Effects of Bilayer Nanoenvironment on the Catalytic Activity of Lipid–Pd–Nanoparticle Assemblies in Water

Our previous work has shown that the bilayer characteristics of lipid–nanoparticle assemblies (LNAs) consisting of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) liposomes and hydrophobic Pd nanoparticles (PdNPs) allow the hydrophobic substrates to enter the hydrophobic region of the assemblies and promote hydrogenation in water. In this paper, to better understand the effects of the bilayer nanoenvironment within liposomes on the catalytic activity of LNAs, the structure/composition-property relationships of LNAs are investigated by manipulating the lipid and nanoparticle compositions. Specifically, lipids with different chain lengths, mixed lipids with varying mass ratios, and PdNPs with different surface ligand densities but similar core sizes were introduced into the bilayers of LNAs to control the immediate environments surrounding nanoparticle catalysts. Catalytic studies showed that the hydrogenation kinetic rate depends on the lipid composition of LNAs. LNAs composed of 1,2-dilouryl-sn-glycero-3-phosphocholine (DLPC) performed hydrogenation more quickly than LNAs of DSPC. Interestingly, binary LNAs with DSPC and DLPC mixed lipids were less catalytically active than monotonic LNAs with either type of lipids. Regarding the effect of the surface ligand density of PdNPs, the enhanced catalytic activities observed for PdNPs with a lower surface ligand density in organic solvents nearly disappeared for hydrophobic PdNPs when embedded into the liposome bilayer.