Sensitive spectrophotometric method for trace amounts of uranium

A sensitive spectrophotometric method for the determination of uranium with Pyrogallol Red (PGR) and cetyltrimethylammonium bromide (CTAB) is described. The sensitivity of the colour reaction between uranium and Pyrogallol Red is greatly increased in the presence of cetyltrimethylammonium bromide. The blue ternary complex (λ_max580 nm) has composition 1:2:4 [U(VI):PGR:CTAB] at pH 5.6. Beer's law is obeyed over the range 19.0-0.24 ppm of uranium and the molar absorptivity is 3.3 × 10⁴ l.mole⁻¹.cm⁻¹ at 620 nm. A tentative structure for the ternary complex is suggested. A simple method is suggested for evaluation of stability constants of such ternary complexes.     

Sensitive microdetermination of scandium,yttrium, and lanthanides using Eriochrome azurol B in the presence of a micelle-forming cationic surfactant

The chelation reactions of Sc³⁺, Y³⁺, and some lanthanides with Eriochrome azurol B in the presence and absence of cetyltrimethylammonium bromide has been studied in detail. The complexes show a marked bathochromic shift in their λ_max at pH 6.0. The composition of the complexes in the absence and presence of cetyltrimethylammonium bromide was found to be 1:2 (Metal:ligand). The values of the conditional formation constants have also been evaluated. The studies were further extended to the analytical aspects of the complex equilibria and a suitable procedure has been recommended for the spectrophotometric microdetermiantion of Sc³⁺, Y³⁺, and some lanthanides under study using Eriochrome azurol B in the presence of cetyltrimethylammonium bromide which considerably increases the sensitivity of the color reaction. The use of Eriochrome azurol B in the presence of cetyltrimethylammonium bromide as a complexometric indicator has also been reported.The effect of surfactant concentration and the effect of mineral salts on the absorption spectra of Eriochrome azurol B at pH 11.6 and 6.0 have also been reported.     

Effect of reactive and non-reactive counterion micelles upon the alkaline degradation of indomethacin

In the present paper, kinetics of alkaline degradation of well known drug, indomethacin (2-[1-(4-chlorobenzoyl)-5-methoxy-2-methylindol-3-yl]acetic acid), was studied in presence of excess [NaOH]. The rate of hydrolysis of substrate was independent of the [indomethacin] though it increased linearly with increasing the hydroxide ion concentration with a positive slope, suggesting the following rate law: k_obs = k₁[OH⁻]. Cationic surfactants having non-reactive ions (cetyltrimethylammonium bromide, CTAB and cetyltrimethylammonium sulfate (CTA)₂SO₄) first increased the rate constants at lower concentrations and then decreased it at higher concentrations while in case of the surfactant with reactive counterions (cetyltrimethylammonium hydroxide, CTAOH) the rate increases sharply at lower concentrations of surfactant until it reaches to a plateau in contrast to the appearance of maxima in case of CTAB and (CTA)₂SO₄. Anionic surfactant, sodium dodecyl sulfate (SDS), inhibited the reaction rate at all concentrations used in the study. Pseudophase ion-exchange model was used for analyzing the effect of cationic micelles while the inhibition by SDS micelles was fitted using the Menger–Portnoy model. The effect of salts (NaCl, NaBr and (CH₃)₄NBr) was also seen on the hydrolysis of indomethacin and it was found that all salts inhibited the rate of reaction. The inhibition followed the trend NaCl < NaBr < (CH₃)₄NBr.     

Interaction enthalpy of lysozyme with vesicles

Negatively charged vesicles made of non-stoichiometric amounts of sodium dodecylsulfate and cetyltrimethylammonium bromide were characterised by physico-chemical methods. Interactions with lysozyme were examined by calorimetry. A remarkable heat effect is observed upon diluting the protein with the vesicular pseudo-solvent. The maximum ΔH_bind value occurs at complete vesicle charge neutralisation by the protein.     

Reaction of N,N-Dimethyl-N′-(2-hydroxybenzyl)ethylenediamine with Copper(II) in the Presence of Surfactants

The protolytic properties of N,N-dimethyl-N′-(2-hydroxybenzyl) ethylenediamine (HL) and its complexation with copper(II) in the presence of cationic (cetyltrimethylammonium bromide) and nonionic (Triton X-100) surfactants were studied by pH-metry, spectrophotometry, and mathematical simulation of the equilibria. Cetyltrimethylammonium bromide affects the H₂L₂ ⇄ 2HL equilibrium. Along with the protonated monomeric and dimeric species, triprotonated tetrameric species were revealed in surfactant solutions, as in aqueous solutions of isopropyl alcohol. The surfactants affect the complexation of HL with Cu(II). The 1 : 2 complex with the phenolate form in solutions of cetyltrimethylammonium bromide is formed in a more acidic medium (pH ∼5.5) compared to an aqueous solution of isopropyl alcohol (pH ∼11). The apparent stability constants of the complexes increase in the presence of surfactants, especially of cetyltrimethylammonium bromide.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 3, 2005, pp. 379–382.Original Russian Text Copyright © 2005 by Sal’nikov, Boos, Ryzhkina, Ganieva.     

Kinetics of the autoxidation of adrenaline and [copper(II)(adrenaline)]2+ in alkaline aqueous and micellar media

The kinetics of autoxidation of adrenaline and [Cu(adrenaline)]²⁺ complex by dissolved oxygen in alkaline aqueous and micellar media has been studied. The reaction is initiated by the removal of amino-H⁺ protons of adrenaline by hydroxide ion, followed by cyclization. The values of (1/k _obs) for the autoxidation of both species were found to be linearly dependent upon 1/[OH^?]. The reaction follows a consecutive pathway in which the intermediate adrenochrome remains stable for few minutes, and then undergoes further reactions to yield adrenolutin and other products. The [Cu(adrenochrome)]⁺ complex is stable for a few hours. Studies on the effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the reactivity of both species revealed different behaviors. The micelles of CTAB catalyzed the rates of autoxidation for both species, whereas SDS micelles inhibited the autoxidation of adrenaline but catalyzed the rate of autoxidation of [Cu(adrenaline)]²⁺. Addition of the reactive counterion surfactant, cetyltrimethylammonium hydroxide (CTAOH) initially increased the rate constant with the increasing [CTAOH], until it reached a plateau for k _ψ ?[CTAOH]. Salts such as NaCl, NaBr, tetramethyl ammonium bromide, and tetraethyl ammonium bromide increased the rate when added at lower concentrations, but had negligible effect at higher concentrations. The results obtained in micellar media were treated according to Berezin’s Pseudophase Model. The various kinetic parameters for the reactions occurring in aqueous and in micellar media are reported.     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Simple Hydrothermal Synthesis of Nickel Hydroxide Flower-Like Nanostructures

α-Ni(OH)₂ flower-like nanostructures were successfully synthesized through one-step hydrothermal method with nickel acetate tetrahydrate, ethylene-1,2-diamine (en), hexamethylenetetramine (HMT) and cetyltrimethylammonium bromide (CTAB) as morphology-directing agents. Optimum conditions to obtain high yield and pure phase α-Ni(OH)₂ were identified by varying experimental parameters such as: en, HMT and CTAB concentration and reaction temperature. The products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared and thermogravimetric analysis. These results indicated that the α-nickel hydroxide contains water molecules and anions. The hierarchical NiO nanostructures were obtained by the as-synthesized α-Ni(OH)₂ nanostructures annealed at 300 °C for 4 h.     

Extraction by reversed micelles of triton N-42 for the spectrophotometric determination of cetyltrimethylammonium bromide

Micellar preconcentration of 1 : 2 associates of Bromophenol Blue with cetyltrimethylammonium bromide is proposed to improve the procedure for the spectrophotometric determination of cationic surfactants. The preconcentration procedure involves quantitative extraction by reversed micelles of Triton N-42 in decane followed by the decomposition of the micellar solution with chloroform. The loss of 10^–7–10^–5 M cetyltrimethylammonium bromide in 5–100-fold preconcentration was not supported by the added-found method (RSD = 3–5%). The determination limit for cetyltrimethylammonium bromide is 2 × 10^–7 M.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 17–21.Original Russian Text Copyright © 2005 by Demidova, Bulavchenko.     

Micellar-mediated shifts of ionization constants of amino acids and peptides

The acid-base dissociation constants, K_a, of amino acids and small peptides were determined in both aqueous and micellar solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide by potentiometric and chromatographic means. The observed differences in pK_a values between micellar media and aqueous solutions ranged between 0.23 and 2.21 units. The micellar-mediated pK_a shifts can be attributed to different solute-micelle interactions, mainly hydrophobic and electrostatic forces. The implications of the change in acid-base behavior on separation selectivity in micellar liquid chromatography and micellar electrokinetic capillary chromatography are discussed.     

Comparative study of the cationic surfactants and their influence on the alkaline hydrolysis of acetylsalicylic acid

A kinetic study of the reaction of acetylsalicylic acid (aspirin) with sodium hydroxide has been studied in the presence of some conventional and novel cationic surfactants. The pseudo‐first‐order rate constant increases with the surfactant concentration initially and then decreases. In comparison to conventional cationic surfactants, i.e., cetyltrimethylammonium bromide and cetylpyridinium bromide, novel alkyldiethylethanolammonium bromide (R = C₁₆) surfactant accelerated the alkaline hydrolysis significantly. The pseudophase ion‐exchange model has been applied to fit the experimental results. Activation parameters have also been evaluated. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 1–8, 2011     

Electrochemical crystal growth in the cesium molybdate-molybdenum trioxide system

A systematic investigation of crystal growth in the cesium molybdate/molybdenum trioxide system is described. A previously unknown blue cesium molybdenum bronze phase has been prepared as well as the known red bronze, Cs_0.33MoO₃, and high-quality crystals of the Magneli-phase compound, γ-Mo₄O₁₁. This new blue bronze, with empirical formula, Cs_0.19MoO_2.85, is monoclinic with cell constants, a = 19.198(4) Å, b = 5.519(2) Å, c = 12.213(2) Å, and β = 119.44(2)°. Measurements of the susceptibility and of the resistivity vs temperature are reported. As is the case for other alkali molybdenum bronzes, the product formed is determined by the molar ratio of alkali molybdate to molybdenum trioxide and the melt temperature.     

Kinetic study of the hetero Diels-Alder reaction in surfactant solutions

The kinetics of the cycloaddition of nitrosobenzene with 2,3-dimethyl-1,3-butadiene in solutions of anionic sodium di(2-ethyl-1-hexyl) sulphosuccinate (AOT) and cationic cetyltrimethylammonium bromide was investigated. The significant acceleration of the reaction rate by a factor of 5 compared to that in a pure ethylene glycol was observed. Isobaric activation parameters were determined, and the activation energy E _a was shown to decrease upon increasing AOT concentration in solutions with low surfactant concentrations.     

Structure determination of low-dimensional conductor sodium molybdenum purple bronze Na0.9Mo6O17

Structure determination of the molybdenum purple bronze Na_0.9Mo₆O₁₇ is carried out by single-crystal X-ray diffraction. The crystal is monoclinic with space group A2 and the lattice constants are a = 12.983(2), b = 5.518(1), c = 9.591(2) Å, β = 89.94(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R(F) = 0.028 and R_w(F) = 0.040 for 1484 independent reflections, in which the occupancy factor of the sodium atom becomes 0.899(12). The present structure is built up of the linkage of the MoO₄ and MoO₆ polyhedra. There are slabs which consist of four layers of distorted MoO₆ octahedra sharing corners. Both the structure and the molybdenum valence distribution estimated from the MoO bond lengths are considered to lead to the two-dimensional electronic transport. This structure is compared with those of other members of molybdenum purple bronzes, K_0.9Mo₆O₁₇ and Li_0.9Mo₆O₁₇. The difference of the electronic properties among these compounds can be well understood on the basis of their structural characteristics.     

Enzymeless determination of cholesterol using gold and silver nanoparticles as electrocatalysts

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10^–5 c _chol + 5.8 × 10^–5 (R ² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5 c _chol + 3.0 × 10^–4 (R ² = 0.95) possess optimal electrocatalytic characteristics.     

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.     

Paramagnetic absorption of pentavalent molybdenum in polycrystalline tin dioxide

Part of molybdenum introduced in SnO₂ by various methods is found to be stabilized in the pentavalent state at substitutional positions. The ESR spectra of Mo⁵⁺ ions are characterized by the following parameters: g_xx = 1.891; g_yy = 1.835 and g_zz = 1.923, A_xx = 24 G, A_yy = 30 G and A_zz = 70 G. There are, in addition, two sets of superhyperfine structures due to the two tins located along the crystallographic c axis (290 G) and to the four tins lying in a diagonal plane of the unit cell containing four oxygens (51 G), consistent with a 3d_x²-y² + λ 3d_z2 ground state. The variations of the Mo⁵⁺ ESR spectrum upon heating the samples in various atmospheres (O₂, H₂) suggest that molybdenum enters the SnO₂ lattice also as Mo⁴⁺.     

Spectrofluorimetric determination of niobium with morin enhanced by cetyltrimethylammonium bromide micelles

The effect of surfactants on the fluorescence of the niobium—morin system is described. Cationic surfactants strongly enhanced the intensity (e.g., cetyltrimethylammonium bromide (CTAB) gives an 80-fold increase), while anionic and non-ionic surfactants are without effect. The formation of 1:1 and 1:3 (Nb:morin) complexes is demonstrated spectrophotometrically. The conditional stability constants for these complexes in CTAB micelles are β₁ = (1.14 ± 0.01) × 10⁴ l mol^?1 amd β₃ = (5.66 ± 0.02 × 10¹⁰ l³ mol^?3. The micellar-enhanced fluorimetric method has a 1 μg l^?1 detection limit, and is highly selective. The r.s.d. for the determination of 50 μg l^?1 Nb is 3.5%.     

The unexpected decarbonylation of a molybdenum(O) dithiocarbamate and the formation of a molybdenum(V) dimeric product: Crystal structure of di-μ-sulfido-bis[oxo(pyrrolidinedithiocarbamato)molybdenum(V)]

The interaction of molybdenum hexacarbonyl with ammonium pyrrolidinedithiocarbamate in warm dimethylsulfoxide solution gives not the expected complex [NH₄][Mo(CO)₄(S₂CN(CH₂)₄)] but the molybdenum(V) dimer, di-μ-sulfido-bis[oxo(pyrrolidinedithiocarbamato)molybdenum(V)]. The structure of this oxidized product [MoO(S₂CN(CH₂)₄)S]₂ (1) was determined by single-crystal X-ray diffraction analysis. The crystals are triclinic, space group P$\text{I}$ with two molecules in a unit cell of dimensions a = 8.775(1), b = 16.592(2), c = 6.661(1) Å, α = 97.67(1), β = 97.89, γ = 80.23(1)°. The structure was solved by the heavy-atom method and refined by block-diagonal least-squares calculations to R = 0.037 for 3772 observed data. In the binuclear complex the two Mo atoms are bridged via two S atoms [Mo-S 2.303-2.317(1) Å]. Each Mo atom is also coordinated by a terminal O atom [1.688(4) and 1.682(4) Å] and two S atoms from the bidentate ligand [Mo-S 2.455-2.475(1) Å]. The geometry around the metal atoms is distorted square pyramidal.     

Spectrophotometric determination of molybdenum in steels with o-nitrophenylfluorone and cetyltrimethylammonium bromide

A method has been developed for determining microamounts of molybdenum(VI) in aqueous solution by means of the Mo-o-nitrophenylfluorone—cetyltrimethylammonium bromide system, in which micellar solubilization is applied. A red complex is formed in 0.2–0.6M hydrochloric acid medium. The sensitivity of the method is high, and the apparent molar absorptivity is 1.55 × 10⁵ l.mole⁻¹. cm⁻¹. The absorption peak of the complex appears at 530 nm. The colour of the complex develops quickly and is stable for more than 24 hr. The composition of the complex is Mo: o-NPF = 1:1, and the system obeys Beer's law in the range 0–10 μg of Mo per 25 ml. The method has been used for the rapid determination of molybdenum in alloy steels with satisfactory results.