ChemInform Abstract: Structure-Protection Mechanism of Dipalmitoylphosphatidylcholine Liposomes by Adsorption of Sucrose Molecules in the Liposome Surface

Abstract

Molecular mechanism of structure-protection of dipalmitoylphosphatidylcholine (DPPC) liposomes by sucrose adsorption on/in the liposome surface was studied by performing fluorescence decay, quartz-crystal microbalance (QCM), and infrared reflection-absorption (IRRA) spectroscopic measurements. Thermally hydrated DPPC monolayers were newly introduced in place of the conventional DPPC liposomes, since the hydrated monolayers were expected to have similar surface property to that of liposomes. Studies of the fluidity and permeability of membrane in the monolayers and liposomes suggested that the thermally hydrated DPPC monolayers could be used as a model membrane in place of DPPC liposomes. With the hydrated DPPC monolayers, the adsorption rate of sucrose molecules in the DPPC monolayer was investigated by a combined technique of QCM and IRRA by the use of Langmuir-Blodgett (LB) technique. It was found that the incorporation rate of sucrose into the monolayer in the liquid-expanded state was proportional to the bulk concentration of sucrose in the Langmuir trough. The linear relationship depicts the incorporation mechanism that sucrose molecules were deeply incorporated in the DPPC molecules, and the layer is formed as a single mingled layer. This molecular scheme readily supports the conventional hypotheses based upon water-replacement and vitrification mechanisms. The IRRA spectra were further studied using newly found property of principal component analysis (PCA). PCA was found to have great potential to detect minute bands hidden in dominantly large bands, after theoretical speculation and simulations. The new analytical technique was employed to search for an unknown minute spectrum in the collection of raw spectra. The calculated abstract spectra yielded by PCA strongly suggested that there remained minute quantity of water in the dried LB films. The water molecules were also found to bind to PO2 group in the head group moiety of DPPC. The mass change of adsorbed and incorporated sucrose molecules in the DPPC monolayer were readily distinguished by PCA without any probe molecule, and they were followed semi-quantitatively by calculation of scores.