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POSTER:

SUPPORT:

National Graduate School in Materials Physics



Prof. Håkan Wennerström


 
 
Department of Physical Chemistry 1
Box 124 
Chemical Center
S-221 00 Lund, Sweden
http://www.fkem1.lu.se/
Hakan.Wennerstrom@fkem1.lu.se

Summer School Lectures:

    1. ELECTROSTATIC INTERACTIONS IN AN AQUEOUS ENVIRONMENT

    Water is the dominant solvent in biological systems. The polarity is high enough so that it can stabilize atomic ions as well as charges on the solvent exposed parts of macromolecules and aggregates. The charge - charge interaction provides one of the basic organising interactions in biological systems. Nucleic acids are highly charged, membrane surfaces carry a sizeable charge density and globular proteins have an ampholytic character with a charge that is highly pH dependent.

    These charges generate both repulsive and attractive interaction between the (macro)molecular species. The standard model to describe these interactions uses the Poisson-Boltzmann equation, which is a mean field approximation of a system where the solvent is described as a dielectric continuum.

    The themes of the lecture are:

    1. A discussion of the relation between the PB and a full molecular description of the system.
    2. The use of the PB equation to obtain free energies and chemical potentials, including applications.
    3. The breakdown of the mean field approximation at high charge densities and/or high valencies of counterions.

    Reference: An introduction to the topics can be found in Evans & Wennerstrom: The Colloidal Domain 2nd ed. (Wiley 1999) Chapter 3 and chapter 5.1 and 5.3

    2. TRANSMEMBRANE ELECTROSTATIC INTERACTIONS

    Transport of charge across a membrane is one of the most central molecular events in a living cell. The two basic physiological functions of this process is to store or use (free) energy and to produce a signal. A typical example of energy storage/usage by charge transport is found in the mithochondrion while the signalling in nerve cells is basically electrical. Time permitting the lecture will deal briefly with three topics:

    1. The basic principles of free energy transformations in the mithochondrion
    2. The effect of transmembrane potentials on the kinetics of ion pumps
    3. Electrical description of a nerve puls

Conference abstract - invited talk:

    1. PHOSPHOLIPID BILAYER INTERACTIONS, HYDRATION AND PERMEABILITY

    The hydration of polar groups is an essential aspect of interactions in the aqueous environment of a biological system. Zwitterionic phospholipids, self assembled into bilayers have provided one of the most valuable model systems in the investigations of hydration effects and the closely related question of surface forces in aqueous systems. For a series of phospholipids we have simultaneously measured heat of water sorption and the water vapor pressure as a function of the adsorbed amount. This yields both the enthalpy and the free energy of the water binding and thus, for the first time, a complete thermodynamic characterization of the energetics of the hydration process. The data show that from a thermodynamic perspective the hydration is enthalpy driven for the first few (<4) water of hydration , while for higher water contents the process is entropy dominated. We will discus the implications of this observation for the understanding of the molecular mechanism leading to the spontaneous swelling of these systems usually expressed in terms of a repulsive surface force. As is well known and confirmed by the measurements the swelling can trigger a transition from a gel to a liquid crystalline phase. The last part of the talk deals with the consequencies of such transitions for the permeability of a stack of bilayers exposed to different environments on the two sides. The results are used to discuss some of the permeability properties of the outer part of the skin; the stratum corneum.