Ogawa’s nipponium and its re-assignment to rhenium

Foundations of Chemistry - We re-examine the history of the element “nipponium” discovered by a Japanese chemist Masataka Ogawa in 1908. Since 1996 H.K. Yoshihara has made extensive...     

Liquid structures of 1-butyl-3-methylimidazolium tetrafluoroborate and carbon dioxide mixtures by X-ray diffraction measurements

X-ray diffraction measurements for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF₄], mixed with CO₂ were carried out at high pressures using our developed polymer cell. The intermolecular distribution functions obtained for [BMIM][BF₄]–CO₂ mixtures showed that CO₂ molecules are preferentially solvated to the [BF₄]⁻ anion. The similar preferential solvation was previously observed in analogous 1-btuyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF₆], with a different anion, which is in harmony with the present results in [BMIM][BF₄]–CO₂.     

Fluorescence quenching detection of peanut agglutinin based on photoluminescent silole-core carbosilane dendrimer peripherally functionalized with lactose

A glycocluster peripherally functionalized with a lactose (Lac: Galβ1→4Glcβ1–) derivative possessing a silole moiety as a luminophore was synthesized. The photoluminescence spectrum of the glycocluster showed extremely strong emission at 474 nm and the absolute quantum yield was estimated to be 92% in distilled water. The emission intensity was decreased by increasing the amount of peanut agglutinin (PNA), a lactose-binding lectin, and plots of the relative fluorescence intensity revealed a decline of 95% in emission intensity. Fluorescence quenching of the glycocluster upon mixing with PNA could be easily observed by the naked eye under UV irradiation, whereas no distinct change in fluorescence properties of the glycocluster was observed when wheat germ agglutinin (WGA) was employed.     

Pochonins K-P: new radicicol analogues from Pochonia chlamydosporia var. chlamydosporia and their WNT-5A expression inhibitory activities

WNT-5A, a secretory glycoprotein, is related to the proliferation of dermal papilla cells. To develop a hair-growth stimulant, we have been searching for an inhibitor of WNT-5A expression, and have identified an active compound, radicicol (1), and isolated six new radicicol analogues, pochonins K-P (2-7), together with ten known radicicol analogues, including monorden analogue-1 (8), pochonin E (9), and pochonin F (10), from a culture broth of the fungus Pochonia chlamydosporia TF-0480. This report describes the structural elucidation of 2-7, determination of the stereochemistries of 8-10, and their biological activities against WNT-5A.     

Pressure-induced structural, magnetic, and transport transitions in the two-legged ladder Sr3Fe2O5

The layered compound SrFeO(2) with an FeO(4) square-planar motif exhibits an unprecedented pressure-induced spin state transition (S = 2 to 1), together with an insulator-to-metal (I-M) and an antiferromagnetic-to-ferromagnetic (AFM-FM) transition. In this work, we have studied the pressure effect on the structural, magnetic, and transport properties of the structurally related two-legged spin ladder Sr(3)Fe(2)O(5). When pressure was applied, this material first exhibited a structural transition from Immm to Ammm at P(s) = 30 ± 2 GPa. This transition involves a phase shift of the ladder blocks from (1/2,1/2,1/2) to (0,1/2,1/2), by which a rock-salt type SrO block with a 7-fold coordination around Sr changes into a CsCl-type block with 8-fold coordination, allowing a significant reduction of volume. However, the S = 2 antiferromagnetic state stays the same. Next, a spin state transition from S = 2 to S = 1, along with an AFM-FM transition, was observed at P(c) = 34 ± 2 GPa, similar to that of SrFeO(2). A sign of an I-M transition was also observed at pressure around P(c). These results suggest a generality of the spin state transition in square planar coordinated S = 2 irons of n-legged ladder series Sr(n+1)Fe(n)O(2n+1) (n = 1, 2, 3, ...). It appears that the structural transition independently occurs without respect to other transitions. The necessary conditions for a structural transition of this type and possible candidate materials are discussed.     

Synthesis of uniform and dispersive calcium carbonate nanoparticles in a protein cage through control of electrostatic potential

We have synthesized calcium carbonate nanoparticles (Ca-NPs) in the cavity of a cage-shaped protein, apoferritin, by regulating the electrostatic potential of the molecule. The electrostatic potential in the cavity was controlled by pH changes resulting from changes in the dissolved carbon dioxide (CO(2)) concentration in the reaction solution. Recombinant L-apoferritin was mixed with a suspension of calcium carbonate (CaCO(3)), and the mixture was pressurized with gaseous CO(2) at 2 MPa. The pH of the solution decreased from 9.3 to 4.4; the CaCO(3) dissolved during pressurization, and then precipitated after the pressure was reduced to ambient. After repeating the pressurization/depressurization process three times, about 70% of the apoferritin molecules were found to contain nanoparticles with an average diameter of 5.8 ± 1.2 nm in their cavity. Energy-dispersive X-ray spectroscopy and electron diffraction analysis showed that the nanoparticles were calcite, one of the most stable crystal forms of CaCO(3). Electrostatic potential calculations revealed a transition in the potential in the apoferritin cavity, from negative to positive, below pH 4.4. The electrostatic potential change because of the change in pH was crucial for ion accumulation. Since the Ca-NPs synthesized by this method were coated with a protein shell, the particles were stably dispersed in solution and did not form aggregates. These Ca-NPs may be useful for medical applications such as synthetic bone scaffolds.     

Specific Induced Circular Dichroism and Enhanced B to Z Transitions of Duplexes Stabilized by Chromophore‐Linked Alkynylnucleoside Residues

We have developed an induced circular dichroism (ICD) probe with a chromophore‐linked alkynyldeoxyribose skeleton for analyzing higher‐order structures of DNA duplexes in the visible‐light region. When CG‐repeated oligonucleotides (ODNs) with the probe at their 5′ ends adopted Z‐form duplexes at a high NaCl concentration, strong ICD signals were observed at the absorptive region of the chromophore. On the other hand, their B‐form duplexes, formed at a low NaCl concentration, produced a faint ICD signal. The specific ICD for the Z‐form duplexes was found to appear only when the chromophores were attached at the 5′ ends of each of the ODNs. Furthermore, the chromophoric alkynylnucleoside residues effectively promoted the B to Z transition of the ODN.     

Novel aziridination of olefins: direct synthesis from sulfonamides using t-BuOI

tert-Butyl hypoiodite (t-BuOI) was found to be a powerful reagent for synthesis of aziridines from olefins and sulfonamides. The aziridination of olefins was achieved by using sulfonamides with t-BuOI. Our preliminary findings represent the example of metal-free aziridination of olefins with readily accessible sulfonamides as a nitrogen source.