Electronic structure and bonding in antimony and its high pressure phases

The effects of pressure on the electronic structure and on the bonding properties of Sb are studied by first-principles electronic structure methods. A commensurate approximate structure is used in the calculations for the modulated incommensurate Sb-II phase. It is found that the overlap of s and p bands increases with increasing pressure resulting in pressure-induced metallization of Sb. Analyses based on the electron localization function show that there is no chemical bond between the chain atoms of a previously suggested Sb-II structure. The high total energy of this structure with respect to other structures considered is a result of the absence of this binding.

Electronic structure and thermodynamic properties of CeRh(2)Sn(4) and LaRh(2)Sn(4)

The electronic structure and thermodynamic properties of CeRh(2)Sn(4) and LaRh(2)Sn(4) are reported. The crystal structure of CeRh(2)Sn(4) has been determined from single-crystal diffraction experiments. The Ce core-level x-ray photoemission spectra and Ce L(III) x-ray absorption data unanimously indicate a stable trivalent state of the Ce ions in CeRh(2)Sn(4), consistent with static magnetic susceptibility. Thermodynamic measurements for CeRh(2)Sn(4) show a noncollinear antiferromagnetic ordering with a ferromagnetic component at T(N)≈3.2 K. There is evidence for spin fluctuations in both CeRh(2)Sn(4) and LaRh(2)Sn(4). A Fermi surface analysis reveals sections, which could generate 'nesting' instabilities and be responsible for the spin fluctuation effects. Both CeRh(2)Sn(4) and LaRh(2)Sn(4) exhibit slight homogeneity ranges and can be described by RE(1+x)Rh(2)Sn(4-x), where [Formula: see text] for Ce and [Formula: see text] in the case of La. Implantation of additional Ce atoms into the CeRh(2)Sn(4) structure leads to a distinct lowering of T(N) and the weakening of the ferromagnetic component of the magnetic ground state, whereas for the La-based systems the alloying reduces the strong diamagnetism.

Superconductivity and field-induced magnetism in SrFe_{1.75}Co_{0.25}As_{2}

Using muon-spin rotation, we studied the in-plane (lambda_{ab}) and the out of plane (lambda_{c}) magnetic field penetration depth in SrFe_{1.75}Co_{0.25}As_{2} (T_{c} approximately 13.3 K). The penetration depth anisotropy gamma_{lambda} = lambda_{c}/lambda_{ab} increases from gamma_{lambda} approximately 2.1 at T_{c} to 2.7 at 1.6 K. The mean internal field in the superconducting state increases with decreasing temperature, just opposite to the diamagnetic response seen in magnetization experiments. This unusual behavior suggests that the external field induces a magnetic order which is maintained throughout the whole sample volume.

Superconducting state in SrFe2-xCoxAs2 by internal doping of the iron arsenide layers

In the strontium iron-cobalt arsenides SrFe2-xCoxAs2 (0.2 < or = x < or = 0.4) superconductivity with T_{c} up to 20 K is observed in magnetic susceptibility, electrical resistivity, and specific heat data. This first observation of bulk superconductivity induced by electron doping in this family of compounds-despite strong disorder in the Fe-As layer-favors an itinerant electronic theory in contrast to the strongly correlated cuprates and renders a p- or d-wave pairing unlikely. The magnetic ordering present in SrFe2As2 is rapidly suppressed by substitution of Fe by Co. Density functional theory calculations show that this is due to a rigid downshift of the Fe-3d_{x;{2}-y;{2}}-related band edge in the density of states.

Modified kagome physics in the natural spin-1/2 kagome lattice systems: kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2

The recently discovered natural minerals Cu3Zn(OH)6Cl2 and Cu3Mg(OH)6Cl2 are spin 1/2 systems with an ideal kagome geometry. Based on electronic structure calculations, we develop a realistic model which includes couplings across the kagome hexagons beyond the original kagome model that are intrinsic in real kagome materials. Exact diagonalization studies for the derived model reveal a strong impact of these couplings on the magnetic ground state. Our predictions could be compared to and supplied with neutron scattering, thermodynamic data, and NMR data.

The in vitro anti-denaturation effects induced by natural products and non-steroidal compounds in heat treated (immunogenic) bovine serum albumin is proposed as a screening assay for the detection of anti-inflammatory compounds, without the use of animals, in the early stages of the drug discovery process

There are emerging ethical issues with regards to the use of animals in the early stages of drug discovery for anti-inflammatory and degenerative diseases from natural products using the activity-directed isolation pathways when many compounds (eg > 100) are present in the crude extract or fraction and are to be tested The above-mentioned is the main reason for proposing the use of the in vitro anti-denaturation (stabilization) effects of heat treated (immunogenic) bovine serum albumin (BSA) as an assay. Current methods used for detecting and isolating a wide range of anti-inflammatory compounds in the early stages of the drug discovery process utilize a large number of animals. When BSA is heated and is undergoing denaturation, it expresses antigens associated to Type III hypersensitive reaction and which are related to diseases such as serum sickness, glomerulonephritis, rheumatoid arthritis and systemic lupus erythematosus. Thus, the assay that is being proposed should be applicable to the discovery of drugs for treating the above mentioned diseases and others, once the compounds stabilize the denaturation process.

Anisotropic multiband many-body interactions in LuNi2B2C

We present a comprehensive de Haas-van Alphen study on the nonmagnetic borocarbide superconductor LuNi2B2C. The analysis of the angular-dependent effective masses for different bands in combination with full-potential density functional calculations allowed us to determine the mass-enhancement factors, lambda, for the different electronic bands and their wave-vector dependences. Our data clearly show the anisotropic multiband character of the superconductivity in LuNi2B2C.

Quasi-one-dimensional magnetism driven by unusual orbital ordering in CuSb2O6

Essentially all undoped cuprates exhibit a quasiplanar, fourfold Cu-O coordination responsible for the magnetically active antibonding 3d(x(2)-y(2)) like state. Here, we present an electronic structure study for CuSb(2)O(6) that reveals, in contrast, a half-filled 3d(3z(2)-r(2)) orbital. This hitherto unobserved ground state originates from a competition of in- and out-of-plaquette orbitals where the strong Coulomb repulsion drives the surprising and unique orbital ordering. This, in turn, gives rise to an unexpected quasi-one-dimensional magnetic behavior. Our results provide a consistent explanation of recent thermodynamical and neutron diffraction measurements.

Superconductivity in the platinum germanides MPt4Ge12 (M = rare-earth or alkaline-earth metal) with filled skutterudite structure

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The crystal structure and composition were investigated by x-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3 K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet ground state is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower Tc was observed for SrPt4Ge12 and BaPt4Ge12.

Ferromagnetism induced by orbital order in the charge-transfer insulator Cs2AgF4: an electronic structure study

Cs2AgF4 was proposed to be an orbitally ordered ferromagnet based on recent neutron scattering data. Here, we report a detailed electronic structure study within the local spin density approximation also including strong Coulomb repulsion U. We investigate the influence of an orthorhombic distortion of the Ag environment and the importance of the on-site Coulomb repulsion. We find good quantitative agreement with both the experimentally observed exchange coupling and structural changes. Thus, our results strongly support that Cs2AgF4 is a strongly correlated charge-transfer insulator where the ferromagnetism is driven by orbital order.

Frustrated cuprate route from antiferromagnetic to ferromagnetic spin-1/2 Heisenberg chains: Li2ZrCuO4 as a missing link near the quantum critical point

From thermodynamics, local spin density approximation+Hubbard U studies and exact diagonalizations of a five-band Hubbard model on CuO2 stripes we find that Li2ZrCuO4 (Li2CuZrO4 in traditional notation) is close to a ferromagnetic critical point. Analyzing its susceptibility chi(T) and specific heat cp(T,H) within a Heisenberg model, we show that the ratio of the 2nd to the 1st neighbor exchange integrals alpha=-J2/J1 approximately 0.3 is close to the critical value alphac=1/4. Comparing with related chain cuprates we explain the rather strong field dependence of cp, the monotonic downshift of the peak of chi(T), and its increase for alpha-->alphac+0.

A critical review of the therapeutic potential of dibenzyl trisulphide isolated from Petiveria alliacea L (guinea hen weed, anamu)

The data compiled in the present review on dibenzyl trisulphide (DTS) isolated from Petiveria alliacea L (the guinea hen weed or anamu) revealed that the compound and its derivatives could be of tremendous pharmaceutical interest. The mode of action elucidated for DTS revealed that it is a mitogen activated protein extracellular regulated kinases 1 and 2 (MAPKinases erk1 and erk 2) signal transduction molecule. Dibenzyl trisulphide caused hyper-phosphorylation of growth factor induced MAPKinases (erk 1 and erk 2) phosphorylation, a process critical for the improvement of long term memory, and is implicated in neuronal growth. Dibenzyl trisulphide and its derivatives exhibited potent anti-proliferation/cytotoxic activity on a wide range of cancer cell lines. The cytotoxic activity of DTS was increased by 70-1000 fold when bound to albumin in vitro. Dibenzyl trisulphide seems to have a cytokine switching mechanism in which it down regulates cytokines from the Type I helper cells (Th -1 cell) pathway which contained several pro-inflammatory cytokines and up-regulates those on the Type 2 helper cells (Th-2) pathway. The trisulphide up-regulates some reticuloendothelial system parameters eg granulocyte counts and increased thymic and Peyer's patches masses via cell proliferation processes which are known to be regulated via the MAPKinase signal transduction pathway. When the zygotes ofAsternia pectinifera (Starfish) were exposed to DTS at concentration of 10 mM, a dose lethal to all cancer cells tested, it was observed that the sensitive process of protein biosynthesis was not affected Similarly, the proliferation of the HOFA human fibroblast, a noncancerous cell line, was not severely affected by DTS at 8.9 microM over seven days, a concentration also lethal to most cancer cell lines tested The implications of the findings will be highlighted in the present review.