Rigidity in synkinetic molecular monolayers of functional lipids containing Angstrom Gaps

Abstract

Bolaamphiphiles ("bola") are compounds with a hydrophobic core and hydrophilic head groups at both ends. The head groups as well as the hydrophobic core may be functional in nonsymmetric arrangements. One end group may, for example, be bound to a solid subphase, the other may dissolve and react with solutes in the bulk water phase. The hydrophobic core may contain reactive C=C double bonds. If a monolayer membrane is formed from the bolaamphiphile, only the outer head groups and the double bonds at the edges of the membrane can react with polar reagents in the bulk water phase, provided the membrane is rigid enough. Rigidity may be achieved either by rigid hydrophobic skeletons (carotenes, steroids, porphyrins) or by two hydrogen bond chains between secondary amide groups within an oligomethylene chain. Rigid monolayers have so far been used to prepare water-free, dry vesicle membranes, to protect solid surfaces from aggressive reagents by an ultrathin lipid layer and, most important, to construct functionalized gaps in membranes on solid surfaces. The latter are thought to contain water molecules, which do not exchange with the bulk water ("hydrophobic water") and may bind watersoluble molecules.

Engineered Lipids That Cross-Link the Inner and Outer Leaflets of Lipid Bilayers

“…Upon self-assembly into a lipid bilayer, the reactive amphiphiles then cross-link to form bolaamphiphiles via a thermally activated reaction within the hydrophobic core of the membrane. The approach described here for incorporating bolaamphiphiles into lipid bilayers is different from previous reports, where the entire bolaamphiphile is first synthesized and then the molecules are self-assembled into their supramolecular structures. − ,− The problem with the approach of synthesis followed by self-assembly is that bolaamphiphiles spread at the air/water interface often assume a U-shaped conformation, which prohibits there use in building up asymmetric supported lipid bilayers. , …”

“…The approach described here for incorporating bolaamphiphiles into lipid bilayers is different from previous reports, where the entire bolaamphiphile is first synthesized and then the molecules are self-assembled into their supramolecular structures. [23][24][25][26][35][36][37] The problem with the approach of synthesis followed by self-assembly is that bolaamphiphiles spread at the air/water interface often assume a U-shaped conformation, which prohibits there use in building up asymmetric supported lipid bilayers. 23,38 Inspired by archaebacteria that use bolaamphiphiles to stabilize their membranes against high temperatures, high salinity, and low pH environments, [13][14][15] incorporating bolaamphiphiles into lipid bilayers is thus a promising strategy for membrane stabilization.…”

Design and interfacial behavior of two series of gemini amphiphiles with different charge positions based on imidazole moiety

“…Gemini amphiphiles have been investigated extensively also and they have superior performance in gene transfection [12][13][14][15][16][17], as low-molecular-weight gelators [18,19], and as templates for the preparation of nanoparticles [20,21]. Besides the enormous interest of the use of these amphiphiles in solution systems, as film-forming amphiphiles, both bolaamphiphiles and gemini amphiphiles show some interesting interfacial properties at the air/water interface [2,[21][22][23][24][25][26][27][28]. Our group has been interested in the interfacial behavior of both bolaamphiphiles and gemini amphiphiles and has investigated the interfacial behavior and the interactions with metal ions, DNA, and dyes of some bolaamphiphiles Scheme 1.…”

Methylammonium Groups at the Solid Walls of Nanometer-Sized, Water-Filled Monolayer Gaps as Binding Sites for a Tetraanionic Porphyrin

“…We have described earlier self-assembly procedures for bolaamphiphiles (“bolas”) containing two secondary amide groups close to both headgroups on poly(acrylonitrile) and on gold. − Bolas are amphiphiles with headgroups on each end of a hydrophobic core . Rigid, impermeable monolayers have been obtained, which were impermeable to amines 1 and formed rigid walls around 1−3 nm-wide gaps around steroids 3 or porphyrins. , When the gold electrodes were submersed in aqueous ferricyanide solutions, the gaps were filled with water, and cyclic voltammograms (CVs) of the solute in the bulk solution were obtained.…”

“…Rigid, impermeable monolayers have been obtained, which were impermeable to amines 1 and formed rigid walls around 1−3 nm-wide gaps around steroids 3 or porphyrins. , When the gold electrodes were submersed in aqueous ferricyanide solutions, the gaps were filled with water, and cyclic voltammograms (CVs) of the solute in the bulk solution were obtained. Furthermore, the 2 nm gaps were surrounded by solid walls, in which the monomeric building blocks were fixed by covalent gold−sulfur bonds as well as by two hydrogen-bond chains. − Fitting metalloporphyrins diffused into these gaps and reached their bottom. They quantitatively quenched the fluorescence of free-base porphyrins there, if they carried opposite charges and paramagnetic central ions .…”