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The aim of the present work was to elucidate the binding mechanism and kinetics of anionic cyanine dye 3,3-disulfopropyl-5,5-dichlorothiacyanine sodium salt (TC) J-aggregation on the surface of silver nanoparticles (AgNPs, particle size similar to 6 nm). The hybrid J-aggregateAgNPs assembly was characterized by TEM analysis, UVvis spectrophotometry, and fluorescence measurements. In the elucidation of TC binding on the surface of AgNPs, they were considered as macromolecules with several binding sites and TC dye was considered as a ligand. Scatchard and Hill analysis revealed that TC binding was a random process rather than cooperative, with similar to 200 bonded TC molecules per AgNP and a binding constant K-a = 4.8 x 10(7) M. The TC-AgNP assembly exerted concentration-dependent fluorescence quenching properties. The linearity of the SternVolmer relation, accounting for both static and dynamic quenching, indicated that only one type of quenching occurred, suggesting that AgNPs quenched the fluorescence of TC with an extraordinarily high SternVolmer constant (KSV) in the range of 10(8) M-1. Additionally, the kinetics of J-aggregation of TC in the presence of AgNPs was studied using a stopped flow technique. Kinetic measurements were performed as a function of the TC and AgNP concentration, yielding sigmoidal kinetic curves. The concentration dependence of the parameters of the kinetic curves indicated that J-aggregate formation on the AgNP surface occurred via a two-step process; the first was adsorption of the initial dye layer, followed by the growth of consecutive layers.

Nanoparticles (NPs) modified with fluorescent cyanine dyes can exhibit fluorescent quenching properties due to energy and/or electron transfer, and these systems have many applications in catalysis, drug delivery, nanoelectronics, medical diagnostics, and chemical sensing. The aim of this work was to investigate the adsorption of cyanine dye 5,5-disulfopropyl-3,3-dichlorothiacyanine (TC) on the surface of citrate capped gold nanoparticles (AuNPs) with the average core sizes of 9, 17, and 30 nm using various experimental techniques. The measurements of fluorescence corrected for inner filter effects (IFE) of the particle dye assembly clearly indicated that the fluorescence of TC was quenched by AuNPs on the concentration dependent 3 manner, and the equilibrium constants for the sorption of TC on the NP surface were calculated. Significant increase of fluorescence quenching was noticed when NP size increased, keeping the concentration of NPs of different size constant. By comparing experimental and calculated results for quenching of TC dye fluorescence, we assumed that the maximum quenching was restricted to full monolayer coverage of TC on the NP surface. The conclusion was drawn that the most probable orientation of TC dye molecules on the NP surface was slanted and that the dye approached NP surface with its positively charged thiazole ring.

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.

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 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.

The thermal properties of four copper(II) complexes with N , N ′, N ″, N ‴-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and several bidentate ligands N,S (thiosemicarbazide and thiourea) or N,O donors (semicarbazide and urea), of the general formula [Cu 2 (X)tpmc](ClO 4 ) 4 , have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal stability order can be recognized for the examined complexes, depending on coordinated bidentate bridging N,S or N,O ligand. Kinetic data demonstrated first-order thermal decomposition. A plausible mechanism has been proposed which explains the major products of the degradation.

Four new mixed complexes of Co(II) with N,N′ N″,N′″-tetrakis(2-pyridylmethyl)-1, 4, 8, 11-tetraazacyclotetradecane (tpmc) and bridged α- or β-aminocarboxylato ligands of general formula [Co2(Y)tpmc](C1O4)3 zH2O where Y = glycinato, S-alaninato, S-aminobutyrato, β-aminobutyrato ion, and z = 0, 0.5 or 1 were isolated. The complexes were characterised by elemental analysis, electronic and IR spectroscopy, magnetic measurements and cyclic voltam-metry. A structure with μ-O, O′-coordination of the aminocarboxylato ligand, and exo coordination of Co(II) ions and tpmc is proposed. The complexes exhibit different electrochemical activities; glycinato and S-alaninato complexes are electrochemically active, whereas S-aminobutyrato and β-aminobutyrato complexes are electrochemically inactive under the given conditions.

Two new dinuclear cobalt(II) complexes which, besides macrocyclic ligand N′,N′,N″,N‴-tetrakis (2-pyridylmethyl)-l,4,8,11-tetraazacyclotetradecane (tpmc) contain α- or β-aminoisobutyrato ions (α-aibu − and β-aibu −, respectively) were synthesized. The complexes having general formula [Co2(aibu)tpmc](CIO4)3 were characterized by elemental analysis, electronic and 1R spectroscopy, magnetic measurements and cyclic voltammetry. It was assumed that in both complexes an exo coordination of the macrocyclic ligand is achieved. Cobalt(II) ions are bridged with O,O′-aminoisobutyrato ligand. Both complexes are stable against air oxidation, whereas the oxidation of the complex containing the α-aibu− ion by hydrogen-peroxide gave the coresponding mixed-valence Co11/Co111 complex. The complexes are also electrochemically stable in the potential range from-0,6V to 0,4V vs SCE.

Two new platinum(IV) complexes (1, trifluoperazinehydrochloride-aquapentachloridoplatinate(IV) and 2, chlorpromazine-chlorpromazinehydrochloridepentachloridoplatinate(IV)) were synthesized in the reaction of K-2[PtCl6] with trifluoperazine dihydrochloride (TF center dot 2HCl) or chlorpromazine hydrochloride (CP center dot HCl). The complexes were characterized by elemental analysis, molar conductivity measurement, and spectral (IR, H-1, C-13, 2D H-1-C-13 heteronuclear correlation spectra, Pt-195 NMR, and MS) methods. Outer-coordination sphere was proposed for 1; while in 2, the ligand was coordinated to the metal. The complexes exhibit antibacterial effect on strains of Bacillus subtilis, Bacillus cereus, Bacillus pumilus, and methicillin-resistant Staphylococci as Gram-positive bacteria and an Escherichia coli as Gram-negative bacteria, as well as the reference strains. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3513]

The aim of this work was to investigate the formation of J-aggregates of thiacyanine dye (TC, 5,5′-disulfopropyl-3,3′-dichlorothiacyanine sodium salt) in the presence of 6 nm spherical silver nanoparticles (Ag NPs) using spectrophotometric and fluorescence methods. The formation of J-aggregates was concentration dependent and characterized by the appearance of the new absorption band with the maximum at 481 nm. Spectrophotometric study of J-aggregate formation and time stability suggested that they were formed on the account of monomer form of TC. Moreover, the stability of J-aggregates increased with the lowering AgNPs concentration. The measurements of fluorescence of the NPs—dye assembly clearly indicated that the fluorescence of TC was quenched by Ag NPs on the concentration dependent manner. The spectrophotometric and fluorescence properties of NPs—dye assembly were found to be quantitatively related to the surface coverage of the dye on the Ag NPs.

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.

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

4-Morpholine-, piperidine-, 4-piperazine- and N-methyl- piperazine-dithiocarbamate complexes of Cobalt (III) with 1, 4, 8, 11-tetraazacyclotetradecane, of general formula [Co(Rdtc)cyclam] (C104)2, have been prepared and have been characterized. The complexes adopt cis-octahedral geometry with folded macrocyclic ligand and with the dithiocarbamate bound as a bidentate. trans-influence of the dithiocarbamate ligands was studied by NMR spectroscopy and established the order piperidine-dtc > 4-morpholine-dtc > N-methyl-piperazine-dtc.