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The complexation reactions between octaazamacrocyclic ligand N,N',N '',N'"-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and Co2+, Ni2+, Zn2+ and Cu2+ metal cations have been studied conductometrically in acetonitrile and aqueous solutions. The conductance data exhibit different stoichiometry of the complexes in two studied solutions. In most cases 1:1 (ML) complexes were formed while in some cases 2:1 (M2L) complexes are evident. The stability constants of the resulting 1:1 complexes were determined by computer fitting of the conductance/mole ratio data. Theoretical DFT calculations were used to explain metal binding capability of tpmc ligand and the binding sequences were found to follow the order: Cu2+ gt gt Ni2+ gt Co2+ gt Zn2+. The combination of results obtained by this theoretical approach and conductometric study successfully explains sensitivity and selectivity of recently developed tpmc based ISE and could play a guiding role in planning experiments with large macrocyclic ligands. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3473]

Mixed ligand dinuclear copper(II) complexes of the general formula [Cu2(Rdtc)tpmc)](ClO4)3 with octaazamacrocyclic ligand tpmc and four different heterocyclic dithiocarbamate ligands Rdtc-, as well as the complexes [Cu2(tpmc)](ClO4)4 and [Cu(tpmc)](ClO4)2 center dot 2H2O were studied in aqueous NaClO4 and HClO4 solutions by cyclic voltammetry on glassy carbon electrode. The electrochemical properties of the ligands and Cu(II) complexes were correlated with their electronic structure. Conductometric experiments showed different stoichiometry in complexation of tpmc with Cu2+ ions and transport of ions in acetonitrile and in aqueous media. These studies clarified the application of this macrocyclic ligand as ionophore in a PVC membrane copper(II) selective electrode and contributed elucidation of its sensor properties.

The kinetics of J-aggregate assembly on the surface of noble metal nanoparticle colloids are described, providing new mechanistic insight into the interaction of the dye molecules with the surface of metal nanoparticles. We specifically studied the J-aggregation of a thiacyanine dye (TC, 3,3′-disulfopropyl-5,5′-dichlorothiacyanine sodium salt) on the surface of gold nanoparticle colloids. The hybrid J-aggregate–Au colloidal dispersions were characterized by UV–vis spectrophotometry, fluorescence measurements, zeta potential measurements, and TEM analysis. Kinetic measurements were carried out using a stopped-flow method, indicating that the J-aggregate formation on the surface occurs via a two-step process. The first step includes adsorption of the initial dye layer, followed by an order of magnitude slower growth of consecutive layers. Activation parameters determined from the fluorescence measurements yielded further details about the nature of the interaction.

The thermal decomposition of [RuCl2(eta(6)-p-cymene)](2) (1) and its biologically active N-alkylphenothiazine compounds of composition L[RuCl3(eta(6)-p-cymene)] where L = CPH+ (2), TFH+center dot HCl (3), and TRH+ (4) (chlorpromazine hydrochloride, CP center dot HCl; trifluoperazine dihydrochloride, TF center dot 2HCl; and thioridazine hydrochloride, TR center dot HCl, respectively) has been studied. The crystal and molecular structure of compound 3 was determined earlier by single crystal X-ray diffraction analysis. The thermal data were collected by simultaneous TG/DSC measurements. For evolved gas detection, the qualitative reaction of chlorides with AgNO3 in an acidic solution was applied. The measurements were carried out in the temperature range to 700 A degrees C in nitrogen atmosphere. Compounds of L[RuCl3(eta(6)-p-cymene)] crystallize with water or water/2-propanole. On the basis of thermal data, the trend in the solvent bonding energies was assessed.

Thermal decomposition of chlorpromazine hydrochloride (CP center dot HCl), trifluoperazine dihydrochloride (TF center dot 2HCl) and thioridazine hydrochloride (TR center dot HCl), and the ruthenium complexes with dimethyl sulfoxide (dmso) of composition [RuCl(2)(dmso)(4)] and L[RuCl(3)(dmso)(3)]center dot xEtOH, L = CP center dot HCl, TF center dot 2HCl or TR center dot HCl is described. The phenothiazines are stable to temperature range of 200-280 A degrees C with an increasing stability order of TF center dot 2HCl < CP center dot HCl < TR center dot HCl. The decomposition of all the compounds takes place in superposing steps. For detection of chlorides and sulfides, EGD analysis was performed. The decomposition pattern of the complexes, due to their similar structure, is similar. The thermal data unambiguously resolve the contradiction between the elemental analysis and X-ray structural data for (TF center dot 2HCl)[RuCl(3)(dmso)(3)]Cl center dot EtOH. The compound crystallizes with one EtOH, evaporating in part at room temperature.

The simple PVC-based membrane containing N',N',N '',N '''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) as an ionophore and dibutyl phthalate as a plasticizer, directly coated on a glassy carbon electrode was examined as a new sensor for Cu2+ ions. The potential response was linear within the concentration range of 1.0x10(-1)-1.0 x 10(-6)M with a Nernstian slope of 28.8 mV/decade and detection limit of 7.0 x 10(-7)M. The electrode was used in aqueous solutions over a wide pH range (1.3-6). The sensor exhibited excellent selectivity for Cu2+ ion over a number of cations and was successfully used in its determination in real samples.

Platinum electrode decorated with three different mixed-ligand cobalt(III) complexes of the general formula [Co(Rdtc)cyclam](ClO4)(2) [cyclam = 1,4,8,11-tetraazacyclotetradecane, Rdtc(-) = morpholine-(Morphdtc), piperidine-(Pipdtc), and 4-methylpiperidine-(4-Mepipdtc) dithiocarbamates, respectively] was used to study oxidation of formic acid in acidic solution. The complexes were adsorbed on differently prepared Pt surfaces, at open circuit potential. The preliminary results show increased catalytic activity of Pt for formic acid oxidation with complex ion adsorbed on the polycrystalline surfaces. The increase in catalytic activity depends on the structure of the complex applied and follows the order of metal-coordinated bidentate ligand as Morphdtc > Pipdtc > 4-Mepipdtc. Based on IR and NMR data, the main characteristics of the Rdtc ligands do not vary dramatically, but high symmetry of the corresponding complexes decreases in the same order. Accordingly, the complexes are distinctively more mobile, causing chemical interactions to occur on the surface with appreciable speed and enhanced selectivity. The effect of the complexes on catalytic activity presumably depends on structural changes on Pt surfaces caused by their adsorption.

The influence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB) on the kinetics of the spontaneous reduction of the analytically important compound, sodium hexanitrocobaltate(III), was studied. The spontaneous reduction was monitored spectrophotometrically at pH 2 and 5 and at concentrations of CTAB from 1 x 10(-5) to 5 x 10(-4) M. The mechanism of this process was described using two consecutive first-order reactions. A decrease in the rate constant for reduction at pH 5 in solutions containing CTAB in concentrations of 5.6 x 10(-5) M (critical micelle concentration) compared with its rate in an aqueous solution was observed. These effects could be explained by electrostatic and hydrophobic/hydrophilic interactions between the micellar pseudophase and the hexanitrocobaltate(III) ion.

The inhibiting effect of cobalt(III) complexes with macrocyclic ligand cyclam (1,4,8,11-tetraazacyclotetradecane) and β-diketonato ligands have been investigated on iron corrosion in 0.1 M HClO 4 by potentiodynamic, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements. Analysis of the polarization curves and impedance spectra, by adding complex compounds to the acid solution and comparing with inhibitor-free solution, show corrosion current decrease and charge transfer resistance increase, respectively. Impedance data are fitted with equivalent circuit models. The stability of the adsorbed film was followed by LPR. Scanning electron microscopy (SEM) was used to screen physical changes of the reacted surfaces both treated and untreated. The differences in inhibitor efficiencies depend on the substituent group of the coordinated β-diketone ligand. Structural and electronic properties of this group of compounds in relation to inhibitor efficiency were analyzed by using the molecular modeling structures and correlated with previously reported spectroscopy data.

Five new CuII complexes of general formula [Cu2(Rdtc)tpmc](ClO4)3, (1)–(5), where tpmc and Rdtc − refer to N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of CuII ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the ν(C=N) and ν(C=S) vibrations which decrease in the order of the complexes: Pipdtc > N-Mepipdtc > Pzdtc > Morphdtc > Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria.

The syntheses of a new ligand 2-(diphenylphosphino)benzaldehyde selenosemicarbazone (HL) and the corresponding complex with Ni(II) of the formula [Ni(L)(NCS)] are reported. The complex was characterized by single crystal X-ray analysis. The compound complex is diamagnetic and has a markedly deformed square-planar structure with PNSe set of donor atoms of the ligand, the Schiff base monoanion, and the N atom of the coordinated NCS group. The phosphorus atom deviates even by 0.494(3) Angstrom from the mean plane defined by the other coordination atoms (NSeN) and the metal atom. (C) 2003 Published by Elsevier B.V.

Electrochemical stability of eight complexes of the general formula [co 111 Rdtc(1-8)cyclam](ClO 4 ) 2 , where cyclam=1,4,8,11-tetraazacyclotetradecane and Rdtc - (1-8)=4-morpholine (Morphdtc), 4-thiomorpholine (Timdtc), 4-piperazine (Pzdtc), N-methyl piperazine (N-Mepzdtc), piperidine (Pipdtc), 2-, 3- or 4-methylpiperidine (2-, 3- or 4-Mepipdtc) dithiocarbamates, respectively, were studied. The substances were examined in aqueous NaClO 4 solution and nonaqueous LiClO 4 in CH 3 CN solution by cyclic voltammetry. In aqueous solution, macrocyclic ligand cyclam is characterized by the anodic peak at 0.95 V. The Rdtc - ligands have two anodic peaks, one in the region 0.25-0.30 V and the other in the 0.78-0.95 V region. Absence of these anodic peaks in the case of the complexes indicates that coordination to cobalt(III) stabilizes both cyclam and Rdtc - ligands, but reversible peaks in the range -0.68 to -0.78 V support the Co(III) redox reaction. In nonaqueous solutions cyclam has one anodic peak at 1.75 V. The ligands with heteroatom in the ring (Morphdtc, Timdtc, Pzdtc, N-Mepzdtc) have two anodic peaks, while the other four ligands (Pipdtc, 2-, 3- and 4-Mepipdtc) have only one anodic peak. In nonaqueous solution again, coordination to Co(III) ion stabilizes the Rdtc - ligands and contrary to aqueous solution no Co(III) redox reaction occurs, indicating a greater stability of the complexes in this media. Finally, the electrochemical results are compared with spectroscopic data obtained previously.

The effect of the substituents, solvent polarities and hydrogen ion concentration on the electronic structure and UV/VIS absorption spectra of some Schiff bases, derivatives of N-(R-benzylidene)benzidine (R = o-NO2 and o-OH, p-OH) and N-(R-furfurylidene)benzidine (R = H and 5 - NO2), have been studied. The spectral shifts obtained in various organic solvents were discussed on the basis of the specific solute - solvent interactions through the formation of hydrogen bonds between hydrogen-bond donor (HBD) solvents and the benzidine nitrogen atom of the Schiff bases. Some interpretations of the electronic aspects of this type of hydrogen bonding were discussed as well as the stabilization effects due to the solvation. Finally, the pK values of the compounds were determined.

An all solid-state Ag(I) ion-selective electrode has been prepared by simply immersing a glassy carbon rod coated with PVCAc, which contained plasticizer and additive but no ionophore, into the AgNO3 solution. The response of the electrode was linear with a Nernstian slope of 60.25 mV/decade within the concentration range from 1 x 10(-1) to 1 x 10(-5) M and with a detection limit of 4.25 x 10(-6)M. The stability as an effect of various cations was defined. The electrode is suitable for use in high acidic solutions (pH LT 1 to 7) and has successfully been applied for the determination of silver(I) concentrations in different samples.

The reactions between 1,8-dihydroxy-2(imidazole-2-ylazo)-naphthalene-3,6-disulphonic acid (MONO-IACA) with Pd(II), Cu (II) and Ni(II) were studied spectrophotometrically in the acidity range from 3M HClO 4 to pH 8. The reactions involve the formation of [Cu(LH 2 ) 2 ] 4− , [NiLH 2 ] − and [PdLH 4 ] + chelate species with release of protons from imidazole and hydroxy groups. The equilibrium constants for the reaction Me + nLH x ⇄ MeL n H z + H + , log K eg , and stability constants of complexes, β, were determined from spectrophotometric measurements. The theoretical calculations of the complex structures confirmed the reagent acting as tridentate ligand, forming two five membered chelate rings.

The kinetics of the reaction between the tetrachloroaurate(III) ion and L-methionine (L-Met) (0.1 M HClO4, pH 1.0-2.5) have been studied spectrophotometrically using a stopped-flow technique at different temperatures. Initially, the fast substitution reaction was ascribed to the formation of the short-lived square-planar Au(III)-(L-Met) that was followed by the replacement of a Cl- ligand and a subsequent, slower reduction to Au(I)-(L-Met). This is an intermolecular process, involving attack on the [AuCl4](-) Complex by an outer-sphere L-methionine. The activation parameters (Delta H-not equal and Delta S-not equal) for substitution and reduction were determined. IR spectroscopy indicates that L-methionine acts as a bidentate ligand, most likely coordinating via the S and N atoms, while H-1 and C-13 NMR data indicate methionine sulfoxide as the final product. Finally, the components of the reaction were treated thermally in order to investigate the solid phase synthesis of the resulting complex. (C) 2008 Elsevier Ltd. All rights reserved.

Cytotoxicity and cell growth inhibition studies were performed for five distinct cobalt(ll) [Co(2)(acac)tpmc](ClO(4))(3), [Co(2)(dibzac)tpmc](ClO(4))(3), [Co(2)(hfac)tpmc](CIO(4))(2), [Co(2)(tmhd)tpmc](CIO(4))(3) and [Co(2)(ox)tpmc](CIO(4))(2).3H(2)0 and five molybdenum(Vl) complexes, [MoO(2)(pipdtc)(2)], [MoO(2)(morphdtc)], [MoO(2)(timdtc)(2)], [MoO(2)(pzdtc)(2)] and [MoO(2)(N-Mepzdtc)(2)]. The former were tested in two leukemia cell lines: chronic myelogenic leukemia (K562) and human promyelocytic cell line (U937). They showed to have relatively high toxicity in K562 cells and a relatively low cytotoxicity in U937 cells, as assessed by both MTT and Trypan Blue assays. The five molybdenum complexes were tested in human promyelotic U937 cell line and they showed to have high toxicity.

Hydrogen production via electrolysis of water from alkaline aqueous electrolytes is a well-established conventional technology. However, due to high energy requirements of about 4.5-5 kWh/m(n)(3) H-2 in most industrial electrolysers, the cost of hydrogen produced in such a way is n high. This is a limiting factor for the use of this method on a large scale, except in countries where the electricity is very cheap. There were various attempts to improve this process, like zero-gap cell geometry, developmentof new diaphragm materials, development of new electrocatalytic materials for electrodes, etc. We tried here to use ionic activators to reduce energy consumption. Two types of activators, both ethylenediamine complexes of cobalt, were used separately or in combination with some molybdates. The activation energies were significantly decreased in the presence of single ionic activators. However, the best results regarding the activation energy reduction were obtained when combinations with the molybdate were used. On the basis of the results of our experiments there is a strong indication that the activation with ionic activators reduces energy needs per mass unit of hydrogen produced for more than 10% in some cases, compared to those of non-activated electrolytes. (C) 2003 Elsevier Science B.V. All rights reserved. Conference on Scientific Advances in Fuel Cell Systems, Sep 25-26, 2002, Amsterdam, Netherlands

The thermal properties of four cobalt(III) complexes with cyclam (1,4,8,11-tetraazacyclotetradecane) and the heterocyclic dithiocarbamates Rdtc(-) [2-, 3-, 4-methylpiperidine (2-, 3-, 4-Mepipdtc(-)) or 4-thiomorpholine (Timdtc(-)) dithiocarbamates], of the general formula [Co(Rdtc)cyclam](ClO4)(2), have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal decomposition pathways of these complexes were also proposed. The following thermal stability order can be recognized for the examined complexes. depending on the position of the methyl group on the piperidine ring coordinating dithiocarbamates 2- GT 3- GT 4 -Mepipdtc(-). Generally, the same order was found to affect the decrease in kinetic and activation parameters. Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavia

The kinetics of the spontaneous reduction of hexanitrocobaltate(III) ion have been investigated spectrophotometrically (λ=360 nm at 298 K) in ethanol or acetone water mixtures containing 0, 10, 25 and 50 % of organic solvents. The mechanism of this process was expressed by means of two consecutive first-order reactions. Both of the first-order rate constants decrease with the increasing nonaqueous species content. The reduction of hexanitrocobaltate(III) ion in the mixtures was much slower than the corresponding reaction in water.