title: Thermodynamics of monolayers formed by mixtures of phosphatidylcholine/phosphatidylserine.
abstract: In this work we obtain the thermodynamic properties of mixed (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) PC and (1-stearoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (sodium salt)) PS monolayers. Measurements of compressibility (isotherms, bulk modulus, and excess area per molecule) and surface potential show that the properties of monolayers at the air-water interface depend on the concentration of ions (Na(+) and K(+)) and the proportion of PS in the mixture. The dependence on PS arises because the molecule is originally bound to a Na(+) counterion; by increasing the concentration of ions the entropy changes, creating a favorable system for the bound counterions of PS to join the bulk, leaving a negatively charged molecule. This change leads to an increase in electrostatic repulsions which is reflected by the increase in area per molecule versus surface pressure and a higher surface potential. The results lead to the conclusion that this mixture of phospholipids follows a non ideal behavior and can help to understand the thermodynamic behavior of membranes made of binary mixtures of a zwitterionic and an anionic phospholipid with a bound counterion.
authors: Fischell Department of Bioengineering, University of Maryland at College Park, College Park, MD 20740, USA.
authors: Carlos
authors: C
authors: Luna
authors: Kimberly M
authors: KM
authors: Stroka
authors: Harry
authors: H
authors: Bermudez
authors: Helim
authors: H
authors: Aranda-Espinoza
mesh_terms: D000465:Algorithms; D008567:Membranes, Artificial; D008956:Models, Chemical; D010713:Phosphatidylcholines / Q000737:chemistry*; D010718:Phosphatidylserines / Q000737:chemistry*; D011189:Potassium Chloride / Q000737:chemistry / Q000494:pharmacology; D012965:Sodium Chloride / Q000737:chemistry / Q000494:pharmacology; D013499:Surface Properties / Q000187:drug effects; D013816:Thermodynamics; D053835:Unilamellar Liposomes / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D053835:Unilamellar Liposomes; D014867:Water; D012965:Sodium Chloride; D011189:Potassium Chloride