Theoretical study of selenium and tellurium impurities in (ZnO)6 clusters using DFT and TDDFT

Zinc oxide (ZnO) nanostructures have attracted much interest due to their potential applications in various fields including optoelectronics, glass industries, and solar cells. These compounds hold the promise of creating new materials that can advance energy technologies. In this work, a series of (ZnO)₆ clusters with selenium and tellurium applied as substitutional impurities has been studied. The investigated structures have been produced through the doping of (ZnO)₆ clusters by replacing an oxygen atom with a selenium or a tellurium atom at each time. The ground state geometric parameters of (ZnO)₆ structures, containing selenium or tellurium atoms as substitutional impurities, were calculated using density functional theory (DFT) with B3LYP and LanL2DZ basis set. Excited state energies and absorption wavelengths were computed using time‐dependent‐DFT (TDDFT). For the calculation of emission wavelengths, Hartree–Fock configuration interaction singles (HF/CIS) has been used in order to perform the excited state geometry optimization. This work led to some important results that can be helpful for developing novel THz sensitive materials and imaging detectors that may be an alternative to x‐rays detectors for radiology as well as for the development of solar cells and electroluminescent diodes. Zinc oxide (ZnO) nanostructures have attracted growing interest due to their potential applications in many technological fields, including optoelectronics, the glass industry, and energy. The presence of impurities, in particular selenium and tellurium, in ZnO‐based clusters can affect their structural and spectroscopic properties. Some of these doped nanostructures have favorable Terahertz emission characteristics that make them good candidates for applications in biology and medicine.     

Asymptotic decay under nonlinear and noncoercive dissipative effects for electrical conduction in biological tissues

We consider a nonlinear model for electrical conduction in biological tissues. The nonlinearity appears in the interface condition prescribed on the cell membrane. The purpose of this paper is proving asymptotic convergence for large times to a periodic solution when time-periodic boundary data are assigned. The novelty here is that we allow the nonlinearity to be noncoercive. We consider both the homogenized and the non-homogenized version of the problem.     

Improvement of kinetics,yield, and colloidal stability of biogenic gold nanoparticles using living cells of <Emphasis Type="Italic">Euglena gracilis</Emphasis> microalga

Recent years have witnessed a boom in the biosynthesis of a large variety of nanomaterials using different biological resources among which algae-based entities have been gaining much more attention within the community of material scientists worldwide. In our previously published findings, we explored some factors that governed the biofabrication of gold nanoparticles using living cultures of microalgae, such as the utilized microalgal genera, the phylum they belong to, and the impact of tetrachloroauric acid concentrations on the ability of these strains to perform the biosynthesis of gold nanoparticles once in contact with these cations. As a follow-up, we present in this paper an improvement of the features of bioproduced gold colloids using living cells of Euglena gracilis microalga when this species is grown under either mixotrophic or autotrophic conditions, i.e., exposed to light and grown in an organic carbon-enriched culture medium versus under autotrophic conditions. As an outcome to this alteration, the growth rate of this photosynthetic microorganism is multiplied 7–8 times when grown under mixotrophic conditions compared to autotrophic ones. Therefore, the yield, the kinetics, and the colloidal stability of the biosynthesized gold nanoparticles are dramatically enhanced. Moreover, the shape and the size of the as-produced nano-objects via this biological method are affected. In addition to round-shaped gold nanoparticles, particular shapes, such as triangles and hexagons, appear. These findings add up to the amassed knowledge toward the design of photobioreactors for the scalable and sustainable production of interesting nanomaterials.     

Surface patch binding induced intermolecular complexation and phase separation in aqueous solutions of similarly charged gelatin-chitosan molecules

The formation of selective surface patch binding induced complex coacervates between polyions, chitosan (cationic polyelectrolyte), and alkali-processed gelatin (polyampholyte), both carrying similar net charge, was investigated for two volumetric mixing ratios: r = [chitosan]/[gelatin] = 1:5 and 1:10. Formation of soluble intermolecular complexes between gelatin and chitosan molecules was observed in a narrow range of pH, though these biopolymers had the same kind of net charge, which was evidenced from electrophoretic measurement. This clearly established the role played by selective surface patch binding driven interactions. The temperature sweep measurements conducted on these coacervate samples through rheology and differential scanning calorimetry (DSC) studies yielded two characteristic melting temperatures located at approximately 68 +/- 3 degrees C and 82 +/- 3 degrees C. In the flow mode, the shear viscosity (eta) of the coacervate samples was found to scale with (power-law model) applied shear rate (gamma*) as eta(gamma*) approximately (gamma*)(-k); this yielded k = 0.76 +/- 0.2 (1 s(-1) < gamma* < 100 s(-1)), indicating non-Newtonian behavior. The static structure factor (I(q)) deduced from small angle neutron scattering (SANS) data in the low q (q is the scattering wavevector) (0.018 A(-1) < q < 0.072 A(-1)) region was fitted to the Debye-Bueche regime, I(q) approximately 1/(1 + zeta(2)q(2))2 that yielded a size of zeta approximately 215 +/- 20 A (for r = 1:10) and zeta approximately 260 +/- 20 A (for r = 1:5) samples, implying change in the size of inhomogeneities present with mixing ratio. In the intermediate q region, called the Ornstein-Zernike regime, I(q) approximately 1/(1 + xi(2)q(2)) gave a correlation length of xi approximately 10.0 +/- 2.0 A independent of the mixing ratio. The results taken together imply the existence of a weakly interconnected and heterogeneous network structure inside the coacervate phase separated by domains of polymer-poor regions.     

A nearly optimal preconditioning based on recursive red–black orderings

Considering matrices obtained by the application of a five-point stencil on a 2D rectangular grid, we analyse a preconditioning method introduced by Axelsson and Eijkhout, and by Brand and Heinemann. In this method, one performs a (modified) incomplete factorization with respect to a so-called ‘repeated’ or ‘recursive’ red–black ordering of the unknowns while fill-in is accepted provided that the red unknowns in a same level remain uncoupled. Considering discrete second order elliptic PDEs with isotropic coefficients, we show that the condition number is bounded by 𝒪(n ${}^{\text{½ log}{}_{\text{2}}\text{(√(5) −1)}}$ ) where n is the total number of unknowns (½ log₂(√(5) − 1) = 0.153), and thus, that the total arithmetic work for the solution is bounded by 𝒪(n^1.077). Our condition number estimate, which turns out to be better than standard 𝒪(log² n) estimates for any realistic problem size, is purely algebraic and holds in the presence of Neumann boundary conditions and/or discontinuities in the PDE coefficients. Numerical tests are reported, displaying the efficiency of the method and the relevance of our analysis. © 1997 John Wiley & Sons, Ltd.     

A study of random Weyl trees

We study binary search trees constructed from Weyl sequences {nθ}, n≥1, where θ is an irrational and {·} denotes “mod 1.” We explore various properties of the structure of these trees, and relate them to the continued fraction expansion of θ. If H_n is the height of the tree with n nodes when θ is chosen at random and uniformly on [0, 1], then we show that in probability, H_n∼(12/π²)log n log log n. © 1998 John Wiley & Sons, Inc. Random Struct. Alg., 12, 271–295, 1998     

Synthesis of 7-(E)-alkenyl-4-amino-3-quinolinecarbonitriles via Pd-mediated Heck, Stille, and Suzuki reactions

A regio- and stereoselective synthesis of 7-(E)-alkenyl-4-amino-3-quinolinecarbonitriles via Pd-mediated coupling reactions was developed. The comparison and optimization of stereoselectivity of the Heck, Stille, and Suzuki reactions of 7-bromo or 7-triflate-3-quinolinecarbonitrile are described. Compound 7 and 10 were potent inhibitors of Src kinase and Raf/Mek activity, respectively.     

Strong CH⋅⋅⋅Halide Hydrogen Bonds from 1,2,3‐Triazoles Quantified Using Pre‐Organized and Shape‐Persistent Triazolophanes

The structures associated with halide (F^?, Cl^?, Br^?) complexation inside CH hydrogen‐bonding macrocyclic receptors, called triazolophanes, are characterized using density functional theory (DFT). The associated binding energies in the gas and solution phases are evaluated. The ruffles in the empty triazolophane become smoothed‐out upon Cl^?‐ and Br^?‐ion binding directly into the middle of the cavity. The largely pre‐organized cavity morphs into an elliptical shape to facilitate shorter hydrogen bonds in the north and south regions and longer ones west and east. The smaller F^? ion sits in, and flattens‐out, only the north (or south) region. The 1,2,3‐triazoles show shorter CH???Cl^? contacts than for the phenylenes. Both Cl^? and Br^? show the same binding geometries but Cl^? has a larger binding energy consistent with its stronger Lewis basicity. Model triads were used to decompose the overall binding energy into those of its components. In the course of this triad analysis, anion polarization was identified and its contribution to the triad???Cl^? binding energy estimated. Consequently, the binding energies for the individual aryl units within the comparatively non‐polarized triazolophanes were estimated. The 1,2,3‐triazoles are twice as strong as the phenylenes thus contributing most of the interaction energy to Cl^?‐ion binding. Therefore, the 1,2,3‐triazoles appear to approach the hydrogen bond strengths of the NH donors of pyrrole units.