An efficient method for synthesis of acylals from aldehydes using multi-walled carbon nanotubes functionalized with phosphonic acid(MWCNTs-C-PO_3H_2)

MWCNTs-C-PO_3H_2 has been used as an efficient,heterogeneous and reusable nanocatalyst for synthesis of acylals from aldehydes under solvent-free conditions at room temperature.A wide range of aldehydes was studied and corresponding products were obtained in good to excellent yields in short reaction times.Nanocatalyst can be easily recovered by centrifuge and reused for subsequent reactions for at least five times without deterioration in catalytic activity.The major advantages of the present method are high yields,short reaction time,recyclable catalyst and solvent-free reaction conditions at room temperature.     

Synthesis,characterization, anticancer activity,thermal and electrochemical studies of some novel uranyl Schiff base complexes

Some tetradentate N₂O₂ Schiff base ligands, such as N,N′-bis(naphtalidene)-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-methyl-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-chloro-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-nitro-1,2-phenylenediamine, N,N′-bis(naphtalidene)-4-carboxyl-1,2-phenylenediamine, and their uranyl complexes were synthesized and characterized by ¹H NMR, IR, UV–Vis spectroscopy, TG (thermogravimetry), and elemental analysis (C.H.N.). Thermogravimetric analysis shows that uranyl complexes have very different thermal stabilities. This method is used also to establish that only one solvent molecule is coordinated to the central uranium ion and this solvent molecule does not coordinate strongly and is removed easier than the tetradentate ligand and also trans oxides. The electrochemical properties of the uranyl complexes were investigated by cyclic voltammetry. Electrochemistry of these complexes showed a quasireversible redox reaction without any successive reactions. Also, the kinetic parameters of thermal decomposition were calculated using Coats–Redfern equation. According to Coats–Redfern plots the kinetics of thermal decomposition of the studied complexes is first-order in all stages. Anticancer activity of the uranyl Schiff base complexes against cancer cell lines (Jurkat) was studied and determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide) assay.     

Runge-Kutta methods without order reduction for linear initial boundary value problems

Summary. It is well-known the loss of accuracy when a Runge–Kutta method is used together with the method of lines for the full discretization of an initial boundary value problem. We show that this phenomenon, called order reduction, is caused by wrong boundary values in intermediate stages. With a right choice, the order reduction can be avoided and the optimal order of convergence in time is achieved. We prove this fact for time discretizations of abstract initial boundary value problems based on implicit Runge–Kutta methods. Moreover, we apply these results to the full discretization of parabolic problems by means of Galerkin finite element techniques. We present some numerical examples in order to confirm that the optimal order is actually achieved. Received July 10, 2000 / Revised version received March 13, 2001 / Published online October 17, 2001     

Application of graphene oxide nanosheets as probe oligonucleotide immobilization platform for DNA sensing

In this work, a simple and novel electrochemical biosensor based on a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) was developed for detection of DNA sequences. The morphology of prepared nanoplatform was investigated by scanning electron microscopy, infrared (FTIR) and UV/Vis absorption spectra. The fabrication processes of electrochemical biosensor were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in an aqueous solution. The optimization of experimental conditions such as immobilization of the probe BRCA1 and its hybridization with the complementary DNA was performed. Due to unique properties of graphene oxide nanosheets such as large surface area and high conductivity, a wide liner range of 1.0 × 10^?17–1.0 × 10^?9 M and detection limit of 3.3 × 10^?18 M were obtained for detection of BRCA1 5382 mutation by EIS technique. Under the optimum conditions, the proposed biosensor (ssDNA/GO/GCE) revealed suitable selectivity for discriminating the complementary sequences from non-complementary sequences, so it can be applicable for detection of breast cancer.     

Ab initio investigation of the structural and unusual electronic properties of α-CuSe （klockmannite）

In this article, a computational analysis has been performed on the structural properties and predominantly on the electronic properties of the α-CuSe （klockmannite） using density functional theory. The studies in this work show that the best structural results, in comparison to the experimental values, belong to the PBEsol-GGA and WC-GGA functionals. However, the best results for the bulk modulus and density of states （DOSs） are related to the local density approximation （LDA） functional. Through utilized approaches, the LDA is chosen to investigate the electronic structure. The results of the electronic properties and geometric optimization of α-CuSe respectively show that this compound is conductive and non-magnetic. The curvatures of the energy bands crossing the Fermi level explicitly reveal that major charge carriers in CuSe are holes, whose density is estimated to be 0.86×1022 hole/cm3. In particular, the Fermi surfaces in the first Brillouin zone demonstrate interplane conductivity between （001） planes. Moreover, the charge carriers among them are electrons and holes simultaneously. The conductivity in CuSe is mainly due to the hybridization between the d orbitals of Cu atoms and the p orbitals of Se atoms. The former orbitals have the dual nature of localization and itinerancy.     

Ground state and excited state dipole moments of 6,8-diphenylimidazo[1,2-α]pyrazine determined from solvatochromic shifts of absorption and fluorescence spectra

Electronic absorption and dual fluorescence spectra of 6,8-diphenylimidazo[1,2-α]pyrazine (68DIP) was recorded in various solvents with different polarity at room temperature. The ground state (μg) and the excited state (μg) dipole moments of 68DIP were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (?) and refractive index (n). The results show that the value of excited state dipole moment in SE: μeSE=2.8772 D and twisted intramolecular charge transfer (TICT) excited equilibrated state dipole moment value of μeLE=2.9744 D was found. The solvent dependent spectral shifts in absorption and fluorescence spectra were analyzed by the polarizability-polarity and Kamlet-Taft parameters.     

Synthesis of Dendrimer‐Like Polyindolyl Compounds

Syntheses of polyindolyl compounds from the Friedel–Crafts reaction of indoles and tri‐ or tetra‐aldehydes catalyzed by silica sulfuric acid are described. These dendrimeric supramolecules were effectively prepared at room temperature in quantitative yield. These novel products have potential in the synthesis of dyes and pigments and also in various pharmaceutical applications.