Effect of electrolyte temperature on the formation of self-organized anodic niobium oxide microcones in hot phosphate-glycerol electrolyte

Nanoporous niobium oxide films with microcone-type surface morphology were formed by anodizing at 10 V in glycerol electrolyte containing 0.6 mol dm⁻³ K₂HPO₄ and 0.2 mol dm⁻³ K₃PO₄ in a temperature range of 428-453 K. The microcones appeared after prolonged anodizing, but the required time was largely reduced by increasing electrolyte temperature. The anodic oxide was initially amorphous at all temperatures, but crystalline oxide nucleated during anodizing. The anodic oxide microcones, which were crystalline, appeared on surface as a consequence of preferential chemical dissolution of initially formed amorphous oxide. The chemical dissolution of an initially formed amorphous layer was accelerated by increasing the electrolyte temperature, with negligible influence of the temperature on the morphology of microcones up to 448 K.     

Curcumin as a colorimetric and fluorescent chemosensor for selective recognition of fluoride ion

The binding properties of curcumin with anions in acetonitrile were examined for the first time by UV-vis absorption and fluorescence spectroscopies. The results showed that curcumin highly and selectively responded to F⁻ over other anions such as AcO⁻, H₂PO₄⁻ and Cl⁻ because of anionic complex formation via hydrogen bond. Curcumin gave rise to the red-shift of absorption spectra and its fluorescence was quenched with concomitant color change from yellow to purple upon addition of F⁻, which was detected by naked eyes. The addition of other anions such as AcO⁻, H₂PO₄⁻, HSO₄⁻, NO₃⁻, Cl⁻ and Br⁻ did not result in observable spectral change and solution color change. The binding constant between curcumin and F⁻ was 2.0×10⁵ mol⁻¹ L and the recognizing mechanism was investigated as well.     

The role of adsorption of sodium bis(2-ethylhexyl) sulfosuccinate in wetting of glass and poly(methyl methacrylate) surface

Advancing contact angles, θ, for aqueous solutions of the anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were measured on glass and poly(methyl methacrylate) (PMMA) surface. Using the obtained results we determined the properties of aqueous AOT solutions in wetting of these surfaces. It occurs that the wettability of glass and PMMA by these solutions depends on the concentration of AOT in solution. There is almost linear dependence between the contact angle (θ) and concentration of AOT (log C) in the range from 5 × 10⁻⁴ to 2.5 × 10⁻³ M/dm³ (value of the critical micelle concentration of AOT—CMC) both for glass and PMMA surface. For calculations of AOT adsorption at solid (glass, PMMA)-solution drop-air system interfaces the relationship between the adhesion tension (γ_LV cos θ) and surface tension (γ_LV) and the Gibbs and Young equations were taken into account. From the measurement and calculation results the slope of the γ_LV cos θ − γ_LV curve was found to be constant and equal 0.7 for glass and −0.1 for PMMA over the whole range of AOT concentration in solution. From this fact it can be concluded that if Γ_SV is equal zero then Γ_SL > 0 for the PMMA-solution and Γ_SL < 0 for glass-solution systems. It means that surfactant concentration excess at PMMA-solution interface is considerably lower than at solution-air interface, but this excess of AOT concentration at glass-solution interface is lower than in the bulk phase. By extrapolating the linear dependence between the adhesion and surface tension the value of the critical surface tension (γ_c) of wetting for glass and PMMA was also determined, that equaled 25.9 and 25.6 mN/m for glass and PMMA, respectively. Using the value of the glass and PMMA surface tension as well as the measured surface tension of aqueous AOT solutions in Young equation, the solid-liquid interface tension (γ_SL) was found. There was a linear dependence between the γ_SL and γ_LV both for glass and PMMA, but there were different slope values of the curves for glass and PMMA, i.e. −0.7 and 0.1, respectively. The dependence between the work of adhesion (W_A) and surface tension (γ_LV) was also linear of different slopes for glass and for PMMA surface.     

Dual fluorescence and laser emissions from fluorescein-Na and eosin-B

Dual laser emissions were observed from fluorescein-Na and eosin-B in ethanolic solutions individually in the concentration range from 10⁻² to 10⁻³ mol dm⁻³ under N₂ laser excitation. The first compound was found to lase at two distinct regions with wavelength maxima around 540, 550 nm, while the second one around 558, 574 nm. Steady-state absorption, fluorescence excitation, fluorescence polarization, fluorescence emission and decays of the dyes in various solvents under varying conditions of excitation and detection systems were carried out to identify the nature of the emitting species responsible for laser emissions in two distinct regions. Both the dyes exhibited concentration and excitation wavelength dependence of fluorescence and the effects were found to be more pronounced in binary solution. The fluorescence decays of dyes were monoexponential in ethanol, while in some other solvents used, the decays showed biexponential behavior. The absorption and excitation studies using thin layers of solutions revealed the formation of dimers with the dye concentration around 1×10⁻³ mol dm⁻³. Fluorescence polarization and decay studies confirmed the presence of dimers. The two laser bands observed in the shorter and longer wavelengths were respectively ascribed to monomeric and dimeric species.     

Diffusion of ions in supercritical water: Dependence on ion size and solvent density and roles of voids and necks

We have performed molecular dynamics simulations of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and halide (F⁻, Cl⁻, Br⁻, I⁻) ions in supercritical water at 673 K. The calculations were done for water at three different densities of 1.0, 0.7 and 0.35 g cm⁻³ to investigate the effects of solute size on the diffusion of ions in supercritical water. On increase of ion size, we observe a maximum for diffusion of ions in supercritical water of higher densities (1.0 and 0.7 g cm⁻³). However, no such maximum is found for ion diffusion in the supercritical water of low density (0.35 g cm⁻³) or for diffusion of neutral solutes at all densities. These results are analyzed in terms of passage through voids and necks present in supercritical water. Correlations of the observed diffusion behavior with the sizes of ions and voids present in the systems are discussed.     

Sorption of selenium(IV) and selenium(VI) onto magnetite

In this work, we have studied the sorption of selenium (⁷⁹Se is one of the main radionuclides in a spent nuclear fuel repository) on magnetite (Fe₃O₄), a mineral present in the near-field of a nuclear waste repository that might represent an important retardation factor for the mobility of many radionuclides.The sorption of both Se(IV) and Se(VI) onto magnetite has been fitted by a non-competitive Langmuir isotherm with Γ_max = (3.13 ± 0.07) × 10⁻⁶ mol m⁻² and K_L = (1.19 ± 0.07) × 10⁶ dm³ mol⁻¹ for Se(IV) and Γ_max = (3.5 ± 0.2) × 10⁻⁶ mol m⁻² and K_L = (3.0 ± 0.1) × 10⁵ dm³ mol⁻¹ for Se(VI).The variation of the sorption of selenium with pH has been modeled using the Triple Layer Surface Complexation Model and the equilibrium constants between selenium and magnetite have been obtained using the FITEQL program. For the case of Se(IV), the best fitting has been obtained using two inner-sphere complexes, FeOHSeO₃²⁻ and FeHSeO₃, while for Se(VI), the best fitting has been obtained considering only an outer-sphere complex, FeOH₂⁺SeO₄²⁻.The surface complexation reactions derived in this work are in agreement with those stated by other authors for sorption of Se(IV) and Se(VI) on hydrous iron oxides.     

The ν4 and ν2 + ν5 high resolution infrared bands of FClO3 and FClO3

The high resolution infrared spectra of monoisotopic F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃ have been studied in the region of the ν₄ fundamentals, centered at 1278.3 and 1263.3 cm⁻¹, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν₂ + ν₅ combination bands, centered at 1270.7 cm⁻¹ in F³⁵Cl¹⁸O₃ and 1257.3 cm⁻¹ in F³⁷Cl¹⁸O₃. In particular, they affect the kl > 0 levels of the v₄ = 1 and v₂ = v₅ = 1 states which cross at kl ? 18 in F³⁵Cl¹⁸O₃ and kl ? 3 in F³⁷Cl¹⁸O₃, due to the opposite values of and . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F³⁵Cl¹⁸O₃, while in F³⁷Cl¹⁸O₃ only the Δl = Δk = ±2 one is active. In the spectrum of F³⁵Cl¹⁸O₃ 3423 transitions have been assigned, 10% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants between the v₄ = 1 and v₂ = v₅ = 1 levels have been obtained. The depertubed band origins of ν₄ and ν₂ + ν₅ are 1277.310567(165) and 1271.753733(195) cm⁻¹, respectively, and the anharmonic resonance constant is 2.804416(153) cm⁻¹. For F³⁷Cl¹⁸O₃, 3022 transitions have been assigned, 38% belonging to the ν₂ + ν₅ combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm⁻¹, for ν₄and ν₂ + ν₅ and the constant is 2.9350669(405) cm⁻¹. The equilibrium geometry of perchloryl fluoride, r_e (ClO) = 139.7(3) pm, r_e (ClF) = 161.0(5) pm, and α_e (OClO) = 115.7(4) degree, has been determined using the A_e and B_e equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F^35/37Cl¹⁶O₃ and F^35/37Cl¹⁸O₃.     

Removal of nickel(II) ions from aqueous solutions using the natural clinoptilolite and preparation of nano-NiO on the exhausted clinoptilolite

The natural zeolite tuff (clinoptilolite) from a Serbian deposit has been studied as adsorbent for Ni(II) ions from aqueous solutions. Its sorption capacity at 298 K varies from 1.9 mg Ni g⁻¹ (for the initial solution concentration of 100 mg Ni dm⁻³) to 3.8 mg Ni g⁻¹ (for C₀ = 600 mg Ni dm⁻³) and it increases 3 times at 338 K. The sorption is best described by the Sips isotherm model. The sorption kinetics follows the pseudo-second-order model, the activation energies being 7.44, 5.86, 6.62 and 6.63 kJ mol⁻¹ for C₀ = 100, 200, 300 and 400 mg Ni dm⁻³, respectively. The sorption involves a film diffusion, an intra-particle diffusion, and a chemical cation-exchange between the Na⁺ ions of clinoptilolite and the Ni²⁺ ions. The sorption is endothermic (ΔH° being 37.9, 33.4, 30.0, 27.7 and 24.3 kJ mol⁻¹ for C₀ = 100, 200, 300, 400 and 600 mg Ni dm⁻³, respectively) and spontaneous in the 298-338 K temperature range. Thermal treatment of the Ni(II)-loaded clinoptilolite results in the formation of spherical nano-NiO particles of approx. 5 nm in diameter which are randomly dispersed in the clinoptilolite lattice.     

Improved luminescent properties of red-emitting Ca0.54Sr0.16Eu0.08Gd0.12(MoO4)0.2(WO4)0.8 phosphor for LED application by charge compensation

The red-emitting Ca_0.54Sr_0.16Eu_0.08Gd_0.12(MoO₄)_0.2(WO₄)_0.8 phosphor is improved in the emission charateristics by charge compensation, of which chromaticity coordinates (CIE) are x=0.66 and y=0.33. Three approaches to charge compensation are investigated, namely (a) 3Ca²⁺/Sr²⁺→2Eu³⁺/Gd³⁺+vacancy, (b) 2Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+M⁺(M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ employed as a charge compensator) and (c) Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+N⁻ (N⁻ is a monovalent anion like F⁻, Cl⁻, Br⁻ and I⁻ employed as charge compensation ions). Through photoluminescent spectra analyzing the radiative and non-radiative relaxation mechanisms of luminescent system are obtained. Under 20 mA forward-bias current, one red-emitting LED is made by combining 390-405 nm-emitting LED chip and the phosphor. The red-emitting phosphor has broad prospects in LED application field.     

Velocity modulation spectroscopy of molecular ions I: The pure rotational spectrum of TiCl (XΦr)

The pure rotational spectrum of the TiCl⁺ ion in its X³Φ_r ground state has been measured in the frequency range 323-424 GHz, using a combination of direct absorption and velocity modulation techniques. The ion was created in an AC discharge of TiCl₄ and argon. Ten, eleven, and nine rotational transitions were recorded for the ⁴⁸Ti³⁵Cl⁺, ⁴⁸Ti³⁷Cl⁺, and ⁴⁶Ti³⁵Cl⁺ isotopomers, respectively; fine structure splittings were resolved in every transition. The rotational fine structure pattern was irregular with the Ω = 4 component lying in between the Ω = 2 and 3 lines. This result is consistent with the presence of a nearby ³Δ_r state, which perturbs the Ω = 2 and 3 sub-levels, shifting their energies relative to the Ω = 4 component. The data for each isotopomer were analyzed in a global fit, and rotational and fine structure parameters were determined. The value of the spin-spin constant was comparable to that of the spin-orbit parameter, indicating a large second-order spin-orbit contribution to this interaction. The bond length established for TiCl⁺, r₀ = 2.18879 (7) Å, is significantly shorter than that of TiCl, which has r₀ = 2.26749 (4) Å. The shorter bond length likely results from a Ti²⁺Cl⁻ structure in the ion relative to the neutral, which is thought to be represented by a Ti⁺Cl⁻ configuration. The higher charge on the titanium atom shortens the bond.     

Photoinduced energy transfer from the triplet state of naphthalene moiety in the Tb/Eu complexes of a specially designed naphthalene cryptand

The paper reports time-resolved emission and energy transfer (ET) studies of metal ion complexes of a specially designed rigid macrocyclic naphthalene cryptand (L) under different conditions. Complex formation of L with Li⁺ and H⁺ causes an appreciable increase in singlet state quantum yield and lifetime of L implying photoinduced electron transfer (PET) from the cryptand moiety to naphthalene unit in the free L. The system exhibits photoinduced ET at 77 K in its Tb³⁺ and Eu³⁺ complexes with either NO₃⁻¹ or Cl⁻¹ as counter-anion. The extent of ET is higher for the Tb³⁺ complex as compared to that for the Eu³⁺ complex. In both Tb³⁺ and Eu³⁺ complex, the NO₃⁻¹ ions influence the relative orientation of donor (L) and acceptor (Ln³⁺) more in favour of ET than the Cl⁻¹ ions. The rate constants for the ET from the naphthalene moiety of L to the acceptor (Ln³⁺) have been evaluated at 77 K. The results suggest ET from the triplet state of naphthalene using an exchange mechanism. The ground state geometries of the system L and its complexes with Li⁺, Cs⁺ and Tb³⁺ have been determined using DFT methods to interpret our results.     

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10⁻³ mol dm⁻³ of DEAC gives laser emission in the blue region on pumping with nitrogen laser (λ_ex=337.1 nm). The laser parameters such as tuning range, gain coefficient (α), emission cross section (σ_e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl₄ at a wavelength of 366 nm. The values of photochemical yield (?_c) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH₃CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.     

Effects of Cl, NO3 and SO4 anions on the anodic behavior of carbon steel in deaerated 0.50 M NaHCO3 solutions

The effects of Cl⁻, NO₃⁻ and SO₄²⁻ aggressive anions on the corrosion and passivation behavior of carbon steel electrode in deaerated 0.50 M NaHCO₃ solutions were studied using potentiodynamic anodic polarization and SEM techniques. It was found that the presence of Cl⁻, NO₃⁻ and SO₄²⁻ anions stimulates the anodic dissolution rate in both the active and the pre-passive potential regions. Moreover, significantly great effects were observed in both the passive and the trans-passive potential regions. Pitting corrosion was observed only in the presence of Cl⁻ anions, while the presence of NO₃⁻ and SO₄²⁻ anions facilitate only passivation by oxygen of water without themselves participating in the cathodic process. Also, it was observed that the effect of NO₃⁻ anion, which is a strong oxidizing agent acting “primarily” as stimulator of the cathodic process and then its reaction product acts “indirectly” retarding the anodic process. On the other hand, the effect of SO₄²⁻ anion, which is a non-oxidizing agent, exerts an “indirect” effect on the cathodic reaction increasing its rate and then “directly” influence on the anodic reaction, retarding it.     

Ultrafast motion of liquids C2H4Cl2 and C2H4Br2 studied with a femtosecond laser

Transient optical Kerr effect of liquids C₂H₄Cl₂ and C₂H₄Br₂ is investigated, for the first time to our knowledge, with a femtosecond (fs) probe laser delayed with respect to a coherent fs pump laser. Coherent coupling and electronic Kerr signals are observed around zero delay when pump and probe overlap. Persisting after the pump-probe overlap are Kerr signals arising from the torsional and other intramolecular vibrations of the trans and gauche conformations; Kerr signals arising from the intermolecular motion are also observed. Vibrational quantum interference is only observed in liquid C₂H₄Br₂ and the related beats data are fitted with the torsional vibrations, 91 cm⁻¹ (gauche) and 132 cm⁻¹ (trans), and the CCBr angle-bending vibrations, 231 cm⁻¹ (gauche) and 190 cm⁻¹ (trans), with dephasing times, 0.45 ps, 0.45 ps, 2 ps, and 1.5 ps, respectively. These vibrational frequencies agree with those obtained in the frequency-domain. That no vibrational mode is observed for C₂H₄Cl₂ might be attributed to ineffective Raman-pumping. Kerr signals observed after the pump-probe overlap are Fourier transformed to give the spectra of the intermolecular motion and the vibrational spectrum, which agrees with the one observed in the infrared absorption and/or Raman scattering heretofore.     

The high resolution infrared bands ν1, ν2, ν4 and ν2 + ν5 of FClO3

The high resolution infrared spectrum of mono-isotopic F³⁷Cl¹⁶O₃ has been studied in the regions of ν₁, ν₂, ν₄ and ν₂ + ν₅ bands, centered at 1060.20, 707.16, 1301.71 and 1292.15 cm⁻¹, respectively. The ν₁ and ν₂ parallel bands are unperturbed so their analysis was straightforward and 3355 and 2433 transitions were assigned, respectively. The band origins, the rotational and centrifugal molecular constants in the v₁ = 1 and v₂ = 1 states have been determined, with standard deviation of the fits σ = 0.00019 and 0.00018 cm⁻¹. The ν₄ fundamental is affected by an anharmonic resonance with the ν₂ + ν₅ combination band. The kl > 0 sublevels cross at kl ? 27 because of the opposite values of and . The anharmonic resonance constant  cm⁻¹ has been derived. The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances have been found to be effective in ν₄, while in ν₂ + ν₅ only the Δl = Δk = ±2 one was active. A total of 5721 transitions have been assigned, 25% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants of F³⁷Cl¹⁶O₃ have been obtained. The standard deviation of the fit is 0.0006 cm⁻¹, six times the estimated data precision. The equilibrium geometry of perchloryl fluoride has been determined from the A_e and B_e constants of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃. Using the A₀ and B₀ constants of all the symmetric species the r₀ geometry has also been derived.     

Growth and characterization of two new NLO materials from the amino acid family: l-Histidine nitrate and l-Cysteine tartrate monohydrate

Single crystals of organic nonlinear optical (NLO) materials l-Histidine nitrate (C₆H₁₀N₃O₂)⁺ · (NO₃)⁻ and l-Cysteine tartrate monohydrate (C₃H₈NO₂S)⁺ · (C₄H₅O₆)⁻ · H₂O were grown by submerged seed solution method. Characterization of the crystals was made using single crystal X-ray diffraction. Fourier transform infrared (FTIR) spectroscopic studies, optical behaviour such as UV-visible-NIR absorption spectra and second harmonic generation (SHG) conversion efficiency were investigated to explore the NLO characteristics of the above materials. Microhardness measurements and dielectric studies of the compounds were also carried out.     

Theoretical investigations of the spin Hamiltonian parameters for the tetragonal [Rh(CN)4Cl2] complex in KCl

The spin Hamiltonian parameters (g factors, hyperfine structure constants and superhyperfine parameters) for the tetragonal [Rh(CN)₄Cl₂]⁴⁻ complex in KCl are theoretically investigated from the perturbation formulas of these parameters for a 4d⁷ ion in a tetragonally elongated octahedron. This center can be assigned to the substitutional Rh²⁺ on host K⁺ site reduced from Rh³⁺ by capturing one electron during the electron irradiation, associated with the two axial ligands CN⁻ replaced by two Cl⁻. The crystal-fields of the two axial Cl⁻ are weaker than those of the four planar CN⁻, yielding the tetragonal elongation distortion. This system belongs to the case of low spin (S = 1/2) under strong crystal-fields, different from that of high spin (S = 3/2) under weak and intermediate crystal-fields (e.g., 3d⁷ ions such as Fe⁺ and Co²⁺ in conventional chlorides). The calculated spin Hamiltonian parameters show good agreement with the experimental data. The above [Rh(CN)₄Cl₂]⁴⁻ complex due to the different axial and perpendicular ligands is unlike the tetragonally elongated [RhCl₆]⁴⁻ complex due to the Jahn–Teller effect in the similar NaCl:Rh²⁺ crystals.     

Removal of chloridazon by natural and ammonium kerolite samples

The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 °C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (X_m) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for X_m1 (first stage) ranged from 1.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 5.1 × 10⁻² mol kg⁻¹ for ammonium kerolite at 10 °C and the values for X_m2 (second stage) ranged from 9.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 14 × 10⁻² mol kg⁻¹ for natural kerolite at 10 °C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied.     

Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO₃)₂(CH₃OH)](NO₃) and [NdL(NO₃)₂(CH₃OH)](NO₃) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV-vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol⁻¹, ΔS=56.54 J mol⁻¹ K⁻¹ for [PrL(NO₃)₂(CH₃OH)](NO₃) and ΔH=−24.63 kJ mol⁻¹, ΔS=22.07 J mol⁻¹ K⁻¹ for [NdL(NO₃)₂(CH₃OH)](NO₃)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes-BSA system. The binding average distance between complexes and BSA was obtained on the basis of Förster's theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.     

Hydrogen peroxide biosensor based on gold nanoparticles/thionine/gold nanoparticles/multi-walled carbon nanotubes-chitosans composite film-modified electrode

In this paper, an amperometric electrochemical biosensor for the detection of hydrogen peroxide (H₂O₂), based on gold nanoparticles (GNPs)/thionine (Thi)/GNPs/multi-walled carbon nanotubes (MWCNTs)-chitosans (Chits) composite film was developed. MWCNTs-Chits homogeneous composite was first dispersed in acetic acid solution and then the GNPs were in situ synthesized at the composite. The mixture was dripped on the glassy carbon electrode (GCE) and then the Thi was deposited by electropolymerization by Au-S or Au-N covalent bond effect and electrostatic adsorption effect as an electron transfer mediator. Finally, the mixture of GNPs and horseradish peroxidase (HRP) was assembled onto the modified electrode by covalent bond. The electrochemical behavior of the modified electrode was investigated by scanning electron microscope, cyclic voltammetry and chronoamperometry. This study introduces the in situ-synthesized GNPs on the other surface of the modified materials in H₂O₂ detection. The linear response range of the biosensor to H₂O₂ concentration was from 5 × 10⁻⁷ mol L⁻¹ to 1.5 × 10⁻³ mol L⁻¹ with a detection limit of 3.75 × 10⁻⁸ mol L⁻¹ (based on S/N = 3).