bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Study on the Mechanism of Catalysis of Coenzyme B12-Dependent Diol Dehydratase
Authors: Eda Masataka , Kamachi Takashi , Yoshizawa Kazunari , Toraya Tetsuo 
Published: September 2002

Abstract
The energy profile of the diol dehydratase reaction is discussed from theoretical calculations at the B3LYP/6-311G* level of density functional theory. The differences between the energy diagrams of models with and without K+ ion are rather small except for the substrate binding and the OH group migration. The most important role of K+ ion in the diol dehydratase catalysis is to fix substrates and intermediates in proper positions in order to ensure the hydrogen abstraction and recombination between them and the adenosyl group. In the course of the reaction, substrates and reaction intermediates would always be kept bound to K+ ion until the release of product aldehyde from the active site. Given the neutral radical state of the substrate, the OH group migration proceeds in a concerted mechanism. In this process, K+ ion can work as an inhibitor of intramolecular hydrogen bond, which decreases the activation energy by 4.0 kcal/mol, due to the destabilization of reactant 1,2-dihydroxypropyl radical. The lowering of the activation energy by K+ ion, however, is rather small, and thus the contributions of active-site amino acid residues to the OH group migration must be taken into consideration to explain that the hydrogen abstraction is the rate-determining step for the overall reaction.
Study of the Reactions of O- with CF4 and CHF3 by Ab Initio Calculations
Authors: Yamamoto Mitsuo , Yamashita Koichi , Sadakata Masayoshi 
Published: September 2002

Abstract
Previous experiments on the reactions of O- with CF4 and CHF3 using a selected ion flow tube (SIFT) have indicated that many species, such as CF3-, F-, and HF2-, are produced in the O- + CHF3 reaction, although no reaction proceeds in the O- + CF4 reaction under thermal conditions. Ab initio molecular orbital calculations were carried out in this study to clarify the reason for the difference in the reactivity between these two reactions. Potential energy surfaces (PESs) for the possible reaction channels were computed at the UMP2/6-31+G** level. Although the SN2-type reactions, such as the CF3O- + F channel, are exothermic, the calculated activation energy for the O- + CF4 reaction is rather high, 222 kJ/mol. The energies of the transition states in the O- + CHF3 reaction are below that of the reactant. We may conclude that the difference in reactivity between the two reactions is attributable to the charge distribution of each molecule. The H atom in CHF3 has a large effect on increasing the reactivity because the positively charged H atom attracts O-, whereas O- has difficulty approaching the CF4 molecule because of the four negatively charged F atoms.
Electrochemical-ESR Detection of Hydrogen Atom Adducts of 5-Membered Ring Nitrone Spin Traps
Authors: Endo Nobuyuki , Higashi Kousuke , Kanaori Kenji , Tajima Kunihiko , Makino Keisuke 
Published: September 2002

Abstract
In order to make the spin trapping technique more useful in biological free radical studies, using an specially designed ESR cell for in situ electrochemical reactions, five 5-membered ring nitrones, which are analogues of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), one of the most conventionally used spin traps, have been explored for their hydrogen atom (•H) adducts formation. ESR spectra consisting of only •H adducts and the resulting ESR parameters are discussed.
Spectroscopic and Structural Studies on Adsorption of Azo Dye in Cationic Langmuir–Blodgett Films
Authors: Ray Krishanu , Nakahara Hiroo 
Published: September 2002

Abstract
The monolayer properties of octadecylamine at various pHs on the Naphthalene Red (NR) aqueous solution were studied from the measurements of surface pressure–area isotherms. It was observed that the presence of the azo dye substituted with the –OH group (NR) in the subphase affects the compressibility of the octadecylamine monolayer. The adsorbability of the cationic Langmuir–Blodgett (LB) films was investigated by NR as an adsorbate. The cationic LB films before and after the azo dye adsorption were characterized by UV–vis absorption and emission spectroscopy, polarized visible absorption, X-ray diffraction, FTIR spectroscopy, and atomic force microscopy. Strong dipole–dipole interaction between the NR molecules in functionalized LB films was observed in accordance with the exciton model. It was found that the adsorption of the azo dye induced rearrangement of the layer structure of the cationic LB films where the hydrocarbon chains of the amine molecules exhibited an interdigitated structure and the azo dye molecules adsorbed in the LB films were oriented in an edge-on configuration. Furthermore, the substituent position of the –OH group of NR plays a crucial role in the different ways on the orientation of the other azo dyes in organized assembly.
Anisotropic Intermolecular Interactions and Through-Space/Through-Bond Intramolecular Interactions Observed by Collision-Energy-Resolved Penning Ionization Electron Spectroscopy
Authors: Kishimoto Naoki , Ogasawara Hideyuki , Ohno Koichi 
Published: September 2002

Abstract
Ionization of 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,4-cyclohexadiene (CHD), and 2,5-norbornadiene (NBD) with He*(23S) metastable atoms was studied by (collision-energy/electron-energy-resolved) two-dimensional Penning ionization electron spectroscopy. Anisotropic interaction around the molecule was investigated by determining collision energy dependence of partial ionization cross sections (CEDPICS) and spatially anisotropic distribution of ionized molecular orbitals (MOs). The negative slope of CEDPICS for HOMO was smaller than that for the next HOMO of DABCO and CHD; this was due to the repulsive interaction around the σCC,CH bond region, which is related to the through-bond interaction via the electron distribution. The trend of CEDPICS for DABCO was confirmed by classical trajectory calculations. For NBD, the negative CEDPICS for the next HOMO was larger than that for HOMO; this was due to the attractive endo region for the in-phase next HOMO with the through-space interaction.
A Facile Preparation of 5-Isopropylidene-3,8-dimethyl-1(5H)-azulenone and Its Crystal Structure
Authors: Takekuma Shin-ichi , Jyoujima Syougo , Sasaki Masato , Matsumoto Takuya , Fukunaga Hideo , Takekuma Hideko , Yamamoto Hiroshi 
Published: September 2002

Abstract
Oxidation of 5,5′-biguaiazulene-3,3′(5H,5′H)-dione (2) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in CH2Cl2 at 25 °C under aerobic conditions rapidly gives the title compound, 5-isopropylidene-3,8-dimethyl-1(5H)-azulenone (4), in 52% isolated yield. The crystal structure of 4 is reported as the first example for azulenequinonemethides.
Kinetics and Mechanism of the Cobalt(III) Tetraammine Complex-Promoted Hydrolysis of 4-Nitrophenyl Glycinate
Authors: Phulambrikar Alka Anant , Chatterjee Chinmay 
Published: September 2002

Abstract
The kinetics of the hydrolysis of 4-nitrophenyl glycine ester (PNPG) catalysed by [Co(OH)(trien)(OH2)]2+, [Co(OH)(tren)(OH2)]2+ and [Co(OH)(en)2(OH2)]2+ complexes has been studied spectrophotometrically in weakly basic aqueous media (pH = 6.5 to 7.4). Kinetic experiments were carried out as a function of the pH, complex concentration and temperature. The rate of hydrolysis increases linearly with the complex concentration with a trend to wards rate saturation, suggesting the formation of associative species in a pre-equilibrium step. The pseudo-first order rate constant, kobs, increases rapidly with a decrease in the hydrogen-ion concentration. The complexes promote the hydrolysis of 4-nitrophenyl glycinate significantly, and the acceleration rate is about 400–600. An attack of external OH- on the chelated ester is suggested as a probable mechanism for the hydrolysis. The lower rate enhancements observed in the present study could probably be ascribed to a weaker cobalt(III) alkoxy carbonyl interaction in the chelate, owing to a decreased nucleophilicity of the carbonyl oxygen in the p-nitrophenyl ester. The activation parameters for all three complex-promoted reactions are found to be comparable, thus suggesting a common mechanism operative in all complex catalysed reactions.
Hydrothermal Syntheses, Structures and Luminescent Properties of Lanthanide-Zinc Coordination Polymers, [Ln2Zn(pzdc)4(H2O)6·2H2O]n (pzdc = pyrazine-2,3-dicarboxylate, Ln = Gd, Nd, Sm)
Authors: Liang Yucang , Hong Maochun , Cao Rong , Su Weiping , Zhao Yingjun , Weng Jiabao , Xiong Rengeng 
Published: September 2002

Abstract
The hydrothermal reactions of Ln2O3, Zn(NO3)2·6H2O, pyrazine-2,3-dicarboxylic acid (H2pzdc) and H2O resulted in the formation of three isostructural coordination polymers [Ln2Zn(pzdc)4(H2O)6·2H2O]n (Ln = Gd, 1; Nd, 2; and Sm, 3). The crystal structures of complexes 1 and 2 were determined by X-ray diffraction methods. Compounds 1, 2 and 3 are isomorphous and crystallize in the monoclinic space group P21/n with a = 6.1196(2), b = 22.5318(8), c = 11.9617(1) Å, β = 91.766(2), V = 1648.56(8) Å3, Z = 2 for 1, a = 6.1644(3), b = 22.6577(12), c = 12.0384(6) Å, β = 91.513(2), V = 1680.8(2) Å3, Z = 2 for 2. X-ray diffraction analyses confirm that complexes 1 and 2 possess a 3-D brick-like framework structure, each framework being surround by metal atoms, with a size of 16.37×6.12 Å, accommodating two water molecules as guests. The Ln(III) ions in compounds 1 to 3 are coordinated by seven oxygen and two nitrogen atoms. In addition, the zinc(II) ions are bonded by two carboxyl oxygen, two nitrogen and two apical carboxyl oxygen atoms in an octahedral geometry. The excitation spectrum and luminescent properties of 1 and 3 were studied qualitatively.
Supramolecular Crown Ether Probe/γ -Cyclodextrin Complex Sensors for Alkali Metal Ion Recognition in Water
Authors: Yamauchi Akiyo , Hayashita Takashi , Kato Ayako , Teramae Norio 
Published: September 2002

Abstract
Crown ether probes C3-12C4 and C3-18C6, in which the pyrenyl moieties as fluorophore and benzo-12-crown-4 or benzo-18-crown-6 acting as ion recognition sites are connected by a trimethylene spacer, have been synthesized. Their supramolecular function for alkali metal ion sensing in water is compared with that of the previously designed C3-15C5/γ -CyD complex sensor. The C3-12C4, C3-15C5, and C3-18C6 are found to selectively form 2 : 1 complexes with Na+, K+, and Cs+, respectively, in the presence of γ -CyD and to exhibit pyrene dimer emission in water. These results demonstrate that the selectivity of the crown ether probe/γ -CyD complexes can be tuned by simply altering their crown ether ring size. The apparent 2 : 1 binding constants of the probes with alkali metal ions are determined at the optimum γ -CyD concentrations for each probe. For C3-12C4/γ -CyD complex, the accurate binding constant could not be obtained due to the relatively large deviation for the response. However, the fitting curve reveals that the binding constant is about 107 M-2. The 2 : 1 binding constants of the C3-15C5/γ -CyD complex for K+ and C3-18C6/γ -CyD complex for Cs+ are (3.8 ± 1.3)×109 M-2 and (5.8 ± 4.6)×107 M-2, respectively. These values are considerably larger than those of the corresponding benzocrown ethers in organic solvents. In the suparamolecular sensing system, the dimer formation of the probes inside the γ -CyD is selectively promoted by alkali metal ion binding in water. This is a novel sensing mechanism in which the dynamic molecular recognition events are successfully utilized for ion sensing in water.
Urea as a Nitrogen Source in the Formation of Polyaspartic Acid from Malic, Maleic, and Fumaric Acids
Authors: Terasaki Masanori , Nomoto Shinya , Mita Hajime , Shimoyama Akira 
Published: September 2002

Abstract
We have demonstrated an excellent feature of urea in the molten state as a nitrogen source and a polar reaction medium in the nitrogen-incorporating thermal polycondensation of malic, maleic, and fumaric acids to produce polyaspartic acid.
Synthesis and Characterization of Stable Bis(methoxo)platinum(IV) Complexes. A Facile Synthesis via Fluorenylidene-philic Interactions
Authors: Lee Young-A , Jung Ok-Sang 
Published: September 2002

Abstract
Stable mono- and bis(methoxo)platinum(IV) species via the oxidation of PtII to PtIV have been prepared and characterized. The reaction of [PtII(fpd)(dpda)] (fpd = 9-fluorenylidenepropanedioate; dpda = 2,2-dimethyl-1,3-propanediamine) with hydrogen peroxide in methanol at room temperature affords [PtIV(OH)(OCH3)(fpd)(dpda)], and further reaction at boiling methanol produces a bis(methoxo)platinum(IV) compound, [PtIV(OCH3)2(fpd)(dpda)]. The bis(methoxo)platinum(IV) compound can be prepared by the direct reaction of [PtII(fpd)(dpda)] with hydrogen peroxide in boiling methanol or by the simple stirring of [PtIV(OH)2(fpd)(dpda)] in boiling methanol. The crystal structures of [PtII(fpd)-(dpda)]·2(CH3)2NCHO (Pna21, a = 10.125(2) Å, b = 26.141(4) Å, c = 10.845(6) Å, V = 2870(2) Å3, Z = 4, R = 0.0370), [PtIV(OH)2(fpd)(dpda)]·3C2H5OH (P21/a, a = 10.312(2) Å, b = 22.044(5) Å, c = 14.225(3) Å, β = 110.25(2)°, V = 3034(1) Å3, Z = 4, R = 0.0572), and [PtIV(OCH3)2(fpd)(dpda)]·1.5CH3OH·0.5C2H5OH·0.5H2O (P1-, a = 13.333(2) Å, b = 15.386(3) Å, c = 18.446(5) Å, α = 66.80(2), β = 69.06(2)°, γ = 68.84(1), V = 3140(1) Å3, Z = 2, R = 0.0437) have been solved and refined. For [PtIV(OCH3)2(fpd)(dpda)], the 9-fluorenylidene moiety of fpd ligand snugly interacts with the methoxo group (C(22)···C(9), 3.34 Å; C(22)-H···C(9), 2.65 Å). The mono- and bis(methoxo)platinum(IV) compounds are stable even in solution.
Redox Reaction of Quinones at a Silver-Deposited Gold Electrode in Acetonitrile and Aqueous Solutions
Authors: Ando Isao , Miyake Hiroto , Ujimoto Kikujiro , Kurihara Hirondo 
Published: September 2002

Abstract
Silver-deposited gold electrodes were prepared in order to investigate the role of deposited silver onto a gold electrode in the electrochemical behavior of p-benzoquinone at the electrode. Using the electrodes as a working electrode, the electrochemical behavior of p-benzoquinones was examined in acetonitrile and aqueous solutions. In the acetonitrile solution, cyclic voltammograms for p-benzoquinone derivatives were measured and the relations between the potentials of the second-redox peak and the sum of Hammett’s σ value were examined. A potential-pH diagram was obtained for p-bezoquinone in an aqueous solution. Both relations were also obtained at other solid electrodes. The mechanism for a redox reaction at a silver-deposited gold electrode was considered based on a comparison of the observation data at the electrode with different materials.
Interaction Modes with a Halide Anion of Metal Centers of Edge-Sharing Dinuclear Complexes Bearing a Bent Form
Authors: Mizuta Tsutomu , Nakayama Koji , Aoki Shizuka , Miyoshi Katsuhiko 
Published: September 2002

Abstract
Two types of diphosphido ligands, mpe and ppe (mpe = MePCH2CH2PMe2- and ppe = PhPCH2CH2PPh2-), were used as a bridging unit in the edge-sharing bis-squareplanar complexes, [{Pt(dppe)}2(μ-mpe or μ-ppe)]Cl2 (dppe = Ph2PCH2CH2PPh2), which were prepared by the reaction of [Pt(dppe)(H2mpe or H2ppe)]Cl2 with [PtCl2(dppe)] in the presence of Na2CO3. X-ray crystal structure analyses were performed for the following diplatinum complexes: [{Pt-(dppe)}2(μ-mpe)]X2 (X = Cl- and I-) and [{Pt(dppe)}2(μ-ppe)]X2 (X = Cl- and BArf-), and their palladium analogs: [{Pd(dppe)}2(μ-ppe)]X2 (X = I- and BArf-) (BArf- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion). Regarding an M2P6 core framework, all of the dinuclear complexes in the above six crystals adopted a common bent form reported previously. It is only in [{Pd(dppe)}2(μ-ppe)]2+ that a chloride or iodide anion is incorporated into a “pocket” located under the bent bis-squareplanes to allow the two metal centers to interact simultaneously with the halide anion. The factors responsible for the above interaction mode are discussed.
Characterization of Chromium-Substituted Zeolite BEA
Authors: Yuvaraj Shanmugam , Palanichamy Muthiah Pillai 
Published: September 2002

Abstract
Chromium-incorporated BEA zeolite samples (CAB) are synthesized via a hydrothermal procedure, and their chemical compositions are analyzed by both the ICP-AES and EDX techniques. Synthesized samples are characterized for the local environment of chromium through FTIR, thermal analysis and cyclic voltammetry. An observation of a notable band in FTIR (at 955 cm-1) of calcined/acetic acid-washed samples of CAB revealed that at least a part of chromium is associated with the framework. In a thermal analysis, a high-temperature (643–773 K) desorption peak of TEA+ was noticed; the peak size increased along with an increase in the chromium content. Cyclic voltammograms of as-synthesized, calcined and acetic acid-treated samples gave ample evidence for the incorporation of chromium into the framework. Acid-washed CAB samples showed framework-stabilized chromium in a zeolite BEA structure, possibly under two different local environments, i.e. tetrahedral and square pyramidal sites.
Synthesis, Characterization, and Redox Behavior of New Dicobalt Complexes Having Monoanionic Imine/Oxime-Type Ligands
Authors: Shimakoshi Hisashi , Koga Masaomi , Hisaeda Yoshio 
Published: September 2002

Abstract
New dicobalt complexes, [CoIII2LBr4], with monoanionic ligands (L) have been synthesized by the reaction of a tetraamine and oximes, followed by an aerobic reaction with CoBr2·6H2O. The complexes were characterized by elemental analyses, IR, ESR, and NMR as well as mass spectroscopies. The redox behavior of the complexes was examined in DMF by means of cyclic voltammetry in comparison with that of the corresponding mononuclear complex. Redox waves identified to CoIII/CoII and CoII/CoI for [CoIII2L] were observed at -0.19 V and -0.69 V vs Ag/AgCl, respectively. These potentials are quite similar to those for the corresponding mononuclear complex. An electrogenerated [CoI2L] species reacts with methyl p-toluenesulfonate to give an organocobalt complex. Two-electron reduction of the dinuclear organocobalt compound yields an unstable intermediate that undergoes rapid decomposition by cleavage of the cobalt–carbon bond. The dimethylated complex, which has cobalt–carbon bonds at one axial site of each cobalt, was disproportionated to a tetramethylated complex, involving two cobalt–carbon bonds at both axial sites, and a dicobalt(I) species by two-electron reduction. The tetramethylated cobalt complex was inactive for an electrochemical reduction, but transformed into the dimethylated complex via cleavage of the cobalt–carbon bonds upon electrochemical oxidation.
Reactions of [Cd(SCN)2] and Isonicotinonitrile, Synthesis and X-ray Characterization of 1- and 3D Coordination Polymers, [Cd(SCN)2(pyCN)n] (pyCN = isonicotinonitrile, n = 1, 2)
Authors: Chen Wanzhi , Liu Fenghui , You Xiaozeng 
Published: September 2002

Abstract
Two adducts of [Cd(SCN)2] and isonicotinonitrile, [Cd(SCN)2(pyCN)n] (pyCN = isonicotinonitrile, n = 1, 2), have been synthesized and characterized by X-ray diffraction analysis. The coordination environment of the cadmium atoms in both 1 and 2 is a distorted octahedron with a 2S4N coordination geometry. Compound 1 crystallizes via the SCN- functionality, resulting in infinite linear chains. Compound 2 crystallizes via both SCN- and isonicotinonitrile functionality, thus forming an infinite 3D framework material based on 22- and 8-membered rings.
Synthesis and Structural Characterization of N,N′-Dialkylimidazolium Tetrachloroplatinate and Monoaquatrichloroplatinate Salts
Authors: Chen Wanzhi , Matsumoto Kazuko 
Published: September 2002

Abstract
N,N′-Dialkylimidazolium salts, [m-C6H4(CH2ImMe)2]-[PtCl4] (Im = imidazolium) (1) and [Mes2Im][PtCl3(H2O)] (Mes2Im = N,N′-di(2,4,6-trimethylphenyl)imidazolium) (2), were prepared and characterized by X-ray diffraction. Compound 2 is the first structurally characterized aquatrichloroplatinate compound.
The Position of Aib Residues Defines the Antimicrobial Activity of Aib-Containing Peptides
Authors: Yamaguchi Hiroshi , Kodama Hiroaki , Osada Satoshi , Jelokhani-Niaraki Masood , Kato Fumio , Kondo Michio 
Published: September 2002

Abstract
2-Aminoisobutyric acid (Aib,1 2-amino-2-methylpropionic acid) is an unusual amino acid, which is present in some antimicrobial peptides. To elucidate the impact of Aib residues on the conformation and biological activity of ion channel forming peptides, Aib residues in Ac-(Aib-Lys-Aib-Ala)5-NH2 were partially and fully replaced by Ala residues. A total of three analogs were thus synthesized. Two of these analogs, Ac-(Aib-Lys-Ala-Ala)5-NH2 (BKAA-20) and Ac-(Ala-Lys-Aib-Ala)5-NH2 (AKBA-20), had similar amino acid composition and were not hemolytic. BKAA-20 exhibited comparable antimicrobial activity to gramicidin S against Gram-positive bacteria (minimum inhibitory concentration: ∼3.13 µg ml-1), whereas AKBA-20 was not active. Single-channel measurements showed that there was a clear correlation between the antimicrobial activity and the ion channel activity in these analogs. The third analog, Ac-(Ala-Lys-Ala-Ala)5-NH2, was biologically inactive. Circular dichroism spectroscopy revealed that the helix forming propensities of BKAA-20 and AKBA-20 were independent of the position of Aib residues in negatively charged phospholipid vesicles, as mimics of external cell membranes of bacteria. However, different positions of Aib residues in BKAA-20 and AKBA-20 affected their antimicrobial activity. It is indicated that the introduction of Aib residues into the peptide backbone not only promotes the generation of stable helical conformations, but also modulates the antimicrobial activity. The results of this study can implicate a deeper understanding of the role of Aib residues in the structure-activity relationships of helical pore forming peptides, which in turn promotes the rational design of effective antimicrobial peptides.