²H and ¹³⁹La NMR Spectroscopy in Aqueous Solutions at Geochemical Pressures

Abstract

Nuclear spin relaxation rates of (2) H and (139) La in LaCl3 +(2) H2 O and La(ClO4 )3 +(2) H2 O solutions were determined as a function of pressure in order to demonstrate a new NMR probe designed for solution spectroscopy at geochemical pressures. The (2) H longitudinal relaxation rates (T1 ) vary linearly to 1.6 GPa, consistent with previous work at lower pressures. The (139) La T1 values vary both with solution chemistry and pressure, but converge with pressure, suggesting that the combined effects of increased viscosity and enhanced rates of ligand exchange control relaxation. This simple NMR probe design allows experiments on aqueous solutions to pressures corresponding roughly to those at the base of the Earth's continental crust.

17 O NMR as a Tool in Discrete Metal Oxide Cluster Chemistry

“…In 2013, however, molecular-dynamic simulations were used to estimate the dielectric constant to 1200°C and 5 GPa [130,131]. These new conditions motivated scientists to design new NMR probes to reach GPa pressures and that are suitable for solution spectroscopy [135][136][137][138]. Additionally, there are separate very promising efforts to establish chemical-shift accuracy in defective diamonds using optical detection [139].…”

“…The increased viscosity contributes directly to broader NMR line widths by slowing molecular tumbling, even in the absence of chemical causes such as enhanced rates of chemical exchange. Although pressureenhanced increases in viscosity can usually be ignored for aqueous solutions in the 0.2-0.4 GPa range (but not in organic solvents [147]) [40][41][42][44][45][46][47][48]131,[134][135][136][137][138][139][140][145][146][147][148][149], increased viscosities in the pressure range 0.5-2.0 GPa causes significant broadening of an NMR line width. This broadening must be accounted in interpreting 17 O NMR spectra to yield rates of reactions, or changes in equilibrium constants (Fig.…”

“…With some changes in alloys, it should be possible to heat these probes to ca 500°C, although these temperatures have not been reached yet. One of the first discoveries when using these new NMR probes is that the presence of electrolyte can easily double the freezing pressure of water or D 2 O [136,137], from 0.9 to 2.0 GPa for LaCl 3 solutions. There are two apparent causes: (i) the electrolyte enhances the freezing pressure by normal colligative processes, and (ii) the freezing of solution into the high-pressure ices (Ice VI, VII) is slow on the NMR timescale, so that one can collect NMR spectra on solutions that are considerably superpressured.…”

Aqueous geochemistry at gigapascal pressures: NMR spectroscopy of fluoroborate solutions

“…This gap in technology inspired us to design a high-pressure NMR probe that can resolve signals from solute species in aqueous solutions at gigapascal pressures (Pautler et al, 2014;Ochoa et al, 2015Ochoa et al, , 2016.…”

29Si NMR of aqueous silicate complexes at gigapascal pressures

“…In recent years, developments of high-pressure solution NMR probes yielded information about the complexation of borate species, up to 1.2 GPa in pressure 25,26 . Efforts have also been made to increase the pressure threshold, robustness, and sensitivity of these types of probes, to the point where they can now reach 2.8 GPa [27][28][29] . Furthermore, there are active efforts to increase this pressure threshold but most designs limit the sample volume to sub microliter volumes where induction NMR detection of solutes is difficult (see Supplementary note 1) [30][31][32][33] .…”