Elucidation of the stereochemistry of Tl+ in oxide glasses by electron spin resonance spectroscopy

The relation has been elucidated between the stereochemistry of Tl⁺ and the chemical composition of host oxide glasses by measuring the ESR of paramagnetic Tl²⁺ induced with γ-irradiation at 77 K. The spectra have been analyzed by using a new solution of the spin-Hamiltonian developed by the authors. The results indicate: (1) there are two sites for Tl⁺ in a wide variety of oxide glasses (site I and site II). Tl⁺ in site I has a heavily distorted ligand field (lone pair electrons of Tl⁺ occupy a s-p(-d) hybridized non-bonding orbital extruding in one direction). The geometry of the Tl⁺-complex in site II is nearly spherically-symmetric (lone pair electrons locate in an anti-bonding sigma orbital to which the Tl 6s atomic orbital mainly participates); (2) site I appears in the glasses where both the bridging and non-bridging oxygens coexist. Site II is observed in the other glasses; (3) a drastric change in lineshape of Tl²⁺ induced with 77 K irradiation was observed upon thermal annealing. A structural model for this change was proposed; the Tl²⁺ with an excess plus charge is stabilized by the cooperative motion of the alkali ion pairing with Tl²⁺ and intervening non-bridging oxygens, the alkali being repelled and the oxygens being attracted.     

Facile deallylation protocols for the preparation of N-unsubstituted triazoles and tetrazoles

Two facile deallylation protocols have been developed for the preparation of N-unsubstituted triazoles and tetrazoles. The first protocol is a direct deallylation using a combination of a catalytic amount of nickel complex, NiCl2(dppe), and a stoichiometric amount of Grignard reagent, tBuMgCl. The second protocol is a stepwise deallylation through consecutive reactions of isomerization and ozonolysis. The isomerization from N-allylazoles to N-vinylazoles is catalyzed by a ruthenium complex, HRuCl(CO)(PPh3)3, and the following ozonolysis of the derived N-vinyl intermediates affords N-unsubstituted azoles. These protocols can be used complementarily depending on the type of functional groups in the parent allylated azoles.     

Catalytic action of metallic salts in autoxidation and polymerization. IX. Polymerization of methyl methacrylate with sodium hexanitrocobaltate(III) in mixed solvent of acetone and water

Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na₃[Co(NO₂)₆] in a water-acetone mixed solvent gave the following over-all rate equation: R_p = 8.04 × 10⁴ exp{ ?13,500/RT} [I]^1/2[M]² (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.     

Polymerization of N-carboxy-amino acid anhydrides in the solid state. I. Polymerizability of the various α-amino acid NCAs in the solid state

The solid-state polymerization of various α-amino acid NCAs was investigated and the results were compared with those obtained by heterogeneous polymerization in acetonitrile. Essential differences were found in the polymerizability of the NCAs in these two systems. In the solid state, L-leucine NCA was the most reactive among the NCAs examined, and its reactivity was even higher than in the precipitation polymerization of acetonitrile solutions. On the other hand, glycine NCA was the most inert among the NCAs examined in the solid state. The difference between the reactivities of glycine NCA and L-alanine NCA was interpreted in terms of their crystal structures. Several kinetic features of the solid-state polymerization were studied on γ-benzyl-L -glutamate NCA.     

Synthetic studies on terpenic compounds—XI : Stereospecific total synthesis of portulal,

A stereospecific total synthesis of portulal 1 has been accomplished starting from the Diels-Alder adduct 2 from chloromethylmaleic anhydride and 1-vinylcyclohexene. Firstly 2 was converted by an efficient sequence of reactions to perhydroazulenoid lactone 5, which possesses the correct relative configuration with respect to three chiral centers out of the four present in 1. The fourth chiral center at C-6 was introduced stereospecifically together with the one-carbon substituent at C-4 by the ring formation between C-4 and C-6, and its cleavage to give an exomethylene lactone 35. At this stage the stereochemical validity of the crucial intermediate 35 was confirmed by chemical correlation with the hydroxy lactone 37 which was derived from natural 1 through a systematic degradation. Then 35 was transformed to 37 and the synthesis continued further by using 37 as a relay compound to afford 1.     

Low-barrier hydrogen bond between phosphate and the amide group in phosphopeptide

As the conversion between the monoionic (1) and diionic (2) form of the phosphate occurs, the phosphorylated peptides or proteins can not only cause the formation of a hydrogen bond between the phosphate group and the amide group but also change the strength of the hydrogen bond to form low-barrier hydrogen bonds (LBHBs). This reversible protonation of the phosphate group, which changes both the electrostatic properties of the phosphate group and the strength of the hydrogen bond, provides a possible mechanism in regulating protein function.     

Aqueous chromatographic system for separation of biomolecules using thermoresponsive polymer modified stationary phase

We have investigated a new method for HPLC using packing materials modified with a functional polymer, such as thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm-modified silica exhibits temperature-controlled hydrophilic-hydrophobic surface property changes in aqueous systems. Temperature-responsive chromatography is performed with an aqueous mobile phase without using an organic solvent. We designed ternary copolymers of NIPAAm introduced 2-(dimethyl-amino) ethyl methacrylate (DMAEMA) as a cationic monomer and butyl methacrylate (BMA) as a hydrophobic monomer. A cationic thermoresponsive hydrogel grafted surface would produce an alterable stationary phase with both thermally regulated hydrophobicity and charge density for separation of bioactive compounds. In this study, we achieved successful separation of lysozyme without the loss of bioactivity by temperature-responsive chromatography. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase, thus the separation system would have potential applications in the separation of biomolecules.     

放射性束辐照生物学效应及相关生物物理机理

介绍了β缓发粒子衰变放射性束 9C辐照处于不同贯穿深度上人类唾液腺细胞的深度存活效应。 与稳定的 12C束流相比, 放射性 9C束流在其Bragg峰区附近展示了增强的生物学效应, 即细胞的致死效率明显增强。 探讨了放射性束 9C在其Bragg峰区展示增强生物学效应的生物物理机制, 并介绍了利用另一种放射性束 8B进行辐照生物学效应研究的新进展。 最后, 提出了一些利用放射性束可进行的辐照生物学效应前沿研究。 The depth survival effect of a β delayed particle decay 9C beam on human salivary gland (HSG) cells is presented in this paper. Compared with a stable 12C ion beam, the radioactive 9C ion beam showed an enhanced biological effect, i.e., remarkably enhanced efficiency in cell killing, at the penetration depths around its Bragg peak. The biophysical mechanisms underlying the enhanced biological effect are discussed herein, and the latest progress in biological effect induced by another radioactive 8B ion beam is introduced. In the end of this paper, several topics concerning the frontier of the radiation induced biological effects using radioactive ion beams are proposed.