Mapping structures and dynamics with frequency-correlated diffusion exchange

Nuclear Magnetic Resonance (NMR) methods offer the determination of pore size distributions of loose sediments, which is the basis of investigations concerning ground water dynamics, i.e. water content and hydraulic conductivity of the subsurface. The NMR resolution range of pore radii depends on many parameters such as the technology of the applied NMR system, the Larmor frequency and the properties of the pore fluid and the pore surface, respectively. Different NMR methods do not necessarily show the same results at the same samples. At core samples from a shallow aquifer we compare Earth’s field NMR measurements with conventional lab NMR measurements and show the influence of the dead time and the Larmor frequency on the resolution limits of the pore size distribution.

Characterization of porous media using NMR methods

Nuclear magnetic resonance (NMR) methods for the noninvasive, chemically specific investigation of living tissue have proliferated in number and advanced greatly in power since the first NMR images of anatomy appeared in the 1970s. By 1994, about 50 different NMR measurements had become available for the study of normal and pathological brain. These include aspects of biochemistry, angiography, perfusion, activation- sensitive metabolic rates for glucose and oxygen, monitoring of function through activation-induced changes in blood flow and water diffusion, and normal and pathological anatomy with submillimeter resolution. At least as many more measurements of biomedical importance are under development. Neuroscience research and management of neurological illness will be profoundly affected by NMR methods as they mature and become routine. The Neuroscientist 1:84-94, 1995

Chemical shift assignment and conformational structure of small molecules are fundamental for their study of interaction with biological targets, like proteins and nucleic acids. Chemical shift assignments are usually obtained with the very efficient nuclear magnetic resonance (NMR) methods COSY, HSQC, HMBC, TOCSY and NOESY. When these NMR methods do not afford all information or need the results confirmation to determine the complete molecular chemical shift assignment, it is necessary to use other procedures, especially for determination of long range 1H-13C coupling constants and 13C multiplicity. In this work, it is demonstrated that Gated decoupling 13C NMR spectrum, which is a simple and easy to use method, is very appropriate to complete the unambiguous chemical shift assignment and the conformational condition of arylidene barbiturates. The NMR conformational results were also confirmed by molecular modeling.

We present a simple, accurate, stability-indicating nuclear magnetic resonance (NMR) method for determining active (S,S) and inactive (R,S) epimers of S-adenosyl-L-methionine (SAM) in tablets. The SCH3 resonances of SAM epimers were well resolved at 300 MHz. Individual assays of 5 SAM tablets gave SAM values of 101.3 +/- 1.7% of declared amounts. Tablet solutions were assayed at a level of 8.0 mg/mL, but the method was linear for SAM concentrations ranging from 64 to 1 mg/mL (correlation coefficient, 0.9996). Reproducibility was indicated by a relative standard deviation of 0.33% for 6 replicate assays for total SAM at a concentration of 8 mg/mL. In contrast to the propietary liquid chromatographic (LC) method, which requires SAM as an external standard, the NMR method uses sodium trimethylsilylpropionate-d4 (TSP) both as an internal standard and as a chemical shift reference. The method was used to test the stability of SAM analytes under various pH levels and temperatures. We found 8% inactivation of SAM due to epimerization over a 24 h period at room temperature and pH 5. SAM solutions showed no detectable inactivation after 14 days when stored below 0 degrees C.

The size of elongated micelles in a system containing 2 wt.% sodium dodecylsulfate (SDS), 3.5 wt.% NaCl and 94.5 wt.% water has been studied by means of two different nuclear magnetic resonance (NMR) methods and time-resolved fluorescence quenching with special emphasis on a comparison between the results from the three methods. The two NMR methods were the determination of self-diffusion coefficients by means of the pulsed-gradient spin–echo method and the determination of relaxation rates for specifically deuterium labelled SDS. In the analysis of the former data, the obstruction effect due to the finite micellar concentration was taken into account. In the analysis of the relaxation data, the combined effect of lateral surfactant diffusion over the micellar surface and micellar rotational tumbling was taken into account in an exact manner for the case of prolates and in an approximate way for the case of hemisphere-capped rods. The results obtained from the three methods were in reasonable agreement. If the micelles are modelled as prolates, the axial ratios obtained was ca. 6 while if they are described as hemisphere-capped rods, the axial ratio is ca. 5.

P034 Z-99 MOBILE INSTRUMENT FOR NMR MEASURE- Introduction 1 MENTS ON SAMPLES IN THE EARTH’S MAGNETIC FIELD TINO RADI� Radic Research Zehntwerderweg 188A 13469 Berlin Germany E-mail: radic@radic-research.de Web: www.radic-research.de The Nuclear Magnetic Resonance (NMR) method (Abragam 1983) allows beside other parameters a non-destructive measurement of the water content and the pore radii distribution of a rock sample. Therefore it is not surprising that the NMR method has developed into an important geophysical instrument. But up to now the main application area is still the laboratory. Unfortunately samples show many unwanted modifications on their way from the field to the

Miscibility, Morphology and Molecular Motion in Polymer Blends

Quantitative characterization of multiphase methane and investigation of the methane dynamic adsorption process of coals were performed by a low-field nuclear magnetic resonance (NMR) method. Meanwhile, methane diffusion behaviors during the step-by-step pressurization adsorption process were evaluated by three diffusion models. The results indicate that the transverse relaxation time (T2) spectra of methane demonstrate two distinct peaks of adsorbed methane (P1, T2 < 2.5 ms) and porous medium-confined methane (P2) at a low-pressure step (∼1.0 MPa), and the third peak of bulk methane (P3) obviously appears when the pressure >2.0 MPa. The integrated T2 amplitude of adsorbed methane increases quickly during the first 2 h (>75% of total) and then gradually reaches a maximum value in the last 4 h during the initial pressure step of ∼1.0 MPa, whereas it reaches >90% of total amplitude in 1 h as the pressure is increased step-by-step. According to the strong linear relationship between the adsorbed methane volume and the integrated T2 amplitude, the real-time methane adsorption volume can be determined, and adsorption isotherms from the NMR method are found to be mostly overlapped with those of the volumetric method. Moreover, the effective diffusion coefficient of the unipore model (10–6 to 10–5 s–1) coincides with the micropore diffusion coefficient of the bidisperse model and the slow diffusion coefficient of the multiporous model, which is generally 1–3 orders of magnitude less than the macropore diffusion coefficient (10–3 to 10–2 s–1) and the fast diffusion coefficient (10–2 s–1) or transitional diffusion coefficient (10–4 to 10–3 s–1). The dynamic changes in diffusion parameters with pressure may be related to the comprehensive effects of methane diffusion mechanisms and coal matrix swelling under different adsorption pressures.

Methane adsorption capacity is an important parameter for coalbed methane (CBM) exploitation and development. Traditional examination methods are mostly time-consuming and could not detect the dynamic processes of adsorption. In this study, a modified low-field nuclear magnetic resonance (NMR) method that compensates for these shortcomings was used to quantitatively examine the methane adsorption capacity of seven medium-rank coals. Based on the typical T 2 amplitudes obtained from low-field NMR measurement, the volume of adsorbed methane was calculated. The results indicate that the Langmuir volume of seven samples is in a range of 18.9–31.85 m3/t which increases as the coal rank increases. The pore size in range 1-10 nm is the main contributor for gas adsorption in these medium-rank coal samples. Comparing the adsorption isotherms of these coal samples from the modified low-field NMR method and volumetric method, the absolute deviations between these two methods are less than 1.03 m3/t while the relative deviations fall within 4.76%. The absolute deviations and relative deviations decrease as vitrinite reflectance ( R o ) increases from 1.08% to 1.80%. These results show that the modified low-field NMR method is credible to measure the methane adsorption capacity and the precision of this method may be influenced by coal rank.

Protein kinases are ubiquitous enzymes with critical roles in cellular processes and pathology. As a result, researchers have studied their activity and regulatory mechanisms extensively. Thousands of X-ray structures give snapshots of the architectures of protein kinases in various states of activation and ligand binding. However, the extent of and manner by which protein motions and conformational dynamics underlie the function and regulation of these important enzymes is not well understood. Nuclear magnetic resonance (NMR) methods provide complementary information about protein conformation and dynamics in solution. However, until recently, the large size of these enzymes prevented researchers from using these methods with kinases. Developments in transverse relaxation-optimized spectroscopy (TROSY)-based techniques and more efficient isotope labeling strategies are now allowing researchers to carry out NMR studies on full-length protein kinases. In this Account, we describe recent insights into the role of dynamics in protein kinase regulation and catalysis that have been gained from NMR measurements of chemical shift changes and line broadening, residual dipolar couplings, and relaxation. These findings show strong associations between protein motion and events that control kinase activity. Dynamic and conformational changes occurring at ligand binding sites and other regulatory domains of these proteins propagate to conserved kinase core regions that mediate catalytic function. NMR measurements of slow time scale (microsecond to millisecond) motions also reveal that kinases carry out global exchange processes that synchronize multiple residues and allosteric interconversion between conformational states. Activating covalent modifications or ligand binding to form the Michaelis complex can induce these global processes. Inhibitors can also exploit the exchange properties of kinases by using conformational selection to form dynamically quenched states. These investigations have revealed that kinases are highly dynamic enzymes, whose regulation by interdomain interactions, ligand binding, and covalent modifications involve changes in motion and conformational equilibrium in a manner that can be correlated with function. Thus, NMR provides a unique window into the role of protein dynamics in kinase regulation and catalysis with important implications for drug design.

Optimization of key parameters for porosity measurement of shale gas reservoirs

A nuclear magnetic resonance advance. Imaging fluorinated anesthetics in the brain.

Unveiling the impact of second-order 1H-17O Quadrupolar-Dipolar interaction on solid-state NMR spectroscopy

Measurement of body composition (fat mass) is an important item in pathophysiological and pharmacological studies using small animals (mice) in the fields of obesity and diabetes. The existing methods are, however, difficult, time consuming, and require a shielding facility. Now a novel system using nuclear magnetic resonance (NMR) technique was developed for measurement of body composition in small animals (mice) that provides noninvasive and rapid measurement without anesthetics; we introduced and evaluated this system and tried another application of this system. First, we validated this system using canola oil, soft tissues (adipose and skeletal muscle), and various kinds of rodent chows. Accuracy, precision, and reproducibility of this system were demonstrated to be equal to those in standard chemical methods. A strong positive correlation (y=x) between the results of NMR and chemical methods was found. Secondly, we evaluated accuracy and assay range of the NMR method using live mice that were fasted overnight or fed high fat diet (HFD). In fasted mice, a small but quantitative decrease of fat mass (5.1% from 9.1%) was detected. Total decrease of fat and lean mass (5.0 g) in fasted mice was equivalent to the decrease of body weight (5.0 g). In mice fed the HFD, increase of fat mass with relative decrease of lean mass were qualitatively detected in a time-dependent manner. We would like to emphasize that operation of the system was actually easy and measurements were accomplished in a short time (1 minute). Thirdly, we tried to use the NMR system for determination of hepatic fat contents using mice fasted or treated with a PPARgamma agonist; our results showed a quantitative increase in fat by fasting or in decrease in fat by the drug treatment. The changes of fat contents determined by the NMR method were well correlated with the changes in triglyceride and total cholesterol values obtained by the biochemical assays. In conclusion, body composition data acquired by the new NMR system are equivalent in accuracy and precision to classical chemical methods. The NMR analysis is simple, fast, and does not require anesthesia for acquisition of data, which are remarkable advantages compared to the existing methods. This system is expected to contribute to drug discovery and appropriate evaluation in the fields of obesity and diabetes.