bluuebunny/crossref_metadata_2025_split huggingface dataset:
Charge Distribution Dependent on the Chelating Ratio. [Co(μ-bpym)(dbbq)2] vs. [{Co(dbbq)2}2(μ-bpym)] (bpym = 2,2′-bipyrimidine; dbbq = 3,6-di-t-butyl-1,2-benzoquinone)
Authors: Jung Ok-Sang , Jo Du Hwan , Lee Young-A , Chae Hee Kwon , Sohn Youn Soo 
Published: June 2006

Abstract
The preparation and characterization of [Co(μ-bpym)(dbbq)2] and [{Co(dbbq)2}2(μ-bpym)] (bpym = 2,2′-bipyrimidine; dbbq = 3,6-di-t-butyl-1,2-benzoquinone) have been established. The temperature-dependent magnetic moments (100—400 K) and variable-temperature near-infrared (NIR) absorption spectra are presented to show that the title complexes exhibit an equilibrium via a catechol to a cobalt intramolecular electron transfer. At temperatures below 200 K the mononuclear complex [Co(μ-bpym)(dbbq)2] has a charge distribution of [CoIII(μ-bpym)(dbcat)(dbsq)] (dbsq = 3,6-di-t-butyl-1,2-semiquinonato; dbcat = 3,6-di-t-butylcatecholato), whereas at temperatures beyond 290 K the mononuclear complex is predominantly in the [CoII(μ-bpym)(dbsq)2] form. From 200—290 K a mixture of Co(III) and Co(II) redox isomers exists at equilibrium in the solid state. In particular, a thermal analysis of a solid sample of the mononuclear complex discloses that the transition for the Co(III)/Co(II) is accompanied by a change in the heat content of 36 kJ mol−1, which may be closely related to the band at 3878 cm−1, assigned as a dbcat to Co(III) charge transfer. In striking contrast, the dinuclear complex [{Co(dbbq)2}2(μ-bpym)] is locked in a charge distribution of [{CoII(dbsq)2}2(μ-bpym)] when the temperature is 100—400 K.
Conformation Control of Model Peptides by Metal Ions. A New Type of Turn Structure Found in [(Boc–Cys–Pro–Leu–Cys–Gly–Ala)Hg]
Authors: Yamamura Takeshi , Arai Masaya , Yamane Tsutomu , Ukai Takeshi , Ushiyama Masato , Hirota Hiroshi 
Published: June 2006

Abstract
The structure of [(Boc–Cys1–Pro–Leu–Cys4–Gly–Ala–OMe)Hg], 1, in DMF(-d7) and DMSO(-d6) solutions was studied by X-ray absorption fine structure (XAFS), rotating frame nuclear Overhauser effect spectroscopy (ROESY), distance geometry (DG), molecular dynamics (MD), and restrained molecular dynamics (RMD). The XAFS study clarified that the inorganic center of compound 1 adopts a linear coordination with r(HG–S) = 2.33 Å. The NMR experiment revealed 33 atom approximate distances for the 1H-1H pairs of the main chain loop, including the side chains of the cysteinyl residues (ROESY). By a complementary use of DG, plain MD, and RMD for distance information from NMR as well as XAFS, we established that compound 1 adopts a new type of hybridized turn structure. The compound has two hydrogen bonds, Cys1 S-Leu HN and Pro CO-Cys4 HN, among which the former is common to the core sites in proteins, Cysi–X–Y–Cysi+3/M2+ (Zn2+, Fe2+), whereas the latter is common to the mirror image of the γ turn structure in proteins.
PM3 Analysis of Nitrone Cycloadditions to Methyl 4,4,4-Trifluoro-2-butenoate
Authors: Tanaka Kiyoshi , Imase Tatsuya , Iwata Satoru 
Published: June 2006

Abstract
3,4-Dihydroisoquinoline N-oxide (1) cycloadded with methyl 4,4,4-trifluoro-2-butenoate at 20 °C to give a mixture of the cycloadduct with a 1,10b-cis-configuration, methyl (1R*, 2R*, 10bR*)-2-trifluoromethyl-1,5,6,10b-tetrahydro-2 H-isoxazolo[3,2-a]isoquinoline-1-carboxylate, and its stereoisomer with a 1,10b-trans-configuration in a ratio of 3 : 1. Nitrone 1 cycloadded with methyl 2-butenoate to afford the cycloadduct with a 1,10b-cis-configuration exclusively. The stereoselectivity in the cycloadditions was reproduced by calculations of the transition structures by the PM3 method.
Novel Reaction between 3,4,5,6-Tetrachloro-1,2-benzoquinone and Bis-azomethines
Authors: Aly Ashraf A , Mohamed Nasr K , Hassan Alaa A , Mourad Aboul-Fetouh E 
Published: June 2006

Abstract
3,4,5,6-Tetrachloro-1,2-benzoquinone (o-CHL) reacted with N,N′-dicyclohexyl-1,2-ethanediimine 1a to give a transient condensation product, which underwent [4 + 2]cycloaddition reaction with another molecule of 1a. In a different manner, utilizing N,N′ -diaryl-1,2-ethanediimines 1b,c as a dienophile led to an initial production of substituted o-CHL, followed by a [4 + 2]cycloaddition reaction with another molecule of 1b,c. A similar behavior was observed on the reaction of N,N′-di(alkyl/aryl)-p-xylenediimines 1a—f with the same acceptor.
Synthesis of Cadinanolide Type of Tricyclic α-Methylene-γ-lactone Using Intramolecular Cyclization of α-Trimethylsilylmethyl-α,β-Unsaturated Ester with Cyclic Ketone
Authors: Kuroda Chiaki , Ito Kunihito 
Published: June 2006

Abstract
Fluoride-promoted intramolecular cyclization of ethyl 6-(2-oxocyclohex-1-yl)-2-(trimethylsilylmethyl)hex-2-enoate afforded ethyl 2-(1-hydroxybicyclo[4.4.0]decan-2-yl)acrylate as the major product, together with tricyclic α-methylene-γ-lactone, a model compound of cadinanolides. The former product was also converted to γ-lactone. The cyclization reaction promoted by TiCl4 gave the hydroxy ester and its dehydrated product. Both Lewis acid- and fluoride-promoted cyclizations gave a trans-decaline system mainly. This stereoselectivity is completely different from that of Reformatsky cyclization observed by Dreiding and co-workers.
Interaction of Carbodiimide with Human Erythrocytes: Hemolytic Properties Induced by High Pressure, Heating, and Hypotonic Medium
Authors: Yamaguchi Takeo , Miyamoto Yoshiya , Terada Shigeyuki 
Published: June 2006

Abstract
The effects of 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) on the hemolysis of human erythrocytes were examined. To hemolyze, the erythrocytes were exposed to high pressure (200 MPa), heating (52 °C), or a hypotonic medium. Upon EDC treatment, the hemolysis induced by high pressure or heating was completely suppressed, whereas osmotic hemolysis was enhanced. In EDC-treated erythrocytes, high-molecular-weight aggregates of membrane proteins were formed by cross-linking of the membrane with the cytoskeleton, in addition to that of membrane proteins themselves. In such a cross-linking reaction, however, iron(II) in hemoglobin and thiol groups in membrane proteins remained stable. Although phosphate transport via band 3 was considerably suppressed by EDC, the intracellular K+ concentration was almost constant. These results suggest that high-pressure- or heat-induced hemolysis, compared with osmotic hemolysis, is suppressed by a stabilization of the cytoskeletal network.
Sulfonylation and Phosphinylation of Olefinic Compounds with Radical Species Generated by the Oxidation of Sodium Sulfinates and Diphenylphosphine Oxide
Authors: Mochizuki Takashi , Hayakawa Satoshi , Narasaka Koichi 
Published: June 2006

Abstract
Sodium arenesulfinates are oxidized with manganese(III) 2-pyridinecarboxylate or ammonium cerium(IV) nitrates to generate sulfonyl radicals, which add to olefinic compounds to afford sulfonylated products in good yield. When 1-vinyl cyclic alcohols are used as sulfonyl radical acceptors, sulfonylation proceeds with ring-enlargement. Diphenylphosphinyl radical can also be generated by treating diphenylphosphine oxide with manganese(III) 2-pyridinecarboxylate and reacts with olefinic compounds, giving phosphinylated products.
Theoretical Study of the Electronic Structure of 2,2′-Bisilole in Comparison with 1,1′-Bi-1,3-cyclopentadiene: σ*–π* Conjugation and a Low-Lying LUMO as the Origin of the Unusual Optical Properties of 3,3′,4,4′-Tetraphenyl-2,2′-bisilole
Authors: Yamaguchi Shigehiro , Tamao Kohei 
Published: June 2006

Abstract
The purpose of this work is the theoretical elucidation of the origin of the unusually long UV-vis absorption maximum, λmax = 398 nm, of 3,3′,4,4′-tetraphenyl-2,2′-bisilole, which we have observed recently. Several semiempirical and ab initio calculations have been performed for some model compounds, silole and 2,2′-bisilole, in comparison with their carbon analogs, cyclopentadiene and 1,1′-bi-1,3-cyclopentadiene, respectively. The PM3 calculations indicate that the silole ring has a considerably low-lying LUMO, arising from σ*–π* conjugation between a π-symmetry σ* orbital of the exocyclic σ bonds on silicon and a π* orbital of the butadiene skeleton. Ab initio calculations at the CIS/6-31G* level of theory suggest that the experimental large differences in the absorption maximum in the UV-vis spectra between the bisilole and the bicyclopentadiene derivatives are ascribed also to the low-lying LUMO level of the bisilole compared with the bicyclopentadiene. It is further demonstrated that the σ*–π* conjugation is enhanced by the molecular distortions, twisting and folding, of the bisilole skeleton present in the X-ray structure, resulting in the lowering of the LUMO level. The calculated data are supported by the redox potentials of some representative compounds, as determined by cyclic voltammetry measurements. The σ*–π* conjugation and the low-lying LUMO would thus be the origin of the unusual optical properties of bisilole derivatives.
Preparation of a DNA Complex with Lipoglutamide Having Tetraethylene Glycol Tails, and Its Application to DNA Delivery into Tumor Cells
Authors: Sato Toshinori , Akino Hiroyuki , Okahata Yoshio 
Published: June 2006

Abstract
We newly prepared a polyion complex of DNA with lipoglutamide, N,N′-bis(18-hydroxy-7,10,13,16-tetraoxaoctadecyl)-L-glutamide hydrochloride (abbreviated to 2EO4C6N+). Formation and characterization of the DNA/2EO4C6N+ complex were investigated by elemental analysis, melting temperature, and light-scattering measurements. Compaction of DNA by binding with the cationic 2EO4C6N+ was seen by multi-angle light scattering. Aggregation of the DNA/2EO4C6N+ complex was significantly depressed compared with the DNA complex without tetraethylene glycol. The DNA/2EO4C6N+ complex had low cytotoxicity and efficient internalization into tumor cells compared with native DNA.
Reactions of Benzyne with 1,3-Benzodithiole-2-thione and Related Compounds: Formation of Novel Tetracyclic Sulfonium Salts and Their Reactions Leading to Dibenzo-1,3,6,-trithiocin Derivatives
Authors: Nakayama Juzo , Kimata Atsuko , Taniguchi Hideki , Takahashi Fumihiko 
Published: June 2006

Abstract
A sulfur ylide intermediate, produced by a 1,3-dipolar cycloaddition of 1,3-benzodithiole-2-thione (5) with benzyne, was successfully trapped by hydrogen chloride to give a novel tetracyclic sulfonium salt, 9aH-9,10-dithia-4b-thioniaindeno[1,2-a]indene chloride (7), in good yield when benzyne was generated by the thermolysis of 2-carboxybenzenediazonium chloride (4). The reaction of ethylene trithiocarbonate with excess 4 provided a convenient one-pot synthesis of 7 in large quantities. The reduction of 7 with NaBH4 gave a novel ring compound, dibenzo[d,g][1,3,6]trithiocin (15), in 95% yield, while alkaline hydrolysis produced the 12-oxide derivative of 15. The treatment of 7 with t-BuOK gave 6,6′-bi(dibenzo[d,g][1,3,6]trithiocinylidene) in 84% yield. Also described are the reactions of benzyne with related compounds of 5.
Comparative Study of the Mutual Separation Characteristics and Mechanism for Neighboring Rare-Earth Elements from Binary Chloride Mixtures and Oxide Mixtures via Vapor Complexes
Authors: Wang Zhi-Chang , Yu Jin , Yu Yong-Li 
Published: June 2006

Abstract
A comparative study of the mutual separation characteristics and mechanism was made for neighboring rare-earth elements La, Ce, Pr, and Nd from their binary chloride mixtures and oxide mixtures using a chemical vapor-transport reaction under a suitable temperature and pressure gradient. The separation factors, expressed as the atomic ratios for the resulting chlorides, were observed within 6 h up to 21.4 for La : Ce, ≥100 for Pr : Ce, and 1.84 for Pr : Nd from the oxide mixtures; however, they were only 12.3 for La : Ce, 5.79 for Pr : Ce, and 1.32 for Pr : Nd from the chloride mixtures under identical reaction conditions, using AlCl3 as the sole complex former. It was also observed for the mutual separation from the oxide mixtures that the separation factors increased when KCl was added as another complex former, but decreased several times when either without chlorine in the carried gas, or without active carbon in the raw material, or under a poor vapor-transport condition. These results provide evidence that this reaction for the oxide mixtures would mainly be the combination of a carbothermic reduction-chlorination of the oxides, complexation of the chlorides, and transportation of the vapor complexes.
Preparation of Metallic Palladium Catalysts with Thermally Stable Surface Areas and Activities
Authors: Yada Satoru , Sasaki Tomoaki , Hiyamizu Makoto , Takagi Yuzuru 
Published: June 2006

Abstract
Pd metal catalysts were prepared by the reaction of palladium(II) chloride with sodium aluminate at pH 6—10. The Pd catalysts prepared at pH 10 contained only small amounts of Al (0.14 wt%), were the most thermally stable, and kept large specific surface areas and high catalytic activities in the hydrogenation of nitrobenzene even after hydrogen treatment at high temperatures up to 380 °C.
Novel Syntheses of Poly(o-aminobenzoic acid) and Copolymers of o-Aminobenzoic Acid and Aniline as Potential Candidates for Precursor of Polyaniline
Authors: Yan Hu , Wang Hung-Jen , Adisasmito Sanggono , Toshima Naoki 
Published: June 2006

Abstract
Poly(o-aminobenzoic acid) and copolymers of o-aminobenzoic acid and aniline were synthesized as excellent candidates for the precursor of polyaniline. The reaction conditions were optimized with emphasis on the isolated yield. The polymers were characterized by a number of techniques including infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, thermal analyses, and scanning electron microscopy. The yield of poly(o-aminobenzoic acid) was remarkably improved by addition of sodium hydroxide (an equivalent mole amount to the monomer) into the reaction system. Spectroscopic results indicate that the polymer has principally an Emeraldine structure. The copolymers were also obtained at high yield by addition of sodium hydroxide (an equivalent mole amount to o-aminobenzoic acid). The polymerization mechanism was briefly discussed on the basis of the pH effect upon the yield and easy elimination of the carboxyl group via a ring structure. The copolymer as well as poly(o-aminobenzoic acid) were found to be the precursors to produce polyaniline with elimination of carbon dioxide by heat treatment.
Chalcogenide Cluster Complexes of Chromium, Molybdenum, Tungsten, and Rhenium
Authors: Saito Taro , Imoto Hideo 
Published: June 2006

Abstract
Trinuclear, tetranuclear, hexanuclear, and dodecanuclear chalcogenide cluster complexes of chromium, molybdenum, tungsten, and rhenium have been synthesized and their molecular and electronic structures have been characterized. The structure-cluster valence electron relationships are analyzed and a new isoelectronic analogy is proposed.
Solid State NMR of 11B and 13C in Boron Carbide, B12C3 and 11B Enriched B12C3
Authors: Harazono Toshie , Hiroyama Yukiyo , Watanabe Tokuko 
Published: June 2006

Abstract
11B- and 13C-solid state NMR of boron carbide with different isotope ratios, B4C(11B/10B = 80.42/19.58; natural abundance isotope) and 11B4C(11B/10B = 99.5/0.5; 11B enriched sample), has been investigated. The linewidth of the icosahedral B (6h1and 6h2) in 11B-static NMR signal in 11B4C was greater in 11B4C than in B4C, which indicates that the B–B dipole–dipole interaction is the main mechanism for the broadening of the 11B-static NMR signal. The quadrupole coupling constant calculated from the signal position of (±1/2 ↔ ±3/2) transition was about 0.1 MHz. 11B-MAS spectra revealed the presence of at least two additional B sites (37 ppm and near −60 ppm) besides the icosahedral B sites (−6 ppm).
Quantum Mechanical Theory of Electron Transfer Reactions at Metal Electrodes
Authors: Sakata Tadayoshi 
Published: June 2006

Abstract
The quantum theory of electron transfer reactions at metal electrodes was studied. The obtained potential dependence of the electron transfer rate in the weak coupling case resembles the Butler–Volmer equation of classical electrochemistry. The volcano-shaped dependence of the hydrogen exchange current on the adsorption energy of hydrogen on various metals was explained microscopically, based on this theory. The mechanism of hydrogen evolution was also explained microscopically based on this theory. The exchange current density for hydrogen evolution at Pt electrode calculated quantitatively agreed well with the experimental value.
Unusual Spectral Shifts of Bis(4-aminophenyl)ether
Authors: Rajendiran Narayanasamy , Swaminathan Meenachisundram 
Published: June 2006

Abstract
Absorption and fluorescence spectra of Bis(4-aminophenyl)ether (DADPE) have been studied in different solvents and at various acid concentrations. The results are compared with the spectral data of 4-Aminodiphenyl ether (ADPE). The fluorescence spectra of DADPE are blue shifted relative to that of ADPE in polar and hydrogen-bonding solvents. A small, but unusual, red shift is observed in the fluorescence spectrum of the monocation relative to that of DADPE in water. These observations reveal that the effect of two amino groups in polar solvents is less than that of one amino group in the excited singlet state. The abnormally red-shifted fluorescence with a peak at around 422 nm at pH 3.5 is due to a dication-solvent exciplex. The formation of the dication-solvent exciplex leads to an excited state equilibria quite different from that in the ground state.
Charge-Transfer Complexation in an Aqueous Polyelectrolyte Solution. III. Complexation between Pyrenesulfonate or Anthracenesulfonate and Anthraquinonesulfonate Ions
Authors: Kawabata Yoshiya , Itaya Tomoyuki , Sasaki Yuki , Ochiai Hiroshi , Ueda Kazuyoshi , Imamura Akira 
Published: June 2006

Abstract
Charge-transfer (CT) complexations between 1-pyrenesulfonate ion (PyS−; donor) and 9,10-anthraquinone-2-sulfonate ion (2-AQS−; acceptor), and between anthracene-2-sulfonate ion (ACS−; donor) and 2-AQS− ion around the cationic polymers were studied by means of absorption and fluorescence spectroscopies as well as molecular-orbital calculations. The cationic polymers used in this study were poly(allylammonium) (PAAH+) and poly(1,1-dimethyl-3,5-dimethylenepiperidinium) (PDDP+). When solutions included only donor and acceptor molecules at low concentration, such as solutions of PyS− (1 × 10−4 M)/2-AQS− (1 × 10−4 M) and ACS− (1 × 10−4 M)/2-AQS− (1 × 10−4 M), they did not show any CT complex formation. However, the addition of polymers to these solutions exhibited charge-transfer absorption bands (CT band). A continuous variation method for CT bands of Na+PyS−/Na+2-AQS− in both PAAH+Cl− and PDDP+Cl− systems showed that a 1 : 1 type (PyS− : 2-AQS−) complex preferentially formed in the vicinity of these polyions. On the other hand, in the Na+ACS−/Na+2-AQS− system, a 1 : 2-type (ACS− : 2-AQS−) complex preferentially formed around PAAH+ and a 1 : 1-type complex formed around PDDP+. By comparing these results with our previous study between 9,10-dimethoxyanthracene-2-sulfonate and 2-AQS− in aqueous solution with the same polymers, it has become clear that the stoichiometries of the CT complexes and the peak positions of the observed CT bands are dependent upon the varieties of donor molecules. Molecular-orbital calculations have shown that there is a linear relationship between the calculated energy levels of the highest occupied molecular orbital (HOMO) of the donor molecules and the energies of the observed CT bands; that is, the donor molecule with a higher HOMO energy has the lower energy of the CT band.
Electrochemical Behavior of the Naphtoquinone Anchored onto a Gold Electrode through the Self-Assembled Monolayers of Aminoalkanethiol
Authors: Mukae Fumihiko , Takemura Hiroyuki , Takehara Kô 
Published: June 2006

Abstract
2,3-Dichloro-1,4-naphtoquinone (NQ) was anchored to a gold electrode surface through the self-assembled monolayers of aminoalkanethiols (AAT, HS(CH2)nNH2: n = 2, 5, and 8). The effect of the alkyl chain length of the AAT monolayer, which also acts as the spacer between the NQ molecule and the gold electrode surface, on the redox behavior of the immobilized NQ has been studied by using a voltammetric technique. The surface coverage of the anchored NQ was estimated to be 3.8 × 10−10 mol cm−2 in the case that 2-aminoethanethiol (HS(CH2)2NH2) was used as the monolayer constituent. The electron-transfer rate constant, ket, associated with the redox process of anchored NQ decreased from 9.7 s−1 at n = 2 to 0.78 s−1 at n = 8, with increasing the chain length of the AAT monolayer, though the redox potential of NQ was scarcely affected by the chain length. The tunneling barrier coefficient, β, of the electron transfer was estimated to be 0.36 Å−1, from the observed linear relationship between the ket value and the monolayer chain length.
Kinetics of Complexation between β-Cyclodextrin and 1-Propanol in Aqueous Solution by Ultrasonic Relaxation Method
Authors: Nishikawa Sadakatsu , Yamaguchi Sachiko 
Published: June 2006

Abstract
Ultrasonic absorption coefficients in aqueous solutions containing β-cyclodextrin and alcohols (ethanol and 1-propanol) have been measured in the frequency range from 3 to 220 MHz at 25 °C. Although a single relaxational absorption has been observed in solution with β-cyclodextrin and 1-propanol, it has not been found when the alcohol is ethanol. From the concentration dependence of the ultrasonic relaxation parameters, the cause of the relaxational absorption has been attributed to the perturbation of an equilibrium associated with the 1 : 1 complex formation (complexation) between β-cyclodextrin and 1-propanol. The rate and equilibrium constants as well as the standard volume change were determined for the complexation reaction of β-cyclodextrin and 1-propanol. The equilibrium constant determined in this study was found to be very consistent with the reported value for β-cyclodextrin and 1-propanol. The kinetic process for complexation between β-cyclodextrin and popular alcohols is discussed in relation to the sizes of the guest molecules.
Excimer Formation in Inclusion Complexes of β-Cyclodextrin with 1-Alkylnaphthalenes in Aqueous Solutions
Authors: Hamai Sanyo , Hatamiya Akira 
Published: June 2006

Abstract
In aqueous solutions, β-cyclodextrin (β-CD) has been found to form inclusion complexes with 1-methylnaphthalene, 1-ethylnaphthalene, 1-(chloromethyl)naphthalene, and 2-ethylnaphthalene. Addition of β-CD to aqueous solutions of 1-methylnaphthalene and 2-ethylnaphthalene has resulted in the observation of the excimer fluorescence of each compound. From simulations of the observed excimer fluorescence intensities of 1-methylnaphthalene and 2-ethylnaphthalene, the excimer fluorescence is concluded to be due to a 2 : 2 β-CD–alkylnaphthalene inclusion complex. In the cases of 1-ethylnaphthalene and 1-(chloromethyl)naphthalene, the excimer formation within the β-CD cavities seems to be prohibited due to the steric hindrance caused by a substituent, although the 2 : 2 β-CD–alkylnaphthalene inclusion complex is likely to be formed. Equilibrium constants for the formation of these 1 : 1 and 2 : 2 inclusion complexes have been evaluated from the monomer and excimer fluorescence intensity changes with β-CD concentration.