Dynamics of [C3H5N2]6[Bi4Br18] by means of 1H NMR relaxometry and quadrupole relaxation enhancement

Abstract

(1)H spin-lattice field cycling relaxation dispersion experiments in the intermediate phase II of the solid [C3H5N2]6[Bi4Br18] are presented. Two motional processes have been identified from the (1)H spin-lattice relaxation dispersion profiles and quantitatively described. It has been concluded that these processes are associated with anisotropic reorientations of the imidazolium ring, characterized by correlation times of the order of 10(-8) s-10(-9) s and of about 10(-5) s. Moreover, quadrupole relaxation enhancement (QRE) effects originating from slowly fluctuating (1)H-(14)N dipolar interactions have been observed. From the positions of the relaxation maxima, the quadrupole coupling parameters for the (14)N nuclei in [C3H5N2]6[Bi4Br18] have been determined. The (1)H-(14)N relaxation contribution associated with the slow dynamics has been described in terms of a theory of QRE [Kruk et al., Solid State Nucl. Magn. Reson. 40, 114 (2011)] based on the stochastic Liouville equation. The shape of the QRE maxima (often referred to as "quadrupole peaks") has been consistently reproduced for the correlation time describing the slow dynamics and the determined quadrupole coupling parameters.

Aspects of structural order in 209Bi-containing particles for potential MRI contrast agents based on quadrupole enhanced relaxation

“…It manifests itself as a fast decay of the proton magnetisation interpreted as an enhanced spin-lattice relaxation rate R 1 = 1/T 1 [1][2][3][4][5][6][7][8] referred to as quadrupole peaks. The position of the quadrupole peaks is a function of the static magnetic field B 0 , the electric field gradient (EFG) at the location of the nucleus, the electrical quadrupole moment of the QN, its spin quantum number I and the angle Θ between EFG and B 0 [1][2][3][4][5][6][7][8][9][10][11].…”

“…The most special feature is that, in contrast to typical paramagnetic MRI contrast agents, [12][13][14][15][16] QRE leads to narrow peaks and steep slopes [1,2,4,5,[8][9][10][11]. In fact, such QRE peaks were observed for 14 N in the amide groups of proteins [17][18][19] and used for the first time for MRI contrast at very low B 0 [20] in humans.…”

Dynamics of Molecular Crystals by Means of 1H NMR Relaxometry: Dynamical Heterogeneity versus Homogenous Motion

“…The contributions to the 1 H spin-lattice relaxation caused by 1 H-X (X = 14 N, Bi, Br) dipoledipole interactions can lead to an effect referred to as quadrupole relaxation enhancement ("quadrupole peaks"). [31][32][33][34][35] H-X contribution to the overall relaxation is almost negligible, except for the frequencies at which the "quadrupole peaks" appear. [10,36] This effect is as ource of information on the timescale of molecular dynamics and molecular arrangement (structure) around the quadrupole nucleus, as the positions of the peaks depend on the electric field gradient at the position of this nucleus.…”

Estimation of the magnitude of quadrupole relaxation enhancement in the context of magnetic resonance imaging contrast

“…1,2,[8][9][10][11][12][13][14][15] In this work we demonstrate the prospective of a novel contrast mechanism for MRI, referred to as Quadrupole Relaxation Enhancement (QRE). [16][17][18][19][20][21][22][23][24][25] QRE is a complex, quantummechanical phenomenon which, in the context of MRI, is sometimes regarded as a counterpart of PRE, although this analogy is not fully justified. QRE leads to a frequency specific relaxation of 1 H spin-lattice relaxation (referred to as quadrupole peaks) originating from dipole-dipole interactions between protons ( 1 H nuclei) and nuclei possessing a quadrupole moment.…”