Ion distribution profiles between polar and charged membranes as observed by anomalous X-ray diffraction

¹ Medizinische Biophysik, Klinikum r.d. Isar, Technische Universität München, Ismaninger Str. 22, D-81675 München, Germany
² Max-Planck Institut für Kolloid- und Grenzflächenforschung, Kantstraße 55, D-14513 Teltow, Germany

Received: 1 December 1995
Accepted: 11 April 1996

Abstract

The distribution profiles of rubidium ions near polar, zwitterionic 1,2-di stearoyl-sn-glycero-3-phospho choline (DSPC) and charged, anionic 1,2-di stearoyl-sn-glycero-3-phospho glycerol (DSPG^-) membranes were determined by means of anomalous X-ray diffraction close to the K-absorption edge of , which was measured to be 15.225 keV. The samples were kept in the L-phase at 30. The DSPC suspensions in 2 M RbCl were examined at 15.125 keV, 15.196 keV, 15.210 keV, the suspensions in 0 M RbCl and 2 M RbCl at 14.667 keV and 15.196 keV. This gave up to seven peaks in the powder-like diffraction pattern and revealed, for the first time directly, different rubidium ion distributions in either of the investigated systems: rubodium ions are enriched by 100% in the proximity of the charged headgroups and depleted by 25% from the vicinity of the zwitterionic DSPC headgroups. The latter phenomenon results in rubidium ion concentration maximum in the aqueous compartment between polar, but uncharged bilayers.