Abstract
Lipids bearing net electric charges in their hydrophilic headgroups are ubiquitous inbiological membranes. Recently, the interest in cationic lipids has surged because of theirpotential as non-viral transfection vectors. In order to utilize cationic lipids in transfer ofnucleic acids and to elucidate the role of charged lipids in cellular membranes in general,their complex interactions within the membrane and with the molecules in thesurrounding media need to be thoroughly characterized. Yet, even interactions betweenmonovalent counter-ions and charged lipids are inadequately understood. We studiedthe interactions of the cationic gemini surfactant (2R,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (RR-1) with chloride, bromide, fluoride, and iodideas counter-ions by differential scanning calorimetry and Langmuir balance. Chlorideinteracts avidly with RR-1, efficiently condensing the monolayer, decreasing the collapsepressure, and elevating the main transition temperature. With bromide and iodide clearlydifferent behaviour was observed, indicating specific interactions between RR-1 and thesecounter-ions. Moreover, with fluoride as a counter-ion and in pure water identical resultswere obtained, demonstrating inefficient electrostatic screening of the headgroups ofRR-1 and suggesting fluoride being depleted on the surface of RR-1 membranes.
Published Version
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