Effects of ions on water structure: a low‐field ¹H T₁ NMR relaxometry approach

Abstract

Aqueous salt solutions play an important role in nature because of their effects on environmental biogeochemical processes and on structural properties of biomolecules. Upon dissolution, salts split in ions that are solvated. Water in hydration shells is subjected to molecular motions that can be monitored by (1)H T1 NMR relaxometry. This technique allowed the evaluation of the nature of the interactions between water and ions via variable temperature experiments. Examination of relaxometry properties of aqueous solutions at variable salt concentrations allowed acknowledgement of the role played by ions in either structuring or destructuring water aggregates. A mathematical model has been applied on six environmentally relevant salts: NaCl, KCl, CaCl2, CaCO3, NaNO3, and NH4NO3. It was linear only for the concentration dependence of KCl-R1. This model accorded with the one reported in literature where it has been considered valid only for diluted solutions. However, in the present study, the range of linearity for KCl was extended up to the saturation point. The model was modified for NaCl, CaCl2, and CaCO3 by using it as an exponential form in order to account for the nonlinearity of the R1-versus-concentration curves. Nonlinearity was explained by the nonnegligible ion-ion interactions occurring as concentration was increased. Finally, further modification was needed to account for the asymmetric distribution of water around nitrate (in NaNO3 and NH4NO3) and ammonium (in NH4NO3). This study is preliminary to the comprehension of the diffusion mechanisms of ions in water solutions at the equilibrium condition with solid surfaces such as soils and biochar-amended soils.

Plant growth improvement mediated by nitrate capture in co-composted biochar

“…The interactions between water and the organic constituents of biochar can be obtained through the electron-donation from the π-clouds of the polyaromatic systems towards the electron-deficient hydrogens in water. This may lead to weak unconventional H-bonds between the asymmetrically shaped hydrated nitrate ions 58 and the porous biochar surfaces. Moreover, Conte et al 56 recently showed that water movement in a pyrogenic poplar biochar was slow at temperatures up to 50 °C due to strong surface bonding forces; these forces considerably weakened at 80 °C.…”

On Water and its Effect on the Performance of T1‐Shortening Contrast Agents

“…Therefore r 1 was determined through a single point measurement of R 1 according to Eqn 1. The value of R 1W was calculated according to Eqn 2 for chaotropic salts and to Eqn 3 for kosmotropic salts . The values of β + were −0.019 (K + ), +0.057 (Na + ) and +0.24 (Ca 2+ ) and the value β − was −0.019 (Cl − ) .…”

“…The value of R 1W was calculated according to Eqn 2 for chaotropic salts and to Eqn 3 for kosmotropic salts . The values of β + were −0.019 (K + ), +0.057 (Na + ) and +0.24 (Ca 2+ ) and the value β − was −0.019 (Cl − ) . R 1 obs is the measured relaxation rate constant (=1/ T 1 ), R 1W is the relaxation rate constant of the solvent in the absence of the Gd 3+ chelate, and R 1 0 is the longitudinal relaxation rate constant of water in the absence of both Gd 3+ and salt. …”

Biochar‐Based Fertilization with Liquid Nutrient Enrichment: 21 Field Trials Covering 13 Crop Species in Nepal

“…The capturing and release of cations and anions in biochar are most likely because of the following: Water bridging – i.e. water bridges between the hydration shells surrounding the dissolved ions and the hydrophilic systems, such as inorganic ashes and oxy‐genated organic functions, on biochar surfaces (Conte, ). Ionic bonding – i.e. direct ion bonding to positive, respectively, negative charged micro sites, functional surface groups or precipitated metal oxides or pyrolytic tars. Covalent bonding – i.e.…”

“…(1) Water bridgingi.e. water bridges between the hydration shells surrounding the dissolved ions and the hydrophilic systems, such as inorganic ashes and oxy-genated organic functions, on biochar surfaces (Conte, 2014).…”