Viscoelastic behaviour of partly hydrolysed polyacrylamide/chromium(III) gels

This paper reports an experimental investigation of the crosslinking process of high molecular weight partly hydrolysed polyacrylamides (HPAAm) in aqueous brine solution by trivalent chromium ions (Cr(III)). Crosslinking took place in the presence of a retardant agent (sodium citrate). First, sol-gel phase diagrams (in the polymer and concentration space) were established using the tilting tube method. Then, for a fixed composition, the gelation process was monitored systematically using dynamic viscoelastic measurements, varying the main parameters (pH, time, temperature and retardant concentration). Network formation proceeds rather slowly and an equilibrium state was not reached within 12 h. The gel was formed only at pHs between 5 and 9 and thus two gel points (i.e. at two pHs) were determined with the Winter-Chambon method. This is in agreement with the chemistry of aqueous chromium and of acrylic acid groups along the polymer backbone. Kinetics of network formation depends strongly on retardant concentration. Temperature plays an important role: network formation proceeds much faster at high temperature, in agreement with chemical kinetics.     

Target grafting of poly(2-(dimethylamino)ethyl methacrylate) to biodegradable block copolymers

A series of copolymers composed of methoxy poly(ethylene glycol) and a hydrophobic block of poly(ɛ-caprolactone-co-propargyl carbonate) grafted with poly(2-[dimethylamino]ethyl methacrylate) was synthesized by combining ring opening polymerization, azide-alkyne click reaction, and atom transfer radical polymerization (ATRP). Well-defined copolymers with a target composition and a tailored structure were achieved via the grafting from approach by using a single catalytic system for both click reaction and ATRP. Kinetic studies demonstrated the controlled/living character of the employed polymerization methods. The thermal properties and self-assembly in aqueous medium of the graft copolymers were dependent on their composition. The resulting polymeric materials showed low cytotoxicity toward L929 cells, demonstrating their potential for biomedical applications. This type of materials containing cationic side chains tethered to biocompatible and biodegradable segments could be the basis for promising candidates as drug and gene delivery systems.     

Effect of High Pressure on Paracoccus denitrificans Growth and Polyhydroxyalkanoates Production from Glycerol

The performance of fermentation under non-conventional conditions, such as high pressure (HP), is a strategy currently tested for different fermentation processes. In the present work, the purpose was to apply HP (10–50 MPa) to fermentation by Paracoccus denitrificans, a microorganism able to produce polyhydroxyalkanoates (PHA) from glycerol. In general, cell growth and glycerol consumption were both reduced by HP application, more extensively at higher pressure levels, such as 35 or 50 MPa. PHA production and composition was highly dependent on the pressure applied. HP was found to decrease polymer titers, but increase the PHA content in cell dry mass (%), indicating higher ability to accumulate these polymers in the cells. In addition, some levels of HP affected PHA monomeric composition, with the polymer produced at 10 and 35 MPa showing considerable differences relative to the ones obtained at atmospheric pressure. Therefore, it is possible to foresee that the changes in polymer composition may also affect its physical and mechanical properties. Overall, the results of this study demonstrated that HP technology (at specific levels) can be applied to P. denitrificans fermentations without compromising the ability to produce PHA, with potentially interesting effects on polymer composition.

     

Development of a qualitative, multiplex real-time PCR kit for screening of genetically modified organisms (GMOs)

The number of commercially available genetically modified organisms (GMOs) and therefore the diversity of possible target sequences for molecular detection techniques are constantly increasing. As a result, GMO laboratories and the food production industry currently are forced to apply many different methods to reliably test raw material and complex processed food products. Screening methods have become more and more relevant to minimize the analytical effort and to make a preselection for further analysis (e.g., specific identification or quantification of the GMO). A multiplex real-time PCR kit was developed to detect the 35S promoter of the cauliflower mosaic virus, the terminator of the nopaline synthase gene of Agrobacterium tumefaciens, the 35S promoter from the figwort mosaic virus, and the bar gene of the soil bacterium Streptomyces hygroscopicus as the most widely used sequences in GMOs. The kit contains a second assay for the detection of plant-derived DNA to control the quality of the often processed and refined sample material. Additionally, the plant-specific assay comprises a homologous internal amplification control for inhibition control. The determined limits of detection for the five assays were 10 target copies/reaction. No amplification products were observed with DNAs of 26 bacterial species, 25 yeasts, 13 molds, and 41 not genetically modified plants. The specificity of the assays was further demonstrated to be 100% by the specific amplification of DNA derived from reference material from 22 genetically modified crops. The applicability of the kit in routine laboratory use was verified by testing of 50 spiked and unspiked food products. The herein described kit represents a simple and sensitive GMO screening method for the reliable detection of multiple GMO-specific target sequences in a multiplex real-time PCR reaction.     

Structural Characterization of Na<Subscript>0.96</Subscript>Ho<Subscript>9.04</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>0.02</Subscript>O<Subscript>1.98</Subscript> Apatite Prepared by Mechanical Milling

Abstract  

In this paper we report the synthesis and structural characterization of Na_0.96Ho_9.04(SiO₄)₆Cl_0.02O_1.98 apatite prepared by mechanical milling at room temperature, in which well crystallized sample was obtained after heating the sample at 1123 K. The crystal structure study was carried out by synchrotron radiation diffraction. This apatite crystallizes in the hexagonal space group P6 ₃ /m (No. 176) with cell parameters a = 9.3444(1) ?, c = 6.7611(1) ?, unit cell volume of 511.27(1) ?³ and Z = 1. As in other rare-earth orthosilicate apatites, it was found that sodium cations are mixed with holmium occupying the 4f position at the center of tricapped trigonal prisms; while holmium fully occupies the 6h position at the center of a seven-coordinated polyhedron. No vacancies are present in the two crystallographic sites available for holmium atoms. The chemical composition was established by wavelength dispersive spectroscopy.     

Organogermanium polymers prepared from s‐indacene and carbodiimide compounds

The synthesis of bis‐organogermanium compounds including s‐indacene structure was described and showed the formation of one type of trans isomer characterized by spectroscopic methods. In the same way, the digermyl‐s‐indacene dichlorides were prepared and structural characterizations confirmed the unique formation of trans isomers. These digermyl‐s‐indacene dichlorides were used as monomers in a polymerization reaction in order to prepare poly(germyl‐s‐indacenes) and poly(germyl‐s‐indacene carbodiimides). However, only the products obtained from tetraalkyl‐s‐indacene reached high molecular weight, probably due to a minor steric hindrance compared to the hexaalkyl‐s‐indacene. Thermal degradation only starts from 250°C for poly(germyl‐s‐indacene carbodiimides) and from 350°C for poly(germyl‐s‐indacenes). The structures of the first digermyl‐s‐indacene dichlorides were determined by X‐ray analysis, confirming that the chlorogermyl groups are located in trans positions. Copyright © 2012 John Wiley & Sons, Ltd.     

Spatio-temporal organization in alloy electrodeposition: a morphochemical mathematical model and its experimental validation

This paper proposes a novel mathematical model for the formation of spatio-temporal patterns in electrodeposition. At variance with classical modelling approaches that are based on systems of reaction–diffusion equations just for chemical species, this model accounts for the coupling between surface morphology and surface composition as a means of understanding the formation of morphological patterns found in electroplating. The innovative version of the model described in this work contains an original, flexible and physically straightforward electrochemical source term, able to account for charge transfer and mass transport: adsorbate-induced effects on kinetic parameters are naturally incorporated in the adopted formalism. The relevant non-linear dynamics is investigated from both the analytical and numerical points of view. Mathematical modelling work is accompanied by an extensive, critical review of the literature on spatio-temporal pattern formation in alloy electrodeposition: published morphologies have been used as a benchmark for the validation of our model. Moreover, original experimental data are presented—and simulated with our model—on the formation of broken spiral patterns in Ni–P–W–Bi electrodeposition.     

Development of an on-line high performance liquid chromatography detection system for human cytochrome P450 1A2 inhibitors in extracts of natural products

An on-line HPLC screening method for detection of inhibitors of human cytochrome P450 1A2 in extracts was developed. HPLC separation of extracts is connected to a continuous methoxyresorufin-O-demethylation (MROD) assay in which recombinant human P450 1A2 converts methoxyresorufin to its fluorescent metabolite resorufin. The system was tested with three P450 1A2 inhibitors, for which minimum detectable amounts (MDA) ranging from 0.7 to 9.5 ng were obtained. Analysis of a kava kava and a basil extract showed that the on-line system is applicable to complex mixtures, since in both extracts, peaks with P450 1A2 inhibiting activity were observed.