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Molecular recognition of dipeptide (DP) compounds is performed with a ternary cobalt(III) complex containing thetripodal tetradentate ligand bis-N,N-carboxymethyl-L-phenylalanine (H3bcmpa). The coordination structure of the complex [Co(bcmpa)(dp)]– (1–14) was spectroscopically assigned by UV/Vis, CD, and 1H NMR spectroscopic methods. Site-specific recognition of the dipeptide on the ternary complex is achieved by various weak, non-covalent, inter-ligand interactions, such as hydrogen bonding, steric repulsion, and electrostatic interaction, etc. Some dipeptides having C-terminal aromatic side-chains also demonstrate inter-ligand CH–π interactions between the aromatic ring and the α-hydrogen of bcmpa. Coordination of the N-terminal nitrogen atom of the dipeptide to cobalt at the trans(N)-position to the tertiary nitrogen of bcmpa in the octahedral geometry provides an aminopeptidase model. Under slightly alkaline conditions, the dipeptide ligand of some of these complexes is cleaved to give the ternary complex, [Co(bcmpa)(aa)]– (aa = amino acidato). The rate for the hydrolysis of dipeptide decreases upon increasing the steric bulkiness of the C-terminal side-chain. In the cases of the ternary complexes [Co(bcmpa)(gly-phe)]– (6 and 11), which have C-terminal L- or D-phenylalanine, the hydrolysis of gly-phe to gly was completely prevented. On the other hand, the ternary cobalt(III) complexes [Co(bcmga)(gly-phe)]– (18 and 19), where H3bcmga (bis-N,N-carboxymethyl-L-glutamic acid) is the more hydrophilic tripodal ligand, give a small amount of the corresponding cleavage product [Co(bcmga)(gly)]–. The hydrophobic sphere generated around the metal complex in 6 and 11 regulates approach of OH– ion to the amide carbonyl group. Multi-site interactions mediated on the ternary complexes are available for the design of an artificial hydrolysis enzyme. This is the first report describing the substrate-specific cleavage of peptides using a simple enzyme model complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The bis-N,N-carboxymethy-(S)-phenylalaninato carbonato cobalt(III) complex, [Co(bcmpa)(CO3)]2−, has been prepared as a simple model that enables the recognition of an amino acid (Haa) whose coordination behaviours in solution have been characterized by electronic absorption (AB), circular dichroism (CD) and 1H NMR spectroscopies. The reaction of the K2[Co(bcmpa)(CO3)] complex with amino acids (Haa) has predominantly afforded the [Co(bcmpa)(aa)] complex in the trans(N)-configuration mode, rather than in the cis(N)-form. By using amino acid derivatives with bulky substituents at their amino or carboxylate sites under a neutral condition, the reactions have been demonstrated to be initiated by coordination of the amino nitrogen site. Interestingly, the cis(N)-complex, which is isolated as a minor product, isomerizes to the trans(N)-form in the presence of active charcoal under pH 7 in an aqueous solution. The site-selective coordination of Haa to the [Co(bcmpa)(CO3)]2− complex and the stereoselective isomeri...

The release of nucleobases from oligonucleotides (12-mer, d(5′-CGCTTTAAAGCG)2, 8-mer, d(5′-AAACGTTT)2, 7-mer, d(TCGCGCG)2, and 6-mer, d(CGCGCG)2) by copper(II) complex and hydrogen peroxide systems was investigated in terms of HPLC. The [Cu(bdpg)Cl]Cl complex gave a large quantity of free nucleobases in the reaction mixture, but the activities of other compounds, such as [Cu(tpa)Cl]ClO4, were much lower than that of the (bdpg)-complex; where (bdpg) and (tpa) represent a N,N-bis(2-pyridylmethyl) derivative of β-alanineamide and 2-aminomethylpyridine, respectively. The above results and the electrospray mass spectral data on the solutions strongly suggest that the remarkable activity of the (bdpg)-compound is due to the high electrophilic nature of the copper(II)–hydroperoxide adduct, whose formation is greatly promoted through hydrogen bonding with the amide-oxygen atom coordinated to the copper(II) atom, and this electrophilic copper(II)–peroxide adduct attacks the sugar ring of nucleoside, to give the corresponding hydroxylated species, and from which free nucleobases are released.

Eight adducts of Rh2(O2CCH3)4 with axial pyridine derivatives that contain hydrogen-bonding amino and/or steric methyl substituents in the 2- and 6-positions have been prepared and examined by electronic absorption and 1H NMR spectroscopy in solution and by elemental, IR, thermogravimetric, and X-ray diffraction analyses in the solid state. The results indicated that strong hydrogen bonding interactions between Rh2(O2CCH3)4 and axially coordinated pyridine derivatives with a 2- or 6-amino group occur in both solution and the solid state and contribute to the higher thermal stability of the molecular assembly of dirhodium complexes. It was demonstrated that such a combination of coordinate and hydrogen bonds is useful as a building tool in designing and constructing new organic-inorganic hybridized compounds and supramolecular architectures.

A unique triple hydrogen-bonding system has been constructed between the transition metal (Ni(II), Cu(II), Co(III)) complexes with bis(biphenylbiguanidato) and ortho-phenylenebis(biuretato) ligands...

This paper reports the synthesis and structures of (catecholato)iron(III) complexes with tetradentate tripodal ligands (L R′,R″ ={2-hydroxy-3-R′-5-R″-phenyl-bis(2-pyridylmethyl)amine}) containing substituted phenol and pyridine units: [Fe III (L R′,R″ )(DBC)] ( 1a : R′,R″=H,H; 1b : R′,R″=Me,Me; and 1c : R′,R″=H,Cl, DBC=3,5-di- tert -butylcatecholato). X-ray structure analysis has revealed that the coordination arrangement around the iron atom of 1a is similar to that proposed for the active site of the catechol-bound intermediate of protocatechuate 3,4-dioxygenase (3,4-PCD). The series of complex 1 derivatives has been synthesized by two different methods: (i) reaction of [Fe III (L R′,R″ )(acac)] + ( 2a : R′,R″=H,H; 2b : R′,R″=Me,Me; and 2c : R′,R″=H,Cl, acac=acetylacetonato) with 1 equiv. of DBC and 1 equiv. of Et 3 N in N,N -dimethylformamide (abbreviated as DMF), and (ii) reaction of [Fe III (L R′,R″ )Cl 2 ] ( 3a : R′,R″=H,H; 3b : R′,R″=Me,Me; and 3c : R′,R″=H,Cl) with 2 equiv. of AgOTf (OTf=O 3 SCF 3 − ), 1 equiv. of the catechols, and 2 equiv. of Et 3 N in DMF. The exogenous acac ligand of 2 acts as a Lewis base like the Tyr447 ligand in the active site of 3,4-PCD in the formation of the catechol-bound intermediate. Complexes 1 , 2 , and 3 have been characterized by X-ray analysis, visible and EPR spectroscopies, and cyclic voltammetry. Oxygenation of the bound DBC on 1 in the presence of O 2 has also been investigated and is discussed based on the Lewis basicity of the tripodal ligand containing the substituted phenolato group which is introduced to mimic the Tyr408 ligand of 3,4-PCD.

水素結合により自己組織化した錯体超構造の機能発現を検討した. 相補的な水素結合部位を有するビグアニダド配位子 (BG) とビオルル酸配位子 (VA) を用いた [Co (bg) 3 ] 錯体と [Co (va) 3 ] 錯体の1: 1の反応により, 配位子間プロトン移動を伴う三重水素結合が形成された. この水素結合系は中心金属から3方向に展開した3次元的な錯体ネットワーク構造を形成し, その内部空孔に水を強く捕捉した. また, エチレンジビグアニダド (ENBG) を配位子とする [Mn (enbg) (OH) (H2O)] 錯体と, これと相補的三重水素結合を形成する [Cu (va) 2 ] 錯体が自己組織化した系では, Cu (II) +Mn (III) →Cu (I) +Mn (IV) の酸化還元反応が確認できた. Mn錯体とCu錯体は配位子間三重水素結合によってテープ状構造を形成し, このテープ間でマンガンと銅が架橋したMn-O-Cuを経由して電子が移動したと考えられる. これは錯体の自己組織化構造で電子移動を発現した非常に興味深い結果である.

The existence of a CH-π interaction has clearly been demonstrated by use of the ternary metal (Cu(II), Pd(II)) complexes involving o-/m-/p-methyl substituted L-phenylalanine (L-o-mPhe, L-m-mPhe, L-p-mPhe) and 1,10-phenanthroline (phen) on the basis of 1H NMR, electronic absorption, and CD spectroscopies, and X-ray diffraction method. The crystal structure of [{Cu(p-mPhe)(phen)}2{Cu(phen)2}(μ3-CO3)](ClO4)2 has revealed a marked structural feature suggesting CH-π and/or π–π interactions, although [Cu(L-o-mPhe)(phen)(H2O)]ClO4 does not show any interaction. CD spectra in the d–d region for [Cu(L-o-mPhe)(phen)]ClO4, [Cu(L-m-mPhe)(phen)]ClO4, and [Cu(L-p-mPhe)(phen)]ClO4 in aqueous solution have exhibited an obvious negative Cotton effect, and the magnitudes have significantly been reduced in dioxane/water in the order: [Cu(L-p-mPhe)(phen)]ClO4 ≤ [Cu(L-m-mPhe)(phen)]ClO4 < [Cu(L-o-mPhe)(phen)]ClO4. 1H NMR spectra of [Pd(L-o-mPhe)(phen)]ClO4, [Pd(L-m-mPhe)(phen)]ClO4, and [Pd(L-p-mPhe)(phen)]ClO4 have exhibited...

Reaction of Cu(ClO4)2·6H2O with l -glutamic acid ( l -glu) in 1:1 or 1:2 molar ratio at pH 5 gave only the complex [Cu( l -glu)-(H2O)]·H2O, whose crystal structure revealed that the copper atom was coordinated in square-planar geometry, with the amino nitrogen and the carboxylate oxygen of l -glu, the side-chain carboxylate oxygen of a neighboring l -glu, and the oxygen of a water molecule in the equatorial positions. Weak coordination of two additional glutamate oxygens to both axial positions complete a distorted octahedron. The [Cu( l -glu)(H2O)] units linked by coordination of the side-chain carboxylate group form an infinite left-handed single helix; the use of d -glu in place of l -glu gives a right-handed helix, indicating that the glu enantiomerism determines the helicity. Thermogravimetric and differential thermal analyses of the complex showed reversible desorption of just two water molecules at 95–130°C, whose behavior was examined by ESR and circular dichroism spectral and powder X-ray diffraction methods in solid state. The crystals obtained from the reaction of Cu(II) ion with dl -glu showed spontaneous resolution.

With a view to understanding the effect of the outer coordination sphere of metal complexes on the redox potential, the electronic absorption spectra, X-ray crystal structure and cyclic voltammograms were investigated of aqueous and ethanol solutions containing the complexes [Co(X)(aa)], where X denotes an NO3-type ligand such as bcmpa (N,N-bis(carboxymethyl)- l -phenylalanine), nta (nitrilotriacetic acid), bcmga (N,N-bis(carboxymethyl)- l -glutamic acid), bcmle (N,N-bis(carboxymethyl)- l -leucine), and aa is an amino acid. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the Co(III) complexes did not exert any influence on the inner coordination sphere of the Co(III) ion. The Co(III) complex systems showed irreversible redox behavior in both the aqueous and ethanol solutions. This is discussed on the basis of the relationship between the hydrophobicity of the outer coordination sphere and the electron transfer reaction by use of reduction potentials.

A copper complex with a new tripodal tetradentate ligand, bis{(6-pivaloylamino-2-pyridyl)-methyl}{(5-carboxyl-2-pyridyl)methyl}amine (BPCA), has been prepared as a model metal centre of copper enzymes that react with dioxygen, the behaviour of which in solution has been examined on the basis of absorption and ESR spectra. Addition of NaN3 to an H2O/CH3OH solution containing Cu(ClO4)2 6H2O-BPCA with 1:1 molar ratio has afforded the complex [Cu-(bpca)(N3)]ClO4. It crystallizes in the monoclinic space group P2/a, a= 17.478(3), b= 9.773(1), c = 22.388(5) A, β = 102.92(2)°, Z = 4. The crystal structure reveals that the coordination around the central metal ion forms a trigonal bipyramid with three pyridine nitrogen atoms of BPCA (Cu-N(2) = 2.01(2), Cu-N(3) = 2.09(1) and Cu-N(4) = 2.22(1) A), in the trigonal plane and with a tertiary amino nitrogen atom of BPCA (Cu-N(l)= 1.99(1)A) and an azide anion (Cu-N(7) = 1.96(2) A) in axial positions. The azide ion is coordinated in an end-on configuration, the c...

Mononuclear copper complexes with a tripodal tetradentate ligand, tris(6-pivaloylamino-2-pyridylmethyl)amine (Htppa), and several anions have been prepared as a model metal centre of copper enzymes, whose structures have been examined by electronic absorption, ESR and NMR spectral, cyclic voltammetry, and X-ray diffraction methods. Those with an anion such as OH−, Cl−, Br−, and I− were shown to form a trigonal-bipyramidal geometry. The X-ray structures of [Cu(Htppa)](ClO4)2·2H2O·CH3OH, [CuCl(Htppa)]ClO4, [Cu(OH)(Htppa)]ClO4, [Cu(OH)(tppa)], and [Cu(tppa)](BPh4), obtained as a single crystal, revealed all trigonal-bipyramidal geometry with four nitrogen atoms of Htppa in trigonal plane and axial position and with the anion in another apical position. The reaction with NaN3 gave [Cu(N3)2(Htppa)], whose crystal structure was a square-pyramid with three nitrogen atoms of Htppa and N3− in square-planar positions and with another N3− in apical position. The redox potentials of [CuCl(Htppa)]ClO4 in MeCN or CH2Cl...

Reaction of K3[Co(CO3)3] with 2 equivalents of N-pyridoxy-L-amino acid (pyridoxy = 3-hydroxy-5-hydroxymethyl-2-methylpyridin-4-ylmethyl; amino acid = alanine, leucine, phenylglycine, phenylalanine, p-nitrophenylalanine, p-methoxyphenylalanine, or tryptophan) afforded the bis(N-pyridoxy-L-amino acidato)cobalt(III) complex as a single band on anion-exchange chromatography. Each complex has been isolated as its sodium salt and characterized in aqueous solution by UV/VIS circular dichroism (CD), and 1H NMR spectra and by X-ray crystallographic analysis in the solid state. The cobalt(III) atom is co-ordinated to two trans(N)-meridional N-pyridoxy-L-amino acid ligands. The 2-methyl group of one pyridoxal moiety lies over the aromatic ring of another pyridoxal ring with separations of 3.67 and 3.56 A. The 1H NMR resonance of the 2-methyl group shows an upfield shift when compared with that of the free pyridoxyamino acid. The selective formation of the trans(N)-meridional-Λ-[R(N), R(N)] diastereoisomer is interpreted in terms of an interligand CH · · · π interaction. The CD and 1H NMR spectra suggest that addition of 1 equivalent HCl weakens this interaction. The biological significance of the pyridoxy 2-methyl group in vitamin B6 coenzyme is discussed.

A triply hydrogen-bonding system has been constructed between bis(biphenylbiguanidado)nickel(II) ([Ni(bpbg)2]) and phenobarbital (Phbar), which has been characterized by the IR and 1H-NMR spectroscopies and the X-ray structure analysis.

The polypyrrole (PPy)-polytungstate anion (H2W12O406-, PW) composite film formed by electrochemical polymerization was studied by two in situ optical methods: absorption spectroscopy and Raman spectroscopy. The PPy doped by chloride anions was also studied as a comparison. The potential dependence of the absorption band and the Raman shift indicates that the PPy-Cl film reduces in turn from the bipolaron-loaded PPy to the polaron-loaded PPy, and further to the neutral PPy with decrease of potential. The PPy-PW film does not, however, reach the neutral PPy even at a relatively low potential, where the reduction of tungsten ions of W(V1) to W(V) in the PW preferentially takes place.

The formation of the aluminium(III) complexes of new types of bifunctional multidentate ligands, 7-(2-carboxyethyl)amino-8-hydroxy-5-quinolinesulphonic acid ( 1 , H 3 ceahqs) and 7-(2-carboxymethyl)amino-8-hydroxy-5-quinolinesulphonic acid ( 2 , H 3 cmahqs), have been investigated in an aqueous sodium nitrate solution of constant ionic strength (0.10 mol dm −3 ) at 25.0°C. These ligands form yellow bis(ligand)aluminium(III) complexes with two linkage isomers of ONO type that have the coordination mode of an o -(2-carboxyalkyl)aminophenolato moiety, i.e. Al(Hceahqs-O,N,O) 2 − and Al(Hcmahqs-O,N,O) 2 − , below pH 3 and of NO type that have the coordination mode of an 8-quinolinolato moiety, i.e. Al(ceahqs-N,O) 2 3− and Al(cmahqs-N,O) 2 3− , above pH 3, thus exhibiting linkage isomerism controlled by ambient solution acidity. The complex formation reaction mechanism is different in these two isomers: the ONO isomer forms through pathways of Al 3+ with H 3 L and H 2 L − and of Al(OH) 2+ with H 3 L, with the mechanistic rate-determining donation of the imino nitrogen preceded by a rapid ionic association of the central metal atom with the deprotonated carboxylate group, whereas the NO isomer forms through pathways of Al 3+ and HL 2− and of Al(OH) 2+ with H 2 L − and HL 2− , with the mechanistic rate-determining donation of the phenolato oxygen to the central metal atom (H 3 L  H 3 ceahqs or H 3 cmahqs). In both of these isomers, the formation of the mono(ligand)aluminium(III) complex is slower than its reaction with another ligand molecule to form the bis(ligand)aluminium(III) complex. Details of the coordination reaction mechanism are described.

Kinetics and mechanisms of coordination by ligand-substitution of HCO 3 - for Cl - on the cobalt(III) complexes of [CoCl(N) 5 ] 2+ -type having different (N) 5 backbone chelate ring structures to form those of [Co(CO 3 )(N) 5 ] + -type have been investigated in a weakly alkaline aqueous 0.10 mol dm -3 sodium perchlorate solution at ambient temperatures, in order to elucidate any possibility for the fixation of atmospheric CO 2 on the coordination sphere of the transition metal center in the form of CO 3 2- . The HCO 3 - in the aqueous solution easily and substitutionally coordinates to the cobalt(III) complexes in place of coordinated chloro ligand via two consecutive rate-determining steps, the faster one with two parallel pathways of aquation and hydroxide-anation and the slower one with a pathway of carbonate-anation. Of these reaction pathways, the hydroxide-anation was explained by a dissociative interchange mechanism via conjugate base (I d CB), whereas the carbonate-anation was explained by a nucleophilic attack of coordinated oxygen atom on the central cobalt(III) atom to the carbon atom of HCO 3 - while maintaining the Co-O bond throughout the step by taking the result of an EHMO calculation into consideration. The (N) 5 backbone chelate ring structure served to enhance the rate of coordination of HCO 3 - on the cobalt(III) center as well as that of preceding aquation and hydroxide-anation steps chiefly by its entropy effect. The pentadentate tetren backbone structure was recommended for the rapid fixation of CO 2 in the form of CO 3 2- on the cobalt(III) complexes of [CoCl(N) 5 ] 2+ -type.

Coordination reaction kinetics and mechanisms of 7-substituted-8-hydroxy-5-quinolinesulphonic acid ligands that have ligating substituents of nitrogen whose nature is different from that at the 1-position, i.e. 7-amino-8-hydroxy-5-quinolinesulphonic acid (1, H2ahqs) and 7-phenylazo-8-hydroxy-5-quinolinesuphonic acid (2, H2phqs), have been investigated spectrophotometrically in an aqueous sodium nitrate solution of constant ionic strength (0.10 mol dm−3) at 25.0°C. These ligands selectively coordinate to aluminium(III) with its 8-quinolinolato moiety through pyridyl nitrogen and phenolato oxygen to form yellow and red complexes, indicating that the donor ability is higher for the aromatic than for the amino and azo nitrogens towards aluminium(III). The complex formation reaction proceeds through two parallel pathways of Al3+ with Hahqs− and Hphqs− and of Al(OH)2+ with H2ahqs and H2phqs, the coordination of the phenolato oxygen to the central metal atom being the mechanistic rate-determining step. The role of substituent groups at the 7-position of the 8-quinolinolate framework on its coordinating nature as a bidentate ligand towards the central metal atom is emphasized.

Coordination reaction kof kinetics of a bifunctional multidentate ligand 8-hydroxy7-(2-hydroxy-5-carboxyphenyl)-azo]-5-quinolinesulphonic acid (H4hcqs), to iron(III) has been investigated in an aqueous 0.10 mol dm−3 sodium perchlorate solution at 22°C. This ligand initially coordinates to the metal ion to form an intermediate complex with its bidentate quinolinolato (NO) moiety, Fe (H2hcqs-N, O)+, which then transforms to a complex with its terdentate dihydroxyazo(ONO) moiety, Fe(H2hcqs-O,N,O)+, with the stability constant (β11) of log β11 (mol−1 dm3) of 18.32±0.11, thus showing a kinetic linkage isomerism. The first step proceeds through the parallel pathways of Fe3+ + H2hcqs2− (k32) and FeOH2+ + H4hcqs (k20) with the composite rate constant of k32+k20Ka(qyNH), KOH (mol−1 dm3 s−1) of 1.92±0.35 × 103 showing the greater importance of the pathway of k20 as compared with that of k32, where K(qyNH) and KOH are the protonation constant of the quinolinol nitrogen of H4hcqs and the hydrolysis constant of Fe3+, respectively; the second step of the linkage isomerization from Fe(H2hcqs-N,O)+ to Fe(H2hcqs-O,N,O)+ has the rate constant (kisom of 1.3±0.1 × 10−1 s−1. Thermodynamic and kinetic characteristics of these sequential reactions and those for the related ligands to the metal ion are described in detail.

A new terdentate ligand, N -pyridoxyl- o -hydroxyaniline ( 1 , H 2 pha), was synthesized and the formation of its iron(III) complex was thermodynamically and kinetically investigated (0.10 mol dm −3 NaClO 4 ; 25°C). The ligand forms a very stable bis(ligand)iron(III) complex (log β 12 = 45.8±0.2; β 12 (mol −2 dm 6 ) = [Fe(Hpha) 2 + ]/[Fe 3+ ][Hpha − ] 2 ) in comparison with other N α -pyridoxyl-L-amino acid-type terdentate ligands with benzyl ( 2 ), methyl ( 3 ), and indolylmethyl ( 4 ) groups, indicating that an intramolecular interaction as well as a high affinity of phenolato oxygen to the central metal atom greatly contributes to the stability of the bis(ligand)iron(III) complex of 1 . The rate constants for the iron(III) complex of 1 are (1.40±0.20) × 10 2 mol −1 dm 3 s −1 for the two parallel pathways of Fe 3+ + H 3 pha + ( k 33 ) and FeOH 2+ + H 4 pha 2+ ( k 24 ) ( k 33 + k 24 K OH 11 Ka (amNH) , where K OH 11 and K a (amNH) are the hydrolysis constant of iron(III) and protonation constant of 1 at the amino nitrogen) and (2.44±0.30) × 10 2 mol −1 dm 3 s −1 for the pathway of FeOH 2+ + H 3 pha + ( k 23 ). The comparison of these rate constants with those of the iron(III) complexes of 2 , 3 , and 4 suggest that the complex formation mechanism is given by the rate-determining coordination of the phenolato oxygen of pyridoxyl moiety to iron(III), followed by the rapid donations of other ligating groups.

Thermodynamic stability and kinetics and mechanism of the formation of the iron(II) complex of 4-methyl-8-di(carboxymethyl)aminomethyl umbelliferrone (1, H3muia) have been studied spectrophotometrically in an aqueous sodium perchlorate solution (0.10 mol dm−3) at 25°C. A 1:1 (metal:ligand) complex of iron(II) with 1 forms in an acidic medium with a stability constant, log β11 (mol dm−3), of 14.42±0.20, in contrast to no formation of the iron(II) complex with related terdentate ligands having a mono(carboxymethyl) ligating group. This complex formation reaction proceeds through a single pathway of Fe2+ with Hmuia2− ligand species with a rate constant, k2 (mol−1 dm3 s−1), of (7.04±0.20) × 104. The coordination reaction mechanism is discussed in detail.

The single crystal of cis-β-Λ-S,S-[Co(CO3)(trien)](ClO4)·H2O (trien = triethylenetetramine) has spontaneously resolved from the aqueous solution of cis-α-[CoCl(NH3)(trien)](ClO4)2 containing hydrogencarbonate anion, whose crystal structure has been determined by X-ray diffraction method. The complex crystallizes in the monoclinic space group P21 with a = 7.410(1), b = 12.354(3), c = 8.676(1) A, β = 108.88(1)°, and Z = 2. The final R and Rw values for the 3056 observed reflections with Io > 3σ(Io) are 0.045 and 0.055, respectively. The tetradentate ligand, trien, is linked to the cobalt atom in cis-β-configuration, and the carbonato anion is coordinated to the metal atom as a didentate ligand. The Co–N bond lengths are 1.904(6), 1.928(4), 1.941(4), and 1.955(5) A, and the two Co–O bond lengths are both 1.909(4). The absolute configuration of the complex cation can be designated as Λ(λλδ) and those about two secondary nitrogen atoms are both S.

A composite film comprising polypyrrole (PPy) and isopoly tungstate (PW) anion was prepared by electropolymerization of pyrrole in an aqueous solution of polytungstic acid. The formation of the PPy-PW film was traced using an electrochemical quartz crystal microbalance (EQCM). The oxidation-reduction behavior of the film was also investigated by the EQCM and compared with that of PPy film prepared in acidic KCl solution. From the EQCM measurements, the growth rate of the PPy-PW film under constant current oxidation at 0.186 mA cm −2 was evaluated as 0.97 μg mC −1 , which was 2.8 times as high as that of PPy-Cl film prepared in acidic KCl solution. From emission spectroscopic analysis, the composite PPy-PW film was found to contain 51 wt.% tungsten, or 67 wt.% meta-polytungstate anion, H 2 W 12 O 40 6− The PPy-PW film behaved like a redox polymer film in which the W(V)/W(VI) couple of the doped polytungstate anion functions as a reversible redox center. The doped PW changes the ionic permeating property of the polymer film; the PPy-PW film reveals protonic permeability, although the ordinary chloride ion doped PPy has anionic permeability.

The thermodynamic stability and the formation reaction mechanism have been investigated for the iron(III) complexes with a new tetradentate ligand, N α -carboxymethyl-N α -salicyl- l -phenylalanine ( 1 , H 3 cslpa) and the related N α -salicyl- l -phenylalanine ( 2 , H 2 slpa). The mono(ligand)iron(III) complex of 1 formed under both conditions for the metal ion concentration ( C M ) being in large excess over the ligand 1 ( C L ) and vice versa , while 2 formed a bis(ligand)iron(III) complex in consecutive stages under the conditions C L ⪢ C M . The stability constant of the mono(ligand)iron(III) complex of 1 (logβ 11 = 21.61 ± 0.10; β 11 = [Fe(cslpa)]/[Fe 3+ ][cslpa 3− ]) was larger than the constant of the complex of 2 (log β 11 = 17.71 ± 0.09; β 11 = [Fe(slpa) + ]/[Fe 3+ ][slpa 2− ]), which was mainly caused by the chelate effect of an additional methylcarboxylate group. The complexes of 1 and 2 were formed through the composite pathways of Fe 3+ + H 2 L −(or 0) ( k 32 ) and FeOH 2+ + H 3 L 0(or + ( k 23 ) and another single pathway of FeOH 1+ + H 2 L −0 (itk 22 ) [L 3−(or 2−) = cslpa 3− (or slpa 2− )]. The rate constants of each pathway for 1 and 2 are the same in magnitude as the corresponding constants of iron(III)-N α -pyridoxyl-L-aspartic acid ( 4 , H 3 plas) and-N α -salicyl- l -alanine systems, respectively. This good agreement in the rate constants suggests a mechanism that the complexes of 1 and 2 form through the slow coordination of the phenolato oxygen followed by the rapid donations of other coordinating atoms.

The reaction of salicylidene-L-alanine with the Co(III) complex involving 2,2′:6′,2″-terpyridine (terpy) in aqueous ethanol solution afforded a peculiar transamination to form the complex, [Co(α-hydroxy salicylidene-o-hydroxybenzylamine)(terpy)]+, whose structure has been confirmed by X-ray structure analysis and positive FAB mass spectrometry.

The difference in the electrical conduction behavior of various kinds of MnZr2n(PO4)3n (Mn=alkali metals, alkaline earth metals, Ag, Mn, Co, Ni, Zn, Cd, Pb, Al, Ga, and In) compounds (abbreviated as MZP) has been investigated by using frequency dispersion analysis. The conductivity of MZP with a NASICON-type structure mainly depended on the hopping rate of mobile cation; the conductivity of MZP with a sFe2(SO2)3-type structure was more affected by the mobile ion concentration than that with the NASICON-type one. These conclusions agree well with those obtained from crystallographic investigation.

The formation kinetics and the thermodynamic stability of iron(III) complexes with a new tetradentate ligand, Nα-salicyl- l -alaninehydroxamic acid (1, H2slalh), have been investigated by the use of UV-vis and stopped-flow spectrophotometric methods. Two types of mono(ligand)iron(III) complex species of 1 are found to exist under both conditions of the metal ion concentration in large excess over the ligand and vice versa, by comparing the pH-dependent absorbance change behaviour of the iron(III) complex of 1 with that of the iron(III) complexes of l -alaninehydroxamic acid (2, Halh) and Nα-salicyl- l -alanine (3, H2slal), i.e. Fe(H2slalh)3+, which takes the coordination of the hydroxamate moiety below pH 1.8, and Fe(slalh)+, which takes the quadridentate coordination above pH 1.8. The complex formation reaction proceeds through one pathway of Fe3+ + H3slalh+ (k33I) for Fe(H2slalh)3+ and two pathways of Fe3+ + H3slalh+ (k33II) and FeOH2+ + H3slalh+ (k23II) for Fe(slalh)+. The mechanism of the complex formation was explained by the slow coordination of the carbonyl oxygen to iron(III) for Fe(H2slalh)3+ [and also Fe(Halh)3+] and of the phenolato oxygen for Fe(slalh)+ [and also Fe(slal)+], followed by the rapid donations of other coordinating atoms. The stability constants are calculated to be log β11 = 10.29 ± 0.09 mol−1 dm3 for Fe(H2slalh)3+ and 23.17 ± 0.18 mol−1 dm3 for Fe(slalh)+, respectively. The introduction of the hydroxamate moiety to the carboxylate group of 3 increases the affinity of the ligand to iron(III), which indicates that the combination of hydroxamic acid is necessary to design a new type of siderophore based on the salicylamino acid ligand.

The bis-(N-pyridoxy-L-phenylalaninato)cobalt(III) complex exhibiting an anomalous assembly of aromatic rings around the pyridoxy 2′-methyl group has been synthesized and characterized by 1H-NMR spectroscopy and X-ray analysis. The 1H-NMR spectrum of the complex in D2O, methanol-d4 and dimethylsulfoxide-d6 revealed peculiar upfield shift in 2′-methyl group. The detailed examination of the crystal structure demonstrated that the two C–H bond vectors of 2′-methyl group were directed toward the planes of the pyridoxy pyridine and phenylalanyl benzene rings, respectively. These findings indicate the induced assembly of aromatic rings through a CH···π interaction.

The formation of an iron(III) complex with a new multidentate ligand, Nα-pyridoxyl-L-tryptophan(1, H2pltp), has been investigated thermodynamically and kinetically in an aqueous 0.10 mol dm−3 sodium perchlorate solution at 25°C. A 1:2(metal : ligand) complex of 1 forms with much higher stability constant (logβ12/mol−2 dm6 = 38.29±0.28) than the related complex, bis(pyridoxylidene-L-tryptophan)iron(III), having the azomethine group (log β12/mol−2 dm6 = 18.38±0.10 [3]). This effect was explained by the contribution of amino nitrogen of higher basicity to the thermodynamic stability. The complex formation reaction proceeds through two parallel pathways of Fe3+ +H3pltp+ and FeOH2+ +H4pltp2+ and also another pathway of FeOH2+ +H3pltp+ with slower coordination of the first ligand to iron(III). The mechanistic rate-determining step for the formation of the complex was the coordination of the phenolato oxygen to a central metal atom, followed by the rapid donations of the amino nitrogen and carboxylato oxygen atoms.

The coordination reaction characteristics and mechanisms of the title new ligands (1(H2plpa), 2(H2plal), and 3(H3plas) stated in the order) to iron(III) have been investigated in an aqueous 0.10mol dm−3 sodium perchlorate solution at 25°C by means of electronic absorption spectral and stopped-flow spectrophotometric methods. They equally form the corresponding bis(ligand)iron(III) complexes with slower coordination of the first one through the same two parallel pathways of Fe3+ +H3+L + (or 0) and FeOH2+ +H4L2+(or +) and also another pathway of FeOH2+ +H3L+(or0) (L is fully deprotonated species of 1, 2, and 3); the mechanistic rate-determining step is the coordination of phenolato oxygen of the first ligand. The thermodynamic stability constant (log β12/mol−2dm6. 0.10mol dm−3 (NaClO4), 25°C) of iron(III)-3 complex (48.33±0.21) is very large in comparison with the constants of the iron(III) complexes of 1(39.06 ±0.26) and 2(39.81 ± 0.20). A possibility is concluded for the formation of more stable iron(III) complexes without changing the complex formation reaction mechanism by designing the ligand structure of the amino acid moiety of pyridoxal-L-amino acid derivatives as a siderophore.

Full geometry optimizations have been carried out for the complex formations of Cu+ and Cu(2,2′-bipyridine)+ with CO2 by using the density functional methods. The calculation demonstrated that the end-on coordination mode was mainly favored for all cases, while the binding of 2,2′-bipyridine (bpy) to Cu(CO2)+ largely labilized the end-on coordination mode and stabilized the in-plane side-on coordination mode. The detailed examination of the population analysis indicate that the coordination of bpy to Cu+ weakens the electron donating character of CO2 to Cu+ and promotes the important participation of π-back-donative interaction from the metal ion to CO2.

The structures and the formation energies of [MCl4]2− (M = Cr, Mn, Fe, Co, Ni, Zn) have been examined by the density functional method. The optimized structures of [MnCl4]2−, [CoCl4]2− and [ZnCl4]2− are a regular tetrahedron with the M–Cl distances of 236, 227, and 231 pm, respectively. The structures of [CrCl4]2− and [FeCl4]2− are a flattened tetrahedron with the M–Cl distances of 236 and 231 pm, respectively, and with the flattening angles of 156 and 112°, respectively, while that of [NiCl4]2− is a tetrahedron elongated along an S4 axis with the Ni–Cl distance of 226 pm and the corresponding angle of 97°. The formation energies of [MCl4]2− have been compared with their experimental data, and the relative energies of the transformation from [M(H2O)6]2+ to [MCl4]2− are also evaluated in connection with the stability of the anions in aqueous solutions.

Transformation of amino acid to α-hydroxy amino acid has been discovered in the Co(III) complex with pyridoxylidene-amino acid ligand, which has been discussed on the basis of the 1H-NMR and FAB mass spectroscopic data and X-ray crystallographic analysis.

The intrinsic structures of [CuCl4]2− and [CuBr4]2− have been investigated by ab initio density functional method and determined to be D2d symmetry with the flattening X-Cu-X angles of 138° and 130° for the case of X = Cl and Br, respectively, and the Cu-X distances of 228 pm and 241 pm, respectively, which are good agreement with the experimental data.

The formation of the iron(III) complex of 4-methyl-8-(carboxymethyl)aminomethyl umbelliferrone (1, H2mug) and its N-methyl (2, H2mugm) and N-carboxymethyl (3, H3muia) derivatives has been investigated spectrophotometrically in an aqueous sodium nitrate solution (0.10 mol dm−3) at 25°C. A 1 : 1 (metal : ligand) complex forms uniquely for all three ligands, indicating a steric interference between the coordinated and a coordinating ligand. The stability constant [log β11/(mol−1 dm3(] is 15.74 ± 0.20 for 4 [Fe(mug)+], 15.69 ± 0.20 for 5 [Fe(mugm)+] and 18,67 ± 0.20 for 6 [Fe(muia)]. The complex formation reaction proceeds through two parallel pathways of Fe3+ and Fe(OH)2+ with diprotonated ligand species of 1, 2 and 3; a slow coordination of the phenolato oxygen, followed by rapid donations of the amino nitrogen and carboxylato oxygen(s) to form a mono_terdentato- and tetradentato)iron(III) complex was deduced as the reaction mechanism. The possibility of changing the thermodynamic stability with no variation in the reaction mechanism by the introduction of substituent groups on the amino nitrogen of 1 is suggested.

The electronic character of the ruthenium complexes with tripodal polypyridine ligands, which is controlled by the substituted groups at pyridine 6-position, gives rise to differences in the reactivity for the ruthenium catalyzed hydroxylation of adamantane and epoxidation of cyclohexene with PhIO as an oxidant; Ru complexes containing electron-withdrawing groups ( 1 , 3 , and 5 ) promote the epoxidation, while those containing electron-donating groups ( 2 , 4 , and 6 ) promote the hydroxylation.

With a view to constructing an artificial metalloenzyme model complex which can recognize and capture a small molecule, a new tripodal ligand, tris(6-pivaloylamino-2-pyridylmethyl)amine, and its mononuclear copper(II) complex has been synthesized, and they were characterized by 1H-NMR and positive-ion FAB mass spectra, cyclic voltammetry and X-ray structure analysis.

The crystal structure, phase transition, electrical conduction behavior of various kinds of MIIZr4(PO4)6 (MIIZP) compounds (MII = Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn, Cd, and Pb) have been investigated. The Mg, Co, Ni, and Zn compounds are of the β-Fe2(SO4)3-type structure and show an order-disorder transition between 600 and 720 °C; the Ca, Sr, Ba, Cd, and Pb compounds, however, are of the NASICON-type structure and do not show any phase transition between r.t. and 1000 °C. The Mn compound sintered at 900 °C shows the former characteristics (the phase transition temperature is around 560 °C), and that sintered above 900 °C the latter. The ZnZP and MnZP show the highest conductivity, ca. 2 × 10−3 and ca. 8 × 10−4 S cm−1 at 800 °C, in the β-Fe2(SO4)3- and the NASICON-type structure, respectively. The ionic size of the mobile cation is the predominant factor regarding ionic conduction in the zirconium phosphate framework.

An enhancement of electric conductivity was observed by substitution of Si4+ for P5+ in LiZr2(PO4)3, MgZr4(PO4)6, and ZnZr4(PO4)6 solid electrolytes with a β-Fe2(SO4)3-type structure. An increase in the concentration of interstitial Li+ ion resulted in the conductivity enhancement for the Li compound, whereas an increase in the compactness of sintered specimen for the Mg and Zn compounds.

Thermodynamic stability and kinetics and mechanism of formation of iron(II) complex with 8-hydroxy-7-(2-thiazolyl)azo-5-quinoline-sulfonic acid (THQS) have been studied spectrophotometrically in an aqueous 0.10 mol dm−3 sodium chloride solution at 25°C. The iron(II) complex with coordinated 8-quinolinolato moiety of THQS forms with the stability constant (β11) of logβ11/mol−1 dm3 = 8.52 ± 0.20. This complex exhibits a metal-to-ligand charge-transfer band in the visible region. Stopped-flow kinetics revealed biphasic processes with a faster formation of the complex with coordinated 2-thiazolylazophenolato moiety followed by a slower linkage isomerization of this intermediate to the final, more stable complex with coordinated 8-quinolinolato moiety. The reaction pathways and concomitant rate constants are elucidated and determined; the reaction mechanism is discussed in detail.

Electrospray mass spectrometry (ESI–Mass) gave clear evidence for complex formation between an iron(III) complex and a DNA chain, and also between a binuclear iron(III)–peroxide adduct and a DNA chain.

In order to investigate the electron-transfer site of azurin, one of the electron-transfer proteins, some optically active Ru(III) complexes bearing hydrophobic amino acid side-chains as the molecular recognition probe have been prepared, and have been applied for the reaction with azurin-1Cu(I) from Alcaligenes xylosoxidans GIFU 1051. The estimated second-order rate constants and activation parameters, Δ H ≠ and Δ S ≠ , have indicated enantio- and stereoselectivities. The comparison with that for azurin-2, another species isolated from the same source, has strongly suggested that the electron-transfer site of azurin is His117.

Reaction between Na3H2(HXTA) and Na3Co(CO3)3 in an aqueous solution gave a binuclear cobalt(III) complex, Na2Co2(HXTRA), where in the (HXTRA)4− ligand one of the four acetate arms of the (HXTA)5− ligand is lost; H5(HXTA) denotes N,N′-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-carboxymethylglycine). This may be attributed to the oxidative degradation of one acetato arm of the (HXTA)5− ligand due to a peroxide-Co(III) species.

The formation of an iron(II) complex with 8-hydroxy-7-(8-quinolyl)azo-5-quinolinesulfonic acid (QHQS,H2qhqs) has been investigated on the basis of the electronic absorption spectra, the equilibrium, and the stopped-flow kinetics in a 0.10 mol dm−3 aqueous sodium chloride solution at 25°C with a view to elucidating the coordination selectivity of the ligand. A 1:2 (metal:ligand) complex forms in an acidic medium with a selective coordination of QHQS to iron(II), with its 2-(8-quinolylazo)phenol moiety acting as a terdentate ligand. The complex formation reaction proceeds through a single pathway of Fe2+ with Hqhqs−, a ligand species singly protonated at the phenolate oxygen, with the rate constant (k21) of k21=(3.16±0.20)×105 mol−1dm3s−1, to form a mono-ligand complex as the rate-determining step. The coordination of the ligand by 8-quinolyl nitrogen, followed by a rate-determining bonding of phenolato oxygen, was suggested as the reaction mechanism.

The cis configuration between the hydroxo and the carboxylato and the three amino groups of the tetradentate, tripodal ligand tris(6-neopentylamino-2-pyridylmethyl)amine favors the formation of hydrogen bonds which stabilize the hydroxo-Feiii complex 1. Thus, its structure closely resembles that of the active center of Feiii -soybean lipoxygenase-1, which also contains a six-coordinate Feiii atom.

The Co(III) complex with the (N)(O)3-type tripodal tetradentate ligand, bis-N,N-carboxymethyl- L -phenylalanine (BCMPA, H3bcmpa), can site-specifically coordinate a bidentate amino acid (AA, Haa) in the trans-N configuration rather than the cis-N form through the non-covalent weak interligand interactions of hydrogen bondings, steric repulsion, and electrostatic repulsion, on the basis of the 1H NMR spectroscopic data and X-ray crystallographic analysis. In addition, the [Co(bcmpa)(aa)]− complex with cis-N form isomerizes to the trans-N form, which confirms that the trans- N complex is thermodynamically more stable than the cis-N one. These interactions between the coordination sites of bcmpa and aa ligands are of interest as a molecular recognition model for the enzyme(bcmpa)-substrate(aa) complex.

Thermodynamically extremely stable alkylperoxo−iron(III) complexes have been prepared for the first time from reaction of the ternary iron(III) complex with a tripodal pyridylamine ligand with alkylperoxide in MeCN. These complexes have been characterized on the basis of the electronic absorption, ESR, resonance Raman, and ESI mass spectra and cyclic voltammetry.

The NH-pi interaction has been detected in the crystal structures of Co(III) ternary complexes with N,N-bis(carboxymethyl)-(S)-phenylalanine (BCMPA) and aromatic amino acids including (S)-phenylalanine ((S)-Phe), (R)-phenylalanine ((R)-Phe), and (S)-tryptophan ((S)-Trp)). Additionally, this interaction has been studied in solution for Co(III) ternary complexes with BCMPA or NTA (NTA = nitrilotriacetic acid) and several amino acids (AA) by means of electronic absorption, circular dichroism (CD), and (1)H NMR spectroscopies. The CD intensities of the Co(III) complexes with aromatic amino acids measured in the d-d region ( approximately 20.5 x 10(3) cm(-)(1)) are significantly decreased in ethanol solutions relative to water. Analogous complexes with aliphatic amino acids do not exhibit this solvent effect. The (1)H NMR spectra of the Co(III) complexes with aromatic amino acids measured in DMSO-d(6) exhibit upfield shifts of the NH peaks compared with those with aliphatic amino acids, which suggest a shielding effect due to the aromaticity. The upshift values coincide with those experimentally evaluated from the crystal structures. The magnitude of the upfield shifts agrees well with Hammett's rule, indicating that the increase of pi-electron densities on the aromatic rings leads attractive NH-pi interaction that exerts a larger shielding effect for the NH protons. In ligand-substitution reactions of the carbonatocobalt(III) complexes with amino acids, the yields of those with aromatic amino acids are higher than the yields obtained for complexes with aliphatic amino acids. This observation is discussed in connection with the important contribution of the NH-pi interaction as one of the promotion factors in the reaction.