Probing the analogy of the proton relaxation in biological tissues and porous media

Summary Experimental data are reported that show the analogy of longitudinal and transverse proton relaxation in heterogeneous systems as different as biological tissues and water-saturated rocks. Published data on the τ-dependence of the transverse-relaxation rate for biological tissues with magnetite grains, used as a contrast agent in MRI, are discussed in the light of our recent results on water-saturated porous media, and give for the liver another case of a behaviour parallel to that in rocks. There are enough similarities between NMR relaxation in tissues and in other porous media that, for work in either area, attention to the other is likely to be fruitful. Work supported by Italian CNR and MURST grants     

B 1 inhomogeneity effects on spin density andT 1 contrast in MRI

Summary An analysis of the effect ofB ₁ inhomogeneity on spin density andT ₁ contrasted images is here given. Distortions both in saturation recovery and inversion recovery sequences are found. The impact of these distortions onin vivo spectroscopy, where quantitative data are required, is also discussed. In general, these aspects are found to be reduced at shortertime parameters of the pulse sequences. Work partially supported by Progetto Finalizzato Tecnologie Biomediche of CNR and by Esacontrol, Genova.     

Signal-to-noise improvement in NMR imaging byB 1 homogeneity optimization

Summary The role of the RF magnetic-field homogeneity for the quality of the signal-to-noise ratio is here discussed. Its effects on the e.m.f. generated by the nuclear magnetization is analysed as well. We also report here some results of a modified coil which improves the RF field homogeneity and thus the signal to noise. Work partially supported by Progetto, Finalizzato Tecnologie Biomediche of CNR and by Esacontrol, Genoa.     

NMR and IR investigations of biologically active peptides in solution

Summary Nuclear-magnetic-resonance and infra-red spectroscopic features in solution have been investigated for the delineation of conformation and dynamics of the chemotactic peptide formyl-L-methionyl-L-leucyl-L-phenylalanine. The main conformation is unfolded and characterized by a certain degree of weak intermolecular hydrogen bounding. The steric hindrance of neighbouring side chains limits the motional averaging of the several possible conformers by excluding some of the rotamers. Dipolar and scalar connectivities, as detected by 2D NMR spectroscopy, point to a cis configuration of the H−N−C−H_α moiety in the case of leucine and trans in the cases of methionine and phenylalanine.

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Riassunto Per il chiarimento della conformazione e della dinamica molecolare del peptide chemotattico formil-L-metionil-L-leucil-L-fenilalanina sono stati studiati i parametri spettroscopici di risonanza magnetica nucleare ed infrarosso in soluzione. La conformazione principale è distesa e caratterizzata da un certo grado di deboli legami a idrogeno intermolecolari. L’impedimento sterico di catene laterali vicine limita la possibilità che i vari conformeri possibili siano mediati dai moti molecolari, escludendo alcuni rotameri. Le connettività dipolari e scalari, messe in evidenza dalla spettroscopia 2D NMR, suggeriscono una configurazione cis del residuo H−N−C−H_α nel caso della leucina e trans nei casi della metionina e della fenila lanina.

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Реэюме Исследуются ядерный магнитный резонанс и инфра-красные спектроскопические характеристики в растворе с целью описания конформации и динамики хемотактичного пептида формия-Л-метионил-Л-лейцил-Л-фенилаланина. Основная конформация явлется раэвернутой и характериэуется определенной степенью слабой межмолекулярной водородной связй. Стерическое припятствие для соседних боковых цепей ограничивает динамическое усреднение для некоторых конформаций, исключая некоторые ротамеры. Дипольнье и скалярные связности, зарегистрированные с помощью 2D ЯМР-спектроскопии, указывают на цис-конфигурацию H−N−C−H_α в случае лейцина и на транс-конфигурацию в случаях метионина и фенилаланина.

     

CaSO4·(1/2) H2O粉末中结晶水与吸附水1H的Goldman-Shen实验

本文利用Goldman-Shen脉冲序列测量了CaSO₄·(1/2) H₂O样品中结晶水与吸附水¹H的交叉弛豫时间为55.1ms。在实验中,发现剩余窄线的磁化矢量随时间的衰减有三个过程。本文对此现象作了一些分析讨论。     

Nuclear spin-lattice relaxation due to dissipative domain walls

The influence of the dissipative motion of domain walls in the nuclear spin-lattice relaxation rate is studied as a function of the external magnetic field and the temperature. Although only the specific case of the TMMC antiferromagnet below T_N is presented, the results are valid for all magnets described within the semiclassical approach by a double sine-Gordon equation for the spin degree of freedom.     

Selective measurements of heteronuclear overhauser effects: Structural applications

Summary A NMR method for determining internuclear distances between dipolarly coupled nuclei is here proposed. As a model system, salicylaldehyde has been investigated. A selective presaturation of C₁H and O ₂ ^′ H protons yields Overhauser effects on C₁, C ₁ ^′ and C ₂ ^′ resonances. From a combined use of these Overhauser effects and¹³C spin-lattice relaxation rates, internuclear distances between irradiated protons and carbon nuclei dipolarly coupled to them can be calculated. Furthermore, the obtained selective Overhauser effects can simultaneously evidentiate donor and acceptor moieties of hydrogen bonds, as in the present study in which the hydrogen bonding between the C₁ carbonyl and the O ₂ ^′ H proton was clearly delineated.

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Riassunto Si propone un metodo NMR per determinare distanze tra nuclei diversi nel caso che questi siano dipolarmente accoppiati. La salicilaldeide è stata studiata come composto modello. Per questa molecola l'eccitazione selettiva dei protoni C₁H e O ₂ ^′ H e O ₂ ^′ H genera effetti Overhauser sui picchi dei C₁, C ₁ ^′ e C ₂ ^′ . Un uso combinato di questi effetti Overhauser e delle velocità di rilassamento spin-lattice dei nuclei¹³C della salicilaldeide permette di calcolare le distanze internucleari tra i protoni irradiati ed i carboni ad essi dipolarmente accoppiati. Inoltre in questo modo è stata messa in evidenza la presenza di un legame a idrogeno tra il gruppo C₁=O e l'idrogeno O ₂ ^′ H.

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Резюме В работе предагается метоя ЯМР для определения расстояний между ядрами в случае, когда ядра связаны дипольным образом. Исследуется модельная система: салициловый альдегид. Селективное возбуждение протонов в C₂H и O ₂ ^′ H приводит к возникновению эффекта Оверхаузера на резонансах C₁, C ₁ ^′ и C ₂ ^′ . Объединяя эффекты Оверхаузера и скорости спих-решеточной релаксации¹³C, можно вычислитю расстояния между облученными протонами и ядрами углерода, связанными дипольным образом. Кроме того, в предложенном подходе подтверждено наличие водородной связи между группой C₁=0 и протоном O ₂ ^′ H.

     

Multicomponent water proton transverse relaxation and T2-discriminated water diffusion in myelinated and nonmyelinated nerve

The influence of compartmental boundaries on water proton transverse relaxation and diffusion measurements was investigated in three distinct excised nerves, namely, the non-myelinated olfactory nerve, the Schwann cell myelinated trigeminal nerve, and the oligodendrocyte myelinated optic nerve of the garfish. The transverse relaxation decay curves were multiexponential and their decomposition yielded three primary components with T₂ values 30–50, 150, and 500 ms, which were subsequently assigned to water protons in the myelin, axoplasm, and interaxonal compartments. The short T₂ component was absent in the non-myelinated olfactory nerve, but present in both myelinated nerves and thus provides supporting evidence for the use of quantitative T₂ measurements to measure the degree of myelination. The signal contribution of each T₂ component to the apparent diffusion coefficient measurements was varied by incrementing the spin-echo time with a preparatory CPMG train of radiofrequency pulses. The apparent diffusion coefficient and its anisotropy were shown to be independent of the spin-echo time over the range of 70 to 450 ms.     

Myocardial proton spin-lattice relaxation times in vitro: Effect of elapsed time after excision

An assumption made in using excised tissue for in vitro nuclear magnetic resonance (NMR) studies is that variables of interest, such as spin-lattice (T₁) relaxation times, remain stable for periods of time after excision sufficient to perform NMR spectroscopy. In this study, we evaluated the changes in T₁ of rat myocardium, measured at two NMR field strengths, at serial time intervals up to 72 hours postmortem. Left ventricular myocardium from six male Sprague-Dawley rats was excised and stored at room temperature in sealed NMR sample tubes. Spin-lattice relaxation times were determined with a modified inversion-recovery pulse sequence immediately postmortem and at intervals up to 72 hours post-excision; NMR studies were performed using 90 MHz and 360 MHz spectrometers. A gradual decrease in T₁ was noted with increasing time post-excision; T₁ was not significantly shorter than baseline until 72 hours postmortem at either field strength. The rate of change of T₁ was similar at the two field strengths. At any given time post-excision, T₁ was significantly higher (p < 0.001) at 360 MHz than at 90 MHz. We conclude that, with proper tissue handling and storage techniques, rat myocardial T₁ is stable postmortem sufficiently long to permit meaningful NMR studies of excised tissue.     

1H relaxation study in (NH4)2SbF5

¹H spin-lattice relaxation rate (T ₁ ⁻¹ ) has been measured using inversion recovery technique in polycrystalline (NH₄)₂SbF₅ system in the temperature range 140–400 K. From the plot of log (M ₀−M) againstτ, we have estimated two differentT ₁ corresponding to two inequivalent ammonium ions in the unit cell. Temperature-dependence ofT ₁ in each case exhibits features of double minima indicating the influence of different correlation times corresponding to different types of motion. Activation energies at different temperature regions have been estimated. Some features of dynamics of motion of the different groups of ions across the phase transitions have been discussed.     

Spin-wave contributions to nuclear magnetic relaxation in magnetic metals

The longitudinal and transverse nuclear magnetic relaxation rates 1/T ₁(T) and 1/T ₂(T) are calculated for three- and two-dimensional (3D and 2D) metallic ferro- and antiferromagnets (FM and AFM) with localized magnetic moments in the spin-wave temperature region. The contribution of the one-magnon decay processes is strongly enhanced in comparison with the standard T-linear Korringa term, especially for the FM case. For the 3D AFM case this contribution diverges logarithmically, the divergence being cut at the magnon gap ω due to magnetic anisotropy, and for the 2D AFM case as ω^-1. The electron-magnon scattering processes yield T ²ln(T/ω) and T ²/ω^1/2-terms in 1/T ₁ for the 3D AFM and 2D FM cases, respectively. The two-magnon (“Raman”) contributions are investigated and demonstrated to be large in the 2D FM case. Peculiarities of the isotropic 2D limit (where the correlation length is very large) are analyzed. Received 29 November 1999 and Received in final form 6 June 2000     

Solution dynamics of the natural bioactive molecule capsaicin: a relaxation study

Nuclear magnetic resonance spectroscopy is a straightforward technique for studying molecular dynamics that range in timescale from picosecond (motions faster than molecular reorientation) to those that occur in real-time. This approach is important to highlight the behavior of bioactive molecules in solution, and to acquire information about action mechanisms and potential pharmacological effects. Proton and carbon-13 spin–lattice relaxation experiments were performed to calculate the reorientational correlation time for protonated carbons. Capsaicin showed complex dynamical properties and the results revealed two regions with different dynamical properties: the aliphatic region with fast reorientation motions and the aromatic region with slow motions.     

Study of the ferroelectric–paraelectric phase transition of NaH3(SeO3)2 single crystals by H and Na NMR

The ¹H and ²³Na spin–lattice and spin–spin relaxation times of NaH₃(SeO₃)₂ single crystals grown using the slow-evaporation method were measured as functions of temperature and frequency in the ferroelectric and paraelectric phases. The changes in the symmetry of the (SeO₃)²⁻ dimers as a result of the ferroelectric–paraelectric phase transition are associated with large changes in the spin–lattice and spin–spin relaxation times, and in the number of resonance lines. The large changes in the relaxation times at 195 K indicate that the H and Na ions are significantly affected by this transition. The change in the number of resonance lines for the ¹H and ²³Na nuclei means that the orientations of the (SeO₃)²⁻ dimers and the environments of the Na ions change at T_C. Therefore, the orientations of the (SeO₃)²⁻ dimers and the environments of the Na ions play important roles in the phase transitions. In conclusion, the ferroelectric–paraelectric phase transition of NaH₃(SeO₃)₂ is accompanied by changes in hydrogen-bond structure and distortions of the (SeO₃)²⁻ and Na⁺ ion lattices, which form a slightly distorted octahedron.     

Water dynamics in ionic magnetic colloids studied by H nuclear magnetic resonance

In a previous nuclear magnetic resonance (NMR) study we observed that the NMR spectra of water in both surfacted and ionic ferrofluids are asymmetric and several orders of magnitude wider than the one of pure water. It has been proposed that this effect is produced by extremely strong magnetic field gradients in the intergrain volume and/or by surface interactions between the carrier liquid molecules and the grains surface. In the case of aqueous ionic ferrofluids the latter possibility should be interpreted as electric interactions between water (polar) molecules and the charges in the grain surface.

In this work we study a series of ionic and surfacted ferrofluids prepared at different magnetic grain concentrations and sizes, and with different surface charge densities. Our experiments clearly show that the sign and the density of the electric charge on the magnetic grains have no influence on NMR spectra. On the other hand, spectral widths increase with the magnetic grain concentration.     

Mechanical detection of nuclear spin relaxation in a micron-size crystal

A room temperature nuclear magnetic resonance force microscope (MRFM), fitted in a 1 tesla electromagnet, has been used to measure the nuclear spin relaxation of ¹H in a micron-size (70 ng) crystal of ammonium sulfate. NMR sequences, combining both pulsed and continuous wave radio-frequency fields, have allowed us to measure mechanically T₂ and T₁, the transverse and longitudinal spin relaxation times. Because two spin species with different T₁ values are measured in our 7 μm thick crystal, magnetic resonance imaging of their spatial distribution inside the sample section have been performed. To understand quantitatively the measured signal, we carefully study the influence of spin-lattice relaxation and non-adiabaticity of the continuous-wave sequence on the intensity and time dependence of the detected signal. Received 23 February 2000     

Anelastic relaxation and around the critical Sr content x = 0.02

Anelastic relaxation and ¹³⁹LaNQR relaxation rates in La_2–xSr_xCuO₄ for Sr content around 2 and 3 percent are discussed in terms of spin and lattice excitations and of the related ordering processes. It is argued how the phase diagram of La_2–xSr_xCuO₄ at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02) could be more complicate than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data. On the other hand, the ¹³⁹LaNQR spectra are compatible with a transition to an AF phase around K, in agreement with the phase diagram commonly accepted in literature. In this case the peaks in NQR and anelastic relaxation rates around 150 K and 80 K respectively in La_1.98Sr_0.02CuO₄, yield the first evidence of freezing process involving simultaneously lattice and spin excitations, possibly corresponding to motion of charged stripes. Received 18 May 2000 and Received in final form 11 July 2000     

NMR of water in biological systems

Summary A simple relationship has been thought to exist between the dynamics of water in heterogeneous (liquid-solid) systems and the NMR response. This relationship is usually expressed by the Bloembergen-Purcell-Pound (BPP) equations for relaxation and the phase model. However, a requirement for the use of the BPP theory is that motions take place in an isotropic, infinite and three-dimensional space. It is shown that the mere presence of solid surfaces causes the appearance of solidlike features in the NMR response of the liquid even if its dynamics is directly affected by the surfaces. Some of these ?topological? or ?indirect? surface effects are of the same kind as the low-dimensionality effects. Their order of magnitude is estimated for simple geometries and by treating the liquid motion in a hydrodynamic approximation. Comparison with the experiment is carried on in a companion paper. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Probing spatial correlations in the inhomogeneous glassy state of the cuprates by Cu NMR

We discuss the crossover of the form of the Cu Nuclear magnetic resonance (NMR) spin echo decay at the onset of Cu wipeout in lanthanum cuprates. Experimentally, the echo decay undergoes a crossover from Gaussian to exponential form below the temperature where the Cu NMR intensity drops. The wipeout and the change in behavior both arise because the nuclei experience spatially inhomogeneous spin fluctuations at low temperatures. We argue that regions where the spin fluctuations remain fast are localized on length scales of order 1-2 lattice spacings. The inhomogeneity is characterized by the local activation energy E_a(r); we estimate the functional form of E_a(r) for points where E_a>(r)∼0.     

2H NMR in nearly stoichiometric yttrium dideuteride

²H NMR spectra and spin-lattice relaxation rates, R₁ are measured as functions of temperature (4.2-310 K) for YD_1.99 and YD_1.99+0.04. In YD_1.99 the measured temperature dependence of R₁ is explained by the interaction of deuteron spins with conduction electrons and the value s^-1 K^-1 is obtained for the inverse Korringa product . Most of the spectral features in the “rigid” lattice regime are described by the dipolar interaction. No evidence of the deuterium self-diffusion was observed in the measured temperature range. The low-temperature spectra in YD_1.99+0.04 consisted of two components: a central line and a doublet characteristic for the quadrupole interaction. The central line corresponds to zero electric field gradients (EFG) at the sites of the deuterons which have a surrounding with cubic symmetry like in YD_1.99. The doublet indicates a non-zero EFG which can be explained in terms of the presence of short-range ordered domains of the hypothetical YD_2.25 stoichiometry. Other possible interpretations of the spectra are also discussed. In the vicinity of 250 K both spectra and R₁ reflect the onset of the rapid motion of deuterium atoms. The linear dependence of R₁ at low temperatures yields s^-1 K^-1. Received 8 September 1998     

Korringa-like nuclear spin–lattice relaxation in a 2DES at

Via a resistively detected NMR technique, the nuclear spin–lattice relaxation time T₁ of ⁷¹Ga has been measured in a GaAs/AlGaAs heterostructure containing two weakly coupled 2D electron systems (2DES) at low temperatures, each at Landau level filling . Incomplete electronic spin polarization, which has been reported previously for low density 2DESs at , should facilitate hyperfine-coupled nuclear spin relaxation owing to the presence of both electron spin states at the Fermi level. Composite fermion theory suggests a Korringa-law temperature dependence: T₁T=constant is expected for temperatures . Our measurements show that for temperatures in the range , T₁ rises less rapidly with falling temperature than this law predicts. This may suggest the existence of alternate nuclear spin relaxation mechanisms in this system. Also, our data allows for an estimate of the composite fermion mass.