Delayed Onset of Crystallinity in Ion-Containing Aqueous Nanodrops

Abstract

Water exhibits remarkable properties in confined spaces, such as nanometer-sized droplets where hundreds of water molecules are required for crystalline structure to form at low temperature due to surface effects. Here, we investigate how a single ion affects the crystallization of (H2O)n clusters with infrared photodissociation spectroscopy of size-selected La(3+)(H2O)n nanodrops containing up to 550 water molecules. Crystallization in the ion-containing nanodrops occurs at n ≥ 375, which is approximately 100 more water molecules than what has been reported for neutral water clusters. This frustration of crystallinity reveals that La(3+) disrupts the hydrogen-bonding network of water molecules located remotely from the ion, a conclusion that is supported by molecular dynamics simulations. Our findings establish that a trivalent ion can pattern the H-bond network of water molecules beyond the third solvation shell, or to a distance of ∼1 nm from the ion.

Sequential water molecule binding enthalpies for aqueous nanodrops containing a mono-, di- or trivalent ion and between 20 and 500 water molecules

“…Indications for a water–ice phase transition for water clusters with 60–79 water molecules at 133 ± 6 K and for a phase transition to crystalline ice for La 3+ ·(H 2 O) 375 at 133 K have been reported previously. 63–66 Therefore, our interpretation of the increased average water molecule binding enthalpies within a modified 133 K TLDM is consistent with these findings. With bulk ice parameters and optimizing γ and ∂ln( p / p 0 )/∂ T , the experimental values can be reproduced with accuracies of ±0.8 kJ mol –1 between n = 20–500 water molecules.…”

“…Evidence for the influence of ions on the water phase in large water clusters comes from a recent study that showed that La 3+ ions can affect the onset of crystallinity in clusters as large as 375 water molecules. 63 …”

“…The use of ice parameters for the TLDM calculations is consistent with recent results, which indicate that large clusters are “ice-like” at low temperature. 63–66 It is still debated at what cluster size the thermodynamic concept of phase is applicable to nanodrops and it has been shown that spectroscopic features for amorphous and crystalline ice can coexist for clusters with up to 550 water molecules, 63 hence, we use the phrase “ice-like” in what follows as a synonym for the presence of amorphous or crystalline ice phases.…”

Nanometer patterning of water by tetraanionic ferrocyanide stabilized in aqueous nanodrops

“…These interactions are especially important in environments where water is scarce, such as in living cells and reverse micelles, and will manifest as changes to the dynamics of surrounding water molecules as well as freezing point depression. 40 Long-distance forces originating from ions may also partially account for Hofmeister and other ion-related phenomena.…”

“…37,38 Using IRPD spectroscopy of mass-selected, ion-containing water clusters, orientation effects on water by a single solvated ion free of any counterion contributions can be measured. 21,39,40 The sensitivity of this technique is not limited by the ratio of water molecules to ions. As a result, ion–water interactions can be measured to a hypothetical infinite dilution.…”