87Rb NMR Research Articles

85,87Rb, 14N NMR Studies of Successive Phase Transitions and Incommensurate Phase in R2Pb[Cu(NO2)6] (R = NH4, Rb)

85,87Rb and 14N NMR spectra and spin-lattice relaxation time (T1) were measured for R2Pb[Cu(NO2)6] (R = Rb, NH4). The quadrupole coupling constant (e2Qq/h), asymmetry parameter (η), and the effective transverce relaxation time (T2) were estimated from the simulation of NMR spectra. The NMR spectra in commensurate phase III can be explained by the superposition of two components corresponding to two inequivalent sites of the R+ ion. In the incommensurate phase II, e2Qq/h and T2 decreased with increasing temperature, while was almost temperature independent. T1 in phase II is found to be determined by the contribution of acoustic phason with multi-soliton limits

Satellite-Transition MAS NMR of Spin I=3/2, 5/2, 7/2, and 9/2 Nuclei: Sensitivity, Resolution, and Practical Implementation

The satellite-transition MAS (STMAS) experiment offers an alternative approach to established methods such as dynamic angle spinning (DAS), double rotation (DOR), and multiple-quantum MAS (MQMAS) for obtaining high-resolution NMR spectra of half-integer quadrupolar nuclei. Unlike the multiple-quantum experiment, STMAS involves two-dimensional correlation of purely single-quantum coherences; satellite transitions in t 1 (or F 1) and the central transition in t 2 (or F 2). To date, STMAS has primarily been demonstrated for nuclei with spin quantum numbers I=3/2 and, to a lesser extent, I>5/2. However, many chemically relevant nuclei possess I>3/2, such as 17O and 27Al (both I=5/2), 59Co ( I=7/2), and 93Nb ( I=9/2). Here, we discuss the application of STMAS to nuclei with spin quantum numbers from I=3/2 to 9/2. First, we consider the practical implementation of the STMAS experiment using 87Rb ( I=3/2) NMR as an example. We then extend the discussion to include nuclei with higher spin quantum numbers, demonstrating 27Al, 45Sc ( I=7/2), 59Co, and 93Nb STMAS experiments on both crystalline and amorphous samples. We also consider the possibility of experiments involving satellite transitions other than m I =±1/2↔±3/2 and, using 93Nb NMR, demonstrate the correlation of all single-quantum satellite transitions up to and including m I =±7/2↔±9/2. The absolute chemical shift scaling factors in these experiments are discussed, as are the implications for isotropic resolution.

Phase Transition Mechanism Studied by1H and87Rb Spin-Lattice Relaxation Time in a RbHSO4Single Crystal

The 1 H and 87 Rb NMR spin-lattice relaxation times for a RbHSO 4 single crystal were measured in the temperature range of 300–170 K for study of the paraelectric (I) to ferroelectric (II) phase transition near T c =264 K. Proton spin-lattice relaxation time on the RbHSO 4 yielded a minimum, attributed to the effect of molecular motion. The activation energy for the reorientational motion in phase I was determined to be 16.54 kJ/mol, whereas, for the molecular motion in the phase II it was 25.53 kJ/mol. The change of the 87 Rb spin-lattice relaxation rate near 264 K corresponds to a phase transition in the crystal. The temperature dependences of the relaxation rate for 87 Rb in this crystal were in accordance with the single phonon process dominated by the phonon mechanism. The activation energies in phases I and II were obtained to be 2.66 kJ/mol and 17.25 kJ/mol, respectively. From 1 H and 87 Rb NMR investigations, the phase transition does play an important role by Rb nucleus, although the activation e...

Effects of flow and energy metabolism on injury and Rb uptake in pig hearts: An 87Rb and 31P NMR study

Effects of flow and energy metabolism on injury and Rb uptake in pig hearts: An 87Rb and 31P NMR study

Solid-state rubidium exchange of zeolite NH 4Y

NH 4Y has been ion exchanged by reaction with solid Rb 2CO 3 to form RbY. This process has been followed with X-ray powder diffraction, mass spectrometry and NMR. Both 1 H and 87 Rb MAS NMR are very sensitive to the hydration level of the zeolite and have been used to investigate the solid-state exchange process. 87 Rb NMR shows that exchange begins instantaneously on grinding the two solids together: decomposition of Rb 2CO 3 is observed, together with the migration of Rb + into the zeolite pores. X-ray diffraction indicates that the reaction proceeds to completion by 400 °C. The structure of the final RbY product has been refined with Rietveld analysis and rubidium cations have been located at the SI ′ SII and SIII ′ positions. Residual sodium cations from the incomplete exchange of the ammonium starting material have been located at the SI position; this result was confirmed by 23 Na MAS NMR. No evidence for Rb occupation of the SI positions was observed. Considerable disorder is observed in the cages of the zeolite during the ion-exchange process, but refinements of the structures, using the in situ data, indicate that Rb + cations have entered the sodalite cages by 200 °C.

Rb+ and Na+ spin relaxation in aqueous gellan solutions and implication of selective site binding of alkali metal ions.

87Rb NMR was applied to investigate the site binding of Rb+ ions in gellan gum gels. The temperature dependence of the transverse and longitudinal relaxation NMR relaxation rates of 87Rb+ ion and 23Na+ ion have been compared in aqueous 5% (w/v) rubidium-type and sodium-type gellan. In each sample, the relaxation rates were sensitive to the conformation (helix or random coil). In rubidium-type gellan, significant line-broadening effects (losses in intensity) were found, which is due to the presence of cation-binding sites in the ordered conformation. In sodium-type gellan, such an enhancement of the relaxation was not observed. These results indicated that gellan gum produced highly selective binding sites for alkali metal ions, in which Rb+ ion bound more strongly than Na+ ion. The 87Rb NMR line shift suggested selective site binding of ions to form the cross-linking domains in gellan gels.

7Li and 87Rb nuclear magnetic resonance in aLiRbSO4 single crystal with the growth twin domain

The 7Li and 87Rb NMR in a LiRbSO4 single crystal with the growthtwin domain grown by the slow evaporation method were investigated byemploying a Bruker FT NMR spectrometer. Instead of the simple one set ofsignals caused by quadrupole interaction, three sets of NMR signals wereobtained. From these results, all parameters were determined, and all lead tothe same values for the quadrupole coupling constant and asymmetry parameter.The 7Li NMR parameter in the LiRbSO4 crystal was axially symmetric,whereas the 87Rb NMR parameter was non-axially symmetric; the lithium ionis surrounded by oxygen atoms located on a regular tetrahedron, and theresultant coordinating rubidium ion is surrounded by slightly distorted oxygenatoms located at nine regular tetrahedra. The obtained results can beexplained by the existence of three kinds of growth twin domain, rotatedwith respect to each other by 120° around the c-axis.

Effects of ischemia on intracellular rubidium in pig and rat hearts: 87Rb NMR imaging and spectroscopic study

87Rb MR imaging and spectroscopy were used to study the effects of ischemia on the properties of K+ in cardiac tissue. Isolated pig and rat hearts perfused by the Langendorff method with Krebs-Henseleit buffer were preloaded with Rb+. Ischemia (Isc) was induced by 120-min occlusion of the left anterior descending artery in the pig hearts or by stopping perfusion for 33 min in the rat hearts. Serial 87Rb MR images or spectra from the anterior (An) LV wall of pig hearts were acquired continuously. The intensities of the Rb images of the An and posterior (Pos) walls were similar and stable during the first 45 min of ischemia. The intensity of signal from the An wall (Isc) then gradually increased by 60 ± 8% relative to the preischemic value (vs. 31 ± 5% increase in Pos wall) and necrosis (19 ± 5% of the LV wall mass) developed upon reperfusion. The Rb+ content was lower in the ischemic (An) than in the normal (Pos) area (22.3 ± 3 vs. 28.4 ± 1.3 mmol/g wet wt). A similar pattern was observed in the peak heights of 87Rb spectra from the An wall, which increased by 40 ± 16% (vs. 21 ± 11% in control) due to a 12% decrease in the apparent Rb linewidth (LW) and a 24 ± 14% increase in the peak area. The Rb peak comprised narrow (297 ± 21 Hz) and broad (1098 ± 40 Hz, 59 ± 3% of total area) Lorentzian components. The LW of the broad component decreased by 14%, while the narrow component did not change markedly. In the rat hearts ischemia caused a 33 ± 4% increase in the 87Rb peak height as a result of peak narrowing (13 ± 1%), and an increase in peak area (17 ± 5%). The decreases in LW and increases in Rb+ visibility can be explained by an increase in Rb+ mobility caused by displacement of Rb+ from anionic binding sites by H+ (ischemic acidosis) and changes in intracellular compartmentalization of Rb+. Magn Reson Med 44:193–200, 2000. © 2000 Wiley-Liss, Inc.

Three‐dimensional 87Rb NMR imaging and spectroscopy of K fluxes in normal and postischemic pig hearts

Three‐dimensional 87Rb NMR imaging and spectroscopy of K fluxes in normal and postischemic pig hearts

Solid-State 87Rb NMR Study in Powdered RbMnCl3

Structural phase transition at 290 K and the implication on the intermediate phase above 290 K in powdered RbMnCl3 are observed by using a solid-state 87Rb NMR spectroscopy. Quadrupole coupling constants (e2qQ/h), the asymmetry parameters (η), and the relative peak intensities for two physically nonequivalent Rb sites, Rb(I) and Rb(II), are determined from nonlinear least-squares fits to the 87Rb NMR powder patterns in the temperature range from 260 to 330 K. Quadrupole coupling constants and the asymmetry parameters are examined for the detection of the phase transition resulting in a significant structural change in the Rb(II) site. In addition, changes in the relative peak intensity between the Rb(I) and Rb(II) sites seem to suggest the existence of an anomalous intermediate phase, which is complemented by the differential scanning calorimetry and X-ray diffraction studies.

Alkali Metal NMR Chemical Shielding as a Probe of Local Structure: An Experimental and Theoretical Study of Rb+ in Halide Lattices

When Rb+ is incorporated into different cubic halide lattices at very low concentrations, the 87Rb NMR chemical shift becomes more shielded by as much as 282 ppm when the cation is changed from Na+ to Cs+. Similarly, in mixed crystals of KCl and RbCl, the average resonance frequency shifts with the degree of incorporation. The 87Rb chemical shift data for each halide show a near-linear correlation with the average alkali metal−halide interionic distance in the different crystals studied, in good agreement with ab initio calculations which show that indeed the chemical shielding has a strong dependence on the nearest neighbor shell of halide anions and their distance from the Rb+. When the Rb concentration is increased as in KCl/RbCl solid solutions, the 87Rb NMR spectra are influenced by a large distribution of K/Rb configurations in the next-nearest-neighbor shell of 12 cations. While the total shift is still largely dependent on the Rb−Cl distance, shells containing both K and Rb atoms give rise to seco...

Three-dimensional (87)Rb NMR imaging and spectroscopy of K(+) fluxes in normal and postischemic pig hearts.

K(+) uptake rates were measured in the anterior (An) and posterior (Pos) LV walls of pig hearts before and after regional ischemia and reperfusion using Rb(+) as a K(+) congener and 3D (87)Rb NMR imaging and spectroscopy as detection methods. The hearts were perfused by the Langendorff method with Krebs-Henseleit (KH) buffer and loaded with Rb(+) (4.7 mM, Rb-KH) after 120-min ischemia and 60-min reperfusion. A second protocol involved Rb(+) loading prior to ischemia. Ischemia was produced by occlusion of the left anterior descending artery, which after 110 min of reperfusion resulted in infarction in the An wall (24 +/- 6% of the LV mass) determined by triphenyltetrazolium chloride staining. At the end of reperfusion pressure-rate product and oxygen consumption rate decreased to 58 +/- 10 and 74 +/- 4% of their preischemic values, respectively. Phosphocreatine, ATP, and intracellular pH (pHi), measured by (31)P NMR spectroscopy in the infarcted area, decreased to 59 +/- 17, 32 +/- 6%, and 6.7 +/- 0.36 (from 7.05 +/- 0.13), respectively. Serial (87)Rb images were acquired according to both protocols. Rate constants (k x 10(3), min(-1)), relative amount of intracellular Rb(+) (A, %) and relative fluxes (F = kA, %/min) for the An and Pos walls were determined from the images. Before ischemia, F and k were comparable in the Pos and An walls. Ischemia + reperfusion decreased F in the An wall (from 4.4 +/- 0.3 to 1.4 +/- 0.85) due to a decrease in A (20 vs. 73) and increased F in Pos wall (from 3.2 +/- 0.6 to 6.6 +/- 0.23) due to an increase in k (from 42 +/- 3 to 93 +/- 6). The intensities of the Rb images correlated with the Rb(+) content measured in tissue samples. Magn Reson Med 44:83-91, 2000. Published 2000 Wiley-Liss, Inc.

Effects of ischemia on intracellular rubidium in pig and rat hearts: (87)Rb NMR imaging and spectroscopic study.

87Rb MR imaging and spectroscopy were used to study the effects of ischemia on the properties of K(+) in cardiac tissue. Isolated pig and rat hearts perfused by the Langendorff method with Krebs-Henseleit buffer were preloaded with Rb(+). Ischemia (Isc) was induced by 120-min occlusion of the left anterior descending artery in the pig hearts or by stopping perfusion for 33 min in the rat hearts. Serial (87)Rb MR images or spectra from the anterior (An) LV wall of pig hearts were acquired continuously. The intensities of the Rb images of the An and posterior (Pos) walls were similar and stable during the first 45 min of ischemia. The intensity of signal from the An wall (Isc) then gradually increased by 60 +/- 8% relative to the preischemic value (vs. 31 +/- 5% increase in Pos wall) and necrosis (19 +/- 5% of the LV wall mass) developed upon reperfusion. The Rb(+) content was lower in the ischemic (An) than in the normal (Pos) area (22.3 +/- 3 vs. 28.4 +/- 1.3 mmol/g wet wt). A similar pattern was observed in the peak heights of (87)Rb spectra from the An wall, which increased by 40 +/- 16% (vs. 21 +/- 11% in control) due to a 12% decrease in the apparent Rb linewidth (LW) and a 24 +/- 14% increase in the peak area. The Rb peak comprised narrow (297 +/- 21 Hz) and broad (1098 +/- 40 Hz, 59 +/- 3% of total area) Lorentzian components. The LW of the broad component decreased by 14%, while the narrow component did not change markedly. In the rat hearts ischemia caused a 33 +/- 4% increase in the (87)Rb peak height as a result of peak narrowing (13 +/- 1%), and an increase in peak area (17 +/- 5%). The decreases in LW and increases in Rb(+) visibility can be explained by an increase in Rb(+) mobility caused by displacement of Rb(+) from anionic binding sites by H(+) (ischemic acidosis) and changes in intracellular compartmentalization of Rb(+). Magn Reson Med 44:193-200, 2000.

87Rb NMR spin-lattice relaxation in the charge-density wave phase of Rb0.3MoO3

The 87 Rb NMR spin-lattice relaxation rate (SLRR) has been measured in the charge-density wave (CDW) phase of the quasi-one-dimensional conductor Rb 0.3 MoO 3 in a magnetic field of 2 T perpendicular to the conducting chains. The SLRR exhibits a peak at the critical temperature T c = 180 K, attributed to the critical fluctuations at the phase transition. Two more broad peaks are observed within the CDW phase: one peak at 150 K (0.8 T c ) and another one at 60 K (0.3 T c ). We discuss the 0.8-T c peak in terms of quantum coherence effects in analogy with the Hebel-Slichter peak in superconductors. The 60 K peak is attributed to the phase excitations of the CDW.

New aspects in the interpretation of the T′ and T [formula omitted] NMR lines in Rb 3C 60

It is shown that the intensity ratio of the T′/T 87 Rb NMR lines can be influenced by a variation of the cooling rate from the preparation temperature to ambient temperatures. We discuss the origin of the appearance of the T′ line in Rb 3C 60 and the changes in the intensity ratio of the T′ and T 87 Rb NMR lines with respect to magnetically different surroundings of the Rb + ions caused by the two standard orientations of the C 60 3− ions. This interpretation of the T lines in 87 Rb NMR is consistent with the structural results of X-ray analyses. Additionally, the sample's superconducting volume fraction is influenced by the cooling rate after the annealing process.

Solid-state [formula omitted] NMR of RbVO 3. A comparison of experiments for retrieving chemical shielding and quadrupole coupling tensorial interactions

Solid-state 87 Rb NMR spectra for a powder and single crystal of RbVO 3 have been acquired for the central transition at two magnetic field strengths (9.4 and 14.1 T) and using two single-crystal NMR probes of different design. The powder spectra have been obtained using spin–echo techniques without sample spinning because the widths of the spectra are in the range 100–150 kHz. The spectra are analyzed in terms of the chemical shielding and quadrupole coupling interactions and the parameters are compared in an evaluation of the precision for the techniques. Parameters of high precision including the relative orientation for the two tensors are obtained from the single-crystal spectra at 14.1 T. Finally, the orientations of the two tensors in the crystal frame are deduced from the crystal symmetry and an XRD analysis.

PH regulation of K(+) efflux from myocytes in isolated rat hearts: (87)Rb, (7)Li, and (31)P NMR studies.

This study investigates the effects of intracellular (pH(i)) and extracellular pH (pH(e)) on the efflux of Rb(+) and Li(+) in isolated rat hearts. (87)Rb and (7)Li NMR were used to measure Rb(+) and Li(+) content, respectively, of hearts, and (31)P NMR was used to monitor pH(i), pH(e), and phosphate levels. After 30-min equilibration with Rb(+) or Li(+), effluxes were initiated by switching perfusion to a Rb(+)- or Li(+)-free, high-K(+) (20.7 mM) Krebs-Henseleit buffer with 15 microM bumetanide. Monensin (2 microM) increased pH(i) from 7.10 +/- 0.05 to 7.32 +/- 0.07 and resulted in activation of Rb(+) efflux; the first-order rate constant (k x 10(3), in min(-1)) increased from 42 +/- 2 to 116 +/- 16. Glibenclamide (4 microM) did not inhibit monensin-activated Rb(+) efflux (k = 110 +/- 17), whereas quinine (0.2 mM) slightly inhibited it by 19 +/- 9%. Infusion of 15 mM NH(4)Cl during Rb(+) washout increased k for Rb(+) efflux by 93% (81 +/- 8), which was glibenclamide and quinine insensitive, and caused a transient increase in pH(i) to 7.25 +/- 0.08. Intracellular Li(+) inhibited NH(4)Cl-stimulated Rb(+) efflux by 55%. Monensin and NH(4)Cl stimulated Li(+) efflux by 40%, increasing k from 29 +/- 3 to 43 +/- 7 and 41 +/- 3, respectively. The stimulation was not sensitive to 10 microM dimethylamiloride. Intracellular acidosis that resulted from the washout of NH(4)Cl (pH 6.86 +/- 0.2) slightly inhibited Rb(+) efflux (k = 36 +/- 5), whereas NH(4)Cl itself in the absence of pH(i) changes did not markedly affect Rb(+) efflux. A moderate increase in pH(i) (7.17 +/- 0.06) produced by washout of 15 mM 2, 2-dimethylpropionate (DMP)-Tris from hearts preequilibrated with DMP did not markedly affect Rb(+) efflux. Neither global alkalosis (pH(i) 7.4, pH(e) 7.55) nor acidosis (pH(i) approximately pH(e) 6.8) produced by 3 mM Tris base or 5 mM MES, respectively, affected Rb(+) efflux. We suggest that intracellular alkalosis stimulates Rb(+) (K(+)) and Li(+) effluxes by activating a nonselective sarcolemmal K(+) (Li(+))/cation exchanger or a K(+) (Li(+))-anion symporter.

The effects of low-flow ischemia on K+ fluxes in isolated rat hearts assessed by 87Rb NMR.

This study investigated whether Na+/K+ ATPase is inhibited and KATP channels activated during low flow ischemia (LFI) by monitoring Rb+ uptake and efflux from rat hearts using 87Rb NMR. In the uptake experiments, isolated Langendorff perfused hearts were exposed to Rb+-containing Krebs-Henseleit buffer (2.14 m m+3.76 m m K+) for 60 min. When Rb+ uptake started the flow of perfusate was decreased from 10 to 1 ml/min/g wet weight for 44 min and then returned to normal. The rate of Rb+ uptake and its equilibrium level decreased to 40 and 65% of the control (no ischemia) levels, respectively. Phosphocreatine and cytoplasmic [ATP]/[ADP] measured by 31P NMR decreased by half, intracellular pH (pHi) decreased to 6.8+/-0.1, and Pi increased two-fold. In wash-out experiments the hearts were pre-loaded with Rb+ for 30 min following which Rb+ wash-out was initiated. Four minutes later, flow was either decreased in the absence or presence of 10 microm 2,4-dinitrophenol (DNP), or 0.1 m m DNP was infused at normal flow for 20 min. LFI resulted in biphasic Rb+ efflux; during the initial phase, which lasted 8 min, the rate constant (kx10(3)/min) did not differ from control (43+/-3). The efflux was slightly inhibited by 5 microm glibenclamide (36+/-6) or 100 microm 5-hydroxydecanoic acid (32+/-4). In the second phase k decreased to half its initial value (18+/-2). More significant changes in energy state caused by LFI+10 microm DNP had no effect on the efflux kinetics. Similar changes in energy state induced by 0.1 m m DNP at normal flow were associated with activation of Rb+ efflux (71+/-5). DNP-stimulated Rb+ efflux was inhibited by acidosis (pHi approximately pHe = 6.7) produced with 5 m m morpholinoethane sulphonic acid (53+/-5) and by 100 microm adenosine (58+/-7). We suggest that accumulation of ischemic products such as H+and adenosine decreases activation of KATP channels in rat hearts.

87Rb NMR Studies of Molten and Glassy 2Ca(NO3)2−3RbNO3

Calcium rubidium nitrate, 2Ca(NO3)2−3RbNO3 (CRN), has been studied in its molten and glassy states using 87Rb NMR techniques. In the solid phase asymmetric and smeared quadrupole perturbed spectra of the central Rb resonance reflect a highly disordered ionic local structure. At low temperatures, T < 80 K, the spin−lattice relaxation times follow a power law, T1 ∝ T-α with α = 3. A local T1 minimum near T = 145 K reveals the slow down of the 3-fold rotation of the planar nitrate group. The NMR results are compared with the conductivity relaxation in CRN.

87RB NMR STUDIES OF MOLTEN AND GLASSY 2CA(NO3)2-3RBNO3

Calcium rubidium nitrate, 2Ca(NO3)2−3RbNO3 (CRN), has been studied in its molten and glassy states using 87Rb NMR techniques. In the solid phase asymmetric and smeared quadrupole perturbed spectra of the central Rb resonance reflect a highly disordered ionic local structure. At low temperatures, T < 80 K, the spin−lattice relaxation times follow a power law, T1 ∝ T-α with α = 3. A local T1 minimum near T = 145 K reveals the slow down of the 3-fold rotation of the planar nitrate group. The NMR results are compared with the conductivity relaxation in CRN.