Despite the availability of many water-soluble organometallic and nanoparticulate catalysts, the direct application of water-soluble catalysts for the reaction of immiscible and hydrophobic substrates has been hindered by the low solubility of nonpolar reactants in water. Our research group has shown that alkanethiolate-capped palladium nanoparticles (PdNP) exhibit excellent catalytic activity and selectivity for hydrogenation of unsaturated compounds in organic solvents. This PdNP was synthesized using the thiosulfate protocol using sodium S-dodecylthiosulfate as ligand precursor.  The purpose of this study is to examine the catalytic activity of PdNP embedded in the bilayers of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) lipids in water. After the liposome film assembly of PdNP with PC in chloroform, the solvent was removed under vacuum and the hybrid was hydrated with phosphate buffered saline (PBS) solution. The resulting liposome-PdNP hybrids dissolved in water were characterized using UV-vis spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), dynamic light scattering (DLS), and transmission electron microscopy (TEM). During the catalysis reaction, the bilayer characteristics of liposome-PdNP hybrid would allow the hydrophobic substrate such as 1-octene and its isomers to momentarily enter the hydrophobic region of the catalysts with adequate stirring force. After the reaction, the resulting products from bi-phasic system were subsequently extracted with organic solvents and analyzed using <sup>1</sup>H NMR spectroscopy and gas chromatography. The results suggested that the transformation of 1-octene to <i>trans</i>-2-octene and cis-2-octene initially occur after 1 h of reaction time. Hydrogenation of trans-2-octene and cis-2-octene to octane takes place as the reaction proceeds. Final results suggest complete transformation of 1-octene to octane within 24 h of catalysis reaction under atmospheric pressure and at room temperature. In comparison, the catalytic reaction of 1-octene with the same PdNP in chloroform produces mostly the isomerization product, 2-octene. The increase in hydrogenation activity of PdNP in water after liposome encapsulation indicates that the surrounding environment of PdNP further controls its catalytic activity and selectivity.

Liposome-embedded hydrophobic palladium nanoparticles for biphasic catalysis in water

2019 Fall National Meeting

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