SciCombinator

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Concept: Magnetic susceptibility

284

Disadvantaged social environments are associated with adverse health outcomes. This has been attributed, in part, to chronic stress. Telomere length (TL) has been used as a biomarker of chronic stress: TL is shorter in adults in a variety of contexts, including disadvantaged social standing and depression. We use data from 40, 9-y-old boys participating in the Fragile Families and Child Wellbeing Study to extend this observation to African American children. We report that exposure to disadvantaged environments is associated with reduced TL by age 9 y. We document significant associations between low income, low maternal education, unstable family structure, and harsh parenting and TL. These effects were moderated by genetic variants in serotonergic and dopaminergic pathways. Consistent with the differential susceptibility hypothesis, subjects with the highest genetic sensitivity scores had the shortest TL when exposed to disadvantaged social environments and the longest TL when exposed to advantaged environments.

Concepts: Telomere, Child, The Fragile, Scientific method, Sociology, Family, Magnetic susceptibility, Highly sensitive person

28

The synthesis of the novel macrocyclic octadentate amino-thiophenolate ligand H(2)L2 (3,7,11,19,23,27-hexaaza-33,34-dithiol-15,31-di(tert-butyl)-tricyclo[27,3,1(13.17)]-tetratriaconta-1(32),13,15,17(34),29,30-hexane) and its ability to support binuclear nickel(ii) complexes with dithiolato-bridged square-pyramidal Ni(II) ions are reported. H(2)L2 is obtained as the hexahydrobromide salt from a Schiff-base condensation reaction between 1,2-bis(4-tert-butyl-2,6-diformylphenylthio)ethane and bis(3-aminopropyl)amine followed by two successive reductions with NaBH(4) and Na/NH(3). The ligand forms a green, paramagnetic, binuclear nickel(ii) complex dication [Ni(II)(2)L2](2+), which can be isolated as a ClO(4)(-) () or BPh(4)(-) salt (). The binuclear nickel(ii) complex contains a central N(3)Ni(μ-S)(2)NiN(3) core with two square-pyramidal coordinated Ni(II) ions. The [Ni(2)L2](2+) dication does not bind further coligands, in striking contrast to the behaviour of the parent [Ni(2)L1](2+) dication supported by the smaller (L1)(2-) macrocycle (containing diethylenetriamine in place of the dipropylenetriamine units) which readily binds a variety of other coligands (L') to form bisoctahedral [Ni(2)L1(L')](+) structures. The unusual behaviour of relates to two different N configurations which leads to a steric shielding of the third bridging position by the CH(2)-groups of the dipropylenetriamine chains. An analysis of the temperature-dependent magnetic susceptibility data of reveals the presence of a weak antiferromagnetic exchange interaction between the spins of the nickel(ii) ions with a value for the magnetic exchange coupling constant J of -23.5 cm(-1) (H = -2JS(1)S(2)). These results are further substantiated by DFT calculations.

Concepts: Porphyrin, Permeability, Antiferromagnetism, Paramagnetism, Magnetic susceptibility, Aldol condensation, Ferromagnetism, Magnetism

28

A detailed magnetization study for the novel FeSe superconductor is carried out to investigate the behavior of the intrinsic magnetic susceptibility χ in the normal state with temperature and under hydrostatic pressure. The temperature dependences of χ and its anisotropy Δχ = χ(‖) - χ(⊥) are measured for FeSe single crystals in the temperature range 4.2-300 K, and a substantial growth of susceptibility with temperature is revealed. The observed anisotropy Δχ is very large and comparable to the averaged susceptibility at low temperatures. For a polycrystalline sample of FeSe, the significant pressure effect on χ is determined to be essentially dependent on temperature. Ab initio calculations of the pressure-dependent electronic structure and magnetic susceptibility indicate that FeSe is close to magnetic instability, with dominating enhanced spin paramagnetism. The calculated paramagnetic susceptibility exhibits a strong dependence on the unit cell volume and especially on the height Z of chalcogen species from the Fe plane. The change of Z under pressure determines a large positive pressure effect on χ, which is observed at low temperatures. It is shown that the literature experimental data on the strong and nonmonotonic pressure dependence of the superconducting transition temperature in FeSe correlate qualitatively with the calculated behavior of the density of electronic states at the Fermi level.

Concepts: Ideal gas, Magnetic susceptibility, Magnetic field, Permeability, Condensed matter physics, Thermodynamics, Magnetism, Fundamental physics concepts

28

We herein present the synthesis and magneto-structural study of a new family of heterobimetallic chains of general formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n)·pnH(2)O [dmbpy = 4,4'-dimethyl-2,2'-bipyridine; M = Mn (2), Cu (3), Ni (4) and Co (5) with p = 4 (2), 3 (3), 9 (4) and 3.5 (5)] which were prepared by using the mononuclear PPh(4)[Fe(III)(dmbpy)(CN)(4)]·3H(2)O (1) building block (PPh(4)(+) = tetraphenylphosphonium) as a ligand toward fully solvated M(II) ions. The structure of 1 consists of discrete [Fe(III)(dmbpy)(CN)(4)](-) anions, tetraphenylphosphonium cations and noncoordinated water molecules. Complexes 2-5 are isostructural compounds whose structure consists of neutral 4,2-wave like heterobimetallic chains of formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n) where the [Fe(III)(dmbpy)(CN)(4)](-) entity adopts a bis-monodentate coordination mode toward trans-[M(II)(H(2)O)(2)] units through two of its four cyanide groups in cis positions. 1 exhibits the magnetic behaviour of magnetically isolated six-coordinate low-spin Fe(iii) complexes with an important orbital contribution. 2 behaves as ferrimagnetic Fe(III)(2)Mn(II) chains, whereas 3-5 exhibit intrachain ferromagnetic couplings between the low-spin Fe(iii) and either Cu(ii) (3), Ni (4) or Co(ii) (5) as well as frequency-dependence of the out-of-phase ac susceptibility signals below 3.0 (3), 5.5 (4) and 5.0 K (5). The relaxation time and the energy to reverse the magnetization of 3-5 are related to the anisotropy of the M(ii) center and to the intra- and interchain magnetic interactions. Unprecedentedly in the world of cyanide-bearing complexes, 5 exhibits a double slow relaxation of the magnetization.

Concepts: Chemical formula, Time, Ferromagnetism, Magnet, Magnetic susceptibility, Magnetism, Magnetic field, Ion

28

The microcrystalline sample of a parent complex, [CoCl(2)(py)(4)], showed a single-molecule magnet (SMM) behavior with an effective activation barrier, U(eff)/k(B), of 16 K for reversal of the magnetism in the presence of a dc field of 3 kOe. Pyridine ligands having 2-4 diazo moieties, DYpy; Y = 2, 3l, 3b, and 4, were prepared and confirmed to be quintet, septet, septet, and nonet in the ground state, respectively, after irradiation. The 1 : 4 complexes, CoCl(2)(DYpy)(4); Y = 2, 3l, 3b, and 4 in frozen solutions after irradiation showed the magnetic behaviors of SMMs with total spin multiplicity, S(total) = 17/2, 25/2, 25/2, and 33/2, respectively. Hysteresis loops depending on the temperature were observed and the values of coercive force, H©, at 1.9 K were 12, 8.4, 11, and 8.1 kOe for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively. In dynamic magnetic susceptibility experiments, ac magnetic susceptibility data obeyed the Arrhenius law to give U(eff)/k(B) values of 94, 92, 93, and 87 K for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively, while the relaxation times for CoCl(2)(CYpy)(4); Y = 2 and 3l, obtained by dc magnetization decay in the range of 3.5-1.9 K slightly deviated downward from Arrhenius plots on cooling. The dynamic magnetic behaviors for CoCl(2)(CYpy)(4) including [CoCl(2)(py)(4)] and CoCl(2)(C1py)(4) suggested that the generated carbenes interacted with the cobalt ion to increase the relaxation time, τ(q), due to the spin quantum tunneling magnetization, which became larger with increasing S(total) of the complex.

Concepts: Condensed matter physics, Spin, Magnet, Permeability, Electric and magnetic fields in matter, Magnetic susceptibility, Magnetic field, Magnetism

28

The A-site ordered perovskite oxide with the formula CaCu(3)Sn(4)O(12) has been synthesized in polycrystalline form under moderate pressure conditions (3.5 GPa) in combination with high temperature (1000 °C). This oxide crystallizes in the cubic space group [Formula: see text] (no. 204) with the unit-cell parameter a = 7.64535(6) Å at 300 K. The SnO(6) network is extremely tilted, giving rise to a square planar coordination for Cu(2+) cations. The non-magnetic character of Sn(4+) offers an excellent opportunity to probe the magnetism of Cu(2+) at the A sublattice in CaCu(3)Sn(4)O(12). Magnetic susceptibility shows that this compound is ferromagnetic below T© = 10 K, which is an unusual magnetic behaviour in cuprates. This peculiar aspect has been examined by neutron powder diffraction. The refinement of the magnetic structure at 4 K indeed indicates a parallel coupling between Cu(2+) spins with a magnetic moment of 0.5 μ(B)/Cu atom.

Concepts: Fundamental physics concepts, Crystallography, Magnetic susceptibility, Magnet, Paramagnetism, Magnetic field, Neutron diffraction, Magnetism

28

Biomimetic complexes are artificially engineered molecules that aim to reduce the structural complexity of biological systems in order to unveil the key electronic and structural factors relevant to a protein’s function. In this work, a novel coordination compound () which mimics non-heme binuclear proteins was synthesized from the Schiff-base ligand HL = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinohydrazide. The crystal structure of showed that the intramolecular Fe-Fe distances (3.1-3.2 Å) were analogous to those found in non-heme binuclear ferric proteins. However, in , two methoxide groups act as bridging units for oxidized iron (Fe(3+)). Such a bridging motif is unprecedented in the biological realm. Magnetic susceptibility measurements demonstrated that is characterized by a singlet (S = 0) ground state and a very small magnetic coupling constant J (≪ -1 cm(-1)). The J value featured by differs considerably from the values observed in non-heme binuclear proteins in the oxidized form (-100 cm(-1) < J < -10 cm(-1)), which encompass oxo/hydroxo and carboxylate bridging residues. The singlet ground state of as well as the weak magnetic interaction between the two ferric cations was successfully predicted by density functional theory (DFT).

Concepts: Complex, Ligand, Oxygen, Magnetism, Density functional theory, Scientific method, Magnetic susceptibility, Iron

28

A three-dimensional coordination polymer, [Cu(btix)(2)(BF(4))(2)](n) [btix = 1,4-bis(triazol-1-ylmethyl)benzene], with antiferromagnetic interactions occurring via the organic ligand, has been prepared and characterized. It has been shown to permit the exchange of anionic species in the crystalline network with modification of the magnetic properties. Coordinated BF(4)(-) can be reversibly exchanged by different anions with (NO(3)(-) and Cl(-)) or without (PF(6)(-) and ClO(4)(-)) dynamic response of the organic ligand, which acts as the only linker between the metal centers. Interestingly, an irreversible exchange occurs with N(3)(-) anions to generate a new coordination polymer, [Cu(btix)(N(3))(2)](n), whose structure has been determined ab initio by powder X-ray diffraction, revealing a totally different connectivity between the Cu(II) centers. These structural transformations are accompanied by a change of the magnetic properties, which have been detected by electron paramagnetic resonance and magnetic susceptibility measurements.

Concepts: X-ray, Magnetic field, Chemistry, Electron, Magnetic susceptibility, Magnetic moment, Ferromagnetism, Magnetism

28

Phase images obtained with gradient echo MRI provide image contrast distinct from T1- and T2-weighted images. It is commonly assumed that the local contribution to MRI signal phase directly relates to local bulk tissue magnetic susceptibility. Here, we use Maxwell’s equations and Monte Carlo simulations to provide theoretical background to the hypothesis that the local contribution to MRI signal phase does not depend on tissue bulk magnetic susceptibility but tissue magnetic architecture–distribution of magnetic susceptibility inclusions (lipids, proteins, iron, etc.) at the cellular and subcellular levels. Specifically, we show that the regular longitudinal structures forming cylindrical axons (myelin sheaths and neurofilaments) can be locally invisible in phase images. Contrary to an expectation that the phase contrast in multiple sclerosis lesions should always increase in degree along with worsening of lesion severity (which happens for all known MR magnitude-based contrast mechanisms), we show that phase contrast can actually disappear with extreme tissue destruction. We also show that the phase contrast in multiple sclerosis lesions could be altered without loss of nervous system tissue, which happens in mild injury to the myelin sheaths or axonal neurofilaments. Moreover, we predict that the sign of phase contrast in multiple sclerosis lesions indicates the predominant type of tissue injury-myelin damage (positive sign) vs. axonal neurofilament damage (negative sign). Therefore, our theoretical and experimental results shed light on understanding the relationship between gradient echo MRI signal phase and multiple sclerosis pathology.

Concepts: Magnetic susceptibility, Axon, Maxwell's equations, Nervous system, Neuron, Multiple sclerosis, Myelin, Magnetic resonance imaging

27

Dicationic magnetic ionic liquids with heteroanionic anions allow for tunability of physicochemical properties while retaining magnetic susceptibility.

Concepts: Ionic liquid, Ions, Physical chemistry, Magnetic susceptibility