π-Hydrogen Bonding in Liquid Water

We report the experimental observation and quantitation of pi-hydrogen bond formation between liquid water and benzene using Raman multivariate curve resolution (Raman-MCR) combined with quantum and classical (cluster and liquid) calculations. Our results establish that pi-hydrogen bonds between liquid water and benzene are weaker and more flexible (have a more positive enthalpy and entropy) than bulk water hydrogen bonds. We further establish that such bonds also form between water and other aromatics, including the amino acid phenylalanine, thus implying their common occurrence at hydrated biological interfaces.