Effective electrostatic interactions in solutions of polyelectrolyte stars with rigid rodlike armsStructure and phase behavior of polyelectrolyte star solutions Influence of salt on the structure of polyelectrolyte solutions: An integral equation theory approach Polyion conformation and the distribution of small ions near the polyion have been investigated using Monte Carlo simulations. The systems of interest contained one polyion and its monovalent counterions, and variable amount of a 3:1 salt. With monovalent counterions only, the polyion is strongly extended. As salt is added, the polyion folds, and the most compact and spherical-like structure appears at a three-fold excess of the trivalent counterions. The polyion exerts a strong influence on the nearest-neighbor distance among the trivalent ions, an effect being relevant for energy transfer reactions.

The interaction of trivalent lanthanides with sodium dodecyl sulfate micelles (SDS) in aqueous solution has been studied by a variety of experimental techniques. Potentiometric measurements with a sodium selective electrode, steady-state fluorescence spectra of Ce(III), emission lifetime measurements of Ce(III), Tb(III), and Eu(III), and electronic paramagnetic resonance spectra (EPR) of Gd(III) all show that the lanthanide ions bind to the micellar surface. From analysis of the Tb(III) lifetime measurements in water and D 2 O solutions, it is found that the lanthanide ions lose one hydration water on binding to SDS. However, the EPR measurements suggest that the lanthanide ions still have considerable freedom of movement. Energy transfer between Ce(III) and Tb(III) has been used to obtain further information on multiple lanthanide ion binding. From steady-state fluorescence measurements in aqueous solution in the absence of SDS no energy transfer is observed, although there is quenching of Tb(III) emission by Ce(III), which is found to follow good SternVolmer kinetics. In the presence of SDS micelles, very different behavior is observed and energy transfer occurs from excited Ce(III) to Tb(III). This is only possible when the two ions are on the same micelle. The energy transfer phenomena is highly dependent on micelle concentration and has been analyzed theoretically via a Monte Carlo simulation. This shows that the lanthanide ions bind close to the micelle surface, and are consistent with the loss of a water molecule. Also, assuming a Dexter-type model in which the energy transfer intensity is proportional to the inverse of the square root of the average distance between cerium and the closest terbium it is possible to reproduce qualitatively the experimental cerium(III)-sensitized Tb(III) luminescence intensity data.

MbetaCD proved to be an efficient enhancer of OME solubility, thus possessing characteristics for being an useful excipient in pharmaceutical formulations of this drug.

Compaction of negatively charged polyanions by polycations with different characteristics is investigated using Monte Carlo simulation in a coarse-grain model. Two different routes are tested and the results compared. In one, the polycation/polyanion charge ratio is varied by increasing the amount of polycations, keeping all the chain characteristics constant. In the other, the linear charge density of the polycations is altered but their number is kept constant. The set of systems in which the linear charge density changes is used as a model for a system comprising chains with different degrees of ionization under different pH conditions. In both cases, polycation/polyanion charge ratios ranging from 0.25 to 1.25 are addressed. The system with unitary charge ratio is common to both routes. It is seen that, although the overall trends followed by the two sets of systems are similar, marked differences can be discerned both for low charge ratios, and for the higher ones, where the systems are overcharged. Coexistence regimes are clearly detected in some of the systems. The results obtained computationally can be used to guide practical applications.