Results Of Nuclear Magnetic Resonance Experiments Research Articles

Pore-pressure and stress-coupled creep behavior in deep coal: Insights from real-time NMR analysis

Understanding the variations in microscopic pore-fracture structures (MPFS) during coal creep under pore pressure and stress coupling is crucial for coal mining and effective gas treatment. In this manuscript, a triaxial creep test on deep coal at various pore pressures using a test system that combines in-situ mechanical loading with real-time nuclear magnetic resonance (NMR) detection was conducted. Full-scale quantitative characterization, online real-time detection, and visualization of MPFS during coal creep influenced by pore pressure and stress coupling were performed using NMR and NMR imaging (NMRI) techniques. The results revealed that seepage pores and microfractures (SPM) undergo the most significant changes during coal creep, with creep failure gradually expanding from dense primary pore fractures. Pore pressure presence promotes MPFS development primarily by inhibiting SPM compression and encouraging adsorption pores (AP) to evolve into SPM. Coal enters the accelerated creep stage earlier at lower stress levels, resulting in more pronounced creep deformation. The connection between the micro and macro values was established, demonstrating that increased porosity at different pore pressures leads to a negative exponential decay of the viscosity coefficient. The Newton dashpot in the ideal viscoplastic body and the Burgers model was improved using NMR experimental results, and a creep model that considers pore pressure and stress coupling using variable-order fractional operators was developed. The model’s reasonableness was confirmed using creep experimental data. The damage-state adjustment factors ω and β were identified through a parameter sensitivity analysis to characterize the effect of pore pressure and stress coupling on the creep damage characteristics (size and degree of difficulty) of coal.

Study on the affinity sites of cadmium's binding to ligands by thermodynamics and nuclear magnetic resonance spectroscopy.

The affinity sites of cadmium (Cd(II)) when binding to cysteine (Cys) and glutathione (GSH) were studied via thermodynamics and nuclear magnetic resonance (NMR) spectroscopy methods. The results showed that the Cd(II) binding sites of Cys and GSH were -SH (exothermic), -NH2 (endothermic) and -COOH (endothermic). The thermodynamic behaviour of Cd(II) binding to Cys/GSH in boric acid and HEPES buffers differed, with the former being mainly endothermic and the latter mainly exothermic. It could be inferred that, in the boric acid system, the main binding site of Cd(II) with Cys and GSH is changed from -SH in HEPES to -COOH and -NH2 in boric acid. This was confirmed by the results of NMR experiments of Cd(II) with Cys/GSH. 1D 1H-NMR experiments showed that, after the combination of Cd(II) and Cys, the changes in the chemical shifts and peak strengths of protons near the -SH group for the reaction in HEPES were greater than when boric acid buffer was used. Changes in the chemical shift and peak strength of the -NH2 protons due to the binding of Cd(II) to GSH were evident in the boric acid buffer but not in HEPES. The screening of functional monomers is very important in the process of preparation of cadmium ion-imprinted materials. This research provides important theoretical and experimental guidance for the screening of functional monomers.

Pore structure characterization based on NMR experiment: A case from the Shanxi Formation tight sandstones in the Daning-Jixian area, eastern Ordos Basin

The study of pore structure requires consideration of important factors including pore throat size, pore radius composition, and pore-throat configuration. As the nuclear magnetic resonance (NMR) experimental results contain rich information about pore structures and fluid occurrence states, this study investigated the pore structures of the tight sandstone reservoirs of the Shanxi Formation in the Daning-Jixian area, eastern Ordos Basin. Firstly, by making the inverse cumulative curve of the NMR T2 spectrum coincide with the capillary pressure curves which were obtained by the mercury injection capillary pressure (MICP) technique, this study derived a conversion coefficient that can be used to convert the NMR T2 spectrum into the pore throat radius distribution curves based on the NMR experimental results. Subsequently, we determined the pore radius intervals corresponding to irreducible water distribution using the NMR-derived pore radius distribution curves. Finally, the NMR T2 distribution curves based on the fractal theory were analyzed and the relationships between fractal dimensions and parameters, including permeability, porosity, reservoir quality index (RQI), flow zone indicator (FZI), irreducible water saturation, RT35, and RT50, were also discussed. The NMR-derived pore throat radius distribution curves of the study area are mainly unimodal, with some curves showing slightly bimodal distributions. The irreducible water mainly occurs in small pores with a pore radius less than 100 nm. As the permeability decreases, the contribution rate of small pores to the irreducible water gradually increases. The NMR-based fractal dimensions of pores show a two-segment distribution. Small pores have small fractal dimensions and are evenly distributed, while large pores have large fractal dimensions and complex pore structures. The fractal dimension of large pores (Dmax) is poorly correlated with porosity but strongly correlated with FZI, RQI, RT35, and RT50. These results indicate that large pores are the main pore zones that determine the seepage capacity of the reservoirs. Additionally, there is a certain correlation between Dmax and the irreducible water saturation.

Biradical Polarizing Agents at High Fields.

The sensitivity enhancements available from dynamic nuclear polarization (DNP) are rapidly reshaping the research landscape and expanding the field of nuclear magnetic resonance (NMR) spectroscopy as a tool for solving complex chemical and structural problems. The past decade has seen considerable advances in this burgeoning method, while efforts to further improve its capabilities continue along many avenues. In this report, we examine the influence of static magnetic field strength and temperature on the reported 1H DNP enhancements from three conventional organic biradicals: TOTAPOL, AMUPol, and SPIROPOL. In contrast to the conventional wisdom, our findings show that at liquid nitrogen temperatures and 700 MHz/460.5 GHz, these three bisnitroxides all provide similar 1H DNP enhancements, ε ≈ 60. Furthermore, we investigate the influence of temperature, microwave power, magnetic field strength, and protein sample deuteration on the NMR experimental results.

Formation damage of sandstone geothermal reservoirs: During decreased salinity water injection

Water reinjection was widely implemented in the geothermal development for not only disposing tailwater but also maintaining reservoir pressure. Accompanying this was the formation damage, especially in the injection of decreased salinity water which was synthesized by adding surface water and condensed water into produced water for inhibiting the process equipment corrosion, treating the cooling tower condensate, and etc. Fine migration is the prevailing mechanism; however, it is insufficient in some scenarios. Multiple experiments were conducted to investigate the characteristics and mechanisms of formation damage of sandstone geothermal reservoirs during the decreased salinity water injection. First, coreflooding (CF), nuclear magnetic resonance (NMR), and contact angle (CA) experiments were conducted to analyze the characteristics of the formation damage. Subsequently, scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), and nanoindentation experiments were implemented to study the corresponding mechanisms. Finally, the damage mode of sandstone geothermal reservoirs in decreased salinity water injection was proposed. The CF, NMR, and CA experimental results indicated that the decreased salinity water injection resulted in severe formation damage, as manifested by the reduction of permeability, shrinkage of the pore-throat, and enhancement of the water-wettability of core samples. That is, formation damage not only indicates that the fluid is more difficult to be injected but also that it is more difficult for the injected fluid to flow. As the salinity decreases, these trends gradually enhance. The SEM results illustrated that fine migration is noticeable in decreased salinity water injection, meanwhile mineral dissolution which causes secondary pores and microfracture is also apparent. Both reactions are enhanced as the salinity decreases. The same conclusion was validated by the XRD and ICP-OES results, as manifested by the decrease in the concentrations of clay, K-feldspar, and plagioclase, and the increase in quartz, as well as the emergence of Si4+, Mg2+, Ca2+, and K+ in the effluents produced during the decreased salinity water injection. The nanoindentation results explicated that mineral dissolution weakened the mechanical strength of the minerals, which might effectively facilitate compaction. The elastic modulus and hardness of the quartz, K-feldspar, and plagioclase decreased from 107.5&93.7&72.3GPa and 13.7&10.1&7.4GPa of the original sandstone to 108.1&86.0&69.5GPa and 13.6&10.3&6.4GPa of the deionized water flushed one, respectively. In conclusion, formation damage was synergistically dominated by the external cause of compaction and the internal causes of fine migration and mineral dissolution. These factors compressed the pore-throat, decreased the connectivity of the porous media, enhanced the water-wettability of the sandstone surface, and consequently impeded water flow.

Host-guest interaction of trimethoprim drug with cyclodextrins in aqueous solutions: Calorimetric, spectroscopic, volumetric and theoretical approach

Owing to the internal cavity of cyclodextrins, they are very notable to form the inclusion complexes with various drugs. In present work, the binding of trimethoprim (TMP) drug with native α-, β-, and γ-cyclodextrins (CDs) were systematically examined using the isothermal titration calorimetry (ITC), spectroscopic {UV–visible, nuclear magnetic resonance (NMR)} methods, dynamic light scattering (DLS) and molecular modeling of the complex formed by host (cyclodextrins) and guest (trimethoprim) molecules. The stability of the TMP-CDs inclusion complexes increases in the following order: α-CD < γ-CD < β-CD. UV–visible and ITC measurements show similar binding affinity i.e., of the order 104 M−1 indicating the better fitting of TMP drug molecules into β-CD. The NMR (DOSY) experimental results also depicted the maximum change of TMP diffusion rate in the case of complexation of TMP with β-CD followed by γ-CD. It is also clear from the molecular docking and DLS studies that β-CD interact more with the guest molecule. The transfer values (∆tV2o) are positive increased with the complexity of CDs as: α- < β- < γ-CDs, indicating that there is greater ability of β-CD and γ-CD to interact strongly with trimethoprim as compared to α-CD.

Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification

Nuclear magnetic resonance (NMR) is used widely to characterize petrophysical properties of siliciclastic and carbonate rocks but rarely to study those of mixed siliciclastic–carbonate rocks. In this study, 13 different core samples and eight acidified core samples selected amongst those 13 from the Paleogene Shahejie Formation in Southern Laizhouwan Sag, Bohai Bay Basin, were tested by scanning electron microscopy (SEM), micro-nano-computed tomography (CT), and NMR. SEM and CT results revealed a complex pore structure diversity, pore distribution, and pore-throat connectivity in mixed reservoirs. Sixteen groups of NMR experiments addressed changes in these properties and permeabilities of mixed siliciclastic–carbonate rocks before and after acidification to determine its effects on such reservoirs. NMR experimental results showed no “diffusion coupling” effect in mixed siliciclastic–carbonate rocks. Distributions of NMR T2 cutoff values (T2C) are closely related to the pore structure and lithologic characteristics before and after acidification. The T2C index separates irreducible and movable fluids in porous rocks and is a key factor in permeability prediction. Centrifugation experiments showed that, before acidification, the T2C of mixed siliciclastic–carbonate rocks with 60–90% siliciclastic content (MSR) ranged widely from 1.5 to 9.8 ms; the T2C of mixed siliciclastic–carbonate rocks with 60–90% carbonate content (MCR) ranged from 1.8 to 5.6 ms. After acidification, the T2C of MSR ranged widely from 2.6 to 11.6 ms, the T2C of MCR ranged from 1.5 to 5.6 ms, and no significant difference was observed between MCR reservoirs. Based on an analysis of the morphology of NMR T2 spectra, we propose a new T2 cutoff value prediction method for mixed siliciclastic–carbonate rocks based on a normal distribution function to predict various T2C values from morphological differences in NMR T2 spectra and to calculate the irreducible water saturation (Swir), i.e., the ratio of irreducible total fluid volume to effective porosity. The reliability of the proposed method is verified by comparing predicted T2C and Swir values with those from NMR experimental results. New experiments and modeling demonstrate the applicability of NMR for the petrophysical characterization of mixed siliciclastic–carbonate rock reservoirs. Our results have potential applications for identification and evaluation of mixed siliciclastic–carbonate rock reservoirs using NMR logging.

Optimising magnetic resonance sampling patterns for parametric characterisation

Sampling strategies are often central to experimental design. Choosing efficiently which data to acquire can improve the estimation of parameters and reduce the acquisition time. This work is focused on designing optimal sampling patterns for Nuclear Magnetic Resonance (NMR) applications, illustrated with respect to the best estimate of the parameters characterising a lognormal distribution. Lognormal distributions are commonly used as fitting models for distributions of spin-lattice relaxation time constants, spin-spin relaxation time constants and diffusion coefficients. A method for optimising the choice of points to be sampled is presented which is based on the Cramér–Rao Lower Bound (CRLB) theory. The method’s capabilities are demonstrated experimentally by applying it to the problem of estimating the emulsion droplet size distribution from a pulsed field gradient (PFG) NMR diffusion experiment. A difference of <5% is observed between the predictions of CRLB theory and the PFG NMR experimental results. It is shown that CLRB theory is stable down to signal-to-noise ratios of ∼10. A sensitivity analysis for the CRLB theory is also performed. The method of optimizing sampling patterns is easily adapted to distributions other than lognormal and to other aspects of experimental design; case studies of optimising the sampling scheme for a fixed acquisition time and determining the potential for reduction in acquisition time for a fixed parameter estimation accuracy are presented. The experimental acquisition time is typically reduced by a factor of 3 using the proposed method compared to a constant gradient increment approach that would usually be used.

A method to determine nuclear magnetic resonance (NMR) T2cutoff based on normal distribution simulation in tight sandstone reservoirs

The T2cutoff is an important input parameter in nuclear magnetic resonance (NMR) applications. The accuracy of the T2cutoff affects the prediction reliability of parameters associated with the identification and evaluation of formations. Current methods are based on regional statistics; they have limited applications and the predicted values are not always reliable. In this study, a total of 36 core samples, drilled from Triassic tight sandstone reservoirs of the southwest Ordos Basin in China, were used for laboratory NMR measurements under fully brine saturated and irreducible water conditions. Based on the morphological character analysis of experimental NMR T2 spectra, we demonstrate that NMR T2 spectra can be fully simulated using the normal distribution function. In addition, a new method was proposed, which can predict various T2cutoffs based on the morphological differences of NMR T2 spectra, and the irreducible water saturation (Swirr) was calculated, which represents the ratio of the sum volume of clay bound water and capillary bound water to total pore volume. The reliability of this method was verified by comparing the predicted T2cutoff and Swirr values with those of core NMR experimental results. Finally, we extended this method into field applications in several tight sandstone reservoirs in China. The results show that total T2 distributions of the formation were fully simulated by the normal distribution function, and various T2cutoff and Swirr values were precisely predicted. Meanwhile, tight sands permeability curves, predicted based on the Timur-Coates model, were also accurately estimated. The results of our study may be applied to improve tight sandstone reservoir identification and evaluation using NMR logs.

Molecular origin of the shape memory properties of heat-shrink crosslinked polymers as revealed by solid-state NMR

Understanding the shape memory properties of heat-shrink polymers (HSPs) at the molecular level is crucial for the design and synthesis of advanced HSP materials. Herein, we employed a variety of in situ variable-temperature (VT) solid-state nuclear magnetic resonance (NMR) techniques, in combination with other methods, to investigate the evolution of the individual components of a poly(ethylene-co-vinyl acetate)-based HSP with mobility contrast and segmental orientation during the heat-shrink process. In situ VT 1H T2 relaxometry experiments clearly revealed the presence and evolution of rigid, semi-rigid and mobile components associated with stable crystallites and crosslinkage, less-stable crystallites and the amorphous phase in HSPs with increasing temperature, respectively. In particular, the reversible switching phase should be predominately attributed to the semi-rigid crystalline components, which dramatically decreased after the onset temperature and completely disappeared at the end temperature used in the heat-shrink process. The fixed phase associated with the rigid crosslinkage was observed at high temperatures. Furthermore, the activation energy (Ea) of the mobile components decreased after the heat-shrink process, indicating the chain relaxation of deformed segments in the expanded sample. This was confirmed by Baum−Pines 1H double-quantum experiments, which also revealed an inflection point of the chain mobility at the onset temperature (∼330 K) of the heat-shrink process, at which the restricted mobile chains in the expanded sample are nearly completely relaxed. This imbues HSPs with the ability to shape change. In addition, two-dimensional wide-angle X-ray diffraction (WAXD) indicated that the weak orientation of crystalline domains in HSP disappears after the heat-shrink process. Based on the NMR and WAXD experimental results, a model was proposed to describe the molecular mechanism underlying HSPs' shape memory properties. Finally, proton T2 relaxometry combined with multiple-quantum NMR was confirmed to be a powerful method to study HSPs shape memory properties.

Comparative Analysis on Water Movability in Pores of Different Reservoir Rocks by Nuclear Magnetic Resonance

Based on nuclear magnetic resonance (NMR) relaxation theory, the mathematical model between T2 value and pore size was proposed. The model results showed that small pores have low T2 values, while large pores have high T2 values. Thus, different reservoir rocks, owing to their diverse pore structures, have different T2 distribution characteristics when water-saturation condition is 100%. NMR experiments with different reservoir rocks under different centrifugal speeds were performed. The comparison of pore structures and water movability in diverse rocks was analyzed based on the NMR experimental results. As centrifugal speed increased, water was progressively expelled from the rocks. There are significant differences in the declining in the water saturation and the area of T2 spectrum per unit volume (ST) of all the four samples. The water saturation declining in clastic rocks is higher than that of coals. Moreover, both T2 peaks of clastic rocks corresponding to small and large pores successively decreased, while for coals, the peaks with low T2 values were hardly affected, which is consistent with the results of water saturation declining. This is because the low T2 values correspond to the adsorption pores in coal, from which water is hard to drain out, and since coal rocks are dominant by adsorption pores, the water movability of coals is lower than that of clastic rocks.

Optimal pathway reconstruction on 3D NMR maps

A three-dimensional Nuclear Magnetic Resonance (NMR) map displays the results of NMR experiments, that allow to determine the shape of a biological molecule. Shape calculation starts from a reconstruction of a sequence of NMR signals, which is equivalent to finding a specific path in a graph representation of the problem. Let G=(V,E) be a graph that models the interactions reflected on an NMR map. Its edges are colored with c colors, where each color corresponds to one of c different relationships between the signals. The sequence of interactions under consideration is represented using a concept of an orderly colored path in the c-edge-colored graph.In this paper, we consider the problem of finding the required arrangement of NMR signals on the 3D map and we present its graph representation. We discuss the computational complexity of the problem, we consider its two alternative integer programming models, and evaluate the performance of an optimization algorithm based on the solution of their relaxation combined with the separation of fractional cycles in a Branch & Cut scheme.

Preparation and characterization of poly(ethylene terephthalate) copolyesters modified with sodium‐5‐sulfo‐bis‐(hydroxyethyl)‐isophthalate and poly(ethylene glycol)

ABSTRACTTwo types of poly(ethylene terephthalate) (PET) copolyesters were successfully prepared with sodium‐5‐sulfo‐bis‐(hydroxyethyl)‐isophthalate (SIPE) and poly(ethylene glycol) (PEG) units with different molecular weights named as cationic dyeable polyester and easy cationic dyeable polyester. Their chemical and crystalline structures were characterized by the nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering measurement, and their thermal properties were tested by differential scanning calorimetry and thermogravimetric analysis, respectively. NMR experimental results showed that the actual molar ratio of comonomers was basically consistent with the correlative feed ratio. WAXD results indicated that the crystalline structures of prepared copolyesters were similar to that of PET. Moreover, the glass transition temperature, melting temperature, and thermal degradation temperature were found to decrease with the reduction of the of PEG units as the incorporation of lower of PEG units brought more ether bonds into molecular chains, which increased the irregularity of molecular chain arrangement and led to lower crystallinity. In addition, because the incorporation of PEG units with lower molecular weight led to more ether bonds and hydroxyl end‐groups in molecular chains, the value of contact angle of PET copolyesters dropped, manifesting PET copolyesters had better hydrophilicity with the decreasing molecular weight of PEG units.© 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39823.

Conformations of Carnosine in Aqueous Solutions by All-Atom Molecular Dynamics Simulations and 2D-NOSEY Spectrum

All-atom molecular simulations and two-dimensional nuclear overhauser effect spectrum have been used to study the conformations of carnosine in aqueous solution. Intramolecular distances, root-mean-square deviation, radius of gyration, and solvent-accessible surface are used to characterize the properties of the carnosine. Carnosine can shift between extended and folded states, but exists mostly in extended state in water. Its preference for extension in pure water has been proven by the 2D nuclear magnetic resonance (NMR) experiment. The NMR experimental results are consistent with the molecular dynamics simulations.

A new solvent suppression method via radiation damping effect

Radiation damping effects induced by the dominated solvent in a solution sample can be applied to suppress the solvent signal. The precession pathway and rate back to equilibrium state between solute and solvent spins are different under radiation damping. In this paper, a series of pulse sequences using radiation damping were designed for the solvent suppression in nuclear magnetic resonance (NMR) spectroscopy. Compared to the WATERGATE method, the solute signals adjacent to the solvent would not be influenced by using the radiation damping method. The one-dimensional (1D) 1H NMR, two-dimensional (2D) gCOSY, and J-resolved experimental results show the practicability of solvent suppression via radiation damping effects in 1D and 2D NMR spectroscopy.

Bridging, non-bridging and free (O 2–) oxygen in Na 2O-SiO 2 glasses: An X-ray Photoelectron Spectroscopic (XPS) and Nuclear Magnetic Resonance (NMR) study

High resolution Na 1s, O 1s and Si 2p core level XPS spectra of six Na 2O–SiO 2 glasses ranging in composition from 100 to 45 mol % SiO 2 have been collected using the Kratos Ultra Axis instrument with its unique charge compensation system. The O 1s spectra for the glasses are well resolved so that bridging oxygen (BO, Si– O–Si) and non-bridging oxygen (NBO, Na– O–Si) signals can be accurately fitted and quantified without resorting to constraints or assumptions. The same samples were analysed by 29Si MAS NMR to obtain Q-species abundances from which BO and NBO proportions were calculated. Similar BO:NBO ratios were obtained by both methods over the entire compositional range studied. They are also consistent with most previous XPS and NMR results for glasses containing more than ~ 65 mol % SiO 2. Our XPS and NMR experimental results, however, differ somewhat from previously published XPS and NMR results for glasses containing less than about 65 mol % SiO 2. Na is mobile in the X-ray beam and mobility causes BO:NBO ratios to increase with time of exposure. Na mobility here has been circumvented to yield reliable BO:NBO ratios of the glasses. The ratios are lower than previously reported in XPS studies and are similar to ratios obtained from our 29Si MAS NMR results on the same glasses. The XPS and 29Si MAS NMR results also indicate the presence of a third oxygen species in sodic glasses. As has been proposed for CaSiO 3 glass and for sodic and potassic glasses containing La, we suggest that O 2− is present in sodic glasses at small concentrations. The O 2− content correlates with increased soda content and may be associated with, and instrumental in development of, three dimensional percolation channels in the glasses. The XPS O 1s line width of the BO peak is broader than the NBO peak, indicating more than one contribution to the BO peak. As observed in crystalline Na metasilicate and Na disilicate, BO of Na-silicate glasses may be of two types, one arising from BO bridging two Si atoms, and the second BO signal arising from BO bonded not only to two Si atoms but also to Na.

R 87 b and C133s nuclear magnetic resonance study of the structural properties of mixed RbxCs2−xZnCl4 (x=, 1, and 2) crystals

The structures of mixed RbxCs2−xZnCl4 (x=0, 1, and 2) single crystals grown by using the slow evaporation method were determined with x-ray diffraction. In addition, the NMR spectra and the spin-lattice relaxation times, T1, of the R87b and C133s nuclei of the three crystals were determined by using nuclear magnetic resonance (NMR) spectroscopy. The spin-lattice relaxation times, T1, of the Cs-based compounds are very much longer than those of the Rb-based compounds. The differences between the T1 values of the Rb and Cs nuclei are due to the difference between their electric quadrupole moments. Further, we analyzed the crystallographic structures of these crystals by considering the occupation probabilities (Rb or Cs) of the two cationic sites. Our NMR experimental results confirm that there are two crystallographically inequivalent Rb sites, Rb(1) and Rb(2), in Rb2ZnCl4 and two crystallographically inequivalent Cs sites, Cs(1) and Cs(2), in Cs2ZnCl4. And, only one Rb site and only one Cs site in RbCsZnCl4 was obtained. The Cs and Rb occupation rates of each of the two available sites, A1 and A2, were determined from the NMR signals.

The EB-DNA Liquid Crystalline Complex with High Concentration of Mg2+

The effects of ethidium bromide (EB) on the DNA cholesteric phase in the high ionic strength of Mg2+ were investigated by polarized optical microscopy (POM), 31P and 23Na nuclear magnetic resonance (NMR). It was found that the cholesteric pitch in the EB-DNA cholesteric phase is obviously smaller than that in the EB-free DNA cholesteric solutions with the same ionic strength of Mg2+ at room temperature. The fraction of liquid crystal phase in both the EB-free and the EB-DNA solutions is decreased with increasing the Mg2+ concentration. But the fraction of liquid crystal phase in the EB-DNA solutions is higher than that in the EB-free DNA solutions at the same Mg2+ concentration, which is attributed to the change of the surface charge distribution on the DNA chains and the stiffness of DNA due to intercalation of EB. The results of the 23Na NMR experiments suggested that the intercalation of EB results in the changes of the ionic environment close to the DNA chains, by which the liquid crystal behavior of DNA is affected.

Multinuclear NMR spectroscopy in the gas phase

Nuclear magnetic resonance (NMR) of some nuclei (e.g. 1H, 13C, 19F, 29Si or 31P, I=1/2) gives strong signals which allow analytical studies of gaseous compounds. The other magnetic nuclei have low natural abundance or/and contain an electric quadrupole moment and their NMR signals are rather weak. In our laboratory we have developed new experimental techniques, which permit us to monitor several micrograms of chemical compounds in gaseous matrices. Applying this approach we have observed magnetic shielding of various nuclei, including 17O and 33S at the natural abundance, in the gas phase as a function of density. Density-dependent spin–spin couplings were also found for many chemical compounds. It has been shown that NMR gas-phase studies can easily be extended on molecules, which exhibit strong intermolecular interactions and are liquids at room temperature. All the latter NMR experimental results obtained for gaseous matrices are reviewed in this paper.

The dynamical susceptibility based on the Hubbard model of the body centered tetragonal lattice

We investigated the dynamical susceptibility related to the spin correlation within planes and that between planes based on the Hubbard model of the body centered tetragonal lattice (BCT) above the magnetic ordered temperature without a magnetic field. The dynamical susceptibilities are studied within the random-phase approximation. The criterion of the occurrence of the Neel order is also studied. We find that the expressions of the dynamical susceptibilities and the one of the criterion are more complicated than those of the simple cubic lattice because there are two atoms in the unit cell of the BCT. It is possible for us to analyze the neutron scattering and nuclear magnetic resonance experimental results in the BCT within the present approach. The present result is compared with the dynamical susceptibilities based on the Hubbard model of the hexagonal-close packed lattice (HCP). We predict that it is possible for us to observe two-component Knight shifts in URu2Si2 similar to those in UPt3 for μSR because the crystalline structure of U atoms in URu2Si2 is approximately BCT and because that in UPt3 is approximately HCP.