Quantitative Chirality Measures Applied to Domain Formation in Langmuir Monolayers

A quantitative chirality measure previously developed by Zabrodsky et al. (Zabrodsky, H.; Peleg, S.; Avnir, D. J. Am. Chem. Soc. 1992, 114, 7843-7851) has been applied to the analysis of liquid-condensed domain shapes in Langmuir monolayers of the phospholipid D-α-phosphatidylcholine, dipalmitoyl (dipalmitoylphosphatidylcholine or DPPC). We present data on the variation of the quantitative chirality measure as a function of in-plane molecular area and temperature, as well as different subphase electrolyte concentration. Upon compression, the chirality is shown to grow monotonically with decreasing molecular area (increasing surface pressure) and to correlate linearly with the domain shape factor (a measure of noncompact growth). The chirality was similar for temperatures 25 °C and decreased substantially by 30 °C. For a subphase electrolyte concentration high enough to screen out electric dipole interactions, the dependence of chirality measure on molecular area is the same as that measured for low-electrolyte concentration data taken at 30 °C. Sample chirality calculations are also presented for a variety of other amphiphiles using previously published data.