A complete homologous series of fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl-(NBD) labelled fatty amines of varying alkyl chain lengths, NBD-Cn, inserted in 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) or N-palmitoyl sphingomyelin (SpM) bilayers, with 50 mol% and 40 mol% cholesterol (Chol), respectively, was studied using atomistic molecular dynamics simulations. For all amphiphiles in both bilayers, the NBD fluorophore locates at the interface, in a more external position than that previously observed for pure POPC bilayers. This shallower location of the NBD group agrees with the lower fluorescent quantum yield, shorter fluorescence lifetime, and higher ionisation constants (smaller pKa) determined experimentally. The more external location is also consistent with the changes measured in steady-state fluorescence anisotropy from POPC to POPC/Chol (1 : 1) vesicles. Accordingly, the equilibrium location of the NBD group within the various bilayers is mainly dictated by bilayer compositions, and is mostly unaffected by the length of the attached alkyl chain. Similarly to the behaviour observed in POPC bilayers, the longer-chained NBD-Cn amphiphiles show significant mass density near the mixed bilayers' midplanes, and the alkyl chains of the longer derivatives, mainly NBD-C16, penetrate the opposite bilayer leaflet to some extent. However, this effect is quantitatively less pronounced in these ordered bilayers than in POPC. Similarly to POPC bilayers, the effects of these amphiphiles on the structure and dynamics of the host lipid were found to be relatively mild, in comparison with acyl-chain phospholipid analogues.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.