Postchaos random island structure of a mixed monolayer of phospholipid and crystal violet dye at the air/water interface

Abstract

A mixed monolayer composed of dipalmitoylphosphatidylcholine (DPPC) and crystal violet derivative (CV probe) was investigated by observation of the surface pressure-area isotherms and the Vis absorption spectrum of the CV probe in situ with a spectrophotometer. At surface pressures from 0.1 to 2 mN/m corresponding to a liquid expanded phase, the maximum wavelength of the spectrum varied on repeated runs, but the shape of the spectrum remained unchanged by compression, and frequent disappearance of the absorption was observed. In the region to 20 mN/m, a continuous red shift in the spectrum was observed with increasing surface pressure, as was the continuous variation with the packing density of the mixed monolayer. At a surface pressure greater than 20 mN/m, corresponding to a solid phase, the spectrum resembled that of the CV dimer at a high surface pressure of the CV probe monolayer. In the region below 0.1 mN/m (from 100 to 2000 Å 2), the occasional appearance of absorption was observed. It was concluded that the islands of phospholipid monolayer drift on the water surface and there is equilibrium between the liquid expanded phase (island) and the gaseous phase.