Re: CCL:Two questions



 Dear Prof. Shapiro,
 >    (ii) Does anyone have any information on experimental (preferred)
 >         or theoretical (OK) values for the dielectric constant in
 >         the interior of lipid bilayers, artificial membranes, or
 >         (preferred) biological membranes?
 There is no simple answer to this question. In the experimental as well as
 in the theoretical case the answer depends on what property you are
 concentrating.
 Membranes, especially biological ones, are highly inhomogeneous. Thismeans
 that the local dielectric constant does vary from place to place (perhaps
 in the range between 2.5 for hydrocarbones to 6 for more polarizable
 materials).
 The situation get more complicated if you consider the effective dielectric
 constant, a measure of the screening of two charges due to the presence of
 the dielectric properties of water and the membrane. In this case, the
 value cannot be lower than the membrane dielectric constant but can become
 large than the water dielectric constant.
 This problem has been considered for estimating the energy barriers for
 ions permeating through ion channels. For this problem there exists a huge
 amount of literature (see below). In these studies, however, the effect of
 the electrolyte has often been neglected. Counter ions always increase the
 charge-charge screening.
 %0 Journal Article
 %A Parsegian, V. Adrian
 %D 1969
 %T Energy of an Ion crossing a Low Dielectric Membrane: Solutions to Four
 Relevant Electrostatic Problems
 %J Nature
 %V 221
 %P 844-846
 %K continuum theory, dielectric constant, membrane, ion channels, ion
 carriers, mirror image, image charge, image force
 %X The influences on ion energy of membrane thickness, ion-pair formation,
 pores, and carriers have been estimated. Only pores and carriers lower the
 energy barrier significantly
 %0 Journal Article
 %A Parsegian, V. Adrian
 %D 1975
 %T Ion-Membrane interactions a structural forces
 %J Annals of the New York Academy of Sciences
 %V 264
 %P 161-174
 %K continuum theory, dielectric constant, membrane, ion channels, ion
 carriers, mirror image, image charge, image force
 %0 Book Section
 %A Jordan, Peter C.
 %D 1993
 %T Interactions of ions with membrane proteins
 %B Thermodynamics of Membrane Receptors and Channels
 %E Jackson, Meyer B.
 %I CRC Press
 %C Boca Raton
 %P 27-80
 %K continuum model, effective dielectric constant, Born energy, Eyring
 theory, Nernst-Planck equation, energy profiles, gramicidine, ionic
 strength effects, conductivity, alamethicin, acetylcholin receptor channel,
 voltage gated channels, anion channels
 %0 Journal Article
 %A Partenskii, Michael B.
 %A Dorman, Vladimir
 %A Jordan, Peter C.
 %D 1994
 %T Influence of a channel-forming peptide on energy barriers to ion
 permeation, viewed from a continuum dielectric perspective
 %J Biophysical Journal
 %V 67
 %N 4
 %P 1429-1438
 %K ** gramicidin channel; dynamics; water; model; electrostatics;
 simulations; movement; constant; membrane electrostatic barrier;
 electrostatic screening; ion transport; ionic conductivity; dielectric
 screening
 %0 Journal Article
 %A Zhou, F.
 %A Schulten, K.
 %D 1995
 %T Molecular-dynamics study of a membrane water interface
 %J Journal of Physical Chemistry
 %V 99
 %N 7
 %P 2194-2207
 %F Review
 %K ** lipid bilayer-membranes; hydration forces; phospholipid-bilayers;
 computer-simulation; dilauroylphosphatidylethanolamine bilayers;
 electrostatic interactions; amphiphilic surfaces; dielectric-constant;
 boundary-conditions; magnetic-resonance;
 -------------------------------------------------------------------------
 Eberhard von Kitzing
 Max-Planck-Institut fuer Medizinische Forschung
 Jahnstr. 29, D69120 Heidelberg, FRG
 Carl-Zuckmayer Str. 17, D69126 Heidelberg (privat)
 FAX : +49-6221-486 459  (work)
 Tel.: +49-6221-486 467  (work)
 Tel.: +49-6221-385 129  (home)
 internet: vkitzing-0at0-sunny.MPImF-Heidelberg.mpg.de
 http://sunny.mpimf-heidelberg.mpg.de/people/vkitzing/Eberhard.html