head and tail groups with the solvent. It is also assumed that the micelle's size and shape can be explained by simple arguments involving volumetric packing parameters and electrostatic interactions. By using wide Q-range neutron diffraction measurements of H/D isotopically substituted solutions of decyltrimethylammonimum bromide (C(10)TAB) surfactants, we are able to determine the complete, atomistic structure of a micelle and its surroundings in solution. The properties of the micelle we extract are in agreement with previous experimental studies. We find that ~45 surfactant molecules aggregate to form a spherical micelle with a radius of gyration of 14.2 Å and that the larger micelles are more ellipsoidal. The surfactant tail groups are hidden away from the solvent to form a central dry hydrophobic core. This is surrounded by a disordered corona containing the surfactant headgroups, counterions, water, and some alkyl groups from the hydrophobic tails. We find a Stern layer of 0.7 bromide counterion per surfactant molecule, in which the bromide counterions maintain their hydration shells. The atomistic resolution of this technique provides us with unprecedented detail of the physicochemical properties of the micelle in its solvent.

Keggin tungstophosphoric acid supported onto mesoporous and meso-microporous materials was studied by ammonia microcalorimetry. Experiments were performed at high and low temperatures to separate the contributions of chemisorption and physisorption, low-temperature data being potentially important for the ambient temperature purification processes. Analysis of thermokinetic data obtained from heat output curves at an elevated temperature allows one to distinguish the transition between reaction of ammonia with the acid sites and the onset of physical sorption. Thermokinetic data are also sensitive to the pore structure of the support materials, with faster sorption registered in the case of materials with the open mesoporous structure. The SBA-15 supported acid shows the maximum ammonia uptake and the strongest acid sites among the three materials studied. The dynamics of sorption, characterized by the thermokinetic parameter, appears to be better in the two materials possessing open pore structure, mesoporous carbon Novacarb and especially the mesoporous silica SBA-15.

A fragment-based docking procedure followed by substructure search were used to identify active-site beta-secretase inhibitors from a composite set of about 300 000 and a library of nearly 180 000 small molecules, respectively. EC(50) values less than 10 microM were measured in at least one of two different mammalian cell-based assays for 12 of the 72 purchased compounds. In particular, the phenylureathiadiazole 2 and the diphenylurea derivative 3 are promising lead compounds for beta-secretase inhibition.