Studies on metal carboxylates. VIII. Reactions of acetylacetonates of the first row transition elements with pyridine-2,6-dicarboxylic acid

The acetylacetonates VO(acac)₂, M(acac)₃, where M = V, Mn or Fe and [M′(acac)₂]_n, where M′ = Co, Ni or Cu, have been reacted with pyridine-2,6-dicarboxylic acid (dipicH₂) in acetone to afford the complexes VO(dipic)·2H₂O, M(acac)(dipic)·xH₂O [M = V, Mn or Fe and x = 1 or 0] and M₂(dipic) (dipicH)₂·yH₂O [M = Co, Ni or Cu and y = 2 or 0]. The cobalt(II) and nickel(II) complexes are converted to polymeric [M(dipic)]_n in ethanol and all three complexes formulated as M₂(dipic)(dipicH)₂ react with 2,2′2″-terpyridyl to yield M(dipic)(terpy)·3H₂O. The vanadium(III) complex V(acac)(dipic) is oxidized to VO(dipic)·4H₂O in aqueous solution via the vanadium(III) intermediate V(OH)(dipic)·2H₂O. Tentative structural conclusions are drawn for certain of these new complexes based upon room temperature spectral and magnetic measurements. The characterization of these complexes has included selected studies of their X-ray photoelectron spectra.     

Synthesis and characterization of thiolato-bridged cadmium(II) complexes with NNS-chelating thiolic ligands

Cadmium(II) complexes with 2-[(2-aminoethyl)amino]ethanethiol (HL¹), 2-[(3-aminopropyl)amino]ethanethiol (HL²), 2-[(2-pyridylmethyl)amino]ethanethiol (HL³), and 2-[[2-(2-pyridyl)ethyl]amino]ethanethiol (HL⁴), [Cd(L¹)](ClO₄) (1), [Cd(L²)](ClO₄)·1/2CH₃OH (2), [Cd{Cd(L²)₂}₂](ClO₄)₂·CH₃CON(CH₃)₂ (3a·CH₃CON(CH₃)₂), [Cd{Cd(L²)₂}₂]Cl₂·2CH₃OH (3b·2CH₃OH), [Cd{Cd(L³)₂}₂](ClO₄)₂ (4), [Cd(L⁴)](ClO₄) (5), have been synthesized and characterized by measurements of the infrared and electronic spectra. The X-ray crystal structures show that 3a and 3b have a thiolato-bridged trinuclear core with a linear arrangement of three metal atoms.     

Speciation of dimethyltin(IV) – and trimethyltin(IV) – carbocysteinate and – glutamate systems in aqueous media

Abstract

The formation of complex species in the dimethyltin(IV) and trimethyltin(IV)-carboxymethyl-L-cysteinate (carbocysteinate) systems in NaCl_aq, at different ionic strengths, and in a multicomponent Na⁺, K⁺, Ca²⁺ ,Mg²⁺, Cl^? and SO₄^2-? medium representative of the seawater major composition, is discussed. Experimental results give evidence for the formation of the following species (L = carbocysteinate): [(CH₃)₂Sn(L)]⁰, [(CH₃)₂Sn(HL)]⁺, [(CH₃)₂Sn(OH)(L)]^?, [(CH₃)₂Sn(OH)₂(L)]^2? in the DMT–CCYS system, and [(CH₃)₃Sn(HL)]⁰, [(CH₃)₃Sn(L)]^? and [(CH₃)₃Sn(OH)(L)]^2? in the TMT-CCYS system. The ionic strength dependence of formation constants was taken into account by an extended Debye Hückel type equation and by the SIT (Specific ion Interaction Theory). Measurements were carried out also on the dimethyltin(IV)-glutamate and trimethyltin(IV)-glutamate systems in NaCl_aq, owing the strict similarity of glutamate and carbocysteinate. Results obtained show the formation of complex species having the same stoichiometry as those formed in the DMT- and TMT-carbocysteinate systems, with very similar stability, confirming that carbocysteinate behaves as a dicarboxylic amino acid without involving the sulfur-bridge potential binding site in metal coordination.     

A density functional theory study on the hydrogen bonding interactions between luteolin and ethanol

Ethanol is one of the most commonly used solvents to extract flavonoids from propolis. Hydrogen bonding interactions play an important role in the properties of liquid system. The main objective of the work is to study the hydrogen bonding interactions between flavonoid and ethanol. Luteolin is a very common flavonoid that has been found in different geographical and botanical propolis. In this work, it was selected as the representative flavonoid to do detailed research. The study was performed from a theoretical perspective using density functional theory (DFT) method. After careful optimization, there exist nine optimized geometries for the luteolin ? CH₃CH₂OH complex. The binding distance of X ? H···O, and the bond length, vibrational frequency, and electron density changes of X ? H all indicate the formation of the hydrogen bond in the optimized geometries. In the optimized geometries, it is found that: (1) except for the H2’, H5’, and H6’, CH₃CH₂OH has formed hydrogen bonds with all the hydrogen and oxygen atoms in luteolin. The hydrogen atoms in the hydroxyl groups of luteolin form the strongest hydrogen bonds with CH₃CH₂OH; (2) all of the hydrogen bonds are closed-shell interactions; (3) the strongest hydrogen bond is the O3’ ? H3’···O in structure A, while the weakest one is the C3 ? H3···O in structure E; (4) the hydrogen bonds of O3’ ? H3’···O, O ? H···O4, O ? H···O3’ and O ? H···O7 are medium strength and covalent dominant in nature. While the other hydrogen bonds are weak strength and possess a dominant character of the electrostatic interactions in nature.     

Syntheses and crystal structures of di- and trimethyltin (IV) derivatives with phenylphosphonic acid

Three types of methyltin phosphonates, {[(CH₃)₃Sn]₄(O₃PPh)₂}_n (1), {[(CH₃)₃Sn]₂(O₃PPh) · CH₃OH}_n (2) and {[(CH₃)₂SnO₃PPh]₄}_n (3) were synthesized by the reaction of phenylphonic acid with trimethyltin (IV) chloride and dimethyltin (IV) dichloride, respectively. Complexes 1, 2 and 3 were characterized by elemental analysis, IR, NMR (¹H, ¹³C, ³¹P and ¹¹⁹Sn) spectroscopy, TGA and X-ray crystallography diffraction analysis. The X-ray analysis of complex 1 shows that the structure is a polymeric infinite 1D zigzag chain. In complex 2, the oxygen atom of methanol molecule is coordinated to the tin atoms, and a 2D network is generated via O–H?O hydrogen bonds. In complex 3, a novel 2D network containing 12-membered (Sn₃O₆P₃) rings is formed.     

Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

Metal-penicillamine interactions. Part 1. Preparation and crystal structure of a 1:1 complex of mercuric chloride with d-penicillamine, 2[μ3-Cl){HgSC(CH3)2CH(NH3)COO}3·3(μ2-Cl)· 2(H3O)·(H2O·Cl)3

A 1:1 complex of mercuric chloride with D-peniccillamine has been isolated and characterised as 2[(μ₃-Cl){HgSC(CH₃)₂CH(NH₃)COO}3]·3(μ₂-Cl)·2(H₃O)·(H₂O·Cl)₃. The compound crystallises in cubic space group P4₁32, with a = 18.679(5) Å and Z = 4. The structure, refined to R_F = 0.086 for 443 observed Mo-Kα diffractometer data, features a triply bridging chloride ion linking three equivalent [HgSC(CH₃)₂CH(NH₃)COO]⁺ units [Hg-Cl = 2.37(1) Å, Hg-Cl-Hg′ = 98.5(9)°]. The carboxylate groups of a pair of adjacent penicillamine ligands are strongly linked via a symmetrical O?H?O hydrogen bond of length 2.24(8) Å, and neighboring pyramidal trinuclear [μ₃-Cl){HgSC(CH₃)₂CH(NH₃)-COO}₃]²⁺ moieties are further connected by symmetrical chloride bridges [Hg-Cl = 3.06(2) Å; HgClHg′' = 79.6(7)°] to form a three-dimensional network. The voids in the lattice are filled by hydronium ions and novel planar cyclic hydrogen-bonded (H₂O·Cl^?)₃ rings of edge O-H?Cl = 2.46(4) Å.     

Kinetic and mechanistic studies on the ruthenium induced activation of methylamine to oxidation

When aqueous solutions containing [Ru(NH₂CH₃)₆]²⁺ are exposed to oxygen [Ru(NH₂CH₃)₅(OH]²⁺ is produced as an identifiable intermediate as a result of the slow replacement of co-ordinated methylamine by water, and the subsequent rapid oxidation of this ruthenium(II) aquo complex. The [Ru(NH₂CH₃)₅(OH)]²⁺ ion then undergoes another slow reaction, probably the replacement of another methylamine ligand by water. All subsequent reactions leading to Ru(CN)₃·3H₂O are rapid. Rate data are reported, and a mechanism involving β-elimination from co-ordinated methylamine is postulated.     

Pulse-radiolytic investigations of catechols and catecholamines II. Reactions of Tiron with oxygen radical species

Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O₂^?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·10⁹ M^?1·s^?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O₂^? of 1.0·10⁷ M^?1·s^?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O₂^? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds.     

A theoretical study on the hydrogen-bonding interactions between flavonoids and ethanol/water

Ethanol and water are the solvents most commonly used to extract flavonoids from propolis. Do hydrogen-bonding interactions exist between flavonoids and ethanol/water? In this work, this question was addressed by using density functional theory (DFT) to provide information on the hydrogen-bonding interactions between flavonoids and ethanol/water. Chrysin and Galangin were chosen as the representative flavonoids. The investigated complexes included chrysin–H₂O, chrysin–CH₃CH₂OH, galangin–H₂O and galangin–CH₃CH₂OH dyads. Molecular geometries, hydrogen-bond binding energies, charges of monomers and dyads, and topological analysis were studied at the B3LYP/M062X level of theory with the 6?31++G(d,p) basis set. The main conclusions were: (1) nine and ten optimized hydrogen-bond geometries were obtained for chrysin–H₂O/CH₃CH₂OH and galangin–H₂O/CH₃CH₂OH complexes, respectively. (2) The hydrogen atoms except aromatic H1 and H5 and all of the oxygen atoms can form hydrogen-bonds with H₂O and CH₃CH₂OH. Ethanol and water form strong hydrogen-bonds with the hydroxyl, carbonyl and ether groups in chrysin/galangin and form weak hydrogen-bonds with aromatic hydrogen atoms. Except in structures labeled A and B, chrysin and galangin interact more strongly with H₂O than CH₃CH₂OH. (3) When chrysin and galangin form hydrogen-bonds with H₂O and CH₃CH₂OH, charge transfers from the hydrogen-bond acceptor (H₂O and CH₃CH₂OH in structures A, B, G, H, I, J) to the hydrogen-bond donor (chrysin and galangin in structure A, B, G, H, I, J). The stronger hydrogen-bond makes the hydrogen-bond donor lose more charge (A> B> G> H> I> J). (4) Most of the hydrogen-bonds in chrysin/galangin?H₂O/CH₃CH₂OH complexes may be considered as electrostatic dominant, while C?O2···H in structures labeled E and C?O5···H in structures labeled J are hydrogen-bonds combined of electrostatic and covalent characters. H9, H7, and O4 are the preferred hydrogen-bonding sites.     

Adenine complexes with divalent 3d metal chlorides

Upon refluxing 2:1 mixtures of adenine (adH) and divalent 3d metal chloride hydrates in a 7:3 (v/v) mixture of ethanol-triethyl orthoformate for several days, partial substitution of ad^? for Cl^? ligands occurs, and solid complexes of the M(ad)Cl· 2H₂0 (M = Mn, Zn), Fe₂(ad)(adH)₂Cl₃·2H₂O, M(ad)- (adH)Cl·H₂O (M = Co, Cu) and Ni₂(ad)₃Cl·6H₂O types are eventually isolated [1]. It is probably of interest that during analogous previous synthetic work, involving interaction of ligand and salt in refluxing ethanol, no substitution reactions between Cl^? and ad^? took place, and MCl₂ adducts with neutral adH were reportedly obtained. Characterization studies suggest that the new complexes reported are linear chainlike polymeric species, involving single adenine bridges between adjacent M²⁺ ions. Terminal chloro, adenine and aqua ligands complete the coordination around each metal ion. The new Ni²⁺ complex is hexacoordinated, whilst the rest of the complexes are pentacoordinated. Most likely binding sites are considered to be N(9) for terminal unidentate and N(7), N(9) for bridging bidentate adenine [1].     

Structural comparison of octahedral MoO22+ complexes of bidentate and linear tetradentate N,S-donor ligands

The structures of MoO₂[NH₂C(CH₃)₂CH₂S]₂ and MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] have been determined using X-ray diffraction intensity data collected by counter techniques. MoO₂[NH₂C(CH₃)₂CH₂S]₂ crystallizes in space group Pbca with a = 11.234(3), b = 11.822(3) and c = 20.179(5) Å, V = 2680(2) ų and Z = 8. Its structure is derived from octahedral coordination with cis oxo groups [MoO = 1.705(3) and 1.705(3)], trans thiolate donors cis to the oxo groups [MoS = 2.416(1) and 2.402(1) and N donors trans to oxo [MoN = 2.325(3) and 2.385(4) Å]. MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] crystallizes in the space group P2₁/c with a = 10.798(5), b = 6.911(2), c = 20.333(9) Å, β = 95.20°, V = 1511(2) Å₃ and Z = 4. Its structure is very similar to that of MoO₂[NH₂C(CH₃)₂CH₂S]₂ with MoO = 1.714(2) and 1.710(2), MoS = 2.415(1) and 2.404(1) and MoN = 2.316(3) and 2.362(3). The small differences in the geometries of the two compounds are attributed to the constraints of the extra chelate ring in the complex with the tetradentate ligand. The structures in this paper stand in contrast to those reported for complexes of similar ligands wherein steric hindrance produces complexes with a skew trapezoidal bipyramidal structure.     

Cobalt(III)-promoted hydrolysis of atp

The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH₃)₄ATP-has been examined in the presence and absence of [Co(cyclen)(H₂O)₂]³⁺. The rate of hydrolysis of Co(NH₃)₄ATP- in the absence of [Co(cyclen)(H₂O)₂]³⁺ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10^?5 sec ^?1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH₃)₄ATP- in the presence of [Co(cyclen)(H₂O)₂]³⁺ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10^?3 sec^?1 for 16 mM Co(NH₃)₄ATP- in the presence of 10 mM [Co(cyclen)(H₂O)₂]³⁺. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH₃)₄ATP- by [Co(cyclen)(H₂O)₂]³⁺ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain.     

An assessment of DFT methods for predicting the thermochemistry of ion-molecule reactions of group 14 elements (Si, Ge, Sn)

Experimental mass-spectrometry data on thermochemistry of methide transfer reactions (CH₃)₃M⁺ + M'(CH₃)₄ ? M(CH₃)₄?+?(CH₃)₃M'⁺ (M, M'?=?Si, Ge or Sn) and the formation energy of the [(CH₃)₃Si-CH₃-Si(CH₃)₃]⁺ complex are used as benchmarks for DFT methods (B3LYP, BMK, M06L, and ωB97XD). G2 and G3 theory methods are also used for the prediction of thermochemical data. BMK, M06L, and ωB97XD methods give the best fit to experimental data (close to chemical accuracy) as well as to G2 and G3 results, while B3LYP demonstrates poor performance. From the first three methods M06L gives the best overall result. Structures and formation energies of intermediate “mixed” [(CH₃)₃M-CH₃- M′(CH₃)₃] complexes not observed in experiment are predicted. Their structures, better described as M(CH₃)₄?[M′(CH₃)₃]⁺ complexes, explain their fast decompositions.

Some metal alloxides

Tetraalloxygermanium(IV), (CH₂·CH·CH₂·O)₄Ge, has been synthesized from germanium tetrachloride, allyl alcohol, and ammonia. The alloxides [(CH₂·CH· CH₂·O)₄Ti]₂and[(CH₂·CH·CH₂O)₅M]₂ (M = Nb and Ta) have been synthesized by reactions of the corresponding metal isopropoxides with allyl alcohol followed by removal of the isopropanol by azeotropic distillation with benzene. These four metal alloxides can be purified by distillation under reduced pressure. The spectroscopic properties of these new compounds are discussed.     

Theoretical study about the 5-azido-1H-tetrazole and its ion salts

Periodic DFT method has been firstly used to calculate the bulk structure, electronic structure, electrical transferring and thermodynamic properties of crystalline 5-azido-1H-tetrazole (HCN₇) and its four different salts. The anion CN₇ ^? was included in all of the salts such as ammonium 5-azidotetrazolate ([NH₄]⁺[CN₇]^?), hydrazinium 5-azidotetrazolate ([N₂H₅]⁺[CN₇]^?), guanidinium 5-azidotetrazolate ([CH₆N₃]⁺[CN₇]^??·?H₂O) and 1-aminoguanidinium 5- azidotetrazolate ([CH₇N₄]⁺[CN₇]^?). The simulation is in reasonable agreement with the experimental results. It is found the salts of HCN₇ are more stable than itself because the band gap of the salts is larger. The density of state shows the p states of them (including HCN₇ and its four salts) have played a very significant role in the reaction.

Computational investigation of carbon dioxide absorption in alkanolamine solutions

We investigated CO₂ absorption in aqueous alkanolamine solutions using density functional theory with dielectric continuum solvation models (SMD/IEF-PCM and COSMO-RS). We varied the alkyl chain length (m?=?2, 3, 4) and the alcohol chain length (n?=?2, 3, 4) in the alkanolamine structures, H(CH₂) _m NH(CH₂) _n OH. Using the SMD/IEF-PCM/B3LYP/6-311++G(d,p) and COSMO-RS/BP/TZVP levels of theory, our calculations predict that the product of CO₂ absorption (carbamate or bicarbonate) is strongly affected by the alcohol length but does not differ significantly by varying the alkyl chain length. This prediction was confirmed experimentally by ¹³C-NMR. The observed sensitivity to the alcohol chain length can be attributed to hydrogen bonding effects. The intramolecular hydrogen bonds of HN · · · HO, NH₂ ⁺ · · · OH, and NCOO^? · · · HO induce ring structure formation in neutral alkanolamines, protonated alkanolamines, and carbamate anions, respectively. The results from our studies demonstrate that intramolecular hydrogen bonds play a key role in CO₂ absorption reactions in aqueous alkanolamine solutions.     

The transformation of chlorophenols by lactoperoxidase

The lactoperoxidase-catalyzed transformations of penta-, 2,3,4,6,-tetra-, 2,4,6,-tri, 2,4,-di- and 4-monochlorophenol were followed spectrophotometrically. Apparent stoichiometries of chlorophenol: H₂O₂ ranged from 1:1 for the tri- and tetrachlorophenol at pH 7 to 5:2 for pentachlorophenol at pH 4. The initial velocity (ν₀) was only slightly influenced by changes in [H₂O₂] ? 5 μM. ν₀ responded to [chlorophenol] according to the empirical expression ν₀ = [lactoperoxidase]·(k₁[chlorphenol] + k₂[chlorophenol]²). The constant k₁ was found to be 5.8 · 10⁵, 1.8 · 10⁶, 1.9 · 10⁶ M^?1 · s^?1 for the protonated forms of penta-, tetra- and trichlorophenol, respectively, at pH 7. With the di- and monochlorophenol the solution soon became opaque, and the reaction ceased. The results show that more than one reaction occurs. Some comparisons were also made with horseradish peroxidase A and C. Cetyltrimethylammonium bromide prevented opaqueness, but was shown to be a substrate for lactoperoxidase. Assuming an average concentration of 0.1 μM for H₂O₂ and pentachlorophenol in man, the metabolic rate becomes 30 ng/h per g peroxidase-containing tissue, possibly with deposition of the products.     

Tandem crystallization strategies for resolution of 3,3,3‐trifluorolactic acid [CF3CH(OH)COOH] by chiral benzylamines

Resolution of rac‐3,3,3‐trifluorolactic acid by diastereomeric salt formation was reinvestigated. The use of (S)‐1‐phenylethylamine gives coprecipitation of two diastereomeric phases, 1 (S)‐[NH₃CH(CH₃)Ph](S)‐[CF₃CH(OH)COO] and 2 (S)‐[NH₃CH(CH₃)Ph](R)‐[CF₃CH(OH)COO]·H₂O. Pure phase 1 may be obtained using molecular sieves as desiccants. Resolution by (S,S)‐2‐amino‐1‐phenylpropan‐1,3‐diol gives monoclinic (S,S)‐[NH₃CH(CH₂OH)CHOHPh] (R)‐[CF₃CH(OH)‐COO] 3 with minor (S)‐3,3,3‐trifluorolactate contamination, which is precluded in the recrystallized orthorhombic form 4 . A new resolution using inexpensive phenylglycinol gives pure phase 5 (S)‐[NH₃CH(CH₂OH)Ph] (S)‐[CF₃CH(OH)COO] in 76% yield, 94% ee in a single step, in preference to its (S)‐(R) diastereomer 6 . Overall efficient resolution for both enantiomers of the trifluorolactic acid (each ca. 70% yield, 99% ee) may be achieved by various two‐step “tandem” crystallizations, involving direct addition of either water or a second base to the filtrate from the initial reaction.     

A polyethylene-glycol-functionalized ring-like isopolymolybdate cluster

A new organic-inorganic hybrid compound, Na₆[HO(CH₂CH₂O)₄H]₃{Mo₃₆O₁₀₈(H₂O)₁₄(OH)₆[HO(CH₂CH₂O)₃H]₂} · ∼75H₂O (1) has been obtained in polyethylene glycol (PEG)/H₂O system with a good yield, and characterized by element analysis, IR, UV, TG, ¹³C NMR spectroscopy, electrochemistry and X-ray single crystal diffraction analysis. Compound 1 consists of the {Mo₃₆} clusters as the structural motif covalently decorated by PEG fragments. Such hybrid polyoxoanions are linked by Na⁺ counter-cations, leading to one-dimensional chains. The adjacent chains are closely packed together into a three-dimensional supramolecular framework via extensive H-bonding interactions among polyoxoanions and the isolated water molecules.