Evolution of Hydrogen-Bonding Networks in Glycerol Dimer and Trimer: How Close Are They to Water Clusters?

Glycerol, a flexible triol, has found widespread use in biological and industrial applications due to its intricate intra- and intermolecular hydrogen (H)-bonding capability. Using a combination of experimental broadband rotational spectroscopy and high-level quantum chemistry calculations, we probed low-energy isomers of binary and ternary glycerol aggregates. Seven binary isomers and one ternary isomer were identified experimentally, with the aid of theoretical modeling. The experimental results offer critical benchmarks for theoretical geometry and relative energy ordering predictions across various levels of theory, especially for systems unusually rich in OH groups. Importantly, by detecting these isomers experimentally, we can trace the evolution of the 3D H-bonding networks up to the trimer, thereby gaining molecular-level insights into the initial stages of glycerol self-aggregation. The observed binary and ternary isomers reveal a delicate interplay of intra- and intermolecular H-bonds. The H-bonding networks of their respective most stable isomers show remarkable similarities to those of the observed isomers of (H₂O)₆ and (H₂O)₉ clusters. These findings shed new light on the origin of glycerol's miscibility with water and its related biological functions.