The determination of magnetic structures using low temperature nuclear orientation:166mHo-Ho

It is demonstrated that the low temperature nuclear orientation technique can be used to determine the axes of quantization in a multiaxial ordered ensemble of nuclear spins. Expressions for the anisotropic -ray intensity from particular geometries are derived for the case in which each subsystem has its own axial symmetry. The determination of the atomic magnetic structure in antiferromagnets is discussed and the results of recent experiments on helically ordered^166mHo-Ho are presented. In these experiments, the angular variation of the intensities of some of the more intense -rays were measured and compared to theory. A value of 80.4(1)°, not including systematic errors, was obtained for the semi-cone angle of the helix formed by the atomic magnets.     

Experimental and Computational Study of the Thermal Decomposition of 3‐Methyl‐3‐buten‐1‐ol in m‐Xylene Solution

An experimental study of the thermal decomposition of a β‐hydroxy alkene, 3‐methyl‐3‐buten‐1‐ol, in m‐xylene solution, has been carried out at five different temperatures in the range of 513.15–563.15 K. The temperature dependence of the rate constants for the decomposition of this compound in the corresponding Arrhenius equation is given by ln k (s^?1) = (25.65 ± 1.52) ? (17,944 ± 814) (kJ·mol^?1)·T^?1. A computational study has been carried out at the M05–2X/6–31+G(d,p) level of theory to calculate the rate constants and the activation parameters by the classical transition state theory. There is a good agreement between the experimental and calculated rate constants and activation Gibbs energies. The bonding characteristics of reactant, transition state, and products have been investigated by the natural bond orbital analysis, which provides the natural atomic charges and the Wiberg bond indices. Based on the results obtained, the mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state, being a concerted and slightly asynchronous process. The results have been compared with those obtained previously by us (Struct Chem 2013, 24, 1811–1816) for the thermal decomposition of 3‐buten‐1‐ol, in m‐xylene solution. We can conclude that in the compound studied in this work, 3‐methyl‐3‐buten‐1‐ol, the effect of substitution at position 3 by a weakly activating CH₃ group is the stabilization of the transition state formed in the reaction and therefore a small increase in the rate of thermal decomposition.     

Structural and Kinetic Aspects of Blood Plasma Protein Adsorption on the Surface of Hydrophobic Polymers

Abstract

Due to the wide use of polymers in medicine, researchers are required to solve a very important problem–to understand the interaction between materials of nonphysiological origin and the surrounding biological liquids, and tissues, particularly blood.     

Nuclear magnetic resonance of oriented54Mn nuclei in antiferromagnetic MnCl2 · 4H2O

Nuclear magnetic resonance of oriented⁵⁴Mn nuclei in antiferromagnetic MnCl₂ · 4H₂O has been observed. The first two lines of the sextuplet split by quadrupole interaction are at frequencies 500.4 and 514.7 MHz, implying a hyperfine field of 643(5) kG. The stronger line at 500.4 MHz has a half-width at half maximum of 60 kHz and is shifted downward and split in frequency on application of a magnetic field. The nuclear spin-lattice relaxation time is dependent both on the applied field and the size and/or quality of the crystal.     

Pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material:54Mn−MnCl2.4H2O

The first observation of pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material is reported. The system studied was the ordered antiferromagnet⁵⁴Mn−MnCl₂.4H₂O. The response of the⁵⁴Mn spins to a single pulse of variable length, the free induction decay, and Hahn spin-echo have all been observed. A discussion of the transverse decoherent relaxation timeT ₂ in MnCl₂.4H₂O is given.     

Pulsed NMRON measurements on insulators

Selective single and double quantum excitation pulsed NMRON has been utilized to obtain rotation patterns, free induction decays, and spin echoes in antiferromagnetic⁵⁴Mn−MnCl₂·4H₂O and the quasi-2 dimensional ferromagnet⁵⁴Mn−Mn(COOCH₃)₂·4H₂O. The pulsed technique is well suited to observing fast spin-lattice relaxation and T₁ values down to 100 ms have been measured in these systems. These short times may make magnetic insulators viable hosts for on-line experiments. The dependence on field and temperature of the⁵⁴Mn spin-lattice relaxation time T₁ has been investigated and a T₁ minimum at high fields observed in both systems. A spin-spin relaxation time T₂≈50 μs is measured in⁵⁴Mn−MnCl₂·4H₂O. The observation of NMRON in the paramagnetic phase of MnCl₂·4H₂O allows the resonant frequencies in the antiferromagnetic and paramagnetic phases to be compared, yielding a value for the zero point spin deviation in the former phase.