Potential docking sites and positions of hydrogen in high-pressure silicates
-
Nancy L. Ross
,
G.V. Gibbs
Abstract
A method based on an analysis of the Laplacian of the electron density distribution is used to locate positions of nonbonding electron-pairs and favorable docking sites for hydrogen in high-pressure silicates, including stishovite, akimotoite, wadsleyite, ringwoodite, MgSiO3, and CaSiO3 perovskite. In stishovite, model hydrogen positions (h) are located off the shared O···O edge of the octahedra with the Oh vector oriented perpendicular to [001]. In akimotoite, two model positions for hydrogen are found, one along an edge of the MgO6 octahedron with an Oh vector aligned close to [001] and the other within the face of the MgO6 octahedra, with Oh vectors oriented perpendicular to [001]. Geometric and electrostatic considerations suggest that both of these sites would require vacant Mg sites. In wadsleyite, potential sites for protonation exist for all O atoms. Hydrogen bonded to O1 resides in a cage-like site with the Oh dipole oriented parallel to [001]. Two symmetrically equivalent sites for hydrogen exist at O2 in a second cage-like structure with Oh vectors aligned approximately along [100]. The calculations also identify potential sites for hydrogen at O3 and O4, but suggest that these could only be occupied by hydrogen if vacancies exist at adjacent Mg sites. Model hydrogen positions in ringwoodite are predicted along O···O edges of the MgO6 octahedron, and, if occupied, would require vacancies at adjacent Mg sites. MgSiO3 perovskite is distinguished by having only one potential site for hydrogen. The Oh vector lies within the (110) plane and geometric and electrostatic considerations suggest that a vacancy is required at the Mg site if this site is protonated. No localized sites for hydrogen are found in CaSiO3 perovskite. We suggest that non-bonded electron pairs associated with oxide anions involved in octahedral frameworks with tilt angles of less than 180° provide more favorable docking sites for protons than those involved in wider angles. The results from the electron density calculations show very good agreement with available crystallographic and spectroscopic data and demonstrate that the strategy used in this study can be useful in locating protons in Earth materials.
© 2015 by Walter de Gruyter Berlin/Boston
Artikel in diesem Heft
- Structural systematics of hydrous ringwoodite and water in earth’s interior
- Compressibility of phase Egg AlSiO3OH: Equation of state and role of water at high pressure
- Synchrotron infrared spectroscopy of OH-chondrodite and OH-clinohumite at high pressure
- Structural deformation mechanisms of zeolites under pressure
- Variation of hydrogen bonded O···O distances in goethite at high pressure
- Pressure-controlled polytypism in hydrous layered materials
- OH– in synthetic and natural coesite
- Pressure-induced phase transformation of kalicinite (KHCO3) at 2.8 GPa and local structural changes around hydrogen atoms
- Potential docking sites and positions of hydrogen in high-pressure silicates
- Contrasting bonding behavior of two hydroxyl-bearing metamorphic minerals under pressure: Clinozoisite and topaz
- Experimental investigation of crystallization kinetics in a haplogranite system
- Assessment of cation substitutions along the gallium and fluorine analogue of the tremolite-glaucophane join
- Experimental hydrothermal alteration of partially metamict zircon
- On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion
- Ordering in spinels—A Monte Carlo study
- Single-crystal in situ high-temperature structural investigation of the I1̅ –I2/c phase transition in Ca0.2Sr0.8Al2Si2O8 feldspar
- New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho
- Fe and Ni impurities in synthetic diamond
- Phase transformations and reaction kinetics during the temperature-induced oxidation of natural olivine
- Thermal infrared spectroscopy and modeling of experimentally shocked plagioclase feldspars
- Oxygen isotopic composition of nano-scale uraninite at the Oklo-Okélobondo natural fission reactors, Gabon
- Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: Origin and evolution of garnet exsolution in clinopyroxene
- Letters. An assessment of nuclear microprobe analyses of B in silicate minerals
- Incommensurate phase in the kosmochlor-diopside join: A new polymorph of clinopyroxene
- Elastic properties of hydrous ringwoodite
- Thermochemistry of guest-free melanophlogite
- A simple model for the pressure preservation index of inclusions in diamond
Artikel in diesem Heft
- Structural systematics of hydrous ringwoodite and water in earth’s interior
- Compressibility of phase Egg AlSiO3OH: Equation of state and role of water at high pressure
- Synchrotron infrared spectroscopy of OH-chondrodite and OH-clinohumite at high pressure
- Structural deformation mechanisms of zeolites under pressure
- Variation of hydrogen bonded O···O distances in goethite at high pressure
- Pressure-controlled polytypism in hydrous layered materials
- OH– in synthetic and natural coesite
- Pressure-induced phase transformation of kalicinite (KHCO3) at 2.8 GPa and local structural changes around hydrogen atoms
- Potential docking sites and positions of hydrogen in high-pressure silicates
- Contrasting bonding behavior of two hydroxyl-bearing metamorphic minerals under pressure: Clinozoisite and topaz
- Experimental investigation of crystallization kinetics in a haplogranite system
- Assessment of cation substitutions along the gallium and fluorine analogue of the tremolite-glaucophane join
- Experimental hydrothermal alteration of partially metamict zircon
- On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion
- Ordering in spinels—A Monte Carlo study
- Single-crystal in situ high-temperature structural investigation of the I1̅ –I2/c phase transition in Ca0.2Sr0.8Al2Si2O8 feldspar
- New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho
- Fe and Ni impurities in synthetic diamond
- Phase transformations and reaction kinetics during the temperature-induced oxidation of natural olivine
- Thermal infrared spectroscopy and modeling of experimentally shocked plagioclase feldspars
- Oxygen isotopic composition of nano-scale uraninite at the Oklo-Okélobondo natural fission reactors, Gabon
- Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: Origin and evolution of garnet exsolution in clinopyroxene
- Letters. An assessment of nuclear microprobe analyses of B in silicate minerals
- Incommensurate phase in the kosmochlor-diopside join: A new polymorph of clinopyroxene
- Elastic properties of hydrous ringwoodite
- Thermochemistry of guest-free melanophlogite
- A simple model for the pressure preservation index of inclusions in diamond
