Short Spin-spin Relaxation Times Research Articles

Effects of Cyclic Glycopolymers Molecular Mobility on their Interactions with Lectins.

Cyclic polymers, which are found in the field of biopolymers, exhibit unique physical properties such as suppressed molecular mobility. Considering thermodynamics, the suppressed molecular mobility of cyclic polymers is expected to prevent unfavorable entropy loss in molecular interactions. In this study, we synthesized cyclic glycopolymers carrying galactose units and investigated the effects of their molecular mobility on the interactions with a lectin (peanut agglutinin). The synthesized cyclic glycopolymers exhibited delayed elution time on size exclusion chromatography and a short spin-spin relaxation time, indicating typical characteristics of cyclic polymers, including smaller hydrodynamic size and suppressed molecular mobility. The hemagglutination inhibition assay revealed that the cyclic glycopolymers exhibited weakened interactions with peanut agglutinin compared to the linear counterparts, attributable to the suppressed molecular mobility. Although the results are contrary to our expectations, the impact of polymer topology on molecular recognition remains intriguing, particularly in the context of protein repellent activity in the biomedical field.

Thermoresponsive behavior of poly(DEGMA)-based copolymers. NMR and dynamic light scattering study of aqueous solutions

We studied temperature behavior of diblock copolymers of poly[2-(2-methoxyethoxy)ethyl methacrylate] (PDEGMA) with poly(N-(2-hydroxypropyl)methacrylamide and a statistical copolymer PDEGMA-co-N-propargylmethacrylamide in aqueous solutions. NMR spectra and dynamic light scattering showed that the copolymers exhibit a reversible phase transition which depends on the composition of the block copolymer and slightly on polymer concentration. In contrast to statistical copolymer, different behavior of proton groups in polymer backbone (and in the nearest side chain OCH2 group) on the one hand and in other side chain groups of the PDEGMA on the other hand was observed for diblock copolymers. Additionally, two types of water molecules were detected in solutions of the diblock copolymers above the phase transition –“free” with long and “bound” with short spin-spin relaxation times T2. NOESY spectra indicate that a core- to- shell morphology is unlikely in these block copolymers. This report emphasizes the importance of understanding of the self-association of copolymers in solution on the molecular level and provides important information for the design of “smart” thermoresponsive polymer-based drug delivery systems.

Measuring of short spin-spin relaxation times distributions using NQR nutation experiments

Experiments using nutation interferograms and nutation spectra in nuclear quadrupole resonance (NQR) are used for the first time to find the distribution of short spin-spin relaxation times in powder samples. Instead of the traditional method of the inversion of the Laplace transform, the inversion of the integral transformations of nutation interferograms and nutation spectra are used in this work. The use of the distributions of NQR relaxation times can provide new information on dynamic processes in complex molecular systems in the solid state. To illustrate the capabilities of the method, experimental results for 35Cl, 75As NQR and for 1H NMR are provided.

Solution Structure of Molecular Associations Investigated Using NMR for Polysaccharides: Xanthan/Galactomannan Mixtures.

Although the intermolecular nuclear Overhauser effect (NOE) signal was valuable to elucidate molecular association structure, it could not always be observed for associated molecules due to the short spin-spin relaxation time T2 in NMR measurements, especially for high molar mass systems. While almost no study has been reported for high molar mass polymers (>1 × 10(6)), especially for polysaccharide-polysaccharide interactions, NOE signals were observed for the first time between two different types of polysaccharides, xanthan and galactomannan (locust bean gum), forming a synergistic gel, as a direct evidence of intermolecular binding of polysaccharides. The NOE peak was found between pyruvic acid in xanthan and anomeric proton of mannose of galactomannan. This NOE signal was observed only when mixing time >0.5 s, indicating indirect NOEs caused by spin diffusion. Therefore, this NOE could not be used to construct the molecular models. However, it is a direct evidence for the binding between two different types of polysaccharide to elucidate the synergistic gelation. This NOE signal was observed only for low molar mass galactomannans (1.4 × 10(4)). T2 of pyruvate methyl drastically decreased at low temperatures in the presence of synergistic interaction, suggesting that pyruvate group at terminal end of side chain in xanthan plays an essential role in synergistic interaction.

Accelerated 4D quantitative single point EPR imaging using model‐based reconstruction

Electron paramagnetic resonance imaging has surfaced as a promising noninvasive imaging modality that is capable of imaging tissue oxygenation. Due to extremely short spin-spin relaxation times, electron paramagnetic resonance imaging benefits from single-point imaging and inherently suffers from limited spatial and temporal resolution, preventing localization of small hypoxic tissues and differentiation of hypoxia dynamics, making accelerated imaging a crucial issue. In this study, methods for accelerated single-point imaging were developed by combining a bilateral k-space extrapolation technique with model-based reconstruction that benefits from dense sampling in the parameter domain (measurement of the T2 (*) decay of a free induction delay). In bilateral kspace extrapolation, more k-space samples are obtained in a sparsely sampled region by bilaterally extrapolating data from temporally neighboring k-spaces. To improve the accuracy of T2 (*) estimation, a principal component analysis-based method was implemented. In a computer simulation and a phantom experiment, the proposed methods showed its capability for reliable T2 (*) estimation with high acceleration (8-fold, 15-fold, and 30-fold accelerations for 61×61×61, 95×95×95, and 127×127×127 matrix, respectively). By applying bilateral k-space extrapolation and model-based reconstruction, improved scan times with higher spatial resolution can be achieved in the current single-point electron paramagnetic resonance imaging modality.

75As NMR local probe study of magnetism in (Eu1−xKx)Fe2As2

75As NMR measurements were performed as a function of temperature and doping in (Eu1-xKx)Fe2As2 (x=0,0.38,0.5,0.7) samples. The large Eu2+ moments and their fluctuations are found to dominate the 75As NMR properties. The 75As nuclei close to the Eu2+ moments likely have a very short spin-spin relaxation time (T2) and are wiped out of our measurement window. The 75As nuclei relatively far from Eu2+ moments are probed in this study. Increasing the Eu content progressively decreases the signal intensity with no signal found for the full-Eu sample (x=0). The large 75As NMR linewidth arises from an inhomogeneous magnetic environment around them. The spin lattice relaxation rate (1/T1) for x=0.5 and 0.7 samples is nearly independent of temperature above 100K and results from a coupling to paramagnetic fluctuations of the Eu2+ moments. The behavior of 1/T1 at lower temperatures has contributions from the antiferromagnetic fluctuations of the Eu2+ moments as also the fluctuations intrinsic to the FeAs planes and from superconductivity.

Single Acquisition Quantitative Single‐Point Electron Paramagnetic Resonance Imaging

Electron paramagnetic resonance imaging has emerged as a promising noninvasive technology to dynamically image tissue oxygenation. Owing to its extremely short spin-spin relaxation times, electron paramagnetic resonance imaging benefits from a single-point imaging scheme where the entire free induction decay signal is captured using pure phase encoding. However, direct T2 (*)/pO2 quantification is inhibited owing to constant magnitude gradients which result in time-decreasing field of view. Therefore, conventional acquisition techniques require repeated imaging experiments with differing gradient amplitudes (typically 3), which results in long acquisition time. In this study, gridding was evaluated as a method to reconstruct images with equal field of view to enable direct T2 (*)/pO2 quantification within a single imaging experiment. Additionally, an enhanced reconstruction technique that shares high spatial k-space regions throughout different phase-encoding time delays was investigated (k-space extrapolation). The combined application of gridding and k-space extrapolation enables pixelwise quantification of T2 (*) from a single acquisition with improved image quality across a wide range of phase-encoding time delays. The calculated T2 (*)/pO2 does not vary across this time range. By utilizing gridding and k-space extrapolation, accurate T2 (*)/pO2 quantification can be achieved within a single data set to allow enhanced temporal resolution (by a factor of 3).

新混練指標の検討

The effect of mixing on filler dispersion has been shown to have remarkable affects on material properties. Many methods of measuring filler dispersion have been developed. However, none of them provides a filler dispersion index that gives the best way to control a mixing process.We developed a new method of measuring filler dispersion named FDI in order to evaluate objectively a kneading state of the compound that consists of EPDM, carbon black, and oil. A filler dispersion index (FDI) is defined as a percent ratio of complex modulus G* at 1% strain versus that at 0.01% strain.A FDI value increases along with an increase of mixing time. A FDI value of cured EPDM is proportional to that of uncured EPDM. Treating the rubber composition with an open role does not affect on a FDI value. Consequently, the FDI is found to be a better method to measure carbon dispersion comparing the optical microscope method of ASTM 2663-69.A free induction decay curve of pulsed NMR indicates a presence of hard segments with a short spin-spin relaxation time (T2). The short-T2 value measured by pulsed NMR increases along with an increase of mixing time, which is similar to the FDI.

Solid-state nuclear magnetic resonance microscopy demonstrating human dental anatomy.

Magnetic resonance imaging has become a common diagnostic tool in medical practice. It is a common view that solid-state material lacking a sufficient amount of unpaired nuclear spins, in particular proton spins, is impossible to depict with clinically used magnetic resonance devices. Characteristically rapid dephasing, caused by relatively short spin-spin relaxation (T(2) time) also leads to broad resonance lines. A newly introduced technique, constant-time imaging, uses 3 phase-encoding gradients for the acquisition of only one complex data point per phase-encoding step, resulting in detection times of only a few microseconds and extremely sharp resonance lines. Using a Bruker spectrometer AMX 300 WB (300 MHz, 7.1 T) with a microimaging attachment, we performed solid-state magnetic resonance imaging of whole teeth. Data processing was carried out by means of 3-dimensional Fourier analysis, and reconstructions were performed by the ParaVision (Bruker) software system. Dental hard tissues (enamel, dentin, and root cementum) and pulpal soft tissue could be depicted in 2-dimensional and 3-dimensional images. The voxel resolution isotropically reached 195 microm. The constant-time imaging technique enabled a naturalistic and nondestructive visualization of the teeth without application of ionizing radiation. This technique bears the potential to help us overcome the limitations of clinically used standard magnetic resonance tomography devices and offers new perspectives for dental imaging.

Broadband DC SQUID NMR Spectrometry on Bulk Metals

We report on experiments in which we have used a DC SQUID with additional positive feedback (APF) in a broadband pulsed NMR spectrometer, of bandwidth 3.4 MHz, to observe directly the free precession of nuclear spins in bulk metallic samples. The sample is located inside a superconducting receiver coil, which forms a flux transformer with the input coil of the SQUID. The broadband response of the flux transformer, combined with the relatively large bandwidth of the APF SQUID when operated in flux-locked-loop mode, results in a short recovery time. This enables the study of solid-state samples with a short spin-spin relaxation time at frequencies below 1MHz, appropriate at millikelvin temperatures. A further advantage of this scheme is that the NMR frequency can be varied without changes in the detection electronics being necessary. The sensitivity of the DC SQUID detection system, compared with conventional NMR, allows the study of small single crystal samples. The decay of eddy currents following the transmitter pulse is governed by sample size, geometry and resistivity. Typical decay times of less than 10 us are expected on 0.5 mm diameter cylindrical samples. We discuss progress on experiments with aluminium wires at a temperature of 20 mK.

In vivo imaging of a stable paramagnetic probe by pulsed‐radiofrequency electron paramagnetic resonance spectroscopy

Imaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin-spin relaxation times, typically under 1 microsecond, of most biologically relevant paramagnetic species. Recent advances in radiofrequency (RF) electronics have enabled the generation of pulses of the order of 10-50 ns. Such short pulses provide adequate spectral coverage for EPR studies at 300 MHz resonant frequency. Acquisition of free induction decays (FID) of paramagnetic species possessing inhomogenously broadened narrow lines after pulsed excitation is feasible with an appropriate digitizer/averager. This report describes the use of time-domain RF EPR spectrometry and imaging for in vivo applications. FID responses were collected from a water-soluble, narrow line width spin probe within phantom samples in solution and also when infused intravenously in an anesthetized mouse. Using static magnetic field gradients and back-projection methods of image reconstruction, two-dimensional images of the spin-probe distribution were obtained in phantom samples as well as in a mouse. The resolution in the images was better than 0.7 mm and devoid of motional artifacts in the in vivo study. Results from this study suggest a potential use for pulsed RF EPR imaging (EPRI) for three-dimensional spatial and spectral-spatial imaging applications. In particular, pulsed EPRI may find use in vivo studies to minimize motional artifacts from cardiac and lung motion that cause significant problems in frequency-domain spectral acquisition, such as in continuous wave (cw) EPR techniques.

Self-diffusion coefficients in plastic crystals by multiple-pulse NMR in large static field gradients.

Measurements of self-diffusion coefficients in solids with the gradient spin echo technique have until now been limited due to short spin-spin relaxation times. Here we make use of multiple-pulse sequences, which average out the nuclear dipole interaction, to expand the measurable range for macroscopic self-diffusion coefficients by 2 orders of magnitude. By combining multiple-pulse NMR, in our case using the MREV-8 sequence, with a high static gradient we measured the self-diffusion coefficient in a molecular crystal of camphene down to a value of $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{m}}^{2}{\mathrm{s}}^{\ensuremath{-}1}$ at 219 K in the plastic phase.

Continuous-wave NMR imaging of solids.

Current pulsed nuclear magnetic resonance methods of imaging samples such as solids with short spin-spin relaxation times are restricted to use with T2 values longer than approximately 10 microseconds. In the present study a method of imaging ultra-short T2 samples using continuous- wave, swept-field NMR is presented that, in principle, will be able to overcome this restriction. The technique is identical to that used in continuous-wave electron paramagnetic resonance imaging of paramagnetic species and involves irradiating the sample continuously with a radiofrequency excitation in the presence of a strong stationary magnetic field gradient. When the main magnetic field is swept over a suitable range, the variation of the NMR absorption signal with applied magnetic field yields a one-dimensional projection of the object under study along the gradient direction. Two- or three-dimensional image data sets may be reconstructed from projections that are obtained by applying the gradient in different directions. Signal-to-noise ratio can be improved by modulating the magnetic field and employing a lock-in amplifier to recover signal variations at the audio modulation frequency. Preliminary experiments were performed using a 7 Tesla magnet and a 300 MHz continuous-wave radiofrequency bridge with lock-in detection. The apparatus is described and the results of pilot experiments that employed vulcanized rubber samples are presented. The ability of the technique to detect short T2 samples was demonstrated by the presence of a background signal from the Perspex former of the birdcage resonator used for signal reception.

Accurate measurement of homonuclear coupling constants using JHH-TOCSY

The homonuclear JHH coupling constant is one of the most important NMR parameters. In complex molecules with quite long relaxation times, E.COSY (1) in combination with the DISCO procedure (2) seems to be the best homonuclear method for quantifying J couplings. Other homonuclear methods are z-filtered COSY (3)) J-6 spectroscopy (4)) and selective excitation (5). These methods fail, however, in molecules with short spin-spin relaxation times where the linewidth is in the range of coupling constants. For these situations, some triple-resonance methods have been proposed recently (6-8), which can be used for 15Nand “Ccuenriched peptides and proteins. Their pulse sequences include a heteronuclear coherence transfer from “N to 13C. Additionally the magnetization transfer using a 13C spin lock works well for completely 13C-enriched molecules (9). In these spectra, the signal is split in Fi by the ‘JCH coupling constant, whereas the 3J(HN-H~) coupling constant can be extracted from the displacement in F2. From these methods, precisely estimated coupling constants are obtained, and they are, in distinction to E.COSY, independent of the linewidth. Until now no similar method has been proposed that could be used for molecules at natural abundance. For this purpose, we have developed two new pulse sequences shown in Figs. la and 1 b, called JHH-TOCSY. Sequence 1 a is a H,H correlation and sequence 1 b is a H,X correlation. As for the methods mentioned above, these sequences provide the JHH splitting for XH groups only, whereas XH2 groups show no splitting. For overlapping XH and XH2 groups, and for spectral simplification, XH selection may be used as shown in Fig. 1 c. Figure 1 d shows the 30 extension of sequence 1 a with and without XH selection. JHH-TOCSY is well suited to molecules at natural abundance or for 13Cor “N-monolabeled compounds. In comparison with the triple-resonance methods, the sequences are much shorter, because there is no need for the long 1 /( 2 JCN) delay. The evolution of the magnetization after 2, is as follows (only the relevant operators are shown); cf. Fig. la:

Magnetic resonance imaging: A new window into industrial processing

Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given.

Spatial localization in NMR spectroscopy in vivo.

Spatial localization techniques are necessary for in vivo NMR spectroscopy involving heterogeneous organisms. Localization by surface coil NMR detection alone is generally inadequate for deep-lying organs due to contaminating signals from intervening surface tissues. However, localization to preselected planar volumes can be accomplished using a single selective excitation pulse in the presence of a pulsed magnetic field gradient, yielding depth-resolved surface coil spectra (DRESS). Within selected planes, DRESS are spatially restricted by the surface coil sensitivity profiles to disk-shaped volumes whose radii increase with depth, notwithstanding variations in the NMR signal density distribution. Nevertheless, DRESS is a simple and versatile localization procedure that is readily adaptable to spectral relaxation time measurements by adding inversion or spin-echo refocusing pulses or to in vivo solvent-suppressed spectroscopy of proton (1H) metabolites using a combination of chemical-selective RF pulses. Also, the spatial information gathering efficiency of the technique can be improved to provide simultaneous acquisition of spectra from multiple volumes by interleaving excitation of adjacent planes within the normal relaxation recovery period. The spatial selectivity can be improved by adding additional selective excitation spin-echo refocusing pulses to achieve full, three-dimensional point resolved spectroscopy (PRESS) in a single excitation sequence. Alternatively, for samples with short spin-spin relaxation times, DRESS can be combined with other localization schemes, such as image-selected in vivo spectroscopy (ISIS), to provide complete gradient controlled three-dimensional localization with a reduced number of sequence cycles.

NMR Line Shape‐Spin‐Lattice Relaxation Correlation Study of Portland Cement Hydration

The proton free induction decay of a portland cement paste in an advanced stage of hydration can be roughly divided into three main components: (1) a component with a very short spin‐spin relaxation time, T2, representing the protons of the solid OH groups and the water of crystallization, (2) a component with an intermediate T, representing the bonded water in the gel phase, and (3) a third component with a relatively long T2 representing the water in the micropores and layers. The dependences of the intensities, T2's, and spin‐lattice relaxation times (T1's) of these three components on the cement hardening time have been determined. The proton spin‐lattice relaxation time of the “solid” component increases with hardening time whereas T1 decreases for the other two components. The observed time dependence of the diffusion coefficient, D, of water in a tricalcium silicate paste supports the findings of the above correlation study.

Measurement of spin-lattice relaxation times on a high resolution CW NMR spectrometer using audio modulation pulses

Nuclear magnetic resonance lines with relatively short spin-spin relaxation times ( T 2) may be inverted for the purpose of measuring their spin-lattice relaxation times ( T 1) by applying a large audio frequency field modulation pulse to a high resolution sideband detection NMR spectrometer. The frequency, amplitude, and length of such a pulse is evaluated and the trajectory of the magnetization as it is inverted is approximately calculated. It is found, in agreement with Anderson's cw result, that the spins invert in a time π γ H 1 J 1 (β), as if a field H 1 J 1 (β) had been applied, where H 1 is the actual rotating rf field amplitude, J 1 is the first Bessel function and β equals γH m ω m , where H m is the modulation amplitude and ω m is the modulation angular frequency. The implementation of this technique on a Varian HA-100 spectrometer equipped with a Varian Spectro System accessory is described. Examples of the use of the technique are given. One example is on a sample with a T 1 of 342 msec.

Water in agarose gels studied by nuclear magnetic resonance relaxation in the rotating frame

The dependence of the spin-lattice relaxation time in the rotating frame (T1rho) on radio frequency (RF) field strength and temperature has been studied for agarose gels in order to investigate molecular motion. The results indicate the presence of slow motions with a correlation time of ca. 5-10(-6) s at room temperature. This interaction is responsible for the short spin-spin relaxation times (T2) for water protons in agarose gels and is ascribed to firmly bound water. The fraction of bound water is estimated to about 0.003 for a 7.3% agarose gel. The motion of the more mobile protons in agarose-water systems can not be characterized by single correlation time. This fraction is presumably composed of water in different motional states and some of the agarose hydroxyl protons. Higher mobilities are the most common.

Nuclear Magnetic Relaxation Study of Tobacco Mosaic Virus Solutions

The molecular order of water in liquid-crystalline 5-28% tobacco mosaic virus (TMV) solutions was studied by proton spin-spin, spin-lattice, and translational self-diffusion coefficient measurements at various concentrations as well as by deuteron D(2)O nuclear magnetic resonance (NMR) studies. The results show that the average H(2)O molecule spends less than 1% of its time in an ordered state bound to the TMV backbone. The protons on the TMV molecules themselves, on the other hand have a very short spin-spin relaxation time T(2) of about 20 mus, demonstrating the existence of a high degree of liquid-crystalline order.