Plasmon-activated water can form stronger intermolecular hydrogen bonding with water-soluble alcohols and dissolve more hydrophobic solutes

Abstract

Liquid water, as the most environmentally friendly polar solvent, is popularly used in physical processes and chemical reactions. Its unique properties and activities come from the presence of intermolecular hydrogen bonds (HBs) with itself and other species. Scientists have been discussing properties other than known bulk water for a long time. However, the particular application of water being researched is limited today. Mass-produced active and stable plasmon-activated water (PAW) with a reduced HB network based on hot electron transfer (HET) from resonantly illuminated gold (Au) nanoparticles (NPs) was first created in 2014. In this work, we report its distinct intermolecular HBs with water-soluble alcohols and the solubility of hydrophobic solutes. Interestingly, the densities of PAW in methanol, ethanol, and propanol at various ratios all increased due to stronger HBs between PAW and the alcohols, particularly seen with propanol, compared to deionized water (DIW)-based systems. Moreover, these results reflect the decreased evaporation rates of PAW/alcohol solutions, especially observed for the solution with the maximum increased density, compared to DIW-based systems. Compared to DIW, the solubilities of hydrophobic antioxidants of curcumin and melatonin in PAW increased by ca. 240% and 120%, respectively. Moreover, sunflower oil was more soluble in the more-lipophilic PAW compared to conventional DIW. The distinct increased density of the alcohol/PAW solution lasted for at least 1 week. Innovative PAW has emerged as a promising green active solvent applicable for both hydrophilic and hydrophobic solutions.