bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and Mechanism of the Cobalt(III) Tetraammine Complex-Promoted Hydrolysis of 4-Nitrophenyl Glycinate
Authors: Phulambrikar Alka Anant , Chatterjee Chinmay
Published: September 2002

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

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

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

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

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

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

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

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

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

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

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

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.
1H and 13C NMR Detection of the Carbocations or Zwitterions from Rhodamine B Base, a Fluoran-Based Black Color Former, Trityl Benzoate, and Methoxy-Substituted Trityl Chlorides in the Presence of Alkali Metal or Alkaline Earth Metal Perchlorates in Acetonitrile Solution
Authors: Hojo Masashi , Ueda Tadaharu , Yamasaki Masanori , Inoue Akihiko , Tokita Sumio , Yanagita Mitsuhiro
Published: September 2002

The cleavage of C–O bonds in two fluoran-based dyes by the addition of alkali metal (M+ = Li+, Na+) and alkaline earth metal (M2+ = Mg2+, Ba2+) perchlorates in acetonitrile solution was examined by means of UV-visible absorption and 1H and 13C NMR spectroscopy at room temperature. Although the 1H NMR signals of the xanthene part of Rhodamine B base (3′,6′-bis(diethylamino)fluoran) were shifted toward lower fields, those of the isobenzofuran (or the benzoate) part were not shifted much upon the addition of M+ and M2+. The appearance of 13C signals at 163.6 and 162.4 ppm (vs TMS) in the presence of Li+ and Ba2+, respectively, confirmed the formation of the zwitterions from Rhodamine B base. The assignments of the 1H and 13C signals were performed by the HMBC method. The colored zwitterion of a practical black color former, 2′-anilino-6′-dibutylamino-3′-methylspiro[3H-isobenzofuran-1, 9′-(9H)xanthene]-3-one, was produced by the addition of M+ and M2+. The 13C NMR signals at 162.2 and 159.8 ppm in the presence of 2.0 mol dm-3 Mg(ClO4)2 and Ba(ClO4)2, respectively, gave conclusive evidence of the formation of the sp2-hybrid carbon center for the black color former. The interaction between the metal ions and the zwitterions from the fluoran-based dyes decreased as Mg2+ > Ba2+ > Li+ > Na+. The 1 : 1 complex formation constants with the metal ions for both dyes were evaluated based on the UV-visible absorption data. The smaller formation constants of the black color former, compared with those of Rhodamine B base, indicate some more difficulty in the cleavage of the γ-lactone ring, which is probably based on the asymmetric structure of the compound, i.e, only a single dibutylamono-group at the 3′- and 6′-positions. The evidence for the formation of both the trityl cation and the benzoate ion was obtained by the 1H NMR signals from trityl benzoate in the presence of Mg(ClO4)2 in CD3CN containing a small amount of CF3SO3D. The C–Cl bond cleavage of 4-methoxy, 4,4′-dimethoxy, and 4,4′,4′′-trimethoxytrityl chlorides, through the chemical interaction between Ba2+ and Cl- in acetonitrile soluition, was justified by our 13C NMR results.
Effects of an Axial Ligand on the Reduction Potential, Proton Dissociation, and Fluorescence Quantum Yield of Hydroxo(porphyrinato)antimony(V) Complexes
Authors: Shiragami Tsutomu , Andou Yoshito , Hamasuna Yuichiro , Yamaguchi Futoshi , Shima Kensuke , Yasuda Masahide
Published: September 2002

The substituent effects on the reduction potentials (E1/2red), the proton dissociation constants of a hydroxo ligand (Ka), and the fluorescence quantum yields (Φ) in aryloxo(hydroxo)tetraarylporphyrinatoantimony(V) complexes were investigated. The E1/2red and Ka values were affected by substituents in the axial aryloxo ligand but, little affected by substituents in the porphyrin ring. Since E1/2red of tetraarylporphyrinatoantimony(V) complexes were higher than those of other metal-porphyrin complexes, it was suggested that the metal orbital greatly contributed to the LUMO level of the complex which can be related to the E1/2red and Ka values. Therefore, the substituent effects of the axial aryloxo ligand on the E1/2red and Ka values were attributed to the electron density of the antimony ion, which affected the LUMO level of the complexes. Moreover, the Φ of the porphyrin moiety depended on both the oxidation potential of the axial aryloxo ligands and the polarity of the solvent used. The fluorescences of the porphyrin moiety were quenched by the axial aryloxo ligands at rate constants of 108 – 1011 s-1.
Novel Synthesis of the Main Central 2,3,6-Trisubstituted Pyridine Skeleton [Fragment A-B-C] of a Macrobicyclic Antibiotic, Cyclothiazomycin
Authors: Shin Chung-gi , Okabe Akihiro , Ito Akinori , Ito Akio , Yonezawa Yasuchika
Published: September 2002

The useful synthesis of the main central 2,3,6-trisubstituted pyridine skeleton [the protected Fragment A-B-C] of a macrobicyclic antibiotic, cyclothiazomycin, was first accomplished. First, the 2-[2-(2-substituted thiazol-4-yl)]-4,5-dihydrothiazole-4-carboxylate [Fragment A derivative], attached to the 6-substituent of the main pyridine skeleton, was synthesized by two consecutive thiazolations of the protected Ser thioamide derivative with 3-bromopyruvate, and then thiazolination of the C-terminal Ser residue of the sequence. Secondly, an efficient synthesis of the central 2-(2-{2-[(1R)-1-aminoethyl]pyridin-6-yl}thiazol-4-yl)-4,5-dihydrothiazole-4-carboxylate [Fragment B derivative] was also achieved by thiazolation of the formyl group of the 2-(1-aminoethyl)-6-formylpyridine derivative, and then thiazolination. Thirdly, a convenient synthesis of the protected dehydrotetrapeptide [Fragment C derivative], which is bound to the 2-substituent of the pyridine skeleton, was attained by the usual stepwise elongation of the appropriate α-amino acids and β-elimination of a Thr residue of the sequence. Finally, the facile fragment condensation of the three Fragments thus obtained gave the protected Fragment A-B-C derivative via Fragment A-B. Furthermore, the configurational structures of the three Fragments (A, B, and C) were also investigated.
Fluorination of Sulfides Using IF5–Et3N–3HF
Authors: Ayuba Shinichi , Yoneda Norihiko , Fukuhara Tsuyoshi , Hara Shoji
Published: September 2002

Mono- and difluorinations of sulfides were achieved using a novel fluorinating reagent, IF5–Et3N–3HF. The reagent is applicable for substrates having various electron-withdrawing groups, such as an ester, amide, ketone, nitrile, sulfone, or trifluoromethyl. Because more than one fluorine atom on IF5 is used, a large excess amount of the reagent is not necessary, even for the difluorination reaction.
The Interaction of DNA and Water-Soluble Polymeric Schiff-Base Nickel Complexes
Authors: Xiao Yao-Nan , Zhang Chun-Xia
Published: September 2002

The modes and activities of the interaction of DNA and water-soluble polymeric Schiff-base nickel complexes, prepared by polymeric analogous reaction, have been discussed according to the absorption spectra, circular dichroism spectra, and fluorescent probe results. The polymeric matrix effect and increasing solubility in water can increase the interaction of these water-soluble polymeric metal complexes with DNA.
Properties of SiO2–MxOy Composites Doped with the Europium(III) Di(1,10-phenanthroline) Complex
Authors: Li Huihui , Ueda Daisuke , Inoue Satoshi , Machida Ken-ichi , Adachi Gin-ya
Published: September 2002

The europium(III) 1,10-phenanthroline complex ([Eu(phen)2]Cl3) was doped into the SiO2–MxOy xerogel matrices derived from tetraethyl orthosilicate (TEOS) and metal alkoxides (M(OR)n, M = Zr, Ta) by the sol-gel method. The resultant composites were characterized by X-ray diffraction, luminescence, UV-visible, and FT-IR spectroscopic measurements. In addition, phonon sideband (PSB) and luminescence quantum efficiency measurements have been conducted on some of the (SiO2–ZrO2) : Eu(phen)23+ composites. The luminescence emission intensity of the (SiO2–MxOy) : Eu(phen)23+ composites was found to be dependent on the matrix composition, i.e. the emission intensity maximized at the matrix composition of Si : M = 9 : 1. This observation was interpreted from various factors, such as the –OH groups in the matrices, the UV-absorbance and coupling with the lattice-vibration of the host matrices, and the non-radiative energy transfer between the neighboring Eu3+ ions, that affect the luminescence intensities of the resultant composites.
Weak Nonbonded S···X (X = O, N, and S) Interactions in Proteins. Statistical and Theoretical Studies.
Authors: Iwaoka Michio , Takemoto Shinya , Okada Mai , Tomoda Shuji
Published: September 2002

Sulfur-containing functional groups of cystine (an SSC group) and methionine (a CSC group) are usually considered as hydrophobic moieties or weak hydrogen-bond acceptors in folded protein structures. However, database analysis as well as theoretical calculations carried out in this study have provided strong evidence for the presence of specific nonbonded interactions between the divalent sulfur atoms (S) and nearby polar non-hydrogen atoms (X). Close S···X (X = O, N, S, C, etc.) atomic contacts were statistically analyzed in 604 high-resolution heterogeneous X-ray structures selected from a protein databank (PDB_SELECT). The S···O interactions found for both SSC and CSC groups showed a specific character as a π(C=O) → σ*(S) orbital interaction based on the directional preferences. The interactions were most frequently observed in α-helices. Ab initio calculations applying the second order Møller–Plesset perturbation theory (MP2) suggested the primary importance of electron correlations. The total stabilization energies were calculated to be ∼3.2 and ∼2.5 kcal/mol for SSC and CSC groups, respectively, including the contribution from a coexisting CH···O hydrogen bond. On the other hand, the S···N interactions observed for a CSC group exhibited structural characters as a π(N) → σ*(S) orbital interaction and an NH···S hydrogen bond, and the S···S interactions for an SSC group showed a structural character as an n(S) → σ*(S) orbital interaction. The S···C(π) interactions should be rather weak and long-range.
UV-Irradiated DNA Matrix Selectively Accumulates Heavy Metal Ions
Authors: Yamada Masanori , Kato Kozue , Nomizu Motoyoshi , Haruki Masahiro , Ohkawa Kousaku , Yamamoto Hiroyuki , Nishi Norio
Published: September 2002

We recently demonstrated the preparation of a water-insoluble DNA matrix by UV irradiation. The UV-irradiated DNA matrix selectively accumulated DNA-intercalating compounds and some endocrine disruptors. We evaluated the accumulation of metal ions in the UV-irradiated DNA matrix using a UV-irradiated DNA-film and DNA-immobilized glass beads. When DNA-immobilized glass beads were incubated with an aqueous solution of Hg2+, Cd2+, Pb2+, Zn2+, Cu2+, or Fe3+, the heavy metal ions were accumulated in the DNA-beads. The maximum amounts of the accumulated Hg2+, Cd2+, and Cu2+ in the DNA-beads were approximately 0.21, 0.13, and 0.22 mmol per gram of immobilized-DNA, respectively. The amounts of the accumulated Pb2+, Zn2+, and Fe3+ were lower than that of Hg2+, Cd2+, and Cu2+. Further, Fourier transform infrared (IR) studies using a UV-irradiated DNA-film with heavy metals suggested that the heavy metal ions interacted with not only the nucleic acid bases but also the phosphate groups. In contrast, the DNA-immobilized glass beads could not accumulate Ca2+ and Mg2+. These results suggested that the UV-irradiated DNA could selectively accumulate metal ions. The UV-irradiated DNA matrix has potential utility as a functional material to remove harmful heavy metal ions from contaminated water.
Electric Field Effects on Photochemical Dynamics in Solid Films
Authors: Ohta Nobuhiro
Published: September 2002

Electric field effects on photochemical dynamics have been examined with particular regard to photoinduced electron transfer (PIET) and excimer formation, based on the measurements of the field effects on emission spectra and emission decays. In various pairs of electron donor and acceptor and in their linked compounds, the following processes are shown to be significantly influenced by an electric field in a polymer film: the initial step of PIET, back-electron transfer which produces an fluorescent state, charge recombination, and dissociation of radical–ion pairs generated by PIET. With an oriented molecular system where vectorial interlayer PIET occurs, PIET is shown to be controlled by an electric field; the rate is depressed or enhanced by an electric field, depending on the field direction relative to the direction of the electron transfer. Electric field effects on excimer formation processes suggest that not only the level shift but also the change in orbital overlap between different chromophores play an significant role in electric field effects on photochemical dynamics.
Inorganic Chemistry Based on Tp Ligands —From Dioxygen Complexes to Organometallic Systems—
Authors: Akita Munetaka , Hikichi Shiro
Published: September 2002

Our recent research on transition metal complexes containing hydrotris(pyrazolyl)borato ligands (TpR), which ranges from bioinorganic chemistry of dioxygen complexes to organometallic systems, is reviewed. The TpR ligand turns out to be versatile in a wide variety of inorganic studies, because the coordination properties (both steric and electronic) can be finely tuned in a systematic manner by choosing appropriate substituents on the pyrazolyl rings to serve the purpose of the study (e.g. stabilization, activation, functionalization). For first row transition metal complexes, TpR serves as a tetrahedral enforcer to form a coordinatively unsaturated tetrahedral species, which is interconverted with five- and six-coordinate structures via coordination/dissociation of donor(s). In addition to the traditional view of TpR as a ligand system isoelectronic with cyclopentadienyls (η5-C5R5), the TpR ligand is now recognized as a unique ancillary ligand suitable for bioinorganic studies, because the tripodal ligand can mimic the coordination environment created by three imidazolyl groups from histidine residues, which is frequently found in the active sites of metalloenzymes. Through extension of the metal in TpRM-O2 adducts to those not related to biological systems we have unveiled the following new aspects of the chemistry of transition metal dioxygen complexes: (1) formation of higher valent bis(μ-oxo) species, TpRM(μ-O)2MTpR (M = Co, Ni), via O–O cleavage of TpRM(μ-η2 : η2-O2)MTpR intermediates and their relevance to the active intermediate of methane monooxygenase, (2) formation and full characterization of a variety of peroxo, hydroperoxo (Pd, Rh) and alkylperoxo species (Mn, Co, Ni, Pd), (3) structural evidence for conversion of molecular oxygen into hydroperoxide via protonation of the η2-peroxo intermediate (Rh), and (4) formation of an active species which undergoes oxidative C–C cleavage reaction (Ru). The property of the TpR ligand as a tetrahedral enforcer is best demonstrated in organometallic systems. The hydrocarbyl complexes, TpRM-R′ (M= Fe, Co), are stable with respect to thermal decomposition processes involving β-hydrogen elimination despite their highly coordinatively unsaturated electronic structure [Fe(14e), Co(15e)], when they are kept under inert atmosphere. The stability has been ascribed to a high spin configuration caused by the tetrahedral geometry. All frontier orbitals are occupied by unpaired electrons or electron pairs and no vacant frontier orbital is left for interaction with the electron pairs of a donor. Dinuclear xenophilic complexes, TpRM–M′Ln, with a polar metal–metal bond which bridges a Werner complex type hard open-shell metal center and a coordinatively saturated metal carbonyl fragment are also synthesized and fully characterized.
Single-Crystalline Photochromism of Diarylethene Mixtures
Authors: Yamada Taro , Kobatake Seiya , Irie Masahiro
Published: September 2002

Crystal structures of 1,2-bis(2,4-dimethyl-3-thienyl)perfluorocyclopentene 1a, 1,2-bis(2,4,5-trimethyl-3-thieny)per-fluorocyclopentene 2a and their mixture were determined by X-ray crystal structure analysis and their photochromic reactivities were compared. In the crystal of 1a, 17 mol% of molecules adopted a photoactive anti-parallel conformation and underwent photochromism. The crystal of 2a was not photochromic, because the dithienylethenes are packed in a photochemically inactive anti-parallel conformation. In the co-crystal of 1a and 2a, 2a adopted a photoactive anti-parallel conformation and the ratio of molecules in a photoactive conformation increased to 27 mol%. In the co-crystal, the spectrum of the closed-ring form isomers, 1b and 2b, generated by UV irradiation was broader and blue-shifted by ca. 10 nm in comparison with that of the 1a homocrystal.
Strategies and Development of Molecular Probes for Nitrogen Monoxide Monitoring
Authors: Katayama Yoshiki , Soh Nobuaki , Maeda Mizuo
Published: September 2002

Current methods for monitoring nitrogen monoxide (NO) and new strategies for designing NO probes are reviewed. The production of endogenous NO must be monitored if we are to understand the physiological and pathological roles of NO. Many methods have been reported for this purpose, including colorimetry, fluorometry, electrochemical methods, and electron paramagnetic resonance (EPR). Among these methods, one of the most promising for practical use is EPR using (dithiocarbamato)iron(II) complex as a spin trap. In the structure–sensitivity relationship, it was found that an electron-donating group on the dithiocarbamato ligand is favorable for enhancing the sensitivity of NO detection due to the stabilization of the Fe(II) complex form. A new concept, “radical-exchange”, is also introduced to solve the issue of low sensitivity in EPR methods. This concept has been used to develop two types of NO probe: spin trap and fluorescent probes. These reagents detect NO to a detection limit of 10 nM–sub-µM. This strategy, using radical exchange in conjunction with EPR, is potentially useful for the design of sensitive probes that can detect NO directly.
A Bimetallic Magnetic System Exhibiting Reversible Ferromagnetism/Metamagnetism Modulation
Authors: Usuki Naoki , Ohba Masaaki , Okawa Hisashi
Published: September 2002

A cyanide-bridged bimetallic compound, [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5·4H2O (1) (1,1-dmen = 1,1-dimethylethylenediamine, BPDS2− = biphenyl-4,4′-disulfonate), has been prepared. It has a pseudo 2-D network structure based on a Fe4Ni4 square unit with two Fe–CN–Ni–NC–Fe and two Fe–CN···H2O–Ni–NC–Fe linkages and shows a metamagnetic ordering with TC = 3.3 K. The dehydration of 1 at 150 °C has afforded [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5 (1a). It has a definite 2-D network structure based on a Fe4Ni4 square unit with four Fe–CN–Ni–NC–Fe linkages and shows essentially a ferromagnetic ordering with TC = 10.7 K under weak applied field (> 250 G). 1a is hygroscopic and adsorbed atmospheric moisture to afford [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5·2H2O (1b), which has a pseudo 2-D network structure similar to that of 1 and shows a metamagnetic ordering with TC = 4.0 K. 1a and 1b can be interconverted by dehydration at 150 °C and hydration in open air at room temperature, producing a unique molecular magnetic system exhibiting a reversible ferromagnetism/metamagnetism modulation.
Laser (248 nm) Flash Photolysis and Pulse Radiolysis of CF2Br2 in Aqueous Solution: Atmospheric Implications
Authors: Saini Rameshwar D , Dhanya Suresh , Das Tomi Nath
Published: September 2002

Henry’s law constant (Kh) of CF2Br2 was measured to be 0.058 M atm−1 at room temperature. The steady state as well as laser (248 nm) flash photolysis of CF2Br2 was carried out in aqueous solution. The formation of Br2•− radicals involving two primary photodissociation channels was observed in the flash photolysis. One channel produced CF2Br• and Br• radicals, and the other led to the formation of Br− and H+. The spectrum and reactions of CF2Br• were studied in aqueous solution by pulse radiolysis. The CF2Br• radical was found to absorb in the 230–270 nm region with a molar absorbance (ε) of 710 M−1 cm−1 at λmax = 245 nm. The rate constants of some of the reactions were measured at 299 K as follows: k (eaq− + CF2Br2) = 1.20 ± 0.13 × 1010, 2k (CF2Br• + CF2Br•) = 1.4 ± 0.4 × 109, k(CF2Br• + O2) = 1.9 ± 0.5 × 109 M−1 s−1. The CF2BrO2• radical absorbed in the 245–360 nm region with ε = 593 M−1 cm−1 at λmax = 265 nm. An apparatus used to measure Kh, and a closed-loop flow system used to carry out the flash photolysis/pulse radiolysis of sparingly soluble gases, like CF2Br2, are reported.
Monolayer Formation of Cytochrome b562 on Gold Surfaces and Its Reconstitution Reaction, Studied by Surface Plasmon Resonance Spectroscopy
Authors: Kobayashi Kazutoshi , Shimizu Masafumi , Nagamune Teruyuki , Sasabe Hiroyuki , Fang Yu , Knoll Wolfgang
Published: September 2002

Association and dissociation reactions of cytochrome b562 on solid surfaces were investigated by means of surface plasmon resonance spectroscopy. Propionates of side chains in the heme molecule were modified with sulfur moiety as an anchor part to be adsorbed on the gold substrate. This modified heme was firstly reconstituted with apo-protein in solution. This reconstituted holo-protein was then adsorbed on either bare gold substrate or pre-modified gold substrate. Native cytochrome b562 was also adsorbed to the same substrates for the control experiment. The reconstituted cytochrome b562 was successfully adsorbed on the pre-treated gold substrate without denaturation in structure, probably with homogeneous anisotropic orientation. Guanidine hydrochloride in the buffer of pH 5.0 was applied to remove the apo-protein from the surface, with the thiolated heme derivative remaining on the surfaces. Apo-protein was again introduced to the same surface for the reconstitution of holo-cyt.b562. The success of the association and dissociation reactions between apo-protein and tethered heme molecules on the surfaces was confirmed by the optical thickness changes.
A Theoretical Study of the Substituent Effects on the P–X (X = H, F, Cl) Bond Dissociation Energies in para- and meta-Substituted Aromatic Phosphines
Authors: Cheng Yu-Hui , Fang Ying , Zhao Xin , Liu Lei , Guo Qing-Xiang
Published: September 2002

The P–X (X = H, F, and Cl) bond dissociation energies (BDEs) for a number of para- and meta-substituted aromatic phosphines were calculated using R(O)MP2/6-311++g(d, 2p)//(U)B3LYP/6-31g(d) method. The results showed the importance of the radical effect as well as the ground effect on the BDEs. For X = H case, because the substituent affected the neutral phosphine to the same extent as it affected the radical, substituent effects on the P–H BDE were small (ρ+ = 0.28 kJ/mol). In comparison, for X = F or Cl case, because the substituent affected the neutral phosphine much more strongly than it affected the radical, substituent effects on the P–F (ρ+ = −3.25 kJ/mol) or P–Cl (ρ+ = −1.31 kJ/mol) BDEs were significant. Therefore, the substituent effects on BDEs of the Z–X bonds in compounds of the general formula 4-YC6H4Z–X varied when X changed, which meant that a recent proposal (J. Am. Chem. Soc., 123, 5518 (2001)) was unfortunately not supported.
The Relation between the Eigenvalue Sum and the Topological Index Z Revisited
Authors: Gutman Ivan , Vidovic Dusica , Hosoya Haruo
Published: September 2002

The topological index Z (put forward by one of the present authors, Bull. Chem. Soc. Jpn., 44, 2332 (1971)) has proved to be a structure-descriptor suitable for modeling physico-chemical properties of both saturated and conjugated unsaturated organic compounds. A linear relation between log Z and the Hückel molecular orbital total π-electron energy Eπ was established a long time ago (Theor. Chim. Acta  38, 37 (1975)), but was restricted to π-electron species without non-bonding molecular orbitals (n0 = 0, where n0 is the number of zero eigenvalues of the molecular graph). Recently a novel structure-descriptor ES was put forward, the “eigenvalue sum” equal to Eπ/2, but applicable to saturated hydrocarbons. In this case n0 need not be zero. We demonstrate that, for each group of alkane isomers with a fixed value of n0, there is a linear relation between ES and log Z.
Mass-Spectrometric Study of Ion-Molecule Reactions of CH5+, C2H5+, and C3H5+ with C8–C18 Alcohols in an Ion Trap
Authors: Tanaka Yuki , Tsuji Masaharu
Published: September 2002

Chemical ionization of n-alkyl alcohols (n-CxH2x+1–OH = M; x=8–18) by the CH5+, C2H5+, and C3H5+ ions has been studied under a reactant-ion selective mode of an ion-trap type of GC/MS. In all reactions, [M – H]+, alkyl CyH2y+1+ (y = 3−x), and alkenyl CyH2y−1+ (y = 4−x) ions were observed. On the basis of observed initial distributions and calculated thermochemical data, it was concluded that the major reactions for the formation of CyH2y+1+ were proton transfer to a hydroxy group in the CH5+ reactions, proton transfer and/or hydroxide-ion abstraction in the C2H5+ reactions, and CzH2zOH−-ion (z < x) abstraction in the C3H5+ reactions, while the major reactions for the formation of CyH2y−1+ ions were proton transfer to alkyl chain in the CH5+ reactions, hydride-ion abstraction in the C2H5+ reactions, and alkanide-ion abstraction in the C3H5+ reactions.
Application of 57Fe Mössbauer Spectroscopy to a Study of the Difference in Interactions between Guest and Host Molecules among (R), (S) and Racemic Isomers for (2-Methylbutyl)-, (2-Phenylpropyl)- and (2-Phenylbutyl)ferrocenes Enclathrated in Deoxycholic Acid
Authors: Nakashima Satoru , Ichikawa Naoki , Okuda Tsutomu
Published: September 2002

57Fe Mössbauer spectroscopy was applied to determine the difference, if any, in the interactions between host and guest molecules among the (R)-, (S)- and racemic isomers for (2-methylbutyl)-, (2-phenylpropyl)- and (2-phenylbutyl)ferrocene-deoxycholic acid (DCA) clathrates. The (S) isomer is included into DCA, while the (R) isomer is not in the case of (2-phenylpropyl)ferrocene. There is no significant difference in the temperature dependences of the 57Fe Mössbauer spectra between the (S) and racemic isomers-DCA for (2-phenylpropyl)ferrocene. For 2-methylbutyl and 2-phenylbutyl derivatives, all isomers form DCA clathrates. 57Fe Mössbauer spectroscopy revealed a difference in the molecular motion of guest molecules in the DCA lattice among them. For the 2-phenylbutyl derivative, the (S) isomer-DCA clathrate has one solvated molecule per guest molecule, a racemic isomer-DCA 0.7 solvated molecule, while the (R) isomer includes no solvated molecule. There was a difference in the powder X-ray diffraction patterns among them. An interesting phase transition was observed in (S)- and racemic (2-phenylbutyl)ferrocenes-DCA, which was accompanied by a desolvation, and then a change of crystal structure to that of (R) isomer-DCA heated up to the same temperature. Such a phase transition was not observed in (R) isomer-DCA. 57Fe Mössbauer spectroscopy revealed that (R) isomer-DCA changes in lattice vibration around 160 K, while (S) isomer-DCA does not.
Acid Dissociation of (5,10,15,20-Tetraphenylporphyrinato)zinc(II) in Cetyltrimethylammonium Chloride Reversed Micellar Solutions
Authors: Nakashima Toshiyuki , Nishida Ikuko , Fujiwara Terufumi
Published: September 2002

Acid dissociation of (5,10,15,20-tetraphenylporphyrinato)zinc(II), Zn(tpp) dispersed in reversed micellar media of cetyltrimethylammonium chloride (CTAC) in chloroform/water and chloroform–cyclohexane/water has been investigated using a stopped-flow spectrophotometer. When Zn(tpp) is mixed with the reversed micellar solution containing a concentrated acid, spectral data reveal that its dissociation, following immediate formation of the chloro-coordinated complex Zn(tpp)Cl− in the interfacial phase of the reverse micelle, occurs rapidly to produce the diacid salt of 5,10,15,20-tetraphenylporphyrin, H4(tpp)2+(Cl−)2. The dissociation rate increases with an increase of acid concentration in the reversed micellar aqueous pool. At higher acid concentrations (> 3 mol dm−3 in the pool), the rate constant and the fraction of Zn(tpp)Cl− formed increase in the order: HNO3 < HCl ≤ H2SO4 < HBr < HClO4, and decrease with an increase in volume fraction of cyclohexane in the reversed micellar bulk solvent. These observations may be explained by assuming selective distribution of the Cl− ion to the interfacial surfactant and bulk organic phases, which is affected by affinities of the acid anions for the surfactant head group and by the Cl− solvation.
Synthesis of 4-Alkoxy-2-substituted-benzenethiols and Their Application to Thermotropic Liquid Crystals
Authors: Okamoto Hiroaki , Wu Jianwei , Morita Yuki , Takenaka Shunsuke
Published: September 2002

A new synthetic method of 4-alkoxy-2-X-benzenethiols (X = H, halogens, CH3) has been established. In order to confirm the validity as a component of liquid crystal materials, some derivatives of S-(4-alkoxy-2-X-phenyl) 4-R-thiobenzoates (R = CnH2n+1O, CN, NO2, X = halogens, CH3) were prepared. Most of the thioesters exhibit a nematic phase, while the lateral substituents (X) tend to reduce the mesophase thermal stability as well as the melting point. The effect of lateral substituents on the mesomorphic properties is discussed.
Polymer Complexes of Rhodium(II) Trifluoroacetamidate with Pyrazine, 4,4′-Bipyridine, and 1,4-Diazabicyclo[2.2.2]octane
Authors: Handa Makoto , Muraki Yasuhiro , Mikuriya Masahiro , Azuma Hiroshi , Kasuga Kuninobu
Published: September 2002

Polymer complexes of rhodium(II) trifluoroacetamidate dimers bridged by bidentate ligands [{Rh2(HNOCCF3)4(L)}n], L = pyrazine (pyz), 4,4′-bipyridine (4,4′-bpy), and 1,4-diazabicyclo[2.2.2]octane (dabco), have been prepared and characterized.
O-Alkylation of Dihydroxo(tetraarylporphyrinato)phosphorus(V) and Antimony(V) Complexes with Alkyl Halides
Authors: Andou Yoshito , Ishikawa Kazuki , Shima Kensuke , Shiragami Tsutomu , Yasuda Masahide , Inoue Haruo
Published: September 2002

The O-alkylation of dihydroxo(tetraarylporphyrinato)phosphorus(V) complexes with several kinds of alkyl bromide in MeCN in the presence of K2CO3 and 18-crown-6 ether produced dialkoxo(tetraarylporphyrinato)phosphorus(V) complexes in-moderate-good yields. Similar O-alkylation was applied to dihydroxo(tetraarylporphyrinato)antimony(V) complexes. The O-alkylation proceeded by the occurrence of an SN2 attack of the alkoxide anion of the complexes at the carbon substituted with halides.
Efficient Reductive Deoximation by Tungsten(VI) Chloride (WCl6) or Molybdenum(V) Chloride (MoCl5) in the Presence of Zn Powder in CH3CN
Authors: Firouzabadi Habib , Jamalian Arezu , Karimi Babak
Published: September 2002

Tungsten(VI) chloride (WCl6) or molybdenum(V) chloride (MoCl5) in the presence of zinc powder in CH3CN provides an efficient and facile procedure for the deprotection of oximes to their corresponding aldehydes and ketones in high yields.
Synthesis and Complexing Ability of a C-Pivot Type of Double-Armed 15-Crown-5 Ethers toward Alkali Metal Cations
Authors: Nakatsuji Yohji , Muraoka Masahiro , Kajiya Hiroyuki , Zhang Wanbin , Kida Toshiyuki , Ikeda Isao
Published: September 2002

Three kinds of positional isomers of the C-pivot type of double-armed 15-crown-5 ethers (cis and trans isomers for each positional isomer) bearing two 8-quinolyloxy moieties as part of the electron-donating sidearms were prepared, and their complexation properties were evaluated by measuring the stability constant in THF, the extractability, and passive transport velocity. Cis isomers were found to be much better host compounds toward alkali metal cations than trans isomers possibly because of the potential cooperative coordination of two electron-donating sidearms. All trans isomers showed almost the same stability constants toward Na+ and K+. On the other hand, in the case of cis isomers, the difference in the position of the two sidearms on the crown ring was found to remarkably affect the complexation properties toward alkali metal cations.
Dimethyl 3-Hydroxy-4-hydroxymethylcyclopentane-1,1-dicarboxylate: an Optically Pure Precursor of Spiro Carbocylic Deoxyribonucleosides
Authors: Renard Annabelle , Lhomme Jean , Kotera Mitsuharu
Published: September 2002

A concise, two-step preparation of dimethyl 3-hydroxy-4-hydroxymethylcyclopentane-1,1-dicarboxylate, an optically pure precursor of spiro carbocyclic nucleosides is described.