Determination of trace amounts of nickel by differential pulse adsorptive cathodic stripping voltammetry using calconcarboxylic acid as a chelating agent

A method for the determination of nickel(II) by stripping voltammetry is described. The method is based on the adsorptive accumulation of nickel(II) calconcarboxylic acid complex onto a hanging mercury drop electrode (HMDE), followed by the reduction of the adsorbed complex using differential pulse voltammetry. The optimum operating conditions and parameters were found to be 0.05 M NH₃/NH₄Cl buffer (pH = 9.5) as the supporting electrolyte, a ligand concentration of 1 × 10^?6 M, accumulation potential of ?0.5 V (vs. Ag/AgCl) and accumulation time of 60 s. At the optimized conditions, the peak current is proportional to the concentration of nickel in the range of 1.7 × 10^?9 to 4.7 × 10^?7 M (0.1–28 ng ml^?1) with a detection limit of 0.05 ng ml^?1. The relative standard deviation (n = 10) at nickel concentrations of 2, 10 and 15 ng ml^?1 varies in the range 0.76 to 2.1%. Possible interferences by metal ions, which are of great significance in real matrices, have been studied. The method was successfully applied to the determination of nickel content in a chocolate sample.     

Electrochemically catalyzed synthesis of cyclic carbonates from CO2 and propargyl alcohols

A convenient and efficient electrochemical method has been developed for the synthesis of the α-alkylidene cyclic carbonates from carbon dioxide (CO₂) and propargyl alcohols at room temperature. The electrosynthesis was successfully carried out with a copper anode and a nickel cathode in an undivided cell containing n-Bu₄NBr-MeCN electrolyte with a constant current under 3 MPa pressure of CO₂, and the α-alkylidene cyclic carbonates were obtained in good to excellent isolated yields in the secondary and tertiary terminal propargylic alcohols cases. The experimental results show that the electrogenerated Cu⁺ ions and strong bases in situ could efficiently catalyze or promote the coupling reaction under the cooperation of electrolytic medium MeCN and supporting electrolyte n-Bu₄NBr. The plausible mechanism of the coupling reaction was also discussed briefly.     

Selective Electrocatalytic Hydrogenation of trans-2-Allyl-6-methyl(allyl, phenyl)-1,2,3,6-tetrahydropyridines on the Nickel and Copper Cathodes

It is shown that the electrocatalytic hydrogenation (ECH) of trans-2-allyl-6-R-1,2,3,6-tetrahydropyridines (R = Me, All, Ph) on a nickel cathode (Ni_disp/Ni) in 40-% aqueous DMF in the presence of excess AcOH yields products of total hydrogenation of all double bonds—relevant trans-2-propyl-6-R₁-piperidines (R₁ = Me, Pr, Ph). Selective hydrogenation of terminal double bonds of allyl substituents in piperideines under study with the retention of the intracycle double bond may be realized on a copper cathode (Cu_ann), provided the stoichiometric ratio between AcOH and the initial substance is observed exactly. In either case, at points of maximum selectivity of ECH processes, the ratio c _AcOH/c _ini = n+ 1, where nis the number of hydrogenated bonds. The difference in the ECH mechanisms on the Cu_ann and Ni_disp/Ni cathodes is discussed. The results of hydrogenation of the trans-2-allyl-6-R-1,2,3,6-tetrahydropyridines at the Cu_ann and Ni_disp/Ni cathodes confirm the general character of regularities discovered earlier during ECH of citral.     

Removal of organic dye pollutants from wastewater by electrochemical oxidation

The removal of chemical oxygen demand (COD) and color from simulated dye wastewater containing organic dyes, direct yellow 4, C₂₆H₂₀N₄O₈S₂Na₂ and acid yellow 17, C₁₆H₁₀O₇N₄S₂Cl₂Na₂ experimentally investigated using an electrochemical undivided cell reactor with Pt as anode and steel as cathode. Particular attention was paid to probe the effect of supporting electrolyte (NH₄Cl), cell voltage, pH, and treatment time on the electrochemical treatment efficiency. Experiments were also carried out using 0.2?M NH₄Cl as supporting electrolyte under the condition of free pH. The experimental results showed that the process could efficiently remove the color and COD from simulated dye waste water. The overall COD removal reached at 69.9% by using supporting electrolyte and increasing voltage. The process can be described by pseudo first-order kinetics for the removal of COD.     

Structure,synthesis, and thermal properties of trans-[Ru(NO)(NH3)4(SO4)]NO3·H2O

In treatment of trans-[Ru(NO)(NH₃)₄(OH)]Cl₂ with concentrated sulfuric acid on heating trans-[Ru(NO)(NH₃)₄(SO₄)](HSO₄)·H₂O (I) is obtained with a yield close to quantitative. In the interaction of the saturated solution of I with a saturated NaNO₃ solution a trans-[Ru(NO)(NH₃)₄(SO₄)]NO₃·H₂O (II) precipitate forms whose structure is determined by single crystal XRD: space group P2₁2₁2₁, a = 6.8406(3) Å, b = 12.6581(5) Å, c = 13.3291(5) Å. A monodentately coordinated sulfate ion is in the trans-position to the nitroso group. Compound II is characterized by IR spectroscopy, powder XRD, and diffuse reflectance spectroscopy. The process of its thermolysis is studied; by differential scanning calorimetry the thermal effect of the dehydration reaction occurring on heating to 120°C (ΔH = 58.9 ± 1.5 kJ/mol) is estimated. The final product of the thermolysis of II is a mixture of Ru and RuO₂.     

Reduction of metol on mechanically renewed metal electrodes

The electroreduction of metol on mechanically renewed metallic electrodes is studied by direct voltammetry with linear potential sweep. Reduction peaks of metol are found in a neutral supporting electrolyte (0.02–0.5 M Na₂SO₄) on nickel, silver, and mercury electrodes before the potential of hydrogen liberation from the supporting electrolyte. The shape and parameters of the cathodic peak depend on an electrode material, and also on the composition and pH of the supporting solution. A probable mechanism of the electroreduction of metol is proposed. The regeneration of nickel and silver electrodes by in situ mechanical cutting of a 0.5-μm surface layer provides good reproducibility of the value of peak current; it is proportional to the concentration of metol in the range 2 × 10⁻³–1.8 × 10⁻² M.     

Homogeneous electro-mediated reduction of unsaturated compounds using Ni and Fe as mediators in DMF

The homogeneous electro-mediated reduction (HEMR) of several organic compounds (cyclohexene, cyclohexanone, acetophenone, benzaldehyde, styrene, linalool, 1,3-cyclohexadiene, citral, trans-4-phenyl-3-buten-2-one, and piperine) was carried out using Fe²⁺, Ni²⁺, and [Ni^II(bpy)]Br₂ (bpy=2,2′-bipyridine) as electron mediators. An electrochemical system composed of sacrificial anode (Fe, Ni or Zn), nickel cathode, NaI (0.2 M) as supporting electrolyte in DMF and an undivided cell, was used. A constant current ≤100 mA was applied with a maximum cell potential of 2.0 V. Non-conjugated olefins are not reactive, but ketones may be easily reduced to the respective alcohol. In the case of conjugated olefins and ketones, [Ni^II(bpy)]Br₂ or Ni²⁺ mediator presented good reactivity and selectivity in most cases. Fe²⁺ more efficiently mediates the reduction of carbonyl containing systems. Preliminary electroanalytical studies indicate the complexation of the organic substrate by Fe²⁺ and Ni²⁺ ions and [Ni^II(bpy)]Br₂ complex.     

Reaction of trans-[RuNO(NH3)4(OH)]Cl2 with nitric acid and synthesis of ammine(nitrato)nitrosoruthenium complexes

The reaction of trans-[RuNO(NH₃)₄(OH)]Cl₂ with nitric acid has been studied. Reaction products have been identified by IR spectroscopy, NMR, mass spectrometry, powder and single-crystal X-ray diffraction, and chemical analysis. Synthesis methods have been developed for amminenitrosoruthenium complexes containing outer-sphere and coordinated nitrate ions: trans-[RuNO(NH₃)₄(H₂O)](NO₃)₃ (I), trans-[RuNO(NH₃)₄(NO₃)](NO₃)₂ (II), and fac-[RuNO(NH₃)₂(NO₃)₃] (III). Complex II has two polymorphs: monoclinic and tetragonal. The latter has been studied by X-ray crystallography.     

Voltammetric Determination of Aflatoxin B1

For the first time the possibility of voltammetry used for the determination of aflatoxin B1 on a glassy carbon electrode was shown. The effect of pH of a supporting electrolyte on the analytical signal of aflatoxin B1 has been investigated and it was shown that there is a more pronounced peak with a maximum current at pH of 5.33. The most favorable supporting electrolyte for a linear range of detectable concentrations of aflatoxin B1 – 0.1 M (NH₄)₂SO₄ was determined. The results of research on the development of conditions of voltammetric measurement of aflatoxin B1 are presented.     

Cytotoxic properties of platinum(IV) and dinuclear platinum(II) complexes and their ligand substitution reactions with guanosine-5′-monophosphate

The substitution reaction of the Pt(IV) complex [PtCl₄(bipy)] with guanosine-5??-monophosphate (5??-GMP) was studied by UV?CVis spectrophotometry. This reaction was investigated under pseudo-first-order conditions at 37?°C in 25?mM Hepes buffer (pH?=?7.2) in the presence of 10?mM NaCl to prevent the hydrolysis of the complex. The substitution of chlorides in [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complex by 5??-GMP was followed by ¹H NMR spectroscopy under second-order conditions. Very similar values for the rate constants of both substitution steps were obtained. The Pt(IV) complexes, [PtCl₄(bipy)] and [PtCl₄(dach)], as well as dinuclaer Pt(II) [{trans-Pt(NH₃)₂Cl}₂(??-pyrazine)](ClO₄)₂ (Pt1), [{trans-Pt(NH₃)₂Cl}₂(??-4,4??-bipyridyl)](ClO₄)₂?·?DMF (Pt2) and [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complexes, displayed potent cytotoxic activity against human ovarium carcinoma cell line TOV21G and lower activity toward human colon carcinoma HCT116 cell line at the same concentrations. Our data indicate that these platinum complexes could be explored further, as potential therapeutic agents for ovarian cancer.     

含有NH2CH2CH2CH2NH2和o-C6H4(NH2)2配体的镍配合物的合成、结构和它们在乙烯聚合中的作用

两种镍的配合物[Ni(NH2CH2CH2CH2NH2)3]Cl2 (1)和[Ni(C6H4N2H4)2Cl2] (2)已经被合成并且通过红外和单晶X射线衍射分析对其进行了表征。在配合物1中,镍原子处于手性假八面体[NiN6]的几何构型中,它与三个1,3-丙二胺分子形成了三个六元环。在配合物2中,镍原子除了与两个o-苯二胺分子通过四个Ni-N键形成两个五元环外,它还与两个Cl原子配位形成了反式Ni-Cl2,这不同于以往报道过的镍的二胺配合物。这两个镍的配合物被MAO, MMAO或Et2AlCl活化后,对乙烯的二聚合或三聚合显示了很好的催化活性[对于配合物2,催化活性达到3.59×106 g mol-1 (Ni) h-1]。     

New method for the synthesis of trans-hydroxotetraamminenitrosoruthenium(II) dichloride and its characterization

A procedure for the synthesis of mpa h c-[Ru(NO)(NH₃)₄(OH)]Cl₂ in a nearly quantitative yield (～95%) comprising treatment of a solution of (NH₄)₂[Ru(NO)Cl₅] with ammonium carbonate at t ～80°C was developed. It was found that [Ru(NO)(NH₃)₄(H₂O)]Cl₃·H₂O and trans-[Ru(NO)(NH₃)₄Cl]Cl₂ formed in the reaction of [Ru(NO)(NH₃)₄(OH)]Cl₂ with hydrochloric acid at various temperatures most often contain some initial hydroxy complex. The former compound is unstable, even at room temperature, it slowly eliminates water and HCl. A procedure for preparing the latter compound in a pure state in 85–90% yield was proposed. The acidity constant of the complex trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺ at room temperature (K _a = (4 ± 1) × 10^?2) was estimated by ¹⁴N NMR spectroscopy.     

Preparation,characterization and cytotoxic activity of new compounds trans-[PtCl2NH3(3-(hydroxymethyl)-pyridine)] and trans-[PtCl2NH3(4-(hydroxymethyl)-pyridine)]

We report the synthesis, characterization and cytotoxic assays of new trans-platinum compounds, trans-[PtCl₂NH₃(3-(hydroxymethyl)-pyridine)] and trans-[PtCl₂NH₃(4-(hydroxymethyl)-pyridine)]. In the present work, we found that the replacement of the ammine ligand in “classical” transplatinum with the two new ligands does not increase the cytotoxic activity, maybe because these complexes do not produce a stability of the intrastrand cross-links in DNA.     

N-donor ligand complexes of nickel,zinc and copper: Comparisons with tetradentate N-donor ligands derived from Schiff bases

The nickel and zinc complexes of 2-aminomethylaniline (AMA) are reported. Both metals form the octahedral complex [M(AMA)₂(ONO₂)₂] (M = Ni, Zn) where the aromatic ligands lie in the meridial plane with the anilino donors trans to one another. The remaining nitrates coordinate axially. A simple comparison with the nitrogen donor disposition (cis/trans) in nickel complexes of tetradentate N₄ donor ligands derived from symmetric Schiff base ligands is presented. The discussion is extended to interrogate the bonding motifs of the nitrate ligands viz –ONO₂ in the nickel complexes of AMA compared to the two motifs (viz O₂NO and ONO₂) that are isolated for the nickel complexes of the macrocycle hexamethyltetraazacyclotetradecane.     

Electrocarboxylation of Carbon Dioxide with Polycyclic Aromatic Hydrocarbons Using Ni as the Cathode

Using Ni cathode and Al sacrificial anode, the electrocarboxylation of polycyclic aromatic hydrocarbons (naphthalene, 5‐methylnaphthalene, anthracene, phenanthrene and 1H‐indene) with carbon dioxide (4 MPa) could be successfully performed in an undivided cell containing n‐Bu₄NBr‐DMF supporting electrolyte with a constant current at room temperature, affording the corresponding trans‐dicarboxylic acids in good to excellent yields (62% –90%). Among the examined cathode materials (Ni, Pt, Ag, Cu and Zn), Ni and Pt cathodes exhibited a good catalytic activity for the electrocarboxylations. In addition, the experimental results indicated that electrolytic conditions (conducting salts, electricity, CO₂ pressure and temperature) could also affect the result of the electrocarboxylation. According to the results of the electrocarboxylations and CV (cyclic voltammetry), a possible electrochemical reaction mechanism was also proposed.     

Hydrothermal synthesis and crystal structure of a new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4

A new ammonium gallium hydroxyphosphate (NH₄)Ga(OH)PO₄ was synthesized under mild hydrothermal conditions (200°C, τ = 168 h). The equimolar content of Ga and P was determined by chemical analysis and electron probe X-ray microanalysis. The presence of NH₄ and OH groups was demonstrated by IR and Raman spectroscopy. An ab initio model of the crystal structure was refined by the Rietveld method (space group P2₁/m, Z = 2): a = 4.4832(1) Å, b = 6.0430(1) Å, c = 8.5674(1) Å, β = 98.019(1)°, R _p = 0.0552, R _wp = 0.0723. A zero SHG signal (T = 300 K) confirmed a centrosymmetric structure of the compound. The structure contains layers composed of GaO₄(OH)₂ octahedra and PO₄ tetrahedra. The interlayer space accommodates ammonium cations. The layer is based on linear chains of edge-sharing GaO₄(OH)₂ octahedra with a zigzag trans-arranged-Ga-(OH)-Ga-(OH)-backbone. The construction of the layer in (NH₄)Ga(OH)PO₄ was found to be topologically related to that in (En)_0.5Fe(OH)PO₄. The effect of the gradual F^? → OH^? substitution in the quasi-morphotropic series (NH₄)GaF_1-δ(OH)_δPO₄ (δ = 0, 0.5, 1.0) on the degree of polarization of the mixed anionic radical was considered. (NH₄)Ga(OH)PO₄ is thermally unstable: removal of NH₃ and H₂O molecules in the range 170–450°C is accompanied by the formation of two polymorphs of GaPO₄.     

NH_4~+对甲酸在炭载Pd催化剂上氧化性能的影响

为了解HClO4、NH4ClO4和NaClO4电解液对炭载Pd(Pd/C)催化剂电极对甲酸氧化的电催化性能的影响,在用X射线衍射(XRD)谱、能量色散谱(EDS)和透射电子显微镜(TEM)对Pd/C催化剂进行表征的基础上,采用电化学方法测量了Pd/C催化剂在不同电解液中对甲酸氧化的电催化性能.发现在不同电解液中,Pd/C催化剂对甲酸氧化的电催化活性和稳定性按NH4ClO4NaClO4HClO4的次序降低.由于甲酸的存在,不同电解液的pH相差较小,因此,电解液的pH影响较小,而阳离子的影响较大.在NaClO4电解液中的性能优于在HClO4电解液中的性能是pH的影响.在NH4ClO4电解液中的性能优于在NaClO4电解液中是由于NH4+能降低CO在Pd/C催化剂电极上的吸附强度和吸附量,这一发现对提高直接甲酸燃料电池(DFAFC)的性能很有意义.     

Synthesis and characterisation of the amidine complexes trans-[PtCl(NH3){HNC(NH2)R}2]Cl (R = Me, Ph, CH2Ph) derived from addition of NH3 to the coordinated nitriles in trans-[PtCl2(NCR)2]

The di-nitrile complexes trans-[PtCl₂(NCR)₂] (R = Me, Ph, CH₂Ph) react with an excess of gaseous NH₃ in CH₂Cl₂ at −10 °C to form, in high yield, the corresponding di-amidine complexes trans-[PtCl(NH₃){HNC(NH₂)R}₂]Cl in which also one chlorine ligand has been displaced by NH₃. The ¹H NMR spectra in DMSO showed the formation of different species which were characterized through NOESY, TOCSY and ¹H/¹³C heteronuclear correlations as trans-[Pt(NH₃){HNC(NH₂)R}₂(DMSO)]Cl₂ and trans-[PtCl{HNC(NH₂)R}₂(DMSO)]Cl.     

Kinetic characterization of the interactions of trans-dichloro-platinum(IV) anticancer prodrugs and a model compound with thiosulfate

Sodium thiosulfate has been utilized as a rescuing agent for relief of the toxic effects of cisplatin and carboplatin. In this work, we characterized the kinetics of reactions of the trans-dichloro-platinum(IV) complexes cis-[Pt(NH₃)₂Cl₄], ormaplatin [Pt(dach)Cl₄] and trans-[PtCl₂(CN)₄]^2? (anticancer prodrugs and a model compound) with thiosulfate at biologically important pH. An overall second-order rate law was established for the reduction of trans-[PtCl₂(CN)₄]^2? by thiosulfate, and varying the pH from 4.45 to 7.90 had virtually no influence on the reaction rate. In the reactions of thiosulfate with cis-[Pt(NH₃)₂Cl₄] and with [Pt(dach)Cl₄], the kinetic traces displayed a fast reduction step followed by a slow substitution involving the intermediate Pt(II) complexes. The reduction step also followed second-order kinetics. Reductions of cis-[Pt(NH₃)₂Cl₄] and [Pt(dach)Cl₄] by thiosulfate proceeded with similar rates, presumably due to their similar configurations, whereas the reduction of trans-[PtCl₂(CN)₄]^2? was about 1,000 times faster. A common reduction mechanism is suggested, and the transition state for the rate-determining step has been delineated. The activation parameters are consistent with transfer of Cl⁺ from the platinum(IV) center to the attacking thiosulfate in the rate-determining step.     

Stereoisomeric Pt(IV) complexes with threonine

Stereoisomeric Pt(IV) complexes with threonine (ThrH = HOCH(CH₃)CH(NH₂)COOH, ??-amino-??-hydroxybutyric acid) were obtained. In the complexes trans-[Pt(S-ThrH)₂Cl₄] and trans-[Pt(R-ThrH)(S-ThrH)Cl₄], the ThrH molecules act as monodentate ligands coordinated through the NH₂ group. In the complexes cis- and trans-[Pt(S-Thr)₂Cl₂] and trans-[Pt(R-Thr)(S-Thr)Cl₂], the deprotonated ligands are coordinated in a bidentate fashion through the NH₂ and COO^?-groups (R,S is the absolute configuration of the asymmetric carbon atom). All the complexes were identified using elemental analysis, IR spectroscopy, and ¹⁹⁵Pt, ¹³C, and ¹H NMR spectroscopy. The complexes trans-[Pt(S-ThrH)₂Cl₄] · 3H₂O and cis-[Pt(S-Thr)₂Cl₂] · 2H₂O were additionally characterized by X-ray diffraction.