Dependence Of Spin-lattice Relaxation Rate Research Articles

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry.

Associative block copolymers of the type (EO) x(PO) y(EO) x (where EO and PO represent ethylene and propylene oxides, respectively) in aqueous solution have far reaching commercial applications such as solubilization, controlled-drug delivery, etc. The molecular dynamics of a self-associating triblock copolymer (EO)20(PO)70(EO)20 (known as P123 with a molecular weight of ∼5800), in aqueous solution (D2O), consisting of various lyotropic liquid crystalline phases such as isotropic micellar, cubic, hexagonal, and lamellar phases, is investigated using the fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique in the Larmor frequency range from 5 kHz to 30 MHz. A nuclear spin-relaxation model consisting of chain modes (Rouse modes) and order fluctuation (OF) modes typical for polymers and liquid crystals, respectively, is considered to explain the observed proton magnetic relaxation dispersion (PMRD) data in the lyophases under investigation. The PMRD analysis in both isotropic micellar and cubic phases revealed a Rouse frequency dependence of spin-lattice relaxation rate ( R1), i.e., R1 ∝ -τs ln(ωτs), in the entire frequency range of study. Hexagonal and lamellar phase data show Rouse modes as well as OF modes, leaving the signature of the latter as R1 ∝ ω- p, where p ∼ 0.5 is typical for nematic mesogens. The activation energies were also determined from segmental correlation times in the lyophases of study. To the best of our knowledge, the present FFC NMR relaxometry study is unique and quantitative in unraveling molecular dynamics of the associative copolymer P123 in aqueous solution.

Molecular Dynamics of Water in Wood Studied by Fast Field Cycling Nuclear Magnetic Resonance Relaxometry

Water plays a very important role in wood and wood products. The molecular motion of water in wood is susceptible to thermal activation. Thermal energy makes water molecules more active and weakens the force between water and wood; therefore, the water molecules dynamic properties are greatly influenced. Molecular dynamics study is important for wood drying; this paper therefore focuses on water molecular dynamics in wood through fast field cycling nuclear magnetic resonance relaxometry techniques. The results show that the spin-lattice relaxation rate decreases with the Larmor frequency. Nuclear magnetic resonance dispersion profiles at different temperatures could separate the relaxation contribution of water in bigger pores and smaller pores. The T1 distribution from wide to narrow at 10 MHz Larmor frequency reflects the shrinkage of pore size with the higher temperature. The dependence of spin-lattice relaxation rate on correlation time for water molecular motion based on BPP (proposed by Bloembergen, Purcell, and Pound) theory shows that water correlation time increases with higher temperature, and its activation energy, calculated using the Arrhenius transformation equation, is 9.06±0.53 kJ/mol.

11B NMR study on rare earth ternary borides RRuB2

11B NMR measurements have been performed on rare earth ternary borides, YRuB2, LuRuB2 and (Tm0.4Y0.6)RuB2 to investigate their electronic states. From the measurements of temperature dependence of spin-lattice relaxation rate 1/T1, YRuB2 and LuRuB2 are found to be Bardeen-Cooper-Schrieffer (BCS) superconductors with the energy gap 2Δ(0)=3.52 kBTc and the superconducting transition temperatures Tc=7.6 K (YRuB2) and 10.2 K (LuRuB2). A very broad and temperature dependent spectrum is observed in (Tm0.4Y0.6)RuB2. The magnitude of 1/T1T is considerably larger in (Tm0.4Y0.6)RuB2 than in YRuB2 and LuRuB2. These facts suggest the contribution of 4f electrons to the hyperfine field at 11B nuclei in (Tm0.4Y0.6)RuB2.

NQR study of neutral–ionic phase transition and quantum paraelectric state in organic charge-transfer complexes

NQR measurements were performed for the charge-transfer complexes DMTTF–QBr n Cl n −4 under ambient and hydrostatic pressures in order to understand the neutral–ionic phase transition and the quantum critical behavior. The 35Cl NQR spectrum of DMTTF–QCl 4 showed a splitting and a shift below T c, indicating the occurrence of dimerization and charge transfer. The spin-lattice relaxation rate 1/ T 1 showed a peak anomaly around T c, reflecting the critical slowing down. The quantum paraelectric states in DMTTF–2,6-QBr 2Cl 2 and pressured DMTTF–QBr 4 were studied by the 79Br NQR. We found the microscopic evidence for the evolution of the critical fluctuations at low temperatures in the temperature dependence of spin-lattice relaxation rate.

Determination of dependence of spin-lattice relaxation rate in serum upon concentration of added iron by magnetic resonance imaging

Dependence of spin-lattice relaxation rate (1/T1) in serum upon concentration of added iron was studied in the concentration range 0.0179-0.179 mmol l-1 for each of ferrous and ferric iron. In conjunction with the serum study, 1/T1 in solutions of transferrin and a mixture of albumin and gamma globulin was also studied as a function of added iron concentration. At low concentrations 1/T1 in serum increases linearly with increasing amounts of iron for each ion, and then reaches saturation for ferrous iron, whereas it shows an inflection for ferric iron. To explain the partition of added iron between various serum components, the effect of iron on 1/T1 in serum was compared with those of transferrin and the mixture. This effect can be defined as relaxivity or the incremental increase in relaxation rate per millimolar of added iron. At low concentrations the relaxivities of iron in serum, about 0.91 mmol-1 l s-1 for ferric and 0.95 mmol-1 l s-1 for ferrous ion, approximate well to the relaxivity of iron in transferrin solutions, which was measured to be about 0.92 mmol-1 l s-1. Furthermore, at high concentrations the relaxivity of ferric iron in serum, 0.44 mmol-1 l s-1, becomes similar to that of the mixture which is about 0.39 mmol-1 l s-1. These findings imply that iron added to serum first satisfies the binding requirements of transferrin, and the binding of iron to the other serum proteins occurs at high concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Spin-Lattice Relaxation of Shallow Donors In Heavily Doped Si

A theory is proposed to explain the dependence of spin-lattice relaxation rate, 1/ T s , of donors on the concentration and the degree of compensation. In the theory donor electrons are classified into two groups according to their spin-lattice relaxation rate being rapid or slow. The first is those electrons belonging to the close pairs of phosphorus atoms which are few in number. One site of a close pair is occupied and the other occupied. These electrons relax rapidly through the hopping motion accompanied by reversal of spin orientation. The second group is those electrons associated with the isolated phosphorus atoms. They approach to the first group via the hopping motion without changing their spin orientations and finally relax at the sites of the fast-relaxing centers associated with the first group. Qualitative agreement between calculation and the experimental data of Igo is obtained with the exception of the heavily compensated samples.