Charge states of Ca atoms in β-dicalcium silicate

In order to study the crystal structure of β‐Ca₂SiO₄, time-of-flight neutron powder diffraction experiments were carried out at temperatures between room temperature (RT) and 600 °C. Rietveld refinement at RT has shown that β‐Ca₂SiO₄ is monoclinic based on P2₁/n symmetry and two different types of Ca sites, Ca(1) and Ca(2). All interatomic distances within 3 Å were calculated, with the valences of Ca(1) with seven CaO bonds and Ca(2) with eight were estimated to be 1.87+ and 2+ by the Zachariasen-Brown-Altermatt formula (bond valence sum). Applying charge neutrality the two charge states of Ca in β‐Ca₂SiO₄ are [Ca(1)SiO₄]²⁻ and Ca(2)²⁺, respectively. Furthermore, the [Ca(1)SiO₄]²⁻ unit has the shortest Ca-O distance, and its length kept constant at 2.23 Å at all temperatures. In the short-range structure analysis at RT, the shortest Ca-O bond was also observed in a radial distribution function. These results imply that the [Ca(1)SiO₄]²⁻ unit has covalency on the shortest Ca-O in addition to Si-O.     

Electron-phonon interactions of Si100 and Ge100 superconductors with Ba atoms inside

The absolute density of states of isostructural Ba24Si100 and Ba24Ge100 near the Fermi level, which is very relevant for discussion on phonon-mediated superconductivity, is quantitatively evaluated to be 0.28 states eV?1/Ge atom and 0.18 states eV?1/Si atom by combining soft x-ray photoelectron spectroscopy and magnetic susceptibility measurements. The energetics of the anharmonic motions of the endohedral Ba atoms are also discussed on the basis of the 4d-core-level spectra. The discussion based on these important physical parameters concludes that the unique electron-phonon interactions do not occur due to the local Jahn-Teller distortion of the fragile open cage structure in the phonon-mediated BCS formalism. Compounds with a rigid cage would be essential to give rise to anticipated unique interactions as a key ingredient favored for superconducting paring.     

Modeling of life deterioration by ion bombardment of a dispenser cathode coated with an Ir/W film

We have developed the calculation method for ion bombardment traces. When an M type dispenser cathode is operated in a cathode ray tube (CRT), the surface coating film is subjected to ion bombardment due to ionized residual gas. With long-time use, the coating film is dissipated and a change to an S type occurs. This occurrence of an S type causes a deterioration of emission and focus characteristics. A method for calculating the life time dependency of the shape of ion bombardment traces using the degree of vacuum in the tube, the grid voltage, and the cathode current was studied. The calculated results and measured results were in close agreement. As a result, it was confirmed that modeling is possible using (1) an electron and ion beam trajectory calculation program, and (2) formulas for calculating the ionization cross-section and sputtering yield.     

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l ‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d ,l ‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T_g = approximately ?40 °C). Successive polymerization of l ‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (T_m = approximately 150 °C) for the crystalline PLLA segments and still low T_g (approximately ?30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their T_m as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 489–495     

Influence of cationic antibiotics on phase behavior of rough-form lipopolysaccharide

The rough-form lipopolysaccharide (LPS) interacted with cationic antibiotic polymyxin B and gramicidin S in solution, and showed altered thermotropic phase behavior and viscoelasticity. The phase behavior was measured by differential scanning calorimetry and quartz crystal microbalance (QCM). Addition of polymyxin B of up to 0.5 mg/mL to the 5.0 mg/mL LPS solution increased gel-to-liquid crystalline phase transition enthalpy (ΔH) and raised the transition temperature (t_max). The further addition of polymyxin B reduced the ΔH value. Gramicidin S produced a different effect, whereby a minor addition reduced t_max and ΔH value of the LPS. The LPS film on the platinum electrode of the QCM indicated a downward shift of resonant frequency and an upward shift of resonant resistance when in contact with the antibiotic solution. An interpretation of these variations is that the LPS on the QCM electrode changed not only film weight, but also viscoelasticity owing to contact with the antibiotic solution. The different effects between the antibiotics between polymyxin B and gramicidin S on the LPS are induced by the difference of the governing effect. Polymyxin B interacts with the LPS electrostatically, whereas gramicidin S interacts by hydrophobic moieties.     

Total synthesis of cyclic ADP-carbocyclic-ribose, a stable mimic of Ca2+-mobilizing second messenger cyclic ADP-ribose

The synthesis of cyclic ADP-carbocyclic-ribose (cADPcR, 4) designed as a stable mimic of cyclic ADP-ribose (cADPR, 1), a Ca2+-mobilizing second messenger, was achieved using as the key step a condensation reaction with the phenylthiophosphate-type substrate 14 to form an intramolecular pyrophosphate linkage. The N-1-carbocyclic-ribosyladenosine derivative 16 was prepared via the condensation between the imidazole nucleoside derivative 17, prepared from AICA-riboside (19), and the readily available optically active carbocyclic amine 18. Compound 16 was then converted to the corresponding 5' '-phosphoryl-5'-phenylthiophosphate derivatives 14. Treatment of 14 with AgNO3 in the presence of molecular sieves (3 A) in pyridine at room temperature gave the desired cyclization product 32 in 93% yield, and subsequent acidic treatment provided the target cADPcR (4). This represents a general method for synthesizing biologically important cyclic nucleotides of this type. 1H NMR analysis of cADPcR suggested that its conformation in aqueous medium is similar to that of cADPR. cADPcR, unlike cADPR, was stable under neutral and acidic conditions, where under basic conditions, it formed the Dimroth-rearranged N6-cyclized product 34. cADPcR was also stable in rat brain membrane homogenate which has cADPR degradation activity. Furthermore, cADPcR was resistant to the hydrolysis by CD38 cADPR hydrolase, while cADPR was rapidly hydrolyzed under the same conditions. When cADPcR was injected into sea urchin eggs, it caused a significant release of Ca2+ in the cells, an effect considerably stronger than that of cADPR. Thus, cADPcR was identified as a stable mimic of cADPR.