bluuebunny/crossref_metadata_2025_split huggingface dataset:
First Synthesis of Both “Head-to-Head” and “Head-to-Tail” Polyimides Using a Common Unsymmetric Alicyclic Tetracarboxylic Dianhydride
Authors: Li Jun , Shiraishi Shinsaku , Kudo Kazuaki 
Published: November 2002

Abstract
A structurally ordered polyimide with the main chain having the complete “head-to-tail” bonding sequence (HTPI) or the complete “head-to-head” bonding sequence (HHPI) was prepared. The synthesis was based on the unique reactivity of an unsymmetric spiroalicyclic tetracarboxylic dianhydride, rel-(1R,5S,6R)-spiro[3-oxabicyclo[3.2.1]octane-6,3′-tetrahydrofuran]-2,2′,4,5′-tetrone (DAn), which has one 5-membered and one 6-membered anhydride. Equimolar amount of amine reacts with this compound predominantly at the 6-membered ring. Thus, the reaction of DAn with 1 molar amount of 4-nitroaniline and the subsequent methanolysis and reduction gives a monomer for a head-to-tail polyimide, which was successfully converted to HTPI through a polycondensation-dehydration sequence. Additionally, a new dianhydride monomer MHH, which is a 2 : 1 adduct of DAn and p-phenylenediamine (PPD), was prepared. MHH was subjected to polycondensation with 1 molar amount of PPD and the condensate was dehydrated to give HHPI. Slow addition of PPD into the solution of DAn also afforded a semi head-to-head polyimide. The polyimides had inherent viscosity in the range of 0.20–0.73 dL/g and were characterized by NMR and IR spectra through a comparison with those of their random isomer RPI. No obvious differences in properties, such as solubility and thermal stability, between the ordered polyimides (HTPI and HHPI) and the random counterpart were found in this study.
Infrared Spectroscopic Study of Water–Aromatic Hydrocarbon Mixtures at High Temperatures and Pressures.
Authors: Furutaka Seiya , Kondo Hitomi , Ikawa Shun-ichi 
Published: November 2002

Abstract
This paper reviews recent infrared studies on water–aromatic hydrocarbon mixtures. It mainly deals with infrared absorption of HDO in hydrocarbons measured as a function of temperature and pressure in the 373–648 K and 100–350 bar ranges, respectively. The intensity ratio of a hydrogen-bonded OH band to a hydrogen-bond-free OH band increases with increasing temperature. This fact indicates that the rate of increase in water solubility in the hydrocarbons is large enough to surmount the entropy effect which is unfavorable to water–water association. A good correlation between the peak frequency of the hydrogen-bond-free band and ionization potential of solvent hydrocarbons suggests that the concept of π-hydrogen bonding between water and aromatic hydrocarbons is useful even at high temperatures and pressures. At higher temperatures, the two OH bands mentioned above merge into a single band, which suggests that a water molecule rotates rather freely even in a hydrogen-bonded water cluster at high enough temperature. Water concentration and density of a hydrocarbon-rich phase are estimated from infrared intensities. Both of them show remarkable pressure dependence near an extended line of the three-phase coexistence curve in the phase diagram. This behavior should be characteristics of fluid mixtures near the critical region.
Synthesis, Optical, and Conductive Properties of Long Oligothiophenes and Their Utilization as Molecular Wires
Authors: Otsubo Tetsuo , Aso Yoshio , Takimiya Kazuo 
Published: November 2002

Abstract
This account reviews the current development of extraordinarily long oligothiophenes involving the 48-mer and 72-mer, which correspond to mono-disperse polymers. The systematic studies of the homologous series have provided valuable information on the optical and conductive properties of α-conjugated thiophene systems: an effective conjugation length extends to around 20 thiophene units in the neutral state and around 30 thiophene units in the oxidation state; this length plays a critical role in determining the electronic structures and conductivities. In addition, the active charge carrier species are both π-dimers and chain dimers, and charge transport occurs through the transfiguration of both species. This account also describes how useful oligothiophenes are as molecular wires allowing photoinduced electron- and/or energy-transfer. The molecular-wire behaviors of sophisticated oligothiophenes that are functionalized with a donor unit and an acceptor unit at the terminal α-positions are demonstrated.
Experimental Studies on Complex Oscillations in a Mn2+-Catalyzed Acidic Bromate–Glucose Reaction
Authors: Li Hexing , Wang Qin 
Published: November 2002

Abstract
Under batch-reactor conditions, the BrO3−–glucose–Mn2+–H2SO4 system exhibits several types of oscillations, depending on the concentrations of the reactants. In certain cases, dual-frequency oscillations are observed owing to a sequential appearance of different types of oscillations. Since glucose is not subject to bromination, these oscillations may be considered as being typically radical-controlled, and can be distinguished from bromide-controlled oscillations by adding acetone, which also results in dual-frequency oscillations due to the presence of both radical-controlled and bromide-controlled oscillations. Further experimental results demonstrate that the different types of oscillations observed in the absence of acetone can be possibly attributed to the Mn2+-catalyzed reactions between bromate and glucose, or various intermediates produced from the oxidative degradation of glucose. The effects of the [BrO3−]/[glucose] ratio and [H2SO4] on the oscillatory behaviors are discussed on the basis of their effects on either the depth of oxidative degradation of glucose or the oxidizing ability of bromate.
Photoexcited State Properties of Silicon Phthalocyanine Monomer, Dimer, and Trimer
Authors: Fujitsuka Mamoru , Ito Osamu , Konami Hideo 
Published: November 2002

Abstract
Properties of the excited states of silicon phthalocyanine monomer and its coplanar-stacked dimer and trimer have been investigated. Absorption bands of the oligomers showed blue-shift due to exciton coupling. Weak fluorescence bands of the dimer and trimer appeared in the near-IR region. The lifetimes of the singlet excited states of the dimer and trimer were estimated to be 196 and 53 ps, respectively, from the absorption-time profiles of the singlet excited states. The T–T absorption bands showed decays according to the intermolecular T–T annihilation processes. The rate constants for the intermolecular T–T annihilation processes were one-order smaller than the diffusion-limiting rates of the solvents, indicating some steric hindrance by the substituted group at the axial position. The quantum yields for the intersystem crossing processes of the dimer and trimer were quite small compared to that of the monomer. These findings indicate the extensive contribution of the non-radiative processes in the excited states of the dimer and trimer. The energy transfer rate constants between of the triplet excited phthalocyanines and O2 decreased in the order of monomer &gt; dimer &gt; trimer. The small rate constants of the dimer and trimers can be attributed to the lower triplet energy levels of the dimer and trimer compared to that of the monomer.
Realization of Three-Dimensional Solvation-Structures from the Site–Site Radial Distribution Functions in Liquids
Authors: Sato Hirofumi , Hirata Fumio 
Published: November 2002

Abstract
We propose a new procedure to realize a three-dimensional (3D) solvation structure around a solute molecule from a set of radial distribution functions (RDF), or distance information. The method consists of the minimization of a penalty function defined as the mean-square difference of the solute–solvent interatomic distances obtained from trial 3D configurations and from target RDFs. The hydration structures around several different solute molecules are visualized to demonstrate the method.
The solvation structures realized with the present method correspond to the most plausible solvation structure (MPSS), which looks like a “snap shot” of the molecular dynamics trajectory. However, the MPSS is essentially different from the “snap shot,” since it represents an average configuration, and is therefore an observable quantity. The present procedure was originally developed for analyses of the RDF results obtained from the reference interaction site model (RISM), but can be applied straightforwardly to RDFs from other sources, such as molecular simulations and scattering experiments.
Effect of Additives on the Stability of Pd/Al2O3 for Carbon Dioxide Reforming of Methane
Authors: Nagaoka Katsutoshi , Aika Ken-ichi 
Published: November 2002

Abstract
The effect of additives such as alkaline earth metal (Ca and Ba) and rare earth metal (La and Ce) oxides to Pd/Al2O3 catalyst for the CH4/CO2 reforming was investigated at 1023 K under 0.1 MPa in terms of catalytic stability and coke deposition. Catalytic stability of Pd/Al2O3 was improved by all additives; the rare earth metal oxides were more effective than the alkaline earth metal oxides. Temperature programmed hydrogenation (TPH) for those catalysts after exposure to CH4/CO2 showed that rate of coke deposition (deactivating catalysts), probably due to CH4 decomposition, was in the order: Pd/Al2O3 &gt; Ba/Pd/Al2O3 &gt;&gt; La/Pd/Al2O3, being in accordance with the catalytic stability. Temperature programmed oxidation (TPO) showed that rate of CH4 decomposition was in the order: Pd/Al2O3 &gt; Ba/Pd/Al2O3 &gt; La/Pd/Al2O3. Further, the peak on La/Pd/Al2O3 was observed at lower temperature than on the others during the TPO, implying that the reaction between CHx and CO2 on La/Pd/Al2O3 occurs more easily than on the others. Therefore, the (slow) decomposition of CH4 and the (fast) removal of the CHx would be balanced on Pd/Al2O3 with the rare earth metal oxides. Thus the catalysts do not show significant coke deposition and keep stable activity for a long time during the CH4/CO2 reforming.
Theoretical Conformational Analysis of the Tandem Repeat Sequence in RNA Polymerase II
Authors: Ohiso Isao , Oka Masahito , Nishi Norio 
Published: November 2002

Abstract
The largest subunit of RNA polymerase II has an interesting C-terminal domain, which consists of a multiple tandem repeat of a heptapeptide with the consensus sequence Ser-Pro-Thr-Ser-Pro-Ser-Tyr. However, the functional role of this sequence is unclear. One might assume that the conformation of the tandem repeat is very important for its function. A theoretical conformational analysis based on molecular mechanics using the energy functions of ECEPP was carried out for a heptapeptide in the repeating unit (Ac-Ser-Pro-Thr-Ser-Pro-Ser-Tyr-NHMe) and a periodic polyheptapeptide corresponding to the tandem repeat sequence (Ac-(Ser-Pro-Thr-Ser-Pro-Ser-Tyr)16-NHMe). The minimum conformations of Ac-Ser-Pro-Thr-Ser-Pro-Ser-Tyr-NHMe had two turn structures, an open turn at Pro2-Thr3 and a γ -turn at Pro5. The contiguous residues to the turns are extended or semi-extended conformations. The low-energy conformations of Ac-(Ser-Pro-Thr-Ser-Pro-Ser-Tyr)16-NHMe were long-periodic helices with a large number of residues per turn. Their helical radiuses are approximately 10–13 Å. They mostly have tyrosyl side-chains at the helical interior. They are composed of alternative backbone conformations, which are extended and turn structures, patterned on the feature of the low-energy conformations of Ac-Ser-Pro-Thr-Ser-Pro-Ser-Tyr-NHMe. It was shown that the long-periodic helices contain turn structures as possible conformations of the C-terminal domain.
Hydration of Glucose and Galactose Derivatives
Authors: Uedaira Hisashi , Okouchi Shoichi , Tsuda Sakae , Uedaira Hatsuho 
Published: November 2002

Abstract
The spin-lattice relaxation times, T1, of H217O have been measured for aqueous solutions of glucose and galactose derivatives, which are substituents of the 2-OH or 6-OH of these sugars, as a function of the concentration at 25 °C. The values of the coordination numbers, nh, have been estimated on the basis of the water-accessible surface areas (ASA) of the solute molecules. The rotational correlation times, τch, of water molecules around the solute were estimated and compared with that of pure water, τc0. All values of the τch/τc0 for the derivatives were smaller than those of the parent sugars, and the value of τch/τc0 = 1.26 for glucosamine was the smallest among these derivatives. The greater the hydration of the parent sugars is, the more the hydration layer will be disturbed by the substituted groups.
Solvent Density and Species Dependence of the Fluorescence Stokes-Shift and Lifetime of Coumarin 152
Authors: Kimura Yoshifumi , Iwasa Masaki , Hirota Noboru 
Published: November 2002

Abstract
Absorption spectra, fluorescence spectra, and fluorescence lifetime of Coumarin 152 (C152) have been measured in ethane (C2H6), carbon dioxide (CO2), and trifluoromethane (CF3H) at 343 K and in CF3H at 323 K from ρr ≈ 0.1 to 2.0. The fluorescence Stokes-shift slightly decreases in C2H6 and CO2 with an increase of the solvent density, while it increases up to ρr ≈ 0.5 in CF3H and remains almost constant above ρr ≈ 0.5, where ρr is the reduced density by the solvent critical density. All these features are common to the case of C153 (Y. Kimura and N. Hirota, J. Chem. Phys., 111, 5474 (1999)). The fluorescence lifetime of C152 is found to be strongly dependent on the solvent density and temperature below ρr = 1.0 in C2H6. On the other hand, very large density dependence is observed in CF3H below ρr = 0.1, although the lifetime slightly decreases with increasing the solvent density above ρr = 0.1. The fluorescence lifetime is discussed in relation with the energy difference between the S0 and S1 states. The quenching of the S1 state by oxygen is also found to make a contribution to the density dependence of the fluorescence lifetime.
Mechanisms of Oxidation Reactions of Iodide and Hexacyanoferrate(II) Ions, Induced by the Reaction between Phosphinate Ion and Molecular Oxygen in an Aqueous Solution
Authors: Kimura Masaru , Ieyama Noriko , Matsumoto Masami , Shimada Kimiko , Tsukahara Keiichi 
Published: November 2002

Abstract
When an I− solution was mixed with a PH2O2− solution which had been kept standing for given times of 5–40 min in the presence of molecular oxygen (O2), the I2 (or I3−) was rapidly formed and then gradually reduced. The maximum amounts of the formed I2 (or I3−) increased with increasing standing times of the PH2O2− solution, and with increasing concentrations of PH2O2− and H+ in the solution. When the [Fe(CN)6]4− solution was mixed with the PH2O2− solution, [Fe(CN)6]3− was formed quantitatively, but an induction period appeared under the conditions of low concentrations of PH2O2− and high pH’s. The induction period was shortened at higher concentrations of PH2O2−, O2, and/or H+. Both oxidation reactions of I− and [Fe(CN)6]4− were extremely accelerated by the addition of small amounts of the peroxodiphosphate salt (K4P2O8) into the solution, both were inhibited by the presence of radical scavengers, and never occurred in the N2-saturated solution. The mechanisms for such O2-induced/radical reactions, which are regarded as a new type of Fenton-like reagent, are discussed.
Water Molecules in Organic Solvents Involved in the Synergistic Extraction of Europium(III) with β -Diketones and Lewis Bases
Authors: Hasegawa Yuko , Nakaya Kiyotaka , Matsubayashi Izuru 
Published: November 2002

Abstract
To explain the difference in the magnitude of synergistic extraction among organic solvents, the water solubility in hexane, carbon tetrachloride, benzene, and chloroform was measured, and then the residual hydration number of europium(III) in the β-diketonato chelate and in their adducts with 1,10-phenanthroline as well as the adduct formation constants were determined. Using the data, the formation constants of the adduct according to a novel definition, in which the water concentration in the organic phase is treated as one variable, were determined. The constants are approximately constant irrespective of the organic solvents, although those according to the conventional definition are different among the solvents. It has been concluded that one of the most important factors controlling the magnitude of synergistic effects is the presence of water, such as the water content dissolved in organic solvents, and the hydration and dehydration of the relevant species, because water molecules compete with a Lewis base in complexation to the metal(III) chelates in the organic solvents.
Axial Hydration and Adsorption of Chloro(5,10,15,20-tetraphenylporphyrinato)manganese(III) at the Toluene/Water Interface, Studied by External Reflection Spectrophotometry
Authors: Fujiwara Kazuhiko , Watarai Hitoshi 
Published: November 2002

Abstract
Interfacial adsorption of chloro(5,10,15,20-tetraphenylporphyrinato)manganese(III), [Mn(tpp)Cl], at the interface of toluene/aqueous sodium hydrogensulfate was studied by means of an UV/vis external reflection (ER) spectroscopy and interfacial tension measurements. The s-polarized ER spectrum showed higher sensitivity than the p-polarized one at the incident angle of 70.8°. A linear correlation sililar to Beer’s law was obtained between the s-polarized ER absorbance and the interfacial concentration determined from the interfacial tension. The molar ER coefficient at the maximum wavelength of 478 nm was determined as −8.41×105 (mol−1 dm2). The effect of chloride ion concentration on the ER spectra suggested that the interfacial species at toluene/0.1 mol dm−3 sodium hydrogensulfate solution (pH 1.7) was Mn(tpp)(H2O)+i. The interfacial adsorption could be analyzed according to the Langmuir isotherm; the equilibrium constant for the adsorption reaction of Mn(tpp)Clo + H2O →← Mn(tpp)(H2O)+i + Cl− was determined as 59.6. Furthermore, it was suggested that chloride ions were preferentially distributing at the diffuse layer under low chloride ion concentrations.
Synthesis, Stereochemistry, and Spin Transition of Heterometal Dinuclear Fe(II)–Cr(III) Complex Bridged by 3,5-Bis(pyridin-2-yl)-pyrazolate
Authors: Ni-iya Keiko , Fuyuhiro Akira , Yagi Takashi , Nasu Saburo , Kuzushita Kaori , Morimoto Syotaro , Kaizaki Sumio 
Published: November 2002

Abstract
We have synthesized and characterized a new heterometal dinuclear complex, [(nta)CrIII(μ-bpypz)FeII(picen)]BF4 (1), where nta = nitritotriacetate; bpypz− =3,5-bis(pyridin-2-yl)-pyrazolate; and picen = N,N′-bis-(2-pyridylmethyl)ethylenediamine. The X-ray structure of the Fe(II)–Cr(III)·H2O·3dmf demonstrated that this has a dinuclear structure with a highly distorted octahedron around a high-spin Fe(II) and intramolecular bifurcated three-centered hydrogen bonds between the carboxylate oxygens of the nta and an amine proton of the picen with an abnormal conformation. A magnetic susceptibility measurement and/or the Mössbauer spectra of 1 substantiated a gradual spin-transition from 130 K to 300 K in a heating process centered around 250 K with a small hysteresis dip in the Fe(II) complex. The spin-transition temperature of 1 is lower than that of the mononuclear complex, [FeII(picen)(Hbpypz)](BF4)2(2), resulting from the weaker ligand field of 1 with a distorted octahedron than that of 2.
Europium(III) Fluorescence Lifetime in Poly(methacrylic acid) Related to Its Conformational Transition
Authors: Takahashi Yoshio , Kimura Takaumi 
Published: November 2002

Abstract
The number of water molecules (NH2O) in the inner-sphere of Eu(III) complexed with poly(methacrylic acid) and poly(acrylic acid) was reported at various temperatures and α (degree of ionization) of these polyelectrolytes using laser-induced fluorescence spectroscopy. It is suggested that the conformational transition of poly(methacrylic acid) is reflected in the α dependence of NH2O.
Stereoselective Formation of trans-2,5-Disubstituted Tetrahydropyrans by Intramolecular Nucleophilic Substitution and a Computational Study at the AM1 Level
Authors: Takagi Ryukichi , Nishitani Hiroko , Takenami Sigeharu , Okada Kazumasa , Kojima Satoshi , Ohkata Katsuo 
Published: November 2002

Abstract
The synthesis of 2,5-disubstituted tetrahydropyrans bearing a hydrophobic moiety at the C5 position from (E)- and (Z)-7-hydroxy-6-substituted 2,3-unsaturated esters by way of intramolecular nucleophilic substitution proceeded with high stereoselectivity. A theoretical study at the AM1 level of the cyclization reaction suggested that the reaction is kinetically controlled and that the preferred path for the cyclization reaction proceeds via a transition state in which 1,3-diaxial-like repulsions are minimized to give the trans product in accordance with experimental results.
Characterizing Pressure Effects on Winding of the DNA Double Helix
Authors: Tang Guo-Qing , Kunugi Shigeru 
Published: November 2002

Abstract
In order to characterize pressure effects on DNA topological conformations in terms of supercoiling, DNA topoisomerase- and ligase-induced supercoiling assays were applied to analyze several DNA samples from different sources (DNA of bacteriophage φX174 RFI, plasmid pBR322, and pUC19). Pressure generally enhanced winding of the DNA double helix. The results were analyzed with respect to the linking number, the rotation angle, and the torsional energy factor (K). K describes the energy cost of increasing DNA linking by one unit; it appeared to decrease linearly with pressure elevations up to at least 180 MPa, which suggested a volume shrinkage with DNA supercoiling.
Synthesis and Conformational Studies on 3-o-Tolylhydantoins by NMR and Molecular Modeling: Dipole-π Attractions in Peptides and Proteins
Authors: Park Sang Hyun , Bose Ajay K 
Published: November 2002

Abstract
5-Pentafluorobenzyl-3-o-tolylhydantoin (2) was synthesized for reducing this π-electron density, and NMR studies have shown that we have succeeded in changing the conformation of 2 into an extended system instead of the folded conformation for the non-fluorinated compound, 5-benzyl-3-o-tolylhydantoin (1). Molecular modeling has also confirmed the extended structure for 2. An approach has been found for possibly modulating the physiological activity of peptides containing aromatic amino acids.
Oxidative Addition of Allylic Substrates to Coordinatively Unsaturated Ruthenium Compounds, [Ru(η5-C5Me5)(η-amidinate)]: Preparation, Structure Elucidation, and Catalysis of Novel Ruthenium (IV)-η3-Allyl Complexes
Authors: Kondo Hideo , Kageyama Akira , Yamaguchi Yoshitaka , Haga Masa-aki , Kirchner Karl , Nagashima Hideo 
Published: November 2002

Abstract
Oxidative addition reactions of allylic halides, acetates, and carbonates with [Ru(η5-C5Me5)(η-amidinate)] [amidinate: iPrNC(Me)=NiPr (1a), tBuNC(Ph)=NtBu (1b)], which shows signs of coordinative unsaturation, gave novel cationic π-allyl ruthenium(IV) species. The compounds [Ru(η3-allyl)(η5-C5Me5)(η2-amidinate)]+X− were isolated by anion exchange of the products (X = PF6, BF4, BPh4), and were characterized by spectroscopic analysis. The crystallography of two of the [Ru(η3-allyl)(η5-C5Me5)(η2-amidinate)]+X− revealed a four-legged piano stool structure in which two nitrogen atoms in the amidinate ligand and two carbon atoms in the η3-allyl ligands occupy the positions of four legs; the orientation of the η3-allyl ligand was endo. Although cyclic voltammograms of the precursor, [Ru(η5-C5Me5)(η-amidinate)], indicated possible oxidative addition of organic halides other than allylic halides to [Ru(η5-C5Me5)(η-amidinate)], only allylic halides gave the corresponding Ru(IV) products. The importance of prior coordination of the carbon-carbon double bond of allylic substrates was evidenced by NMR observation of the intermediate in the reaction of 1a or 1b with allyl acetate. Addition of nucleophiles such as PhLi, dimethyl methylsodiomalonate, and piperidine to the [Ru(η3-allyl)(η5-C5Me5)(η2-amidinate)]+X− gave rise to allylation of these nucleophiles and regeneration of [Ru(η5-C5Me5)(η-amidinate)]. The reactions of allyl methyl carbonate with nucleophiles were also achieved by catalysis of either [Ru(η5-C5Me5)(η-amidinate)] or [Ru(η3-allyl)(η5-C5Me5)(η2-amidinate)]+X−.