BOLAFORM AMPHIPHILES WITH A RIGID HYDROPHOBIC BIXIN CORE IN SURFACE MONOLAYERS AND LIPID-MEMBRANES

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 nm2molecule 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 P- and M-helices.