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.