Journal
CHEMISTRY AND PHYSICS OF LIPIDS
Volume 163, Issue 1, Pages 64-73Publisher
ELSEVIER IRELAND LTD
DOI: 10.1016/j.chemphyslip.2009.09.004
Keywords
Liposomes; Ionic liquids; cryo-TEM; Differential scanning calorimetry; Fusion; Leakage
Categories
Funding
- German Research Foundation DFG
- German Academic Exchange Service DAAD
- Swedish Research Council
- Swedish Cancer Society
- Swedish Foundation for International Cooperation in Research and Higher Education STINT
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N,N,N-Trialkylammonioundecahydrododecaborates (1-), a novel class of compounds of interest for use as anions in ionic liquids, interact with DPPC liposomes. Increasing compound concentration causes an increasing negative zeta potential. Dissociation constants demonstrate that the binding capacity increases strongly with longer chain length. NN.N-Trialkylammonioundecahydrododecaborates with longer alkyl chains show a detergent-like behavior: the compounds incorporate into the liposome membrane and differential scanning calorimetric experiment show already low concentrations cause a complete disappearance of the peak representing the gel-to-liquid crystalline phase transition. In contrast, compounds with shorter alkyl chains only interact with the headgroups of the lipids. Investigations by means of cryo-TEM reveal that all derivatives induce significant morphological changes of the liposomes. N,N,N-Trialkylammonioundecahydrododecaborates with short alkyl chains produce large bilayer sheets, whereas those with longer alkyl chains tend to induce the formation of open or multi-layered liposomes. We propose that the binding of N,NN-trialkylammonioundecahydrododecaborates is mainly due to electrostatic interactions between the doubly negatively charged cluster unit and the positively charged choline headgroup; the positively charged ammonium group might be in contact with the deeper-lying negatively charged phosphate. For N,N,N-trialkylammonioundecahydrododecaborates with longer alkyl chains hydrophobic interactions with the non-polar hydrocarbon part of the membrane constitute an additional important driving force for the association of the compounds to the lipid bilayer. (C) 2009 Elsevier Ireland Ltd. All rights reserved.
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