Proton Spin-lattice Relaxation Time Research Articles

Nuclear Magnetic Resonance Study of Hydrated Bentonite

Impedance spectroscopy and nuclear magnetic resonance (NMR) were used to investigate the mobility of water molecules located in the interlayer space of H+ – exchanged bentonite clay. The conductivity obtained by ac measurements was 1.25 × 10−4 S/cm at 298 K. Proton (1H) lineshapes and spin-lattice relaxation times were measured as a function of temperature over the temperature range 130–320 K. The NMR experiments exhibit the qualitative features associated with the proton motion, namely the presence of a 1H NMR line narrowing and a well-defined spin-lattice relaxation rate maximum. The temperature dependence of the proton spin-lattice relaxation rates was analyzed with the spectral density function appropriate for proton dynamics in a two-dimensional system. The self-diffusion coefficient estimated from our NMR data, D ∼ 2 × 10−7 cm2/s at 300 K, is consistent with those reported for exchanged montmorillonite clay hydrates studied by NMR and quasi-elastic neutron scattering (QNS).

Thermal, dielectric and vibrational properties of ferroelastic [(CH 3) 3PH] 3[Sb 2Cl 9] crystal. Molecular motion of trimethylphosphonium cations studied by proton magnetic resonance

[(CH 3) 3PH] 3[Sb 2Cl 9] (abbreviated as TMPCA) was found to undergo numerous reversible structural phase transitions studied by dilatometric and dielectric methods: I ↔ II at 375/372 (heating/cooling), II ↔ III at 272/272, III ↔ IV at 223/216 and IV ↔ V at 212/206 K. Debay-like dispersion of the electric permittivity in the kilohertz frequency region over the phases I and II is disclosed. The molecular parameters of the relaxation process assigned to the motion of the trimethylpyridinium cations are evaluated. The pyroelectric measurements of TMPCA confirmed the polar/pyroelectric nature of the lowest temperature phase (V). Proton spin-lattice relaxation time of polycrystalline TMPCA was studied in the temperature range 80–429 K. A dynamic inequivalence of two trimethylphosphonium cations performing complex reorientational motion (C 3—of methyl groups, C 3 ′ —of the cation around the P—H bond and the isotropic motion of the whole cation) was detected. A ferroelastic domain structure was observed in all phases below 375 K. The infrared and Raman spectra for TMPCA were measured in the region of the internal vibrations of the trimethylphosphonium cations and [Sb 2Cl 9] 3− anions in the wide temperature region (Raman 12–404 K, IR 300–413 K). The possible mechanisms of the phase transitions are discussed on the basis of the presented results.

Calculation of the Raman frequency and the damping constant of a coupled mode in the ferroelectric and paraelectric phases in KH2PO4

AbstractThe Raman frequency of the coupled mode $\omega _ - $ associated with the order parameter is calculated as a function of pressure from the mean field theory in the ferroelecric phase of KDP. Using the frequencies of the coupled mode, the pressure dependence of the damping constant $\Gamma _ - $ is calculated by the proton spin lattice relaxation time and by the energy fluctuation of this mode of KDP in the ferroelectric (FE) phase. For the paraelectric (PE) phase, the Raman frequency of the coupled mode $\omega _ - $ is calculated as a function of temperature at 6.54 kbar. The temperature dependence of the damping constant $\Gamma _ - $ is performed only by the energy fluctuation of the coupled mode $\omega _ - $ in the PE phase of KDP. The values of the activation energy U are extracted from the pressure and temperature dependence of the damping constant $\Gamma _ - $ of this coupled mode $\omega _ - $ for both FE and PE phases of KDP.

Preparation of Modified Montmorillonite with Benzethonium and Benzalconium Chloride for Nanocomposites Preparation

Modified clays were intercalated with benzethonium chloride and benzalkonium chloride by exchanging the sodium ions. The organoclays obtained were characterized by X-ray diffraction (XRD); thermogravimetric analysis (TGA) and low field nuclear magnetic resonance (NMR), through proton spin-lattice relaxation time measurements (T1H). From the characterization data, the formation of organically modified clays was confirmed. These products can probably be used to prepare PVC nanocomposites with superior processing characteristics due to better chemical structure of clay surfactants.

Characterization of low molecular-weight gelator methyl-4,6- O-( p-nitrobenzylidene)- α- d-glucopyranoside hydrogels and water diffusion in their networks

This paper focuses on the thermal properties, the microstructure, and the molecular dynamics of water in the hydrogels (1.5, 2, 3, 4, and 5% [g mL −1]) formed by sugar-based low molecular-weight gelator methyl-4,6- O-( p-nitrobenzylidene)- α- d-glucopyranoside. The energy needed to break the non-covalent interactions such as the hydrophobic, dipole–dipole, and π–π stacking interactions responsible for the gel formation was calculated to be 43 kJ mol −1. The microstructure of the 4% [g mL −1] hydrogel shows a characteristic fibril structure of the gel network with individual gel fibers, the junction points of thicker fibers, and pores occupied by water. The single mode diffusion of water molecules inside the gel network was detected irrespective of the diffusion time Δ (8–75 ms) and hydrogel concentration. For Δ of 10 ms the water diffusion is almost free and characterized by the diffusion coefficient in the range from 2.17×10 −9 to 1.84×10 −9 m 2 s −1 for studied hydrogels. For larger Δ values, so-called restricted diffusions are observed and manifested in the linear decreases of the diffusion coefficient with diffusing time Δ, as shown for 5% gel. Only the one average proton spin-lattice relaxation time T 1 of water was determined for the studied hydrogels, irrespective of gelator concentration.

The Use of Solid State NMR to Characterize High Density Polyethylene/Organoclay Nanocomposites

Recently the development of new materials, in special polymeric nanocomposites, formed by polymer and layered silicates, have gained attention. In this work nanocomposites based on high-density polyethylene matrix (HDPE) and organically modified clay were prepared by melt processing and characterized by the determination of proton spin-lattice relaxation time through solid state nuclear magnetic resonance (NMR) spectroscopy. This work has a proposal to add one quantitative technique to help the researchers to better evaluate polymeric nanocomposite, because NMR is an important tool employed to study both molecular structure and dynamic molecular behavior. The nanocomposites were mixed in a twin-screw extruder, varying the shear rate parameter: 60 and 90 rpm at 463 K. Nanocomposites obtained were characterized through X-ray diffraction; thermal analysis; impact resistance and nuclear magnetic resonance. The T1H results showed that the samples present different molecular domains according to the clay dispersion, forming an intercalated and/or exfoliated nanocomposites. The measurement of relaxation time, using low field NMR, is a useful method to evaluate changes in the molecular mobility of nanocomposite and can infer whether the sample is exfoliated and/or intercalated, since lamellar filler is used.

Magnetic resonance and conductivity study of gelatin-based proton conductor polymer electrolytes

This work report results from proton nuclear magnetic resonance (NMR), continuous-wave (CW-EPR) and pulsed electron paramagnetic resonance (P-EPR) and complex impedance spectroscopy of gelatin-based polymer gel electrolytes containing acetic acid, cross-linked with formaldehyde and plasticized with glycerol. Ionic conductivity of 2 × 10 −5 S/cm was obtained at room temperature for samples prepared with 33 wt% of acetic acid. Proton ( 1H) line shapes and spin-lattice relaxation times were measured as a function of temperature. The NMR results show that the proton mobility is dependent on acetic acid content in the plasticized polymer gel electrolytes. The CW-EPR spectra, which were carried out in samples doped with copper perchlorate, indicate the presence of the paramagnetic Cu 2+ ions in axially distorted sites. The P-EPR technique, known as electron spin echo envelope modulation (ESEEM), was employed to show the involvement of both, hydrogen and nitrogen atoms, in the copper complexation of the gel electrolyte.

NMR study of styrene-butadiene rubber (SBR) and TiO 2 nanocomposites

The chemical behavior of styrene-butadiene rubber (SBR) and of the SBR/TiO 2 and photodegraded SBR/TiO 2 nanocomposites was investigated through nuclear magnetic resonance spectroscopy (NMR) in the solid state with magic angle spinning (MAS). The 13C cross polarization/magic angle spinning (CP/MAS) routine spectrum allowed us to obtain information on the polymer microstructure and also to evaluate the domain mobilities. The variation contact time and the proton spin-lattice relaxation time in the rotating frame (T 1ρH) were determinant factors to evaluate the dynamic molecular motion. The NMR spectrum of the nanocomposites was dislocated 5 ppm to higher chemical shift, indicating the presence of a strong interaction between the polymer chains and the TiO 2 nanoparticles. The VTC experiment showed a rigid domain in the SBR/TiO 2 photodegraded nanocomposite due to cross-linking reactions.

Characterization of High-pressure-induced Murine Erythroleukemia Cell Apoptosis by Proton Spin–Lattice Relaxation Times of Intracellular Water

Abstract In high-pressure-induced apoptosis, the state of intracellular water was examined by measuring proton spin–lattice relaxation time of water. At the early stage of apoptosis, bound water increased owing to water efflux, whereas free water increased due to its influx at the late stage.

Water proton spin-lattice relaxation time during the apoptotic process in ultraviolet-irradiated murine erythroleukemia cells

Ultraviolet (UV) light-induced apoptosis has been extensively examined, but data on properties of intracellular water are insufficient. Thus, we examined the (1)H spin-lattice relaxation time (T1) of intracellular water during apoptosis in murine erythroleukemia (MEL) cells. Values of T1 decreased upon cell shrinkage, whereas increased upon cell swelling. Similar results were obtained in MEL cells exposed to osmotic stress. Furthermore, the increment of T1 values, ultrastructure loss on cell surface, and DNA fragmentation in UV-treated cells were significantly suppressed by pan-caspase inhibitor. Taken together, these results suggest that the T1 of intracellular water can be used to estimate the relative content of bound and free water during UV-induced apoptosis in MEL cells.

14N nuclear quadrupole resonance and proton spin–lattice relaxation study of phase transition in pyridazine perchlorate

The temperature dependence of the 14N nuclear quadrupole resonance frequencies in pyridazine perchlorate has been measured by double resonance. The results show that in the low temperature phase the pyridazinium ions are static, while in the high temperature phase the ions reorient around the normal to the plane of the ring between six equivalent orientations in agreement with the X-ray data. The 14N NQR data have been obtained for the protonated nitrogen position in the pyridazine ring for the first time. Temperature and frequency dependence of the proton spin–lattice relaxation time T 1 has been measured in both crystallographic phases. The results show the ionic mobility dominates T 1 in the low temperature phase. The activation energy for the ionic mobility is 240 meV. In the high temperature phase the pyridazine ring reorientation dominates the proton spin–lattice relaxation.

NMR and Viscosity Coefficients of CuCl<sub>2</sub> and CuSO<sub>4</sub> and Their Relationship to Water Structure

The viscosity coefficient (B) and nuclear magnetic resonance (NMR) coefficient (B') of CuCl2 and CuSO4 and their effects on the 17O NMR chemical shift (δ) of water were determined at low concentrations. From these B and B' values, individual ion's B and B' values were further calculated. These coefficients and the relationship between aqueous solution concentrations and δ(17OH2) represented the effect of ions on water structure and the median water cluster size in aqueous solutions. CuCl2 and CuSO4 were both ”structure-makers”. The effect of CuSO4 on water structure and median water cluster size was more powerful than that of CuCl2. Cl-broke more water clusters than SO(superscript 2- subscript 4). Cu(superscript 2+) had an obvious effect on shortening the proton spin-lattice relaxation time in water and broadening the line width of the NMR spectrum during the NMR relaxation process.

Characterization of pp/regenerated tire-rubber blends using proton spin-lattice relaxation time

Proton spin-lattice relaxation time ( T 1H) in the solid state was used to determine the molecular mobility of PP/regenerated tire-rubber blends (PP/RgR), employing low-field NMR. The blends were prepared with different quantities of regenerated rubber (5, 10, 15 and 20 wt%). The addition of 5 wt% maleic anhydride functionalized polypropylene (PP-g-MAH) was carried out to evaluate the processing behavior of the reclaimed material. Important differences were observed concerning the molecular mobility according to the content of regenerated rubber. A decrease in the relaxation time of the blends with an increase in PP-g-MAH content indicates that enhanced mobility of PP/regenerated tire-rubber blends was obtained and, thus, PP-g-MAH acts as a plasticizer and/or impact modified.

New copper(II) complexes of polyampholyte and polyelectrolyte polymers: Solid-state NMR, FTIR, XRPD and thermal analyses

Novel solid copper(II) complexes were obtained from the polyampholyte poly(EGDE–MAA–IM) and the polyelectrolyte poly(EGDE–MAA) polymers with copper salts at different concentration levels.The materials were characterized employing solid-state Nuclear Magnetic Resonance (NMR), Fourier Transform infrared (FTIR), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and thermogravimetry (TG).The reticulation induced by MAA in these materials against the poly(EGDE–IM) gel was analyzed by DSC. The coordination behavior of the carboxylic acid of MAA, compared to that provided by the imidazole ring, was studied through solid-state 13C NMR and changes in the FTIR spectra. The non-homogenous character of the doped and undoped materials was analyzed by the glass transition temperature (Tg), 2D 1H–13C WISE NMR and proton spin–lattice relaxation time in the rotating frame (TH1ρ). In particular, the TH1ρ and TH1 values in the complexes decreased with the Cu(II) concentration, showing the high sensitivity of both parameters to the presence of a paramagnetic ion. Finally, the thermogravimetric studies indicated that the presence of the imidazole ring was decisive for the stability of the Cu(II) complexes and for the undoped polymers.

Molecular motions of banana-shaped liquid crystals studied by NMR spectroscopy

Recent studies based on NMR spectroscopy put in evidence the occurrence of a slow motion regime in bent-shaped liquid crystals having the aromatic core formed by five phenyl rings linked by ester groups both in the isotropic and in the nematic phases. In this paper a brief overview of these NMR studies is presented and additional new relaxation data recorded on a banana-shaped mesogen are reported and discussed. In particular, proton spin-lattice relaxation times, T 1, were acquired at different Larmor frequencies from 8 MHz to 5 kHz by means of NMR relaxometry in a wide range of temperatures from the isotropic to the crystalline phases. These data confirm that NMR relaxation in bent-core liquid crystals is affected by much slower dynamics than that observed in common rod-like liquid crystals and that overall molecular reorientations are responsible of this slow motion regime. This finding is discussed in the frame of the results obtained by means of several NMR methods, such as 2H NMR T 2 analysis and 1H self-diffusion NMR measurements, on the same bent-core molecule.

Evaluation of enzymatic degradation based on the quantification of glucose in thermoplastic starch and its characterization by mechanical and morphological properties and NMR measurements

Biodegradable polymers represent a promising solution to the environmental problem of plastic waste disposal. Among the candidate polymers, starch, a low-cost natural polymer, can be processed as a thermoplastic. In this work, thermoplastic starch containing glycerol (20, 30 or 40 wt%) was prepared by extrusion. The mechanical properties of the blends were assessed by tensile stress at break, elongation at break and Young's modulus. Nuclear magnetic resonance (NMR), through proton spin-lattice relaxation ( T 1H) measurements, was used to understand the molecular dynamic of the samples. The morphology of the films was assessed by electron scanning microscopy (SEM). The susceptibility to enzymatic degradation was assessed in films incubated with α-amylase in acetate buffer. The loss of mass was determined after 1, 2, 3, 6, 9, 12 and 24 h of enzymatic digestion. The results obtained showed that all of the mechanical properties were improved by the addition of 20% glycerol, but decreased with higher concentrations of glycerol. The amount of free glucose released into the solution during digestion was quantified using a commercial glucose kit. Starch containing 40% glycerol degraded faster than the other blends, because it facilitated the efficiency of the gelatinization process and also the phase separation, as shown by the proton spin-lattice relaxation time. The amount of glucose released was directly proportional to the glycerol content of the samples. These results suggested a short lifetime for this blend, which is in agreement with the values of the T 1H relaxation parameter that suggests a decrease of the average molecular weight.

Discrimination between red blood cell and platelet components of blood clots by MR microscopy

Magnetic resonance imaging (MRI) of pulmonary emboli obtained ex vivo, verified by immunohistochemistry, showed that platelet layers display brighter signal intensity than areas containing predominantly red blood cells (RBC) in T1-weighted MRI. These results were surprising since platelets do not contain paramagnetic haemoglobin that would enhance magnetic relaxation. Our assumption was that the fibrin meshwork areas with entrapped RBC retain abundant extracellular space filled with serum, whereas platelets regroup into tight aggregates lacking serum, essentially mimicking solid tissue structure, rich with cellular proteins that enhance T1-relaxation. Our hypothesis was examined by MRI and NMR relaxometry of in vitro RBC suspensions and sedimented platelets, as well as by MRI of model clots and pulmonary emboli obtained ex vivo. Pure sedimented platelets exhibited shorter proton spin lattice relaxation times (T1 = 874 +/- 310 ms) than those of venous blood of a healthy male with 40% haematocrit (T1 = 1277 +/- 66 ms). T1-values of RBC samples containing high haematocrit (> or = 80%) resembled T1 of platelet samples. In T1-weighted spin-echo MRI echo time and repetition time (TE/TR = 10/120 ms) the ratio of signal intensities between a non-retracted whole blood clot (with a haematocrit of 35%) and a pure platelet clot was 3.0, and the ratio between a retracted whole blood clot with an estimated haematocrit of about 58% and a pure platelet clot was 2.6. We conclude that T1-weighted MRI can discriminate between platelet layers of thrombi and RBC-rich areas of thrombi that are not compacted to a haematocrit level of > or = 80%.

Molecular Dynamics in a New Solid Glucofuranose-Based Low-Molecular-Weight Organogelator as Studied by 1H NMR

The proton spin–lattice relaxation time T1 and the nuclear magnetic resonance second moment were used to study the molecular dynamics of 1,2-O-(1-ethylpropylidene)-α-D-glucofuranose, a new low-molecular-weight organogelator, in the temperature range of 85–308 K. The observed T1 minima were attributed to the motion of methyl groups. The experimental data were interpreted in terms of Haupt's theory assuming the tunneling-assisted relaxation process.

NMR Study of the Molecular Dynamics of D-Amphetamine Sulfate Salt Powder

The temperature dependence of the proton spin–lattice relaxation times was measured for the D-amphetamine sulfate salt in the temperature range from 80 to 466 K. Two minima of T 1 were observed and explained in terms of reorientation of the CH3 and NH3 groups. The T 1 minimum attributed to the motion of methyl groups was analyzed assuming two dynamically inequivalent types of these groups in the unit cell of the studied salt. The activation parameters for the C 3 reorientation of the methyl and ammonium groups were determined. A structural phase transition was evidenced at about 335 K in the polycrystalline sample of the D-amphetamine sulfate salt.

NMR and Conductivity Study of Gelatin-Based Polymer Electrolytes

Nuclear Magnetic Resonance spectroscopy (NMR) and complex impedance spectroscopy have been used to study gelatin-based polymer electrolytes plasticized with glycerol and containing lithium perchlorate. The studied samples were prepared with salt concentration of 7.9 wt% and 10.3 wt%. Ionic conductivity of about 10−5 S/cm was obtained at room temperature for both samples. Lithium (7Li) and proton (1H) lineshapes and spin-lattice relaxation times were measured as a function of temperature. The 7Li NMR relaxation results indicate that the ionic mobility in this system is comparable to those found in other plasticized polymer electrolytes.