Premium
Thin lipid membranes with aqueous interfaces: Apparatus designs and methods of study
Author(s) -
Howard Robert E.,
Burton Robert M.
Publication year - 1968
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02652417
Subject(s) - membrane , aqueous solution , lipid bilayer , biological membrane , bilayer , amphiphile , thermostat , chemistry , thin film , model lipid bilayer , chemical engineering , materials science , analytical chemistry (journal) , chromatography , lipid bilayer phase behavior , nanotechnology , organic chemistry , biochemistry , mechanical engineering , engineering , copolymer , polymer
Thin membranes can be formed in aqueous media from amphiphilic lipids, and will spontaneously approach a limiting thickness of bimolecular dimensions (bilayers). This paper describes apparatus and methods for studying such thin lipid membranes, and illustrates their use in determining some of the basic properties of the membranes, especially bilayers. Several methods of forming thin lipid membranes are described. The early stages in apparatus development are traced, and the theoretical variables and operational parameters relating to apparatus and system design are discussed. Designs for two basic types of apparatus are presented in detail: one is a cylindrical chamber especially constructed to permit optical investigation of the membrane; the second is a multiple chamber system designed for the study of several different membranes either simultaneously or in rapid succession. Interchangeable chamber units are held in a thermostat block, and assemblies of electrodes and provisions for perfusion or sampling of aqueous medium are placed in the chambers as required. Methods are described which enable simultaneous mechanical, electrical, optical, and chemical operations and studies to be performed on the same membrane with either type of apparatus. Membranes were formed from several purified amphiphilic lipids and from mixed‐lipid extracts from a variety of biological membranes. The types and mechanisms of drainage of thin lipid membranes with aqueous interfaces are analogous to those previously described for aqueous soap films in air. The limiting bilayer thickness is confirmed by electrical measurements. The resistivity of the bilayers is ca. 10 12 to 10 14 ohm‐cm, their capacity is ca. 0.4 μfd‐cm −2 and their dielectric breakdown voltage is ca. 3×10 5 V‐cm −1 . Other physical properties of the bilayers are described. Permeability of the bilayers to various substances was determined by diffusion flux, osmotic flux, and electrochemical potential methods using the apparatus described. Substances studied included water, small monovalent ions, glucose, acetylcholine, salicylamide and synaptic vesicles. The chemical, physical, electrical, and permeability properties of the experimentally formed lipid bilayer membranes are similar to those of biological membranes. These similarities strongly support the Danielli‐Davson hypothesis, which proposes that a lipid bilayer is the basic structure of biological membranes. The apparatus, methods, and information presented in this paper provide tools for further investigation of lipid bilayer membrane properties and for further testing of hypotheses relating to membranes.