Measurement of relaxation rates of N(H) and H(alpha) backbone protons in proteins with tailored initial conditions.

Several methods are presented for the selective determination of spin-lattice and spin-spin relaxation rates of backbone protons in labeled proteins. The relaxation rates of amide protons in (15)N labeled proteins can be measured by using two-way selective cross-polarization (SCP). The measurement of H(alpha) relaxation rates can be achieved by combining this method with homonuclear Hartmann-Hahn transfer using doubly selective irradiation. Various schemes for selective or nonselective inversion of the longitudinal proton magnetization lead to different initial recovery rates. The methods have been applied to lysine K6 in (15)N-labeled human ubiquitin and to leucine L5 in (15)N- and (13)C-labeled octapeptide YG*G*F*LRRI (GFL) in which the marked residues are (15)N- and (13)C-labeled.     

Nuclear relaxation rates for 3He adsorbed on zeolite

Transient nuclear magnetic resonance measurements of spin-lattice and spin-spin relaxation times have been carried out as a function of temperature and pressure on ³He adsorbed on two types of commercial zeolite. In addition, the number of atoms adsorbed on unit weights of zeolite was determined by spin counting. Mechanisms for spin-spin relaxation were provided by dipole interactions among helium spins and spin-lattice relaxation was probably due to atomic motion.     

Features of low-frequency spin dynamics in manganite LaMnO3 according to 139La NMR data

The spin-lattice and spin-spin relaxation times of ¹³⁹La are measured in manganite LaMnO₃. Analysis of the frequency dependence of the spin-lattice relaxation rate in the paramagnetic temperature range shows that this quantity is determined by magnetic fluctuations. The magnitude of the fluctuating field is estimated. It is shown that the correlation time for spin fluctuations varies with temperature in accordance with the Arrhenius law. The high value of the spin-spin relaxation rate in the paramagnetic region can be due to strong anisotropy of fluctuating magnetic fields at La nuclei.     

The nuclear spin interaction with paramagnetic impurities in antiferromagnets

The influence of paramagnetic impurities on the relaxation frequencies of the nuclear subsystem in antiferromagnets is investigated. In the framework of the spin operator diagram technique the nuclear spin-spin as well as spin-lattice relaxation rates are calculated. The correlation effects due to indirect spin-spin interaction via magnons both in nuclear and impurity subsystems are taken into account.     

有机磷化合物的NMR研究——Ⅱ0,0-二烷基膦酸酯的1H、13C和31PNMR谱

本文报道了21个0,0一二烷基膦酸酯类化合物的¹H、¹³C和³¹P NMR参数。研究和讨论了不等价的二烷基¹H、¹³C化学位移和磷碳偶合常数与立体化学的关系。测定了(CH₃CH₂O)₂P(O)CH(CH₂NO₂)(p-OCH₃C₆H₄)的¹³C自旋一晶格弛豫时间T₁,二乙基¹³C T₁间的差别,说明在类似化合物中,含有化学位移各向异性对弛豫的贡献。     

Effect of phase transitions of helium-3 in pores of wood carbonizate on the spin kinetics of 3He nuclei

The time of the nuclear magnetic relaxation of ³He gas in pores of Astronium carbonizate powder is studied as a function of gas pressure. Using the results of the measurements of the spin-echo amplitude, the dependences of the rates of spin-lattice and spin-spin relaxations on the number of helium atoms on the surface, in pores, and in the interparticle space of carbonizate powder have been determined. Analysis of the relaxation rates allows the identification of three possible basic phases of ³He in the system under consideration: solid film, gas phase, and liquid. Moreover, the character of spin kinetics in transitions between these phases has been determined.     

A 13C field-cycling NMR relaxometry investigation of proton tunnelling in the hydrogen bond: dynamic isotope effects, the influence of heteronuclear interactions and coupled relaxation

Concerted double proton transfer in the hydrogen bonds of a carboxylic acid dimer has been studied using 13C field-cycling NMR relaxometry. Heteronuclear 13C-1H dipolar interactions dominate the 13C spin-lattice relaxation which is significantly influenced by the polarisation state of the 1H Zeeman reservoir. The methodology of field-cycling experiments for such heteronuclear spin-coupled systems is studied experimentally and theoretically, including an investigation of various saturation-recovery and polarisation-recovery pulse sequence schemes. A theoretical model of the spin-lattice relaxation of this coupled system is presented which is corroborated by experiment. Spectral density components with frequencies omega(C), omega(C) + omega(H), and omega(C) - omega(H) are mapped out experimentally from the magnetic field dependence of the 13C and 1H spin-lattice relaxation and the proton transfer rate at low temperature is determined from their widths. Any dynamic isotope effect on the proton tunnelling in the hydrogen bond arising from 13C enrichment in the skeletal framework of the dimer is found to be smaller than experimental uncertainties (approximately 5%).     

Proton Detection of Heteronuclear Dipolar Couplings

A method is proposed for the calculation of heteronuclear dipolar coupling between two 1/2 nuclei, X and Y, by measuring the spin-lattice relaxation rates of the abundant Y nucleus and of the satellite peaks (¹H, ³¹P, ¹⁹F) due to the scalar coupling of Y with the less abundant X nucleus. The ¹H-¹³C dipolar interaction has been evaluated from the proton spin-lattice relaxation rates of tyrosine in water solution and the effective correlation times of the aromatic moiety have been calculated.     

Electron spin relaxation of copper(II) complexes in glassy solution between 10 and 120 K

The temperature dependence, between 10 and 120 K, of electron spin-lattice relaxation at X-band was analyzed for a series of eight pyrrolate-imine complexes and for ten other copper(II) complexes with varying ligands and geometry including copper-containing prion octarepeat domain and S100 type proteins. The geometry of the CuN4 coordination sphere for pyrrolate-imine complexes with R=H, methyl, n-butyl, diphenylmethyl, benzyl, 2-adamantyl, 1-adamantyl, and tert-butyl has been shown to range from planar to pseudo-tetrahedral. The fit to the recovery curves was better for a distribution of values of T1 than for a single time constant. Distributions of relaxation times may be characteristic of Cu(II) in glassy solution. Long-pulse saturation recovery and inversion recovery measurements were performed. The temperature dependence of spin-lattice relaxation rates was analyzed in terms of contributions from the direct process, the Raman process, and local modes. It was necessary to include more than one process to fit the experimental data. There was a small contribution from the direct process at low temperature. The Raman process was the dominant contribution to relaxation between about 20 and 60 K. Debye temperatures were between 80 and 120 K. For samples with similar Debye temperatures the coefficient of the Raman process tended to increase as gz increased, as expected if modulation of spin-orbit coupling is a major factor in relaxation rates. Above about 60 K local modes with energies in the range of 260-360 K (180-250 cm-1) dominated the relaxation. For molecules with similar geometry, relaxation rates were faster for more flexible molecules than for more rigid ones. Relaxation rates for the copper protein samples were similar to rates for small molecules with comparable coordination spheres. At each temperature studied the range of relaxation rates was less than an order of magnitude. The spread was smaller between 20 and 60 K where the Raman process dominates, than at higher temperatures where local modes dominate the relaxation. Spin echo dephasing time constants, Tm, were calculated from two-pulse spin echo decays. Near 10 K Tm was dominated by proton spins in the surroundings. As temperature was increased motion and spin-lattice relaxation made increasing contributions to Tm. Near 100 K spin-lattice relaxation dominated Tm.     

Temperature dependence of proton relaxation times in vitro

Accurate measurement of tissue relaxation characteristics is dependent on many factors, including field strength and temperature. The purpose of this study was to evaluate the relationship between sample temperature, viscosity and proton spin-lattice relaxation time (T1) and spin-spin relaxation time (T2). A review of two basic models of relaxation the simple molecular motion model and the fast exchange two state model is given with reference to their thermal dependencies. The temperature dependence for both T1 and T2 was studied on a 0.15 Tesla whole body magnetic resonance imager. Thirteen samples comprising both simple and complex materials were investigated by using a standard spin-echo (SE) technique and a modified Carr-Purcell-Meiboom-Gill (CPMG) multi-echo sequence. A simple linear relationship between T1 and temperature was observed for all samples over the range of 20 degrees C to 50 degrees C. There is an inverse relationship between viscosity and T1 and T2. A quantity called the temperature dependence coefficient (TDC) is introduced and defined as the percent rate of change of the proton relaxation time referenced to a specific temperature. The large TDC found for T1 values, e.g. 2.37%/degrees C for CuSO4 solutions and 3.59%/degrees C for light vegetable oils at 22 degrees C, indicates that a temperature correction should be made when comparing in-vivo and in-vitro T1 times. The T2 temperature dependence is relatively small.     

On the dynamic critical behaviour above the nematic-isotropic transition in 8CB

Summary We report here a study on the dynamic critical behaviour (DCB) at the nematic-isotropic (NI) transition in 8CB using the frequency and temperature dependences of proton spin-lattice relaxation rates. Both these dependences and the DCB are very similar in all the members of the cyanobiphenyl series measured so far. The DCB is also similar to that observed in MBBA although the frequency dependence of the total relaxation rates is slightly different. The authors of this paper have agreed to not receive the proofs for correction. Deceased.     

Proton spin-lattice relaxation in MBDBP

We have measured the proton spin-lattice relaxation rate R in 4,4′-methylenebis(2,6-di-t-butylphenol) (MBDBP) and MBDBP-OD (deuteriated hydroxyl proton) between 88 K and 380 K. The experimental results are compared with those from a previous study in the closely related but simpler molecule 4-methyl-2,6-di-t-butylphenol (MDBP). The present experiment is analysed in terms of relaxation resulting from intramolecular reorientation modulation of the proton spin-spin interaction. This intramolecular reorientation involves different combinations of superpositions of methyl, t-butyl, aromatic ring and hydroxyl group reorientation and a discussion is presented concerning the effects on the relaxation of superimposing these motions. The MBDBP-OD data is best fitted with the assumption that only methyl and aromatic ring reorientations occur. In MBDBP it is found that, in addition, an OH flip-flop motion is superimposed on the aromatic ring reorientation.     

NMR relaxation interference effects and internal dynamics in gamma-cyclodextrin

Multiple-magnetic field (9.4, 14.1 and 21.1 T) measurements of (13)C spin-lattice and spin-spin relaxation rates, the heteronuclear Overhauser enhancement and cross-correlated relaxation rates (CCRRs) in the methylene groups are reported for gamma-cyclodextrin in water/dimethylsulfoxide solution at 323 and 343K. The CCRRs are obtained from differences in the initial relaxation rates of the components of the CH(2) triplet in the (13)C spectra. The relaxation data are analyzed using the Lipari-Szabo approach and a novel modification of the two-site jump model. According to the latter model, inclusion of the dipolar (CH,CH(')) cross-correlated longitudinal and transverse relaxation is important for estimating the rate of the conformational jumps in the hydroxymethyl group. Using the dynamic information from the jump model, we have also used the differences in the initial relaxation rates for the triplet components to estimate the anisotropy of the chemical shielding tensor.     

Proton magnetic relaxation in bone marrow related to age and bone mineral density: low-resolution in vitro studies.

Detailed analysis of proton spin-spin and spin-lattice relaxation behaviors of the bone marrow in the presence of trabecular bone network was performed at low-resolution (B(0) = 0.496T) on rat vertebrae specimens deprived of spinal cord. Two groups of samples, from young and old healthy animals, were investigated before cellular necrosis had started. BMD measurements were carried out to quantify the expected age-related modifications of the trabecular bone network. 1H-MR measurements were also performed on the same samples, deprived of marrow and saturated with water, in order to control the validity of a possible interpretation of the marrow 1H-MR characteristics, in terms of marrow components, and to investigate the possible employment of these samples to study the trabecular bone network properties. We pointed out that: 1) a bimodal distribution of T(2i) and T(1i) values (distinguishing "fast" and "slow" relaxations) describes satisfactorily all the 1H-MR experimental decays; 2) age-related modifications of the trabecular bone network are marked by correlate variations of the BMD value and of the proton spin-spin relaxation rates in water saturated samples; 3) age-related modifications of marrow are underlined by variations of the average value of the "fast" T(2i) and of the "slow" T(1i) relaxation time distributions, which could be attributed to the marrow components different from the fat granules of the adipose cells.Our results suggest that studies in vitro on bone tissue, by 1H-MR techniques at low-resolution, may contribute to a better bone function characterization and, therefore, to a better clinical utilization of MRI techniques.     

Proton magnetic relaxation process during the polymerization of hemoglobin S

The proton spin-lattice and spin-spin magnetic relaxation times are investigated at 4 MHz in samples of hemoglobin A and S with intracellular concentrations, at 36 °C, and during spontaneous deoxygenation. Magnetic relaxation behaves differently in the solutions of hemoglobin A and S. The possible causes of this behavior are discussed: changes in molecular mobility, the variations of hemoglobin magnetism, and the appearance of microinhomogeneities in the solutions of hemoglobin S at the end of the polymerization process.     

1H NMR study of water relaxation and self-diffusion in human serum albumin aqueous solutions

Summary Water proton spin-lattice relaxation and self-diffusion in aqueous solutions of human serum albumin have been studied by¹H NMR as a function of the protein concentration. Spin-lattice relaxation data, which display a nonlinear behaviour with the protein concentration, could be fitted with a two-phase model taking into account the experimentally determined hydration (?bound?) water values. Despite a similar trend is registered for the water self-diffusion coefficient, such a model has been found unable to explain the related experimental data taken as a function of the biomolecule concentration. On the other hand, the solute-induced proton self-diffusion decrease could be satisfactorily interpreted by postulating an enhanced probability of hydrogen-bond formation occurring within the ?vicinal? water surrounding the biomolecules for several hydration shells. The consistency within the two models is discussed in connection with the magnetic interactions occurring within the solute-solvent systems.     

The influence of Fe,Cu, SiO<Subscript>2</Subscript>, TiO<Subscript>2</Subscript>, and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in aqueous solution on proton relaxation times

Measurements of proton nuclear spin-spin and spin-lattice relaxation times are applied for determining the concentration of solid-phase nanoparticles in nanofluids. This approach is tested for metal oxides SiO₂, TiO₂, Al₂O₃ and metal-carbon nanoparticles of 3d-metals Fe and Cu. It is shown that the sensitivity of the method for determining concentrations of 3d-metals is much higher than for oxides (by 2–4 orders of magnitude). It is revealed that measurement of the proton spin-spin relaxation time allows one to determine the concentration of Cu nanoparticles to 0.0001 mg/ml and that of Fe nanoparticles to 0.00001 mg/ml.     

Nuclear spin relaxation in liquids due to interaction with paramagnetic ions having anisotropic g tensors

Analytical expressions are derived for spin-lattice and spin-spin relaxation times (T_1M and T_2M) of a nucleus arising from magnetic interactions (dipolar and contact) with a paramagnetic ion which has an anisotropic g tensor. The relaxation rates depend on the orientation of the ion-nucleus vector in the principal-axis system of the g tensor. The deviations caused by this angular dependence with reference to the corresponding relaxation rates for an isotropic g tensor are numerically illustrated by considering a case typical for Co (II) complexes.     

Chain length dependence of high magnetic field effects on lifetimes of radical ion pairs linked by a methylene chain: interpretation by both spin—lattice and spin—spin relaxations

High magnetic field dependence of lifetimes of methylene-chain-linked radical ion pairs (RIPs) generated by photo-induced electron transfer from zinc(II) porphyrin to viologen has been confirmed in aqueous acetonitrile using a pulse magnet-laser flash photolysis apparatus. In the case of a short methylene chain it was first revealed that the dependence was definitely different from that for a long one, and was characterized by a reversal in the dependence. In addition to a long lifetime independent of the magnetic field, RIP in fields above 7T exhibited short lifetimes that depended on the field. These results were interpreted not only by spin-lattice (longitudinal) relaxation but also by spin-spin (transverse) relaxation in RIPs.     

Relaxation rates and diffusion in hybrides of Zr2Ni

Proton spin-spin and rotating frame spin-lattice relaxation in Zn₂Ni hydrides have been investigated. Activation energies for hydrogen motion were determined from Arrhenius plots of the relaxation times and found to be in general agreement with earlier NMR and PAC works. In common with previous studies of hydrides, asymmetric slopes about the relaxation minima are observed as well as adeviation from the motional narrowing behaviour at high temperatures.