Crystallization and melting of polyethylene under high pressure. III. Mixed crystallization of two kinds of extended-chain crystals

Thermal behaviors of extended-chain crystals of polyethylene formed during various crystallization processes and conditions under about 5000kg/cm² were studied by high-pressure dilatometry and differential scanning calorimetry. The experiments indicate that by isothermal crystallization at small undercoolings for prolonged periods, the products show two endothermic peaks in the melting region of the usual extended-chain crystals. This means of the presence of a bimodal lamellar thickness distribution in the extended-chain crystals. A phase diagram has been made for pressures up to 5000 kg/cm². The experimental results confirm the existence of two kinds of extended-chain crystals, i.e., ordinary extended-chain and highly extended-chain crystals, as suggested previously by the authors.     

Palladium(0)-catalyzed cyclization of electron-deficient enynes and enediynes

In the presence of a Pd(0) precatalyst, Pd2(bq)2(nbe)2 or Pd2(dba)3, 1,6-enyne esters were heated in refluxing benzene to give cyclodimers as single regioisomers. On the other hand, the combination of the Pd(0) precatalyst and triphenyl phosphite gave rise to various cycloisomerization products depending on the substitution pattern of the enyne esters. Six-membered ring cycloisomerization products were predominantly obtained from enyne esters bearing methallyl or 2-phenyl-2-propenyl moieties, while other enyne esters afforded normal five-membered ring cycloisomerization products. Intramolecular [2 + 2 + 2] cyclocotrimerization of enediyne esters also proceeded in the presence of the Pd(0) precatalyst and triphenylphosphine to give fused cyclohexadienes.     

Calcium cycling proteins in heart failure, cardiomyopathy and arrhythmias

A growing body of evidence, including studies using genetically engineered mouse models, has shown that Ca2+ cycling and Ca2+-dependent signaling pathways play a pivotal role in cardiac hypertrophy and heart failure. In addition, recent studies identified that mutations of the genes encoding sarcoplasmic reticulum (SR) proteins cause human cardiomyopathies and lethal ventricular arrhythmias. The regulation of Ca2+ homeostasis via the SR proteins may have potential therapeutic value for heart diseases such as cardiomyopathy, heart failure and arrhythmias.     

Chemical attack of optical glass surface by formic acid vapor

The surface deterioration of glass by the attack of formic acid vapor was observed by an optical microscope, an ellipsometer, an X-ray diffractometer and an electron microprobe X-ray analyzer. The refractive index and thickness of the anomalous surface film formed on the glass were measured by means of ellipsometry. In the weathering of SF-3 and KzFS-2 glasses, the presence of water vapor in the atmosphere is necessary to produce stains on the glass surface. In the SF-3 glass with a SiO₂ network, the diffusion of Pb²⁺ and the formation of fine crystalline lead formate play important roles. In the KzFS-2 glass with a B₂O₃ network, both the destruction of the B₂O₃ network and the formation of fine crystals of boric acid play important roles. The diffusion of Pb²⁺ is not so important.     

Structures and colour properties of new red wine pigments

Two new red pigments were synthesized by nucleophilic addition of vinylphenols to malvidin 3-glucoside. The structures of the resulting pyranoanthocyanins were confirmed by electrospray-mass spectrometry and NMR spectroscopy (gHMQC, gHMBC and CIGAR experiments). By means of UV-vis spectroscopy the colour properties of the pigments were characterized; it could be demonstrated that the pyranoanthocyanins retained their red colour at pH 3.6 in model wine and were resistant to bisulfite-mediated bleaching. Finally, HPLC-MS analysis confirmed the presence of both anthocyanin-derived pigments in red wine.     

Palladium(0)-catalyzed intramolecular [2+2+2] alkyne cyclotrimerizations with electron-deficient diynes and triynes

In the presence of 2.5 mol % of [Pd(2)(dba)(3)] (dba=dibenzylideneacetone) and 5 mol % of PPh(3), nearly equimolar amounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 degrees C to afford [2+2+2] cycloadducts in moderate-to-good yields. Similarly, dimethyl trideca-2,7,12-triyne-1,13-dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd(2)(dba)(3)] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd(0) triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 degrees C or treated with PPh(3) in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh(3).     

ADDITIONAL EVIDENCE FOR BLEPHARISMIN PHOTORECEPTOR PIGMENT MEDIATING STEP-UP PHOTOPHOBIC RESPONSE OF UNICELLULAR ORGANISM, Blepharisma

Abstract— In the ciliated protozoan, Blepharisma japonicum, the pink-colored pigment (blepharismin) contained in the pigment granules is believed to be the photoreceptor pigment responsible for the step-up photophobic response. When the cells partially bleached by extrusion of the pigment granules caused by cold shocks were subsequently cultured under illuminated conditions, the pigment-less granules regenerated and the cells were further bleached (pigment content below 0.5%). The photosensitivity of such colorless cells disappeared completely. In contrast, the blepharismin pigment regenerated gradually when such colorless cells were transferred to darkness. The photosensitivity of the cells also recovered with regeneration of the pigment. We found that blepharismin pigment was not photobleached in the absence of O₂. The step-up photophobic response was also completely repressed in the absence of O₂. These results strongly confirm that blepharismin is a photoreceptor pigment mediating photobehavior of Blepharisma and that O₂ is required for the early step in the phototransduction of the light-excited pigment.     

1,4-silatropy of S-alpha-silylbenzyl thioesters: a convenient route to silyl enol and dienol ethers accompanied by C-C bond formation via thiocarbonyl ylides

A novel convenient method for the generation of thiocarbonyl ylides from readily accessible starting materials and the first synthetic application of in situ generated ylides in the synthesis of silyl enol and dienol ethers, accompanied by C-C bond formation, is described. Under completely neutral conditions without any catalyst or additive, thermal reactions of S-alpha-silylbenzyl thioesters in sealed tubes at 180 degrees C provided silyl enol and dienol ethers in good to excellent yields with high stereoselectivities. This procedure consists of a multistep reaction in a one-pot process, i.e., 1,4-silatropy of S-alpha-silylbenzyl thioesters to give thiocarbonyl ylides, 1,3-electrocyclization of the ylides to give thiiranes, and the extrusion of sulfur from thiiranes to give silyl enol and dienol ethers.     

In-situ flow-cell IRAS observation of intermediates during methanol oxidation on low-index platinum surfaces.

Structural effects on intermediate species of methanol oxidation are studied on low-index planes of platinum using in-situ infrared (IR) spectroscopy. A flow cell is designed for rapid migration of reactant and product species on the electrode surface. IR spectra show adsorption of formate and the formation of carbonate species on the Pt(111) surface at potentials higher than that of CO oxidation. The band assignments for carbonate and formate are confirmed by vibrational isotope shifts. On Pt(100), the absorption band of adsorbed formate is much smaller than that on Pt(111). On the other hand, there is no adsorbed formate on Pt(110) in the potential region examined. The band intensity of formate follows the order: Pt(111)>Pt(100)>Pt(110). This order is opposite to that of the current density in the regions of higher potential. Adsorbed formate on Pt(111) behaves like a catalyst-poisoning intermediate, like adsorbed CO.     

Slow Magnetic Relaxation of Ni(III) Complexes toward Molecular Spin Qubits

Molecule-based magnetic materials are promising candidates for molecular spin qubits, which utilize spin relaxation behavior. Various kinds of transition metal complexes with S=1/2 have been reported to act as spin qubits with long spin-spin relaxation times (T₂). However, the spin qubit properties of low-spin Ni(III) complexes are not as well known since Ni(III) compounds are often unstable. We report here the slow magnetic relaxation behavior and T₂ values for three kinds of low-spin Ni(III) based complexes with S=1/2 under magnetically diluted conditions. [Ni(cyclam)X₂]Y (cyclam=1,4,8,11-tetraazacyclotetradecane) with octahedral structures and [Ni(mnt)₂]⁻ (mnt=maleonitriledithiolate) with a square-planar structure underwent slow magnetic relaxations in the presence of a dc magnetic bias field. From electron spin resonance (ESR) spectroscopy, the Ni(III) complexes exhibited observable T₂, indicating that Ni(III) complexes are promising candidates for use as molecule-based spin qubits.