Spin-lattice Relaxation Time T1 Research Articles

Cu-NQR of CeCu2Si2 under high pressure

We have measured 63Cu-NQR spectral lines and nuclear spin-lattice relaxation time T1 under pressure up to 5.4 GPa. Daphne oil 7474 is used as the pressure-transmitting medium to obtain good hydrostaticity. NQR frequency 63νq above 4 GPa suddenly decreases from the linear pressure dependence in the low pressure range (P ≤ 3.5 GPa). The observed sudden downward deviation of 63νq is associated with an increase of Ce valence. Above 4.5 GPa, the linear pressure dependence of 63νq is observed again, most likely related to the sharp crossover to the high valence state.

Dissolution DNP-NMR spectroscopy using galvinoxyl as a polarizing agent

The goal of this work was to test feasibility of using galvinoxyl (2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy) as a polarizing agent for dissolution dynamic nuclear polarization (DNP) NMR spectroscopy. We have found that galvinoxyl is reasonably soluble in ethyl acetate, chloroform, or acetone and the solutions formed good glasses when mixed together or with other solvents such as dimethyl sulfoxide. W-band electron spin resonance (ESR) measurements revealed that galvinoxyl has an ESR linewidth D intermediate between that of carbon-centered free radical trityl OX063 and the nitroxide-based 4-oxo-TEMPO, thus the DNP with galvinoxyl for nuclei with low gyromagnetic ratio γ such as 13C and 15N is expected to proceed predominantly via the thermal mixing process. The optimum radical concentration that would afford the highest 13C nuclear polarization (approximately 6% for [1-13C]ethyl acetate) at 3.35T and 1.4K was found to be around 40mM. After dissolution, large liquid-state NMR enhancements were achieved for a number of 13C and 15N compounds with long spin–lattice relaxation time T1. In addition, the hydrophobic galvinoxyl free radical can be easily filtered out from the dissolution liquid when water is used as the solvent. These results indicate that galvinoxyl can be considered as an easily available free radical polarizing agent for routine dissolution DNP-NMR spectroscopy.

NMR studies of magnetic properties in Heusler-type Mn 3 Si

In order to microscopically investigate the magnetic properties of both paramagnetic and antiferromagnetic phases in Mn3Si (T N = 23 K), the 55Mn NMR has been carried out at temperatures between 2.2 K and 300 K. The temperature dependences of the spectrum, Knight shift (or resonance frequency shift) and spin-lattice relaxation time T 1 of 55Mn NMR have been measured. In the paramagnetic phase, only one resonance spectrum can be obtained. The observed spectrum is identified to be a signal corresponding to the Mn(II) site. In the antiferromagnetic phase, two different spectra corresponding to the Mn(I) and Mn(II) sites are found at the resonance frequencies of 145 and 6 MHz, respectively, by the zero field NMR at 4.2 K. From these results, the internal magnetic fields on the 55Mn(I) and 55Mn(II) nuclei are found to be 13.6 and 0.6 T, respectively. According to the NMR results, the helical structure in incommensurate Mn spin states is better explained compared with the transverse sinusoidal structure.

Atomic Motion in Low-Coverage Helium Films Adsorbed in FSM Nanochannels

4He and 3He films adsorbed in nanoporous silicates have shown similar heat capacities until the quantum-fluid layer appears at coverages over the first-layer completion n 1. To obtain information on dynamics of adatoms at low coverages below the quantum fluid region, we have done pulsed-NMR experiment at 3.3 MHz for 3He films adsorbed in straight 2.4 nm nanochannels of FSM silicates. The spin-lattice and spin-spin relaxation times T 1 and T 2 observed at 0.54–7 K were well described by the two-dimensional version of the Bloembergen-Purcell-Pound model. At coverages 0.4–1.7n 1, minima of T 1, indicating the spin correlation time τ c of 4.8×10−8 sec, were observed at temperatures between 6 and 3 K. With decreasing temperature, changes in T 1 and T 2 become small below about 1.5 K, suggesting crossover from thermally-activated motion to quantum tunneling. In contrast to large variations below n 1, both relaxation times above n 1 are almost independent of coverage, which is likely to indicate that τ c is determined by interlayer exchange of adatoms. Below n 1, onsets for localization of adatoms were suggested by a decrease in T 2.

Isotope ratio of Cl NQR spin-lattice relaxation times in 1D hydrogen-bonding system of tetramethylpyrazine-chloranilic acid at high temperatures

The temperature dependences of spin-lattice relaxation time T1 of 35Cl and 37Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H2ca), TMP-H2ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H2ca. The isotope ratio 37Cl T1 / 35Cl T1 was determined to be 1.0 ± 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T1 with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.

Irreversible change in the T 1 temperature dependence with thermal dose using the proton resonance frequency-T 1 technique

Denaturation of macromolecules within the tissues is believed to be the major factor contributing to the damage of tissues upon hyperthermia. As a result, the value of the spin-lattice relaxation time T1 of the tissue water, which is related to the translational and rotational rates of water, represents an intrinsic probe for investigating structural changes in tissues at high temperature. Therefore, the goal of this work is to investigate whether the simultaneous measurement of temperature and T1 using a hybrid proton resonance frequency (PRF)-T1 measurement technique can be used to detect irreversible changes in T1 that might be indicative of tissue damage. A new hybrid PRF-T1 sequence was implemented based on the variable flip angle driven-equilibrium single-pulse observation (DESPOT)1 method from a standard three dimensional segmented echo-planar imaging sequence by alternating two flip angles from measurement to measurement. The structural changes of the heated tissue volumes were analyzed based on the derived T1 values and the corresponding PRF temperatures. Using the hybrid PRF-T1 technique, we demonstrate that the change of spin lattice relaxation time T1 is reversible with temperature for low thermal dose (thermal dose ≤ 240 cumulative equivalent minutes [CEM] 43°C) and irreversible with temperature after significant accumulation of thermal dose in ex vivo chicken breast tissue. These results suggest that the hybrid PRF-T1 method may be a potentially powerful tool to investigate the extent and mechanism of heat damage of biological tissues.

Fast Dissolution Dynamic Nuclear Polarization NMR of 13C-Enriched 89Y-DOTA Complex: Experimental and Theoretical Considerations

The yttrium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(1′-13C-acetic acid) [13C]DOTA was synthesized. Fast dissolution dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) studies revealed that the 89Y, 13C, and 15N nuclei present in the complex could be co-polarized at the same optimum microwave irradiation frequency. The liquid-state spin–lattice relaxation time T1 of these nuclei were found to be reasonably long to preserve some or most of the DNP-enhanced polarization after dissolution. The hyperpolarized 13C and 89Y NMR signals were optimized in different glassing mixtures. The overall results are discussed in light of the thermal mixing model of DNP.

High-resolution solid-state NMR study of isotactic polypropylenes

The high-resolution solid-state 13 C NMR spectra were recorded for metallocene (m) and Ziegler-Natta (ZN) iso- tactic polypropylenes (iPP) in pelletized form using cross polarization (CP) and magic angle spinning (MAS) techniques within the temperature range of 20-160°C. Besides the CP MAS experiments also the MAS 13 C NMR spectra (without CP), MAS 1 H NMR spectra and rotating frame spin-lattice relaxation times T1 ( 13 C) were measured at elevated temperatures. With the rise of temperature the splitting of CH2, CH and CH3 signals into two components was detected in 13 C NMR spec- tra and assigned to amorphous and crystalline phases. The temperature dependences of chemical shifts and integral intensi- ties obtained from the deconvoluted spectra provided information on the main chain and CH3 groups motions in amorphous and crystalline regions of studied samples. While T1 ( 13 C) values show that the rate of segmental motion in amorphous regions in m-iPP and ZN-iPP is virtually the same, larger linewidths in 13 C and 1 H NMR spectra indicate somewhat larger restraints of the motion in amorphous regions of ZN-iPP.

A joint Raman and EPR spectroscopic study on ball-milled nanographites

Multi-wavelength Raman and EPR spectroscopies have been used on ball-milled graphite to investigate the effect of varying crystallite size and defect concentration. A correlation between Raman ID/IG intensity ratio and EPR T1 spin lattice relaxation time of conduction electrons has been discovered which could represent an appealing characterization technique for graphitic materials.

Nuclear quadrupole resonance and thermally activated molecular mobility in solids: Reorientations of symmetric molecular species and pseudorotation in trigonal-bipyramidal molecules

The specific features revealed in the behavior of temperature dependences of the spin-lattice relaxation time t 1 of quadrupole nuclei involved in different types of thermally activated motions in crystals have been analyzed under the assumption that there exists a temperature dependence of the activation energy of motion. An expression for the spin-lattice relaxation rate has been obtained. This expression includes the effect under consideration and provides an adequate explanation for numerous anomalies in the behavior of the experimental dependences t 1(T), which were revealed in the case of the motion of molecular fragments with a relatively large volume. A nontraditional method for evaluating the activation energy of motion under these conditions has been proposed.

NMR Study of the Dynamics ofHe3Impurities in the Proposed Supersolid State of SolidHe4

The dynamics of (3)He atoms in solid (4)He have been investigated by measuring the NMR relaxation times T(1) and T(2) in the region where a significant nonclassical rotational inertia fraction has been reported. For (3)He concentrations x(3)=16 and 24 ppm, changes are observed for both the spin-lattice relaxation time T(1) and the spin-spin relaxation time T(2) at the temperatures corresponding to the onset of the nonclassical rotational inertia fraction and, at lower temperatures, to the (3)He-(4)He phase separation. The magnitudes of T(1) and T(2) at temperatures above the phase separation agree roughly with existing theory based on the tunneling of (3)He impurities in the elastic strain field due to isotopic mismatch. However, a distinct peak in T(1) and a less well-resolved feature in T(2) are observed near the reported nonclassical rotational inertia fraction onset temperature, in contrast to the temperature-independent relaxation times predicted by the tunneling theory.

Abstract 5290: Imaging biomarkers of response to chemotherapy in neuroblastoma

Abstract Neuroblastoma (NBL) is the most common extracranial solid tumor of childhood, accounting for between 7-10% of paediatric cancers. The proto-oncogene MYCN is amplified in 25% of NBL and is associated with high-risk disease, enhanced tumor angiogenesis and poor survival. A genetically-engineered mouse model for high risk, MYCN-amplified NBL has been generated by directing expression of MYCN to the peripheral neural crest of transgenic mice. As part of a multi-parametric MRI study, we have evaluated the native spin-lattice relaxation time T1, sensitive to the ratio of bound to free water in tissue, as a potential noninvasive biomarker of treatment response of TH-MYCN NBL to three different classes of anti-cancer agent. TH-MYCN mice with abdominal tumors were identified by palpation and imaged prior to and following treatment. Native T1 (ms) was quantified at 7T using an inversion recovery (IR)-trueFISP sequence. In control cohorts, tumor progression over 48 hours and 4 days was associated with no significant change in T1. A single 25mg/kg dose of cylophosphamide, the current standard of care for childhood NBL, caused a significant 54% reduction of tumor volume at 48 hours. Treatment of TH-MYCN NBL with CPM leads to extensive cell death, which occurs primarily through apoptosis, and this response was associated with a highly significant 15% reduction in native T1. Given the hypervascular nature of NBL, their response to anti-vascular therapies was also investigated. Treatment with the pan VEGF receptor inhibitor cediranib (6mg/kg daily over 2 days) resulted in significant 19% anti-tumor activity and 8% reduction in T1 at 48 hours. Furthermore, this response was associated with a significant reduction in uptake of the perfusion marker Hoechst 33342 compared to control, but no difference in necrosis. Treatment with a single 200mg/kg dose of the colchicine derivative ZD6126 resulted in significant and unprecedented 43% anti-tumor activity at 24 hours, and which was also associated with a significant 14% reduction in native T1. Histology revealed a significant reduction in Hoechst 33342 uptake and extensive tumor necrosis. Collectively, these data show a systematic reduction of native T1 in the TH-MYCN model with successful chemotherapy. The CPM and ZD6126-induced reduction in T1 is consistent with a histologically confirmed reduction in cell density and increased extravascular space following cytotoxic therapy. The reduction of T1 following treatment with cediranib may be attributable to the resolution of edema caused by reduced vascular permeability. Accurate quantification of T1 affords a generic noninvasive biomarker for chemotherapy-mediated cell death in the TH-MYCN model. The high sensitivity of T1 will accelerate the pre-clinical evaluation of novel therapeutics for childhood neuroblastoma in this model. Quantitation of native T1 could be easily incorporated into conventional imaging protocols used in clinical trials. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5290. doi:10.1158/1538-7445.AM2011-5290

Probing molecular mobility during crosslinking process of commercial resins by NMR multiexponential relaxation data analysis

AbstractIn this study, we present the experimental results for the crosslinking process of a commercial polyester resin based on measurements of the spin lattice relaxation time T1 of protons, as function of the crosslinking time evolution. Multiexponential decomposition of the evolution of magnetization measured in inversion‐recovery experiments is performed. The population of “rigid” and “mobile” nuclear spin sites was estimated as function of time evolution. In analogy to the usual monomer conversion u, site conversion from “mobile” to “rigid” sites uM were also estimated as a function of time evolution and initial concentrations of the reagents. The multiexponential decomposition approach of T1 relaxation data allows one to follow crosslinking processes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Molecular dynamics of poly(ethylene terephthalate)/poly(phenylene sulfide) nanocomposites with barium titanate

Abstract The relaxation processes and the properties of polymer/ceramic nanocomposites have been studied by the 1H nuclear magnetic resonance methods. Nanocomposites of poly(ethylene terephthalate) PET and poly(phenylene sulfide) PPS with 0.25, 2.5 and 5% wt. barium titanate BT were prepared using a twin screw extruder and injection moulding machine. The spin-lattice relaxation time T1, second moment M2 and the motional parameters as e.g. the activation energies in the nanocomposites were investigated.

Polymer Chain Relaxation Mechanisms in Siloxane-Carbosilane Systems

The effect of sterically hindered carbosilane moieties, situated as end groups in telechelic oligodimethylsiloxanes, was investigated with respect to the mobility of silicon atoms in the main chain. The relaxation phenomena in such crowded systems were studied by DSC and NMR methods. Spin–lattice relaxation times T1 (29Si NMR) of silicon atoms in the oligomer chain were estimated and related to the distance between a given siloxane unit and the carbosilane moiety. It was found that the mobility of terminal siloxane units has been substantially affected. However, in the long range, the effect does not to seem to outweigh the intrinsic flexibility of the siloxane bonds.

Effect of sodium salts of 3α,12α-dihydroxy-7-oxo-5β-cholanoic and 3,7,12-trioxo-5β-cholanoic acids on verapamil hydrochloride in biophysical-chemical model experiments

It is known that certain bile acids have a promotive effect on the action of some drugs. Special attention is paid to bile acids having oxo groups instead of OH groups in the steroid skeleton of their molecule, since these derivatives have a lower hemolytic potential (membrane toxicity). This study examined the effects of sodium salts of 3?,12?-dihydroxy-7-oxo-5?-cholanoic acid (7-oC) and 3,7,12-trioxo-5?- cholanoic acid (3,7,12-toC) on the adsorption of verapamil hydrochloride on activated carbon (model of the cell membrane). The interaction was followed by measuring the effect of verapamil on the functional dependence between the spin-lattice relaxation time T1 (protons of the C18 angular group of the bile acid molecule) and the bile acid concentration in deuterated chloroform (model of the cell membrane lipid phase). Whether a depot effect of verapamil exists when 7-oC and 3,7,12-toC (in the form of methyl esters) are present in chloroform was also investigated. It was found that 7-oC exhibited a significant effect in the experiments with verapamil, whereas 3,7,12-toC showed no difference of the measured parameters with respect to the control. This indicates that bile acid molecules should have OH groups bound to the steroid nucleus, in order to exhibit an effect on the monitored physico-chemical parameters of verapamil.

Solution structures of fluorescent Zn(II) complexes with bis(naphthyl amide)–EDTA

Two EDTA-based bichromophoric isomers form Zn(II) complexes that exhibit distinct fluorescent behaviors; the ligands are abbreviated as (edta1nap)H2 and (edta2nap)H2, each of which consists of an EDTA chain linked to two 1-naphthyl or 2-naphthyl groups. The coordination chemistry of these complexes was studied by UV–Vis, fluorescence and 1H NMR. The formation constants and the inherent emission intensities were determined by the pH dependence of the emission spectra; the species of the most intense emission is ML(OH) for L=(edta1nap)2−, and ML for (edta2nap)2−. The 1H NMR of Zn-(edta1nap)2− exhibits two sets of signals due to a slow exchange between two equivalent coordination geometries, whereas Zn-(edta2nap)2− undergoes a fast exchange to show a single set of NMR signals. The spin–lattice relaxation time T1 determined for the isostructural Mn(II) complexes shows that the naphthyl proton closest to the metal ion is H(8) in the (edta1nap)2− complex, and H(3) in the (edta2nap)2− complex. The two ligands differ only in the substitution position of the naphthyl group, but this apparently small difference leads to the notable difference in structural, dynamic, and consequent emission-spectral properties of their metal complexes as a result of the steric and size effects of the aromatic rings.

Relaxation rates of protons in gadolinium chelates detected with a high-Tc superconducting quantum interference device in microtesla magnetic fields

A nuclear magnetic resonance and imaging system was constructed to study spin-lattice relaxation time T1, spin-spin relaxation time T2, and effective relaxation time T2∗ of gadolinium (Gd) chelates using a high-Tc superconducting quantum interference device in microtesla magnetic fields. In the presence of the magnetic contrast T2∗ is related to T2 by the relation: 1/T2∗=1/T2+γΔB+ΓGd-chelates, where γ=42.58 kHz/mT and γΔB is the relaxation rate due to the inhomogeneity field ΔB in measuring coil at the sample position and ΓGd-chelates is the intrinsic relaxation rate of Gd chelates. It is found that T1, T2, and 1/ΓGd-chelates decay exponentially as the concentration (or magnetic susceptibility) of Gd chelates increases. The Gd chelates cause a diffusive motion of nuclear spins and hence enhance the relaxation rates. Enhanced image contrast has been demonstrated in a water phantom with Gd chelates in microtesla magnetic fields.

MOLECULAR INTERACTION BETWEEN BENZONITRILE AND HEXAMETHYLPHOSPHORIC TRIAMIDE BY <sup>13</sup>C NMR T<sub>1</sub> RELAXATION TIME STUDIES AND AB INITIO QM CALCULATIONS: EXTENDED INVESTIGATION

It has been obtained the anisotropy ratio a = T1(ortho-,meta-13C)/T1(para-13C) of dilute solutions of bn change from 1.7 in fa solution and 1.5 in neat bn to 1.0 in HMPT. Thus the anisotropy ratio comes out to be a = 1. In HMPT, obviously, solvent molecules cluster around Ph-CºN in such a way, that non-covalent interactions lead to isotropic reorientational motion like a spherical molecule. To conform with the T1 times, a layer arrangement with at least two HMPT molecules per Ph-CºN seems to be likely. From computational quantum calculations of non-covalent intermolecular interactions and Mie potential analysis, the solute-solvent molecular pairs in bnּּּHMPT have almost equal interaction energies for the ortho, meta, and para configuration and the layered configurations are energetically permitted Keywords: 13C T1 spin-lattice relaxation times, ab initio quantum chemistry calculations, intermolecular interactions, isotropic and anisotropic rotational motion

Phase transition and proton exchange in 1,3-diazinium hydrogen chloranilate monohydrate

In the hydrate crystal of 1:1 salt with 1,3-diazine and chloranilic acid (H2ca), (1,3-diazineH)·H2O·Hca, an unique hydrogen-bonded molecular aggregate is formed. There exists proton disorder in the N–H...O hydrogen bond between 1,3-diazinium ion and water (H2O) of crystallization. In order to reveal dynamic aspect of this disorder, 35Cl NQR measurements were conducted. Two resonance lines observed at 35.973 and 35.449 MHz at 321 K split into four lines below T c = 198 K clearly showing occurrence of a solid–solid phase transition; 36.565, 36.357, 36.011, 35.974 MHz at 77 K. Temperature dependence of spin-lattice relaxation time T 1 in high-temperature phase was observed to obey an Arrhenius-type relation with the activation energy of 8.5 kJ mol − 1. This result leads to the conclusion that proton exchange in the N–H...O hydrogen bond takes place in the high-temperature phase. Specific heat measurements by DSC resulted in the transition entropy ΔS = 1.3 J K − 1 per 1 mole [(1,3-diazineH)·H2O·Hca]2 which is far less than 2R ln2 = 11.5 J K − 1 mol − 1. It is expected that proton exchange in the two hydrogen bonds within the aggregate does not occur independently but concertedly with strong correlation in the high-temperature phase.