Study of chiral recognition of bilayered phosphatidylcholine vesicles using a helicene probe: characteristic function of cholesterol

Incorporated into bilayered chiral phosphatidylcholine (PC) vesicles, 2-hydroxymethyl[5]thiaheterohelicene (5HM) having a labile helix that functioned as a chirality probe, exhibited induced CD absorptions. The Cotton effects of these absorptions demonstrated opposite signs according to the difference in chirality of PC applied, indicating the chiral recognition of the vesicles. The vesicles formed by PCs with unsaturation or acyl chains shorter than dipalmitoyl-PC (DPPC) exhibited a slightly stronger CD absorptions of 5HM, presumably because of an increase in the constraint by the vesicles. The phenomenon that an increase in fluidity results in a decrease in the CD intensity was examined by CD measurements at various temperatures. The vesicles formed with egg lecithin and bovine heart lecithin also induced CD absorptions of 5HM similar to those of (L)PC vesicles. The influence of cholesterol (Cho) and four kinds of analogs with different structures at the 3- or 5-position of a Cho molecule on the CD intensities was investigated. Following addition of Cho, the CD intensities of 5HM decreased slightly in the (L)DPPC vesicles and increased moderately in the (D)DPPC vesicles. On the other hand, by addition of Cho analogs the CD intensities of 5HM were nearly unchanged in (L)DPPC vesicles and weakened moderately in the (D)DPPC vesicles.