Tomohiro Ozawa

Publications of Tomohiro Ozawa

• Adsorption behavior of microbes on a QCM chip modified with an artificial siderophore-Fe3+ complex.

  Authors: Tomohiko Inomata, Hiroshi Eguchi, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Langmuir : the ACS journal of surfaces and colloids. 12/2011; 28(2):1611-7.

  Three hydroxamate-type artificial siderophores with terminal NH(2) groups, tris[2-{3-(N-acyl-N-hydroxamino)propylamido}propyl]aminomethane (1-3, acyl-R group = Me, Et, and Ph, respectively), andThree hydroxamate-type artificial siderophores with terminal NH(2) groups, tris[2-{3-(N-acyl-N-hydroxamino)propylamido}propyl]aminomethane (1-3, acyl-R group = Me, Et, and Ph, respectively), and their Fe(3+) complexes, 4-6, were prepared. The stability constant (log β) of 4 was estimated to be about 31 by its EDTA titration. The biological activities of 4-6 for Microbacterium flavescens, which is a hydroxamate-type siderophore, auxotrophic gram-positive microbe, clearly indicated that they permeated the cell membrane depending on their terminal bulky acyl-R groups. These artificial siderophore complexes, 4-6, were modified on Au electrode surfaces with the terminal NH(2) group (4-6/Au). The surface modification of 4-6 was confirmed by several electrochemical measurements. The quartz crystal microbalance (QCM) chips were also modified with 4-6. Microbe adsorption measurements using these modified QCM chips for M. flavescens, Pseudomonas putida, and Eschrichia coli were performed. The QCM chips have the ability to adsorb microbes selectively as a result of the differences in the interactions between the structures of Fe(3+)-artificial siderophore complexes and their receptors or binding proteins within the cell membrane.

• A square-planar Ni(II) complex with an N2S2 donor set similar to the active centre of nickel-containing superoxide dismutase and its reaction with superoxide.

  Authors: Daisuke Nakane, Shin-ich Kuwasako, Michiharu Tsuge, Minoru Kubo, Yasuhiro Funahashi, Tomohiro Ozawa, Takashi Ogura, Hideki Masuda

  Chemical communications (Cambridge, England). 03/2010; 46(12):2142-4.

  The structure around the metal centre of a Ni(II) complex with an N(2)S(2) square-planar geometry, 1, prepared as a model compound of the NiSOD active site was drastically changed upon addition ofThe structure around the metal centre of a Ni(II) complex with an N(2)S(2) square-planar geometry, 1, prepared as a model compound of the NiSOD active site was drastically changed upon addition of potassium superoxide (KO(2)).

• Nano-film structures constructed by self-assembly of Co(III) biuretato complexes and long alkyl imidazolium cations.

  Authors: Kazuki Yamada, Yuki Okazaki, Tomohiko Inomata, Keita Kuroiwa, Nobuo Kimizuka, Tomohiro Ozawa, Yasuhiro Funahashi, Hideki Masuda

  Journal of nanoscience and nanotechnology. 02/2009; 9(1):307-12.

  A Co(III) biuretato complex, [Co(III){ph(biu)2}]- (ph(biu)2 = o-phenylenebis(biuretato)) can form layer structures by its self-assembling with a multiply hydrogen bonding network.A Co(III) biuretato complex, [Co(III){ph(biu)2}]- (ph(biu)2 = o-phenylenebis(biuretato)) can form layer structures by its self-assembling with a multiply hydrogen bonding network. PPh4[Co(III)(ph(biu)2}]. 3CHCl3 (PPh4+ = Tetraphenylphosphonium cation) crystallizes in the triclinic, space group P1, with a = 9.740(5) A, b = 13.980(8) A, c = 16.792(9) A, alpha = 103.976(7) degrees, beta = 95.592(8) degrees, gamma = 103.165(8) degrees, V = 2132 A3, and Z=2. In the crystal, counter cations, PPh4+, are inserted between the layer structures of [Co(III){ph(biu)2}]- aggregates, resulting in formation of a multi-layered structure. A treatment of K[Co(III){ph(biu)2}] with C18MelmCl (C18Melm+ = 1-octadecyl-3-methyl-imidazolium cation) in an aqueous solution with a trace amount of PPh4Cl, gave the glaring silver solution containing self-organized nano-film structures. Optical microscopic and AFM studies clearly showed that rectangle-shaped nano-film structures were formed by self-assembly of [Co(III){ph(biu)2}]- and C18Melm+ in the solution, and their sizes were approximately ranged to 6-13 microm in length, 3-7 microm in width and 25.2 +/- 6.2 nm in thickness. Using spectroscopic and XRD data, we concluded that these nano-films have a alternatively accumulated multilayer-structure of [Co(III){ph(biu)2}]- layer and C18Melm+ bilayer structures, the repeating distance being d001 = 2.22 nm.

• Formation of a bridged butterfly-type mu-eta2:eta2-peroxo dicopper core structure with a carboxylate group.

  Authors: Yasuhiro Funahashi, Tomohide Nishikawa, Yuko Wasada-Tsutsui, Yuji Kajita, Syuhei Yamaguchi, Hidekazu Arii, Tomohiro Ozawa, Koichiro Jitsukawa, Takehiko Tosha, Shun Hirota, Teizo Kitagawa, Hideki Masuda

  Journal of the American Chemical Society. 01/2009; 130(49):16444-5.

• Formation of a Bridged Butterfly-Type mu-eta(2):eta(2)-Peroxo Dicopper Core Structure with a Carboxylate Group.

  Authors: Yasuhiro Funahashi, Tomohide Nishikawa, Yuko Wasada-Tsutsui, Yuji Kajita, Syuhei Yamaguchi, Hidekazu Arii, Tomohiro Ozawa, Koichiro Jitsukawa, Takehiko Tosha, Shun Hirota, Teizo Kitagawa, Hideki Masuda

  Journal of the American Chemical Society. 12/2008;

• Self-assembled monolayer electrode of a diiron complex with a phenoxo-based dinucleating ligand: observation of molecular oxygen adsorptionldesorption in aqueous media.

  Authors: Tomohiko Inomata, Kazuma Shinozaki, Yuya Hayashi, Hidekazu Arii, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Chemical communications (Cambridge, England). 02/2008;

  The phenoxo-based dinucleating ligand, 2,6-bis[bis(6-pivalamido-2-pyridylmethyl)amino-methyl-4-aminophenol (1), and its Fe2(II) complex, [Fe2(II)(1)(PhCOO)2](CF3SO3) (2), were prepared and 2The phenoxo-based dinucleating ligand, 2,6-bis[bis(6-pivalamido-2-pyridylmethyl)amino-methyl-4-aminophenol (1), and its Fe2(II) complex, [Fe2(II)(1)(PhCOO)2](CF3SO3) (2), were prepared and 2 deposited on the Au surface (2/Au) is much more stable than in solution and exhibits redox behavior in aqueous media as well as reversible adsorption/desorption of oxygen at room temperature.

• Adsorption of microorganisms onto an artificial siderophore-modified Au substrate.

  Authors: Tomohiko Inomata, Hiroshi Eguchi, Kenji Matsumoto, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Biosensors & bioelectronics. 01/2008; 23(5):751-5.

  The hydroxamate-type artificial siderophore, tris[2-{3-(N-acetyl-N-hydroxamino)propylamido}propyl]aminomethane (TAPPA) and its Fe(III) complex, Fe(III)-TAPPA were prepared and characterized byThe hydroxamate-type artificial siderophore, tris[2-{3-(N-acetyl-N-hydroxamino)propylamido}propyl]aminomethane (TAPPA) and its Fe(III) complex, Fe(III)-TAPPA were prepared and characterized by several spectroscopic methods. Fe(III)-TAPPA exhibits biological activity for the hydroxamate-type siderophore auxotrophic microorganism, Microbacterium flavescens, suggesting that Fe(III)-TAPPA can permeate the cell membrane of the microorganism. The adsorption of the Fe(III)-siderophore complex onto a deposited Au substrate was achieved by a stepwise self-assembling method. The modification of Fe(III)-TAPPA on the surface was confirmed from the cyclic voltammogram of the resultant Au electrode, Fe(III)-TAPPA/Au. The adsorption experiments of M. flavescens with Fe(III)-TAPPA/Au were monitored by optical, scanning electron, and atomic force microscopy and quartz crystal microbalance (QCM) measurements. These results clearly indicate that Fe(III)-TAPPA/Au can immobilize M. flavescens. This adsorption characteristic is due to the interaction between Fe(III)-TAPPA on an Au electrode and a receptor/binding protein within the cell membrane.

• Syntheses, Characterization, and Reactivities of (μ-η2:η2-Disulfido)dicopper(II) Complexes with N-Alkylated cis,cis-1,3,5-Triaminocyclohexane Derivatives

  Authors: Yuji Kajita, Jun Matsumoto, Isao Takahashi, Shun Hirota, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  European Journal of Inorganic Chemistry. 01/2008; 2008(25):3977-3986.

  Three novel (disulfido)dicopper(II) complexes with N-alkylated cis,cis-1,3,5-triaminocyclohexane derivatives, [Cu2(S2)(R3TACH)]X2 [(R, X) = (Et, CF3SO3) (1), (iBu, SbF6) (2), and (Bn, SbF6) (3)],Three novel (disulfido)dicopper(II) complexes with N-alkylated cis,cis-1,3,5-triaminocyclohexane derivatives, [Cu2(S2)(R3TACH)]X2 [(R, X) = (Et, CF3SO3) (1), (iBu, SbF6) (2), and (Bn, SbF6) (3)], have been synthesized and characterized by elemental, electrochemical, and X-ray structure analyses, and electronic absorption, IR, ESI mass, and resonance Raman spectroscopic methods. The X-ray crystal structures indicate that the two sulfur and two copper atoms of these complexes form a Cu2(S2) structure with slight bending of the two planes defined by the CuS2 plane at angles of 166.12° (the individual bending angles are 175.56° for 1a and 156.67° for 1b), 154.74°, and 180° for 1, 2, and 3, respectively. The UV/Vis absorption spectra of 1, 2, and 3 have a sharp band at ca. 360 nm with a broadened shoulder at 400–480 nm and low intensity d–d bands in the range 666–671 nm. The resonance Raman spectra of the complexes have peaks assignable to a ν(S–S) band at 483–484 cm–1. The complexes have reduction waves at –974 to –946 vs. [Fe(C5H5)2]/[Fe(C5H5)2]+ for 1, –993 to –976 for 2, and –948 to –928 mV for 3. These values are in a low-potential region relative to bis(μ-OH)dicopper complexes with R3TACH. This may be explained by the occurrence of strong π-donation from the disulfide ligands as observed for previously reported (disulfido)Ru complexes. Compounds 1, 2, and 3 react with PPh3 to give S=PPh3 in yields of 65 ± 3.5, 76 ± 1, and 50 ± 2 %, respectively. These results are discussed in terms of the relationship between the dihedral angles in the Cu2(S2) core and the reactivity of S22–. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

• Co(III) complexes with N2(SO)2-type equatorial planar ligands similar to the active center of nitrile hydratase: role of the sulfenate group in the enzymatic reaction.

  Authors: Takuma Yano, Yuko Wasada-Tsutsui, Hidekazu Arii, Syuhei Yamaguchi, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Inorganic chemistry. 11/2007; 46(24):10345-53.

  In order to gain an understanding of the role of the sulfenyl group of nitrile hydratase (NHase), a new Co(III) complex with a sulfenyl-type ligand (LC=O:N2(SO)2), Na[CoIII(LC=O:N2(SO)2)(tBuNC)2]In order to gain an understanding of the role of the sulfenyl group of nitrile hydratase (NHase), a new Co(III) complex with a sulfenyl-type ligand (LC=O:N2(SO)2), Na[CoIII(LC=O:N2(SO)2)(tBuNC)2] (2), was synthesized. The compound includes two amide groups, two sulfenate sulfurs in the equatorial plane, and two tBuNC molecules in the axial positions. Characterization of the compound was performed by UV-vis spectroscopic, IR spectral, thermogravimetric (TG), and X-ray structure analytical methods. The results are discussed in the context of Co(III) complexes containing the corresponding sulfur-type (LC=O:N2S2) (1) and sulfinyl-type ligands (LC=O:N2(SO2)2) (3). Complex 2 crystallized with the formula Na[CoIII(LC=O:N2(SO)2)(tBuNC)2].urea.2H2O.0.5EtOH. The X-ray structure revealed that the Co(III) complex has an octahedral geometry with Co-S=av. 2.221 A, Co-N=av. 1.998 A, and Co-C=av. 1.87 A. The sulfenyl oxygen and amidate carbonyl oxygen are linked to urea, water, EtOH, and Na+ and participate in a hydrogen-bond and an electrostatic interaction. IR and TG measurements demonstrated that the coordination strength of tBuNC to the Co atom increases as follows: 1<2<3. Complex 2 has almost the same stability as 3 in all solutions tested, although 1 exhibits a release of axial ligands in nonaqueous solutions. DFT calculations for 1, 2, and 3 demonstrated that Milliken atomic charges of the Co(III) centers are +1.466, +1.536, and +1.542, respectively, indicating that the extent of oxidation of the sulfur atoms increases the Lewis acidity of the Co(III) centers. Interestingly, the solution-state IR spectrum of 2 exhibits a solvent-dependent S-O stretching frequency. The frequency decreases with an increase in the electrophilicity (acceptor number) of the solvent. This solvent dependence was not observed for 3, which has a sulfinate (SO2) group, suggesting that the sulfenyl oxygen atom has nucleophilic character and promotes strong binding of the tBuNC molecule to lower the reaction barrier. These findings may suggest that the sulfenate oxygen in native NHase acts as a base (proton acceptor) and contributes to the activation of a water molecule and/or nitrile molecule.

• Syntheses, characterization, and dioxygen reactivities of Cu(I) complexes with cis,cis-1,3,5-triaminocyclohexane derivatives: a Cu(III)2O2 intermediate exhibiting higher C-H activation.

  Authors: Yuji Kajita, Hidekazu Arii, Takahiro Saito, Yamato Saito, Shigenori Nagatomo, Teizo Kitagawa, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Inorganic chemistry. 05/2007; 46(8):3322-35.

  Six Cu(I) complexes with cis,cis-1,3,5-triaminocyclohexane derivatives (R3CY, R = Et, iBu, and Bn), [Cu(MeCN)(Et3CY)]SbF6 (1), [Cu(MeCN)(iBu3CY)]SbF6 (2), [Cu(MeCN)(Bn3CY)]SbF6 (3),Six Cu(I) complexes with cis,cis-1,3,5-triaminocyclohexane derivatives (R3CY, R = Et, iBu, and Bn), [Cu(MeCN)(Et3CY)]SbF6 (1), [Cu(MeCN)(iBu3CY)]SbF6 (2), [Cu(MeCN)(Bn3CY)]SbF6 (3), [Cu(CO)(Et3CY)]SbF6 (4), [Cu(CO)(iBu3CY)]SbF6 (5), and [Cu(CO)(Bn3CY)]SbF6 (6), were prepared to probe the ability of copper complexes to effectively catalyze oxygenation reactions. The complexes were characterized by elemental analysis, electrochemical and X-ray structure analyses, electronic absorption spectroscopy, IR spectroscopy, 1H NMR spectroscopy, and ESI mass spectrometry. The crystal structures of 1-3 and 6 and the CO stretching vibrations (nuCO) of 4-6 demonstrate that the ability of R3CY to donate electron density to the Cu(I) atom is stronger than that of the previously reported ligands, 1,4,7-triazacyclononane (R3TACN) and 1,4,7-triazacyclodecane (R3TACD). Reactions of complexes 1-3 with dioxygen in THF or CH2Cl2 at -105 to -80 degrees C yield bis(mu-oxo)dicopper(III) complexes 7-9 as intermediates as confirmed by electronic absorption spectroscopy and resonance Raman spectroscopy. The Cu-O stretching vibrations, nu(Cu-O) for 7 (16O2: 553, 581 cm-1and 18O2: 547 cm-1) and 8 (16O2: 571 cm-1 and 18O2: 544 cm-1), are observed in a lower energy region than previously reported for bis(micro-oxo) complexes. The decomposition rates of complexes 7-9 in THF at -90 degrees C are 2.78 x 10-4 for 7, 8.04 x 10-4 for 8, and 3.80 x 10-4 s-1 for 9. The decomposition rates of 7 and 8 in CH2Cl2 were 5.62 x 10-4 and 1.62 x 10-3 s-1, respectively, and the thermal stabilities of 7-9 in CH2Cl2 are lower than the values measured for the complexes in THF. The decomposition reactions obeyed first-order kinetics, and the H/D isotope experiments for 8 and 9 indicate that the N-dealkylation reaction is the rate-determining step in the decomposition processes. On the other hand, the decomposition reaction of 7 in THF results in the oxidation of THF (acting as an exogenous substrate) to give 2-hydroxy tetrahydrofuran and gamma-butyrolactone as oxidation products. Detailed investigation of the N-dealkylation reaction for 8 by kinetic experiments using N-H/D at -90 degrees C showed a kinetic isotope effect of 1.25, indicating that a weak electrostatic interaction between the N-H hydrogen and mu-oxo oxygen contributes to the major effect on the rate-determining step of N-dealkylation. X-ray crystal structures of the bis(micro-hydroxo)dicopper(II) complexes, [Cu2(OH)2(Et3CY)2](CF3SO3)2 (10), [Cu2(OH)2(iBu3CY)2](CF3SO3)2 (11), and [Cu2(OH)2(Bn3CY)2](ClO4)2 (12), which have independently been prepared as the final products of bis(micro-oxo)dicopper(III) intermediates, suggest that an effective interaction between N-H and mu-oxo in the Cu(III)2(micro-O)2 core may enhance the oxidation ability of the metal-oxo species.

• Electron-transfer reactions through the associated interaction between cytochrome c and self-assembled monolayers of optically active cobalt(III) complexes: molecular recognition ability induced by the chirality of the cobalt(III) units.

  Authors: Isao Takahashi, Tomohiko Inomata, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Chemistry (Weinheim an der Bergstrasse, Germany). 02/2007; 13(28):8007-17.

  Self-assembled monolayers (SAMs) of optically active Co(III) complexes ((S)-2/(R)-2) that contain (S)- or (R)-phenylalanine derivatives as a molecular recognition site were constructed on AuSelf-assembled monolayers (SAMs) of optically active Co(III) complexes ((S)-2/(R)-2) that contain (S)- or (R)-phenylalanine derivatives as a molecular recognition site were constructed on Au electrodes ((S)-2-Au/(R)-2-Au). Molecular recognition characteristics induced by the S and R configurations were investigated by measurements of electron-transfer reactions with horse heart cytochrome c (cyt c). The electrochemical studies indicate that the maximum current of cyt c reduction is obtained when the Au electrode is modified by 2 with a moderate coverage of approximately 4.0 x 10(-11) mol cm(-2). Since the Au electrode is not densely packed with the Co(III) units at this concentration, we conclude that the penetrative association process between cyt c and the Co(III) unit plays an important role in this electron-transfer system. The differences in the electron-transfer rates of (S)-2-Au and (R)-2-Au increase with increasing scan rates, a result indicating that the chiral ligand has an influence on the rate of association of the complexes with cyt c. 3-Au has a mixed monolayer composed of 2 and hexanethiol and exhibits electron-transfer behavior comparable to 2-Au. The difference in the association rates of (S)-3-Au and (R)-3-Au is larger than that between (S)-2-Au and (R)-2-Au, which indicates that the molecular recognition ability of 3-Au has been enhanced by filling the gap between molecules of 2 with hexanethiols. The differences in the oxidation rates of cyt c(II) between (S)-2-Au and (R)-2-Au and between (S)-3-Au and (R)-3-Au were larger than the differences in the rates of the reduction of cyt c(III); this suggests that the size of the heme crevice varies according to the oxidation state of cyt c.

• Structures of various cytochromes c evaluated from the redox behaviors using the optically active Co(III) complex-modified Au electrode.

  Authors: Isao Takahashi, Chika Nishijima, Tomohiko Inomata, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Drug metabolism letters. 02/2007; 1(1):73-5.

  Electrochemical studies of three c-type cytochromes (cyt c from horse heart, cyt c(2) from Rhodospirillum rubrum, and cyt c(553) from Alcaligenes xylosoxidans GIFU 1051) were performed by using theElectrochemical studies of three c-type cytochromes (cyt c from horse heart, cyt c(2) from Rhodospirillum rubrum, and cyt c(553) from Alcaligenes xylosoxidans GIFU 1051) were performed by using the optically active Co(III) complex-modified Au electrode. Three cytochromes gave different redox behaviors reflected from the respective structural information. From relationship between their redox behaviors and their structural characteristics, we evaluated the solution structure around heme center of cyt c(553).

• Mononuclear copper(II)-hydroperoxo complex derived from reaction of copper(I) complex with dioxygen as a model of DbetaM and PHM.

  Authors: Tatsuya Fujii, Syuhei Yamaguchi, Yasuhiro Funahashi, Tomohiro Ozawa, Takehiko Tosha, Teizo Kitagawa, Hideki Masuda

  Chemical communications (Cambridge, England). 12/2006;

  A mononuclear copper(II)-hydroperoxo species has been generated by the reaction of Cu(I)-H2BPPA complex with dioxygen, which illustrates the enzymatic reaction process of the CuB site in the DbetaMA mononuclear copper(II)-hydroperoxo species has been generated by the reaction of Cu(I)-H2BPPA complex with dioxygen, which illustrates the enzymatic reaction process of the CuB site in the DbetaM and PHM.

• Self-assembled monolayers of optically active Co(III) complexes: a new promoter electrode recognizing the electron transfer site in cytochrome c.

  Authors: Isao Takahashi, Tomohiko Inomata, Yasuhiro Funahashi, Tomohiro Ozawa, Koichiro Jitsukawa, Hideki Masuda

  Chemical communications (Cambridge, England). 02/2005;

  A new-class of promoter electrode bearing a molecular recognition ability has been constructed; the chirality and/or orientation of promoter on the Au electrode surface have affected the electronA new-class of promoter electrode bearing a molecular recognition ability has been constructed; the chirality and/or orientation of promoter on the Au electrode surface have affected the electron transfer rate of cytochrome c.

• Synthesis, solution behavior, thermal stability, and biological activity of an Fe(III) complex of an artificial siderophore with intramolecular hydrogen bonding networks.

  Authors: Kenji Matsumoto, Tomohiro Ozawa, Koichiro Jitsukawa, Hideki Masuda

  Inorganic chemistry. 01/2005; 43(26):8538-46.

  Previously, an artificial siderophore complex, the iron(III) complex with tris[2-[(N-acetyl-N-hydroxy)glycylamino]ethyl]amine (TAGE), was constructed in order to understand the effect ofPreviously, an artificial siderophore complex, the iron(III) complex with tris[2-[(N-acetyl-N-hydroxy)glycylamino]ethyl]amine (TAGE), was constructed in order to understand the effect of intramolecular hydrogen bonding interaction on the siderophore function, and its structural characterization in the solid state was reported (Inorg. Chem. 2001, 40, 190). In this paper, the solution behavior of the M(III)-TAGE (M = Fe, Ga) system has been investigated using (1)H NMR, UV-vis, and FAB mass spectroscopies in efforts to characterize the biological implication of hydrogen bonding networks between the amide hydrogens and coordinating aminohydroxy oxygens of the complex. The temperature dependence of (1)H NMR spectra for Ga(III) complex of TAGE indicates that hydrogen bonding networks are maintained in polar solvents such as DMSO-d(6) and D(2)O. The UV-vis spectra of the Fe(III)-TAGE system under various pH conditions have shown that TAGE forms a tris(hydroxamato)iron(III) complex in an aqueous solution in the pH range 4-8. By contrast, tris[2-[(N-acetyl-N-hydroxy)propylamido]ethyl]amine (TAPE; TAGE analogue that is difficult to form intramolecular hydrogen bonding networks), which has been synthesized as a comparison of TAGE, forms both of bis- and tris(hydroxamato)iron(III) complexes in the same pH range. Both the stability constants (log beta(FeTAGE) = 28.6; beta(FeTAGE) = [Fe(III)TAGE]/([Fe(3+)][TAGE(3)(-)])) and pM (-log[Fe(3+)]) value for Fe(III)TAGE (pM 25) are comparable to those of a natural siderophore ferrichrome (log beta = 29.1 and pM 25.2). The kinetic study of the TAGE-Fe(III) system has given the following rate constants: the rate of the ligand exchange reaction between Fe(III)TAGE and EDTA is 6.7 x 10(-4) s(-1), and the removal rates of iron from diferric bovine plasma transferrin by TAGE are 2.8 x 10(-2) and 6.0 x 10(-3) min(-1). These values are also comparable to those of a natural siderophore desferrioxamine B under the same conditions. In a biological activity experiment, TAGE has promoted the growth of the siderophore-auxotroph Gram-positive bacterium Microbacterium flavescens, suggesting that TAGE mimics the activity of ferrichrome. These results indicate that the artificial siderophore with intramolecular hydrogen bonding networks, TAGE, is a good structural and functional model for a natural ferrichrome.

• Kinetic resolution of rac-phenylalanine by stereoselective complexation to a chiral cobalt complex through pi-pi stacking interaction.

  Authors: Koichiro Jitsukawa, Akira Katoh, Kentaro Funato, Nayumi Ohata, Yasuhiro Funahashi, Tomohiro Ozawa, Hideki Masuda

  Inorganic chemistry. 11/2003; 42(20):6163-5.

  A cobalt(III) complex with chiral ligand, H2cpel (N-carboxymethyl-N-pyridylethyl-l-leucine), was prepared for chiral recognition of amino acids. Through the competitive coordination of racemicA cobalt(III) complex with chiral ligand, H2cpel (N-carboxymethyl-N-pyridylethyl-l-leucine), was prepared for chiral recognition of amino acids. Through the competitive coordination of racemic phenylalanine to the chiral cobalt complex, [Co(cpel)(CO(3))](-) (1), enantioselective recognition was achieved on the ternary complex, which was determined on the basis of HPLC analysis with a chiral column. The formation rate for the [Co(cpel)(l-phe)] complex (2) was 6-times superior to that of [Co(cpel)(d-phe)] (3). The preferential formation of 2 might be illustrated by the interligand pi-pi stacking interaction. Crystal structural analysis for 2 and 3 revealed that aromatic rings, pyridine ring of CPEL and phenylalanine sidechain, in 2 were very close each other but those in 3 were far apart. Such interligand aromatic interaction in 2 was also examined by the use of (1)H NMR spectra.