Biomedical subjects

G Navon

Publications and source records attributed to G Navon.

At least 37 records · Page 2Linked to original sources

PubMed1998

Determination of the Dipolar Interaction of 23Na in Solution by Triple-Quantum Relaxation Time Measurements

The measurement of the dipolar interaction of 23Na with hydrogen nuclei in glycerol solution is reported. The method, applied previously to 7Li (U. Eliav and G. Navon, J. Magn. Reson. A 123, 32 (1996)), is based on the measurement of the triple-quantum relaxation time of 23Na. Several models of motion are discussed. The analysis of the results yielded 1.9 MHz and 12.5 kHz for the quadrupolar and the 23Na-1H dipolar interaction, respectively. It is shown that under the conditions of long correlation times the triple-quantum relaxation time can be sensitive to dipolar interactions smaller than the quadrupolar interaction by as much as a factor of 5000. This indicates the possibility of measuring interatomic distances for nuclei with sizable quadrupolar moments. Copyright 1998 Academic Press. Copyright 1998 Academic Press

Journal Article↗

PubMed1998

Quantification of the contribution of extracellular sodium to 23Na multiple-quantum-filtered NMR spectra of suspensions of human red blood cells.

23Na double-quantum-filtered (DQF) NMR enables the detection of anisotropic motion of sodium ions due to their interaction with ordered structures in biological tissues. Using the technique, anisotropic motion was found for sodium ions in mammalian red blood cell suspensions (RBC) and the effect was shown to correlate with the integrity of membrane cytoskeleton. In the present study relative contributions to the DQF and triple-quantum-filtered (TQF) spectra of sodium bound to anisotropic and isotropic binding sites in the intra- and extracellular sodium pools (Na content being 15 and 150 mM, respectively) of human RBC were quantified for different hematocrits. DQF spectra were measured by a modified Jeener-Broekaert pulse sequence which enabled exclusive detection of anisotropically moving sodium ions. The relative contributions of the extracellular sodium to the TQF and DQF spectra decreased as the hematocrit increased, but their efficiency relative to the sodium content increased. The contribution of the extracellular sodium to the TQF signal was found to dominate the spectrum of the RBC suspension at all hematocrits studied. The contribution of the extracellular sodium to the DQF was significantly smaller than that to the TQF and was only 22% at a high hematocrit of about 90%.

Animals↗

PubMed1998

The interaction of borate ions with cytochrome c surface sites: a molecular dynamics study.

Ionic interactions of cytochrome c play an important role in the electron transfer process. Molecular dynamics simulations of the binding of borate ion, which serves as a model ion, at three different cytochrome c surface sites are performed. This work is motivated by previous NMR studies of cytochrome c in borate solution, which indicate the existence of two types of binding sites, a slow exchange site and a fast exchange site. These two types of binding behavior were observed in the dynamic simulations, offering a molecular interpretation of "loose" and "tight" binding. At the "loose" binding sites (near Lys25/Lys27 and Lys55/Lys73) the ion forms two to three hydrogen bonds to the nearest lysine residue. This binding is transient on the time scale of the simulation, demonstrating the feasibility of fast exchange. At the "tight" binding site (near Lys13/Lys86), on the other hand, the ion becomes integrated into the protein hydrogen bond network and remains there for the duration of the simulation (exemplifying slow exchange). Binding simulations of the ion at the "tight" site of H26Q mutant cytochrome c also showed integration of the ion into the protein's hydrogen bond network. However, this integration differs in details from the binding of the ion to the native protein, in agreement with previous NMR observations.

Animals↗

PubMed1997

In vivo NMR and MRI using injection delivery of laser-polarized xenon.

Because xenon NMR is highly sensitive to the local environment, laser-polarized xenon could be a unique probe of living tissues. Realization of clinical and medical science applications beyond lung airspace imaging requires methods of efficient delivery of laser-polarized xenon to tissues, because of the short spin-lattice relaxation times and relatively low concentrations of xenon attainable in the body. Preliminary results from the application of a polarized xenon injection technique for in vivo 129Xe NMR/MRI are extrapolated along with a simple model of xenon transit to show that the peak local concentration of polarized xenon delivered to tissues by injection may exceed that delivered by respiration by severalfold.

Humans↗

PubMed1997

Role of nuclear magnetic resonance spectroscopy (MRS) in cancer diagnosis and treatment: 31P, 23Na, and 1H MRS studies of three models of pancreatic cancer.

The role of nuclear magnetic resonance spectroscopy (MRS) in pancreatic cancer diagnosis and its treatment were assessed in three models of pancreatic neoplasms. Perfused MIA PaCa-2 human pancreatic cancer cells, s.c. implanted pancreatic tumors in hamsters, and pancreatic tumors induced in situ in rats by direct application of the carcinogen 7,12-dimethyl benzanthracene, were studied by phosphorous ((31)P), sodium ((23)Na), and proton ((1)H) MRS. (31)P spectra of pancreatic cancer were qualitatively similar to those of intact organs. There were, however, variations in peak intensities and ratios. Phosphomonoester signals were prominent in both normal pancreases and tumors, but their levels depended on the proliferation rate and on environmental conditions. Thus, the phosphomonoester:beta-nucleoside triphosphate ratio was 1.15 +/- 0.32 in 90% confluency and 1.31 +/- 0.43 in 70% confluency, and this ratio increased upon lowering the perfusion rate. Total (intra- and extracellular) sodium concentrations, measured in the solid tumors, were 39-40 micromol/g wet weight in normal pancreases. Contrary to a previous hypothesis that malignant transformation is associated with increased sodium content, our (23)Na MRS data showed that there were no significant differences between pancreatic tumors and intact organs. Proton spectra of perchloric acid extracts revealed several differences between tumors and control pancreases. The principal findings were elevated levels of the amino acid taurine, from 1.17 +/- 0.39 micromol/g wet weight in healthy pancreases, to 2.79 +/- 0.71 micromol/g wet weight in pancreatic carcinoma in rats, and lactate levels that increased from 0.92 +/- 0.2 to 6.19 +/- 1.93 micromol/g wet weight, respectively. On the other hand, creatine and glutamate were higher in the normal pancreases. Pancreatic cancer is usually resistant to chemotherapy, and we evaluated the effects of the metabolic inhibitors 2-deoxyglucose and lonidamine on the human pancreatic cancer cells by MRS and cytotoxicity studies. The IC50 of Adriamycin and 2-deoxyglucose were 1.49 +/- 0.18 x 10(6) and 136 +/- 17 microg/ml, respectively. These results were similar to data obtained previously in multidrug-resistant human breast cancer cells, which were highly resistant (33-fold) to Adriamycin but were more susceptible (9-fold) to 2-deoxyglucose than their parental cells.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1997

Imaging H2(17)O distribution in a phantom and measurement of metabolically produced H2(17)O in live mice by proton NMR.

Previously we suggested a method for indirect detection of H2(17)O via a combination of 1H spin-echo sequence and 17O decoupling. The method is based on the shortening of the water proton T2 due to the residual spin-spin coupling with the 17O nucleus, and on our finding that this shortening is abolished by applying an radio frequency field at the 17O resonance frequency. In the present work we demonstrate how the method can be used for imaging low concentrations of H2(17)O, and report for the first time an application of this method to in vivo detection of H2(17)O in live newborn mice, where the H2(17)O was introduced either directly i.p. or by inhalation of 17O2 where it was formed by oxidative metabolic activity.

Animals↗

PubMed1997

Measurement of strain exerted on blood vessel walls by double-quantum-filtered 2H NMR.

In this study 2H double quantum-filtered (DQF) NMR spectroscopy of water molecules inside the blood vessel wall was used to monitor structural changes after the application of strain. This method was applied to a variety of bovine large blood vessels, including aorta, coronary artery, carotid artery, and vena cava. Inducing strain in coronary arteries by inflating them by air or water revealed dramatic changes in the 2H DQF spectral lineshapes. Uniaxial extensions of longitudinal and circumferential strips led to distinct spectral responses for the different blood vessels. While the spectral lineshapes for the coronary and the carotid arteries were very sensitive to longitudinal strain, they were not affected by circumferential stretching. For the aorta there were no changes in the lineshape upon strain. For the vena cava a large effect of strain was found that was independent of the choice of elongation axis. The effect of elongation on the spectra was assigned to the outer layer, the adventitia, whereas spectral lineshapes that originated from inner layers, media and intima, were almost insensitive to strain. Angular dependence experiments proved the presence of macroscopic order in the strained state superimposed on a broad distribution of the local directors. Our results demonstrate the sensitivity of 2H DQF NMR as a probe for dynamic processes occurring on the microscopic scale in a molecular network.

Animals↗

PubMed1997

In vivo 23Na NMR studies of myotonic dystrophy.

Myotonic dystrophy is an inherited multi-system disease. Its pathophysiology leading to muscle malfunction and damage is not well understood. 23Na NMR spectroscopy was applied here for an in vivo comparative study of the calf muscles of 7 myotonic dystrophy patients at various stages of the disease and 11 healthy volunteers. Both the total sodium content, expressed as the ratio of the 23Na and 1H water signals, and the fast transverse relaxation time, T2f, determined from the triple quantum-filtered spectra, increased in correlation with the severity of the disease. The results demonstrate that 23Na NMR enables the quantitation of myotonic dystrophy progression.

Adolescent↗

PubMed1997

In vivo observation of anisotropic motion of brain water using 2H double quantum filtered NMR spectroscopy.

The 2H DQF NMR spectra of deuterated water molecules were measured for the first time in in vivo rat brain. The observation of the DQF signal indicates that there is a water population that exhibits anisotropic motion. The characteristics of the DQF spectra premortem and postmortem are very similar (lineshape and relaxation times). In the 1st h there is a 10-15% decrease in the signal intensity of the DQF spectra followed by a gradual but a much slower decrease in the DQF signal intensity that reaches 65-70% of its initial value after only 12 h. When the brains were kept at 4 degrees C, a 40% decrease in the DQ signal intensity was observed only after 7 days. Mechanical chopping of the brain tissues causes an immediate loss of more that 97% of the DQ signals. The slow, temperature-sensitive decay of the signal, and its sensitivity to mechanical treatment point out that these signals originate from water molecules that interact with structural components in the brain. The characteristics of the DQF spectra depend on the amount of bulk water as exemplified by increased residual quadrupolar interaction and relaxation rates obtained when dehydrating the brain tissue.

Animals↗

PubMed1997

Intermittent ischemia: energy metabolism, cellular volume regulation, adenosine and insights into preconditioning.

Interruption of ischemia by brief reperfusions (I/R) is better tolerated by the heart than continuous ischemia. The present study aims to determine the metabolic profiles of isolated rat hearts during intermittent ischemia, the possible cardioprotective role of adenosine and the influence of I/R on intracellular volumes, using multinuclear NMR spectroscopy. After five I/R (5/5 min) episodes, hearts paced at 5 Hz developed pressures comparable to those of hearts continuously perfused for 50 min at 37 degrees C (CP). Following the first 5 min episode of no-flow ischemia, [ADP] dropped from 72 +/- 9 to 43 +/- 5 microM (P < 0.001) and remained stable at the end of the following reperfusions, despite a 2.5-4-fold increase during each episode of 5 min ischemia. Intracellular volumes were stable during CP at a value of 2.50 +/- 0.06 ml/g dry weight, and decreased by 4, 8, and 12% after 1, 3, and 5 I/R episodes. The phosphorylation potentials decreased from 54 +/- 8 to 4 mM-1 during each period of 5 min ischemia and were 40 +/- 6 and 28 +/- 6 mM-1 after CP and I/R5, respectively. Cardiac glycogen had decreased during 50 min of CP from 103 +/- 13 to 81 +/- 9 mumol/g dry weight and lactate production was 116 +/- 15 mumol/heart. Five I/R episodes decreased glycogen to 46 +/- 7 mumol/g dry weight (P < 0.005 v CP) and increased lactate efflux to 262 +/- 31 mumol/ heart (P < 0.005 v CP). These findings suggest that a brief ischemia/reperfusion episode increases anaerobic metabolism of exogenous glucose, reduces [ADP] and induces cellular shrinkage. Administration of the adenosine receptor blocker 8-phenyl theophylline (8PT) during intermittent perfusion depressed the developed pressure to 78 +/- 7%, accentuated the decrease in phosphorylation potential (14 +/- 4 mM-1), abolished cellular shrinkage, reduced lactate efflux and blunted the decrease in ADP following the first I/R episode. In variance, no detectable changes were observed during intermittent ischemia when the ATP-sensitive potassium channel blocker glibenclamide was administered. These data demonstrate: (a) a brief episode of ischemia/reperfusion stimulates anaerobic metabolism of exogenous glucose and lowers intracellular ADP concentration: (b) adenosine receptors are partially responsible for the glycolytic stimulation during intermittent ischemia; (c) cellular shrinkage is related to the rate of glycolysis during intermittent ischemia/reperfusion.

Adenosine↗

PubMed1997

Continuous monitoring of intracellular volumes in isolated rat hearts during normothermic perfusion and ischemia.

The present study describes an experimental setup that enables continuous measurement of cellular volumes in isolated organs. The procedure is a modification of a recently reported method that uses multinuclear NMR measured by 59Co NMR of cobalticyanide and 1H NMR of water in isolated rat hearts at normothermia. The new apparatus contains a background flow which is shown to improve the rate of exchange of the marker between the interstitium and the external solution and allows detection of cellular shrinkage during no-flow ischemia. A series of experiments of marker loading and wash-out were performed to validate the method. In the Langendorff preparation, intracellular volumes (in units of milliliters per gram dry weight) of hearts perfused with Krebs-Henseleit solution oscillated around a mean value of 2.50 +/- 0.06 ml/gdw. During 30 min of ischemia the cells swelled to 2.88 +/- 0.08 ml/gdw and residual edema was observed after 30 min of reperfusion (2.62 +/- 0.08 ml/gdw). A hypoosmotic shock was used to assess changes in membrane permeability at different time points of ischemia and reperfusion. Water influx induced by the hypoosmotic shock at the end of ischemia was similar to that elicited in perfused hearts. After 15 and 30 min of reperfusion, the magnitude of the response to hypoosmolarity decreased by 9 and 37%, respectively, indicating a gradual permeabilization of the membranes, presumably to ions. The experimental setup was also used to monitor intracellular volumes as a function of time in anisoosmotic conditions. Cellular swelling/shrinkage were delayed for periods of 5 and 8 min at osmolarities of +/-50 and +/-100 mosmol/liter, suggesting a limited capability of the heart to absorb an anisoosmotic shock. The variation in cellular volumes was proportional to the deviation of the conditions from isoosmolarity, and activation of volume-regulatory mechanisms was demonstrated. The noninvasive technique presented in this study is capable of providing quantitative evidence of changes in cellular volumes in isolated hearts at a temporal resolution of 1 min and a spatial resolution of 4% (of cellular volume). As demonstrated in the cases of global ischemia and anisoosmolar conditions, the technique is expected to provide new insights into the mechanism of cellular-volume regulation.

Animals↗

PubMed1997

Discrimination between the different compartments in sciatic nerve by 2H double-quantum-filtered NMR.

The 2H double-quantum-filtered (DQF) NMR spectrum of isolated rat sciatic nerve, equilibrated with deuterated saline, is composed of three quadrupolar-split water signals. On the basis of the time course of their shift by Co-EDTA2- and CoCl2, the signals with quadrupolar splittings of about 120, 470, and 9 Hz were assigned to water in the epineurium, endoneurium, and intra-axonal compartments, respectively. The signal of the bulk water, which experiences isotropic motion, was eliminated by the DQF pulse sequence. As the maximum intensities of the water signals in the three anisotropic compartments occur at different creation times, in the DQF pulse sequence, it is possible to resolve the signals and measure their properties, such as relaxation times, independently, without perturbing the system with shift reagents.

Animals↗

PubMed1997

The source of NMR-detected motional anisotropy of water in blood vessel walls.

2H Double quantum-filtered (DQF) NMR spectroscopy of deuterated water is sensitive to the presence of order in biological systems. This is because the only nuclei that are detected are those with residual quadrupolar interactions due to their anisotropic motion. In the present study, samples of aorta, coronary and carotid arteries, and vena cava were studied in parallel by 2H DQF NMR and by light microscopy. The average quadrupolar splitting, calculated from the NMR data, varies considerably among the different blood vessels, with high reproducibility for each type of vessel. Polarization microscopy examinations using collagen-specific staining with picrosirius red, have shown a variety of color profiles for the different blood vessels. These reflect different physical modes of aggregation (packing and thickness) of collagen fibers. A correlation was found between the NMR parameters and the color profiles of the picrosirius red-stained sections. Treating the blood vessels with 90% formic acid resulted in the elimination of the 2H DQF NMR signal. Histological analysis demonstrated a complete degradation of collagen and muscle, whereas the elastin filaments were preserved. Evidence is given that the 2H DQF NMR signal is dominated by the contribution of water molecules interacting with the collagen fibers.

Animals↗

PubMed1997

Comparison of action of the anti-neoplastic drug lonidamine on drug-sensitive and drug-resistant human breast cancer cells: 31P and 13C nuclear magnetic resonance studies.

Lonidamine (LND) is a relatively new anti-cancer drug, and several clinical trials have indicated that it may be effective in combinations with other therapeutic modalities. LND is classified within the metabolic inhibitor agents. Multidrug resistance (MDR) phenomenon is often associated with increased energy requirements, and enhanced glycolysis rate. These studies were performed to delineate the mechanism of action of LND on MDR human breast cancer cells, and to investigate whether LND as a single agent, or in combination with another anti-metabolism drug, 2-deoxyglucose (2-DG), may be useful against MDR tumors. The effects of LND on intact perfused drug-sensitive (WT) and 33-fold resistant to Adriamycin (Adr) MCF-7 cells, embedded in alginate micro capsules, were continuously monitored by 31P and 13C nuclear magnetic resonance (NMR) spectroscopy. 31P NMR studies showed that LND induced intracellular acidification and depletion of NTP in both WT and Adr cells. However, pH and NTP levels decreased less in the Adr cells than in the WT cells (p < 0.05 for both parameters). 13C NMR demonstrated that LND inhibited lactate transport, and lactate signals were elevated in both cell lines. However, the intracellular lactate levels increased to a greater extent in the WT than in the Adr cells (p < 0.05). There were major differences in the effects of LND on metabolism between sensitive and resistant cells. While LND enhanced glucose uptake in the WT cells, and its administration was followed by continuous increase of lactate signal, both processes were not affected by LND in the Adr cells. 2-DG is a glucose analogue that inhibits both cellular uptake and utilization of glucose, leading to cell starvation. Combined treatment with LND and 2-DG yielded at best additive, but not synergistic, cellular toxicity, and the metabolic effects of LND were attenuated by 2-DG. These results showed that the principal mechanism of action of LND is inhibition of lactate transport leading to intracellular lactate accumulation and acidification in both WT and Adr cells. The Adr cells were only 2-fold resistant to LND (compared to the WT cells), and since cellular uptake of alkaloid chemotherapy is improved in acidic environment, LND may have a role in the treatment protocols of MDR tumors, especially when given as the initial means for induction of intracellular acidification.

Antineoplastic Agents↗

PubMed1997

Chronic heat improves mechanical and metabolic response of trained rat heart on ischemia and reperfusion.

Cardiac mechanics and metabolic performance were studied in isolated perfused hearts of rats subjected to a combined chronic stress of heat acclimation and swimming training (EXAC) or swimming training alone (EX). Diastolic (DP) and systolic pressures (SP), coronary flow (CF), and oxygen consumption were measured during normoperfusion (80 mmHg), and the appearance of ischemic contracture (IC), DP, and SP were measured during progressive graded ischemia, total ischemia (TI), and reperfusion insults. ATP, phosphocreatine, and intracellular pH were measured during TI and reperfusion with 31P nuclear magnetic resonance spectroscopy. During normoperfusion, SP and cardiac efficiency (derived from rate-pressure product-oxygen consumption relationships) were the highest in the 2-mo EXAC hearts (P < 0.0001). During progressive graded ischemia, the development of IC (percentage of total hearts) was similar in both EXAC and EX hearts; the only significant difference was confined to the 1- vs. 2-mo groups. The onset of IC was delayed in the EXAC hearts and, on reperfusion, recovery, particularly of DP, was significantly improved in the latter. After TI, EXAC hearts retained 30% of the ATP pool and there was a delayed decline in intracellular pH. On reperfusion, these hearts also displayed improved ATP and phosphocreatine recovery, the 2-mo EXAC heart demonstrating significantly faster high-energy phosphate salvage, improved diastolic function, and pulse pressure recovery. The data attest to the beneficial effects of heat acclimation on cardiac mechanics of trained rats during normoperfusion and cardiac protection on ischemia and reperfusion. Possibly, energy sparing, lesser acidosis, and shorter duration of IC on ischemia and improved energy salvage on reperfusion contribute synergistically to this potent beneficial effect.

Acclimatization↗

PubMed1996

NMR of laser-polarized xenon in human blood.

By means of optical pumping with laser light it is possible to enhance the nuclear spin polarization of gaseous xenon by four to five orders of magnitude. The enhanced polarization has allowed advances in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI), including polarization transfer to molecules and imaging of lungs and other void spaces. A critical issue for such applications is the delivery of xenon to the sample while maintaining the polarization. Described herein is an efficient method for the introduction of laser-polarized xenon into systems of biological and medical interest for the purpose of obtaining highly enhanced NMR/MRI signals. Using this method, we have made the first observation of the time-resolved process of xenon penetrating the red blood cells in fresh human blood-the xenon residence time constant in the red blood cells was measured to be 20.4 +/- 2 ms. The potential of certain biologically compatible solvents for delivery of laser-polarized xenon to tissues for NMR/MRI is discussed in light of their respective relaxation and partitioning properties.

Erythrocytes↗

PubMed1996

The relation between cellular sodium, pH and volumes and the activity of Na/H antiport during hypothermic ischemia: multinuclear NMR studies of rat hearts.

The present study evaluates the activity of the Na/H antiport during cold ischemia and aims to determine its influence on cellular sodium. pH and volumes. Cellular parameters; volumes, sodium, pH and high energy phosphates, were measured by multinuclear NMR spectroscopy in rat hearts during 12 h of storage at 4 degrees C and reperfusion, along with functional parameters. Cell volumes were measured by 1H and 59Co NMR using the extracellular marker cobalticyanide, pH and energetics by 31P NMR and sodium compartmental distribution by 23Na NMR spectroscopy using the shift reagent Dy(TTHA)-3. Three storage solutions were applied: Krebs-Henseleit (containing 144 mM sodium, KH), a solution supplemented with 0.20 mM amiloride (KH-ami) and a solution containing 23 mM sodium and 242 mM mannitol (KH-man). Inhibition of the Na/H antiport with amiloride reduced the cellular sodium accumulation by 56%. The end-ischemic concentrations were 45 mM (KH-ami) and 77 mM (KH). Amiloride also reduced the extent of cell swelling by 53% from an end-ischemic volume of 3.56 ml/gdw (KH) to 2.97 ml/gdw (KH-ami), however cell swelling persisted in both groups at reperfusion (33% increase in cell water). The molar ratio of sodium and water cellular accumulation was constant: Na/H2O approximately 3.7 x 10(-3) throughout the whole storage period. Inhibition of the antiport was protective for the high energy phosphates during ischemia and reperfusion. In KH-ami the pH acidified after 6 h of storage to an end-ischemic value of 6.35 (pH = 6.50 in KH): this difference persisted after 60 min of reperfusion, pH = 6.98 in KH-ami and pH = 7.1 in KH. Storage in the low-sodium solution was disadvantageous for the high energy phosphates during ischemia and reperfusion with a recovery of pH to 6.92 when reperfused with KH. Hearts stored with amiloride or mannitol solution failed to resume contraction at reperfusion. It is concluded: (a) the antiport is active at 4 degrees C; (b) during ischemia it mediates sodium influx and contributes to cell swelling with minor effects on the cytosolic pH; (c) at reperfusion the antiport is active it participates in the extrusion of excess protons, but has a minor impact on sodium and water homeostasis; (d) inhibition of the antiport does not protect the cardiac muscle at low temperatures.

Animals↗

PubMed1996

Measurement of Dipolar Interaction of Quadrupolar Nuclei in Solution Using Multiple-Quantum NMR Spectroscopy

Relaxation resulting from the modulation of dipolar interaction is commonly used for estimating distances in molecules in solutions. However, for most nuclei with spin I > ½ the single-quantum-transition relaxation by dipolar interaction is masked by quadrupolar relaxation. In the present study, it is shown that even in systems where single-quantum relaxation times are dominated by quadrupolar interaction, dipolar relaxation can be measured by following the -m $\leftrightarrow$ m transitions. This is demonstrated for 7Li in the complex [Li-Kryptofix 211]+X- (X = Cl, Br) dissolved in glycerol at temperatures for which slow motion prevails and no 1H-7Li NOE can be observed. The relaxation times that are most important for the assessment of the dipolar interaction of 7Li are -½ $\leftrightarrow$ ½ and -${{3}\over{2}}$ $\leftrightarrow$ ${{3}\over{2}}$ and they are measured by multiple-quantum-filtration techniques. For estimating the quadrupolar interaction, the relaxation times of the populations and those of the transitions ±½ $\leftrightarrow$ ±${{3}\over{2}}$ were measured. The longitudinal and transverse relaxation times of 6Li as well as the 1H-6Li NOE were also measured and, together with the 7Li measurements, were used to obtain the strengths of dipolar (D) and quadrupolar (chi) interactions. The experimental data were analyzed using several models to describe the motion. The model that gave the best fit and resulted in parameters that were physically meaningful encompassed a whole-body isotropic motion as well as internal anisotropic motion. For this particular model, the following values for the quadrupolar and the dipolar interactions strength were obtained: D(7Li)/2pi = 6.8 kHz, chi(7Li)/2pi = 85 kHz and D(6Li)/2pi = 1.4 kHz, chi(6Li)/2pi = 2.6 kHz. From the value of D, an estimate of the average lithium-proton distance was calculated to be 3.3 Å, which is in fair agreement with crystallographic studies. The sizes of the quadrupolar and dipolar interactions were independently confirmed by the 7Li NMR powder spectra of the complexes that were used for the solution studies.

Journal Article↗