Yoshitaka Sakai

Syntheses, structures, and antimicrobial activities of remarkably light-stable and water-soluble silver complexes with amino acid derivatives, silver(I) N-acetylmethioninates.

Reaction of L- and DL-N-acetylmethionine (Hacmet) and Ag(2)O in water at ambient temperature afforded the remarkably light-stable silver complexes {[Ag(L-acmet)]}(n) (1) and {[Ag(2)(D-acmet)(L-acmet)]}(n) (2), respectively. The color of the solids and aqueous solutions of 1 and 2 did not change for more than 1 month under air without any shields. The light stability of these two silver(I) complexes is much higher than that of silver(I) methioninate {[Ag(2)(D-met)(L-met)]}(n) (3) (Hmet = methionine), silver(I) S-methyl-L-cysteinate {[Ag(L-mecys)]}(n) (4), and silver(I) L-cysteinate {[Ag(L-Hcys)]}(n) (5). X-ray crystallography of 1 obtained by vapor diffusion revealed that ladder-like coordination polymers with two O- and two S-donor atoms were formed. The acetyl group of acmet(-) prevents chelate formation of the ligand to the metal center, which is frequently observed in amino acid metal complexes, but allows for formation of hydrogen bonds between the ligands in the crystals of 1. These two silver(I) N-acetylmethioninates showed a wide spectrum of effective antimicrobial activities against gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and yeasts (Candida albicans and Saccharomyces cerevisiae), the effectiveness of which was comparable to that of water-soluble Ag-O bonding complexes.

Intercluster Compound between a Tetrakis{triphenylphosphinegold(I)}oxonium Cation and a Keggin Polyoxometalate (POM): Formation during the Course of Carboxylate Elimination of a Monomeric Triphenylphosphinegold(I) Carboxylate in the Presence of POMs

The preparation and structural characterization of a novel intercluster compound, [{Au(PPh(3))}(4)(μ(4)-O)](3)[α-PW(12)O(40)](2)·4EtOH (1), constructed between a tetrakis{triphenylphosphinegold(I)}oxonium cation and a saturated α-Keggin polyoxometalate (POM) are described. The tetragold(I) cluster oxonium cation was formed during the course of carboxylate elimination of a monomeric phosphinegold(I) carboxylate complex, i.e., [Au((R,S)-pyrrld)(PPh(3))] [(R,S)-Hpyrrld = (R,S)-2-pyrrolidone-5-carboxylic acid], in the presence of the free acid form of a Keggin POM, H(3)[α-PW(12)O(40)]·7H(2)O. The liquid-liquid diffusion between the upper water/EtOH phase containing the Keggin POM and the lower CH(2)Cl(2) phase containing the monomeric gold(I) complex gave a pure crystalline sample of 1 in good yield (42.1%, 0.242 g scale). Complex 1 was formed by ionic interaction between the tetragold(I) cluster cation and the Keggin POM anion. As a matter of fact, the POM anion in 1 can be exchanged with the BF(4)(-) anion using an anion-exchange resin (Amberlyst A-27) in BF(4)(-) form. By using other Keggin POMs, such as H(4)[α-SiW(12)O(40)]·10H(2)O and H(3)[α-PMo(12)O(40)]·14H(2)O, the same tetragold(I) cluster cation was also formed, i.e., in the forms of [{Au(PPh(3))}(4)(μ(4)-O)](2)[α-SiW(12)O(40)]·2H(2)O (2) and [{Au(PPh(3))}(4)(μ(4)-O)](3)[α-PMo(12)O(40)](2)·3EtOH (3). Compounds 1-3, as dimethyl sulfoxide-soluble, EtOH- and Et(2)O-insoluble dark-yellowish white solids, were characterized by complete elemental analysis, thermogravimetric and differential thermal analyses, Fourier transform IR, X-ray crystallography, and solid-state (CPMAS (31)P and (29)Si) and solution ((31)P{(1)H} and (1)H) NMR spectroscopy. The molecular structures of 1 and 2 were successfully determined. The tetragold(I) cluster cation was composed of four PPh(3)Au(I) units bridged by a central μ(4)-oxygen atom in the geometry of a trigonal pyramid or distorted tetrahedron.

A first example of polyoxotungstate-based giant molecule. Synthesis and molecular structure of a tetrapod-shaped Ti–O–Ti bridged anhydride form of Dawson tri-titanium(IV)-substituted polyoxotungstate

The preparation and structural characterization of a giant “tetrapod”-shaped inorganic molecule, [(α-1,2,3-P2W15Ti3O60.5)4Cl]37− ,1a (abbreviated to {TiO6}12; FW ∼15700), consisting of four tri-TiIV-1,2,3-substituted α-Dawson substructures and one encapsulated Cl− ion, are described. A water-soluble, all-inorganic composition compound of the tetrameric Ti–O–Ti bridged anhydride form, NaxH33−xK4[1a]·yH2O, 1 (x = 21–26, y = 60–70), being afforded by a stoichiometric reaction in aqueous solution of tri-lacunary Dawson polyoxotungstate Na12[B-α-P2W15O56]·19H2O with 3 equiv of Ti(SO4)2·4H2O in HCl-acidic aqueous solution followed by exchanging the countercation, was obtained as analytically pure, homogeneous colorless plate crystals. Single-crystal X-ray structure analysis revealed that the polyoxoanion 1a was an inorganic, giant “tetrapod”-shaped molecule (described as a sphere with a diameter of ∼31.2 A) with approximately Td symmetry. Characterization of 1 was also accomplished by complete elemental analysis, TG/DTA, FTIR, UV-vis absorption and solution (31P and 183W) NMR spectroscopy.

Synthesis and pH-variable ultracentrifugation molecular weight measurements of the dimeric, Ti–O–Ti bridged anhydride form of a novel di-TiIV-1,2-substituted α-Keggin polyoxotungstate. Molecular structure of the [(α-1,2-PW10Ti2O39)2]10− polyoxoanion

The preparation and characterization of a Keggin-type, novel di-TiIV-1,2-substituted polyoxotungstate are described. The dimeric, Ti–O–Ti bridged anhydride form of the di-TiIV-1,2-substituted α-Keggin polyoxotungstate, K10[α,α-P2W20Ti4O78]·12H2O 1, was unexpectedly found in the varied molar-ratio reactions of tri-lacunary precursor Na9[A-PW9O34]·19H2O with Ti(SO4)2 in aqueous solution. Although this compound was first found as a minor product in the preparation of the dimeric, tri-TiIV-1,2,3-substituted species, K10H2[α,α-P2W18Ti6O77]·17H2O 3, it was successfully prepared as a main product in this work and structurally characterized. Compound 1, as analytically pure, homogeneous colorless needle crystals, was obtained as a major product in 29.2% yield (2.7 g scale) from recrystallization under acidic conditions (at pH 2.2) of the 1 ∶ 2 molar-ratio reaction product. X-Ray structure analysis revealed that the molecular structure of 1 consisted of a dimeric anhydride formed by two Ti–O–Ti bonds linking two [α-1,2-PW10Ti2O40]7− Keggin units. Interestingly, ultracentrifugation molecular weight (MW) measurements of this compound in aqueous solution showed the pH-dependent interconversion between monomer [α-1,2-PW10Ti2O40]7−2 and dimer [α,α-P2W20Ti4O78]10−1; this compound was present as the monomer under less acidic conditions (pH 7.8), while it was in dimeric form under more acidic conditions (pH 1.0 and 2.2). Characterization of 1 was also accomplished by complete elemental analyses, TG/DTA, FTIR and solution (31P and 183W) NMR spectroscopy.

Syntheses, molecular structures and pH-dependent monomer–dimer equilibria of Dawson α2-monotitanium(IV)-substituted polyoxometalates

The preparation and structural characterization of a novel, solid Brønsted acid based on Dawson alpha2-monotitanium(IV)-substituted polyoxometalates (POMs) are described. The free-acid form of the POM, i.e., 13H+-heteropolyacid with the formula H13[1b].55H2O DH-1 (1b = [(alpha2-P2W17TiO61)(alpha2-P2W17TiO61H)(mu-O)]13-), was prepared by passing an aqueous solution containing a potassium salt precursor, K14[1a].17H2O DK-1 (1a=[(alpha2-P2W17TiO61)2(mu-O)]14-), through a cation-exchange resin column. Compound DK-1 was obtained by a stoichiometric reaction of mono-lacunary Dawson POM [alpha2-P2W17O61]10- with Ti(SO4)2 in an aqueous solution. [Note: the abbreviations D, M, K and H stand for dimer, monomer, potassium salt and free-acid form, respectively.] Compounds DK-1 and DH-1 were characterized by using complete elemental analysis, thermogravimetric (TG) and differential thermal analysis (DTA), FTIR, solution (31P and 183W) NMR spectroscopy, pH-varied 31P NMR spectroscopy, solid-state 31P CPMAS NMR, X-ray crystallography and acidity measurements in an organic solvent with a Hammett indicator for DH-1. The monomeric form, K8[alpha2-P2W17TiO62]. 18H2O MK-1, was derived from DK-1. The molecular structure of 1b was composed of a dimer connected through one Ti-O-Ti bond between two alpha2-mono-Ti(IV)-substituted Dawson POM subunits. BVS (bond valence sum) calculation showed that one oxygen atom (O(60A)) in one of the two Dawson subunits was protonated, therefore the two subunits were unequivalent. On the other hand, the molecular structure of la was a Ti-O-Ti bonding dimer of two equivalent Dawson subunits. The pH-varied 31P NMR spectra of DK-1 and DH-1 in aqueous solutions showed that the monomer at pH 7.0, the dimer at pH 1.0-3.0, and the mono-protonated species of the dimer at pH 0.5 were the predominant species in the solutions. The Hammett acidity constant (H0) of DH-1 in CH3CN (-2.87) was estimated to be almost the same as that of homo-Dawson heteropolyacid H6[P2W18O62].17H2O(-2.77).

TETRAVANADATE, DECAVANADATE, KEGGIN AND DAWSON OXOTUNGSTATES INHIBIT GROWTH OF S. cerevisiae

The Willsky group had previously shown that vanadate inhibits growth. By using the combination of yeast growth and 51V NMR spectroscopy we show that the inhibiting species is V4. Similar effects were observed when a structurally similar, chemically stable molybdate tetramer was tested. To extend this result further, detailed studies were conducted exploring the effect of V10 on cell growth and it was observed that V10 is a poorer inhibitor than V4. Furthermore, it appears that the cell concentrates the absorbed vanadium into an acidic compartment where the cell-associated V10 will be generated. Spectroscopic studies suggest that V10 does enter and/or is formed inside the cell, although the mechanism is not known. An initial screen of the inhibitory effects of a series of Keggin and Dawson oxometalate at the 5.0mM level was conducted. Both the Keggin and Dawson structures were found to be more potent inhibitors than V10, but the Dawson complexes were found to be slightly more potent than the Keggins. Further studies at lower concentrations are necessary to effectively compare the oxometalates’ potency.

Synthesis and spectroscopic characterization of 1,2-divanadium(V)-substituted α-Dawson polyoxotungstate-based 1 ∶ 1-type Cp*Rh2+ complex showing three different supporting sites of the Cp*Rh2+ group

A novel Dawson polyoxotungstate-based 1 ∶ 1-type Cp*Rh2+ complex (Cp* = C5Me5), (NBu4)6[(Cp*Rh)(α-1,2-P2W16V2O62)] 2, was synthesized as an analytically pure, brown powder by 1 ∶ 1 molar ratio reaction in ice-cooled CH2Cl2 under air of 1,2-divanadium(V)-substituted α-Dawson polyoxotungstate (NBu4)8[α-1,2-P2W16V2O62] 1 with the dimeric precursor [Cp*RhCl2]2 without the use of AgBF4. The unprotonated polyoxotungstate support 1 was prepared via synthesis of K8[α-1,2-P2W16V2O62], (NBu4)6H2[α-1,2-P2W16V2O62], and deprotonation with aqueous NBu4OH. Solution (51V, 31P, 183W, 1H and 13C) NMR measurements in CD2Cl2 of 2 have revealed that it contained three species, 2a with Cs symmetry, 2b with C1 symmetry and 2c with Cs symmetry, based on different supporting sites of the Cp*Rh2+ group on the surface oxygen atoms in the three edge-shared octahedra (B-site, V2W surface). The Cp*Rh2+ group in 2a, 2b and 2c was covalently bound on the V2W surface, and the distribution of the species in ca. 1 ∶ 2 ∶ 1 ratio was not dependent on the initial concentration of [Cp*RhCl2]2 and temperature of the CH2Cl2 solution (from room temperature to −90 °C). The brown powder containing 2a, 2b and 2c was readily crystallized in CH2Cl2 solution at −20 °C to give dark red crystals, which initially contained one predominant species, but, then, reverted to the 1 ∶ 2 ∶ 1 mixture of the three species during 5 h in CH2Cl2 solution at room temperature. The polyoxoanion-supported Cp*Rh2+ complex 2 is unique and can be compared with the previous Dawson polyoxotungstate-based organometallic complexes.