bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Strongly Coupled Mixed Valence State Between Ru3 Clusters. Intramolecular Electron Transfer on the Infrared Vibrational Time Scale in a Pyrazine (pz) Bridged Dimer of Triruthenium Clusters, [{Ru3(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)] (abco = 1-azabicyclo[2,2,2]octane)
Authors: Yamaguchi Tadashi , Imai Naoyuki , Ito Tasuku , Kubiak Clifford P 
Published: September 2002

Abstract
A pyrazine bridged dimer of triruthenium clusters [{RuIII2RuII(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)] (abco =1-azabicyclo[2,2,2]octane, pz = pyrazine) gives an inter-cluster mixed valence state upon one electron reduction. The splitting of the reduction waves in cyclic voltammetry, ΔE, was 470 mV. This corresponds to a comproportionation constant for formation of the mixed valence state of 9.0 × 107. The IR spectrum of the mixed valence species in the ν(CO) region, measured by reflectance IR spectroelectrochemistry, showed a completely coalesced ν(CO) band. This represents delocalized redox behavior on the infrared vibrational timescale. The rate constant for intramolecular electron transfer was estimated to be 1 × 1012 s-1 at -18 °C by simulating the ν(CO) absorption bandshape. The mixed valence complex showed an intervalence charge transfer (ICT) band at 12500 cm-1. Hush analysis provides a spectroscopic estimate of HAB to be 2490 cm-1. Crystal structures of [{RuIII2RuII(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)]·2CH2Cl2 and its precursor, [RuIII2RuII(μ3-O)(CH3CO2)6(CO)(abco)2]·CH2Cl2, were determined by X-ray crystallography. Trends in Ru-O(oxo) and Ru-O(acetate) distances in these compounds show that the divalent site is localized on the Ru center attached to the carbonyl ligand.
Chemical Stability of Large Organic Molecule-Metal Complexes Dissolved in Natural Water as Studied by Size Exclusion Chromatography/Inductively Coupled Plasma Mass Spectrometry
Authors: Itoh Akihide , Iwata Kosuke , Chiba Koichi , Haraguchi Hiroki 
Published: September 2002

Abstract
The chemical stability of large organic molecule-metal complexes (LOMMCs) dissolved in pond water were investigated by a hyphenated system of size exclusion chromatography/UV absorption detection/inductively coupled plasma mass spectrometry (SEC/UV/ICP-MS) after ultrafiltration using a filter with a molecular permeation limit larger than 10000 Da. LOMMCs dissolved in the preconcentrated pond water sample were observed at the retention times corresponding to molecular weights larger than 300000 Da (Peak I) and that of 10000—50000 Da (Peak II) in the chromatograms measured by UV absorption and ICP-MS. When the pH of the sample solution was varied from 7.0 to 0.5 by adding the HNO3 solution, the peak intensities of both Peak I and Peak II in these chromatograms decreased with the decrease in pH of the sample solution. These results indicate that LOMMCs were decomposed by addition of HNO3. Peak I was rapidly decomposed below pH 4, while Peak II was gradually decomposed over the pH range from 7.0 to 0.5. The decomposition curve of Peak I was similar to the solubility characteristics of hydroxides of Fe and Al. On the other hand, that of Peak II suggested the dissociations of metal complexes (Cu and Zn) with some biogenic organic molecules. It was concluded from these results that some colloidal particles of hydroxides of Fe and Al may be core materials of LOMMCs for Peak I, while some metal complexes with biogenic protein-like compounds may be LOMMCs for Peak II. The possible models for LOMMCs in pond water were proposed as ``a string-ball model'', which might interpret as the removal and preservation mechanisms for trace elements in natural water.
Novel Fluorescent Coumarin Reagents Appending 15-Crown-5 Ether for the Rapid and Self-Catalytic Derivatization of Carboxylic Acids
Authors: Masuda Toshinobu , Kaneko Takeshi , Tanaka Toshiharu , Goya Shujiro , Murata Chiyomi , Takadate Akira 
Published: September 2002

Abstract
Novel fluorogenic coumarin derivatives appending 15-crown-5 ether as more active catalytic site were designed and synthesized for the fluorescence derivatization of carboxylic acids. From the stability constants (Ks) for complexation with metal acetates in methanol, it was found that their catalytic abilities were superior to the corresponding benzo-15-crown-5 ether type reagent. However, the reactivity of these reagents in the derivatization of lauric acid was dependent on not only the catalytic ability of the introduced crown-ether but also on the appending position of that in a reagent molecule. Furthermore, the derivatized products showed remarkably high fluorescence quantum yields of above 0.8 in methanol and acetonitrile. Allowing to hold a certain function such as catalyst in a reagent molecule should serve as a new strategy for the development of excellent analytical reagents.
Synthesis, Crystal Structure, and Some Spectrochemical Properties of Optically Active S-Bridged Trinuclear Complex ΔΔ-[Ni{Co(aet)2(R-pn)}2]4+ (aet = 2-Aminoethanethiolate, R–pn = (R)–1,2-Propanediamine)
Authors: Yamada Yasunori , Maeda Yoko , Miyashita Yoshitaro , Fujisawa Kiyoshi , Konno Takumi , Okamoto Ken-ich 
Published: September 2002

Abstract
The reaction of cis-[CoCl2(R-pn)2]+ (R–pn = (R)–1,2-propanediamine) with [Ni(aet)2] (aet = 2–aminoethanethiolate) in water stereoselectively gave an S-bridged trinuclear complex, [Ni{Co(aet)2(R-pn)}2]4+, accompanied by the ligand-transfer of aet from Ni2+ to Co3+. The ΔΔ isomer of the trinuclear complex was selectively formed. The spectrochemical properties of theΔΔ isomer are also discussed in relation to the stereochemical behavior.
Conformational Studies of Cyclo(Pro-Leu-Aib)2by 1H Nuclear Magnetic Resonance Spectroscopy and Circular Dichroism
Authors: Wang Jun , Osada Satoshi , Kodama Hiroaki , Kondo Michio 
Published: September 2002

Abstract
The synthesis and conformational analysis of cyclo(Pro-Leu-Aib)2 by means of NMR technique are reported. The cyclohexapeptide was synthesized in the classical high-dilution solution method. Its yield in the cyclization reaction from linear hexapeptide active ester was lower than that of the analogous cyclo(Pro-Leu-Gly)2 previously reported. Two sets of amide proton signals for Leu and Aib in NMR spectra and temperature coefficients indicated an asymmetric conformation which contains both cis and trans Aib-Pro bonds. Here Pro amino acids occupy the positions i+2 of β-turns. The CD spectrum gave two negative bands at 202 and 230 nm, which is considered to be the sum of type II′ (when Aib-Pro is trans) and type VI (when Aib-Pro is cis) β-turns.
Practical Synthesis of (6-Chloro-3-pyridyl)methylamine by Highly Selective Hydrogenation of 6-Chloro-3-pyridinecarbonitrile with Improved Raney Nickel Catalyst
Authors: Tanaka Ken , Nagasawa Minoru , Sakamura Hideki 
Published: September 2002

Abstract
A practical synthesis of (6-chloro-3-pyridyl)methylamine (1), one of the key intermediates of neo-nicotinoid insecticides, by a highly selective hydrogenation of 6-chloro-3-pyridinecarbonitrile (4) is described. The use of an improved Raney nickel catalyst, prepared from an alloy of low nickel content (Ni 38%, Al 62%) and subjected to heat treatment in water (98 °C, 2 h) after leaching of aluminum, was highly effective for the selective hydrogenation of 4. The hydrogenation of 4 using this catalyst was carried out in EtOH-H2O [6 : 1 (v/v)] and NH3 at 50 °C and 1.2—1.4 kg cm-2 hydrogen pressure to give 1 in 86% yield and 3-pyridylmethylamine, a dechlorinated by-product, in 2% yield.
Structural/Physicochemical Properties of Corycavidine, a Key Intermetabolite in the Biosynthesis of Isoquinoline Alkaloids, Elucidated by X-Ray Crystallography, Solution Conformation and Thermal Behavior Analyses, and Energy Calculations
Authors: Kamigauchi Miyoko , Yoshida Mayumi , Saiki Kayoko , Sugiura Makiko , Nishijo Jujiro , In Yasuko , Ishida Toshimasa 
Published: September 2002

Abstract
The conformational/physicochemical features of corycavidine (1), 5,7,8,15-tetrahydro-3,4-dimethoxy-6,15-dimethyl-[1,3]benzodioxolo[5,6-e] [2]benzazecin-14(6H)-one, an important protopine-type alkaloid that serves as the key intermetabolite in the biosynthesis of isoquinoline alkaloids, were examined by X-ray crystallography, 1H NMR spectroscopy, as well as thermal analysis and energy calculations. Two stable conformations of 1, as proposed by energy calculations, were also observed in both the crystalline and solution states. Racemization of optically active 1, which was caused by heating of the crystal, was analyzed by differential-scanning calorimetry. By taking advantage of the H-2H replacement reaction at the C13 atom of 1, the rate of racemization in the C2H3O2H/NaO2H solution was measured as a function of the temperature; the energy barrier between both enantiomers was estimated to be 4.7 kcal mol-1. The crystallization of racemic 1 led to two different crystal forms, i.e., the racemic crystal and the conglomerate crystal (1 : 1 mixture of both enantiomeric crystals). This was probably due to the low energy difference between both crystals. These physicochemical behaviors are important for understanding the in vivo nonenzymatic racemization of 1 and its related alkaloids during metabolic processes.
Acylthio- and Thioacylthiophosphines [(RCES)nPPh3-n, E = O, S; n = 1—3]: Synthesis and Structural Analysis
Authors: Tani Kazuyasu , Matsuyama Kazuo , Kato Shinzi , Yamada Kohzaburo , Mifune Hirotaka 
Published: September 2002

Abstract
Stoichiometric reactions of alkali metal thio- and dithiocarboxylates with Ph2PCl, PhPCl2, and PBr3 gave the corresponding acylthio- and thioacylthiophosphines [(RCES)nPPh3-n, E = O, S; n = 1—3] 3—8 in moderate to good yields. The structures of (4-CH3C6H4COS)nPPh3-n (3d: n = 1, 4d: n = 2, 5d: n = 3) and (4-CH3C6H4CS2)2PPh (7b) were analyzed by X-rays. In the thiocarboxylate derivatives 3d, 4d, and 5d, the intramolecular interactions between the carbonyl oxygen and the central phosphorus atoms are weak and the thiocarboxylato ligands act as monodentates through the sulfur atoms. Similarly, in the dithiocarboxylate derivative 7b, the intramolecular interactions between the thiocarbonyl sulfur and the central phosphorus atoms are weak and the dithiocarboxylato ligands act as monodentates. The covalent phosphorus-sulfur and/or phosphorus-phenyl ipso-carbon bonds are nearly at right angles to one another, forming a distorted tetrahedron with the unshared electron pair orbital at the apex. The 31P NMR spectra of the thiocarboxylic acid derivatives 3—5 show downfield shifts with an increase in the number of thiocarboxylato ligands, whereas those of the dithiocarboxylic acid derivatives 6—8 show upfield shifts.
Evaluation of the Relative Magnitude of the β-Effect of Silicon and the γ-Effect of Tin by Intermolecular Competition
Authors: Sugawara Masanobu , Yoshida Jun-ichi 
Published: September 2002

Abstract
The relative magnitude of the β-effect of silicon and the γ-effect of tin was evaluated by intermolecular competition. An acetal was allowed to react with a 1 : 1 mixture of an allylsilane and a homoallylstannane in the presence of TMSOTf (trimethylsilyl trifluoromethanesulfonate); the former was found to be more reactive than does the latter, indicating that the β-silyl group activates the carbon-carbon double bond more effectively than the γ-stannyl group. This is consistent with the results of molecular-orbital calculations which indicate that the HOMO level of the allylsilane is higher than that of the homoallylstannane. The intermolecular competition between a homoallylstannane and a terminal alkene toward electrophilic reactions with an acetal have revealed that the former is more reactive than the latter. This result indicates that the stannyl group at the γ-position definitely activates the carbon-carbon double bond toward electrophiles.
Synthesis and Structural and Electronic Properties of the Mixed Complexes of Vinylene-Bridged Bis- and Tris(octaethylporphyrin)s with Ni(II), Pd(II), and Pt(II) Ions
Authors: Higuchi Hiroyuki , Shinbo Masatoshi , Usuki Masanobu , Takeuchi Makoto , Tani Keita , Yamamoto Koji 
Published: September 2002

Abstract
Various mixed complexes of vinylene-bridged bis- and tris(octaethylporphyrin)s (bis(OEP)-(M1-M2) and tris(OEP)-(M1-M2-M3)) with d8 transition-metal ions M(II) (M: M1, M2, and M3 = Ni or Pd or Pt) were synthesized by step-by-step and selective metallations of the respective free-bases (FB) with limited amounts of the metallation reagent. Metallation of tris(OEP)-(H2-H2-H2) started in the central OEP ring, with the vinylene linkages of the product retaining the same (E,E)-configuration as those in FB. On the other hand, metallation of (E)-bis(OEP)-(H2-H2) afforded the corresponding (E)-bis(OEP)-(M1-M2) predominantly, while metallation of (Z)-bis(OEP)-(H2-H2) was accompanied by a ready isomerization of the vinylene linkage to afford each pair of (E)- and (Z)-isomeric complexes under the similar conditions. Electronic absorption spectra of tris(OEP)-(M1-M2-M3) proved to be affected especially by the central OEP-M2 ring and by the heavier metals more intensively, resulting in the largest splitting of the Soret band for the Ni-Pd-Pt complex. Examination of the oxidation potential E1 values indicated that the electron-releasing abilities of tris(OEP)-(M1-M2-M3) are intensively reduced for the complex carrying at least two consecutive heavier metal OEP rings. In the case of bis(OEP)-(M1-M2), the (E)-isomeric series exhibited the reduction of the electron-releasing abilities regularly in order of the heavy metal complexes similarly to tris(OEP)-M, while the (Z)-isomeric series exhibited little dependence of the electron-releasing abilities upon the incorporated metals M.
Enhancement of Catalytic Activity of Chemically Modified Subtilisin Carlsberg in Benzene by Adjustment of Lyophilization Conditions
Authors: Kwon Oh Hyeong , Imanishi Yukio , Ito Yoshihiro 
Published: September 2002

Abstract
Alteration of the lyophilization conditions significantly enhanced not only the activity of insoluble native subtilisin Carlsberg but also that of solubilized enzyme in benzene. The catalytic activity (kcat/Km) for the transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with 1-propanol in benzene was enhanced more than 1000 times by the solubilization (100-fold enhancement) and the adjustment of lyophilization conditions (10-fold enhancement). Subtilisin Carlsberg was modified with polyethylene glycol (PEG-Sub) so that it could be solubilized in organic solvents. The effects of pH of the aqueous enzyme solution, of salts, or of a substrate analog in the aqueous solution before the lyophilization process, on the catalytic activity of native subtilisin and PEG-Sub were investigated. The activities of both the native subtilisin and PEG-Sub depended on the pH. The activities of both PEG-Sub and the native subtilisin were enhanced by the presence of salts. The presence of a substrate analog, N-Ac-L-Phe, also enhanced the activity of the native subtilisin and PEG-Sub. These results demonstrated that the organic solvent-solubilized subtilisin was affected by the lyophilization conditions.
Effects of the Noncyclic Cyanamides on the Retrogradation of Waxy Corn Starch
Authors: Ogawa Kazuo , Aso Kenji , Ono Shin , Yoshimura Toshiaki , Rengakuji Seichi , Nakamura Yuuko , Yamazaki Isao , Murotani Satoru , Shimasaki Choichiro 
Published: September 2002

Abstract
The suppressive effects of noncyclic cyanamides (guanidine hydrochloride, urea, and thiourea) on the retrogradation of waxy corn starch (WCS) gel were examined using differential scanning calorimetry and X-ray powder diffraction. We demonstrated that thiourea, guanidine hydrochloride, and urea effectively suppressed the retrogradation of the WCS gel in this order.
Catalytic Activity of Rare Earth-Promoted SO42-/SnO2in the Oxidative Dehydrogenation of Ethylbenzene
Authors: Jyothi Thundi Madathil , Sreekumar Kurungot , Talawar Mahadev B , Belhekar Anagha Ashok , Rao Bollapragada S , Sugunan Sankaran 
Published: September 2002

Abstract
Rare earth-promoted (10%) sulfated SnO2 catalysts were prepared by different methods and have been characterized by employing XRD, SEM, Mercury porosimetry, BET surface-area analysis, TG-DTA, and IR spectroscopy. The strength of generated acid sites depends on the preparation method. A thermogravimetric analysis revealed that the removing the sulfate species from the catalyst surface took place at temperatures &gt; 1193 K. The adsorption of butylamine and acetic acid was used to probe the acid-base properties of the catalysts. The catalytic activity of these materials in the oxidative dehydrogenation of ethylbenzene was tested at different temperatures. It was found that rare earth-modified sulfated tin oxide catalysts are more active when compared to the corresponding mixed-oxide systems and sulfated tin oxide. The combined effect of rare earth oxide and the sulfate anion leads to a enhanced oxidation activity. The existence of strong acid sites generated as a result of a sulfate treatment is involved in the activation of ethylbenzene; the addition of rare earth oxides brings about an enhancement of the reaction between the adsorbed oxygen atoms and the adsorbed ethylbenzene.
Preparation and Structure of [RhCl(nbd)(dmap)] (nbd = bicyclo[2.2.1]hepta-2,5-diene; dmap = 4-(N,N-dimethylamino)pyridine)
Authors: Takenaka Yasumasa , Osakada Kohtaro 
Published: September 2002

Abstract
4-(N,N-Dimethylamino)pyridine (dmap) reacts with [{RhCl(nbd)}2] to give [RhCl(nbd)(dmap)] (1), which was characterized by X-ray crystallography and NMR spectroscopy. The crystal structure and dynamic behavior of the molecule in solution are compared with those of [RhCl(nbd)(PPh3)] (2).
Behavior and Origin of Atmospheric NO2, SO2, and O3 in Mountains around the Kyoto Basin
Authors: Yamada Etsu , Kimura Mitsuo , Tomozawa Kenichi , Fuse Yasuro , Yamada Takeshi 
Published: September 2002

Abstract
The behavior and origin of atmospheric NO2, SO2, and O3 in mountains around the Kyoto basin were investigated by using passive samplers. Since these samplers are compact and need no batteries or pumps, they are appropriate for the measurement of atmospheric NO2, SO2, and O3 at low-level concentrations in mountains or forests. The sampling sites were Mt. Hiei, Mt. Daimonji, and 7 other mountains around the Kyoto basin, and 4 clean sites (Seryu, Kuroda, Sasari, Ashu) located about 20—30 km north of the Kyoto basin. The concentrations of atmospheric NO2, SO2, and O3 in mountains on three sides of the Kyoto basin were almost the same at the same altitude in the same season. The source of atmospheric NO2 in mountains around the Kyoto basin may be anthropogenic emission from automobiles or industrial areas, and NO2 concentration at clean sites far away from the Kyoto basin may become lower due to the diffusion of NO2. O3 concentration was higher as the altitude increased. Atmospheric O3 at mountains around the Kyoto basin has its origin in both stratospheric input and O3 production by photochemical reactions.
Synthesis of a Soluble Precursor Possessing an Nb-N Backbone Structure and Its Pyrolytic Conversion into Niobium-Based Ceramics
Authors: Cheng Fei , Sugahara Yoshiyuki , Kuroda Kazuyuki 
Published: September 2002

Abstract
Synthesis and pyrolysis of a soluble precursor possessing an Nb-N backbone structure were investigated. The precursor was prepared by aminolysis reaction of tetrakis(diethylamido)niobium with isopropylamine. The precursor was soluble in benzene, and had a polymeric structure possessing Nb-N-Nb imido-bridges. The precursor was pyrolyzed under NH3-N2 (at 600 °C for 2 h under NH3 and subsequently at 1350 °C for 8 h under N2) and Ar (at 1500 °C for 2 h) atmospheres. δ-NbN was obtained as a main crystalline phase after the pyrolysis of the precursor under NH3-N2, whereas pyrolysis of the precursor under Ar led to the formation of NbC as the only crystalline phase. More than 90% of niobium which was present in the precursor remained in both of the pyrolyzed products.
Photo- and Mechano-Catalytic Overall Water Splitting Reactions to Form Hydrogen and Oxygen on Heterogeneous Catalysts
Authors: Domen Kazunari , Kondo Junko N , Hara Michikazu , Takata Tsuyoshi 
Published: September 2002

Abstract
Recent progress of overall water splitting by photocatalysts and mechanocatalysts is briefly reviewed. In photocatalytic reactions, several new materials have been introduced, and the catalyst preparation has also been improved. As a result, a high quantum efficiency for overall water splitting of about 30% has been accomplished. In addition, recent progress in the understanding of the reaction mechanism is briefly introduced.
On the other hand, mechano-catalytic overall water splitting reaction has been recently discovered by the authors. The phenomenological aspects of this novel reaction are summarized, and some implications of the reaction mechanism are also described.
Mass-Spectrometric Study on Ion-Molecule Reactions of CH5+, C2H5+, and C3H5+ with Monosubstituted Benzenes Carrying a Hydroxy Group
Authors: Tsuji Masaharu , Arikawa Takeshi , Nishimura Yukio 
Published: September 2002

Abstract
The gas-phase ion-molecule reactions of CH5+, C2H5+, and C3H5+ with four monosubstituted benzenes carrying a hydroxy group in the substituent [PhX : X = OH, CH2OH, CH2CH2OH, and CH(OH)CH3] have been studied under a reactant-ion selective chemical ionization mode of an ion-trap type of GC/MS. The major product channel for PhOH is non-dissociative proton transfer leading to (M+H)+ ions, while that for the other three reagents is dissociative proton transfer leading to (M + H-H2O)+ ions in most cases. Small amounts of dissociative alkylation channels are found in some reactions with C2H5+ and C3H5+. The reaction mechanism is discussed based on the dependence of product-ion distributions on the reaction time and semi-empirical calculations of the energies of intermediates and products.
The Experimental Deformation Electron-Density Distributions of 4-Arylmethyleneamino-2,2,6,6-tetramethyl-1-piperidyloxyl (TEMPO) Radicals: Relations between Electron Densities and Intermolecular Interactions
Authors: Yasui Masanori , Kan-nari Eiji , Ishida Takayuki , Nogami Takashi , Iwasaki Fujiko 
Published: September 2002

Abstract
Some of the 4-arylmethyleneamino-TEMPO radicals (TEMPO = 2,2,6,6-tetramethyl-1-piperidyloxyl), such as 4-(4-chlorobenzylideneamino)TEMPO (1) and 4-(benzylideneamino)TEMPO (2), showed intermolecular ferromagnetic interactions at an extremely low temperature. The experimental electron-density distributions of these compounds were investigated by the X-ray diffraction method. Intensity data were measured at 100 K up to 2θmax (Mo K α) = 120° and 95° for 1 and 2, respectively. Deformation electron-density distributions were calculated from the structure factors after the refinements by the multipole expansion method. These electron-density distributions suggested that the unpaired electron of the O radical atom was not located on the O atom, but was rather located in the π*-orbital of the N-O bond. Lone-pair densities of the radical O atom are located in the &gt;N-O plane showing the sp2 hybridization. From the crystal structures, it has been proposed that the ferromagnetic interactions are transferred through CH…O interactions between radical O atoms and β-H atoms of the neighboring TEMPO rings. The β-H atoms of the neighboring TEMPO rings contact with the O atom in the direction toward the π*-orbital of the N-O bond, not in the direction of the lone-pair densities of the O atom. The present studies support the mechanism of the intermolecular ferromagnetic interactions through the β-H atoms. Studies of electron densities from the view point of the intermolecular interactions are important.