Dissolution kinetics of silver metal nanoparticles in their reaction with nitric acid in an reverse micelle solution of AOT

The dissolution of silver nanoparticles in their reaction with aqueous HNO₃ solubilized to an reverse micelle solution of sodium bis(2-ethylhexyl)sulfosuccinate in decane is studied spectrophotometrically. A physicochemical model is advanced for quantifying the process kinetics on th basis of the following autocatalytic scheme: Ag⁰ + H⁺ + NO ₃ ^? → Ag⁺ + products (k ₁), and Ag⁰ + Ag⁺ + NO ₃ ^? → 2Ag⁺ + products (k ₂). The effective rate constant k ₂ decreases with decreasing solubilization capacity V _S/V _O (where V _S is the volume of the solubilized dispersed aqueous phase and V _O is the volume of the micelle solution); the solubilization capacity determines the size of the micelle cavities in which the reaction between Ag⁰ and HNO₃ occurs: k ₂ = 74 (V _S/V _O) · 100% ≈ 3.8%), 41 (2.9), and 35 (2.0) L/(mol s). The effective constant k ₁ is determined with a high uncertainty; the effect of V _S/V _O on k ₁ has the opposite tendency.     

Catalytic effects of cationic nanoparticle (CTABr/NaX/H<Subscript>2</Subscript>O,X = Cl,Br) for the piperidinolysis of phenyl salicylate ions

The expression of pseudo-second-order rate constants (k _X) for cationic nanoparticle (CN) [CTABr/NaX/H₂O, X = Br, Cl, CTABr = cetyltrimethylammonium bromide] catalyzed piperidinolysis-ionized phenyl salicylate (PSa^–), at constant [CTABr]_T, 0.1 M piperidine (Pip), and 35°C, were calculated from the relationship: k _obs = (k ₀ + k _X[NaX])/(1 + K ^X/S[NaX]), in which k ₀, k _X, and K ^X/S are constant kinetic parameters and k _obs represents the pseudo-first-order rate constant for Pip reaction with phenyl salicylate ion in the presence of CN. The source of the large catalytic effect of CN catalyst was shown to be due to the transfer of PSa^– from pseudo-phase of the CNs to the bulk aqueous phase through X^–/PSa^– ion exchange at the surface of the CNs.     

Theoretical and experimental study of the catalytic cathodic stripping square-wave voltammetry of chromium species

The electrocatalytic mechanism of Cr(III) reduction in the presence of diethylenetriaminepentaacetic acid (DTPA) and nitrate ions is studied theoretically and experimentally by using stripping square-wave voltammetry (SWV). Experimental curves are in excellent agreement with theoretical profiles corresponding to a catalytic reaction of second kind. This type of mechanism is equivalent to a CE mechanism, where the chemical reaction produces the electroactive species. Accordingly, the reaction of Cr(III)–H₂O–DTPA and \( {\mathrm{NO}}_3^{-} \) would produce the electroactive species Cr(III)–NO₃–DTPA and this last species would release \( {\mathrm{NO}}_2^{-} \) to the solution during the electrochemical step. In this regard, the complex of Cr(III)–DTPA would work as the catalyzer that allows the reduction of \( {\mathrm{NO}}_3^{-} \) to \( {\mathrm{NO}}_2^{-} \). Furthermore, it was found that the electrochemical reaction is quite irreversible, with a constant of k _s?=?9.4?×?10^?5 cm s^?1, while the constant for the chemical step has been estimated to be k _chem?=?1.3?×?10⁴ s^?1. Considering that the equilibrium constant is K?=?0.01, it is possible to estimate the kinetic constants of the chemical reaction as k ₁?=?1?×?10² s^?1 and k _?1?=?1.29?×?10⁴ s^?1. These values of k ₁ and k _?1 indicate that the exchange of water molecules by nitrate is fast and that the equilibrium favors the complex with water. Also, a value for the formal potential E°’?≈??1.1 V was obtained. The model used for simulating experimental curves does not consider the adsorption of reactants yet. Accordingly, weak adsorption of reagents should be expected.     

Von den Größen der chemischen Kinetik

An Hand der denkbar einfachsten chemischen Reaktion\(A\underset{2}{\overset{1}{\longleftrightarrow}}B\) wird gezeigt, daß die Geschwindigkeitskoeffizienten (Gk)k ₁ undk ₂ sowie ihr Quotient, also die Gleichgewichtskonstante (Glk)K=k ₁/k ₂,keine Eigene xistenz beistzen. Sie werden erst dann physikalischwinklich und sinnvoll, wenn sie mit ihrenStoffgrößen gepaart sind, ink ₁ A undk ₂ B und Geschwindigkeiten, inKA=B zum Gleichgewichte.     

Synthesis,structural and spectroscopic properties of asymmetric Schiff bases derived from 2,3-diaminopyridine

Two Schiff base derivatives, 4-(2-amino-3-pyridyliminomethyl)phenol (I) and 3-(2-amino-3-pyridyliminomethyl)nitrobenzene (II), were synthesised and characterised by spectroscopy. The structure of I was determined by single crystal X-ray diffraction studies. The asymmetric Schiff base derived from 2,3-diaminopyridine selectively recognise transition and heavy metal cations, and some anion. Ligands I and II form stable complexes with Cu²⁺, Zn²⁺, Pb²⁺, Al³⁺ whereas ligand I also binds F~ ions. The stoichiometry for the host: cation is 1: 1 and 2: 1. The addition of F~ ion in CH₃CN to ligand I causes a colour change of the solution from colourless to yellow. The binding behaviour of ligand I towards several ions was investigated using density functional theory calculations.     

Crystallization study of Se<Subscript>86</Subscript>Sb<Subscript>14</Subscript> glass

The present study concerns with high-accuracy determination of crystallization activation energy (\(E_{\text{c}}\)), the frequency factor (\(k_{0}\)), the kinetic exponent (n) for Se₈₆Sb₁₄ glass. Different three methods have been used to investigate the \(E_{\text{c}} \,{\text{and}}\,k_{0 }\) values. It was found that the deduced value of k ₀ based on Kissinger’s method is too small compared with the others. Therefore, it can’t be used to investigate k ₀ value. Where \(E_{\text{c}} \,{\text{and}}\,k_{0}\) values are already known, the overall reaction rate \(k = k_{0 } { \exp }\left( { - E_{\text{c}} /\left( {R \cdot T} \right)} \right)\) at any temperature can be calculated. Now, Avrami’s equation (\(\chi = 1 - { \exp }\left( { - \left( {kt} \right)^{\text{n}} } \right)\)) contains only one unknown which is the kinetic exponent (n). This method enables us to determine n value without any approximations. The values’ crystallization fraction \((\chi_{\text{th}} )\) that theoretically calculated is the same as that experimentally investigated \((\chi_{{{ \exp } .}} )\).     

Development and implementation of Høgdahl convention and Westcott formalism for k<Subscript>0</Subscript>-INAA application at Malaysian Nuclear Agency reactor

The present work shows the development of k₀-instrumental neutron activation analysis (k₀-INAA) method at the Malaysian Nuclear Agency research reactor. To use the k₀-INAA method, two formalisms were regulated according to 1/ν and non-1/ν (n, γ) reaction nuclides. The reactor neutron spectrum parameters, the thermal to epithermal neutron flux ratio (f), the epithermal neutron flux shape factor (α) were measured using the bare bi-isotopic monitor and bare triple monitor methods, respectively, based on the Høgdahl convention. In addition, the modified spectral index \( r(\alpha )\sqrt {T_{n} /T_{0} } \), the Westcott \( g_{Lu} (T_{n} ) \) factor and the absolute neutron temperature T _n parameters were determined using the Westcott formalism. ¹⁷⁶Lu was used as non- 1/ν monitor while ¹⁹⁷Au, ⁹⁶Zr and ⁹⁴Zr were used as 1/ν monitors. The average values of \( r(\alpha )\sqrt {T_{n} /T_{0} } ,\,g_{Lu} (T_{n} ) \) and T _n were determined to be 0.1795 ± 0.0044, 1.9729 ± 0.0234 and 50.12 ± 3.21°C, respectively. The accuracy of the method was evaluated by analysing IAEA-Soil 7, IAEA-SL 1, NBS SRM 1633A-1 and IAEA-Soil 375 as reference materials. The results show an acceptable level of consistency.     

Chlorokomplexe von 3 d5-Ionen in nichtwäßrigen Lösungen

The chloro systems of Mn²⁺ and Fe³⁺ were investigated in acetonitrile (AN), propanediole-1,2-carbonate (PDC) and trimethylphosphate (TMP) by spectrophotometric, potentiometric and conductometric methods. The following coordination forms seem to be present: MnCl₂ (inAN, PDC andTMP), [MnCl₄]^2? (tetrahedral inAN, octahedral inTMP), [MnCl₆]^4? (octahedral inPDC andTMP); [FeCl]²⁺ (tetrahedral inAN andPDC), [FeCl₂]⁺ (tetrahedral inTMP), FeCl₃ (tetrahedral inAN andPDC), [FeCl₄]^? (tetrahedral inAN, PDC andTMP).     

Chlorokomplexe von Ti(III), V(III) und Cr(III) in Propandiol-1,2-carbonat und Trimethylphosphat

Addition of chloride ions to the hexasolvated ions of Ti(III), V(III) and Cr(III) in propandiol-1,2-carbonate (PDC) and trimethylphosphate (TMP) may lead to the following complexes: [TiCl]²⁺ (inPDC), [TiCl₂]⁺ (inTMP), TiCl₃ (inPDC andTMP, low solubility inTMP), [TiCl₄]^? (inPDC andTMP?), [TiCl₆]^3? (inPDC); [VCl]²⁺ (inPDC andTMP), VCl₃ (inPDC andTMP, low solubility inTMP), [VCl₄]^? (inPDC); [CrCl]²⁺ (inTMP), [CrCl₂]⁺ (inPDC), CrCl₃ (inPDC andTMP), [CrCl₄]^? (inPDC).     

Interaction Between an Active Pharmaceutical Ingredient Ionic Liquid Benzalkonium Salicylate and Small Biomolecules in Aqueous Solution: UV Absorption,Conductivity, and Volumetric Study

UV absorption spectroscopy, electrical conductivity and density experiments have been used to investigate the interactions of some small biomolecules (amino acids/dipeptides) with an active pharmaceutical ingredient in ionic liquid form (API-IL), benzalkonium salicylate (BaSal), in aqueous solution. A number of useful parameters, such as critical micellar concentration (cmc), aggregation number (N_agg) and limiting molar conductivity (Λ₀) of BaSal, standard partial molar volumes (\(V_{2,\phi }^{ \circ }\)), corresponding volumes of transfer from water to aqueous BaSal solutions (Δ_trV^o), standard partial molar expansibilities (\(E_{\phi }^{ \circ }\)), hydration number (n_H) of small biomolecules, as well as the binding constants (K_b) for small biomolecule–BaSal complexes have been evaluated. The dependence of the properties on concentration, temperature and alkyl chain length of amino acids/dipeptides is examined. The results are used to identify the solute–solvent physicochemical interactions occurring in the studied systems.     

Synthesis,crystal structure,and kinetics of thermal decomposition of the Zn(II) complex with vanillin

A complex [Zn(C₈H₇O₃)₂(H₂O)₂] (C₈H₈O₃ is vanillin) has been synthesized and characterized by IR, elemental analysis, and X-ray diffraction single-crystal analysis. The crystals are monoclinic, space group C2/c, a = 22.236(8) Å, b = 10.594(2) Å, c = 7.8190(16) Å, α = 89.90(3)°, β = 106.87(4)°, γ = 89.99(3)°, V = 1762.6(8) ų, Z = 4, F(000) = 832, S = 1.079, ρ _c = 1.521g cm^?3, R = 0.0221, R _w = 0.0604, μ = 1.433 mm^?1. The Zn²⁺ ion is six-coordinated with a distorted octahedron geometry. The complex forms a three-dimensional network through intermolecular hydrogen bonds. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal conditions by the TG and DTG methods. The kinetic equation can be expressed as dα/dt = Ae^?E/RT 2(1 ? α)[1 ? ln(1 ? α)]^1/2. The kinetic parameters (E, A), activation entropy ΔS ^≠, and activation free-energy ΔG ^≠ were also gained.     

Chloro- und Azidokomplexe des Vanadyl(IV)-Ions in Acetonitril,Propandiol-1,2-carbonat,Trimethylphosphat und Dimethylsulfoxid

The formation of chloro- and azidocomplexes of VO²⁺(IV) is investigated in acetonitrile (AN), propanediol-1,2-carbonate (PDC), trimethyl phosphate (TMP) by spectrophotometric, potentiometric and conductometric methods. The following coordination forms are indicated: [VOCl]⁺ inAN, PDC andDMSO), [VOCl₂] (inAN, PDC andTMP), [VOCl₃]^? (inPDC andTMP[?]), [VOCl₄]^2? (inAN, PDC andTMP); [VON₃]⁺ (inAN, PDC andDMSO), [VO(N₃)₂] (inAN, PDC, TMP andDMSO), [VO(N₃)_2+n]^n? (inAN, PDC, TMP andDMSO). The results are interpreted by the donor numbers and sterical properties of the solvent molecules.     

How does the extent of substitution of methane with chlorine influence the mechanism and kinetics of the reactions between chloromethanes and atomic chlorine

A theoretical investigation of the reaction mechanism and kinetics of the reaction between chloromethanes CH_4–xCl_x (x = 1–3) and chlorine atoms was performed. The height of the reaction barrier was found to decrease with the degree of substitution of chloromethanes with atomic chlorine. A direct dynamics method was employed to study the kinetic nature of these hydrogen-abstraction reactions. The sequence of calculated reaction rate coefficients is: k(CH₃Cl + Cl) < k(CH₂Cl₂ + Cl) < k(CHCl₃ + Cl).     

Metal-sensitive and thermostable trypsin from the crevalle jack (<Emphasis Type="Italic">Caranx hippos</Emphasis>) pyloric caeca: purification and characterization

Background

Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.

Results

A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-_DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K _m , k_cat, and k _cat /K _m values using BApNA as substrate were 0.689 mM, 6.9 s^-1, and 10 s^-1 mM^-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd²⁺, Al³⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ at 1 mM, revealing high sensitivity of the enzyme to metal ions.

Conclusions

Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.

     

Aromaticity of Bare Iridium Trimers and Ir3M0/+ and $$\rm{Ir}_3M_2^{+/3+}$$ (M = Li,Na, K,and Be,Ca) Bimetallic Clusters

The structural stabilities, bonding nature, electronic properties, and aromaticity of bare iridium trimers \(\rm{Ir}_3^{+/-}\) with different geometries and spin multiplicities are studied at the DFT/B3LYP level of theory. The ground state of the \(\rm{Ir}_3^{+}\) cation is found to be the ³A₂ (C_2v) triplet state and the ground state of the \(\rm{Ir}_3^{-}\) anion the ⁵A₂ (C_2v) quintet state. A detailed molecular orbital (MO) analysis indicates that the ground-state \(\rm{Ir}_3^{+}\) ion (C_2v, ³A₂) possesses double (σ and partial δ) aromaticity as well as the ground-state \(\rm{Ir}_3^{-}\) ion (C_2v, ⁵A₂). The multiple d-orbital aromaticity is responsible for the totally delocalized three-center metal-metal bond of the triangular Ir₃ framework. \(\rm{Ir}_3^{-}\) (C_2v, ¹A₁) structure motif is perfectly preserved in pyramidal Ir₃M^0/+ (C_s, ¹A′) and bipyramidal \(\rm{Ir}_3M_2^{+/3+}\) (C_2v, ¹A₁) (M = Li, Na, K and Be, Ca) bimetallic clusters which also possess the corresponding d-orbital aromatic characters.     

Random packing of monoatomic structures

The dependence of the first coordination number k _n on the packing factor k _y is obtained for four cubic structures: fcc, bcc, simple cubic, and diamond. The k _n (k _y ) dependence is described by a third-degree polynomial k _n = ?71.76782 + 467.78914 k _y ? 925.48451 k _y ² + 603.01146 k _y ³ with the confidence factor R _d = 1. The k _n (k _y ) function has an N loop with a maximum at k _n = 6.32; k _y = 0.454 and a minimum at k _n = 5.84; k _y = 0.573. The tangents intersect the k _n (k _y ) curve at extrema at k _y = 0.4 and k _y = 0.625. Around the N loop, i.e., at 5.84 ≤ k _n ≤ 6.32 and 0.4 ≤ k _y ≤ 0.625, two or three packing factors correspond to a certain value of the coordination number. Therefore, this range of the k _n and k _y values can be defined as a “random packing” region. Estimations presented here agree well with the results of calculations, both geometric and numerical. For monoatomic solids with the random packing parameters, the difference between the specific volumes of the solid and liquid phases is insignificant. The dilatancy effect is possible in the region where ?k _n / ?k _y ≤ 0.     

Sc<Subscript>2</Subscript>S<Subscript>3</Subscript>–Cu<Subscript>2</Subscript>S phase diagram

A phase diagram is constructed for the Sc₂S₃–Cu₂S system. The system forms two incongruently melting complex sulfides: hexagonal CuScS₂ (1Cu₂S: 1Sc₂S₃): a = 0.3734 nm, c = 0.6102 nm, space group P3m1, Т_m = 1635 K, ΔH_m = 1670 kJ/mol; and cubic CuSc₃S₅ (1Cu₂S: 3Sc₂S₃), a = 1.0481 nm, space group Fd3m, Т_m = 1835 K. In the 45–62 mol % Cu2S solid solution (ss) range, there is a singular point corresponding to the composition of compound CuScS₂ (50 mol % Cu₂S). The Sc₂S₃-based solubility at 1070 K is 14 mol % Cu₂S. In the γ-Cu₂S-based solid solution range, there is a peritectic point at 7 mol % Sc₂S₃, 1423 K.     

Kinetics of thermal reaction HOCl ⇄ H(<Superscript>2</Superscript><Emphasis Type="Italic">S</Emphasis>) + OCl(<Emphasis Type="Italic">X</Emphasis><Superscript>2</Superscript>Π<Subscript><Emphasis Type="Italic">i</Emphasis></Subscript>) in gas phase

The kinetics of gas reaction \(HOCl\underset{{k_r }}{\overset{{k_f }}{\longleftrightarrow}}H(^2 S) + OCl(X^2 \Pi _i )\) was analyzed by the MP4 method. In the temperature range of 100–373 K the rate constants k _f and k _r and equilibrium constant K were changed from 1.10 × 10^?220 to 1.17 × 10^?52 s^?1, from 2.89 × 10^?16 to 1.68 × 10^?5s^?1 and from 3.80 × 10^?205 to 6.96 × 10^?48 respectively. In the above temperature range, the activation energy of the forward reaction (E _f) is 105.05 kcal/mol. In the same temperature interval there are two kinetic domains for the reverse reaction with activation energies (E _r1 = 5.53 kcal/mol when T is 100–273 K and E _r2 = 14.50 kcal/mol when T is 273–373 K, respectively.     

Kinetics and mechanism of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II) in aqueous and micellar media

The kinetics of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II), \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) has been studied in aqueous, cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) media at 25, 35 and 45 °C under pseudo-first-order conditions, i.e. \( [ {\text{OH}}^{ - } ]\gg [{\text{Fe(PDT)}}_{ 3}^{2 + } ] \). The reactions are first order in both of substrate \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) and hydroxide ion. The rates decrease with increasing ionic strength in aqueous and CTAB media, whereas SDS medium shows little ionic strength effect. The rate also increases with CTAB concentration but decreases with SDS. The specific rate constant, k and thermodynamic parameters (E _a, ΔH ^#, ΔS ^# and ΔG ^#) have also been evaluated. The near equal values of ΔG ^# obtained in aqueous and CTAB media suggest that these reactions occur essentially by the same mechanism such that \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) reacts with OH^? in the rate-determining step. The ionic strength effect in SDS medium suggests that the rate-determining step involves an ion and a neutral species. The results in this study are compared with those obtained for other iron(II)-bipyridine complexes.     

Synthesis and crystal structure of a Cu(II) complex Cu<Subscript>2</Subscript>(Endc)<Subscript>2</Subscript>(Bipy)<Subscript>2</Subscript> and its photoluminescence properties

A novel Cu(II) complex Cu₂(Endc)₂(Bipy)₂ has been synthesized by the reaction of Cu(NO₃)₂ · 3H₂O, Endc (endo-norbornene-cis-5,6-dicarboxylic acid), and Bipy (2,2-bipyridine) at room temperature. Elemental analysis, IR spectra, and X-ray single-crystal diffraction were carried out to determine the composition and crystal structure. Crystal data for this complex: triclinic, P \(\bar 1\) with a = 9.0373(10), b = 10.1637(11), c = 10.5574(12) Å, α = 65.78(1)°, β = 72.32(2)°, β = 73.23(2)°, Z = 1, V = 827.46(16) ų, ρ _c = 2.160 g/cm³, F(000) = 410.0, R = 0.0483 and wR = 0.0958 independent reflections for 4468 observed ones (I > 2 σ(I)).The Cu²⁺ ion is coordinated by two nitrogen atoms from the Bipy molecule and three oxygen atoms from two Endc, giving a distorted squarepyramidal coordination geometry. Two neighboring Cu²⁺ ions are bridged by a pair of bimonodentate carboxyl groups of different Endc acids, giving a centrosymmetrical binuclear structure which a Cu…Cu distance of 3.2946 Å. The photoluminescence properties of the complex were studied at room temperature. The complex displays an obvious photoluminescent emission upon excitation at 390 nm in the solid state.