Studies of copper (Ⅱ) complexes as catalysts for the hydrolysis of DNA

Hydrolysis of DNA is an important enzymatic reaction , but it is exceedingly difficult to mimic in the laboratory because of the stability of hydrolysis of DNA. In this paper, the cleavage activity of complexes formed between Cu(Ⅱ) and four different amino acid or amino acid methyl ester on DNA is studied by gel elec-trophoresis. It is found that DNA could be cleaved by Cu(Ⅱ)-L-His and Cu(Ⅱ)-L-His methyl ester complexes and the efficiency of cleavage is largely dependent on the metal ion-to-ligand ratio. Further experiments show that the cleavage of DNA mediated by Cu(Ⅱ)-L-His complexes occurs via a hydrolytic mechanism and the active chemical species that affects DNA cleavage is proposed to be MI2H and ML2H22 .     

Ultralow Ag-assisted carbon–carbon coupling mechanism on Cu-based catalysts for electrocatalytic CO2 reduction

Electrocatalytic CO₂ reduction to C₂H₄ supplies an economically viable route for CO₂ fixation with the integration of intermittent renewable energy. Cu-based catalysts are capable of catalyzing CO₂ to C₂H₄,while suffering from the high overpotential and low Faradaic efficiency. In this joint experimentalcomputational work, an Ag-assisted carbon–carbon coupling is exploited on Cu-based catalysts. A systematic characteriz...     

Trinuclear salphen–chromium(III)chloride complexes as catalysts for the alternating copolymerization of epoxides and cyclic anhydrides

Although the alternating copolymerization of epoxides and cyclic anhydrides is a promising route to aliphatic polyesters, improved catalysts are required to realize commercialization of this process. Herein, trinuclear chromium complexes of salicylaldimine, in conjunction with a nucleophilic cocatalyst, are demonstrated as excellent catalysts for epoxide/cyclic anhydride copolymerization, selectively affording perfectly alternating polyesters. The effect of the distance between the chromium species is investigated by varying the bridging skeleton in a series of trinuclear salphen–Cr(III)Cl complexes for obtaining different Cr–Cr distances. Trinuclear salphenCr(III)–complexes with Cr–Cr distances of approximately 7.3 Å are found to be efficient copolymerization catalysts, even at high temperatures and extremely low catalyst loadings. In particular, a high activity of 10,620 h⁻¹ is obtained for the copolymerization of cyclohexene oxide (CHO) and phthalic anhydride (PA) under a low catalyst loading (<0.01 mol%) at 100 °C. In situ infrared spectroscopy studies suggest that the activation energy of the trinuclear Cr(III)–salphen catalyst for CHO/PA copolymerization is 15 kJ mol⁻¹ lower than that of the corresponding mononuclear catalyst owing to an intramolecular synergistic effect among the metal atoms.     

Cyclopentadienyl rhodium(III) complexes as catalysts for the insertion of phenyldiazoacetate into E−H bonds

Rhodium(III) complexes catalyze the insertion of carbenoids generated from diazo compounds into E?H bonds (E = B, Si, N, but not C), although less efficiently than classical rhodium(II) carboxylates, despite formally higher oxidation state of the metal.     

Structural characterization and cytotoxicity studies of ruthenium(II)–dmso–chloro complexes of chalcone and flavone derivatives

A synthetic precursor cis-[Ru^IICl₂(dmso)₄] is complexed separately with 3-(4-benzyloxyphenyl)-1-(2-hydroxylphenyl)-prop-2-en-1-one (L¹H) and 2-(4-benzyloxyphenyl)-3hydroxy-chromen-4-one (L²H). The resulting complexes are assigned the composition fac-[RuCl(S-dmso)₃(L¹)] 1 and fac-[RuCl(S-dmso)₃(L²)] 2 using elemental analyses, FAB mass data and spectroscopic (IR, ¹H NMR, UV–Vis, emission) spectral properties. The X-ray diffraction analysis shows that complexes self-associate through non-covalent interactions and provide 1D and 2D supramolecular structures. These complexes are assayed for their cytotoxicity studies on Dalton Lymphoma cell lines.     

Solubility of β-diketonate complexes for cobalt(III) and chromium(III) in supercritical carbon dioxide

The solubilities of tris(2,2,6,6-tetramethyl-3,5-heptanedionate) cobalt(III) (Co(thd)₃) and chromium(III) (Cr(thd)₃) in supercritical carbon dioxide (scCO₂) were measured at temperatures ranging from 313 to 343 K. The measurements were carried out using a circulation-type apparatus with a UV–vis spectrometer. The solubilities of both Co(thd)₃ and Cr(thd)₃ increased as both the density of scCO₂ and the temperature increased, which has the same tendency as cobalt(III) acetylacetonate (Co(acac)₃) and chromium(III) acetylacetonate (Cr(acac)₃) had in our previous work. The solubilities of Cr(thd)₃ were higher than that of Co(thd)₃, and the solubilities of Co(thd)₃ and Cr(thd)₃ were about 50- and 70-fold higher than those of Co(acac)₃ and Cr(acac)₃, respectively. The measured solubilities of the metal complexes were correlated with the equation based on Chrastil's equation. The parameters were determined by correlating the experimental data for each metal complex, and the correlated results well reproduced the experimental data, especially Co(thd)₃. Moreover, the charge density distributions on the molecular surface of CO₂ and the metal complexes used in the measurement were estimated by the quantum chemical calculation and the COSMO-RS to clear the effect of the molecular structure of the metal complexes on the affinity for CO₂.     

N-Heterocyclic carbene–rhodium complexes as catalysts for hydroformylation and related reactions

Rhodium(I) complexes with N-heterocyclic carbenes (Rh–NHC) can be considered as important candidates for catalysts of hydroformylation of olefins. The high stability of Rh-C(NHC) bonding under reaction conditions allow to expect that NHC ligand will be present in coordination sphere of the catalytically active rhodium complex and therefore influences the reaction yield and regioselectivity. The potential applicability of Rh–NHC complexes containing chiral carbene ligand in asymmetric hydroformylation can be also considered. The excellent review articles relevant to application of Rh–NHC in hydroformylation have been published recently [1], [2], [3]. After that, important contributions to this subject, concerning theoretical and experimental studies, both structural and catalytic, have been reported. Therefore, the reactivity of Rh–NHC complexes can be discussed now in term of these new data. The up to now reported results indicate that the most promising and selective systems for hydroformylation can be composed from Rh–NHC complex and stoichiometric amount of electron-withdrawing phosphorus ligand.     

Platinum–tin complexes as catalysts for the anodic oxidation of borohydride

Platinum–tin complexes were prepared by the reduction of Pt(IV) with Sn(II) in HCl media and studied by light absorption spectrometry, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The formation of three complexes, H₃[Pt(SnCl₃)₅], H₂[Pt(SnCl₃)₂Cl₂], and H₂[Pt₃(SnCl₃)₈], depending on HCl and SnCl₂ concentrations, has been shown. The glassy carbon (GC) electrode modified in the complexes solutions was found to be an electrocatalyst for borohydride oxidation in a 1.0-M NaOH solution. Comparison of BH₄ ⁻ electrooxidation on Pt and on GC modified with platinum–tin complexes has shown that catalytic hydrolysis of BH₄ ⁻ did not proceed in the latter case in contrast to its oxidation on the Pt electrode, and only direct BH₄ ⁻ oxidation has been observed in the positive potentials scan. The activity of Pt–Sn complexes for BH₄ ⁻ oxidation changes with time and eventually decreases due to Sn(II), bound in the complex with Pt(II), oxidation by atmospheric oxygen. The complexes may be renewed by addition of missing amounts of SnCl₂ and HCl.     

A perspective on the PGM-free metal–nitrogen–carbon catalysts for PEMFC

<正>Introduction Atomically dispersed transition metals embedded in nitrogendoped carbons(M–N–C) represent a typical kind of platinum group-free(PGM-free) catalyst which is considered as a potential candidate for the cathode of proton-exchange membrane fuel cells(PEMFCs) [1–3]. Apart from their low cost, the advantage of the M–N–C catalysts over PGM is further underlined by their good poisoning-resistance to impurities in fossil-derived hydrogen, such as carbon monoxide and sulfur-containin...     

Sorption of iron(III)–alginate complexes on cellulose fibres

Multivalent ions take a significant role in the sorption of soluble polysaccharides on solid cellulose substrates and thus demonstrate an important principle in structural polysaccharide organisation. Sorption of Fe(III)–alginate complexes on lyocell fibres as model for the insoluble cellulose matrix has been studied between pH 3–13, at 30 and 60 °C. Sorption maximum of the Fe(III)–alginate complex was observed at pH 3 where the sorbed amounts of alginate and iron were 6,600 and 85 mg iron per kg cellulose respectively. Under the experimental conditions used, a concentration of 0.05 mM Fe(III) is sufficient to achieve surface sorption of Fe(III)–alginate complex. The alginate sorption exhibited minor dependence on molar ratio of Fe(III) to alginate. In environmental scanning electron microscopy no deposition of Fe-hydroxides on the fiber surface was detected. The thickness of the adsorbed Fe(III)–alginate layer on the fiber surface was estimated with 12–22 nm. Tensile strength and abrasion resistance of Fe(III)–alginate treated fibers were not reduced through the sorption treatment. Alginate modified cellulose is of interest as material for medical application, as sorbent and textile finish.     

α-Diimines as nitrogen ligands for ruthenium-catalyzed allylation reactions and related (pentamethylcyclopentadienyl) ruthenium complexes

The new Cp*Ru(II) (Cp*: pentamethylcyclopentadienyl) complexes Cp*(dab-R)RuCl, [Cp*(dab-R)(MeCN)Ru][PF₆] (dab-R: RNCH-CHNR; R: iso-propyl, mesityl), and [Cp*(cod)(MeCN)Ru][PF₆], are synthesized in high yields by reacting the corresponding α-diimine or 1,5-cyclooctadiene with [Cp*RuCl]₄ and [Cp*(MeCN)₃Ru][PF₆], respectively. The α-diimine ligands are strongly bonded to the ruthenium centre as shown by the subsequent formation of the alkynyl derivatives Cp*(dab-R)RuCCR′ (R′ = tert-butyl or phenyl) and of the cationic derivatives [Cp*(dab-R)(L)Ru][PF₆] (L = CO, PMe₃). The neutral and cationic α-diimine or 1,5-cyclooctadiene ruthenium complexes are compared as catalyst precursors for the ruthenium-catalyzed allylation of diethyl-sodiomalonate and diethylamine with cinnamyl acetate or ethyl cinnamyl carbonate.     

Cross-coupling of arene–gold(III) complexes

The reactivity of electron-deficient arene–gold(III) complexes toward nucleophilic aromatic and heteroaromatic counterparts has been studied. 1-Methylindole proved to be the best reaction partner while trimethoxybenzenes did not react. The ancillary ligand on gold also influenced the reactivity in the order PPh₃>P^tBu₃>IPr. An oxidative cross-coupling starting from the corresponding gold(I) complexes in presence of hypervalent iodide oxidants was also studied.     

Binuclear bis(β-diketonato) complexes of ruthenium(III) containing triphenylphosphine or triphenylarsine

Stable bis(-diketonato) bridged binuclear complexes prepared by reacting [RuX₃(EPh₃)₃] (X = Cl or Br; E = P or As) with (RCO)(MeCO)CH–Y–CH(COR)(COMe) [R = Me or Ph; Y = (CH₂)₆, (CH₂)₁₀] in a 2:1 molar ratio in benzene, have been characterised by elemental analyses, i.r., electronic, e.p.r. and cyclic voltammetry. The oxidation state of the metal ion in these complexes is confirmed as + 3 by electrochemical and by e.p.r. measurements. The complexes belong to a low-spin d⁵ configuration. An attempt has been made to ascertain the effect of the length of the bridging ligand on the electron transfer processes by cyclic voltammetry in these binuclear complexes. Based on the above studies an octahedral geometry has been tentatively proposed. The new complexes have been subjected to the antifungal activity studies.     

Raman and UV–vis spectroscopy studies on luteolin–Al(III) complexes

Luteolin is one of the most common flavonoids, but its ability to complex metal ions (e.g. aluminum) is still being discussed. This work presents the results of structural investigation of the luteolin–Al(III) complexes in methanol:water solutions and in the solid state. The analysis was carried out using UV–vis and FT-Raman spectroscopy accompanied by Factor Analysis, deconvolution and quantum-chemical calculations. It was found that in acidic solutions two complexes of luteolin–Al(III) of 1:1 and 1:2 ligand:metal ratio are formed, where luteolin is one- and twofold deprotonated, respectively. Additionally, a third complex precipitated from a basic solution of 1:2 stoichiometry with a threefold deprotonated ligand was obtained.     

Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

Benzoylhydrazone Schiff base–ligated three new ONO pincer–type palladium(II) complexes, [(PdL¹(PPh₃)] ( 1 ), [(PdL²(PPh₃)] ( 2 ), and [(PdL³(PPh₃)] ( 3 ), were synthesized by the reaction of the respective ligand, N-(2-hydroxybenzylidene)benzohydrazide (HL¹), N-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (HL²), or N-(5-bromo-2-hydroxybenzylidene) benzohydrazide (HL³), with Pd(OAc)₂ and PPh₃ in methanol and isolated as air-stable reddish-orange crystalline solids in high yields (78%–83%). All three complexes were fully characterized by elemental analysis, Fourier-transform infrared spectroscopy, UV–Visible, ¹H nuclear magnetic resonance (NMR), ¹³C{¹H} NMR, and ³¹P{¹H} NMR spectroscopic studies. The molecular structure of all three complexes was established unambiguously by single-crystal X-ray diffraction studies which revealed a distorted square planar geometry of all three complexes. The ONO pincer–type ligands occupied three coordination sites at the palladium, while the fourth site is occupied by the monodentate triphenylphosphine ligand. The catalytic potential of all three complexes was explored in the carbonylative Suzuki coupling of aryl bromides and iodides with arylboronic acids to yield biaryl ketones, using CHCl₃ as the source of carbonyl. The reported protocol is convenient and safe as it obviates the use of carbon monoxide (CO) balloons or pressured CO reactors which are otherwise needed for the carbonylation reactions. The methodology has been successfully applied to the synthesis of two antineoplastic drugs, namely, phenstatin and naphthylphenstatin, in good yields (81% and 85%, respectively). Under the optimized reaction conditions, complex 2 exhibited the best catalytic activity in the carbonylative Suzuki couplings. The reported catalysts have wide reaction scope with good functional group tolerance. All catalysts could be retrieved from the reaction after completion and recycled up to three times with insignificant loss in the catalytic activity.     

Hydrazinoaminocarbene–palladium complexes as easily accessible and convenient catalysts for copper-free Sonogashira reactions

Two easily accessible hydrazinoaminocarbene complexes of Pd(II) are shown to be efficient catalysts for copper-free Sonogashira cross-couplings of a variety of aryl iodides with aryl- and alkylalkynes under mild conditions, in ethanol as the solvent and using potassium carbonate as the base. The reactions were carried out with 0.05 mol % of the catalysts which demonstrated exceptional stability in the solid state and in ethanol. Protection from air is not needed. Disubstituted acetylenes were synthesized by the general procedure on up to a gram scale and the yields were 80–98%.     

Nontransition metal–crown ether complexes as hydroperoxide decomposition catalysts

The decomposition of tert-butyl hydroperoxide in a chlorobenzene medium in the presence of complexes of dibenzo-18-crown-6 with calcium, strontium, and barium chlorides has been studied. It has been found and kinetically proven that the decomposition of tert-butyl hydroperoxide is preceded by the formation of an intermediate hydroperoxide–catalyst complex. Kinetic and thermodynamic parameters of the complex formation have been determined.     

Studies on outer-sphere electron transfer reactions of surfactant–cobalt(III) complexes with iron(II) in liposome (dipalmitoylphosphotidylcholine) vesicles

The effect of unilamellar vesicles of dipalmitoylphosphotidylcholine (DPPC), both below and above the phase transfer region, on the second-order rate constants for outer-sphere electron transfer between Fe²⁺ and the surfactant?Ccobalt(III) complexes, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺ and cis-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺ (en?=?ethylenediamine, trien?=?triethylenetetramine, C₁₂H₂₅NH₂?=?dodecylamine) was studied by UV?CVis absorption spectroscopy. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. It is concluded that below the phase transition temperature, there is an accumulation of surfactant?Ccobalt(III) complexes at the interior of the vesicle membrane through hydrophobic effects, and above the phase transition temperature the surfactant?Ccobalt(III) complex is released from the interior to the exterior surface of the vesicle. Through isokinetic plots, we have established that the mechanism of the reaction does not alter during the phase transition of DPPC.     

Observations of carbon–carbon coupling of 4,4'-dibromo-p-terphenyl on Cu(110) surface at molecular level

The carbon–carbon couplings of 4,4'-dibromo-p-terphenyl(DBTP) on Cu(110) surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of parallel non-organometallic and organometallic intermediates of DBTP molecules along the[1–10] direction of the surface has been observed. Further annealing at 393 K causes one group of molecules to form oligomers with para-para and para-meta motifs via Ullmann reaction and the other group of molecules to synthesize oligomers with meta-meta motifs via direct carbon–carbon coupling reaction. Statistical results directly reveal that the occurrence of reaction type is strongly related to the initial binding configuration of DBTP molecules.