A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys

First-principles, density-functional-based electronic structure calculations are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3} and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential approximation method in the atomic sphere approximation (KKR-ASA CPA). As a function of decreasing C at%, we find a steady decrease in the lattice constant and bulk modulus in either alloys. However, the pressure derivative of the bulk modulus displays an opposite trend. Following the Debye model, which relates the pressure derivative of the bulk modulus with the average phonon frequency of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys posses a different phonon spectra in comparison to its MgCNi_{3} counterparts. This is further justified by the marked similarity we find in the electronic structure properties such as the variation in the density of states and the Hopfield parameters calculated for these alloys. The effects on the equation of state parameters and the density of states at the Fermi energy, for partial replacement of Mg by Zn are also discussed.Comment: 19 pages, 15 figure

Phonon spectrum and soft-mode behavior of MgCNi_3

Temperature dependent inelastic neutron-scattering measurements of the generalized phonon density-of-states for superconducting MgCNi_3, T_c=8 K, give evidence for a soft-mode behavior of low-frequency Ni phonon modes. Results are compared with ab initio density functional calculations which suggest an incipient lattice instability of the stoichiometric compound with respect to Ni vibrations orthogonal to the Ni-C bond direction.Comment: 4 pages, 5 figure

Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh

Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature induced metamagnetic phase transition, which experimentally is observed for stoichiometric alpha-FeRh. A first-principle spin-based model allows to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange parameters leads to a realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.

Mast cell glycosaminoglycans

Mast cells contain granules packed with a mixture of proteins that are released on degranulation. The proteoglycan serglycin carries an array of glycosaminoglycan (GAG) side chains, sometimes heparin, sometimes chondroitin or dermatan sulphate. Tight packing of granule proteins is dependent on the presence of serglycin carrying these GAGs. The GAGs of mast cells were most intensively studied in the 1970s and 1980s, and though something is known about the fine structure of chondroitin sulphate and dermatan sulphate in mast cells, little is understood about the composition of the heparin/heparan sulphate chains. Recent emphasis on the analysis of mast cell heparin from different species and tissues, arising from the use of this GAG in medicine, lead to the question of whether variations within heparin structures between mast cell populations are as significant as variations in the mix of chondroitins and heparins

[Br-76]BMK-I-152, a non-peptide analogue for PET imaging of corticotropin-releasing hormone type 1 receptor (CRHR1)

The study of corticotropin-releasing hormone is of significant interest in mental health. We have developed a radiobromination procedure for the preparation of [Br-76]BMK-I-152, a high-affinity corticotropin-releasing hormone type 1 receptor antagonist. The radiobromination procedure resulted in the formation of two radiobrominated products from the same trialkyltin precursor. Utilizing the results of several reaction conditions and the chromatographic and mass spectral data obtained from Waters Acquity and Q-TOF, we determined that both 3-bromo and 4-bromo isomers could be obtained. The authentic sample of the 3-bromo isomer was prepared to confirm the identity of a previously unknown radioactive side product; affinity assays revealed that the 4-bromo isomer had similar to 70 times higher affinity than that of the 3-bromo compound. By manipulation of reaction conditions, the individual products could be selected. Under no-carrier-added conditions at room temperature in aqueous acetonitrile, the major radioactive product (>80%) was identified as the 3-[Br-76]bromo-4-tributylstannyl analogue of BMK-I-152. The 4-[Br-76]bromo isomer accounted for less than 1% of the total activity. The 3-[Br-76]bromo BMK-I-152 could be obtained by treating this intermediate with trifluoroacetic acid to effect removal of the trialkyltin. if the radiobromination was conducted after first evaporating the water from the aqueous ammonium hydroxide solution of [Br-76]bromide, the desired 4-[Br-76]bromo isomer was obtained with a 58% radiochemical yield