Bolaform amphiphiles with a rigid hydrophobic bixin core in surface monolayers and lipid membranes

Abstract

Several bolaform amphiphiles (bolaamphiphiles) with a rigid polyene as hydrophobic core have been prepared from bixin. Concentrated solutions or precipitates tend to the formation of colorless polymers in the dark. A phenylenediamine-bridged dimer with carboxylate head groups dissolved in DPPC vesicle membranes promotes migration of borohydride and dithionite ions through the membrane. Entrapped indigodisulfonic acid is reduced to two different "leucoindigo" dyes. Surface monolayers of bolaamphiphiles with a cis-bixin Chromophore show characteristic plateau regions beginning at approximately 1.0 nm2/molecule and with fully reproducible overshoots. Surface pressure/area diagrams are interpreted with the formation and reversible pileup of islands of aggregated molecules lying parallel to the water surface. Surface potential measurements and reflection spectroscopy support this conclusion. Bolaamphiphiles with an all-trans-bixin chromophore only produce steep slopes around 0.3 nm2/ molecule. Plateaus are not found. A first interpretation favors an erect position of these amphiphiles in surface aggregates, but the spectroscopic data are not unequivocal. Bixin derivates with a gluconamide head group were effectively integrated into helical micellar gluconamide fibers, which is demonstrated by induced circular dichroism in Pand M-helices.Bolaform amphiphilic (bolaamphiphilic) molecules with a hydrophobic core and two hydrophilic head groups form vesicles with a monolayer membrane,' if the hydrophobic core is made of oligomethylene chains. These membranes can be as thin as 1.5 nm and are nevertheless very efficient barriers to ion and electron t r a n~p o r t .~.~ Several natural and synthetic amphiphiles with one hydrophilic and one hydrophobic edge act as ion pores in monolayer membra ne^.^" They form hydrophilic domains and water channels within the membrane. It should, however, also be possible to transport electrons over lipid membranes by reversible redox reactions of the polyene chains as observed in polyacetylene.6 We chose bixin as a possible "electron wire" because we anticipated a reversible "Michael type addition of electrons" to the activated polyene.Bixin (la) is a natural, unsymmetric bolaamphiphile' from seeds of Bixa orellana? which is commercially available in gram q~a n t i t i e s .~ One head group is a carboxylic acid, the other a carbomethoxy group. The hydrophobic chain consists of a rigid polyene with a cisconfigurated double bond toward the methyl ester end and four methyl groups at regular intervals. The nonsymmetry of the bolaamphiphile can be removed by methylation, hydrolysis, or dimerization via a diol or diamine. It can also be accentuated by one-sided condensation with bulky hydrophilic groups. Furthermore, the cis double bond is "straightened out" (trans isomerized) by iodine (5) Fuhrhop, J.-H.; Liman, U.; Koesling, V. J. Am. Chem. SOC. 1988, 2 IO. fiA4MA45. ---, ----(6) Calvert, P. Nature 1987,327,371. (7) Fuhrop, J.-H.; Mathieu, J. Angew. Chem. 1984,96, 124-137. (8) Kaner, P.; Jucker, ...

New Transmembrane Polyene Bolaamphiphiles as Fluorescent Probes in Lipid Bilayers

“…[5] Some transmembrane bolaamphiphiles have been produced previously for altering specific membrane properties: for example, compounds with p-benzoquinone or anthraquinone groups to change the redox behavior, [6] or conjugated polyenes derived from the natural product bixine to modify the charge-transfer rate across the bilayer. [7] Furthermore, bolaamphiphiles that contain photochemically reactive benzophenone [8] or diazirine [9] groups, or emitting fluorene [10] or anthracene groups, [11] have been also synthesized. A different but interesting fluorescent bolaform structure was also produced by linking two rhodamine 101 dye molecules with a C 32 linear chain.…”

New Transmembrane Polyene Bolaamphiphiles as Fluorescent Probes in Lipid Bilayers

“…In the case of lipid ± lipid and lipid ± protein interactions, the dependence of the resonant transfer of electronic excitation on the proximity of donor and acceptor probe molecules can provide very useful information in the 10-nm range. [7] Furthermore, bolaamphiphiles that contain photochemically reactive benzophenone [8] or diazirine [9] groups, or emitting fluorene [10] or anthracene groups, [11] have been also synthesized. [3] These probes accurately report the changes in order and dynamics of the lipid environment in artificial and natural membranes.…”

“…[3] These probes accurately report the changes in order and dynamics of the lipid environment in artificial and natural membranes. [7] Furthermore, bolaamphiphiles that contain photochemically reactive benzophenone [8] or diazirine [9] groups, or emitting fluorene [10] or anthracene groups, [11] have been also synthesized. However, the mobility of the energy-accepting polyene group in fluid bilayers may introduce some uncertainty into the distance evaluation.…”

Rigid Lipid Membranes and Nanometer Clefts: Motifs for the Creation of Molecular Landscapes

“…Positive electric charges at the hydrophilic edge seem to be essential to keep the edge amphiphiles at a distance, thus allowing ion transport. [13] Real channel formation within defined domains or spacious helices can hardly be distinguished from membrane disturbances by current measurements with the patch ± clamp method. The bee poison melittin thus behaves like an adjustable edge amphiphile.…”