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Ben Abu, Mason and colleagues use molecular dynamics, cell-based experiments, mouse models, and human subjects to determine that, unlike ordinary water, heavy water tastes sweet to humans, but not mice. Mechanistically, this effect is mediated by the human TAS1R/TAS1R3 sweet taste receptor.

The interactions of ions with a model peptide (a single melittin α-helix) in solutions of tetrapropylammonium sulfate or guanidinium chloride were examined by molecular dynamics simulations. The tetrapropylammonium cation shares the geometrical property of essentially flat faces with the previously examined guanidinium cation, and it was found that that this geometry leads to a strong preference for tetrapropylammonium to interact in a similar stacking-type fashion with flat nonpolar groups such as the indole side chain of tryptophan. In contrast to guanidinium, however, tetrapropylammonium does not exhibit strong ion pairing or clustering with sulfate counterions in the solution. Sulfate was found to interact almost exclusively and strongly with the cationic groups of the peptide, such that, already in a 0.1 msolution of tetrapropylammonium sulfate, the 6 charge of the peptide is effectively locally neutralized. In combination with previous simulations, neutron scattering studies, and experiments on the conformational stability of model peptides, the present results suggest that the Hofmeister series can be explained in higher detail by splitting ions according to the effect they have on hydrogen bonding, salt bridges, and hydrophobic interactions in the protein and how these effects are altered by the counterion. [ABSTRACT FROM AUTHOR]

Neutron diffraction experiments were carried out on concentrated aqueous solutions of beryllium chloride at three concentrations:  1.5, 3, and 6 molal. By working with a specific (“null”) mixture of heavy water (D2O) and water (H2O), information on the local structure around Be2ions was extracted directly. For all three BeCl2solutions, the results show that the Be2ion has a well-defined 4-fold coordination shell that is dominated by oxygen atoms. There is also a relatively small probability (10−15%) that there are direct contacts between Be2and Cl-at a distance of ∼2.2 Å. The oxygen atoms of the highly structured Be2first hydration shell are found to be situated at 2.6 Å apart, and form a pyramidal structure, in agreement with recent MD simulation results. The Cl-ions have approximately seven oxygen atoms (water molecules) in their hydration shells sited at 3.2 Å. [ABSTRACT FROM AUTHOR]

Recently, it was shown using structural neutron diffraction with isotopic substitutions (NDIS) measurements, combined with molecular dynamics simulations, that in an aqueous solution of d-xylose the hydroxyl group on the C4 position does not significantly occupy the position trans to the H4 atom. Here, a similar combination of NDIS and MD studies is described which uses d-xylose deuterated at the C5 position to further characterize this hydroxyl conformation as being trans to the C5 atom, as predicted by constrained MD simulations, confirming the previous study. [ABSTRACT FROM AUTHOR]