1,4‐Addition polymerization of 1,4‐bis(4‐benzylpyridinium)butadiyne triflate in a dipolar aprotic solvent

1,4‐Bis(4‐benzylpyridinium)butadiyne triflate was aggregated in dimethylformamide and spontaneously converted into the 1,4‐addition type of polydiacetylene. The polymerization took place in a dipolar aprotic solvent with a large dielectric constant that could enhance the aggregation of the ionic diacetylene salt through the electrostatic interaction. The molecular weight of the diacetylene was leveled off after 30 h at 80 °C to reach 1.5 × 10⁴ (number‐average molecular weight) that consisted of the 1,4‐addition type of polydiacetylene similar to polydiacetylenes obtained in the conventional solid‐state polymerization. Electron spin resonance spectra revealed that diradicals were generated at the earlier state aggregation to give rise to a solution polymerization. The UV spectra also suggested the presence of the activated aggregation associated with the polymerization as well as the eximer emission spectra. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3534–3541, 2002     

Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm₂Fe₁₇N_x, prepared by the nitrogenation of Sm₂Fe₁₇ powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm₂Fe₁₇N_x. It was found that there were large differences in thermal behavior between the starting Sm₂Fe₁₇, crystalline Sm₂Fe₁₇N_x (x≈1.7) and amorphous Sm₂Fe₁₇N_x(x～7). The thermal decomposition behavior of Sm₂Fe₁₇N_3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

Interconversion behavior of the C-H bond in the CH4+ radical cation: ab initio molecular dynamics study

Thermal motion of CH4+ is investigated by performing an ab initio molecular dynamics method with the second-order M?ller-Plesset (MP2)/6-311G** force field. In the trajectories obtained at 400 K, we have observed rapid interconversion behavior of the geometrical parameters of CH4+ with the frequency of 0.6/ps, where the C-H pair forming the small angle around 55 degrees is switched to another pair on subpicosecond time scale. The switching patterns are found to be classified into the following two types. Type 1: one C-H of the small angled C-H pair is switched to one C-H of the other C-H pair. Type 2: the small angled C-H pair is switched to the other C-H pair, which has been newly observed in the present ab initio MD calculation. The four C-H bonds of CH4+ are characterized by the long and short C-H bonds in a time region of the trajectories, and also for the time-evolution of C-H bonds such interconversion behavior is observed. The switching patterns of the geometrical parameters are compared with those in the interconversion scheme between six equivalent C2v symmetry structures of CH4+ [Paddon-Row, M. N. et al., J Am Chem Soc 1985, 107, 7696]. We have also investigated the electronic energy fluctuation due to thermal motion of CH4+. The standard deviation of total electronic energy at 400 K is evaluated to be 1.2 kcal/mol.     

ESTABLISHMENT and CHARACTERIZATION OF A MONOCLONAL ANTIBODY RECOGNIZING THE DEWAR ISOMERS OF(6–4)PHOTOPRODUCTS

Abstract— We established a monoclonal antibody(DEM–1) that recognizes UV-induced DNA damage other than cyclobutane pyrimidine dimers or(6–4)photoproducts. The binding ofDEM–1 antibody to 254 nm UV-irradiated DNA increased with subsequent exposure to UV wavelengths longer than 310 nm, whereas that of the 64M-2 antibody specific for the(6–4)photoproduct decreased with this treatment. Furthermore, the increase inDEM–1 binding was inhibited by the presence of the 64M-2 antibody during the exposure. We concluded that theDEM–1 antibody specifically recognized the Dewar photoproduct, which is the isomeric form of the(6–4)photoproduct. TheDEM–1 antibody, however, also bound to DNA irradiated with high fluences of 254 nm UV, suggesting that 254 nm UV could induce Dewar photoproducts without subsequent exposure to longer wavelengths of UV. Furthermore, an action spectral study demonstrated that 254 nm was the most efficient wavelength for Dewar photoproduct induction in the region from 254 to 365 nm, as well as cyclobutane dimers and(6–4)photoproducts, although the action spectrum values in the U V-B region were significantly higher compared with those for cyclobutane dimer and(6–4)photoproduct induction.     

POE incorporation into ionic clusters of ionomer and ion-conduction behaviors

Poly(oxyethylene) (POE) was incorporated into the ionic clusters of ionomers, ethylene and methacrylic acid (7.2% neutralized with KOH) copolymer membrane. The changes of properties were studied from SAXS, DSC, IR and ionic conductivity. The IR study suggested that the coordinated structures in ionic clusters of the membrane were destroyed by POE incorporation, and also SAXS suggested that ionic clusters were swollen by POE incorporation. The ionic conductivity, a carrier being K⁺ in this system, increases from 10^?16 S/cm to 10^?9 S/cm at 30°C by the incorporation of POE (20.5 wt%). On the other hand, a large amount of POE (63 wt%) could be incorporated into ionomer membrane by the esterification of methacrylic acid groups (93%) with POE. When LiClO₄ was added, ionic conduction occurred in the phase-separated POE domain, which had a low glass transition temperature (?55.2°C), showing an ionic conductivity 2.6 × 10^?6 S/cm at 25°C.     

Multiple and irreversible binding of cis-diamminedichloroplatinum(II) to human serum albumin and its effect on warfarin binding.

Irreversible bindings of cis-diamminedichloroplatinum(II) (cis-DDP) to human serum albumin (HSA) were investigated in a pH 7.4 buffer containing 0.1 M NaCl at various molar ratios (cis-DDP/HSA) up to 60 over a 14 d period (37 degrees C). The metal binding seemed to reach a plateau when incubated at less than 10 times excess of cis-DDP. As the molar ratio increased, the reaction rate was relatively fast within the first day, followed by a moderate increase in the metal binding. When incubated at 60 times excess of cis-DDP, the metal bound as much as 20 mol per mol of HSA in 14 d. Fluorescence quenching of the metal-bound protein suggested that the tryptophan residue was gradually exposed to a hydrophilic environment as the metal binding increased. Furthermore, cis-DDP cleaved disulfide bonds at the ratio of 1 mol of disulfide bond per 5.3 mol of the metal binding. It was therefore suggested that the metal binding also occurred at several sites other than the disulfide bond. Warfarin binding to the metal-bound protein, examined by fluorescence changes, also decreased with increasing metal binding or cleavage of the disulfide bonds. Thus, cis-DDP bound to multiple sites in addition to the lone sulfhydryl group (Cys-34), suggesting that massive conformational changes of the protein took place.     

Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

Summary A pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH₂CH₃)₄], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.     

Palladium(0)-catalyzed stereoselective cyclization of allenenes: divergent synthesis of pyrrolidines and 3-azabicyclo[3.1.0]hexanes from single allenenes

Two novel palladium(0)-catalyzed cyclizations of allenenes are described. Treatment of allenenes such as N-(1-alkyl-2,3-butadienyl)-N-allylsulfonamide with an aryl halide and K(2)CO(3) in the presence of a catalytic amount of Pd(PPh(3))(4) in dioxane affords 2,3-cis-pyrrolidines in a stereoselective manner. In sharp contrast, cyclization of the same allenenes using catalytic Pd(2)(dba)(3) x CHCl(3) in the presence of allyl methyl carbonate in CH(3)CN leads to stereoselective formation of a 3-azabicyclo[3.1.0]hexane framework in moderate yields.     

Stark absorption spectroscopy of indole and 3-methylindole

Indole and 3-methylindole (3-MI) doped into a polymethylmethacrylate (PMMA) film are studied by the Stark absorption (electroabsorption) spectroscopy. The 1La and 1Lb absorption bands are distinguished and the change in permanent dipole moment on 1La excitation is determined by a model fit to the measured absorption and electroabsorption spectra. Analysis of the spectra, measured at normal incidence and magic angle conditions, proved the essential role of the electric-field-induced orientation/alignment effects for polar indole and 3-MI molecules in the PMMA environment at room temperature.