Lipases,liposomes and lipid-prodrugs

Colloidal and interfacial phenomena lie at the core of drug formulation, drug delivery, as well as drug binding and action at diseased sites, e.g., in cancer therapy. We review a class of liposome-based drug-delivery systems whose design and functional properties are intimately controlled by the stability of sub-micron structures, lipid-bilayer interfaces, and interfacially activated enzymes that can be exploited to target and deliver drugs. Moreover these drugs can themselves be special lipid molecules in the form of lipid prodrugs that both form the liposomal carrier as well as the substrate for endogenously upregulated lipases that turn the prodrugs into potent drugs precisely at the diseased site.     

Multiple time step update schemes for dissipative particle dynamics

In dynamical simulations of coarse-grained models of soft matter in a solvent a considerable amount of the total simulation time is generically spent on updating the solvent particles, although their dynamics is in most cases not of primary interest. In order to speed up such simulations and as a consequence allow to extend them to cover larger system sizes, we propose and examine various multiple, specifically dual, time step update algorithms for dissipative particle dynamics simulations that are based on the velocity-Verlet scheme [Phys. Rev. 159, 98 (1967)]. Common to all update variants is that the solvent beads are updated with a lower frequency than the bonded interactions within the solute. As a test case we consider a coarse-grained model of a lipid bilayer in water. Our results demonstrate that a considerable saving of simulation time can be gained, while the obtained simulation data are within error brackets virtually identical to those obtained for the reference single time step update scheme.     

Self-assembly based on hydrotropic counterion—single-chain amphiphile ion pairs

We investigate the effect of organic hydrotropic counterions on the self-assembled structures formed by pure counterion—single-chain amphiphile ion pairs. The effect of inorganic counterions on single-chain amphiphiles has been studied for years, taking into account the Hofmeister series that directly affects the micellization. Here, hexadecyldimethylbenzylammonium salicylate (C16Sal) in aqueous solution is used as a model for the influence of organic counterions, and the results have been compared with those previously published for inorganic counterions, specifically hexadecyldimethylbenzylammonium chloride (C16Cl). The studies have been performed by using conductivity, dynamic light scattering, as well as atomic force microscopy. We demonstrate the formation of vesicles and suggest the presence of a vesicle-to-micelle transition at higher concentrations. The Gibbs free energy associated with the self-assembly process has been estimated on the basis of the well-known mass-action model. The main conclusion is that the use of hydrotropic counterions instead of classical inorganic ions dramatically changes the packing parameter of single-chain amphiphiles to higher values, resulting in bilayer structures. We propose that these systems are good and cheap alternatives to double-chain amphiphiles for forming more complex structures like vesicles.