Nuclear Spin-spin Relaxation Times Research Articles

Nuclear spin-spin relaxation of isotopic impurities in solid hydrogen.

We report systematic studies of the transverse nuclear spin-spin relaxation times {ital T}{sub 2} of HD impurities in solid H{sub 2}. The experimental results indicate three different temperature regimes: (1) an exponential temperature dependence at high temperatures, (2) a minimum in {ital T}{sub 2} for 7 K{lt}{ital T}{lt}11 K, and (3) an approximately temperature-independent region for 1.5 K{lt}{ital T}{lt}7 K. The latter is attributed to the quantum diffusion of the impurities at low temperatures. At very low temperatures (0.10 K{lt}{ital T}{lt}1.5 K), {ital T}{sub 2} increases approximately linearly with temperature. This is attributed to the formation of bound ortho-H{sub 2} pairs. The behavior in the intermediate-temperature regime is analyzed in terms of vacancy-impurity scattering with quantum tunneling of vacancies.

Very rapid simultaneous measurement of nuclear magnetic resonance spin-lattice relaxation time and spin-spin relaxation time

A new method for measuring the spin-lattice relaxation time, T 1, and spin-spin relaxation time, T 2 is presented. It is based on a combination of two established pulse sequences. A fast-inversion-recovery sequence consisting of a fixed or variable wait, a 180° pulse, and a variable recovery time is employed. Then a Carr-Purcell-Meiboom-Gill (CPMG) sequence of echoes is integrated. At the end of this sequence the total nuclear magnetization is zero, providing an initial condition for the next measurement cycle. The CPMG sequence is an efficient means of signal accumulation for fast inversion recovery and simultaneously provides a measurement of T 2. The new system is faster than the best previously described means of measuring T 1 by a factor of T 2 T 2∗ . A phase-alternated pulse sequence that suppresses the baseline errors of the new measurement scheme is also introduced.

300 MHz proton NMR study of the differentiation of diploid human epidermal keratinocytes

The nuclear magnetic resonance spin-lattice (T1) and spin-spin (T2) relaxation times are closely related to the molecular motions of the molecules in a liquid sample. T1 and T2 of human epidermal cells were measured at 300 MHz as functions of harvesting methods (i.e., scraping vs trypsinization) and age in culture. It was found that T1 and T2 values have smaller variances when the cell is harvested by trypsinization rather than scraping. The correlation coefficients for both T1 and T2, obtained from cells harvested by scraping. More importantly, this is the first report to monitor in vitro aging through relaxation times measurement. There is a significant increase in the values of T1 and T2 from the third to seventh passages. Human keratinocytes slowed down and even ceased to grow the seventh passage. Therefore, the cellular water molecules of human keratinocytes have higher mobility in a more differentiated state. The factors contributing to the change in relaxation times as cells progress toward senescence are discussed.

The chemical dynamics of Na-in liquid 12-crown-4 solutions deduced from23Na nuclear spin relaxation rates

Solutions containing the sodium anion (Na-) were prepared by dissolving either NaK, NaRb or NaCs alloys in liquid 12-crown-4, 12C4. The 23Na nuclear spin-lattice (T 1n ) and spin-spin (T 2n ) relaxation times of the N.M.R. signal originating from Na- have been measured as a function of temperature, concentration and counter-cation K+, Rb+ or Cs+. The details of the inequality between T 1n and T 2n shown that the lifetime of Na- is limited by a two-step process. In the first step a strong complex of an alkali cation and 12C4 molecules dissociates to yield an uncomplexed cation to which one 3s electron from Na- is transferred in the second step. The 23Na nuclear spin relaxation data are combined with the results of previous EPR and pulse radiolysis experiments to deduce both the reactions generating Na- as well as further equilibria involving both complexed and uncomplexed cations, solvated electrons and a variety of paramagnetic species containing an electron and a cation.

Aggregation in five-coordinate high-spin natural hemins: determination of solution structure by proton NMR

{sup 1}H NMR measurements (at 500 MHz) of nuclear spin-spin relaxation time T{sub 2} (from NMR line width) at different temperatures are reported for aggregates of several five-coordinate high-spin iron(III) complexes of proto-, deutero-, and coproporphyrins in solution and are utilized to determine their solution structure. Extensive aggregation of these complexes in solution is observed, and the dominant form of the aggregates is shown to be dimers. The degree of aggregation for these iron(III) porphyrins follows the order proto- >> deutero- > copro-. The line width of the heme methyl resonances was analyzed by using a nonlinear least-squares fit program working in finite difference algorithm. The values of T{sub 2} were used to determine the structural details of the dimer.

High-frequency1H NMR studies of the effects of growth factors and phorbol esters on normal syrian hamster diploid fibroblast cells

The nuclear magnetic resonance (NMR) parameters, spin-lattice (T1), and spin-spin (T2) relaxation time, are usually longer for neoplastic cells than for normal cells of the same cell type. This has generally been true at low NMR frequencies (less than or equal to 100 MHz) when comparisons have been made between normal and neoplastic cells that have both spent a short time in culture. We have previously demonstrated that although the T1 values of paired normal and neoplastic Syrian hamster (SH) fibroblastic cells in culture are not significantly different when measured at 300 MHz, the 300 MHz T2 values for the neoplastic cells are smaller than those of the normal cells. (Xin et al. (1986), Cell Biophysics 8, 213.) Since treatment of normal diploid cells with polypeptide growth factors or tumor promoters frequently results in reversible expression of neoplasia-associated phenotypes, T1 and T2 were obtained at 300 MHz for treated and untreated SH cells to see if these compounds could also produce smaller 300 MHz T2 values. Secondary culture SH fetal fibroblast cells were treated with epidermal growth factor (EGF), fibroblast growth factor (FGF), phorbol-12,13-didecanoate (PDD) and 4-alpha-phorbol-12,13-didecanoate (4 alpha PDD). Treatment with either growth factor resulted in smaller T2 values, but a statistically significant decrease was not observed for PDD or 4 alpha PDD. The observed reductions in T2 values were correlated with the morphological and growth-stimulatory effects of these compounds on the cells.

NMR study of structure and electron transfer mechanism of Pseudomonas aeruginosa azurin.

The nuclear spin-spin and spin-lattice relaxation times of the C epsilon 1-proton of His-35 and the C delta 2-proton of His-46 of reduced Pseudomonas aeruginosa azurin have been determined at 298 and 320 K and at pH 4.5 and 9.0 at various concentrations of total azurin and in the presence of varying amounts of oxidized azurin. The relaxation times appear strongly influenced by the electron self-exchange reaction between oxidized and reduced protein. The T1 data of the His-35 proton have been analyzed according to the "fast-exchange limit," while the "slow-exchange limit" appears to obtain for the T2 data of the His-46 proton. Analysis of the proton relaxation data yields values of the electron self-exchange rate constants of (9.6 +/- 0.7) X 10(5) M-1 S-1 (pH 4.5) and (7.0 +/- 1.3) X 10(5) M-1 S-1 (pH 9.0) at 298 K. The dipolar correlation time amounts to 1-2.5 ns in the temperature range of 298-320 K. A Fermi-contact interaction of about 100 mG for the C delta 2-proton of His-46 is compatible with the experimental observations. The pH-induced conformational changes lead to variations on the order of about 1 A in the distance from the copper to the His-35 protons. The data implicate the "hydrophobic patch" around His-117 as the site of electron transfer in the self-exchange reaction of the azurin.

Nuclear spin relaxation phenomena in amorphous semiconductors

Recent nuclear magnetic resonance (NMR) measurements of nuclear spin relaxation phenomena in amorphous semiconductors are discussed using examples from several amorphous systems. Studies of nuclear spin-lattice relaxation times (T 1) and spin-spin relaxation times (T 2) are useful probes of several important phenomena in amorphous semiconductors. For example, the anomalous temperature dependences (approximately T β , 1 ⩽ β ⩽ 2) of the spin-lattice relaxation rates in several chalcogenide glasses have been attributed to the presence of disorder modes in these amorphous solids. In some cases the dominant contributions to T 1 are made by defects or impurities, such as trapped molecular hydrogen or “dangling bonds” in a-Si:H. Other localized electronic states can also play important roles in spin lattice relaxation processes. Such states include optically induced ESR centers or optically excited band tail states. Spin-spin relaxation rates are useful probes of dipolar interactions in amorphous semiconductors. From these measurements one can infer such structural details as clustering of hydrogen in a-Si:H and intermediate-range ordering in As 2S 3 and As 3Se 3.

31P nuclear magnetic resonance studies of the association of basic proteins with multilayers of diacyl phosphatidylserine

Lysozyme, cytochrome c, poly( l-lysine), myelin basic protein and ribonuclease were used to form multilayer dispersions containing about 50% protein (by weight) with bovine brain diacyl phosphatidylserine (PS). 31P nuclear magnetic resonance shift anisotropies, spin-spin ( T 2) and spin-lattice ( T 1) relaxation times for the lipid headgroup phosphorus were measured at 36.44 MHz. At pH 7.5, lysozyme, cytochrome c, poly( l-lysine) and ribonuclease were shown to increase the chemical shift anisotropy of PS by between 12–20%. Myelin basic protein altered the shape of the phosphate resonance, suggesting the presence of two lipid components, one of which had a modified headgroup conformation. The presence of cytochrome c led to the formation of a narrow spike at the isotropic shift position of the spectrum. Of the various proteins or peptides we have studied, only poly( l-lysine) and cytochrome c had any effect on the T 1 of PS (1050 ms). Both caused a 20–30% decrease in T 1 of the lamellar-phase phosphate peak. The narrow peak in the presence of cytochrome c had a very short T 1 of 156 ms. The possibility is considered that the cytochrome Fe 3+ contributes to the phosphate relaxation in this case. The effect of all proteins on the T 2 of the phosphorus resonance was to cause an increase from the value for pure PS (1.6 ms) to between 2 and 5 ms. The results obtained with proteins are compared with the effects of small ions and intrinsic membrane proteins on the order and motion of the headgroups of lipids in bilayers.

Pulsed NMR studies in solid H2. I. Solid echoes and nuclear spin-spin relaxation times after a two-pulse sequence

We describe a systematic pulsed NMR study on several solid H2 samples with ortho concentration X between 10% and 70% at temperatures between 0.08 and 2 K, where the intramolecular dipole-dipole interaction is the dominant spin-spin interaction. Nuclear spin echoes from a two-pulse sequence are studied using a rf phase-coherent spectrometer and they show the quasiquadrupolar nature of the echo formations. A density matrix method applied to the system of ortho-H2 molecules can account for most of the observed properties of the echoes. From the decay of the echo envelope we obtain information on the static intermolecular nuclear interactions and the local inhomogeneous magnetic field distribution. Details of the density matrix calculation are presented in an appendix.

Deuterium nuclear magnetic resonance spectroscopy of deuterated pyridine-iron(III) porphyrin complexes. Locations and relaxation times of bound deuterated pyridine resonances.

The first application of deuterium nuclear magnetic resonance spectroscopy (2H NMR) to fully deuterated pyridine (d5-pyridine)-iron(III) porphyrin complexes is described. (1) d5-Pyridine gives very broad 2H NMR signals in the presence of hemin or horseradish peroxidase to which pyridine is hardly (or not) bound, probably due to relatively long electronic relaxation times of the high-spin ferric ions. d5-Pyridine in the presence of horse-heart metmyoglobin gives resolved and less broadened 2H NMR signals, probably due to the relatively short electronic relaxation times of the ferric ion and/or to slow chemical exchange of the ligand. (2) The three resonances of free d5-pyridine coalesce into a single or a double resonance in the presence of a heme octapeptide prepared by trypsin digestion of Candida krusei cytochrome c. Nuclear spin-lattice and spin-spin relaxation times of the d5-pyridine-heme octapeptide complex are markedly shorter than those of free d5-pyridine. These findings are interpreted by the chemical exchange mechanism from the temperature dependences of the relaxation times. Thus, on certain assumptions the residence time of pyridine in the bound state and the exchange rate are estimated as approximately 10(-3) s and approximately 400 s-1, respectively, at 25 degrees C. Since 1H NMR signals of axial ligands of paramagnetic hemoproteins are hard to observe, the usefulness of deuterium magnetic resonance for investigating ligand exchange in the paramagnetic hemoproteins is emphasized.

Nuclear Magnetic Relaxation and Spin Fluctuations in α-Mn by N.M.R.

The temperature dependence of the nuclear spin-lattice ( T 1 ) and spin-spin ( T 2 ) relaxation times in α-Mn metal has been studied for the four different Mn sites between 95 K ( T N ) and room temperature by means of cw and pulsed NMR techniques. The 1/ T 1 for sites I and II estimated from cw NMR linewidth was found to be almost temperature independent as ∼1.9 ×10 5 (s -1 ). This high relaxation rate is interpreted in terms of the existence of localized spin fluctuations at sites I and II. The temperature dependence of 1/ T 1 for sites III and IV was found to be 1/ T 1 =0.50 ×10 3 +4.4 T (s -1 ) from 120 K to room temperature. The first term arises from the localized spin fluctuations at sites I and II via RKKY type interaction. The second T-linear term is Korringa type relaxation effect due to the band electron in α-Mn.

Cholesterol rotation in phospholipid vesicles as observed by 13C-NMR

13C-NMR spectra of cholesterol 90% enriched at C-4 with 13C have been obtained in CHCl 3 and in sonicated egg phosphatidylcholine vesicles. 13C spin-lattice relaxation times, nuclear Overhauser effects and spin-spin relaxation times have been measured for the C-4 carbon of cholesterol in phosphatidylcholine bilayers as a function of cholesterol content and temperature. All the data are consistent with a correlation time for axial rotation of about 10 −10 s. This rotation is one or two orders of magnitude faster than axial rotation of the phospholipid molecule.

Kinetics for ligand exchange in paramagnetic complexes of Ni(DPM) 2 with nitrogen, oxygen and sulfur ligands. A carbon-13 NMR relaxation study

The carbon-13 paramagnetic line widths (T −1 2p) and shifts (Δω p) of 1 M solutions of pyrrolidine (I), tetrahydrofuran (II), and tetrahydrothiophen (III) in the presence of 10 −2 M Ni(dpm) 2 have been studied over a temperature range from 193 to 328 K. ▪ The experimental shift and line width at each temperature depends on the isotropic shift of the complex-bond ligand (Δω M), lifetime of the ligand in the complex (τ M), and the nuclear spin-spin relaxation time in the complex (T 2M) in the manner described by Swift and Connick [1]. Some different models for the temperature dependence of Δω M, τ M and T 2M are set up and tested by simultaneous fitting of the experimental shift and line width data to the Swift and Connick expressions. The paramagnetic shifts show (especially for tetrahydrofuran) a clear non-Curie behaviour in the high temperature range. It was found that a fit to the experimental data could be obtained with an expression for Δω M which, apart from the usal Curie 1/T term due to the contact shift, also included a 1/T 2 term. The temperature dependence of τ M is given by the usual transition state theory expression. For T 2M we adopt a model using the modified Solomon-Bloembergen equations [2] with an assumption that the electronic relaxation is caused by the modulation of the static zero field splitting (ZFS) by molecular reorientation [3]. An advantage of this model is that it also allows calculation of the paramagnetic contribution to the nuclear spin-lattice relaxation time. Using also some 13C T 1 experiments, some of the parameters of the model may therefore be calibrated. With the above model for the temperature dependence, T 2p and Δω p have been simultaneously fitted to the Swift and Connick expressions, using a seven parameter non linear least squares procedure. The activation parameters and the exchange rates for the ligand exchange process in the three different complexes have been obtained. Furthermore, from the data analysis, the zero field splitting parameters, the carbon-13electron hyperfine coupling constants, the molecular reorientation correlation times and the electronic relaxation times in the complexes have been estimated.

The state of water in normal human, bird and fish eye lenses

The state of water was studied in normal human, fish and bird eye lenses. Free induction decay as well as nuclear spin-lattice and nuclear spin-spin relaxation time measurements were carried out by NMR method. The amount of non-freezable water per unit protein quantity was determined and the activation energy of the motion of the water molecules responsible for the relaxation was estimated. These results were compared with the ideas of Kuch and Yu concerning difference in protein conformation of the lens crystallins.

Nuclear magnetic resonance spin-spin relaxation time in hydrated protein powders. A two site dynamic exchange model

Nuclear magnetic resonance spin-spin relaxation time in hydrated protein powders. A two site dynamic exchange model

The Measurement of the Apparent Nuclear Spin-Spin Relaxation Times of N.Q.R. Signals in the Very-High-Frequency Region

The Doolan-Hacobian n.q.r. double pulse detection technique is described for the measurement of n.q.r, apparent spin-spin relaxation times as applied to a v.h.f. lecher line super-regenerative spectrometer. Results are presented for the linewidths of the 79Br and 81Br resonances in p-dibromobenzene. It was found that crystal-field inhomogeneities produce significant broadening of the n.q.r. signal.

The measurement of the apparent nuclear spin-spin relaxation times of N.Q.R. signals in the ultra-high-frequency region

Apparent spin-spin relaxation times, T2*, for the 127I nuclear quadrupole resonances of a series of substituted iodobenzenes were measured by the Doolan-Hacobian double-pulse detection technique. A coaxial line oscillator capable of operation to 800 MHz was used to obtain the signals of the higher frequency transitions. It is shown that the ratio of the T2* measurements of the lower to the upper transition in spin 5/2 systems is of the order of two. This is in accordance with the assumption that the broadening is mainly electrical in nature and arises from the spread in the principal component of the electric field gradients produced by crystal defects.

NMR and Susceptibility Studies of MnSi aboveTc

The itinerant helimagnet MnSi has been studied using NMR and susceptibility techniques above T c . The magnitude and temperature dependence of the 55 Mn Knight shift K, quadrupole coupling ν Q and the nuclear spin-lattice and spin-spin relaxation times T 1 and T 2 have been determined along with new high temperature measurements of the uniform susceptibility χ(0). Both K and ν Q are shown to be proportional to χ(0), with temperature the implicit parameter. T 1 and T 2 are temperature independent well above T c and their magnitudes cannot be explained by the fluctuations of localized moments. The results of all of our measurements are in general accord with the predictions of the renormalized RPA theory of spin fluctuation phenomena in itinerant magnets of Moriya and his collaborators.

Experimental evidence for the role of cross-relaxation in proton nuclear magnetic resonance spin lattice relaxation time measurements in proteins

Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz.