Spectrophotometric determination of bismuth in water samples after preconcentration of its thiourea-bromide ternary complex on activated carbon

A simple, accurate, sensitive and reliable method for the selective extraction and spectrophotometric determination of Bi(III) was developed. Bi(III) was collected on activated carbon after complexation with thiourea and bromide ion in acidic media. The complex retained on activated carbon was then desorbed with the bromide solution in N,N-dimethylformamide (DMF) and determined spectrophotometrically at 375 nm. The linear calibration ranges and limit of detection for the proposed method was 1.00×10⁻⁹-1.50×10⁻⁷ and 8.00×10⁻¹⁰ mol l⁻¹, respectively. The influence of the interfering cations and anions on the determination of bismuth was investigated. The method was successfully applied to the extraction and determination of bismuth in natural water samples.     

Oscillations in the frequency dependence of long-range correlations of waves

We predict new oscillations in the frequency dependence of the intensity autocorrelation functions of waves for a tube geometry. We have performed numerical simulations which clearly confirm the existence of new long-range correlations.     

New phenomena in the propagation of optical waves through random media

A review is presented of some new and exciting phenomena regarding the multiple scattering of optical waves in random systems. In particular, the author develops the important role played by the vector nature of the wave on memory effects (the 'polarization memory effect'), correlations and statistical fluctuations ('microstatistics'). He also describes the recent progress on the effect of a restricted geometry on correlation phenomena and nonRayleigh statistics.     

Square Fermi surface model for conduction in linear chain mercury compounds: Hg3−δAsF6

The unusual temperature dependence of the electrical resistivity of Hg_3?δAsF₆ (δ = 0.18?0.22) is discussed in the framework of a nearly square Fermi surface model. This model predicts a T³ dependence of the resistivity, in close agreement with the recently observed T^2.8 dependence.     

Physical properties of ZnSe films prepared by two-source evaporation and a study of post doping effect

Two-source thermal evaporation method was utilized to prepare hard ZnSe thin films, the films were then immersed in silver nitrate solution for different time periods. The optical properties of the films were measured from the transmittance spectra. X-ray pattern of the films were also included. Final compositions of the resulting films were measured by EMPA method and comparisons between compositions by EMPA vs. optical absorbance were also reported. The dc electrical conductivity increased and a small shift in the optical band gap was also observed.     

Optimum location and influence of tilt angle on performance of solar PV panels

Journal of Thermal Analysis and Calorimetry - With the growing demand of economically feasible, clean, and renewable energy, the use of solar photovoltaic (PV) systems is increasing. The PV panel...     

Acyl Migration versus Epoxidation in Gold Catalysis: Facile,Switchable, and Atom‐Economic Synthesis of Acylindoles and Quinoline Derivatives

We report a switchable synthesis of acylindoles and quinoline derivatives via gold‐catalyzed annulations of anthranils and ynamides. α‐Imino gold carbenes, generated in situ from anthranils and an N,O‐coordinated gold(III) catalyst, undergo electrophilic attack to the aryl π‐bond, followed by unexpected and highly selective 1,4‐ or 1,3‐acyl migrations to form 6‐acylindoles or 5‐acylindoles. With the (2‐biphenyl)di‐tert‐butylphosphine (JohnPhos) ligand, gold(I) carbenes experienced carbene/carbonyl additions to deliver quinoline oxides. Some of these epoxides are valuable substrates for the preparation of 3‐hydroxylquinolines, quinolin‐3(4H)‐ones, and polycyclic compounds via facile in situ rearrangements. The reaction can be efficiently conducted on a gram scale and the obtained products are valuable substrates for preparing other potentially useful compounds. A computational study explained the unexpected selectivities and the dependency of the reaction pathway on the oxidation state and ligands of gold. With gold(III) the barrier for the formation of the strained oxirane ring is too high; whereas with gold(I) this transition state becomes accessible. Furthermore, energetic barriers to migration of the substituents on the intermediate sigma‐complexes support the observed substitution pattern in the final product.     

Acyl Migration versus Epoxidation in Gold Catalysis: Facile,Switchable, and Atom-Economic Synthesis of Acylindoles and Quinoline Derivatives

We report a switchable synthesis of acylindoles and quinoline derivatives via gold-catalyzed annulations of anthranils and ynamides. α-Imino gold carbenes, generated in situ from anthranils and an N,O-coordinated gold(III) catalyst, undergo electrophilic attack to the aryl π-bond, followed by unexpected and highly selective 1,4- or 1,3-acyl migrations to form 6-acylindoles or 5-acylindoles. With the (2-biphenyl)di-tert-butylphosphine (JohnPhos) ligand, gold(I) carbenes experienced carbene/carbonyl additions to deliver quinoline oxides. Some of these epoxides are valuable substrates for the preparation of 3-hydroxylquinolines, quinolin-3(4H)-ones, and polycyclic compounds via facile in situ rearrangements. The reaction can be efficiently conducted on a gram scale and the obtained products are valuable substrates for preparing other potentially useful compounds. A computational study explained the unexpected selectivities and the dependency of the reaction pathway on the oxidation state and ligands of gold. With gold(III) the barrier for the formation of the strained oxirane ring is too high; whereas with gold(I) this transition state becomes accessible. Furthermore, energetic barriers to migration of the substituents on the intermediate sigma-complexes support the observed substitution pattern in the final product.     

Shape Memory Hydrogel based on a Hydrophobically‐Modified Polyacrylamide (HMPAM)/α‐CD Mixture via a Host‐Guest Approach

A novel thermally sensitive shape memory (SM) hydrogel is prepared by block copoly­merization of a cationic surfactant monomer, dimethylhexadecyl[2‐(dimethylamino)ethylmethacrylate]ammoniumbromide (C₁₆DMAEMA), and acrylamide (AM) in the presence of α‐cyclodextrin (α‐CD) using N,N’‐methylenebisacrylamide (MBA) as a crosslinker. XRD, solid state ¹³C NMR, and DSC measurements show that the crystalline domains, induced by the hydrogen bonds between α‐CDs threaded on the hydrophobic units of the polymer chains through the host‐guest approach, can reversibly melt and crystallize at different temperatures. Rheological measurements show that both the elastic modulus G’ and viscous modulus G’’ drastically change due to the formation and dissolution of the crystalline domains. These thermo‐sensitive crystalline domains serve as reversible physical crosslinks, endowing the hydrogel with excellent SM properties. Cyclic experiments show that the hydrogel can recover to almost 100% of the deformation in each cycle and can be reused several times.

     

Nitrous oxide dimer: observation of a new polar isomer

Spectra of the nitrous oxide dimer (N2O)2 are studied in the region of the N2O nu1 fundamental band around 2230 cm-1 using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. The previously known band of the centrosymmetric nonpolar dimer is analyzed in improved detail, and a new band is observed and assigned to a polar isomer of (N2O)2. This polar form of the dimer has a slipped parallel structure, rather similar to the slipped antiparallel structure of the nonpolar form but with a slightly larger intermolecular distance. The accurate rotational parameters determined here should enable a microwave observation of the polar N2O dimer. The need for a modern ab initio investigation of the N2O-N2O intermolecular potential energy surface is emphasized.