Locking water molecules via ternary O-H⋯O intramolecular hydrogen bonds in perhydroxylated closo-dodecaborate

A multitude of applications related to perhydroxylated closo-dodecaborate B12(OH)122- in the condensed phase are inseparable from the fundamental mechanisms underlying the high water orientation selectivity based on the base B12(OH)122-. Herein, we directly compare the structural evolution of water clusters, ranging from monomer to hexamer, oriented by functional groups in the bases B12H122-, B12H11OH2- and B12(OH)122- using multiple theoretical methods. A significant revelation is made regarding B12(OH)122-: each additional water molecule is locked into the intramolecular hydrogen bond B-O-H ternary ring in an embedded form. This new pattern of water cluster growth suggests that B-(H-O)⋯H-O interactions prevail over the competition from water-hydrogen bonds (O⋯H-O), distinguishing it from the behavior observed in B12H122- and B12H11OH2- bases, in which competition arises from a mixed competing model involving dihydrogen bonds (B-H⋯H-O), conventional hydrogen bonds (B-(H-O)⋯H-O) and water hydrogen bonds (O⋯H-O). Through aqueous solvation and ab initio molecular dynamics analysis, we further demonstrate the largest water clusters in the first hydrated shell with exceptional thermodynamic stability around B12(OH)122-. These findings provide a solid scientific foundation for the design of boron cluster chemistry incorporating hydroxyl-group-modified borate salts with potential implications for various applications.

Highly Structured Water Networks in Microhydrated Dodecaborate Clusters

We report a combined photoelectron spectroscopy and theoretical investigation of a series of size-selected hydrated closo-dodecaborate clusters B₁₂X₁₂^2-·nH₂O (X = H, F, or I; n = 1-6). Distinct structural arrangements of water clusters from monomer to hexamer can be achieved by using different B₁₂X₁₂^2- bases, illustrating the evident solute specificity. Because B-H···H-O dihydrogen bonds are stronger than O···H-O hydrogen bonds in water, the added water molecules are arranged in a unified binding mode by forming highly structured water networks manipulated by B₁₂H₁₂^2-. As a comparison, the hydrated B₁₂F₁₂^2- clusters display similar water evolution for n values of 1 and 2 but different binding modes for larger clusters, while water networks in B₁₂I₁₂^2- share similarities with the free water clusters. This finding provides a consistent picture of the structural diversity of hydrogen bonding networks in microhydrated dodecaborates and a molecular-level understanding of microsolvation dynamics in aqueous borate chemistry.

Protective Effect of Solutions Containing Polymers Associated with Fluoride and Stannous Chloride on Hydroxyapatite Dissolution

This study investigated the protective effect of experimental solutions containing 4 polymers (polyoxirane, hydroxypropylmethylcellulose [HPMC], pectin, and an amino methacrylate copolymer [AMC]) in 2 concentrations (low and high) associated or not with sodium fluoride (F; 225 ppm F-) or sodium fluoride plus stannous chloride (FS; 800 ppm Sn2+) on the dissolution of hydroxyapatite crystals (HA). Deionized water was the control. The pretreated HA was added to a 0.3% citric acid solution (pH 3.8). An automatic titrant machine added aliquots of 0.1 N HCl at a rate of 28 μL/min, in a total reaction time of 5 min. Groups were compared with 2-way ANOVA and Tukey's test, and concentrations with Student t test (5%). The zeta potential of the HA treated with the solutions was measured. Significant differences were found for both factors and interaction (p < 0.0001). The treatments with F and FS solutions resulted in a lower amount of dissolved HA than the control. Among the polymers' solutions, only AMC was able to reduce the amount of dissolved HA, changing the surface charge of HA to positive. AMC improved the protective effect of F, but it did not affect FS. Polyoxirane and HPMC reduced the protective potential of the FS solution. No differences were found between the concentrations of the polymers. It was concluded that F and FS reduced the amount of dissolved HA. The protective effect of the experimental solutions against HA dissolution was polymer dependent. The F effect was enhanced by its combination with AMC, but the protection of FS was impaired by polyoxirane and HPMC.

Insights into the Stabilization of Fluoride Ions in Ionic Liquids: Pointers to Better Fluorinating Agents

The fluorination efficiency of a fluorinating agent depends on the free availability of the fluoride ions, which in turn depends on its interaction with its solvation shell. A stable fluoride-based poor solvate ionic liquid (SIL) comprising 1-ethyl-3-methylimidazolium (EMIM) cation and ethylene glycol (EG) was recently reported and demonstrated as a fluorinating agent. Herein, we performed ab initio calculations and ab initio molecular dynamics simulations to gain a microscopic understanding of the intermolecular interactions in this SIL in gas, liquid, and crystalline phases. Ethylene glycol (EG), being capable of forming hydrogen bond(s) with the fluoride ion, prevents the latter from reacting with the EMIM cation. Fluoride forms hydrogen bonds with both the cation and the EG molecule, but it was found to have more affinity toward EG, forming a stronger hydrogen bond with its hydroxyl proton than with the acidic proton of the cation. An optimal concentration of EG in the SIL balances its contribution to stabilizing the fluoride ion and yet making fluoride available for fluorination.