Swift heavy ion irradiation induced modification of BiFeO3 thin films prepared by sol-gel method

We report the preparation of multiferroic BiFeO₃ thin films on ITO coated glass substrates through sol-gel spin coating method followed by thermal annealing and their modification by swift heavy ion (SHI) irradiation. X-ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO₃ evolved on annealing the films at 550°C. Both XRD and Raman studies indicated that SHI irradiation by 200 MeV Au ions result in fragmentation of particles and progressive amorphization with increasing irradiation fluence. The average crystallite size estimated from the XRD line width decreased from 38 nm in pristine sample annealed at 550°C to 29 nm on irradiating these films by 200 MeV Au ions at 1 × 10¹¹ ions cm⁻². Complete amorphization of the rhombohedral BiFeO₃ phase occurs at a fluence of 1 × 10¹² ions.cm⁻². Irradiation by another ion (200 MeV Ag) had the similar effect. For both the ions, the electronic energy loss exceeds the threshold electronic energy loss for creation of amorphized latent tracks in BiFeO₃.     

Modification of Karmarkar’s projective scaling algorithm

This paper presents a new conversion technique of the standard linear programming problem into a homogenous form desired for the Karmarkar’s algorithm, where we employed the primal–dual method. The new converted linear programming problem provides initial basic feasible solution, simplex structure, and homogenous matrix. Apart from the transformation, Hooker’s method of projected direction is employed in the Karmarkar’s algorithm and the modified algorithm is presented. The modified algorithm has a faster convergence with a suitable choice of step size.     

A new numerical approach for solving a class of singular two-point boundary value problems

In this paper, we consider the following class of singular two-point boundary value problem posed on the interval x ?? (0, 1]

$$\begin{array}{@{}rcl@{}} (g(x)y^{\prime})^{\prime}=g(x)f(x,y),\\ y^{\prime}(0)=0,\mu y(1)+\sigma y^{\prime}(1)=B. \end{array} $$

A recursive scheme is developed, and its convergence properties are studied. Further, the error estimation of the method is discussed. The proposed scheme is based on the integral equation formalism and optimal homotopy analysis method in which a recursive scheme is established without any undetermined coefficients. The original differential equation is transformed into an equivalent integral equation to remove the singularity. The integral equation is then made free of undetermined coefficients by imposing the boundary conditions on it. Finally, the integral equation without any undetermined coefficients is efficiently treated by using optimal homotopy analysis method for finding the numerical solution. The optimal control-convergence parameter involved in the components of the series solution is obtained by minimizing the squared residual error equation. The present method is applied to obtain numerical solution of singular boundary value problems arising in various physical models, and numerical results show the advantages of our method over the existing methods.     

Copper mediated coupling of 2-(piperazine)-pyrimidine iodides with aryl thiols using Cu(I)thiophene-2-carboxylate

A copper-mediated synthesis of diaryl sulfides utilizing Cu(I)-thiophene-2-carboxylate (CuTC) is described. We demonstrate the use of CuTC as a soluble, non-basic catalyst in the coupling of aryl iodides and aryl thiols in the synthesis of synthetically advanced diaryl sulfides. This method allows for the successful coupling of challenging substrates including ortho-substituted and heteroaryl iodides and thiols. Additionally, most of the aryl iodide substrates used here contain the privileged piperazine scaffold bound to a pyrimidine, pyridine, or phenyl ring and thus this method allows for the elaboration of complex piperazine scaffolds into molecules of biological interest. The method described here enables the incorporation of late-stage structural diversity into diaryl sulfides containing the piperazine ring, thus enhancing the number and nature of derivatives available for SAR investigation.     

Implication of Threonine-Based Ionic Liquids on the Structural Stability,Binding and Activity of Cytochrome c

Ionic liquids (ILs) are useful in pharmaceutical industries and biotechnology as alternative solvents or sources for protein extraction and purification, preservation of biomolecules and for regulating the catalytic activity of enzymes. However, the binding mechanism, the non-covalent forces responsible for protein-IL interactions and dynamics of proteins in IL need to be investigated in depth for the effective use of ILs as alternatives. Herein, we disclose the molecular level understanding of the structural intactness and reactivity of a model protein cytochrome c (Cyt c) in biocompatible threonine-based ILs with the help of experimental techniques such as isothermal titration calorimetry (ITC), fluorescence spectroscopy, transmission electron microscopy (TEM) as well as molecular docking. Hydrophobic and electrostatic forces are responsible for the structural and conformational integrity of Cyt c in IL. The ITC experiments revealed the Cyt c-IL binding free energies are in the range of 10–14 kJ/mol and the molecular docking studies demonstrated that ILs interact at the surfaces of Cyt c. The results look promising as the ILs used here are non-toxic and biocompatible, and thus may find potential applications in structural biology and biotechnology.     

The 3-Thioxo-1,2-Dithiol-4-yl Group: A Versatile One Endowed Also With a –R Electronic Effect

The pK_a values in an aqueous solution of some 4-aminodithiolethiones, 4-aminodithiolones, 5-phenyl-4-hydroxydithiolethione, and 5-phenyl-4-hydroxydithiolone were determined by UV-VIS spectrophotometry at 298 K. These compounds exhibited unexpectedly very low pK_a values in the range of 0–2 for amino derivatives and in the range of 7 for hydroxy derivatives. Electronic structure calculations by ab initio and DFT methods together with an X-ray measurement indicated that these results may be attributed to a markedly negative π charge on the carbon 5 together with a positive π charge on the basic substituent of the carbon 4. As a result, the dithiole nucleus exerts in this case a strong ─R effect. Although they were very low, pK _a values of 4-aminodithiolethiones remained still higher than those found with 5-aminodithiolethiones, which were also determined in this work for comparison. The latter were not unexpectedly in the range -3 < pH < ?2.     

Equivalence of the Generalized Vertical Block Linear Complementarity Problems and Linear Complementarity Problems

In this paper, generalization of a vertical block linear complementarity problem associated with two different types of matrices, one of which is a square matrix and the other is a vertical block matrix, is proposed. The necessary and sufficient conditions for the existence of the solution of the generalized vertical block linear complementarity problem is derived and the relationship between the solution set of the generalized vertical block linear complementarity problem and the linear complementarity problem is established. It is proved that the generalized vertical block linear complementarity problem has the P-property if and only if the vertical block linear complementarity problem has the P-property.