bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Silica-Supported Nickel Catalysts by the Temperature-Programed Desorption of Hydrogen Adsorbed at Various Temperatures
Authors: Arai Masahiko , Suzuki Kyosuke , Nishiyama Yoshiyuki 
Published: August 2006

Abstract
The temperature-programed desorption (TPD) of hydrogen adsorbed at various temperatures and at nearly saturated coverage has been used to characterize the surface of nickel particles dispersed on silica gel. The TPD spectra have two major peaks, the first and second peaks, at about 375 and 560 K. The second peak has a strong functional relation with the nickel weight loading and the heat-treatment temperature. It decreases with decreasing metal loading and increasing treatment temperature. As the adsorption temperature is increased the amount of hydrogen desorbing in the second peak is mainly increased; this is more remarkable for smaller metal loading. The two observed major peaks suggest the presence of two types of adsorption sites on nickel particles. The adsorption of hydrogen can easily occur on sites for the first peak, while it should go over some energy barrier on sites for the second one. It is assumed that these two types depend on the surface morphology of nickel particles, which is affected by their size and thermal history.
Extended Molecular Mechanics Simulation of Thermodynamic Quantities, Structures, and Vibrational Spectra of Fatty Acids
Authors: Yokoyama Isao , Miwa Yoshihisa , Machida Katsunosuke , Umemura Junzo , Hayashi Soichi 
Published: August 2006

Abstract
An extended molecular mechanics calculation of thermodynamic quantities, structure parameters, infrared absorption spectra, and Raman spectra of normal fatty acids was carried out on the basis of the potential and the intensity parameters transferred from those determined for acetic acid and normal paraffins in the gas phase. The overall features of the infrared absorption spectra of propionic acid and its deuterated species in the solid state at liquid-nitrogen temperature are successfully reproduced. The multiple CH2 wagging bands of the cis-configuration of long-chain fatty acids are ascribed to the coupling between the C–O stretching mode and the CαH2 or the CβH2 wagging mode. The infrared absorption spectra of lauric through palmitic acids at room temperature are well simulated by superimposing the spectra of the cis- and the trans-configurations. The simulated Raman spectrum of crystalline palmitic acid based on the bond polarizability model agrees well with the observed spectrum at room temperature.
Characterization of Amino Hydroxamic Acids and Their Metal Chelates. Determination of Protonation and Formation Constants between 2-Amino-N-hydroxy-3-methylpentanamide and Copper(II), Nickel(II), Cobalt(II), and Hydrogen Ions in Aqueous Solution
Authors: Leporati Enrico 
Published: August 2006

Abstract
The equilibria and relevant stability constant of species present in aqueous solutions of H+, CuII, NiII, and CoII with “l-isoleucinehydroxamic acid” (2-amino-N-hydroxy-3-methyl pentanamide, ahmpe1) have been investigated by using potentiometric and spectrophotometric titrations at 25 ± 0.1 °C and I = 0.5 mol dm−3 (KCl). The protonation constants of the ligand and the overall formation constants of several metal complexes were calculated from potentiometric and spectrophotometric data with the aid of the SUPERQUAD, and SQUAD programs, respectively. The following cumulative association constants (relative standard deviation values are given in parentheses) βpqr = [MpHqLr]/[M]p [H]q [L]r were obtained : log β011 = 9.15(1), log β021 = 16.40(1); CoII-ahmpe1, log β111 = 12.26(1), logβ101 = 5.50(1), logβ102 = 9.46(6), logβ1–11 = −1.71(2); NiII-ahmpe1, logβ101 = 6.90(2), logβ102 = 14.28(5), logβ1–12 = 6.06(2); CuII-ahmpe1, logβ101 = 10.36(1), logβ102 = 19.85(1), logβ2–12 = 20.90(1), logβ1–12 = 10.29(1). The ligand is bound to the metal ions through the coordination of the N atoms of the α-amino and the deprotonated –NHO− groups. The UV-vis studies can be used to follow the appearance of the individual species, to estimate the coordination sphere around the metal ion and to observe the equilibria between different complexes. So the solution electronic spectra have been also employed to suppose a weak tetragonal coordination in the [CuL2(H2O)2] complex. Equilibrium constants for their formation and the probable structure of the chelated compound formed in aqueous solution are the object of discussions in terms of their possible significance to biological reactions, and their stability is compared with that of analogous chelated compounds.
Bis(phenylethynyl)hafnocene as an Organometallic Chelate Ligand
Authors: Lang Heinrich , Herres Mathias , Zsolnai Laszlo 
Published: August 2006

Abstract
The application of (η5-C5H4SiMe3)2Hf(C≡CPh)2 (1) as an organometallic chelate ligand towards different organometallic building blocks will be discussed. 1 reacts with Ni(CO)4 (2) or Co2(CO)8 (4) to yield {(η5-C5H4SiMe3)2Hf(C≡CPh)2}M(CO) (M = Ni: 3, M = Co: 5) and (η5-C5H4SiMe3)2Hf(C≡CPh) [μ-(η2-C≡CPh)Co2(CO)6] (6). In 6 one of the two phenylethynyl units is η2-side-on coordinated to Co2(CO)6 forming a 1,2-dicobaltatetrahedrane unit. However, the reaction of 1 with Fe2(CO)9 (7) affords (η5-C5H4SiMe3)2Hf[(η2-C≡CPh)Fe(CO)4]2 (8), a compound, in which both of the phenylethynyl ligands are η2-side-on coordinated to Fe(CO)4 complex fragments. All new synthesized compounds have been characterized by analytical and spectroscopic data. Additionally, the structure of 3 was established by X-ray diffraction study.
Crystal Structure and Luminescence Site of Na9[EuW10O36]·32H2O
Authors: Sugeta Moriyasu , Yamase Toshihiro 
Published: August 2006

Abstract
Na9[EuW10O36]·32H2O, obtained from aqueous solutions, crystallizes in space group Cc with a = 11.484(5), b = 23.020(7), c = 23.581(6) Å, β = 91.71(3)°, V = 6231(3) Å3, Mr = 3349.4, Dx = 3.57 Mg m−3, and Z = 4. A full-matrix least-squares refinement finally yields R = 0.070 and Rw = 0.086 for 6473 independent reflections. The local symmetry around Eu3+ for the [EuW10O36]9− anion is approximately square antiprismatic. Photoexcitation into the oxygen-to-tungsten charge transfer bands of a solid sample leads to red emission due to f–f transitions within Eu3+, as a result of an intramolecular energy transfer from the W5O18 group to the Eu atom. The spectral transitions of photoluminescence recorded at 4.2 K can be interpreted based on the assumption of a C4v point group for Eu3+, which is consistent with the co-ordination geometry for the Eu atom.
Effect of a Solvent on the Extraction of the Europium(III) 2-Thenoyltrifluoroacetonate Anionic Complex as Ion-Pairs with Tetrabutylammonium Ions
Authors: Noro Junji , Sekine Tatsuya 
Published: August 2006

Abstract
The solvent extraction of europium(III) in aqueous 0.1 mol dm−3 sodium nitrate or sodium chloride solutions with 2-thenoyltrifluoroacetone (Htta) into chloroform, toluene, and 4-methyl-2-pentanone (MIBK) was studied in both the absence and presence of tetrabutylammonium ions (tba+); the results were compared with those into carbon tetrachloride. When the diluent was chloroform or toluene, the extraction was greatly enhanced by the addition of tba+, just as with carbon tetrachloride. This could be explained in terms of the extraction of the Eu(tta)4−tba+ species, in addition to the Eu(tta)3 species. However, this did not occur in the MIBK system, and was explained in terms of stable solvates with MIBK, which interfere with the addition of tta−tba+ ion-pairs on the Eu(tta)3 species. The enhancement due to the extraction of Eu(tta)4−tba+ was not very much different from that in the other solvent systems. This could be explained by assuming that although the amount of tta−tba+ in the organic phase was smaller in the order chloroform &gt; toluene &gt; carbon tetrachloride, the degree of association of this ion-pair with the Eu(tta)3 in the organic phase was larger in the inverse order, and that these two opposite tendencies canceled each other out. The results were compared with the synergistic enhancement of the extraction of europium(III) with Htta by organophilic neutral ligands, such as tributylphosphate.
Crystal Structure and Polymorphism of Antiferroelectric Mesogen, 4-[(S)-1-Methylheptyloxycarbonyl]phenyl 4′-Octyloxybiphenyl-4-carboxylate (MHPOBC)
Authors: Hori Kayako , Endo Kyoko 
Published: August 2006

Abstract
Single crystal X-ray analysis has been carried out for the title compound, –COOCH(CH3)C6H13, which has antiferroelectric liquid crystalline phases. Crystal data; monoclinic, P21, T = 298 K, a = 32.285(7), b = 5.520(2), c = 9.320(2) Å, β = 95.34(2)°, V = 1653.7(7) Å3, Z = 2, dx = 1.123 g cm−3. The crystal has a smectic-like layer structure composed of largely bent molecules; a chain of the chiral group is almost perpendicular (93°) to the core moiety. DSC and temperature dependence of powder X-ray diffraction patterns show that the crystal is a metastable phase, which transforms to a more stable crystalline phase with longer spacing of layer.
Nitriles in Heterocyclic Synthesis. The Reaction of Polyhydric Naphthalenes, 4-Methylcoumarin-3-carbonitrile, and Alkylidenemalononitrile with Methylenemalononitrile
Authors: Elagamey Abdel Ghani Ali , El-Taweel Fathy Mohamed Abdel-Aziz , Khodeir Mohamed Nabil Mohamed , Elnagdi Mohamed Hilmy 
Published: August 2006

Abstract
2-Naphthol and naphthalenediols react with methylenemalononitrile, generated in situ from reaction of formaldehyde and malononitrile, to yield naphthopyrans and naphthodipyrans. 5-Hydroxynaphtho[2,1-b]pyrans reacted further with methylenemalononitrile to yield naphthodipyrans. The reaction of methylenemalononitrile with 4-methylcoumarin-3-carbonitrile afforded benzopyrano[4,3-h]quinoline. 6-Cyanomethyl-3-pyridinecarbonitriles, prepared via reacting 1-arylethylidenemalononitriles with malononitrile, afforded 4H-quinolizines on treatment with methylenemalononitrile.
Syntheses and Reactions of Metal Organics. XVII. Synthesis of Silane Coupling Agent Having Fluorocarbon Chain and Surface Modification of Glass Plate
Authors: Yoshino Norio , Yamamoto Yasushi , Seto Tsuyoshi , Tominaga Shin-ichi , Kawase Tokuzo 
Published: August 2006

Abstract
Four silane coupling agents,1H,1H,2H,2H-polyfluoroalkyl(dimethoxy)(methyl)silanes (1H,1H,2H,2H-henicosafluorododecyl(dimethoxy)(methyl)silane, C10F21C2H4Si(CH3)(OCH3)2, 1H,1H,2H,2H-heptadecafluorodecyl(dimethoxy)(methyl)silane, C8F17C2H4Si(CH3)(OCH3)2, 1H,1H,2H,2H-tridecafluorooctyl(dimethoxy)(methyl)silane, C6F13C2H4Si(CH3)(OCH3)2, and 1H,1H,2H,2H-nonafluorohexyl(dimethoxy)(methyl)silane, C4F9C2H4Si(CH3)(OCH3)2), were prepared by the hydrosilylation of dichloro(methyl)silane with the corresponding 1H,1H,2H-polyfluoro-1-alkene in the presence of hydrogen hexachloroplatinate(IV), followed by the reaction with sodium methoxide. The surface modification of glass plate was attempted using these products. From measurements of the contact angles θ(°) of water and oleic acid against a modified glass plate surface, the coupling agents were found to have high modification ability. The oxidation resistance of the modified glass surface was also investigated.
The Solubility and Conformation of Protected Tri- to Heptapeptides in a Variety of Organic Solvents and the Classification of Organic Solvents Based on Their Solvating Potential for Protected Peptides
Authors: Narita Mitsuaki , Lee Jin-Shik , Hayashi Shizue , Yamazaki Yasunobu , Hitomi Mitsuo 
Published: August 2006

Abstract
The solubility in a variety of organic solvents was examined for 75 kinds of protected tri- to heptapeptide fragments of E. coli ribosomal protein L7/L12. The organic solvents examined were classified into six groups mainly by considering their solvating potential and supplementarily by using their acceptor number (AN) and donor number (DN). The result of the classification of the organic solvents was practically explained by the DN and AN of the organic solvents, indicating that the electron-donating or -accepting ability of organic solvents is much more important for the solvation of protected peptides than their ability to form van der Waals interactions. Nevertheless, the solvation mechanism of protected peptides in organic solvents could be explained by two types of intermolecular interactions, namely, intermolecular hydrogen bonding and van der Waals interactions. The &lt;SPβ&gt; values of protected peptieds, difined in a previous paper, properly reflected their β-sheet-structure stability in a variety of organic solvents regardless of their amino acid sequence. The solubility of protected peptides in organic solvents was also strongly related to their &lt;SPβ&gt; values. In fact, peptides having a low &lt;SPβ&gt; value were easily soluble in various organic solvents and had an unordered structure in solution.
The Heteroselective Solvation of Protected Hexapeptides in a Variety of Mixed Solvents and the Criteria for the Choice of Mixed Solvents Effective for Peptide and Protein Synthesis
Authors: Narita Mitsuaki , Lee Jin-Shik , Hayashi Shizue , Yamazaki Yasunobu , Sugiyama Tomoko 
Published: August 2006

Abstract
Focusing our attention on both the van der Waals interactions between solvents and peptide side chains and the electron donor–acceptor interactions between mixed solvents, the solubility and conformation in a variety of mixed solvents were examined for protected hexapeptide fragments of E. coli ribosomal protein L7/L12. Although it was difficult to precisely evaluate the van der Waals interactions between solvents and peptide side chains, it was confirmed that the van der Waals interactions between solvents and peptide side chains were important for the solvation of protected peptides in mixed solvents. The electron donor–acceptor interactions between mixed solvents remarkably decreased the β-sheet-structure-disrupting potential of a variety of mixed solvents. In connection with the β-sheet-structure-stabilizing potential, &lt;SPβ&gt;, of protected peptides, it was also confirmed that the &lt;SPβ&gt; value of protected peptides properly reflected their β-sheet-structure stability in a variety of mixed solvents. The criteria for the choice of mixed solvents effective in peptide and protein synthesis was led on the basis of both the heteroselective solvation mechanism in mixed solvents and the electron donor–acceptor interactions between mixed solvents. The significance of the present study in the choice of effective solvents for liquid- and solid-phases peptides synthesis is elaborately discussed.
Pressure Dependence of the Rate Constant for the Reaction of CH3O + NO
Authors: Ohmori Kenji , Yamasaki Katsuyoshi , Matsui &lt;FNR RID="N02"&gt;Hiroyuki 
Published: August 2006

Abstract
The reaction of CH3O with NO was examined at room temperature (T = 296 ± 6 K), where, CH3O was produced in 266 and 355 nm photolysis of CH3ONO, and detected by laser-induced fluorescence technique. From the time resolved analysis of CH3O with excess amount of NO, the rate constant for reaction CH3O + NO (+ M) → products (+M) (1) was measured over the total pressure range of 7—100 Torr[He], 10—70 Torr[N2], 15—50 Torr[CF4], and 10—50 Torr[SF6] (1 Torr = 133.322 Pa). The high-pressure limiting rate constant for reaction (1) has been evaluated to be k1∞ = (4.5 ± 1.5) × 10−11 cm3 molecule−1 s−1 with Hinshellwood-Lindemann theory. The present result is found to be consistent with that obtained recently by Frost and Smith.
Addition Reaction of Phenyl Isocyanate and Phenyl Isothiocyanate to Partially Cyclic 1,3-Diaza-1,3-butadienes. Synthesis of Annulated 1,3,5-Triazine-2,4(1H,3H)-diones and -2,4(1H,3H)-dithiones
Authors: Abdel-Rahman Mahmoud A 
Published: August 2006

Abstract
Annulated 1,3,5-triazine-2,4(1H,3H)-diones and -2,4(1H,3H)-dithiones (8 and 9) are synthesized by a 4π+2π cyclodimerization of heterocyclic heterocumulenes (6 and 7). These heterocumulenes are generated from partially cyclic 1,3-diaza-1,3-butadienes (1a—c) by means of a 2π+2π cycloaddition reaction with phenyl isocyanate or phenyl isothiocyanate and followed by dissociation of the resulting cycloadducts (1,3-diazetidinones (3) and 1,3-diazetidithiones (4)).
Effect of Methyl Substitution on Conformation and Molecular Arrangement of BEDT-TTF Derivatives in the Crystalline Environment
Authors: Matsumiya Shigeki , Izuoka Akira , Sugawara Tadashi , Taruishi Tomohiro , Kawada Yuzo 
Published: August 2006

Abstract
Two methylated bis(ethylenedithio)tetrathiafulvalene (ET) derivatives, Me2ET and Me4ET were stereoselectively synthesized to examine the effect of methylation on conformations of dihydrodithiin rings and molecular arrangements in the crystalline state. Since the donating ability of Me2ET and Me4ET are similar to that of ET, the methylated ET derivatives are considered to be appropriate to investigate the “lattice pressure” effect on ET radical salts by changing the volume of donor molecules. The upper limit of an activation energy for the ring inversion of the dimethylated dihydrodithiin in solution was estimated to be 32 kJ mol−1 by 13C NMR spectroscopy. The X-ray structure analyses revealed that orientations of methyl groups are fixed to axial in Me2ET and to equatorial in Me4ET, accompanied by the change of molecular stacking. The “volume of a methyl group” was evaluated by comparing the molecular volumes of Me2ET and Me4ET with that of ET, and the effective volume for the axial methyl group turns out to be 15% larger than that of the equatorial. The solid state 13C NMR (CP/MAS) spectra of ET and its derivatives showed that the chemical shifts of resonance lines reflect the conformations of dihydrodithiin rings in crystals.
Total Synthesis of Grahamimycin A1
Authors: Ohta Kazuo , Miyagawa Osamu , Tsutsui Hironori , Mitsunobu Oyo 
Published: August 2006

Abstract
(3R)- and (3S)-3-Hydroxybutanoates were respectively converted into (2E,5R)- and (2E,5S)-5-t-butyldimethylsiloxy-2-hexenoic acids, corresponding to the O-1–C-6 fragment of grahamimycin A1 (1). The O-7–C-14 fragment [(4S,5S,7R)- or (4R,5R,7R)-7-hydroxy-4,5-isopropylidenedioxyoctanoate] was synthesized from 4,6-dideoxy-α-D-xylo -hexopyranoside. Condensation of the both fragments, followed by deprotection at the terminal hydroxyl- and carboxyl-functions afforded the seco acids of the precursors of 1. While the reaction of the seco acids having 13S-configuration with diethyl azodicarboxylate and triphenylphosphine afforded the corresponding lactones in low yields, macrolactonization of the seco acid having 13R-configuration by Yamaguchi procedure gave the desired lactone in 56% yield. Deprotection of vic-diol moiety of the lactone indicated the completion of relay synthesis of 1.
Preparations of Optically Active Homocysteine and Homocystine by Asymmetric Transformation of (RS)-1,3-Thiazane-4-carboxylic Acid
Authors: Miyazaki Hideya , Ohta Atsushi , Kawakatsu Nobuyuki , Waki Yukitaka , Gogun Yasuhiro , Shiraiwa Tadashi , Kurokawa Hidemoto 
Published: August 2006

Abstract
Dl-Homocysteine [Dl-Hcy] from (RS)-homocysteine thiolactone hydrochloride [(RS)-HTL·HCl] was subjected to reaction with formaldehyde in acetic acid to give (RS)-1,3-thiazane-4-carboxylic acid monohydrate [(RS)-THA·H2O]. An asymmetric transformation of (RS)-THA·H2O was achieved via salt formation with optically active tartaric acid in the presence of salicylaldehyde in acetic acid. The (R)- and (S)-THA obtained, respectively, from the salt of (R)-THA with (2R, 3R)-tartaric acid and its enantiomeric salt were treated with hydroxylamine hydrochloride to give d- and l-Hcy of 100% optical purity, respectively, in 50% yield from (RS)-HTL·HCl. Oxidation of d- and l-Hcy with hydrogen peroxide gave d- and l-homocystine, respectively, in 47% yield.
Reaction of (Cyano)thioacetamide with Arylhydrazones of β-Diketones: Novel Synthesis of 2(1H)-Pyridinethiones, Thieno[2,3-b]pyridines, and Pyrazolo[3,4-b]pyridines
Authors: Elgemeie Galal Eldin Hamza , El-Zanate Ali Mahmoud , Mansour Abdel-Kader E 
Published: August 2006

Abstract
A novel synthesis of 2(1H)-pyridinethiones, thieno[2,3-b]pyridines and pyrazolo[3,4-b]pyridines utilizing (cyano)thioacetamide and arylhydrazones of 1,3-diketones as starting components is described.
Ferroelectric Liquid Crystals Having Various Cores. Effect of Core Structure on Physical Properties
Authors: Sugita Shin-ichi , Toda Susumu , Yamashita Tetsuo , Teraji Tsutomu 
Published: August 2006

Abstract
Ferroelectric liquid crystals (FLC’s) having various cores were synthesized and the effect of the different core structures on the spontaneous polarization (Ps) values was investigated. The results indicate that the core structure has a great influence on the Ps value and introduction of a heterocycles such as pyrimidine and thiadiazole ring in the core increases the Ps value. Moreover, several compounds in this series are interesting as chiral dopants for FLC, because the mixtures containing them showed superior properties as FLC mixture.
General Graph Theory of Superaromaticity
Authors: Aihara Jun-ichi 
Published: August 2006

Abstract
A conjugated super-ring molecule with a cavity inside may exhibit superaromaticity, i.e., extra thermodynamic stabilization due to the super-ring structure. General graph theory of superaromaticity was developed so as to analyze superaromatic character of all kinds of conjugated super-ring molecules. Typical conjugated super-ring molecules, such as kekulene, azulenoid kekulene, anti-kekulene, octadecabenzokekulene, hexa-m-phenylene, and hexabenz[18]annulene, were predicted to be essentially non-superaromatic.
Syntheses and Properties of New Liquid-Crystalline Polymers Having 1,3,2-Dioxaborinane Pendants
Authors: Matsubara Hiroshi , Seto Koji , Tabuchi Hitoshi , Imazaki Hideyuki , Takahashi Shigetoshi 
Published: August 2006

Abstract
Polyacrylates and polymethacrylates having various 1,3,2-dioxaborinane derivatives as pendants have been synthesized and demonstrated to form chiral smectic C and/or smectic A phases which are more stable than those formed by the corresponding monomes. They provide a new family of chiral liquid crystalline side-chain polymers containing boron atoms in the pendant group.
Free Volume Holes of Rubbery Polymers Probed by Positron Annihilation
Authors: Okamoto Ken-ichi , Tanaka Kazuhiro , Katsube Mikio , Kita Hidetoshi , Ito Yasuo 
Published: August 2006

Abstract
The lifetime and the intensity of ortho-positronium (o-Ps), τ3 and I3, respectively, were measured for various polymers below and above glass transition temperatures Tg. The average size of micro-vacancies probed by o-Ps, vh,Ps, was evaluated from τ3 using an empirical equation. Both temperature dependence of τ3 and comparison of magnitude of vh,Ps between the polymers and molecular liquids having similar cohesive energy density reveal that the micro-vacancies probed by o-Ps at temperatures not much above Tg are pre-existing and momentarily frozen free volume holes rather than Ps bubbles. A method to evaluate the volume fraction and the concentration of free volume holes probed by o-Ps, VF, Ps, and Ch, Ps respectively, is proposed by assuming that the size-distribution is approximated by an exponential function with a mean size &lt;vh&gt;, and that the volume fraction of total free volume holes is equal to fractional free volume calculated by the Bondi method. This model predicts clear correlations between &lt;vh&gt; and the concentration of total free volume holes and also between VF,Ps and vh,Ps. There is no clear correlation between Ch,Ps and I3, suggesting that I3 is not a good measure of the concentration of free volume holes.