Binding Mechanism of Sucrose to Dipalmitoylphosphatidylcholine Langmuir Films by Fourier Transform Infrared Reflection−Absorption Spectroscopy and Quartz-Crystal Microbalance Technique

On the normalization method in two-dimensional correlation spectra when concentration is used as a perturbation parameter

Data pretreatment is of importance in two-dimensional (2D) correlation analysis when composition is used as a perturbation parameter. For composition-oriented studies, different normalization methods based on both external parameters (i.e., concentration) and internal parameters (i.e., absorbance from individual components) have been compared. It was found that when there is no overlapping between absorption bands of interest, no normalization is needed for data pretreatment. When overlapped bands must be used for 2D correlation analysis, the mean-centered normalization method could be used to obtain correct signs in synchronous spectra for a transformation process in the specific form of A-->kC. The intensity of the 2D spectrum, however, may not accurately reflect quantitative information of the overall extent of spectral intensity variation observed during experiments.

LIPOPHILIC-FULLERENE DERIVATIVE MONOLAYERS AT THE AIR–WATER INTERFACE

Monolayers of a lipophilic C 60-derivative (FPTL) mixed in dipalmitoyl-phosphatidyl-choline (DPPC) have been studied by the Langmuir film balance technique and Brewster angle microscopy. Previous X-ray scattering studies showed that the FPTL molecules intercalated into the DPPC monolayers and modified the bending and compression modulus of the host DPPC membranes. Combined study of surface pressure–area isotherms and Brewster angle microscopy measurements clearly established that the liquid-condensed domain structures are strongly influenced by an addition of the fullerene bearing lipid molecules, where it caused smaller liquid-condensed domain structures.

Coalescence of Lipid Emulsions in Floating and Freeze-Thawing Processes: Examination of the Coalescence Transition State Theory

Lipid emulsions, triacylglycerol droplets covered with single surface monolayers of phospholipid in aqueous medium, were prepared by high-pressure emulsification and successive ultracentrifugation. Egg yolk phosphatidylethanolamine did not stabilize triolein (TO) droplets in aqueous medium. Phosphatidylcholine (PC) of various long fatty acyl chains dispersed TO and tricaprylin (TC) well in aqueous medium as emulsion droplets of 110 nm. After ultracentrifugation, however, oil separation was observed in the floating creamy layer of TO/dioleoyl-PC emulsions. Dioleoyl-PC contains two bulky unsaturated fatty acyl chains, as well as oleoyl chains, and it has a lower spontaneous curvature than egg PC. Egg PC and dipalmitoyl-PC gave stably dispersed emulsion droplets of TO even after the freeze-thawing (F-T) procedure. On the other hand, TO/egg PC emulsion droplets containing cholesterol of 83 mol% PC and TC/egg PC emulsion droplets coalesced after the F-T procedure. Cholesterol and a medium chain triacylglycerol, TC, were distributed into the surface PC monolayers and occupied an appreciable fraction of the surface area. These neutral lipids have small polar groups and thus decrease the mean spontaneous curvature of surface lipids. The relationship between the droplet coalescence and the spontaneous curvature was discussed on the basis of the coalescence transition state theory recently developed by Kabalnov et al. in 1996. In addition, effects of maltose on the emulsion coalescence in the freeze state were briefly discussed. Copyright 1999 Academic Press.