Measurement Of Longitudinal Relaxation Rates Research Articles

Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond

We present systematic measurements of longitudinal relaxation rates (1/T1) of spin polarization in the ground state of the nitrogen-vacancy (NV–) color center in synthetic diamond as a function of NV– concentration and magnetic field B. NV– centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV– center concentrations. Values of (1/T1) were measured for each spot as a function of B.

Scalar Relaxation of the Second Kind: A Potential Source of Information on the Dynamics of Molecular Movements. 1. Investigation of Solution Reorientation of N-Methylpyridone and 1,3-Dimethyluracil Using Measurements of Longitudinal Relaxation Rates in the Rotating Frame

The practical utility of the method of retrieving the relaxation rate of a quadrupole nucleus via the scalar relaxation of the second kind (SC2) of an I = 1/2 spin nucleus has been considered once again. The study was motivated by the fact that such data are frequently very useful in investigations of reorientational movements of molecules in solutions. At the same time, the parameters describing spin-spin and quadrupolar couplings, necessary in such studies, have become relatively easily accessible owing to a remarkable progress in theoretical methods. It was shown that even in the case of small N-C coupling constants ((1)J = 7-8 Hz) the classical method of approaching SC2 relaxation effects by measurements of the longitudinal relaxation rates in the rotating frame, although somewhat tedious, can yield acceptably accurate results. The whole procedure has been successfully applied in the investigation of molecular movements of N-methylpyridone (1) and 1,3-dimethyluracil (2) in acetone solution.

Relaxation-based distance measurements between a nitroxide and a lanthanide spin label

Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide–spacer–lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.

NMR relaxometric studies of water accessibility to haem cavity in horse heart and sperm whale myoglobin

AbstractThe measurement of longitudinal relaxation rates of water protons in solutions containing horse heart and sperm whale metmyoglobins at various pH values and temperatures shows that the two species differ essentially in the exchange lifetime, τM, of the water molecule in the haem cavity. The 1/T1 nuclear magnetic relaxation dispersion dispersion profiles support this view whereas 17O NMR spectroscopy shows that the exchange mechanism involves the whole water molecule. The lack of any 1H/2H isotope effect on the exchange rate suggests that the displacement of the coordinated water molecule from Fe(III) is not the rate‐determining step in the overall exchange process. In contrast to the parent species, no difference is detectable from the relaxometric investigations on the corresponding fluorometmyoglobin derivatives.

Spatially localized 31P NMR measurements of longitudinal relaxation rates in the canine myocardium

FLAX-ISIS spatial localization was combined with inversion recovery to enable the measurement of spatially localized T1 values. This approach was applied to the transmural determination of creatine phosphate longitudinal relaxation times in the canine myocardium. By examining five voxels spanning the left myocardial wall, we observed that transmural T1 values for creatine phosphate ranged from 3.61 +/- 0.20 in the endocardium to 4.00 +/- 0.20 in the epicardium at 4.7 Tesla. As such, the canine myocardium exhibits no transmural variation in the T1 values of creatine phosphate. This simple approach can be extended to enable the in vivo measurement of transmural enzymatic rates.

Resonant nearly degenerate backward four-wave mixing in open and closed systems.

This paper presents perturbation calculations using the density matrix to describe the nearly degenerate four-wave-mixing spectral response in resonant systems subject to state-specific reservoir coupling. The calculations provide physical insight into the origin of narrow resonances observed in recent experimental work in atomic sodium and ultranarrow resonances in crystals. The calculations are for systems which are homogeneously broadened as well as systems which are inhomogeneously broadened due to velocity effects or random crystal fields. The calculations show that it is possible to eliminate the effects of either kind of broadening and measure the decay rate of the dipole coherence as well as the decay rates of both states of the transition. Furthermore, the calculations indicate that the method of cross-correlated optical fields which was used to eliminate the effects of laser jitter in longitudinal relaxation rate measurements could be extended to the measurements of slow dephasing rates in crystals.

The half-wave triplet pulse sequence for determination of longitudinal relaxation rates of single line spectra

A modified pulse triplet sequence has been developed for the measurement of longitudinal relaxation rates, 1/ T 1. The analysis of this “half-wave” triplet method takes account of transverse relaxation occurring during the triplet, so that the approximation employed in previous use of the triplet sequence, viz., that the interval τ between component pulses of the triplet be much less than the interval δ t-2τ between successive triplets, is no longer required. Values of 1/ T 1 derived from triplet measurements and a Carr-Purcell spin echo measurement of 1/ T 2 on test samples of aqueous polymethacrylate and copper sulfate are in good agreement with values of 1/ T 1 obtained from conventional Carr-Purcell 180°- t-90° measurements. The half-wave triplet sequence would be useful for those cases where a single line is present in the spectrum: two repetitions of the triplet sequence to obtain n points on a magnetization recovery curve and a determination of T 2 are required for the determination of 1/ T 1n this method, compared to at least n repetitions (for n points) in the Carr-Purcell 180°- t-90° method.