Approximated solutions in rational form for systems of differential equations

In this paper we present a technique to study the existence of rational solutions for systems of differential equations — for an ordinary differential equation, in particular. The method is relatively straightforward; it is based on a rationality characterisation that involves matrix Padé approximants. It is important to note that, when the solution is rational, we use formal power series “without taking into account” their circle of convergence; at the end of this paper we justify this. We expound the theory for systems of linear first-order ordinary differential equations in the general case. However, the main ideas are applied in numerical resolution of partial differential equations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Novel guests for porous columnar thin films: the switchable perchlorinated trityl radical derivatives

TiO(2) and SiO(2) porous thin films consisting of tilted nanocolumns prepared by glancing angle evaporation (GLAD) have been infiltrated with guest derivatives belonging to the family of perchlorinated trityl radicals, novel guest molecules presenting an open-shell electronic configuration associated with paramagnetism, fluorescence, and electroactivity. The main driving forces for infiltration from aqueous solutions of the carboxylate-substituted radical derivatives are the electrostatic interactions between their negative charge and the net positive charges induced on the film pores. Positive charges on the internal surface of the films were induced by either adjusting the radical solution pH at values lower than the point of zero charge (PZC) of the oxide or passivating the nanocolumns oxide surface with a positively charged aminosilane. The infiltrated composite thin films are robust and easy to handle thanks to the physical protection exerted by the film columns. They also keep the multifunctionality of the used guests, as confirmed by electron paramagnetic resonance (EPR), UV-vis spectroscopy, and fluorescence spectroscopy. To prove the electroactivity of the infiltrated porous films, a porous TiO(2) host layer was supported onto conductive indium tin oxide (ITO). By application of an appropriate redox potential, the guest radical molecules have been reversibly switched from their open-shell electronic configuration to their diamagnetic state and hence changed their optical properties. On the basis of these results, it is herein proposed that the appropriate surface functionalization of the pore internal surface of GLAD thin films can be used to prepare novel radical-oxide composite thin films usable for the development of robust switchable electrically driven photonic and magnetic devices.     

Effect of supercritical CO2 in modified polystyrene 3D latex arrays

The effect of supercritical CO(2) (scCO(2)) in 3D latex arrays formed by monodispersed particles of polystyrene (PS), PS cross-linked with divinylbenzene (PS-DVB), and PS block copolymers with 2-hydroxyethyl methacrylate (PS-HEMA), methacrylic acid (PS-MA), acrylic acid (PS-AA), itaconic acid (PS-IA), and a mixture of methacrylic and itaconic acid (PS-IA-MA) has been studied. Sorption of CO(2) into the polymer particles leads to a decrease in the glass transition temperature of the polymer and the swelling of the particles and induces their coalescence. 3D-latex arrays of the former compositions were treated in scCO(2) at temperatures and pressures ranging from 40 to 80 degrees C and from 85 to 197 bar, respectively. The effect of CO(2) on the polymeric template was assessed by scanning electron microscopy and N(2) adsorption analysis. Bare PS and PS-HEMA particles sintered readily in scCO(2) at 40 degrees C and 85 bar. On the other hand, particles containing carboxylic acid groups on their surface (PS-MA, PS-AA, PS-IA, and PS-IA-MA) were, at the same temperature and pressure, more resistant to the CO(2) treatment. For a given polymer composition, the sorption of CO(2) inside the polymer particles, the swelling, and the degree of coalescence depend on the pressure, temperature, and time of the CO(2) treatment. Analysis of the pore size distributions from the N(2) adsorption data has allowed us to quantify the degree of coalescence of the particles in the matrix. By careful control of the experimental variables, the coalescence of the 3D latex array could be finely tuned using CO(2).     

Evaluating the "greenness" of chemical processes and products in the pharmaceutical industry--a green metrics primer

This tutorial review presents an overview of the main metrics that have been used to test and compare the 'greenness' of processes and products, primarily in the pharmaceutical industry. The green metrics cover areas of resources, materials, processing, cleaning, life cycle assessment, renewability, amongst others. Application examples of these metrics are also presented to illustrate key points and concepts.     

Synthesis of 3-alkyl enol mimics inhibitors of type II dehydroquinase: factors influencing their inhibition potency

Several 3-alkylaryl mimics of the enol intermediate in the reaction catalyzed by type II dehydroquinase were synthesized to investigate the effect on the inhibition potency of replacing the oxygen atom in the side chain by a carbon atom. The length and the rigidity of the spacer was also studied. The inhibitory properties of the reported compounds against type II dehydroquinase from Mycobacterium tuberculosis and Helicobacter pylori are also reported. The binding modes of these analogs in the active site of both enzymes were studied by molecular docking using GOLD 5.0 and dynamic simulations studies.     

Signaling Pathways of Immobilized FGF‐2 on Silicon‐Substituted Hydroxyapatite

Therapeutic strategies for bone regeneration involve the selection of suitable biomaterials, growth factors, and cell types to mimic the cellular microenvironment where molecular and mechanical signals control the reconstruction of bone tissue. The immobilization of basic fibroblast growth factor (FGF‐2) on powdered silicon‐substituted hydroxyapatite (Si‐HA) allows to prepare a biofunctional biomaterial able to interact with bone cells in a very specific way. The biological activity of FGF‐2/Si‐HA, evaluated in Saos‐2 osteoblasts and MC3T3‐E1 preosteoblasts through the PLCγ and MAPK/ERK signal transduction pathways, shows that FGF‐2 immobilized on Si‐HA provides the right signals to cells stimulating crucial intracellular mechanisms of osteoblast proliferation and differentiation.