Movement and diffusion of paramagnetic ions in a magnetic field

The magnetic movement and thermal diffusion have been studied for Cu(2+) ions in solution. The Cu(2+) ion solution was spotted on the silica gel support and exposed to the magnetic field of 410 kOe(2) cm(-1) intensity x gradient. The Cu(2+) ions were attracted toward the filed center. The moving distance and diffusing distance were observed at various time intervals. It is shown that the Cu(2+) ions move in a large group composed of Cu(2+) ions and H(2)O molecules. The size of the group is approximately estimated to be of 4.6 mum diameter by the analysis of the drift velocity of the group and the Cu(2+) ion concentration in the group.     

Cell-sorption of paramagnetic metal ions on a cell-immobilized micro-column in the presence of an external magnetic field

The cell-sorption of paramagnetic ions of Mn²⁺ and Cr³⁺ onto a Chlorella vulgaris(C. vulgaris) cell-immobilized micro-column was significantly improved in the presence of an external magnetic field generated in a finite solenoid, by placing the micro-column in the center of the solenoid in a sequential injection system. Magnetic field creates an opposite drift velocity on the hydrated paramagnetic ions against the flow of the sample zone, retards the moving velocity of the metal ions and provides extra contacting time with the cells on the micro-column and offers more chances for the paramagnetic ions to interact with the various functional groups or binding sites on the cell surface, which significantly facilitates cell-sorption of the paramagnetic ions. The sorption efficiencies of Mn²⁺ and Cr³⁺ at the 20 μg L⁻¹ level were improved from 45 to 80% and 60 to 90%, respectively, in a magnetic field of 240 mT.The system was applied for the separation/preconcentration of ultra-trace level of manganese. The presence of an external magnetic field significantly alleviated the interfering effects from coexisting metal ions. Within a liner range of 0.025-0.5 μg L⁻¹ and a sampling volume of 500 μL, an enrichment factor of 21.2, a limit of detection of 0.008 μg L⁻¹, along with a sampling frequency of 20 h⁻¹ was attained, achieving a precision of 2.1% R.S.D. (0.2 μg L⁻¹). Manganese contents in a certified reference material of riverine water and a snow water were analyzed.     

On the possibility of orienting rotationally cooled polar molecules in an electric field

We have investigated the effects of initial rotational stateJ and the gas temperature (T) on the rotationally elastic, inelastic and summed processes in CH₄ and SiH₄ molecules by low-energy electron impact. While rotationally summed differential, integral, momentum transfer and energy-loss cross sections are independent of initial stateJ (and hence independent onT), it is found that the same rotationally inelastic differential and integral cross sections, when averaged over rotational distribution function, show a qualitative improvement over the unaveraged results when compared with experimental results. Various theorems regarding the dependence of scattering parameters on the rotational distribution, as described in a series of papers by Shimamura, are discussed by presenting actual calculations on the two spherical tops, namely the CH₄ and SiH₄ molecules.     

Confinement of paramagnetic ions under magnetic field influence: Lorentz versus concentration gradient force based explanations

Concentration variations observed at circular electrodes with their axis parallel to a magnetic and normal to the gravitational field have previously been attributed elsewhere to the concentration gradient force only. The present paper aims to show that Lorentz force driven convection is a more likely explanation.     

Analytical formulas for the magnetic field produced by a spin or a paramagnetic current density in the case of Gaussian basis functions

We present a derivation of simple formulas for the evaluation at any point of space of the magnetic field produced by a spin or a paramagnetic orbital current when Cartesian Gaussian basis functions are used, as is often the case in quantum chemistry. These formulas can be useful to plot the magnetic field vector density obtained from ab initio calculations or from a density operator fitted on experimental data. The magnetic field density is the observable probed in polarized neutron diffraction (PND) experiment, for it is, in fact, with this quantity that the neutron spins interact and not with the spin or magnetization density. The formulas make extensive use of the confluent hypergeometric function. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 11–15, 2001     

On the possibility of structural and magnetic ordering in magnetic colloids

The aggregation stability of a magnetic colloid at an excess content of a surfactant is studied. The presence of aggregates with a nonzero magnetic moments is revealed; on this basis, magnetic ordering of magnetic particles in them is regarded as possible. The possible mechanisms of the formation of periodic structural lattices appearing under the action of a direct electric field on the magnetic colloid are studied. A fundamental difference between the structurization processes induced by a surfactant and by an electric field is noted: structurization processes occurring at the excess of surfactant may be associated with the flocculation, whereas such processes proceeding under the effect of an electric field may be due to phase separation of the colloid.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 161–166.Original Russian Text Copyright © 2005 by Dikanskii, Vegera, Zakinyan, Nechaeva, Gladkikh.     

The induced magnetic field in cyclic molecules

The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C(6)H(6), D(6h)), anti-aromatic (C(4)H(4), D(2h)) and non-aromatic (C(4)H(8), D(4h), and C(6)H(12), D(3d)) molecules. The results show that molecules that contain a pi system possess a long-range magnetic response, while the induced magnetic field is short-range for molecules without pi systems. The induced magnetic field of aromatic molecules shields the external field. In contrast, the anti-aromatic molecules increase the applied field inside the ring. Aromatic, anti-aromatic, and non-aromatic molecules can be characterized by the appearance of the magnetic response. We also show that the magnetic response is directly connected to nucleus-independent chemical shifts (NICS).     

Diamagnetic and paramagnetic currents for an anisotropic harmonic oscillator in a magnetic field

The response of the electronic shell of a molecule to the perturbing action of an external magnetic field has been analyzed by calculating the field-induced electric current of a particle moving under the effect of the potential of an anisotropic harmonic oscillator. Exact analytical expressions have been obtained for the distribution of the current density, the current lines, and the magnetic susceptibility. The dependence of the pattern of the induced current on the degree of excitation of the quantum states and the anisotropy of the potential has been analyzed. The presence of both diamagntic and paramagnetic loop currents has been demonstrated. The expressions for the magnetic susceptibility and the induced current obtained for an anisotropic oscillator can be used in calculations of the magnetic properties of molecules in a basis of ellipsoidal Gaussian functions.Leningrad State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 39–46, March–April, 1991.     

On the possibility of quantum beats in the total fluorescence of large molecules

The temporal evolution of the total emission from excited electronic states of a large molecule which corresponds to the statistical limit for radiationless relaxation is considered within the two-discrete-states model. It is shown that quantum beats in total (spectrally unresolved) emission may be revealed when the excited discrete levels differ in their rate constants for radiationless relaxation even if they have equal rate constants for radiative decay.     

Density-functional calculations of relativistic spin-orbit effects on nuclear magnetic shielding in paramagnetic molecules

Terms arising from the relativistic spin-orbit effect on both hyperfine and Zeeman interactions are introduced to density-functional theory calculation of nuclear magnetic shielding in paramagnetic molecules. The theory is a generalization of the former nonrelativistic formulation for doublet systems and is consistent to O(alpha4), the fourth power of the fine structure constant, for the spin-orbit terms. The new temperature-dependent terms arise from the deviation of the electronic g tensor from the free-electron g value as well as spin-orbit corrections to hyperfine coupling tensor A, the latter introduced in the present work. In particular, the new contributions include a redefined isotropic pseudocontact contribution that consists of effects due to both the g tensor and spin-orbit corrections to hyperfine coupling. The implementation of the spin-orbit terms makes use of all-electron atomic mean-field operators and/or spin-orbit pseudopotentials. Sample results are given for group-9 metallocenes and a nitroxide radical. The new O(alpha4) corrections are found significant for the metallocene systems while they obtain small values for the nitroxide radical. For the isotropic shifts, none of the three beyond-leading-order hyperfine contributions are negligible.     

Calculation of the electric hypershielding at the nuclei of molecules in a strong magnetic field

The third-rank electric hypershielding at the nuclei of 14 small molecules has been evaluated at the Hartree-Fock level of accuracy, by a pointwise procedure for the geometrical derivatives of magnetic susceptibilities and by a straightforward use of its definition within the Rayleigh-Schrodinger perturbation theory. The connection between these two quantities is provided by the Hellmann-Feynman theorem. The magnetically induced hypershielding at the nuclei accounts for distortion of molecular geometry caused by strong magnetic fields and for related changes of magnetic susceptibility. In homonuclear diatomics H(2), N(2), and F(2), a field along the bond direction squeezes the electron cloud toward the center, determining shorter but stronger bond. It is shown that constraints for rotational and translational invariances and hypervirial theorems provide a natural criterion for Hartree-Fock quality of computed nuclear electric hypershielding.     

Quantum-mechanical investigation of the properties of the molecules and ions of acetals in a strong electric field

Theoretical and Experimental Chemistry -     

On the magnetic alignment of metal ions in a DNA-mimic double helix

We computed by spin-polarized DFT the structure and the electronic properties of an infinite periodic wire constituted of planar Cu-bridged hydroxypyridone chelator base pairs and of a similarly stacked finite dimer. The Cu centers undergo electronic hybridization with the bases. There is an unpaired spin per plane, and the majority-spins manifest ordering: The ferromagnetic and antiferromagnetic phases are energetically degenerate. The total magnetization of the ferromagnetic wire depends linearly on the number of planes in the stack. The combination of interplane spin coupling and intraplane metal-hydroxypyridone coupling makes this system very appealing for electronic and magnetic device exploitation.     

On the calculation of average magnetic susceptibility for anistropic paramagnetic systems

It is shown that the expression $\text{x}$=$\text{1}\text{3}$x_|+$\text{2}\text{3}$x_⊥ gives fairly incorrect results when used in the saturation region for highly paramagnetic anistropic systems. Explicit expressions for the average magnetic susceptibility in the saturation region are suggested, which besides being extremely accurate, involve computation of the susceptibility only in 3 or 4 fixed directions.     

Picosecond water dynamics adjacent to charged paramagnetic ions measured by magnetic relaxation dispersion

Measurements of water-proton spin-lattice relaxation rate constants as a function of magnetic field strength [magnetic relaxation dispersion (MRD)] in aqueous solutions of paramagnetic solutes reveal a peak in the MRD profile. These previously unobserved peaks require that the time correlation functions describing the water-proton-electron dipolar coupling have a periodic contribution. In aqueous solutions of iron(III) ion the peak corresponds to a frequency of 8.7 cm-1, which the authors ascribe to the motion of water participating in the second coordination sphere of the triply charged solute ion. Similar peaks of weaker intensity in the same time range are observed for aqueous solutions of chromium(III) chloride as well as for ion pairs formed by ammonium ion with trioxalatochromate(III) ion. The widths of the dispersion peaks are consistent with a lifetime for the periodic motion in the range of 5 ps or longer.     

Cholesterol increases the magnetic aligning of bicellar disks from an aqueous mixture of DMPC and DMPE-DTPA with complexed thulium ions

Aqueous mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-diethylenetriamine pentaacetate (DMPE-DTPA) with complexed thulium ions (Tm(3+)), and cholesterol with varying molar ratio were studied at different temperatures in the presence and absence of a magnetic field. For mixtures without cholesterol weakly magnetically alignable small disks, so-called bicelles, are formed at temperatures below the phase transition temperature (5-22 °C), as shown by cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). In presence of 16 mol % cholesterol the disk size and the magnetic alignability were larger within the entire temperature range studied (5-40 °C). Cholesterol acts as a spacer between DMPE-DTPA with complexed Tm(3+), allowing these molecules to integrate more frequently into the planar part of the bicelles. Replacing DMPC partially by cholesterol thus lead to an increase in magnetic aligning by a higher amount of the magnetic handles (Tm(3+) complexed to DMPE-DTPA) in the plane and by an increased number of phospholipids in the enlarged bicelles. The magnetic aligning was most pronounced at 5 °C. The temperature-dependent structural changes of the DMPC/cholesterol/DMPE-DTPA/Tm(3+) aqueous mixtures are complex, including the transient appearance of holes in the disks at intermediate temperatures.