Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λ_max of [Fe(CN)₅PhNHNH₂]^3?, complex) under the optimum reaction conditions at: 2.5 × 10^?3 M [Fe(CN)₆]^4?, 1.0 × 10^?3 M [PhNHNH₂], 8.0 × 10^?7 M [Ag⁺], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO₃) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10^?8 M with a detection limit of 2 × 10^?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (K_CI), catalyst–substrate (K_s) and Michaelis–Menten constant (K_m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.     

Hydrogen gas yields in irradiated room-temperature ionic liquids

Yields of H₂ produced by electron beam irradiation were investigated in a series of room-temperature ionic liquids comprising 1-hexyl-3-methylimidazolium, 1-hexyl-4-(dimethylamino)pyridinium, 1-butyl-1-methylpyrrolidinium, triethylammonium or trioctyl(tetradecyl)phosphonium cations associated with bis(trifluoromethylsulfonyl)imide anion. The G(H₂) values ranged from 2.6×10⁻⁸ mol/J for the imidazolium and pyridinium-based ionic liquids to 2.5×10⁻⁷ mol/J for the phosphonium liquid. These results correlate well with yields of gaseous hydrogen in studies of nonionic aliphatic and aromatic organic compounds.     

Photophysical and photochemical studies of thifensulfuron-methyl herbicide in aqueous solution

The photophysical and photochemical studies of a sulfonylurea herbicide, thifensulfuron-methyl (THM), have been investigated in a buffered aqueous solution. In the first part, the influence of pH on the spectroscopic properties was studied. This allowed the determination of the ground and excited state acidity constants, pK_a = 4 and 4.4, respectively, thus exhibiting the potential existence of a photoinduced protonation in the singlet state. In the second part, the photolysis kinetics was studied at different pH and varying oxygen concentrations, using an HPK 125 W lamp and followed up by the identification of photoproducts formed under continuous photo-irradiation. The kinetics results suggest that the photolysis process is faster in acidic (k = 3 × 10^?4 s^?1) than in basic medium (k = 9.8 × 10^?5 s^?1). The photolysis products were identified by high performance liquid chromatography HPLC-DAD, HPLC–MS and HPLC–MS–MS. In order to obtain a better understanding of the photodegradation mechanism, a laser flash photolysis study was performed. By comparing the quenching rate constant (k_q = 9.64 × 10⁸ mol^?1 l s^?1) obtained from triplet state quenching by molecular oxygen and from the Stern–Volmer relation (k_q = 0.41 × 10⁸ mol^?1 l s^?1), the role of the singlet state in the photodegradation process was demonstrated. The photoproducts originating from both singlet and triplet excited states have been identified and hypothetical photodegradation pathways of the thifensulfuron-methyl in aqueous solution are proposed.     

Molecular interaction of organic dyes in bulk and confined media

Molecular interactions of five thiazine dyes with increasing alkyl substitution have been studied in aqueous and microemulsion media at 303 K within a concentration range of (1.35–7.00) × 10^?4 M. The dimerization constant (K_d) values for the five dyes are ranged between 1.761 and 6.258 × 10³ l mol^?1 in bulk water media, where as in microemulsion media, K_d's are ranged between 1.760 and 4.110 × 10³ l mol^?1. Thionine (with no methyl substitution) and azure A (with two methyl substitution) displayed slightly larger K_d values in microemulsion water pools compared to bulk water while other dyes recorded significant drop in K_d values. The influence of microemulsion media on the molecular interaction of dyes has been explained in terms of electrostatic and hydrophobic factors. The monomer and the dimer spectra are explained in terms of molecular exciton model and the optical absorption parameters of both the species are reported in bulk and confined media.     

Synthesis and physical characterization of electrically conducting polymers of polynuclear aromatic sulfonyl compounds

Potentially useful conducting polymers of sulfonyl substituted phenanthrene derivatives and non-conducting linear polymers, such as, polystyrene and poly(N-vinylcarbazole) have been synthesized and characterized using IR, thermogravimetric and dielectric measurements. The phenanthrene-based benzene, naphthalene and biphenyl copolysulfones have also been prepared and characterized through these techniques. These pendant and backbone polymer sulfones have exceptionally high thermal stability and electrical conductivity, such that dc conductivity in the range 2.80 × 10^?16 to 2.82 × 10^?7 Ω^?1 cm^?1 and ac conductivity in the range 1.69 × 10^?7 to 2.10 × 10^?6 Ω^?1 cm^?1.     

Reactivity of OH radicals with chlorobenzoic acids—A pulse radiolysis and steady-state radiolysis study

The reactions of OH radicals with 2-, 3-, 4-chlorobenzoic acids (ClBzA) and chlorobenzene (ClBz), k(OH+substrates)=(4.5?6.2)×10⁹ dm³ mol^?1 s^?1, have been studied by pulse radiolysis in N₂O saturated solutions. The absorption maxima of the OH-adducts were in the range of 320?340 nm. Their decay was according to a second-order reaction, 2k=(1?9)×10⁸ dm³ mol^?1 s^?1. In the presence of N₂O/O₂ the formation of peroxyl radicals was detectable for 2-, 4-ClBzA and ClBz, k(OH-adduct+O₂)=(2?4)×10⁷ dm³ mol^?1 s^?1, while this reaction for 3-ClBzA was too slow to be registered. In the presence of N₂O the degradation rates induced by gamma radiation were very similar for all chlorobenzoic acids, yet the chloride formation was distinctly higher for 3-ClBzA. In the presence of oxygen the initial degradation of 2-and 4-ClBzA equaled the OH-radical concentration, whereas in case of 3-ClBzA only ～60% of OH led to degradation. The order for the efficiency of dehalogenation was 4->2->3-ClBzA. Several primary radiolytic products could be detected by HPLC. To evaluate the toxicity of final products a bacterial bioluminescence test was carried out.     

A voltammetric study of the binding of copper(II) to peptide fragments of prion

Binding of copper to three peptide fragments of prion (Cu²⁺ binding sites: 60–91, 92–96 and 180–193 amino acid residues) was investigated by anodic stripping voltammetry to determine the stoichiometries of Cu²⁺-prion peptide interactions. The method relies on the synthesis of N-terminally acetylated/C-terminally amidated peptide fragments of prion by solid-phase synthesis and direct monitoring of the oxidation current of copper in the absence and presence of each prion fragment. Titration curves of Cu²⁺ with Ac-PHGGGWGQ-NH₂, Ac-GGGTH-NH₂ and Ac-VNITKQHTVTTTT-NH₂ were obtained in concentrations ranging from 8.52 × 10^?7 to 5.08 × 10^?6, 3.95 × 10^?7 to 1.94 × 10^?6 and 7.82 × 10^?8 to 4.51 × 10^?7 M, respectively. The acquired data were used to calculate the stoichiometries (one peptide per Cu²⁺ ion for all the three studied systems) and apparent dissociation constants (K_d = 4.37 × 10^?8–3.50 × 10^?10 M) for the three complexes.     

Degradation of n-butylparaben and 4-tert-octylphenol in H2O2/UV system

The degradation of two endocrine disrupting compounds: n-butylparaben (BP) and 4-tert-octylphenol (OP) in the H₂O₂/UV system was studied. The effect of operating variables: initial hydrogen peroxide concentration, initial substrate concentration, pH of the reaction solution and photon fluency rate of radiation at 254 nm on reaction rate was investigated. The influence of hydroxyl radical scavengers, humic acid and nitrate anion on reaction course was also studied. A very weak scavenging effect during BP degradation was observed indicating reactions different from hydroxyl radical oxidation. The second-order rate constants of BP and OP with OH radicals were estimated to be 4.8×10⁹ and 4.2×10⁹ M^?1 s^?1, respectively. For BP the rate constant equal to 2.0×10¹⁰ M^?1 s^?1was also determined using water radiolysis as a source of hydroxyl radicals.     

On the kinetics of thermal electron attachment to perfluoroethers

In this Letter we report the results of the measurements of the rate coefficients for thermal attachment to several perfluoroethers namely perfluorodiglyme (C₆F₁₄O₃), perfluorotriglyme (C₈F₁₈O₄), perfluoropolyether (CF₃–(OCF(CF₃)CF₂)_n–(OCF₂)_m–OCF₃) and perfluorocrownether ((C₂F₄O)₅). Rate coefficients were obtained under thermal conditions in the temperature range 298–378 K. The increase of the rates with temperature follows the Arrhenius law and the activation energies have been obtained from the slope of the ln(k) vs. 1/T. The respective values of the rate coefficients (at 298 K) and activation energies are as follows: 7.7 ± 1.2 × 10^?11 cm³ s^?1 (0.18 ± 0.005 eV), 6.7 ± 2.1 × 10^?11 cm³ s^?1 (0.25 ± 0.004 eV), 2.1 ± 0.2 × 10^?10 cm³ s^?1 (0.16 ± 0.010 eV), 3.1 × 10^?11 cm³ s^?1 (0.27 ± 0.003 eV) for C₆F₁₄O₃, C₈F₁₈O₄, CF₃–(OCF(CF₃)CF₂)_n–(OCF₂)_m–OCF₃ and (C₂F₄O)₅.     

EPR and optical absorption studies of Cu2+ doped bis (glycinato) Mg (II) monohydrate single crystals

Electron paramagnetic resonance (EPR) study of Cu²⁺ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu²⁺ (I), g_x = 2.1577 ± 0.0002, g_y = 2.2018 ± 0.0002, g_z = 2.3259 ± 0.0002, A_x = (87 ± 2) × 10^?4 cm^?1, A_y = (107 ± 2) × 10^?4 cm^?1, A_z = (141 ± 2) × 10^?4 cm^?1; Cu ²⁺ (II), g_x = 2.1108 ± 0.0002, g_y = 2.1622 ± 0.0002, g_z = 2.2971 ± 0.0002, A_x = (69 ± 2) × 10^?4 cm^?1, A_y = (117 ± 2) × 10^?4 cm^?1and A_z = (134 ± 2) × 10^?4 cm^?1. The ground state wave function of the Cu²⁺ ion in this lattice is evaluated to be predominantly |x² ? y². The g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex is discussed.     

Ag NPs decked GO composite as a competent and reusable catalyst for ‘ON WATER’ chemoselective synthesis of pyrano[2,3-c:6,5-c′]dipyrazol]-2-ones

We have synthesized and characterized Ag NPs decked GO composite and studied its role as reusable catalyst for the ‘ON WATER’ chemoselective synthesis of pyranodipyrazolones via the reaction of different carbonyl compounds with 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one. This method illustrates significant selectivity for pyranodipyrazolones over arylmethylene bispyrazolols and arylmethylenepyrazolones. Synergistic effect of heterogenic nature of water with reactants and Ag NPs/GO had profuse outcome on reaction as indicated by high TOF (18.03 × 10^?5 mol g^?1 min^?1). Furthermore, catalyst was recycled for 7-times without significant loss of activity.     

Noncovalent assembly of ferrocene on modified gold surfaces mediated by uracil–adenine base pairs

Redox-active ferrocene was assembled on gold surfaces through the hydrogen bonding interactions between adenine-substituted ferrocene and a uracil-terminated organothiol monolayer. The surface coverage of ferrocene Γ could be varied from ca. 4 × 10^? 11 to 2.0 × 10^? 10 mol cm^? 2 by diluting the thiol-modified uracil derivative with inert 1-octanethiol. A decrease in the apparent electron transfer rate constant for ferrocene, k_app, from ca. 50 to 10 s^? 1 was observed upon increasing Γ.     

Conductometric study of some alkali metal halides in (dimethyl sulfoxide + acetonitrile) at T = 298.15 K

Electrolytic conductivities of some alkali metal halides, MX (M⁺ = Li⁺, Na⁺, and K⁺; X^? = Cl^?, Br^?, and I^?), NaBPh₄ and Bu₄NBr have been investigated in (20, 40, and 60) mass% {dimethyl sulfoxide (DMSO) in DMSO + acetonitrile} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance Λ° the association constant K_A and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu₄NBPh₄ as the “reference electrolyte”. The association constant K_A tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter ΔG° and Walden product Λ°η. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Reply to comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In reply to “Comment on the possible role of reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction Δ_rG=57.26 kJ mol^?1 and the reaction rate constant k=7.23×10^?5 M^?1 s^?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×10⁴ M^?1 s^?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×10⁴ M^?1 s^?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from Δ_rG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures.     

Flow-injection chemiluminescence determination of dihydralazine sulfate in serum using luminol and diperiodatocuprate (III) system

A novel flow-injection chemiluminescence (CL) method for the determination of dihydralazine sulfate (DHZS) is described. The method is based on the reaction of luminol and diperiodatocuprate (K₂[Cu(H₂IO₆)(OH)₂], DPC) in alkaline medium to emit CL, which is greatly enhanced by DHZS. The possible CL mechanism was first proposed based on the kinetic characteristic, CL spectrum and UV spectra. The optimum condition for the CL reaction was in detail studied using flow-injection system. The experiments indicated that under optimum condition, the CL intensity was linearly related to the concentration of DHZS in the range of 7.0 × 10^?9 to 8.6 × 10^?7 g mL^?1 with a detection limit (3σ) of 2.1 × 10^?9 g mL^?1. The proposed method had good reproducibility with the relative standard deviation 3.1% (n = 7) for 5.2 × 10^?8 g mL^?1 of DHZS. This method has the advantages of simple operation, fast response and high sensitivity. The special advantage of the system is that very low concentration of luminol can react with DPC catalyzed by DHZS to get excellent experiment results. And CL cannot be observed nearly when luminol with same concentration reacts with other oxidants, so luminol–DPC system has higher selectivity than other luminol CL systems. The method has been successfully applied to determine DHZS in serum.     

The thioantimonate anion [Sb4S8]4− acting as a tetradentate ligand: Solvothermal synthesis,crystal structure and properties of {[In(C6H14N2)2]2Sb4S8}Cl2 exhibiting unusual uniaxial negative and biaxial positive thermal expansion

The new compound {[In(C₆H₁₄N₂)₂]₂Sb₄S₈}Cl₂ was prepared under solvothermal conditions reacting InCl₃, Sb and S using 1,2-trans-diaminocyclohexane as solvent and structure directing molecule. The compound crystallizes in the monoclinic space group C2/c with a = 29.0259(12), b = 6.7896(2), c = 24.2023(12) Å, β = 99.524(4)°, V = 4703.9(3) ų. The central structural motif is the thioantimonate(III) anion [Sb₄S₈]^4? acting as a tetradentate ligand thus joining two symmetry related In³⁺ centered complexes. This binding mode was never observed before for the [Sb₄S₈]^4? anion. The optical band gap was determined as 2.03 eV in agreement with the red color of the compound. The thermal decomposition was monitored with in-situ X-ray diffraction experiments. After the emission of the amine molecules an amorphous intermediate is formed followed by the crystallization of InSbS₃ which is stable up to about 590 °C. On further heating, InSbS₃ is destroyed and reflections of γ-In₂S₃ appear being contaminated with some elemental Sb. Temperature dependent in-situ X-ray powder diffractometry performed between 30 and 220 °C reveals an unusual reversible negative and positive thermal expansion. The decrease of the a-axis in the temperature range is about 0.74 Å and the increase of the c-axis ca. 0.54 Å. Interestingly, the b-axis exhibits also a thermal expansion, i.e., a biaxial positive and an uniaxial negative thermal expansion coexist which is very unusual. The relative negative expansion coefficients for the a-axis of ?194 × 10^?6K^?1 (30–120 °C) and ?82 × 10^?6K^?1 (120–220 °C) are in the region of so-called colossal thermal expansion.     

Effect of molecular weight on radiation chemical degradation yield of chain scission of γ-irradiated chitosan in solid state and in aqueous solution

Chitosan A₁, A₂ and A₃ with molecular weight of 471, 207 and 100 kDa respectively, produced from squid pen chitin was degraded by gamma rays in the solid state and in aqueous solution with various doses in air at ambient temperature. Effect of molecular weight on radiation chemical degradation yield of chain scission and degradation rate constants of γ-irradiated chitosan in solid state and in aqueous solution was investigated. The radiation chemical degradation yield G_(s) and degradation rate values were calculated. The molecular weight changes were monitored by capillary viscometry method and the chemical structure changes were followed by UV analysis. The results showed that, the degradation of chitosan was faster in solution, than in solid state. The values of G_(s) in solid state and in aqueous solution were respectively 1.1×10^?8 mol/J and 0.074×10^?7 mol/J for A₁, 4.42×10^?8 mol/J and 0.28×10^?7 mol/J for A₂ and 6.08×10^?8 mol/J and 0.38×10^?7 mol/J for A₃. Degradation rate constants values ranged from 0.41×10^?5 to 2.1×10^?5 kGy^?1 in solid state, whereas in solution they ranged from 13×10^?5 to 68×10^?5 kGy^?1. The chitosan A₃ was more sensitive to radiolysis than A₁ and A₂. The chain scission yield, G_(s) and degradation rate constants seems to be greatly influenced by the initial molecular weight of the chitosan. Structural changes in irradiated chitosan are revealed by the apparition of absorption peaks at 261 and 295 nm, which could be attributed to the formation of carbonyl groups. In both conditions the peak intensity was higher in chitosan A₃ than in A₁ and A₂, the oxidative products decreased with increasing molecular weight of chitosan.     

Studies on the interaction between imidacloprid and human serum albumin: Spectroscopic approach

The interaction between imidacloprid (IMI) and human serum albumin (HSA) was investigated using fluorescence and UV/vis absorption spectroscopy. The experimental results showed that the fluorescence quenching of HSA by IMI was a result of the formation of IMI–HSA complex; static quenching was confirmed to result in the fluorescence quenching. The apparent binding constant K_A between IMI and HSA at three differences were obtained to be 1.51 × 10⁴, 1.58 × 10⁴, and 2.19 × 10⁴ L mol^?1, respectively. The thermodynamic parameters, ΔH° and ΔS° were estimated to be 28.44 kJ mol^?1, 174.76 J mol^?1 K^?1 according to the van’t Hoff equation. Hydrophobic interactions played a major role in stabilizing the complex. The distance r between donor (HSA) and acceptor (IMI) was obtained according to fluorescence resonance energy transfer. The effect of IMI on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy CD and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.     

Demonstration of cavity enhanced FTIR spectroscopy using a femtosecond laser absorption source

A proof of principle experiment was performed by recording the cavity enhanced absorption spectrum of the weak b–X transition of molecular oxygen in the atmosphere using a Ti:Sa femtosecond laser as an absorption source and a high resolution continuous scan Fourier transform interferometer. The cavity was mode matched and either continuously scanned or stabilized at the so-called magic point. An optimal rms noise equivalent absorption of 3 × 10^?7 cm^?1 Hz^?1/2 was reached in the latter case, corresponding to α_min = 3 × 10^?7 cm^?1.     

Synthesis,characterization and anti-bacterial activity of divalent transition metal complexes of hydrazine and trimesic acid

Transition metal complexes of trimesic acid and hydrazine mixed-ligands with a general formula M(Htma)(N₂H₄)₂, where, M = Mn, Co, Ni, Cu and Zn; H₃tma = trimesic acid, have been prepared and characterized by elemental, structural, spectral and thermal analyses. For the complexes, the carboxylate ν_asym and ν_sym stretchings are observed at about 1626 and 1367 cm^?1 respectively, with Δν between them of ～260 cm^?1, showing the unidentate coordination of each carboxylate group. The hydrazine moieties are present as bridging bidentates. Electronic and EPR spectral studies suggest an octahedral geometry for the complexes. All these complexes show three steps of decomposition in TGA/DTA. SEM images of CuO and MnO residues obtained from the complexes show nano-sized clusters suggesting that the complexes may be used as precursors for nano-CuO and nano-MnO preparation. The antimicrobial activities of the prepared complexes, against four bacteria have been evaluated.