Dissolved air flotation for treating wastewater of the nuclear industry: preliminary results

Preliminary testing of dissolved air flotation (DAF) for wastewater treatment is presented. A combined coagulation-flocculation/DAF column system is used to remove oil and ⁶⁰Co from nuclear industry wastewater. In this work, operational conditions and coagulant/flocculant concentrations are optimized by varying pH. Determinations of air-solids ratio (G/S), retention time (θ), pressure (P), volume of depressurized air–water mixture (V), turbidity and ⁶⁰Co concentrations are reported. The effect of the treatment on the efficiency of separation of oily residues is also discussed. The results establish that the coagulant/flocculant system, formed by a modified polyamine (25 mgL^?1) and a slightly cationic polyacrylamide (1.5 mgL^?1), under specific operational conditions (pH = 7, mixing intensity Im₁ = 300 s^?1 and Im₂ = 30 s^?1), allowed the destabilization of colloidal matter, resulting in resistant flocs. It was concluded that by using G/S = 0.3, θ = 15 min, P = 620 kPa and V = 0.0012 m³, the greatest percentage removals of oil, turbidity, total cobalt and ⁶⁰Co were obtained. These preliminary results then show that dissolved air flotation represents a good alternative for treatment of nuclear industry wastewater contaminated with radionuclides.     

Sensitive detection of sulfanilamide by redox process electroanalysis of oxidation products formed in situ on glassy carbon electrode

This paper reported a simple method for sulfanilamide determination by redox process electroanalysis of oxidation products (SFDox) formed in situ on glassy carbon electrode. The CV experiments showed a reversible process after applied E _acc = + 1.06 V and t _acc = 1 s, in 0.1 mol L^?1 BRBS (pH = 2.0) at 50 mV s^?1. Different voltammetric scan rates (from 10 to 450 mV s^?1) suggested that the redox peaks of SFDox on the glassy carbon electrode (GCE) is an adsorption-controlled process. Square-wave voltammetry (SWV) method optimized conditions showed a linear response to SFD from 3.00 to 250.0 μmol L^?1 (R = 0.998) with a limit of detection of 0.638 μmol L^?1 and limit of quantification of 2.0 μmol L^?1. The developed the SWV method was successfully used in the determination of SFD pharmaceutical formulation and human serum. The SFD quantification results in pharmaceutical obtained by SWV-GCE were comparable to those found by official analytical protocols.     

Voltammetric determination of mercury(II) using a modified pencil graphite electrode with 4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl

A sensitive and selective method for determination of mercury(II) with “4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl (TKO)-modified pencil graphite electrode” was developed. All factors affecting determination process were optimized. Differential pulse voltammetry with 4-(4-methylphenyl aminoisonitrosoacetyl)biphenyl-modified electrode showed a linear response between 1.0 × 10^?5 and 1.0 × 10^?3 M (R ² = 0.9994). The detection limit of this electrode was found as 5.85 × 10^?7 M (S/N = 3). The effects of different cations on the determination of mercury(II) were investigated and found that modified electrode is highly selective. The developed method was applied for mercury determination in different water samples.     

Electrochemical gating of single osmium molecules tethered to Au surfaces

The electrochemical study of electron transport between Au electrodes and the redox molecule Os[(bpy)₂(PyCH₂ NH₂CO-]ClO₄ tethered to molecular linkers of different length (1.3 to 2.9 nm) to Au surfaces has shown an exponential decay of the rate constant k _ET ⁰ with a slope β = 0.53 consistent with through bond tunneling to the redox center. Electrochemical gating of single osmium molecules in an asymmetric tunneling nano-gap between a Au(111) substrate electrode modified with the redox molecules and a Pt-Ir tip of a scanning tunneling microscope was achieved by independent control of the reference electrode potential in the electrolyte, E _ref ? E _s, and the tip-substrate bias potential, E _bias. Enhanced tunneling current at the osmium complex redox potential was observed as compared to the off resonance set point tunneling current with a linear dependence of the overpotential at maximum current vs. the E _bias. This corresponds to a sequential two-step electron transfer with partial vibration relaxation from the substrate Au(111) to the redox molecule in the nano-gap and from this redox state to the Pt-Ir tip according to the model of Kuznetsov and Ulstrup (J Phys Chem A 104: 11531, 2000). Comparison of short and long linkers of the osmium complex has shown the same two-step ET (electron transfer) behavior due to the long time scale in the complete reduction-oxidation cycle in the electrochemical tunneling spectroscopy (EC-STS) experiment as compared to the time constants for electron transfer for all linker distances, k _ET ⁰.     

Electrochemical sensing of <Emphasis Type="SmallCaps">D</Emphasis>-penicillamine on modified glassy carbon electrode by using a nanocomposite of gold nanoparticles and reduced graphene oxide

A new electrochemical sensor was developed for determination of D-penicillamine using glassy carbon electrode which had been modified by gold nanoparticles–reduced graphene oxide nanocomposite (AuNPs/RGO/GCE) in aqueous solution. Cyclic voltammetry, transmission electron microscopy and electrochemical impedance spectroscopy were used for characterization of the modified electrode. The results indicated that the kinetic of oxidation reaction of D-penicillamine at the surface of the electrode was controlled by both diffusion and adsorption processes. In 0.1 mol L^?1 phosphate buffer (pH 2.0), the oxidation current increased linearly with concentration of D-penicillamine with a linear range of 5.0 × 10^?6 to 1.1 × 10^?4 mol L^?1 and regression coefficient of R ² = 0.9972. Theoretical detection limit, defined based on 3σ of the blank signal (n = 9) divided by the slope of the linear regression equation, was 3.9 × 10^?6 mol L^?1 D-penicillamine using differential pulse voltammetry. The developed method was successfully applied to the determination of D-penicillamine in pharmaceutical formulation and blood serum samples.     

Spectroscopic and electrical characterization of <Emphasis Type="Italic">α</Emphasis>,<Emphasis Type="Italic">γ</Emphasis>-bisdiphenylene-<Emphasis Type="Italic">β</Emphasis>-phenylallyl radical as an organic semiconductor

The semiconductor properties of the earliest known stable radical, α,γ-bisdiphenylene-β-phenylallyl radical (Koelsch radical, 1^?) were assessed using spectroscopic and electrical techniques. This radical undergoes reversible redox processes, and it has low redox potentials. In addition, 1^? possesses long wavelength absorption bands, owing to the existence of a singly-occupied molecular orbital whose energy level lies between those of the HOMO and LUMO. A spin-coated thin-film of 1^? displays photocurrent and an electron mobility of 6.3 × 10^?7 cm² V^?1 s^?1 on a trially-fabricated organic field effect transistor.     

Fabrication and characterisation of a mixed oxide-covered mesh electrode composed of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> and its capability of generating hydroxyl radicals during the oxygen evolution reaction in electrolyte-free water

A mixed oxide-covered mesh electrode composed of NiCo₂O₄ (MOME-NiCo₂O₄) was prepared on a stainless-steel substrate using thermal decomposition (slow-cooling rate method). Surface, bulk and electrochemical properties of MOME were studied using different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) with determination of the electrochemical porosity (?) and morphology factor (φ) parameters, quasi-stationary polarisation curves (PC) and electrochemical impedance spectroscopy (EIS). SEM images revealed a good coverage of the metallic wires by a compact oxide layer (absence of cracks). XRD analysis confirmed the formation of the spinel NiCo₂O₄ with the presence of NiO. The ‘in situ’ surface parameters denoted as ? and φ exhibited values of 0.39 and 0.33, respectively, revealing that the electrochemically active surface area is mainly confined to the ‘outer/external’ surface regions of the oxide layer. The PC was characterised by two Tafel slopes distributed in the low (b ₁ = 46 mV dec^?1) and high (b ₂ = 59 mV dec^?1) overpotential domains. The corresponding apparent exchange current densities were j ₀₍₁₎ = (3.43 ± 0.11) × 10^?6 A cm^?2 and j ₀₍₂₎ = (6.70 ± 0.08) × 10^?6 A cm^?2, respectively. The EIS study accomplished in the low-overpotential domain revealed a Tafel slope (b ₁) of 51 mV dec^?1. According to the spin-trapping reaction using N,N-dimethyl-p-nitrosoaniline (RNO), the MOME-NiCo₂O₄ electrode exhibited good performance for the generation of weakly adsorbed hydroxyl radicals (HO^?) during the OER in electrolyte-free water.     

New acetaminophen amperometric sensor based on ferrocenyl dendrimers deposited onto Pt nanoparticles

In this work, the electrocatalytical properties and kinetic characteristics of new electrodes modified with Pt nanoparticles (PtNPs) and three generations of ferrocene functionalized dendrimers have been investigated as new acetaminophen amperometric sensors. The catalytic synergy of PtNPs with the ferrocene groups is discussed in relation to the ferrocenyl dendrimer generation and their properties. The modified electrodes show excellent catalytic responses toward the oxidation of acetaminophen, with good reproducibility. The overpotential for oxidation of acetaminophen at pH 7 is decreased, and the current response significantly enhanced. The best dendrimer/PtNPs/Pt electrode shows several wide linear concentration ranges for the acetaminophen oxidation from 0 to beyond 17 mM. At 0.5 V vs. SCE, the first linear range extends from 0 to 100 μM (y = 0.0131x ? 0.0028; R ² = 0.9996) and the last from 10 mM to at least 17 mM (y = 0.0024x + 26.6; R ² = 0.9977). This fact turns the developed acetaminophen sensor in the device with the widest application range. In addition, the sensor allows measuring acetaminophen in the presence of interfering substances as glucose, dopamine, uric acid, and ascorbic acid, and it has been successfully applied to the determination of acetaminophen in three pharmaceutical formulations.     

Growth Parameters,Photosynthetic Performance,and Biochemical Characterization of Newly Isolated Green Microalgae in Response to Culture Condition Variations

This work aimed to characterize two native microalgal strains newly isolated from South Mediterranean areas and identified as Chlorella sorokiniana ES3 and Neochloris sp. AM2. The growth properties and biochemical composition of these microalgae were evaluated in different culture media (Algal, BG-11, f/2, and Conway). Among the tested media, nitrate- and phosphate-rich Algal medium provided the maximum biomass productivities (85.5 and 111.5 mg l^?1 day^?1 for C. sorokiniana and Neochloris sp., respectively), while the nitrate- and phosphate-deficient f/2 medium resulted in the highest lipid productivities (24.1 and 35.8 mg l^?1 day^?1 for C. sorokiniana and Neochloris sp., respectively). The physiological state of both microalgae was investigated under different light and temperature levels using the pulse amplitude-modulated fluorometry. The better photosynthetic efficiency of C. sorokiniana was obtained at 23 °C with a light saturation of 156 μE m^?2 s^?1, while that of Neochloris sp. was achieved at 15 °C with a light saturation of 151 μE m^?2 s^?1. The analysis of fatty acid profile and biodiesel parameters revealed that C. sorokiniana, cultivated in Algal and f/2 media, can be considered as a suitable candidate for high-quality biodiesel production.     

High-sensitive amperometric hydrazine sensor based on chemically synthesized zinc nitroprusside nanoparticle-supported carbon ceramic electrode

Zinc nitroprusside (ZnNP) nanoparticles were fabricated at the surface of zinc powder-doped carbon ceramic electrode (CCE) by a chemical derivatization process. This modified electrode was characterized by scanning electron microscopy, atomic force microscopy and cyclic voltammetry techniques. The charge transfer rate constant (k _s) and charge transfer coefficient (α) were calculated for the electron exchange reaction of the ZnNP thin film. The ZnNP nanoparticle-modified CCE (ZnNP|CCE) showed good electrocatalytic activity toward hydrazine oxidation. The limit of detection (S/N = 3) and sensitivity were found to be 0.16 µM and 0.21 µA/µM, respectively. The mechanism of hydrazine electrooxidation at the electrode surface was studied. Finally, the ZnNP|CCE was successfully used for the determination of trace amount of hydrazine in different spiked and real samples.     

Direct electrochemistry of glucose oxidase and sensing glucose using a screen-printed carbon electrode modified with graphite nanosheets and zinc oxide nanoparticles

We have studied the direct electrochemistry of glucose oxidase (GOx) immobilized on electrochemically fabricated graphite nanosheets (GNs) and zinc oxide nanoparticles (ZnO) that were deposited on a screen printed carbon electrode (SPCE). The GNs/ZnO composite was characterized by using scanning electron microscopy and elemental analysis. The GOx immobilized on the modified electrode shows a well-defined redox couple at a formal potential of ?0.4 V. The enhanced direct electrochemistry of GOx (compared to electrodes without ZnO or without GNs) indicates a fast electron transfer at this kind of electrode, with a heterogeneous electron transfer rate constant (K_s) of 3.75 s^?1. The fast electron transfer is attributed to the high conductivity and large edge plane defects of GNs and good conductivity of ZnO-NPs. The modified electrode displays a linear response to glucose in concentrations from 0.3 to 4.5 mM, and the sensitivity is 30.07 μA mM^?1 cm^?2. The sensor exhibits a high selectivity, good repeatability and reproducibility, and long term stability. Figure

Graphical representation for the fabrication of GNs/ZnO composite modified SPCE and the immobilization of GOx     

Synthesis of flower-like cuo hierarchical nanostructures as an electrochemical platform for glucose sensing

Flower-like CuO hierarchical nanostructures were synthesized on copper foil substrate through a simple wet chemical route in alkaline media at room temperature. SEM images collected at different reaction times revealed the transformation of initially formed Cu(OH)₂ nanowires to flower-like CuO nanostructures. The hierarchical structure of the as-prepared CuO showed high electrocatalytic activity towards the oxidation of glucose making it a promising electrode material for the development of non-enzymatic glucose sensor. The amperometric sensor exhibited a wide linear response to glucose ranging from 4.5 × 10^?5 to 1.3 × 10^?3 mol L^?1 (R ² = 0.99317) at fixed potential of 0.3 V. The detection limit was 6.9 × 10^?6 mol L^?1 (LOD = 3σ/s) with a sensitivity of 1.71 μA μmol^?1 cm^?2. Moreover, the developed sensor offers a fast amperometric response, good selectivity and stability.     

The sol–gel chromium-modified V<Subscript>6</Subscript>O<Subscript>13</Subscript> as a cathodic material for lithium batteries

A new V₆O₁₃-based material has been synthesized via the sol–gel route. This sol–gel mixed oxide has been obtained from an appropriate heat treatment of the chromium-exchanged V₂O₅ xerogel performed under reducing atmosphere. This new compound, with the chemical formula Cr_0.36V₆O_13.50, exhibits a monoclinic structure (C2/m) with the following unit cell parameters, a=11.89 Å, b=3.68 Å, c=10.14 Å, β=101.18°. The electrochemical characterization of this compound has been performed using galvanostatic discharge–charge experiments in the potential range 4–1.5 V and completed by ac impedance spectroscopy measurements. It exhibits a specific capacity of about 370 mAh g^?1, which makes the compound Cr_0.36V₆O_13.50 the best one in the V₆O₁₃-based system: 85% of the initial capacity (315 mAh g^?1) after the 35th cycle is still available at C/25 without any polarization. From impedance spectroscopy, a high kinetics of Li transport (D _Li=1.8×10^?9 cm² s^?1) is found at mid-discharge.     

Synthesis,crystal structure and fungicidal activity of 1-(4-chlorophenyl)-2-(5-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-phenyl-4H-1,2,4-triazol-3-ylthio)ethanone

A novel bis-heterocyclic compound was synthesized and characterized. The crystal structure of the title compound (C₂₂H₂₀ClN₅OS, Mr = 437.94) has been determined by single-crystal X-ray diffraction. The crystal is of triclinic, space group P-1 with a = 8.646 (2), b = 9.148 (3), c = 14.540 (4) Å, α = 94.422 (4), β = 98.500 (4), γ = 102.823 (4)°, V = 1101.8 (5) Å³, Z = 2, F(000) = 312, Dc = 1.320 g/cm³, μ = 0.2900 mm^?1, the final R ₁ = 0.041000 and wR ₂ = 0.1160 for 2675 observed reflections with I > 2σ(I). A total of 5623 reflections were collected, of which 3866 were independent (R _int = 0.019000). The fungicidal activity of title compound was determined, the results showed the title compound displayed moderate fungicidal activity against G. zeae Petch, Phytophthora infestans (Mont.) de Bary, Botryosphaeria berengeriana f. sp. piricola (Nose) koganezawa et Sakuma, Fusarium oxysporum f.sp. cucumerinum, and Cercospora arachidicola.     

Structure,bioactivity and theoretical study of 1-cyano-<Emphasis Type="Italic">N</Emphasis>-p-tolylcyclo-propanecarboxamide

A novel cyclopropane derivative, 1-cyano-N-p-tolylcyclopropanecarboxamide (C₁₂H₁₂N₂O, Mr = 200.24) was synthesized and its structure was studied by X-ray diffraction, FTIR, ¹H and ¹³C NMR spectrum and MS. The crystals are monoclinic, space group P2_1/c with a = 7.109 (4), b = 13.758 (7), c = 11.505 (6) Å, α = 90.00, β = 102.731 (8), γ = 90.00 °, V = 1097.6 (9) ų, Z = 4, F(000) = 312, D _c  = 1.212 g/cm³, μ = 0.0800 mm^?1, the final R = 0.0490 and wR = 0.1480 for 1,375 observed reflections with I > 2σ(I). A total of 6,109 reflections were collected, of which 2,290 were independent (R _int = 0.0290). Theoretical calculation of the title compound was carried out with HF/6-31G (d,p), B3LYP/6-31G (d,p), MP2/6-31G (d,p). The full geometry optimization was carried out using 6-31G(d,p) basis set, and the frontier orbital energy. Atomic net charges were discussed, and the structure-activity relationship was also studied. The preliminary biological test showed that the synthesized compound is bioactive against the KARI of Escherichia coli.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

New hybrids of clozapine and haloperidol and their isosteric analogues: synthesis,X-ray crystallography,conformational analysis and preliminary pharmacological evaluation

Schizophrenia is a debilitating mental disorder which affects approximately 1% of the world’s population. Clozapine is an atypical antipsychotic showing unmatched effectiveness in the control of treatment-resistant schizophrenia. Unlike typical antipsychotics, clozapine does not induce extrapyramidal side effects (EPS), tardive dyskinesia or elevate prolactin levels. However, clozapine can induce a potentially fatal blood disorder, agranulocytosis, in 1–2% of patients, severely limiting its clinical use. The model for antipsychotic activity under investigation is based on obtaining a clozapine-like profile with preferential dopamine D₄ and serotonin 5-HT_2A receptor affinity. Profiled herein are three unique members of a series of prospective antipsychotic agents. Compound (I) originated from the structural hybridization of the commercial therapeutics, clozapine and haloperidol, whilst compounds (II) and (III) possess an alternative tricyclic nucleus derived from JL13; a clozapine-like atypical antipsychotic developed by Liégeois et al. These compounds have been synthesized and characterized by means of elemental analysis, IR, ¹H and ¹³C-NMR spectroscopy, MS and X-ray diffraction. Compound (I) crystallizes in space group P(?1) with a = 10.5032(1), b = 10.6261(2), c = 12.6214(3) Å, α = 81.432(1)°, β = 83.292(1)°, γ = 61.604(1)°, Z = 2, V = 1223.62(4) Å³, C₂₈H₂₉ClN₄O, M _r = 473.00, D _c = 1.284 Mg/m³, μ = 0.185 mm^?1, F(000) = 500, R = 0.0506 and wR = 0.1304. Compound (II) crystallizes in the monoclinic space group P2₁/c with a = 10.8212(2), b = 9.3592(2), c = 22.9494(5) Å, β = 106.471(1)°, Z = 4, V = 2228.88(8) Å³, C₂₅H₂₅ClN₄O₂, M _r = 448.94, D _c = 1.338 Mg/m³, μ = 0.202 mm^?1, F(000) = 944, R = 0.0529 and wR = 0.1129. Compound (III) crystallizes in the monoclinic space group P2₁/c with a = 10.5174(2), b = 9.3112(2), c = 24.2949(5) Å, β = 98.666(1)°, Z = 4, V = 2352.03(8) Å³, C₂₅H₂₄Cl₂N₄O₂, M _r = 483.38, D _c = 1.365 Mg/m³, μ = 0.306 mm^?1, F(000) = 1008, R = 0.0478 and wR = 0.1067. The solid state conformations of (I), (II) and (III) exhibit the characteristic V-shaped buckled nature of the respective dibenzodiazepine and pyridobenzoxazepine nuclei with the central seven-membered heterocycle in a boat conformation. The molecules of (I) form a head-to-tail dimeric motif stabilized by hydrogen bonding. The results of a conformational analysis of compounds (I)–(III) investigating the effect of environment (in vacuo and aqueous solution) are presented. These analogues were tested for in vitro affinity for the dopamine D₄ and serotonin 5-HT_2A receptors and their comparative receptor binding profiles to clozapine and JL13 are reported.     

Electrochemical Behavior of a Gold Electrode Modified with SWNTs/DDAB Films and Its Electrocatalytic Activity Towards Ascorbic Acid

A film of single-wall carbon nanotubes (SWNTs) and didodecyldimethylammonium bromide (DDAB) is prepared by casting a solution of SWNTs and DDAB onto the surface of a gold electrode. The electrochemical behavior of the film is investigated by electrochemical impedance spectroscopy and cyclic voltammetry. In a 0.10 M phosphate buffer solution of pH 7.0, the film-modified electrode gives a pair of redox peaks in cyclic voltamograms, with the anodic and cathodic peak potentials of 0.095 and 0.042 V. The peak currents change linearly with the scan rate at 30–500 mV/s. The modified electrode has an excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA). The catalysis currents are proportional to the AA concentration in the range of 5.0 × 10⁻⁴ to 3.2 × 10⁻² M. The linear-regression equation is i (μA) = 1.2079 + 1.3987 × 10³ c _AA (M), with a correlation coefficient of 0.9995. The detection limit is 2.2 × 10⁻⁴ M (signal-to-noise ratio of 3). The Michaelis-Menten constant (K _m) is 1.0 × 10⁻⁴ M by the Lineweaver-Burk equation. __________ From Elektrokhimiya, Vol. 41, No. 10, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Cheng, Jin, Zhang. The text was submitted by the authors in English.     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.