Lattice vibration spectra. Part XCV. Infrared spectroscopic studies on the iron oxide hydroxides goethite (α), akaganéite (β), lepidocrocite (γ), and feroxyhite (δ)

Infrared spectra (IR, FIR, DRIFT, 90 and 295 K) and DSC measurements of the various polymorphs of iron oxide hydroxide, viz. goethite (α), akaganéite (β), lepidocrocite (γ), and feroxyhite (δ), and of deuterated specimens are reported. They are discussed with respect to the crystal structures proposed in the literature, the hydrogen bonds present, the energies of the OH stretching, OH bending (librational), and translational modes, and their thermal decomposition. From the two space groups proposed for β- and γ-FeO(OH), the groups I4/m and Cmc2₁, respectively, seem to be more reliable. The disorder of the OH⁻ ions of γ-FeO(OH) has not been confirmed in contrast to that of δ-FeO(OH). The intraionic O(H,D) distances of γ- and δ-FeO(OH) derived from neutron powder diffraction studies have to be doubted. The greater strength of the OHOH hydrogen bonds of lepidocrocite, for example, compared to that of the OHO hydrogen bonds of goethite despite the larger hydrogen bond acceptor capability of O²⁻ is due to the strong cooperativity of the hydrogen bonds of the γ-polymorph. The extremely different strength of the hydrogen bonds of isostructural α-AlO(OH) (v_OH = 2950 cm⁻¹, 295 K), α-MnO(OH) (v_OH = 2686 cm⁻¹), and α-FeO(OH) (v_OH = 3130 cm⁻¹) is caused by the different synergetic effect of the metal ions involved, especially that of Mn³⁺ due to its Jahn-Teller behaviour. The decomposition temperatures and heats of the various FeO(OH) modifications as well as the halfwidths of the DSC peaks evidence a much faster decomposition rate of akaganéite than those of the other polymorphs. This is obviously due to the Cl⁻ ion impurities present in this compound.     

Polylactones. 13. Transesterification of Poly(L-Lactide) with Poly(Glycoude), Poly(β-Propio-Lactone), and Poly[ε -Caprolactone)

Homogeneous blends of poly(L-lactide) (M _n = 30 000 to 40 000) and poly(β-propiolactone) or poly(ε-caprolactone) were prepared in solution. The solvent-free blends were subjected to transesterification catalyzed by means of methyl triflate, triflic acid, boron trifluoride, or tributyltin methoxide at 100 or 150°C. At 100°C, transesterification was barely detectable even after 96 h. When poly(β-propiolactone) was used as the reactant at 150°C, degradation was faster than transesterification regardless of the catalyst. The same negative result was obtained for heterogeneous blends of poly(L-lactide) and poly(glycolide). In the case of poly(ε-caprolactone), copolyesters with slightly blocky sequences were obtained with tributyltin methoxide as catalyst, whereas the acidic catalysts caused rapid degradation. The copolyesters were characterized by means of ¹H-NMR spectroscopy with regard to their molar composition, by means of ¹³C-NMR spectroscopy with regard to their sequences, and by means of differential scanning calorimetry with regard to crystallinity.     

Technetium(III), Technetium(II), and Technetium(I) Complexes with Pyridine Ligands. Can Pyridine Coordination Stabilize the Low Oxidation States of Technetium?

The substitution chemistry of TcCl(3)(PPh(3))(2)(CH(3)CN) is rather facile relative to the analogous rhenium complex, since both the chloride and phosphine ligands are easily substituted for various pyridine ligands. Consequently a series of Tc(III) complexes with amine, pyridine, and polypyridyl ligands were prepared and characterized by (1)H NMR and cyclic voltammetry. In addition, the zinc reduction of TcCl(4)(py)(2) in the presence of pyridine results in TcCl(2)(py)(4). Structural and spectroscopic data indicate that this Tc(II) complex exhibits strong metal-pyridine interactions characteristic of low-valent amine complexes of Re(II) and Os(II). For example, a decrease of 0.04 and 0.06 ? is observed for the trans-Tc-N bond length in TcCl(2)(py)(4 )relative to mer-TcCl(3)(pic)(3) and [TcCl(2)(py)(3)(PPh(3))](+), respectively. This ability of pyridine to function both as a strong sigma-donor and moderate pi-acid ligand has resulted in the isolation of technetium complexes in various oxidation states with similar ligand environments. As a result, a structural comparison of [TcCl(2)(py)(3)(PPh(3))](+), TcCl(2)(py)(4), TcCl(tpy)(py)(2), and other known Tc(III) and Tc(II) pyridine complexes is presented. Crystals of [TcCl(2)(py)(3)(PPh(3))]PF(6) are triclinic, with space group P&onemacr;, Z = 2, and lattice parameters a = 12.677(4) ?, b = 13.064(4) ?, c = 13.103(5) ?, alpha = 110.14(3) degrees, beta = 101.12(3) degrees, gamma = 96.61 degrees, V = 1959 ?(3), and R = 0.0615 (R(w) = 0.1148). Crystals of TcCl(2)(py)(4) are tetragonal, with space group I4(1)/acd, Z = 8, and lattice parameters a = 15.641(4) ?, c = 16.845(6) ?, V = 4121 ?(3), and R = 0.0373 (R(w) = 0.0290). Crystals of TcCl(tpy)(py)(2) are orthorhombic, with space group C222(1), Z = 4, and lattice parameters a = 9.359(3) ?, b = 16.088(6) ?, c = 18.367(4) ?, V = 2765 ?(3), and R = 0.0499 (R(w) = 0.0599).     

Which one among Zn(II), Co(II), Mn(II), and Fe(II) is the most efficient ion for the methionine aminopeptidase catalyzed reaction?

The catalytic hydrolysis of a methionyl-peptide substrate by a methionine aminopeptidase active site model cluster was investigated at the DF/B3LYP level of theory, in the gas-phase and in the protein environment. Zn(II), Co(II), Mn(II), and Fe(II) transition metals were examined as the potential catalytic metals of this enzyme involved in protein maturation. Two different mechanisms in which Glu204 was present as protonated or deprotonated residue were considered. The energetic profiles show lower barriers as the protonated glutamate is involved. The rate-determining step of the hydrolysis reaction is always the nucleophilic addition of the hydroxide on substrate carbon, followed by less energetically demanding methionine-peptide C-N bond scission. The lowest activation energy is obtained in the case of zinc dication while the other metals show very high energetic barriers, so that methionine aminopeptidase can be in principle recognized as a dizinc enzyme.     

Complexation of the zinc(II) ion with 2,2′-bipyridine and 1,10-phenanthroline in 4-methylpyridine and solvation structure of the manganese(II), cobalt(II), nickel(II), and zinc(II) ions in 4-methylpyridine and 3-methylpyridine

Complexation of the zinc(II) ion with 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) has been calorimetrically studied in 4-methylpyridine (4Me-py) containing 0.1 mol dm^–3 (n-C₄H₉)₄NClO₄ as a constant ionic medium at 25°C. The formation of [ZnL]²⁺, [ZnL₂]²⁺, and [ZnL₃]²⁺ (L=bpy, phen), and their formation constants, reaction enthalpies and entropies were determined. Our EXAFS (extended X-ray absorption fine structure) measurements showed that the solvation structure of the manganese(II), cobalt(II), and nickel(II) ions is six-coordinate octahedral in 4Me-py and 3-methylpyridine (3Me-py), while that of the zinc(II) ion is four-coordinate tetrahedral in 4Me-py. Since [ZnL₃]²⁺ is expected to have an octahedral structure, a tetrahedral-to-octahedral structural change should take place at a certain step of complexation. The thermodynamic parameters, especially reaction entropies, indicate that the structural change occurs at the formation of [Zn(bpy)₂]²⁺ and [Zn(phen)]²⁺.     

Coordination Polymers. IV. Physicochemical Studies on Chelate Polymers of Cr(III), Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) with a Schiff Base of 4,4′-(4,4′-Biphenylylene Bisazo)di-(salicylaldehyde) with m. Toluidine

Coordination polymers of Cr(III), Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) with a Schiff base derived from 4,4′ - (4,4′ -biphenylylene bisazo) di (salicylaldehyde) and m-toluidine have been prepared. All the polychelates are dark colored and insoluble in common organic solvents. Magnetic susceptibility and electronic and IR spectra of the polychelates have been studied. All the polychelates except Cu(II) show octahedral structures while Cu(II) polychelate is suggested to be a square planar.     

Spectral Study on the Interactions Among Cu(Ⅱ), Doxorubicin and CopC

Interactions among Cu(Ⅱ),doxorubicin and copper operon C(CopC)have been investigated in detail by means of fluorescence,UV-Vis,IR spectra,isothermal titration calorimetry(ITC)and molecular docking in Tris-HCl buffer(50 mmol/L,pH=7.4,25℃).The results suggest that Cu(Ⅱ)-doxorubicin is formed in a Cu(Ⅱ)to doxorubicin molar ratio of 1:2,and the conditional stability constant,K[Cu(Ⅱ)-doxorubicin]is 1.90×10^9 L^2/mol^2,CopC and doxorubicin can form a 1:1 complex,the conditional stability constant is greater than 10^5 L/mol.Binding of doxorabicin causes a conformational change in CopC with the reduction of β-sheet and increase of random coil,and the stability of CopC is decreased.Cu(Ⅱ),doxorubicin and CopC can form a CopC-Cu(Ⅱ)-doxorubicin ternary complex.The formation of CopC-Cu(Ⅱ)-doxorubicin reduced greatly the reduction rate of Cu(Ⅱ)by ascorbate(Vc),i.e.,the binding of doxorubicin affects the action of CopC as redox switch.     

Bimetallic palladium(II) and iron(III), titanium(IV), vanadium(V), cobalt(II), and copper(II) complexes with the [As2W19O67(H2O)]14− heteropolyanion

The formation of bimetallic Pd(II) and M = Fe(III), Ti(IV), V(V), Co(II), or Cu(II) complexes with the two-vacancy [As₂W₁₉O₆₇(H₂O)]^14? heteropolyanion (HPA) (below referred to as As₂W₁₉) has been studied by UV/Vis and IR spectroscopy and differential dissolution. In an aqueous solution at pH 6 and a Pd: M: As₂W₁₉ molar ratio of 1: 1: 1, heteropoly complexes (HPC) incorporating two different metals one being Pd(II) are formed. The resulting complexes were precipitated from solution as cesium salts. In the case of Pd(II) and M = Fe(III), Co(II), or Cu(II) ions, the precipitate contained bimetallic HPC [As₂W₁₉FePDO₆₇(H₂O)₂]^9? (65.9 wt %), [As₂W₁₉CoPdO₆₇(H₂O)₂]^10? (45.6 wt %), and [As₂W₁₉CuPdO₆₇(H₂O)₂]^10? (50.7 wt %) mixed with monometallic HPC [As₂W₁₉M₂O₆₇(H₂O)₂]^{(14 ? 2m)?} (As₂W₁₉M₂). In the case of Pd(II) and Ti(IV) or V(V), bimetallic HPC of a different composition were precipitated, namely, [As₂W₁₉Ti₂O₆₇(OH _x )₂ PdO]^{(10 ? 2x)?} (76.8 wt %) and [As₂W₁₉V₂O₆₇(OH _x )₂ PdO]^{(8 ? 2x)?} (15.0 wt %), where palladium ions are not incorporated in the HPC structure but are attached to the HPC surface, possibly, as hydroxide species. Using M = Pd(II), Ti(IV), V(V) ions and the HPA As₂W₁₉ ([M]: [As₂W₁₉] = 2 : 1, pH 6), new monometallic HPC, [As₂W₁₉Pd₂O₆₇(H₂O)₂]^10?, [As₂W₁₉Ti₂O₆₇(OH _x )₂]^{(10 ? 2x)?}, and [As₂W₁₉V₂O₆₇(OH _x )₂]^{(8 ? 2x)?} (x = 0, 1, or 2), were obtained.     

Syntheses and structural characterizations of a new benzyl(4-methoxyphenyl)dithiophosphinic acid and its Ni(II), Co(II), Zn(II), Cd(II), and Ni–pyridine complexes

Benzyl(4-methoxyphenyl)dithiophosphinic acid (HL) was obtained as solid and was treated with the NiCl₂6H₂O, CoCl₂6H₂O, ZnCl_2, and CdCl₂ to prepare its Ni(II), Co(II), Zn(II), and Cd(II) complexes. The nickel complex was further treated with pyridine which led to the formation of octahedral dipyridine derivative. HL was obtained through the addition reaction of the perthiophosphonic acid anhydride Lawesson reagent, (LR), [2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide], with the corresponding Grignard compound (benzylmagnesium bromide) in diethyl ether medium.

The complexes were all of the stoichiometry of [M(L)₂]_x, with x = 1 for M = Ni²⁺ and x = 2 for M = Co²⁺, Cd²⁺ and Zn²⁺. The coordination geometry was square planar in the nickel(II) complex and tetrahedral in the others. Similar to many other nickel(II) complexes, the Ni(L)₂ reacts reversibly with pyridine to yield the octahedral complex ({(Py)₂Ni(L)₂}).

The compounds were characterized by elemental analysis; MS, FTIR, and Raman spectroscopies. The magnetic susceptibilities of the complexes were measured to confirm the hybridization patterns and the geometries. Single-crystal X-ray analyses of Ni(L)₂ and [Co(L)₂]₂ complexes were also carried out to prove the molecular topologies.     

Thermal behavior and other properties of Pr(III), Sm(III), Eu(III), Gd(III), Tb(III) complexes with 4,4′-bipyridine and trichloroacetates

A novel mixed-ligand complexes with empirical formulae: Ln(4-bpy)_1.5(CCl₃COO)₃·nH₂O (where Ln(III) = Pr, Sm, Eu, Gd, Tb; n = 1 for Pr, Sm, Eu and n = 3 for Gd, Tb; 4-bpy = 4,4′-bipyridine) were prepared and characterized by chemical, elemental analysis and IR spectroscopy. Conductivity studies (in methanol, dimethylformamide and dimethylsulfoxide) were also described. All complexes are crystalline. The way of metal–ligand coordination was discussed. The thermal properties of complexes in the solid state were studied under non-isothermal conditions in air atmosphere. During heating the complexes decompose via intermediate products to the oxides: Pr₆O₁₁, Ln₂O₃ (for Sm, Eu, Gd) and Tb₄O₇. TG-MS system was used to analyze principal volatile thermal decomposition and fragmentation products evolved during pyrolysis of Pr(III) and Sm(III) compounds in air.     

Aqueous Equilibrium and Solution Structural Studies of the Interaction of N,N′-bis(4-imidazolymethyl)etylenediamine with Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) Metal Ions

Divalent metal complexes of N,N′-bis(4-imidazolymethyl)etylenediamine (EMI) have been studied using potentiometric and spectroscopic techniques (UV-Vis and NMR methods) in aqueous 0.1 mol⋅L⁻¹ KCl supporting electrolyte at 25 °C. Final models and overall stability constants for the complexes of Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) have been established by potentiometry for all M(II)–EMI systems, except for Co(II)–EMI. The data revealed that EMI forms ML complexes with all M(II)–EMI systems, which is the dominant species over a wide range of pH except for the Ca(II)–EMI and Mg(II)–EMI systems. Formation of the MnHL complex was also found for Mn(II)–EMI solutions. In addition, the UV-Vis and ¹H NMR results allowed us establish the coordination modes for the metal complexes between EMI with Cd(II), Cu(II), Ni(II) and Zn(II).     

Mixed-ligand complexes of iron(II), iron(III), copper(II), and cobalt(II) with pyrazolonic and 2,2′-bipyridine ligands

New mixed-ligand complexes, [M₂(BAMP)(bipy)₂][MCl₄]₂, M=Co⁺²(1), Cu⁺²(2), [M₂(TAMEN)(bipy)₂][MCl₄]₂, M=Fe⁺²(3), Co²⁺(4), and [Fe₂(TAMEN)(bipy)₂][FeCl₆]₂ (5), where BAMP and TAMEN stand for the Mannich bases N,N′-bis(antipyryl-4-methylene)-piperazine and N,N′-tetra(antipyryl-4-methylene)-1,2-ethane-diamine, respectively, have been obtained and characterized by elemental analyses, conductometric and magnetic susceptibility measurements at room temperature, mass spectrometry, UV-Vis, infrared, and mass spectroscopy, and ¹H NMR spectra for the ligands.