Monolayer structures of triple-chain phosphatidylcholines as substrates for phospholipases

The structural properties of monolayers formed by different triple-chain ph osphatidylcholines (PC) have been investigated at the air-water interface. In order to elucidate the competitive interactions between the hydrophilic headgroup and the hydrophobic chain regions, a number of molecular properti es (chain length, linkage to the glycerol, branching) were varied. Film-bal ance pressure-area isotherms and grazing incidence X-ray diffraction (GIXD) experiments were utilized in the present study. At higher lateral pressure s, monolayer structures of all triple-chain compounds investigated show hex agonal packing, as determined by GIXD. Differences are observable at lower lateral pressures. Components substituted (branched) at the two-position re sult in monolayers consisting of rectangular unit cells with tilted chains. Branching at the four-position reduces the stiffness of the molecules, act ing as a hydrophobic spacer. Therefore four-substituted branched components exhibit hexagonal packing of upright-oriented chains already at lower pres sures. The cross-sectional area of the chains is rather large (ca. 20.8 Ang strom(2)). (C) 2000 Elsevier Science B.V. All rights reserved.