Effect of flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip

The detection of samples in a microfluidic nuclear magnetic resonance chip is generally performed under flow condition. To study the effect of sample flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip, theoretical calculations were performed on three microfluidic samples (including deionized water, absolute ethanol, and copper sulfate pentahydrate) for flow velocities in the range 1.7–25?mm/s. A microfluidic nuclear magnetic resonance device with a low cost microfluidic solenoid coil was fabricated to verify the theoretical calculations by experiments. The results show that the apparent transverse relaxation time of the sample is a monoexponential decay with respect to flow velocity. In addition, it was found that the experimental values and the theoretical values of the apparent transverse relaxation time are identical when the samples are prepolarized completely; but for the samples that are not prepolarized completely, all the experimental values are smaller than the theoretical values and their difference increases with the flow velocity of the sample. After further study, it was discovered that the relative error between the experimental values and the theoretical values is a monoexponential decay to the level of the sample to be prepolarized. This discovery is very useful, because it can be used to modify the theoretical calculation model of the apparent transverse relaxation time for the samples that are prepolarized incompletely, as well as improve the application of microfluidics on nuclear magnetic resonance.     

Proton magnetic relaxation in (TMA)2HgBr4 and (TMA)2HgI4

Internal motions of the protonic groups have been studied in polycrystalline [(CH₃)₄N]₂HgBr₄ and [(CH₃)₄N]₂HgI₄ from the temperature dependence of proton spin relaxation time (T ₁) and the data analysed according to the spin lattice relaxation model due to Albert and coworkers. The temperature dependence ofT ₁ in the above compounds is compared with that in (TMA)₂HgCl₄ and (TMA)₂ZnCl₄.     

Effect of Nonhomogeneous Broadening on the Free Induction Signal for a Double-Level Spin System

An investigation of the evolution of the free induction signal as a function of /₁ is made, where is the nonhomogeneous width of the magnetic resonance line of a double-level spin system and ₁ = B ₁, where is the gyromagnetic ratio and B ₁ is the amplitude of a radio-frequency field. It is shown that two stages can be distinguished in the evolution of the free induction signal on excitation of the spin system by a large-area pulse (₁ t ₁ >> 1) of length t ₁. In the first stage (t t ₁), reversible relaxation leads to an oscillatory and exponential dip. With a fixed ₁, an increase in practically does not change the frequency of oscillations and the signal amplitude decreases. In the second stage (t > t ₁), there is only an exponential decay of the signal at a rate equal to . It is demonstrated that, with nonresonant excitation, the coherent properties of the free induction signal manifest themselves in the formation of a single-pulse echo. The theoretical results are in good agreement with the experimental data obtained in nuclear magnetic resonance for protons in glycerin. The conclusion is drawn that the theorem of coherent transients in double-level systems with a finite nonhomogeneous width of the line is valid.     

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     

反演与拟合相结合处理核磁共振弛豫数据的方法

讨论非负最小二乘（NNLS）法和非线性拟合在分析处理核磁共振（NMR）弛豫数据中的应用.同时将二者结合，提出用NNLS的反演结果来设定非线性拟合初值的方法，并用计算机模拟和实验证明了该方法在分析处理NMR弛豫数据中的有效性. 关键词： 非负最小二乘法 非线性拟合 核磁共振 弛豫时间     

Aspects of structural order in 209Bi-containing particles for potential MRI contrast agents based on quadrupole enhanced relaxation

ABSTRACT

Quadrupole relaxation enhancement (QRE) has been suggested as the key mechanism for a novel class of field-selective, potentially responsive magnetic resonance imaging contrast agents. In previous publications, QRE has been confirmed for solid compounds containing ²⁰⁹Bi as the quadrupolar nucleus (QN). For QRE to be effective in aqueous dispersions, several conditions must be met, i.e. high transition probability of the QN at the ¹H Larmor frequency, water exchange with the bulk and comparatively slow motion of the Bi-carrying particles. In this paper, the potential influence of structural order within the compounds (‘crystallinity’) on QRE was studied by nuclear quadrupole resonance (NQR) spectroscopy in one crystalline and two amorphous preparations of Triphenylbismuth (BiPh₃). The amorphous preparations comprised (1) a shock-frozen melt and (2) a granulate of polystyrene which contained homogeneously distributed BiPh₃ after common dissolution in THF and subsequent evaporation of the solvent. In contrast to the crystalline powder which exhibits strong, narrow NQR peaks the amorphous preparations did not reveal any NQR signals above the noise floor. From these findings, we conclude that the amorphous state leads to a significant spectral peak broadening and that for efficient QRE in potential contrast agents structures with a high degree of order (near crystalline) are required.     

核磁共振弛豫时间测量数据处理方法的讨论

分析和讨论了在超小型核磁共振成像仪测量弛豫时间T1的数据处理方法中存在的问题,并提出了测量方法和数据拟合的改进方案.     

Molecular dynamics and interactions of human ceruloplasmin: A spin labelling study

Summary Ceruloplasmin, a paramagnetic copper-containing protein, has been spin labelled with different nitroxide spin labels in order to study its molecular dynamics and to gain further information about its interaction with other biosystems. Spin labelling with a maleimide derivative resulted in an electron spin resonance spectrum which was a superposition of two different absorptions due to paramagnetic species in different microenvironments. The first one, a three-line isotropic spectrum, is due to a fast-moving spin label (with a rotational correlation time τ_c≃10^-9s); the second one is an anisotropic, asymmetrical signal arising from an immobilized spin in a slow-motion domain (τ_c=10^-7). The assumption of a spherical shape for the molecule provided, through the Stokes-Einstein relation, an estimate of the molecular-radius value consistent with smallangle neutron scattering measurements. The interaction with other biosystems, as deduced from the protein molecule dynamics, is discussed.

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Riassunto La ceruloplasmina, una proteina umana contenente ioni Cu⁺⁺ paramagnetici, è stata marcata con differenti spin labels per studiarne la dinamica molecolare e la sua interazione con altri biosistemi. Il marcaggio mediante spin labels di tipo maleimidico ha portato ad uno spettro di risonanza elettronica di spin composto da due differenti gruppi di righe dovuti a specie paramagnetiche in differenti microambienti. Il primo segnale è costituito da un tripletto isotropico dovuto ad uno spin label in rapida rotazione (τ_c≃10^-9s), mentre il secondo è alquanto asimmetrico (anisotropico) e deriva da uno spin label ruotante in un dominio temporale piuttosto lento (τ_c=10^-7). L'assunzione di una forma sferica per la proteina in soluzione ha portato, attraverso la relazione di Stokes-Einstein, ad una determinazione del raggio molecolare in buon accordo con il risultato di misure di diffrazione a basso angolo di neutroni. Si discute inoltre l'interazione con altri biosistemi come desunta dalla dinamica molecolare della proteina.

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Резюме Церулоплазмин, человеческий белок, содержащий парамагнитные ионы меди Cu⁺⁺, помечается с помощью различных спиновых меток для исследования молекулярной динамики и взаимодействий с другими биосистемами. Спиновая метка в случае производной меламида приводит к спектру электронного спинового резонанса, который представляет суперпозицию двух различных групп линий, обусловленных парамагнитными разновидностями при различных микро-окружениях. Первый спектр, изотропный триплет линий, обусловлен быстро движущейся спиновой меткой (с временем ротационной корреляции (τ_c≃10^-9 c); второй спектр представляет анизотропный асимметричный сигнал, возникающий от медленно движущейся спиновой метки (τ_c=10^-7 c). Предположение сферической формы бекла в растворе, которое следует из соотношения Стокса-Эйнштейна, позволяет оценить радиус молекулы, величина которого хорошо согласуется с измерениями малоуг лового рассеяния нейтронов. Обсуждается взаимодействие с другими биосистемами на основе анализа динамики молекул белка.

     

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.     

Expanding the frequency range of the solid-state T1rho experiment for heteronuclear dipolar relaxation

Solid-state spin–lattice relaxation in the rotating frame permits the investigation of dynamic processes with correlation times in the range of microseconds. The relaxation process in organic solids is driven by the fluctuation of the local magnetic field due to the dipole–dipole interaction of the probe nuclei (¹³C,¹⁵N) with ¹H in close proximity. However, its effect is often hidden by a competing relaxation process due to the contact between the rotating frame ¹³C/¹⁵N Zeeman and ¹H dipolar reservoirs. In most cases the latter process becomes superior for the commonly applied low and moderate spin-lock fields and practically does not provide information about the molecular dynamics. To suppress this undesired process and to expand the dynamic range of T_{1 ρ} experiments, we present two approaches. The first one uses a resonance offset of the frequency of the spin-lock irradiation, which leads to a significant enhancement of the effective spin-lock frequency without the application of destructive high transmitter powers. We derive the theory and demonstrate the applicability of the method on various model compounds. The second approach utilizes heteronuclear ¹H decoupling during the ¹³C/¹⁵N spin-lock irradiation which disrupts the contact between the ¹³C/¹⁵N Zeeman and ¹H dipolar reservoirs. We demonstrate the method and discuss the results qualitatively.     

Chain dynamics in a chiral C phase by deuteron spin relaxation study

Molecular reorientations and internal conformational transitions of an aligned chiral liquid crystal (LC) 10B1M7 are studied by means of deuterium spin-lattice relaxation in its smectic A (SmA) and smectic C* (SmC*) phase. The motional model which is applicable to uniaxial phases of many LCs is found to be adequate even when the phase is a tilted SmC* phase. The deuterium NMR spectrum in this phase cannot discern rotations of the molecular director about the pitch axis. The basic assumption is that the phase biaxiality is practically unobservable. However, the relaxation rates can be accounted for by the tilt angle between the molecular director and the layer normal in the SmC* phase. The tumbling motion appears to show a higher activation energy upon entering from the uniaxial SmA into the SmC* phase.     

Measurement of Hartmann-Hahn cross-polarization dynamics with quenching of proton T1ρ relaxation dependence

A simple modification of the standard cross-polarization method designed for quenching the proton T_1ρ dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T_1ρ(¹H) effect, can be observed in dipolar-coupled spin systems.     

Vibrational relaxation of a molecule in strong interaction with a reservoir: Nonmonotonic temperature dependence

This theoretical study of the vibrational relaxation of a molecule in interaction with a reservoir uncovers a noteworthy temperature (T) dependence of the time evolution of the relaxation. Its rate increases with T in one interval but decreases in another. The feature arises not for a weak molecule-reservoir interaction but only for coupling strong enough to require polaronic dressing transformations. Our treatment, based on a recent generalization of the well-known Montroll–Shuler equation for relaxation and an explicit calculation of bath correlations from the microscopically specified Hamiltonian, could provide an alternative explanation of an “inverted” T-dependence of relaxation in an experimental report by Fayer and collaborators on W(CO)₆ dissolved in CHCl₃.     

Uniform-Penalty Inversion of Multiexponential Decay Data: II. Data Spacing, T2 Data, Systematic Data Errors, and Diagnostics

The basic method of UPEN (uniform penalty inversion of multiexponential decay data) is given in an earlier publication (Borgia et al., J. Magn. Reson. 132, 65–77 (1998)), which also discusses the effects of noise, constraints, and smoothing on the resolution or apparent resolution of features of a computed distribution of relaxation times. UPEN applies negative feedback to a regularization penalty, allowing stronger smoothing for a broad feature than for a sharp line. This avoids unnecessarily broadening the sharp line and/or breaking the wide peak or tail into several peaks that the relaxation data do not demand to be separate. The experimental and artificial data presented earlier were T₁ data, and all had fixed data spacings, uniform in log-time. However, for T₂ data, usually spaced uniformly in linear time, or for data spaced in any manner, we have found that the data spacing does not enter explicitly into the computation. The present work shows the extension of UPEN to T₂ data, including the averaging of data in windows and the use of the corresponding weighting factors in the computation. Measures are implemented to control portions of computed distributions extending beyond the data range. The input smoothing parameters in UPEN are normally fixed, rather than data dependent. A major problem arises, especially at high signal-to-noise ratios, when UPEN is applied to data sets with systematic errors due to instrumental nonidealities or adjustment problems. For instance, a relaxation curve for a wide line can be narrowed by an artificial downward bending of the relaxation curve. Diagnostic parameters are generated to help identify data problems, and the diagnostics are applied in several examples, with particular attention to the meaningful resolution of two closely spaced peaks in a distribution of relaxation times. Where feasible, processing with UPEN in nearly real time should help identify data problems while further instrument adjustments can still be made. The need for the nonnegative constraint is greatly reduced in UPEN, and preliminary processing without this constraint helps identify data sets for which application of the nonnegative constraint is too expensive in terms of error of fit for the data set to represent sums of decaying positive exponentials plus random noise.     

Nuclear Spin-Lattice Relaxation of 82BrFe

The field dependence of the nuclear spin-lattice relaxation (SLR) of cold implanted ⁸²Br (T ≤ 25 mK) in α-Fe single crystals was investigated with nuclear magnetic resonance of oriented nuclei (NMR/ON) at low temperatures as experimental technique. The SLR at the lattice sites with the hyperfine fields found by earlier NMR/ON experiments was measured as a function of the applied external magnetic field B _ext parallel to the three principle axes [100], [110] and [111] of the iron single crystal. The data were evaluated with the full relaxation formalism in the single impurity limit and for comparison also with the often employed model of a single exponential function with an effective relaxation time T ₁′. With a phenomenological model the high field values of the relaxation rates r _{∞, [100]′} = 6.6(2) · 10⁻¹⁵ T²sK⁻¹, r _{∞, [110]} = 5.4(2) · 10⁻¹⁵ T²sK⁻¹ and r _{∞, [111]} = 5.2(1) · 10⁻¹⁵ T²sK⁻¹ were obtained.     

14N Pulsed nuclear quadrupole resonance. 4. Two-pulse sequences for the determination of T1 and T2 relaxation times

A general theory, based on density matrix calculations, has been developed for the special case of a two-pulse sequence applied to spin 1 (¹⁴N) nuclear quadrupole resonance (NQR) of a powder sample. It is shown that the homolog of the NMR inversion-recovery experiment leads easily to the spin-lattice relaxation time T ₁ (associated with the diagonal elements of the density matrix) provided that an appropriate phase cycling is used. Conversely, in spite of two-step phase cycling schemes adapted to spin-spin relaxation measurements, the homolog of the NMR Hahn spin-echo sequence may pose some problems if the results are displayed in the magnitude mode. First, at short decay times, the echo may be corrupted by unwanted signals. Secondly, in that case, the amplitude of the resulting signal can evolve unexpectedly and differently as a function of the phase of the second pulse. Thirdly, at long decay times, the echo maximum occurs earlier than expected. All these problems in principle disappear with a complete four-step phase cycling scheme and the echo decay curve yields reliably the spin-spin relaxation time T ₂ (associated with off-diagonal elements). This theory allowed the exploitation of many test experiments performed at different frequencies on hexamethylenetetramine (HMT) and sodium nitrite.     

核磁共振二维谱反演技术综述

二维谱的出现是核磁共振（NMR）检测技术的一次飞跃,从二维谱中可以快速、精确地对不同组分进行区分,因而在测录井和常规实验中被广泛采用. 为了给相关研究提供借鉴和参考,推动二维反演技术的发展,该文对近年来国内外在核磁共振二维谱反演技术领域的研究进展进行了综述. 从实验采集数据中反演出二维谱的过程,比一维反演需要解决更多、更复杂的问题. 通过研究罚函数正则化和子空间正则化两大类方法,分析了不同二维反演算法的优点和不足. 根据对近年来国内外相关文献的深入分析可知,虽说目前已有的二维反演算法都存在一定的局限性,但其仍然具有很大的发展空间.     

Vibrational relaxation study in carbonyl containing molecule: role of hydrodynamic and dispersion forces

The isotropic Raman component of the C = O stretching mode of ethyl acetate (EA) was analyzed using various polar and nonpolar solvents. It was found that the bandshape approaches towards Lorentzian at high dilution using the curve‐fitting method. The isotropic Raman band was also analyzed by estimating the correlation coefficient with reference to the Lorentzian lineshape using a simple method of linear‐curve fitting. The effects of dispersion and hydrodynamic forces on bandwidth were studied in details. The vibrational relaxation rate was studied using certain parameters and it was found that the microscopic based parameter can explain the complexities occurring in solute–solvent interactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetics of NMR cross-polarization from protons to phosphorus-31 in natural brushite

Cross-polarization in natural brushite proceeds according to an isolated spin-pair kinetics.     

不同温度条件下单层石墨烯纳米带弛豫性能的分子动力学研究

分别采用Tersoff-Brenner势和AIREBO势,对三种长宽比的单层石墨烯纳米带在不同热力学温度(0.01—4000 K)下的弛豫性能进行了分子动力学模拟.对基于两种势函数模拟的石墨烯纳米带弛豫的能量曲线和表面形貌进行了分析对比,研究了石墨烯纳米带在弛豫过程中的动态平衡过程.模拟结果表明:单层石墨烯纳米带并非完美的平面结构,边缘处和内部都会呈现一定程度的起伏和皱褶,这与已有的实验结果相符合;石墨烯纳米带的表面起伏程度随长宽比的减小而减小,并且在不同温度条件下,系统动能对石墨烯纳米带的弛豫变形的影响很大,即系统温度越高,石墨烯纳米带的弛豫变形幅度愈大;高长宽比纳米带在一定温度条件下甚至会出现卷曲现象.最后,对采用Tersoff-Brenner势和AIREBO势进行石墨烯的分子动力学模拟进行了深入分析.