posted on 2024-01-16, 17:35authored byShavkat Mamatkulov, Jakub Polák, Jamoliddin Razzokov, Lukáš Tomaník, Petr Slavíček, Joachim Dzubiella, Matej Kanduč, Jan Heyda
The borohydride ion, BH4–, is an essential reducing agent in
many technological processes, yet its full understanding has been
elusive, because of at least two significant challenges. One challenge
arises from its marginal stability in aqueous solutions outside of
basic pH conditions, which considerably limits the experimental thermodynamic
data. The other challenge comes from its unique and atypical hydration
shell, stemming from the negative excess charge on its hydrogen atoms,
which complicates the accurate modeling in classical atomistic simulations.
In this study, we combine experimental and computer simulation techniques
to devise a classical force field for NaBH4 and deepen
our understanding of its characteristics. We report the first measurement
of the ion’s activity coefficient and extrapolate it to neutral
pH conditions. Given the difficulties in directly measuring its solvation
free energies, owing to its instability, we resort to quantum chemistry
calculations. This combined strategy allows us to derive a set of
nonpolarizable force-field parameters for the borohydride ion for
classical molecular dynamics simulations. The derived force field
simultaneously captures the solvation free energy, the hydration structure,
as well as the activity coefficient of NaBH4 salt across
a broad concentration range. The obtained insights into the hydration
shell of the BH4– ion are crucial for accurately modeling and understanding its interactions
with other molecules, ions, materials, and interfaces.