Investigation of DNA cleavage activities of new oxime-type ligand complexes and molecular modeling of complex-DNA interactions

Nucleolytic activities of some new oxime-type ligand complexes were investigated by neutral agarose gel electrophoresis. Analysis of the cleavage products in agarose gel indicated that all complexes used converted supercoiled pUC18 plasmid DNA to its nicked or linear form. It was found that nucleolytic activities of the complexes depend on the complex concentration, reaction time and the presence of a cooxidant (magnesium monoperoxyphthalate, MMPP) in the reaction mixture. However, the complexes cleaved pUC18 plasmid DNA at all investigated pH values. Nucleolytic activities of complexes were investigated for different complex concentrations (0.1–100 μmol L⁻¹), pH values (6.0–10.0) and reaction times (0–60 min). Molecular modeling studies performed by the Hyperchem Software together with DNA-binding studies showed that planar sites of the complexes intercalated into double stranded DNA. It can be concluded that all oxime-type ligand complexes used can be evaluated as nuclease mimics.     

Transient nonlinear optically-thick radiative–convective double-diffusive boundary layers in a Darcian porous medium adjacent to an impulsively started surface: Network simulation solutions

A boundary-layer model is described for the two-dimensional nonlinear transient thermal convection heat and mass transfer in an optically-thick fluid in a Darcian porous medium adjacent to an impulsively started vertical surface, in the presence of significant thermal radiation and buoyancy forces in an (X¹,Y¹,t¹) coordinate system. An algebraic approximation is employed to simplify the integro-differential equation of radiative transfer for unidirectional flux normal to the plate into the boundary-layer regime, by incorporating this flux term in the energy conservation equation. The conservation equations are non-dimensionalized into an (X,Y,T) coordinate system and solved using the Network Simulation Method (NSM), a robust numerical technique which demonstrates high efficiency and accuracy. The transient variation of non-dimensional streamwise velocity component (u) and temperature (T) and concentration (C) functions is computed for various selected values of Stark number (radiation–conduction interaction parameter) and Darcy number. Transient velocity (u) and steady-state local skin friction (τ_X) are also studied for various thermal Grashof number (Gr), species Grashof number (Gm), Schmidt number (Sc) and Stark number (N) values. These computations for the infinite permeability case (Da → ∞) are compared with previous finite difference solutions [Prasad et al. Int J Therm Sci 2007;46(12):1251–8] and shown to be in excellent agreement. An increase in Darcy number is seen to accelerate the flow and boost velocity. A decrease in Stark number (corresponding to an increase in thermal radiation heat transfer contribution) is shown to increase the velocity values. Temperature function is observed to fall in value with a rise in Da and increase with decrease in N (corresponding to an increase in thermal radiation heat transfer contribution). Applications of the study include rocket combustion chambers, astrophysical flows, spacecraft thermal fluid dynamics in debris-laden environments (cosmic dust), heat transfer in forest fire spread, geochemical contamination and ceramic materials processing.     

Dissociative recombination of ammonia clusters studied by storage ring experiments

Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)2, H+(NH3)3, D+(ND3)2, and D+(ND3)3 in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)2 and D+(ND3)2 show no clear isotope effect. Dissociative recombination of X+(NX3)2 (X=H or D) is dominated by the product channels 2NX3+X [0.95+/-0.02 for H+(NH3)2 and 1.00+/-0.02 for D+(ND3)2]. Dissociative recombination of D+(ND3)3 is dominated by the channels yielding three N-containing fragments (0.95+/-0.05).     

Catalytic destruction of brominated aromatic compounds studied in a catalyst microbed coupled to gas chromatography/mass spectrometry

The capability of solid porous catalysts has been studied for the destruction or modification of halogenated aromatic compounds contaminating the pyrolysis oil of recycled plastics from electronic waste. A fast and simple experimental procedure is carried out using a micropyrolyser coupled to GC-MS in such a way that catalyst microbed was placed in the sample tube of the pyrolyser. The pyrolysis products of polycarbonate blended with a frequently applied flame retardant tetrabromobisphenol A (TBBPA) and epoxy resin containing TBBPA monomer units have been analysed, and the brominated components were compared with the thermal decomposition products of TBBPA and its diallyl ether. When TBBPA vapour passes through molecular sieve 4A a slight debromination and a partial cleavage of bisphenol A into phenols occur. Over molecular sieves of larger pore size (13X and NaY zeolite) an important decrease of TBBPA amount is observed indicating effective trapping ability of these catalysts of basic character for brominated aromatic compounds. A total chemical modification of the vapour was achieved by Al-MCM-41 catalyst that split TBBPA into bromophenols. Analogous results were obtained by carrying out similar experiments on diallyl ether of TBBPA. Moreover, it was revealed that brominated bisphenol A compounds are modified essentially the same way, either evaporated or evolved from a polycarbonate blend or produced by pyrolysis from an epoxy resin.     

The Effect of Isopropyl Alcohol and Non-Ionic Surfactant Mixtures on the Wetting of Porous Coated Paper

The influence of isopropyl alcohol and non-ionic surfactant solutions on aqueous droplet wetting behaviour on porous coated paper was determined. Paper coatings provide a micro- and nano-porous surface structure, which strictly speaking cannot be described in simple roughness terms as sub-surface lateral absorption directly impacts on the apparent contact angle. It is this very deviation from an idealised system that leads to novel wetting phenomena. Isopropyl alcohol and surfactant-based systems, both of which are commonly used in the printing industry, show differences in wetting behaviour, on both short and long timescales, with changes in the relative composition of the mixtures. Small variations of 0.1?wt% in surfactant concentration have a dramatic influence on the dynamic surface tension, and thus the wetting. It was observed that the wetting kinetics for isopropyl alcohol and surfactant solutions were different in terms of both wetting area and the penetration rate, even in cases where the dynamic surface tension of the solutions was kept the same. Different stages in the wetting and following drying processes could be observed with near infrared spectral imaging. In addition, the surfactant chemistries such as their degrees of hydrophilicity and molecular weights generated comparative differences in the wetting kinetics. The dominating factor affecting the wetting was, as expected, the solid?Cliquid interfacial energy defined on the practical porous substrate, which differed from the direct comparison with dynamic surface tension, thus exemplifying the deviation from idealised surface roughness behaviour when considering porous materials. An apparent ??equivalent?? surface roughness value for the porous material was determined, and it was seen that an increase in this equivalent parameter enhanced the rate of wetting behaviour with decreasing solution surface tension, and so also affected the wetting evolution. The wetting was enhanced by cavities in the coating layer, which were enlarged by the penetrating liquids.     

Large-Eddy Simulation of the Flow Over a Circular Cylinder at Reynolds Number 3900 Using the OpenFOAM Toolbox

The flow over a circular cylinder at Reynolds number 3900 and Mach number 0.2 was predicted numerically using the technique of large-eddy simulation. The computations were carried out with an O-type curvilinear grid of size of 300 × 300 × 64. The numerical simulations were performed using a second-order finite-volume method with central-difference schemes for the approximation of convective terms. A conventional Smagorinsky and a dynamic k-equation eddy viscosity sub-grid scale models were applied. The integration time interval for data sampling was extended up to 150 vortex shedding periods for the purpose of obtaining a fully converged mean flow field. The present numerical results were found to be in good agreement with existing experimental data and previously obtained large-eddy simulation results. This gives an indication on the adequacy and accuracy of the selected large-eddy simulation technique implemented in the OpenFOAM toolbox.     

Legendre Pseudospectral Approximation of Boussinesq Systems and Applications to Wave Breaking

In this paper, we propose a spectral projection of a regularized Boussinesq system for wave propagation on the surface of a fluid. The spectral method is based on the use of Legendre polynomials, and is able to handle time-dependent Dirichlet boundary conditions with spectral accuracy.The algorithm is applied to the study of undular bores, and in particular to the onset of wave breaking connected with undular bores. As proposed in [2], an improved version of the breaking criterion recently introduced in [5] is used. This tightened breaking criterion together with a careful choice of the relaxation parameter yields rather accurate predictions of the onset of breaking in the leading wave of an undular bore.     

Weakly driven anomalous diffusion in non-ergodic regime: an analytical solution

We derive the probability density of a diffusion process generated by nonergodic velocity fluctuations in presence of a weak potential, using the Liouville equation approach. The velocity of the diffusing particle undergoes dichotomic fluctuations with a given distribution ψ(τ) of residence times in each velocity state. We obtain analytical solutions for the diffusion process in a generic external potential and for a generic statistics of residence times, including the non-ergodic regime in which the mean residence time diverges. We show that these analytical solutions are in agreement with numerical simulations.     

Double-diffusive radiative magnetic mixed convective slip flow with Biot and Richardson number effects

This paper investigates combined heat and mass transfer by mixed magneto-convective flow of an electrically conducting flow along a moving radiating vertical flat plate with hydrodynamic slip and thermal convective boundary conditions. The governing transport equations are converted into a system of coupled nonlinear ordinary differential equations with prescribed boundary conditions using similarity variables developed by Lie group theory. The transformed nondimensional boundary value problem is then solved numerically with MAPLE13 quadrature. Excellent correlation with previous nonmagnetic, no-slip studies is achieved. Surface shear stress function and local Nusselt number (heat transfer gradient at the wall) are increased with Richardson number, whereas local Sherwood number is found to initially decrease then subsequently increase. The “thermally thick” scenario (Biot number > 0.1) is investigated and increasing Biot number is observed to enhance shear stress function (skin friction), local Nusselt number, and local Sherwood number. Increasing thermal radiation flux increases thermal boundary layer thickness as does increasing the magnetic field effect. Increasing hydrodynamic slip parameter reduces skin friction but enhances local Nusselt and Sherwood numbers. The study has applications in high-temperature polymeric synthesis and magnetic field flow control.     

Stereoselective palladium-catalyzed functionalization of homoallylic alcohols: a convenient synthesis of di- and trisubstituted isoxazolidines and β-amino-δ-hydroxy esters

Enantiopure, Boc-protected alkoxyamines 12 and 13, derived from the readily available homoallylic alcohols 4 via a reaction that involves either inversion or retention of configuration, undergo a diastereoselective Pd-catalyzed ring-closing carbonylative amidation to produce isoxazolidines 16/17 (≤50:1 diastereoisomer ratio (d.r.)) that can be readily converted into the N-Boc-protected esters of β-amino-δ-hydroxy acids and their γ-substituted homologues 37. The key carbonylative cyclization proceeds through an unusual syn addition of the palladium and the nitrogen nucleophile across the C=C bond (19→21), as revealed by the reaction of 15, which afforded isoxazolidine 18 with high diastereoselectivity.