Encapsulation of Mithramycin in Liposomes in Response to a Transmembrane Gradient of Calcium Ions

The recent discovery that mithramycin(MTR) in aqueous solution forms a high affinity[Ca(MTR)4]2- complex led us to the idea thatCa2+-loaded liposomes might be able to accumulateMTR in their aqueous internal compartment. Wetherefore investigated the uptake of MTR into largeunilamellar vesicles (LUV) containing NaCl orCaCl2. Our data show that MTR was efficientlyaccumulated within LUV made fromdipalmitoylphosphatidylcholine and cholesterol, onlywhen the liposomes contained Ca2+ and wereresuspended in a Ca2+-free medium. A drugencapsulation efficiency as high as 60% was achieved,at a drug to lipid molar ratio of 1/18. The circulardichroism and fluorescence excitation spectra ofliposome-encapsulated MTR (LMTR) displayed strongsimilarities with those of the [Ca(MTR)4]2-complex. LMTR was found to be stable, when submittedto conditions that destabilized the[Ca(MTR)4]2- complex. Upon dilution andincubation for 24 h at 37 °C, MTR-containingliposomes did not release a significant amount of MTR.These properties were attributed to the formation ofa high affinity complex between MTR and Ca2+inthe aqueous compartment of liposomes.     

Fast Reaction Limit and Large Time Behavior of Solutions to a Nonlinear Model of Sulphation Phenomena

We investigate the qualitative behavior of solutions to the initial-boundary value problem on the half-line for a nonlinear system of parabolic equations, which arises to describe the evolution of the chemical reaction of sulphur dioxide with the surface of calcium carbonate stones. We show that, both in the fast reaction limit and for large times, the solutions of this problem are well described in terms of the solutions to a suitable one phase Stefan problem on the same domain.     

On the theory of slowing down gracefully

We discuss the transport of a tracer particle through the Bose?CEinstein condensate of a Bose gas. The particle interacts with the atoms in the Bose gas through two-body interactions. In the limiting regime where the particle is very heavy and the Bose gas is very dense, but very weakly interacting (??mean-field limit??), the dynamics of this system corresponds to classical Hamiltonian dynamics. We show that, in this limit, the particle is decelerated by emission of gapless modes into the condensate (Cerenkov radiation). For an ideal gas, the particle eventually comes to rest. In an interacting Bose gas, the particle is decelerated until its speed equals the propagation speed of the Goldstone modes of the condensate. This is a model of ??Hamiltonian friction??. It is also of interest in connection with the phenomenon of ??decoherence?? in quantum mechanics. This note is based on work we have carried out in collaboration with D Egli, I M Sigal and A Soffer.     

A discrete BGK approximation for strongly degenerate parabolic problems with boundary conditions

We consider a class of BGK systems with a finite number of velocities, depending on a positive relaxation parameter, that approximate strongly degenerate hyperbolic-parabolic equations with initial boundary conditions. We prove a priori estimates for the solutions of the systems, showing that these functions converge towards the entropy solutions of strongly degenerate problems when the relaxation parameter goes to zero.