Electrochemical synthesis of Ag nanoparticles supported on glassy carbon electrode by means of p-isopropyl calix[6]arene matrix and its application for electrocatalytic reduction of H2O2

The silver nanoparticles were prepared on the glassy carbon (GC) electrode, modified with p-iso propyl calix[6]arene, by preconcentration of silver ions in open circuit potential and followed by electrochemical reduction of silver ions. The stepwise fabrication process of Ag nanoparticles was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared Ag nanoparticles were deposited with an average size of 70 nm and a homogeneous distribution on the surface of electrode. The observed results indicated that the presence of calixarene layer on the electrode surface can control the particle size and prevent the agglomeratione and electrochemical deposition is a promising technique for preparation of nanoparticles due to its easy-to-use procedure and low cost of implementation. Cyclic voltammetry experiments showed that Ag nanoparticles had a good catalytic ability for the reduction of hydrogen peroxide (H₂O₂). The effects of p-isopropyl calix[6]arene concentration, applied potential for reduction of Ag⁺, number of calixarene layers and pH value on the electrocatalytic ability of Ag nanoparticles were investigated. The present modified electrode exhibited a linear range from 5.0 × 10⁻⁵ to 6.5 × 10⁻³ M and a detection limit 2.7 × 10⁻⁵ M of H₂O₂ (S/N = 3) using amperometric method.     

Bose-Einstein Condensation and Spontaneous Symmetry Breaking

After recalling briefly the connection between spontaneous symmetry breaking and off-diagonal long-range order for models of magnets a general proof of spontaneous breaking of gauge symmetry as a consequence of Bose-Einstein condensation is presented. The proof is based on a rigorous validation of Bogoliubov's c-number substitution for the k = 0 mode operator α₀.     

Study on the interaction of tropisetron hydrochloride and l-tryptophan by spectrofluorimetry and its analytical application

A new method to determine tropisetron hydrochloride with l-tryptophan in the medium with pH=9.0 was studied, which is based on the fluorescence quenching effect of tropisetron hydrochloride on l-tryptophan. The fluorescence quenching mechanism and various factors influencing fluorescence quenching were discussed. Under the optimum conditions, the linear range and detection limit were 0.03-12.0 and 0.01 μg/mL (correlation coefficient r=0.9970), respectively. The calibration curve equation was ΔF=6.17+12.56 C (μg/mL). RSD was 3.4% (c=4.0 μg/mL, n=5); the detection limit estimated (S/N=3) was 0.01 μg/mL. The proposed method had been successfully applied to determine tropisetron hydrochloride in real samples and the obtained results were in good agreement with the results of the official method.     

Transverse magneto-optical Kerr effect of Fe at the 2p excitation threshold

The transverse magneto-optical Kerr effect (T-MOKE) was investigated for thin epitaxial Fe films grown on Ag(0 0 1) in the region of the 2p excitation threshold. The experimental reflectivity and asymmetry spectra are compared to those derived from the complex dielectric function tensor calculated by using the first-principles spin-polarized relativistic band theory. We found that the T-MOKE asymmetry in general is a mixture of both the real and imaginary parts of the off-diagonal element of the dielectric function tensor, depending sensitively on the relative magnitudes of real and imaginary parts of the diagonal element. For angles of incidence larger than about 5° the influence of the Ag-substrate is significant. The major features in experimental and calculated reflectivity and asymmetry spectra are in agreement.     

An ab initio study of the electronic structure and elastic properties of the newly discovered ternary carbide

The electronic structure and elastic properties of the newly discovered ternary layered carbide Ti₄GaC₃ were investigated by means of the first-principle plane-wave pseudopotential total energy calculation method based on density functional theory. The computed results, including lattice constants and internal coordinates, are in good agreement with experimental values. The elastic moduli of ideal polycrystalline Ti₄GaC₃ were predicted from the individual elastic constants by Voigt approximation. The band structure shows that the electrical conductivity is metallic and anisotropic, with a high density of states at the Fermi energy. The elastic properties are anisotropic, related to the Ti–Ga bonds being relatively weaker than the Ti–C bonds.     

Isotopic study of the transition of calcium monomethoxide using laser excitation and population depletion spectroscopy

High resolution excitation spectra have been obtained of the 0–0 band of the transition of four isotopologues, CaO¹²CH₃, CaO¹³CH₃, CaO¹²CD₃ and CaO¹³CD₃ of calcium monomethoxide. The deuterated species were found to have unexpectedly complicated spectra, and definitive rotational assignments were possible only from investigation by optical optical double resonance (OODR) population depletion spectroscopy. This confirmed the assignment of the CaO¹²CD₃ spectrum, and proved crucial in assigning the K-structure and spin components for CaO¹³CD₃. The state was found to be well described by the symmetric rotor model with C_3v symmetry for both hydride species but, for the deuterides, the K-structure and spin rotation splittings were irregular, especially for CaO¹³CD₃ where the K = 0 and 1 levels were heavily perturbed. The changes in the A constant determined for the hydride suggest that the CH₃ umbrella opens by 0.4°, i.e., 0.2° further on excitation to the state than on excitation to the lower-lying state (geometry change established in an earlier experiment by Crozet et al. [P. Crozet, A.J. Ross, C. Linton, A.G. Adam, W.S. Hopkins, R.J. Le Roy, J. Mol. Spectrosc. 229 (2005), 224–230]).     

Theoretical study on complexation of the perchlorate,permanganate, pertechnate and perrhenate anions with dodecabenzylbambus[6]uril

By using quantum chemical calculations, the most probable structures of the anionic complex species dodecabenzylbambus[6]uril–ClO₄^?, dodecabenzylbambus[6]uril–MnO₄^?, dodecabenzylbambus[6]uril–TcO₄^? and dodecabenzylbambus[6]uril–ReO₄^? were derived. In these four complexes, each of the considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion. Further, the corresponding interaction energies of the investigated four anionic complexes were calculated; the absolute values of these calculated energies increase in the series of ReO₄^? < TcO₄^? < MnO₄^? < ClO₄^?.     

New observation of the , 1Δg, and 2Πg states and molecular constants with all Li2, Li2, and LiLi data

This paper reports our new observation of the , 1³Δ_g (v = 2–4), and 2³Π_g (v = 2–8) states of ⁶Li⁷Li by continuous wave perturbation facilitated optical–optical double resonance spectroscopy. Combining our new experimental term values of ⁶Li⁷Li with the available experimental data of ⁶Li₂ and ⁷Li₂, molecular constants and potential energy curves by Rydberg–Klein–Rees and direct-potential-fit techniques have been determined. Born-Oppenheimer breakdown parameters of the Li₂ 1³Δ_g and 2³Π_g states are calculated.     

Universal rise of hadronic total cross sections based on forward πp and scatterings

Recently there are several evidences of the increase of the total cross section σ_tot to be log²s consistent with the Froissart unitarity bound, and the COMPETE collaborations in the PDG have further assumed σ_totBlog²(s/s₀) to extend its universal rise with a common value of B for all the hadronic scatterings. However, there is no rigorous proof yet based only on QCD. Therefore, it is worthwhile to prove this universal rise of σ_tot even empirically. In this Letter we attempt to obtain the value of B for πp scattering, B_πp, with reasonable accuracy by taking into account the rich πp data in all the energy regions. We use the finite-energy sum rule (FESR) expressed in terms of the πp scattering data in the low and intermediate energies as a constraint between high-energy parameters. We then have searched for the simultaneous best fit to the σ_tot and ρ ratios, the ratios of the real to imaginary parts of the forward scattering amplitudes. The lower energy data are included in the integral of FESR, the more precisely determined is the non-leading term such as logs, and then helps to determine the leading terms like log²s. We have derived the value of B_πp as B_πp=0.311±0.044 mb. This value is to be compared with the value of B for scattering, B_pp, in our previous analysis [M. Ishida, K. Igi, Eur. Phys. J. C 52 (2007) 357], B_pp=0.289±0.023 mb. Thus, our result appears to support the universality hypothesis.     

Flourimetric and prototropic studies on the inclusion complexation of 2-amino and 4-aminodiphenyl ethers with β-cyclodextrin: Unusual behavior of 4-aminodiphenyl ether

The fluorescence characteristics of diphenyl ether (DPE), 2-aminodiphenyl ether (2ADPE) and 4-aminodiphenyl ether (4ADPE) and prototropic behavior of 2ADPE and 4ADPE on inclusion complexation with β-cyclodextrin have been investigated. DPE forms 1:1 complex whereas 2ADPE and 4ADPE form 1:2 complex with β-CDx. The fluorimetric and prototropic behaviors of 4ADPE in β-CDx are different from those in aqueous solution. The dual fluorescence of 4ADPE in β-CDx is found to be due to twisted intramolecular charge transfer (TICT) character induced by inclusion complexation. The two equilibria viz. monocation↔monocation solvent exciplex↔neutral reported for 4ADPE in aqueous solution are not observed in presence of β-CDx. The ground and excited state pK_a values for monocation-neutral equilibrium of 2ADPE and 4ADPE have been reported.     

Fluorescence enhancement of the aflatoxin B1 by forming inclusion complexes with some cyclodextrins and molecular modeling study

The interaction between the aflatoxin B₁ (AFB₁) and three cyclodextrins, α-cyclodextrin (α-CD), β-cyclodextrin (β-CD) and heptakis-2,6-dimethyl-o-β-cyclodextrin (ome-CD), was studied by spectrofluorescence technique. It was found that the inclusion association behavior occurs for the complexes of cyclodextrins with AFB₁. The fluorescence of AFB₁ is generally enhanced in the complexes with cyclodextrins in aqueous solutions. The inclusion complex constants of the three types of cyclodextrins at different temperatures were evaluated from Benesi-Hildebrand plot and also by non-linear regression analysis. These cyclodextrins can only form the 1:1 (host:guest) inclusion complex in the studied temperature range of 20-50 °C. The enthalpy (ΔH°) and entropy (ΔS°) changes of complexation were extracted from the temperature dependency of complex formation constants (K). Temperature-dependent measurements showed that the association step is controlled by enthalpy-entropy compensation effect. The use of ome-CD generally resulted in the greatest fluorescence intensity. On the other hand, the discrepancy between the exhibited enhanced fluorescence and thermodynamic parameters (ΔG°) is proposed to be different only by the orientation of the AFB₁ within the cyclodextrin cavity. To find the most favorable structure, the geometry of complex was investigated by molecular modeling approach employing the semiemperical HF-SCF calculations.     

High-temperature specific heat and susceptibility of the quadratic S = 12 XY model. Comparison with data on CoCl2.6H2O and CoBr2.6H2O

This susceptibility of the quadratic, $\text{S =}\text{1}\text{2}$, XY model as determined by the high-temperature series expansion is presented and compared with experimental data on CoCl₂.6H₂O and CoBr₂.6H₂O. For the specific heat of CoCl₂.6H₂O a similar comparison is made. For kT/|J| > 1.5 a good agreement between theory and experiment is found, yielding J/k = ?2.05 ± 0.1 and ?2.45 ± 0.1 K for the intralayer exchange of the Cl and the Br salt, respectively. These values compare favourably with those available from other sources.