39K Nuclear Magnetic Resonance Research Articles

Strategic approaches to observing 39K NMR signals from potassium–graphite intercalation compounds

Abstract Solid-state nuclear magnetic resonance (NMR) is an invaluable tool for potassium–graphite intercalation compounds (K-GICs), promising anode materials of K-ion batteries, but it has not yet been applied because of several issues. We attempted 39K NMR measurements of K-GICs sealed in glass using an 18.8 T NMR spectrometer with an NMR probe adjusted to the samples. The first observed 39K NMR signal of K-GICs showed the possibility of evaluating intralayer density, which cannot be ascertained from Raman measurements.

Cation Exchange at the Mineral−Water Interface: H3O+/K+ Competition at the Surface of Nano-Muscovite

This article describes a (39)K nuclear magnetic resonance (NMR) spectroscopic study of K+ displacement at the muscovite/water interface as a function of aqueous phase pH. (39)K NMR spectra and T 2 relaxation data for nanocrystalline muscovite wet with a solid/solution weight ratio of 1 at pH 1, 3, and 5.5 show substantial liquid-like K+ only at pH 1. At pH 3 and 5.5, all K+ appears to be associated with muscovite as inner- or outer-sphere complexes, indicating that H(3)O+ does not displace basal surface K+ beyond the (39)K detection limit under these conditions. In our pH 1 mixture, only approximately 1/3 of the initial basal surface K+ population is located more than 3-4 A from the surface. (29)Si and (27)Al MAS NMR spectra and SEM images show no evidence of dissolution during the (39)K experiments, consistent with the liquid-like (39)K fraction originating from displaced basal surface K+. Assuming no muscovite dissolution or interlayer exchange, the K+/H(3)O+ ratio relevant to the solution/surface exchange equilibrium is controlled by the total amount of K+ on the surface and H(3)O+ in solution (K+(surf)/H(3)O+(aq)). These parameters, in turn, depend on the basal surface area, solution pH, and the solid/solution ratio. The results here are consistent with significant displacement of surface K+ only under conditions where the initial K+(surf)/H(3)O+(aq). ratio is less than approximately 1. Computational molecular models of the muscovite/water interface should account for both K+ and H(3)O+ in the near-surface region.

A study of the ferroelastic phase transition of KH3(SeO3)2 single crystals using nuclear magnetic resonance

Relaxation times in KH3(SeO3)2 crystals were measured as functions of temperature. There are no significant changes in T1 for 1H and 39K nuclei at TC, except for a change in the number of proton and potassium signals. The role of structural changes in this transition is relatively minor. The transition is driven by the protons in the O(2)–H(2)–O(2) bonds, and the change in the number of resonance lines results from the crystal's ferroelastic properties. The results show that the ferroelastic phase transition is associated with the ordering of the O(2)–H(2)–O(2) hydrogens. The T1 and T2 of 1H in the O(2)–H(2)–O(2) bonds are liquid-like, i.e. of the order of milliseconds. In addition, 39K nuclear magnetic resonance results confirm that the phase of this crystal below TC is ferroelastic and that the phase above TC is paraelastic. These results are compared with those obtained for deuterated KD3(SeO3)2 crystals.

Ferroelastic to paraelastic phase transition of K3H(SeO4)2 and Rb3H(SeO4)2 single crystals studied by nuclear magnetic resonance and external stress

AbstractThe temperature dependences of the nuclear magnetic resonance (NMR) and the stress–strain hysteresis curves have been measured for K3H(SeO4)2 and Rb3H(SeO4)2 crystals grown using the slow evaporation method. By analysis of the 39K and 87Rb NMR results, it has been confirmed that the phase below TC is ferroelastic with twin domains and that the phase above TC is paraelastic with a single domain. The ferroelastic domain switching that occurs in the two single crystals due to external stress was also studied. The critical stress values for converting the twin‐domain state to the single‐domain state were obtained. When external stresses of 0.6 and 0.4 MPa were applied to the K3H(SeO4)2 and Rb3H(SeO4)2 crystals, respectively, transitions from twin‐domain to single‐domain states were observed. The ferroelastic domain switching resulting from an external stress may be associated with the atomic rearrangements of the SeO4 tetrahedra in K3H(SeO4)2 and Rb3H(SeO4)2 crystals; the ferroelastic domain switching is explained by the restriction of the rotation of the SeO4 tetrahedra as a result of the breaking of all hydrogen bonds by the external stress. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

39K NMR of Free Potassium in Geopolymers

Nuclear magnetic resonance (NMR) studies of geopolymer gels have shown directly that free Na cations are present in the pore solution of some specimens. Furthermore, it has been suggested previously but not directly proven that potassium is incorporated into these materials, in preference to sodium. Here, the presence of free potassium in the pore solution of geopolymeric gels prepared without sodium hydroxide was confirmed by 39K NMR. The preferential incorporation of potassium was directly shown by the absence of free potassium in the mixed-alkali geopolymer gel.

39K nuclear magnetic resonance and a mathematical model of K+ transport in human erythrocytes

(39)K nuclear magnetic resonance was used to measure the efflux of K(+) from suspensions of human erythrocytes [red blood cells (RBCs)], that occurred in response to the calcium ionophore, A23187 and calcium ions; the latter activate the Gárdos channel. Signals from the intra- and extracellular populations of (39)K(+) were selected on the basis of their longitudinal relaxation times, T (1), by using an inversion- recovery pulse sequence with the mixing time, tau(1), chosen to null one or other of the signals. Changes in RBC volume consequent upon efflux of the ions also changed the T (1) values so a new theory was implemented to obviate a potential artefact in the data analysis. The velocity of the K(+) efflux mediated by the Gárdos channel was 1.19+/-0.40 mmol (L RBC)(-1) min(-1) at 37 degrees C.

Minimum heat of formation of potassium iodo hydride

It was previously reported (R. Mills et al., Synthesis and characterization of potassium iodo hydride, Int. J. Hydrogen Energy, 25(12) (2000) 1185) that a novel inorganic hydride compound KHI which comprised a high binding energy hydride ion was synthesized by reaction of atomic hydrogen with potassium metal and potassium iodide. Potassium iodo hydride was identified by time of flight secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, 1H and 39K nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, electrospray ionization time of flight mass spectroscopy, liquid chromatography/mass spectroscopy, thermal decomposition with analysis by gas chromatography, and mass spectroscopy, and elemental analysis. We report measurements of heats of formation of KHI by differential scanning calorimetry (DSC) on a very reliable commercial instrument, a Setaram HT 1000 calorimeter. With reactant KI present, potassium metal catalyst and atomic hydrogen were produced by decomposition of KH at an extremely slow rate under a helium atmosphere to increase the amount of atomic hydrogen by slowing the rate of molecular hydrogen formation. Since not all of the starting materials reacted, the observed minimum heats of formation were over −2000 kJ/ mol H 2 compared to the enthalpy of combustion of hydrogen of −241.8 kJ/ mol H 2 .

Synthesis and characterization of potassium iodo hydride

A novel inorganic hydride compound KHI which comprises a high binding energy hydride ion was synthesized by reaction of atomic hydrogen with potassium metal and potassium iodide. Potassium iodo hydride was identified by time-of-flight secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, 1H and 39K nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, electrospray ionization time-of-flight mass spectroscopy, liquid chromatography/mass spectroscopy, thermal decomposition with analysis by gas chromatography, and mass spectroscopy, and elemental analysis. Hydride ions with increased binding energies may form many novel compounds with broad applications.

Structure of an LiKSO 4 single crystal studied by 7Li and 39K NMR at low temperature

The 7Li and 39K nuclear magnetic resonances in an LiKSO 4 single crystal grown by the slow evaporation method have been investigated using a Bruker FT nuclear magnetic resonance (NMR) spectrometer. From the experimental data, the quadrapole coupling constant and asymmetry parameter were determined at room temperature and low temperature, respectively. Unlike the case at 300 K, the 7Li NMR line consists of three sets at 180 K, while 39K nucleus exhibits six sets for the rotation around the three crystallographic axes. The three resonance lines of 7Li and 39K at low temperature can be explained by the existence of three kinds of twin domain, rotated with respect to each other by 120° around the c-axis. The three resonance lines are also related to the crystallographic mirror plane. Structure of ferroelastic LiKSO 4 crystals at 180 K can be directly inferred from the domain pattern obtained by 7Li and 39K NMR. The above results show that the equations of the twin boundaries belong to the mm2 F6 mm ferroelastic species. Therefore, the symmetry of phases III and II is given by orthorhombic structure with Cmc2 1 ( mm2) and hexagonal structural with P6 3 mc (6 mm), respectively.

Halotolerance of Methanobacterium thermoautotrophicum delta H and Marburg

Methanobacterium thermoautotrophicum delta H and Marburg were adapted to grow in medium containing up to 0.65 M NaCl. From 0.01 to 0.5 M NaCl, there was a lag before cell growth which increased with increasing external NaCl. The effect of NaCl on methane production was not significant once the cells began to grow. Intracellular solutes were monitored by nuclear magnetic resonance (NMR) spectroscopy as a function of osmotic stress. In the delta H strain, the major intracellular small organic solutes, cyclic-2,3-diphosphoglycerate and glutamate, increased at most twofold between 0.01 and 0.4 M NaCl and decreased when the external NaCl was 0.5 M. M. thermoautotrophicum Marburg similarly showed a decrease in solute (cyclic-2,3-diphosphoglycerate, 1,3,4,6-tetracarboxyhexane, and L-alpha-glutamate) concentrations for cells grown in medium containing > 0.5 M NaCl. At 0.65 M NaCl, a new organic solute, which was visible in only trace amounts at the lower NaCl concentrations, became the dominant solute. Intracellular potassium in the delta H strain, detected by atomic absorption and 39K NMR, was roughly constant between 0.01 and 0.4 M and then decreased as the external NaCl increased further. The high intracellular K+ was balanced by the negative charges of the organic osmolytes. At the higher external salt concentrations, it is suggested that Na+ and possibly Cl- ions are internalized to provide osmotic balance. A striking difference of strain Marburg from strain delta H was that yeast extract facilitated growth in high-NaCl-containing medium. The yeast extract supplied only trace NMR-detectable solutes (e.g., betaine) but had a large effect on endogenous glutamate levels, which were significantly decreased. Exogenous choline and glycine, instead of yeast extract, also aided growth in NaCl-containing media. Both solutes were internalized with the choline converted to betaine; the contribution to osmotic balance of these species was 20 to 25% of the total small-molecule pool. These results indicate that M. thermoautotrophicum shows little changes in its internal solutes over a wide range of external NaCl. Furthermore, they illustrate the considerable differences in physiology in the delta H and Marburg strains of this organism.

Intracellular Compartmentalization of Potassium

The evidence that there is intracellular compartmentalization of potassium is indirect but diverse. Intracellular electrode measurement of potassium activity, 42K radioisotope studies, and more recently 39K nuclear magnetic resonance (NMR) all support such compartmentalization. The use of rubidium to apparently shift potassium between sites with different NMR characteristics (visibility) is strong evidence for such compartmentalization. The evidence that intracellular compartmentalization of potassium is of (patho) physiological significance is also indirect. Postulated roles for regulation of intracellular K+ activity, perhaps by control of compartmentalization, include enzyme activity, protein synthesis, and cell growth. There is also evidence that compartmentalization of potassium may contribute to the maintenance of a stable intracellular environment following potassium loading. The apparent magnetic field dependence of the visibility of K+ by 39K NMR offers the opportunity to explore further the phenomenon of compartmentalization.

Potassium adaptation: 39K-NMR evidence for intracellular compartmentalization of K+.

To investigate the effects of K+ uptake on the intracellular environment, both 39K-nuclear magnetic resonance (NMR) and K+-selective electrodes were used to measure K+ activity with acute K+ loading in control and K+-adapted rats. These results were then compared with tissue K+, measured by flame photometry. There was a lower NMR K+ visibility (ratio of NMR signal to tissue content) in muscle and liver in K+-adapted rats, compared with controls before and after an acute K+ load. This lower K+ visibility in K+-adapted rats was confirmed in liver homogenate with the K+-specific electrode. In liver homogenates from control and K+-adapted rats, addition of RbCl (300 mumol/g) increased the NMR K+ signal more in K+-adapted rats (19 +/- 1.1 mumol/g) than controls (11 +/- 1.0 mumol/g, P less than 0.01). This is consistent with the displacement of K+, by Rb+, from NMR-undetected sites. These results suggest that some 10-15% of intracellular K+ may be within a compartment not detectable by NMR or electrodes and that chronic K+ loading leads to an increased capacity of this compartment.

Measurement of tissue potassium in vivo using 39K nuclear magnetic resonance

39K nuclear magnetic resonance (NMR) spectra were readily obtained, in vivo, from rat muscle, kidney, and brain in 5-10 min with signal-to-noise ratios of approximately 20:1. Quantitation of the K+ signal was achieved by reference to an external standard of KCl/dysprosium nitrate as well as by reference to the proton signal from tissue water. In vitro NMR studies of isolated tissue showed a K+ visibility (NMR K+/total tissue K+) of 96%, 62 +/- 8%, 47 +/- 1.9%, 45 +/- 3.5%, and 43 +/- 2.5% for blood, brain, muscle, kidney, and liver, respectively. Absolute tissue K+ was determined by flame photometry of acid-digested tissue. Changes in tissue K+ status by chronic K+ depletion or acute K+ loading produced changes of 39K NMR signal intensity that were equal to changes of absolute tissue K+. Acidosis, alkalosis, mannitol, or RbCl infusion did not significantly change the NMR K+ signal. These results indicate that the changes in K+ detected by NMR were specifically and accurately detected. To investigate the factors that affect the 39K NMR signal, the effects of liver homogenate on 39K NMR signal intensity were studied. Addition of homogenate produced a 60% loss of signal intensity, suggesting that a large portion of cell K+ may be only 40% visible. Addition of RbCl to undiluted homogenate increased the NMR K+ signal by 11 +/- 2 mumol/g. Addition of H2O or NaCl had no effect, suggesting that Rb+ was replacing K+ in sites of low (less than 40%) NMR visibility. These results demonstrate that 39K NMR experiments can be performed using intact organs. To explain the lack of detectable K+ and changes in K+ NMR visibility, a three compartment model is proposed.

23Na and 39K nuclear magnetic resonance studies of perfused rat hearts. Discrimination of intra- and extracellular ions using a shift reagent

High-resolution 23Na and 39K nuclear magnetic resonance (NMR) spectra of perfused, beating rat hearts have been obtained in the absence and presence of the downfield shift reagent Dy(TTHA)3- in the perfusing medium. Evidence indicates that Dy(TTHA)3- enters essentially all extracellular spaces but does not enter intracellular spaces. It can thus be used to discriminate the resonances of the ions in these spaces. Experiments supporting this conclusion include interventions that inhibit the Na+/K+ pump such as the inclusion of ouabain in and the exclusion of K+ from the perfusing medium. In each of these experiments, a peak corresponding to intracellular sodium increased in intensity. In the latter experiment, the increase was reversed when the concentration of K+ in the perfusing medium was returned to normal. When the concentration of Ca2+ in the perfusing medium was also returned to normal, the previously quiescent heart resumed beating. In the beating heart where the Na+/K+ pump was not inhibited, the intensity of the intracellular Na+ resonance was less than 20% of that expected. Although the data are more sparse, the NMR visibility of the intracellular K+ signal appears to be no more than 20%.

High resolution nuclear magnetic resonance (NMR) studies of cation transport across model and living biological membranes: aqueous shift reagents for 23Na, 39K and 25Mg NMR

High resolution nuclear magnetic resonance (NMR) studies of cation transport across model and living biological membranes: aqueous shift reagents for 23Na, 39K and 25Mg NMR

Potassium-39 nuclear magnetic resonance of potassium-ionophore complexes: Chemical shifts, relaxation times, and quadrupole coupling constants

The complexation of K + by several ionophores was studied by 39K nuclear magnetic resonance. With the use of a high magnetic field (8.5 tesla) and a probe with sideways solenoid transmitter/receiver coil, very good signal-to-noise ratios could be obtained in a reasonable experiment time for concentrations as low as 20 m M and linewidths of the order of 250 Hz. Chemical shifts and spin-lattice relaxation times for 39K in the ionophore complexes are reported. The 39K chemical shifts show a large variation in different ligand environments. 13C spin-lattice relaxation times were measured for the potassium-ionophore complexes in order to derive correlation times. 39K quadrupole coupling constants in the different complexes could thus also be calculated. Despite the low sensitivity of 39K for the NMR experiment, the results indicate that 39K NMR studies of potassium-ligand interactions are feasible at millimolar concentrations.