Multi-quantum quadrupole relaxation enhancement effects in 209Bi compounds.

1H spin-lattice nuclear magnetic resonance relaxation experiments have been performed for triphenylbismuth dichloride (C18H15BiCl2) and phenylbismuth dichloride (C6H5BiCl2) in powder. The frequency range of 20-128 MHz has been covered. Due to 1H-209Bi dipole-dipole interactions, a rich set of pronounced Quadrupole Relaxation Enhancement (QRE) peaks (quadrupole peaks) has been observed. The QRE patterns for both compounds have been explained in terms of single- and double-quantum transitions of the participating nuclei. The analysis has revealed a complex, quantum-mechanical mechanism of the QRE effects. The mechanism goes far beyond the simple explanation of the existence of three quadrupole peaks for 14N reported in literature. The analysis has been supported by nuclear quadrupole resonance results that independently provided the 209Bi quadrupole parameters (amplitude of the quadrupole coupling constant and asymmetry parameter).

209Bi quadrupole relaxation enhancement in solids as a step towards new contrast mechanisms in magnetic resonance imaging.

Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, 1H spin-lattice relaxation has been investigated for tris(2-methoxyphenyl)bismuthane and tris(2,6-dimethoxyphenyl)bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific 1H spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for 209Bi. Knowing the parameters, the QRE pattern has been explained on the basis of a quantum-mechanical picture of the system including single and double-quantum coherences for the participating nuclei (1H and 209Bi). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained.

General rules prospected for the liquid fragility in various material groups and different thermodynamic conditions.

The fragility parameter has been acknowledged as one of the most important characteristics of glass-forming liquids. We show that the mystery of the dramatic change in molecular dynamics of systems approaching the glass transition can be better understood by the high pressure study of fragility parameters defined in different thermodynamic conditions. We formulate and experimentally confirm a few rules obeyed by the fragility parameters, which are also rationalized by the density scaling law and its modification suggested for associated liquids. In this way, we successfully explore and gain a new insight into the pressure effect on molecular dynamics of van der Waals liquids, polymer melts, ionic liquids, and hydrogen-bonded systems near the glass transition.

Molecular dynamics studies on the water mixtures of pharmaceutically important ionic liquid lidocaine HCl.

In this paper the molecular dynamics of a common local-anesthetic drug, lidocaine hydrochloride (LD-HCl), and its water mixtures were investigated. By means of broadband dielectric spectroscopy and calorimetric measurements it was shown that even a small addition of water causes a significant effect on the relaxation dynamics of analyzed protic ionic liquid. Apart from the two well-resolved relaxations (σ- and γ-processes) and the ß-mode, identified as the JG-process, observed for anhydrous LD-HCl, a new relaxation peak (υ) is visible in the dielectric spectra of aqueous mixtures of this drug. Additionally, the significant effect of the water on the glass transition temperature of LD-HCl was found. The sample characterized with mole fraction of water X(w) = 0.44 reveals the glass transition temperature T(g), 42 K lower than that of anhydrous material (307 K). Finally, it was shown that by amorphization of the hydrochloride salt of lidocaine it is possible to obtain its room temperature ionic liquid form.

Temperature-Volume Entropic Model for Viscosities and Structural Relaxation Times of Glass Formers.

In this Letter, an entropic model recently formulated by Mauro et al. for the temperature dependence of viscosity in glass-forming materials is generalized to describe the temperature-volume dependences of viscosities and structural relaxation times near the glass transition. It is found that the generalization shows limitations of its temperature precursor. The extended model describes well the structural dielectric relaxation times τα(T,V) of supercooled van der Waals liquids. The obtained results are discussed in the context of the thermodynamic scaling law for molecular dynamics of viscous systems.