Isotope Fractionation in Hydroxide Mineral Systems

Isotope fractionation among hydrogen and oxygen in hydroxide minerals refers to the preferential partitioning of isotopes between mineral phases and fluid or gas phases, driven by differences in bond strength and vibrational properties. In layered hydroxides such as brucite (Mg(OH)₂), portlandite (Ca(OH)₂) and transition-metal hydroxides, subtle variations in hydrogen bonding and structural disorder under varying pressure and temperature regimes alter the vibrational zero-point energies associated with different isotopic species. The resulting fractionation signatures are recorded in mineral deposits and metamorphic rocks, providing critical constraints on fluid-rock interaction, water cycling in subduction zones, and the thermal history of the crust and mantle. Experimental and computational approaches—including high-pressure diffraction, vibrational spectroscopy and first-principles methods—have converged to reveal the interplay between hydrogen-bond network topology, phase transitions and nuclear quantum effects. These insights establish a mechanistic framework for interpreting stable isotope distributions in hydroxide-bearing systems and extend our capacity to reconstruct geochemical processes on both local and planetary scales.

Research from Nature Portfolio

Recent studies have applied quantum nuclear dynamics to elucidate the role of nuclear quantum effects in hydrogen-bond networks of layered hydroxides under high pressure. One investigation employing neutron diffraction and quantum treatments of proton motion demonstrated that protons can tunnel between potential minima, leading to pressure-dependent disorder in the hydrogen sublattice and altered isotope partitioning. Complementary path-integral molecular dynamics simulations on brucite have revealed a pressure “sweet spot” for proton diffusion, where covalent bond dissociation and rotational motions compete, highlighting how nuclear quantum effects control hydrogen mobility and thus fractionation factors across a range of geologically relevant conditions.

Isotope Fractionation in Hydroxide Mineral Systems publication trend

The graph below shows the total number of articles in isotope fractionation in hydroxide mineral systems across all publications each year (not limited to Nature Index journals).

Technical terms

Isotope fractionation: The redistribution of isotopes between substances or phases due to differences in physical or chemical behaviour.

Zero-point energy: The lowest possible quantum mechanical energy that a system retains even at absolute zero temperature, affecting vibrational frequencies.

Path-integral molecular dynamics: A simulation technique incorporating quantum nuclear effects by representing particles as ring polymers to capture tunnelling and zero-point motion.

Brucite: A naturally abundant magnesium hydroxide mineral (Mg(OH)₂) forming a prototypical layered hydroxide structure used in high-pressure studies.

Hydrogen-bond network: An interconnected arrangement of hydrogen bonds in a material, critical to its structural and vibrational properties.

Vibrational spectroscopy: Analytical methods such as IR and Raman spectroscopy used to probe vibrational modes that inform isotopic substitution effects.

References

1. Pressure Induced Hydrogen Order–Disorder Transition in β‑Ni(OH)2. The Journal of Physical Chemistry C (2021).
2. Quantum Nuclear Dynamics of Protons within Layered Hydroxides at High Pressure. Scientific Reports (2017).
3. Quantum driven proton diffusion in brucite-like minerals under high pressure. Scientific Reports (2020).
4. High-pressure phase transitions in rubidium and caesium hydroxides. Physical Chemistry Chemical Physics (2016).
5. Equation of State, Compressibility, and Vibrational Properties of Brucite over Wide Pressure and Temperature Ranges: Atomistic Computer Simulations with the Modified ClayFF Classical Force Field. Minerals (2023).