Orientation of molecules by magnetic field as a new source of information on their structures

A complex procedure for quantitative allowance for small but significant effects of molecular orientation by strong static magnetic fields was elaborated. A series of high-resolution ¹H NMR spectra of 1,2,3-trichloronaphthalene recorded at magnetic field strength varied over a wide range was analyzed in the framework of a unified approach with high accuracy. The spin-spin coupling constants and the dipole-dipole coupling constants for all pairs of ¹H nuclei and the anisotropy and rhombicity parameters of the magnetic susceptibility tensor of the molecule were determined. Ab initio CSGT/RHF quantum chemical calculations of this property using a wide range of conventional diffuse and polarization basis set functions were carried out. Augmentation of the basis set with polarization functions affects the values of the calculated parameters to a lesser extent compared to augmentation with diffuse functions. The results of calculations using the 6-311G(df) and 6-311++G(df) basis sets are in good agreement with the experimental values of the magnetic susceptibility anisotropy for 1,2,3-trichloronaphthalene. The advantages of the method proposed and specific features of the effects of orientation by magnetic field as a new source of information on the structure of molecules in solution are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1309–1317, August, 2006.     

Ab initio calculation of electronic circular dichroism fortrans-cyclooctene using London atomic orbitals

Summary The second-quantization magnetic dipole operator that arises when London atomic orbitals are used as basis functions is derived. In atomic units, the magnetic dipole operator is defined as the negative of the first derivative of the electronic Hamiltonian containing the interaction with the external magnetic field. It is shown that for finite basis sets, the gauge origin dependence of the resulting magnetic dipole operator is analogous to that of the exact operator, and that the derived operator converges to the exact operator in the limit of a complete basis set. It is also demonstrated that the length expression for the rotatory strength in linear response calculations gives gauge-origin-independent results. Sample calculations ontrans-cyclooctene and its fragments are presented. Compared to conventional orbitals, the basis set convergence of the rotatory strengths calculated in the length form using London atomic orbitals is favourable. The rotatory strength calculated fortrans-cyclooctene agrees nicely with the corresponding experimental circular dichroism spectrum, but the spectra for the fragment molecules show little resemblance with that oftrans-cyclooctene.Dedicated to Prof. Jan Linderberg     

Gauge invariant gaussian orbitals and the ab initio calculation of diamagnetic susceptibility for molecules

It is shown that gauge terms can be introduced into the Gaussian functions used as the basis functions for an ab initio calculation of the energy of a molecule in the presence of a uniform magnetic field so that all the integrals become independent of the origin of the vector potential. The perturbation treatment of the diamagnetic susceptibility is considered in the molecular orbital approximation. The results show that the susceptibility can be calculated using only the unperturbed orbitals and their first-order corrections. All the integrals that arise can be expressed in terms of known functions.     

Magnetic particle‐loaded polymer brushes induced by external magnetic field: A Monte Carlo simulation

The effects of applied magnetic field on the system composed of polymer brushes and magnetic particles are studied by means of Monte Carlo simulation. The direction of the applied magnetic field is chosen to be perpendicular to the substrate plane. Polymer brushes and magnetic particles are attracted to each other. The average heights of polymer brushes depend not only on the strength of applied magnetic field (H) but also on the brush grafting density (σ) and the chain length (N). The applied magnetic field influences the arrangement of magnetic particles, and in turn, the arrangement of magnetic particles affects the spatial distribution of polymer brush monomers. When the strength of the magnetic field is increased, the average height of polymer brushes will be increased accordingly. The reason is that the orientations of the magnetic moments of particles must be along the magnetic field direction, and this leads polymer brushes to rearrange along the magnetic field direction. At the same time, the chain length and the grafting density of polymer brushes have also effects on the properties of the magnetic particles, such as the magnetic particles distribution, magnetic susceptibility, and pair correlation functions. Comparisons with the experimental ones are also made, and this investigation can provide some insights into statistical properties of magnetic particle‐loaded brushes induced by external magnetic field. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1873–1881, 2010     

Intramolecular and Intermolecular Magnetic Coupling Mechanism of a Dinuclear Copper(II) Complex

Abstract. A new dinuclear complex, [Cu₂(μ_{1, 3}‐NCS)₂(Ophen)₂(OH₂)₂], (HOphen = 1, 10‐phenanthrolin‐2‐ol) was synthesized and its crystal structure was determined by X‐ray crystallography. In the complex, the Cu^II ion assumes a distorted square pyramidal arrangement and the thiocyanate anion functions as bridged ligand and Ophen as capped ligand. The analysis of the crystal structure shows that there exists a π–π stacking interaction between the adjacent complexes. The theoretical calculations reveal that the magnetic coupling pathways from the thiocyanate anions bridge ligand and the π–π stacking magnetic coupling pathway resulted in the weak ferromagnetic interactions with 2J = 18.46 cm^–1 and 2J = 10.46 cm^–1, respectively. The calculations also display that the spin delocalization and the spin polarization occur in the bridge magnetic coupling system and the π–π stacking magnetic coupling system, and the magnetic coupling mechanism of the π–π stacking can be explained with McConnell I spin‐polarization mechanism. The fitting for the data of the variable‐temperature magnetic susceptibility with dinuclear Cu^II formula gave the magnetic coupling constant 2J = 2.84 cm^–1 and zJ′ = 0.03 cm^–1, in which the 2J = 2.84 cm^–1 is attributed to the magnetic coupling from the bridge dinuclear Cu^II unit and the zJ′ = 0.03 cm^–1 is ascribed to the π–π stacking magnetic coupling system. The study may benefit to understand the magnetic coupling mechanism of π–π stacking system.     

General quantum mechanical operators. An open-ended approach for one-electron integrals with Gaussian bases

A universal computational approach for evaluating integrals over gaussian basis functions for general operators of the form is presented. The implementation is open-ended with respect to the types of basis functions (s, p, d, f, g, h…) and with respect to the integers that specify the operator. These one-electron integrals comprise operators associated with electrical and magnetic properties of molecules and include those needed to find multipole polarizabilities, multipole susceptibilities, chemical shifts, and so on. The scheme also generates the usual kinetic, nuclear attraction, and overlap operators.     

SIMPRE: A software package to calculate crystal field parameters,energy levels,and magnetic properties on mononuclear lanthanoid complexes based on charge distributions

This work presents a fortran77 code based on an effective electrostatic model of point charges around a rare earth ion. The program calculates the full set of crystal field parameters, energy levels spectrum, and wave functions, as well as the magnetic properties such as the magnetization, the temperature dependence of the magnetic susceptibility, and the Schottky contribution to the specific heat. It is designed for real systems that need not bear ideal symmetry and it is able to determine the easy axis of magnetization. Its systematic application to different coordination environments allows magneto‐structural studies. The package has already been successfully applied to several mononuclear systems with single‐molecule magnetic behavior. The determination of effective point charge parameters in these studies facilitates its application to new systems. In this article, we illustrate its usage with two example studies: (a) an ideal cubic structure coordinating a lanthanoid ion and (b) a system with slow relaxation of the magnetization, LiHo_xY_(1‐x)F₄. © 2013 Wiley Periodicals, Inc.     

Heading to photoswitchable magnets

The review concerns the strategic approaches to the photomodulation of the magnetic properties of molecular hybrid compounds combining magnetic and optical properties. The approaches developed include photocontrol of intra- and intermolecular magnetic coupling and manipulation of the effect of the photochromic sublattice on the bulk behavior of molecular magnets. In the framework of the first approach, we consider photoinduced charge-transfer phase transitions, changes in the spin state of magnetic centers, photoswitching of intramolecular exchange interactions between magnetic centers connected by a photochromic bridge, and generation of high-spin organic molecules forming high-spin groups due to intermolecular exchange interactions. In the framework of the second approach, we discuss hybrid polyfunctional compounds combining magnetic and photochromic sublattices in the same crystal lattice, as well as intercalation of organic photochromes into voids or inter-layer space of organic magnetics (or vice versa). Creation of such materials allows not only several functions to be combined in the same lattice, which is important for reducing the size of hardware components, but also these properties to be controlled and modified through synergistic effects. The results of basic research suggest that novel materials for various practical applications can be created using principles of crystal chemical engineering. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 704–721, April, 2008.     

Calculation of the Magnetic Properties of <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">f</Emphasis> Transition Metal Complexes in Terms of the Angular Overlap Model

The theory of the electronic structures and magnetic properties of mononuclear complexes of d and f transition metals was developed in a complete basis set of products of one-electron functions with the use of the parametrization adopted in the angular overlap model. It was demonstrated that the theory describes well the temperature dependences of the magnetic susceptibilities of these complexes and allows estimation of their detailed electronic structures.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 506–511.Original Russian Text Copyright © 2005 by Rakitin, Rakitina, Kalinnikov.     

Localized impurity states in the Hartree-Fock,LCAO approximation II. The F Center in KCI

We apply the techniques of a previous paper (I) to the F center in KCl. Our purpose is to place the application of Hartree-Fock methods to the F center on a firm theoretical basis by calculating in a consistent manner the magnitude and effect of approximations commonly made in less complete treatments. It is shown that the familiar point-ion approximations and crystal-field approximations with partial consideration of exchange effects are special cases of our results. We compute wave functions and energies step by step for each of the various levels of approximation possible with our model. It is found that the functions resulting from the point-ion model are not good approximations to the final wave functions. Our results show that exchange effects with at least the first two shells of nearest neighbors should be considered since they are of the same order of magnitude as terms in the point-ion model. Overlaps of the F-center function with ion functions out to sixth neighbors are considered. The absorption energy for the F center is calculated to be 0.1619 Ry as compared with the experimentally observed energy of 0.170 Ry. The magnetic hyperfine structure contact terms are calculated for the first two shells of nearest neighbor ions, using approximate orthogonalized functions, and found to be 29.7 Mc/h for the nearest neighbor K⁺ ions and 10.9 Mc/h for the next nearest neighbor Cl^? ions. The experimentally observed values are 21.6 and 7.0, respectively. Given these differences and the excessively low values of the one-electron energies, it is concluded that electronic and ionic polarization effects in the ionized crystal states must be considered to calculate accurate F-center wave functions and absolute energy levels.     

A study of dynamic quadrupolar and octupolar excitations and calculations on excited d and f states of atom and ions: He-sequence

The quadrupolar and octupolar distortion of the ions in the He-sequence caused by an external electro–magnetic field has been studied by a variation–perturbation method in the Hartree–Fock scheme. For certain frequencies singularities appear in the response of the system to the perturbation. Approximate representations for the excited d and f states have been obtained from a study of these resonances. Such a perturbation calculation has the advantage that representations of the different excited states are obtained independently. The orthogonality to all the lower lying levels of the same symmetry is not required. The only source of inaccuracy implicit in the procedure lies in the improper consideration of the inter-electronic interaction. This is corrected for by an independent calculation, which is again formulated in terms of a perturbation treatment. The resulting wave functions for the excited states are accurate in the Hartree–Fock model. Expectation values of several operators have been calculated with these corrected wave functions.     

Poly(amidoamine) dendrimer‐coated magnetic nanoparticles for the fast purification and selective enrichment of glycopeptides and glycans

Glycosylated proteins modulate various important functions of organisms. To reveal the functions of glycoproteins, in‐depth characterization studies are necessary. Although mass spectrometry is a very efficient tool for glycoproteomic and glycomic studies, efficient sample preparation methods are required prior to analyses. In the study, poly(amidoamine) dendrimer‐coated magnetic nanoparticles were presented for the specific enrichment and fast purification of glycopeptides and glycans. The enrichment and purification performance of the developed method was evaluated both at the glycopeptide, and the glycan level using several standard glycoprotein digests and released glycan samples. The poly(amidoamine) dendrimer‐coated magnetic nanoparticles not only showed selective affinity (Immunoglobulin G/Bovine Serum Albumin, 1/10 by weight) to glycopeptides and released glycans but also good sensitivity (0.4 ng/µL for Immunoglobulin G) for glycoproteomic and glycomic applications. Thirty‐five glycopeptides of Immunoglobulin G were detected after enrichment with poly(amidoamine) dendrimer‐coated magnetic nanoparticles. In addition, 55 ¹⁸O tagged deamidated glycopeptides belonging to human plasma glycoproteome were confirmed. Finally, fifty 2‐aminobenzoic acid, and 30 procainamide‐labelled human plasma N‐glycans released from human plasma glycoproteins were determined after purifications. The results indicate that the proposed enrichment and purification method using poly(amidoamine) dendrimer‐coated magnetic nanoparticles could be simply adjusted to sample preparation methods.     

Heat capacity of MnAs0.88P0.12 from 10 to 500 K: Thermodynamic properties and transitions

The heat capacity of MnAs_0.88P_0.12 has been measured by adiabatic shield calorimetry from 10 to 500 K. It is shown that very small energy changes are connected with two magnetic order-order transitions, indicating that these can be regarded as mainly “noncoupled” magnetic transitions. At higher temperatures contributions to the excess heat capacity arises from a magnetic order-disorder transition, a conversion from low- to high-spin state for manganese, and a MnP- to NiAs-type structural transition. The observed heat capacity is resolved into contributions from the different physical phenomena, and the character of the transitions is discussed. In particular it is substantiated that the dilational contribution, which includes magnetoelastic and magnetovolume terms as well as normal anharmonicity terms, plays a major role in MnAs_0.88P_0.12. The entropy of the magnetic order-disorder transition is smaller than should be expected from a complete randomization of the spins, assuming a purely magnetic transition. Thermodynamic functions have been evaluated and the respective values of C_p, {S^O_m(T) - S^O_m(0)}, and -{G^O_m(T) - H^O_m(0)}/T at 298.15 K are 68.74, 72.09, and 32.30 J K⁻¹ mole⁻¹, and at 500 K 56.05, 108.12, and 56.64 J K⁻¹ mole⁻¹.     

Janus Pyrrolopyrrole Aza-dipyrrin: Hydrogen-Bonded Assemblies and Slow Magnetic Relaxation of the Cobalt(II) Complex in the Solid State

A novel pyrrolopyrrole azadipyrrin ( Janus-PPAD ) with Janus duality was synthesized by a Schiff base–forming reaction of diketopyrrolopyrrole. The orthogonal interactions of the hydrogen-bonding ketopyrrole and metal-coordinating azadipyrrin moieties in Janus-PPAD enabled the metal ions to be arranged at regular intervals: zinc(II) and cobalt(II) coordination provided metal-coordinated Janus-PPAD dimers, which can subsequently form hydrogen-bonded one-dimensional arrays both in solution and in the solid state. The supramolecular assembly of the zinc(II) complex in solution was investigated by ¹H NMR spectroscopy based on the isodesmic model, in which a binding constant for the elongation of assemblies is constant. Owing to the tetrahedral coordination, in the solid state, the cobalt(II) complex exhibited a slow magnetic relaxation due to the negative D value of −27.1 cm⁻¹ with an effective relaxation energy barrier U_eff of 38.0 cm⁻¹. The effect of magnetic dilution on the relaxation behavior is discussed. The relaxation mechanism at low temperature was analyzed by considering spin lattice interactions and quantum tunneling effects. The easy-axis magnetic anisotropy was confirmed, and the relevant wave functions were obtained by ab initio CASSCF calculations.     

Synthesis and Properties of Oval‐Shaped Iron Oxide/Ethylene Glycol Mesostructured Nanosheets

We have demonstrated a new and facile bottom‐up protocol for the effective synthesis of oval‐shaped iron oxide/ethylene glycol (FeO_x/EG) mesostructured nanosheets. Deprotonated ethylene glycol molecules are intercalated into iron oxide layers to form an interlayer distance of 10.6 Å. These materials display some peculiar magnetic properties, such as the low Morin temperature T_M and ferromagnetism below this T_M value. CdSe/ZnS nanoparticles can be loaded onto these mesostructured nanosheets to produce nanocomposites that combine both magnetic and fluorescence functions. In addition, iron oxide/propanediol (or butanediol) mesostructured materials with increased interlayer distances can also be synthesized. The developed synthetic strategy may be extended toward the creation of other ultrathin mesostructured nanosheets.     

Applications of weighting and chirality strategies for distance geometry algorithms to an enterotoxin peptide analog

Significant improvements are made to a recent algorithm that finds molecular conformations using distance geometry on nuclear magnetic resonance data. Weighting factors for the nearest approximation of the distance matrix to a data matrix are allowed to vary between iterations of the algorithm. These changes are proportional to the error of the distance between atoms in the configuration and the nuclear magnetic resonance data bounds. The weight changes increase the rate of convergence by an order of magnitude. Penalty functions are proposed to ensure the correct chirality. Numerical results for these modifications and subsequent energy calculations using CHARMm are given for an analog of the heat stable (ST) enterotoxin peptide STh produced byE. coli in humans.     

Calculation of molecular electric and magnetic multipole moment integrals of integer and noninteger n Slater orbitals using overlap integrals

Closed formulas are established for the magnetic multipole moment integrals of integer and noninteger n Slater‐type orbitals (ISTOs and NISTOs) in terms of electric multipole moment integrals for which the analytic expressions through the overlap integrals with ISTOs and NISTOs are derived. The overlap integrals are evaluated by the use of auxiliary functions. Using the derived expressions the multipole moment integrals, and therefore the electric and magnetic properties of molecules, can be evaluated most efficiently and accurately. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Single Phase Formation,Cation Distribution,and Magnetic Characterization of Coprecipitated Nickel-Zinc Ferrites

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni_1-xZn_xFe₂O₄ nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and possible nonmagnetic impurities. The influence of zinc substitution on the magnetic exchange interactions were studied based on molecular-field theory for compositions of 0 ≤x ≤ 0.4.     

Addition Theorem and Matrix Elements of Radiative Multipole Operators

The addition theorem for radiative multipole operators, i.e., electric-dipole, electric-quadropole or magnetic-dipole, etc., is derived through a translational transformation. The addition theorem of the μth component of the angular momentum operator, L_μ (r), is also derived as a simple expression that represents a general translation of the angular momentum operator along an arbitrary orientation of a displacement vector and when this displacement is along the Z-axis. The addition theorem of the multipole operators is then used to analytically evaluate the matrix elements of the electric and magnetic multipole operators over the basis functions, the spherical Laguerre Gaussian-type function (LGTF), . The explicit and simple formulas obtained for the matrix elements of these operators are in terms of vector-coupling coefficients and LGTFs of the internuclear coordinates. The matrix element of the magnetic multipole operator is shown to be a linear combination of the matrix element of the electric multipole operator.