Spin-lattice Relaxation Time T1 Research Articles

14N NQR Study of Mixed Complexes (NaNO2)1-x(ANO3)x : (A=K, Na)

14N nuclear quadrupole resonance of the system (NaNO2)1-x(ANO3) with A = K and Na in the x-range 0≤x<0.5 and the temperature range 77 K≤7<360 K has been studied. The 14N NQR frequency of NaNO2 and its line width do not change with x, the latter fact untrasting the results of other mixed systems such as Na1-xAgxNO2. This indicates that in (NaNO2)1-x(ANO3)x highly mobile lattice defects exist. The dependence on x of the rate of change in the spin-lattice relaxation time T1 near the transition temperature is discussed in terms of a correlated flipping motion of the NO- 2 ion groups.

23Na Nuclear Spin-Lattice Relaxation in Dehydrated Zeolite NaY

Abstract The spin-lattice relaxation time T1 of 23Na-NMR in dehydrated zeolite NaY has been measured from 26 to 300 K. The magnetization recovery curve is not single-exponential at all measured temperatures and T1 -1 increases in proportion to the square of temperature above 200 K. The result is analyzed with a theory of the Raman process based on covalency. The value of T1 is compared with that of NaX in which the concentration of Na is about 2 times larger than in NaY.

Solid-state 2H NMR study of methyl-d3-cobalamin

A solid-state 2H NMR study of methyl-d3-cobalamin has been performed as a function of temperature to provide information concerning the character and energetics of the motion performed by this unique bioorganometallic methyl group. Analysis of the 2H NMR line shape indicates that the methyl group undergoes rapid three-fold rotation, and that the Co-C-2H angle lies between 105.9 and 109.5 degrees. Determination of the spin-lattice relaxation times T1 shows that the relaxation is anisotropic, consistent with a "jumping" motion of the methyl group rather than rotational diffusion. This also provides the activation energy to methyl jumps as 8.3 +/- 1.3 kJ/mol. It is proposed that this energetic barrier may be a useful probe of changes in the electronic character of the Co-C bond that accompany the biological role of this molecule in such enzymes as methionine synthase.

Electron spin relaxation of copper(II) ions in diamagnetic crystals

The electron spin-lattice and spin-spin phase relaxation measurements of Cu2+ ions in various crystals are reviewed and discussed. Examples of the Debye temperature determination from a wide temperature range measurements of the spin-lattice relaxation time T1 are shown. An influence of the Jahn-Teller dynamics on T1 is presented. The phase relaxation described by the phase memory time TM is affected by temperature due to the spin packet width modulation by molecular motions. The TM is anisotropic in crystals and can be different for different hyperfine lines of an EPR spectrum.

CW and Pulsed EPR Study of Silver Nanoparticles in a SiO2 Matrix

Metallic silver nanoparticles were prepared by the sol-gel method in an SiO2 matrix. The process includes complexation of silicon alkoxides with metal salts, hydrolysis, polycondensation, formation of powder, and subsequent thermal treatment first in oxidizing and second in reducing atmospheres. The sizes of metallic particles were determined both by X-ray diffraction and transmission electron microscopy. These measurements revealed sizes of metallic particles between 1 and 20 nm, depending upon processing conditions. The magnetic properties were investigated using electron paramagnetic resonance spectroscopy in the temperature range between 4 and 300 K. The spin-lattice relaxation time T1 was measured by pulsed EPR. The temperature dependence of T1 is described by the relation 1/T1 ∝ Tn, where 0.4 < n < 1. This behavior is unusual and different from any well-known relaxation processes such as Raman, Direct or the Orbach-Aminov.

Solid-state &lt;sup&gt;2&lt;/sup&gt;H NMR study of methyl-&lt;i&gt;d&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt;-cobalamin

A solid-state 2 H NMR study of methyl-d3-cobalamin has been performed as a function of temperature to provide information concerning the character and energetics of the motion performed by this unique bioorganometallic methyl group. Analysis of the 2 H NMR line shape indicates that the methyl group undergoes rapid three-fold rotation, and that the Co-C- 2 H angle lies between 105.9 and 109.5°. Determination of the spin-lattice relaxation times T1 shows that the relaxation is anisotropic, consistent with a jumping motion of the methyl group rather than rotational diffusion. This also provides the activation energy to methyl jumps as 8.3 ± 1.3 kJ/mol. It is proposed that this energetic barrier may be a useful probe of changes in the electronic character of the Co-C bond that accompany the biological role of this molecule in such enzymes as methionine synthase.

Magnetic Resonance Either in Normal or Superconducting Species. Spin-Lattice Relaxation Time

Abstract The spin-lattice relaxation time T1 either in the superconducting and normal phases is investigated by the use of the Green’s function method. The lattice, in this case, means the conduction electrons and the interaction is mainly due to the Fermi contact term. Electrons and nuclei are treated on the same footing, namely both are in the second quantized form. The coherent terms are summarized in a general fashion at the beginning.

Field-cycling nuclear magnetic resonance relaxometry of molecular dynamics at biological interfaces in eye lenses: The Lévy walk mechanism

We have studied the water dynamics in whole rabbit lens and fragments using H1-field-cycling nuclear magnetic resonance relaxometry. We have measured the proton spin–lattice relaxation time T1 as a function of the Larmor frequency. The data can be interpreted well using the reorientation mediated by translational displacement model in combination with the mechanism of bulk-mediated surface diffusion, where individual water molecules perform Lévy walks with a Cauchy diffusion propagator. This gives evidence of anomalous water surface diffusion on proteins in the rabbit lens. We assume that the lens protein surface topology can be modeled by a polyhedral structure of randomly oriented faces with individual correlation lengths s0. For the whole lens we obtained the most frequent s0 value of 2.5 nm whereas for fragments from the rabbit cortex and the nucleus we obtained values of 3 and 0.3 nm, respectively. The correlation length values obtained for the lens can be attributed to the short-range order of the lens proteins necessary for maintaining lens transparency.

NMR Spin lattice relaxation study of Cs1−x(NH4)XH2PO4

Spin-lattice relaxation time T1 for 31P was measured as a function of temperature at 28.2 MHz in a powder sample of Cs1-x (NH4) x H2PO4 (CADP) crystallized from a solution with a molar ratio x = 0.2. This crystal has the same structure as CsH2PO4 (CDP), which exhibits a low-temperature pseudo-one-dimensional ferroelectric phase transition at 159 K and a superionic transition at 504 K on heating. The measured temperature dependence is explained in terms of hydrogen bond dynamics.

Thermal depinning and motions of the flux lines inYBa 2 Cu 4 O 8 from NMR experiments

The spin-lattice relaxation time T1, the spin echo dephasing time T2 and the NMR linewidth δv are used to study the spontaneous fluctuations under thermal excitation of the flux lines (FL) in YBa2Cu4O8. It is shown how the relaxation rate T1-1 is sensitive to the fluctuations of the transverse components of the local field at a frequency around ω = γH0, while T2-1 and δv probe the longitudinal components at frequencies smaller by a factor 103-105. Thus, from a combination of T1 T2 andδv measurements one derives microscopic insights on the degree of correlation in the motion of 2D pancakes belonging to adjacent superconducting planes, on the barriers for the pseudo-diffusion of the FL’s and on their field and temperature dependence. 2D NMR spectroscopy can also be used to evidence the diffusion of the FL’s and a comparison between YBa2Cu3O7 (YBCO123) and YBa2Cu48 (YBCO124) is briefly discussed. Finally for temperatures below Tirr(H the evolution of the amplitude of the63Cu NQR echo after sudden application and/or rotation of a magnetic field is used to investigate the FL flow in the critical state.

Spin-lattice relaxation behaviour of water in cellulose materials in relation to the tablet forming ability of microcrystalline cellulose particles

Medical tablet forming ability of microcrystalline cellulose (MCC) was investigated in relation to the mobility of water molecules in MCC particles. For this purpose, the spin-lattice relaxation time T1 of water in the system was measured by 1H-NMR. Over a wide range of water contents (0.02 ≤ H2O/cellulose (g/g) ≤ 1.79), two different T1 (T1,l and T1,s) values were observed for water in each MCC sample. Below the equilibrium water content, water having these two different T1 values exchange with each other in an MCC particle reaching an equilibrium state within a given time scale (equilibrium constant K). The T1,l, T1,s and K values for water in MCC, estimated at the equilibrium water content, showed fairly good correlations with the hardness of the tablets made by the MCC samples. Sample with a shorter T1, or larger K tended to have a stronger tablet forming ability. In the spin-spin relaxation time T2 measurements for protons in an MCC/D2O system, two T2 components originating from the glassy cellulose solid (T2,G) and the swelling region (T2,l) were observed. It was found that the mole fraction xL of protons with T2,L in the system exhibits a clear linear correlation with K. From these results, a structural model for the distribution of water in MCC particles was propoed by taking the surface of each microfibril and the disordered region within the microfibril into consideration

Electron spin-lattice relaxation in oxide superconductors and fullerides

Using the original technique of measuring very short spin-lattice relaxation times T1, the electron-spin relaxation has been investigated in a number of HTSC materials and related phases. The relaxation of Gd3+ ions in GdBa2Cu3O6+x is shown to be affected by both quasiparticle and antiferromagnetic fluctuations, the latter being increased at lower oxigen content. The pseudo-spin gap of about 200 K is found for both contributions. For Cu2+ EPR in YBaCuO, the T1 values reveal several types of paramagnetic centers including the “green phase” Y2BaCuO5. In the fulleride RbC60, the measuring of T1 and T2 yielded additional support for 1D conductivity and allowed to monitor the metal-insulator phase.

Direct Measurement of the Conduction Electron Spin-Lattice Relaxation Time T1 in Gold.

A time-resolved technique for the direct measurement of the conduction electron spin-lattice relaxation time ${T}_{1}$ is introduced. The method is based on the detection of the polar Kerr rotation induced by optically switched picosecond risetime transient magnetic fields. Demonstrated on polycrystalline gold films, the first direct measurement of ${T}_{1}$ in a metal is presented. The measured value ${T}_{1}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}45\ifmmode\pm\else\textpm\fi{}5\mathrm{ps}$ suggests that Matthiessen's rule is not obeyed for conduction electron spin scattering. The technique can be applied at room temperature to a variety of conduction electron systems with spin relaxation times as short as a few ps.

Spatial structure of β-cyclodextrin clathrates with 1,4-benzodiazepine derivatives

Understanding the mechanisms of mutual recognition and complementary binding of molecules in guest-host complexes is based on analysis of their spatial structure. As guest-host complexes, we have synthesized inclusion compounds of 1,4-benzodiazepine anxiolytic agents gidazepam and cinazepam with β-cyclodextrin, in which these anxiolytic agents manifest increased biological accessibility. The spatial structure of the complexes was determined from the two-dimensional NOESY spectra and analysis of the fragmentary mobility of the guest and host molecules, characterized by spin-lattice relaxation times T1 of the13C nuclei. An analysis of d-contacts showed that the 5-phenyl ring is completely enclosed in the inner hydrophobic cavity of β-CD [(C2′ H-C4′ H)-CIIH(CIVH), CVH (CIIIH, CVIH2), CVIOH]. For the 1:1 complex, intense d-contracts of C8H with CVIOH indicate that C8H is located in the vicinity of both wide and narrow bases of the bracelet. This is only possible for the 2:2 complex, in which both β-CD molecules approach each other by their wide and narrow bases. A comparison between the schemes of d-contacts for the 2:2 and 2:1 associates proves that the β-CD molecules have the same spatial orientation in the dimer. The difference is in the fact that the hydrazinocarbonyl fragment of gidazepam and the hemisuccinate fragment of cinazepam penetrate into an empty molecule of the 2:1 β-CD complex (NH2-CIH contact). The intensities of the cross peaks were measured, due to which the interatomic distances between the guest and host molecules were calculated and the spatial structure of the clathrates was established. The benzodiazepine derivatives are embedded differently into the clathrate molecule, as shown by the value of the angle between the symmetry axis of β-CD and the axis through the centers of the aromatic rings: 0° for gidazepam and 60° for cinazepam. This is a consequence of the fact that the substituents forming hydrogen bonds with hydroxyl groups at the wide base of the β-CD bracelet lie in different positions: the hydrazinocarbonylmethyl fragment of gidazepam lies at N1, and the hemisuccinate fragment of cinazepam is at C3.

Proton nmr study of molecular dynamics and phase transitions in [NH2(CH3)2]3Sb2Cl9

Abstract Tris(dimethy1ammonium) nonachlorodiantimonate (III), [NH2(CH3)2]3Sb2Cl9 (DMACA) crystallizes at room temperature in the monoclinic system, space group P21/a. From dielectric and pyroelectric studies it was found that Dh4ACA undergoes a ferroelectric phase transition at 242 K, and below Tc a polar symmetry m is expected. Dielectric dispersion studies in the microwave frequency region revealed that DMACA is a simple example of a ferroelectric crystal with an “order-disorder” mechanism for the phase transition of second order type, where polarization is due to the 180° reorientation of the dimethylammonium cations. In order to examine the dynamical properties of the dimethylammonium cation in this material we measured the spin-lattice relaxation times T1 and T1ρ of protons over a wide range of temperatures. The relation between NMR correlation times, obtained from an analysis of measured NMR relaxation times T 1ρ and the microscopic relaxation time obtained from dielectric dispersion studies, is discussed.

A Pulsed 35Cl NQR Study on the Molecular Motions and Phase Transition of 4-Chlorobenzyl Alcohol

The spin-lattice and spin-spin relaxation times T1 and T2 of 35Cl NQR were measured for the high (I) and low (II) temperature phases of 4-chlorobenzyl alcohol in the range 50 &lt; T/K &lt; 338 (transition and melting points: 236 and 343.5 K, respectively). In phase II the T1 behavior in the range 50 &lt; T/K &lt; 90 can be explained by lattice vibrations and that in the range 90 &lt; T/K&lt; 190by reorientation with an activation energy of ca. 3.8 kJ/mol. In phase I, the T1 behavior at T &gt; 260 K is explainable by another reorientation with Ea ≈ 4.7 kJ/mol. The T1, vs. T curves revealed that in both phases the crystal dynamics is anomalous in the vicinity of the transition temperature. Lattice defects accumulated in phases I and II by the phase transition were found to be responsible for the extremely short inverse line width parameters (T2*).

23Na Spin-Lattice Relaxation Measurements in Dehydrated Na-X Zeolite

Abstract The spin-lattice relaxation time T1 of 23Na-NMR in a dehydrated Na-X zeolite has been measured from 20 to 300 K. The recovery curve is not single-exponential at all measured temperatures and T1 -1 increases with the square of temperature around room temperature. The results are analyzed by assuming non-equivalent sites and by applying the theory of the Raman process based on covalency.

NQR and NMR Studies of Phase Transitions in R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4)

Abstract 39K, 87, 85Rb, 133Cs, 205T1, and 1, 2H NMR spin-lattice relaxation times T1 and 14N NQR spin-lattice relaxation times T1Q were determined for R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4). T1 of 39K and 87Rb showed very short values in the incommensurate phase as compared with those in the other phases. When the commensurate-incommensurate phase transition point is approached from below, 14N T1Q of the R = K, Rb, Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond the corresponding transition point. The difference of the T1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.

Motion of Water Molecules and Hydrogen Bonds in Zinc Hexachlorostannate (IV) Hexahydrate as Studied by 1H NMR and 35Cl NQR

Abstract The 1H NMR spin-lattice relaxation time T1, 35Cl NQR frequency νQ, and 35Cl NQR spin-lattice relaxation time T1Q of [Zn(H2O)6] [SnCl6] (zinc hexachlorostannate(IV) hexahydrate) have been measured at temperatures between 77 and 350 K. The NQR spin echo signal with νQ = 15.689 MHz at 77 K showed a positive temperature coefficient attributable to O-H-Cl type H-bonds in the crystal. νQ at 77 K is strongly correlated with the electronegativity χM of the metal M in the series of stannates [M(H2O)6] [SnCl6] (M = Mg, Ca, Mn, Co, Ni, Zn). A T1 minimum observed for the Zn salt is ascribed to 180° flips of water molecules with an activation energy of 20 kJ mol-1. The motion is influenced by repulsive forces among the water molecules within a cation rather than by attractive forces between the H-bonded H and CI atoms. T1Q proved to be mainly governed by lattice vibrations, weakly modulated by the fluctuating electric field gradient caused by the 180° flip motions.

Nuclear magnetic relaxation in NdCu2

The nuclear spin-lattice relaxation time T1 of NdCu2 and YCu2 was measured using the Cu NQR technique. The strength of the inter-site interaction between 4f moments and the on-site interaction between 4f and conduction electrons in NdCu2 is discussed on the basis of the temperature dependence of the 4f electron correlation rate 1/τf deduced from T1.