Combined Liposome–Gold Nanoparticles from Honey: The Catalytic Effect of Cassyopea^® Gold on the Thermal Isomerization of a Resonance-Activated Azobenzene

Gold nanoparticles (AuNPs) have been synthesized directly inside liposomes using honey as a reducing agent. The obtained aggregates, named Cassyopea^® Gold due to the method used for their preparation, show remarkable properties as reactors and carriers of the investigated AuNPs. A mean size of about 150 nm and negative surface charge of -46 mV were measured for Cassyopea^® Gold through dynamic light scattering and zeta potential measurements, respectively. The formation of the investigated gold nanoparticles into Cassyopea^® liposomes was spectroscopically confirmed by the presence of their typical absorption band at 516 nm. The catalytic activity of the combined liposome–AuNP nanocomposites was tested via the thermal cis–trans isomerization of resonance-activated 4-methoxyazobenzene (MeO-AB). The kinetic rate constants (k_obs) determined at 25 °C in the AuNP aqueous solution and in the Cassyopea^® Gold samples were one thousand times higher than the values obtained when performing MeO-AB cis–trans conversion in the presence of pure Cassyopea^®. The results reported herein are unprecedented and point to the high versatility of Cassyopea^® as a reactor and carrier of metal nanoparticles in chemical, biological, and technological applications.