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Hydration Shell Structure and Water-Mediated Binding of closo-Dodecaborates Probed by Raman Hydration-Shell Spectroscopy

Year: 2026
Type: preprint
Abstract: The binding of closo-dodecaborates, B12X122- (where X = H, Cl, Br, I), to solutes and interfaces has widely been attributed to a water-mediated (super-)chaotropic effect. The role of water, however, has so far been inferred only indirectly from thermodynamic measurements. Herein, we employ Raman hydration-shell spectroscopy in the OH stretch region to investigate B12X122- in aqueous solution. Specifically, we elucidate i) the water structure in the hydration shell, ii) its temperature dependence, and iii) the water release upon superchaotropic binding. The hydration-shell spectra reveal that all dodecaborates give rise to a sharp Raman band close to 3600 cm-1. This feature is strongly blue-shifted compared to bulk water and represents weakly H-bonded, “almost dangling” OH-groups in the hydration shell. Heating is found to blue-shift the hydration water resonance less than the bulk water resonance. Hydration and bulk water resonances thus become more similar at high temperature. This trend reflects a progressively reduced difference in hydrogen-bonding energy upon heating between hydration and bulk water, and is opposite to that of hydrophobic hydration. Furthermore, hydration difference spectra in the presence of the non-ionic polymer hydroxypropylcellulose (HPC) reveal that weakly H-bonded hydration water is released from B12X122- upon superchaotropic binding, together with more strongly H-bonded hydration water from the hydration shells of both B 12 X 12 2- and HPC. These findings identify weakly bound hydration water, its weak temperature dependence, and its spontaneous release upon binding as molecular hallmarks of the superchaotropic behavior of B 12 X 12 2- .
Source: ChemRxiv
DOI: 10.26434/chemrxiv.15007801/v1
Language: English
Field: Medicine
Open Access status: green
OpenAlex ID: W7204179625
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Cited by: 1
Related to: 10