The effect of chitin nanoparticles on surface behavior of DPPC/DPPG Langmuir monolayers

The effect of chitin nanoparticles on surface behavior of lipid systems containing dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) is studied by surface pressure (π)-area (A) isotherms, polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS), Brewster angle microscopy (BAM). The variation of surface behavior of DPPC/DPPG monolayers is induced mainly by electrostatic interactions between nanoparticles and head groups of phospholipids. At lower surface pressure, nanoparticles can penetrate into the monolayers and the positive charges carried by nanoparticles benefits the enrichment of phospholipid molecules at surface, which not only increases the mean molecular area but also hinders the formation of phospholipid liquid-condensed (LC) phase. However, when surface pressure is higher, the nanoparticles flee away from the surface and some of the phospholipid molecules are pulled out of the monolayers together to the subphase and decrease the order degree of the monolayers. Moreover, nanoparticles can destroy the hydrogen-bond between water molecules and phosphate head groups and thus lead to the dehydration of phosphate groups. This work confirms that chitin nanoparticles can affect the surface behavior of DPPC/DPPG monolayers. Furthermore, the results obtained using mixed monolayer containing two major lung surfactants DPPC/DPPG and nanoparticles will be helpful for deep understanding the harm of PM2.5 to lung health.