Probing the reaction kinetics of vinyl acetate free radical polymerization via living free radical polymerization (MADIX)

Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI^® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of k_t is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of k_t as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of k_t with conversion is more pronounced at increased chain lengths, with a strong decrease in k_t exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800.     

An easy way to Pd–Zn nanoalloy with defined composition from a heterobimetallic Pd(μ–OOCMe)4Zn(OH2) complex as evidenced by XAFS and XRD

The heterobimetallic lantern complex Pd(μ-OOCMe)₄Zn(OH₂) was found to be readily reduced with H₂ under fairly mild conditions (150–250 °C, 5–10% H₂/He) both in the carbon-supported and crystalline states to afford a Pd–Zn nanoalloy as evidenced by the ICP elemental analysis, EXAFS, XANES and XRD data.      

Particle‐Based Synthesis of Peptide Arrays

High‐density peptide arrays with solid amino acid particles: Intermittent “freezing” of activated amino acid derivatives within solid particles allows a laser printer or a chip to spatially address these “postal packages”. Subsequent parallel coupling is started simply by melting a whole layer of 20 different amino acid particles, freeing the hitherto immobilized amino acids and resulting in the coupling of all 20 different amino acids to the support in a single coupling step.

     

Mapping the isoprenoid binding pocket of PDEdelta by a semisynthetic, photoactivatable N-Ras lipoprotein

Biologically functional Ras isoforms undergo post-translational modifications starting with farnesylation of the most C-terminal cysteine. Combined with further processing steps, this isoprenylation allows for the anchoring of these proteins in endomembranes, where signal transduction events take place. The specific localization is subject to dynamic regulation and assumed to modulate the activity of Ras proteins by governing their spatiotemporal distribution. The delta subunit of phosphodiesterase (PDEdelta) has attracted attention as a solubilization factor of isoprenylated Ras. In this study, we demonstrate that critical residues in the putative isoprenoid pocket of PDEdelta can be mapped by coupling with a semisynthetic N-Ras lipoprotein in which the native farnesyl group of the processed protein was replaced by a photoactivatable geranyl benzophenone moiety. The crosslinked product included parts of beta-sheet 9 of PDEdelta, which contains the highly conserved amino acids V145 and L147. Modeling of the PDEdelta-geranyl benzophenone (GerBP) complex supports the conclusion that the photolabeled sequence is embedded in the putative isoprenoid pocket of PDEdelta.     

Modular process for the flexible synthesis of magnetic beads—Process and product validation

Here we present a modular process for the flexible production of magnetic beads with variable magnetic properties and anion or cation exchanger functionalities. Magnetic beads are used in bio‐separations and downstream processing to remove a valuable substance from e.g., a fermentation broth (Magnetic Fishing). The magnetic beads we are presenting here consist of a composite material, containing nanoscale magnetite and ion exchanger particles which are embedded into a polymer matrix. With this composite concept, anion and cation exchanger properties are available in magnetic beads with different matrix polymers (PVB, PVA, PMMA, and PVAc). The content of magnetite was varied in a range between 0 and 40 wt %, ion exchanger particles between 0 and 60 wt % and the matrix polymer between 20 and 60 wt %. The magnetic bead characteristics, which determine the application properties, are shown. Thermo gravimetrical analyses, FTIR spectra and measurements of the ion exchange capacity prove the different properties in respect to the magnetic beads composition. In an adsorption experiment, it was possible to achieve a maximum capacity of 270 mg/g for β‐galactosidase with PVB‐beads. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The use of crack layer theory to predict the lifetime of the fatigue crack growth of high density polyethylene

In the case of high density polyethylene (HDPE), the fatigue crack propagates in a discontinuous manner, which can be observed by distinct striations. In this article, fatigue crack growth (FCG) experiments were conducted on two grades of HDPE pipe with compact‐tension (CT) and cracked round bar (CRB) specimens. The effects of the stress ratio (R‐ratio) which is defined as the ratio of minimum stress and maximum stress of fatigue loadings and the frequency on FCG behavior were experimentally studied. Although FCG rates showed a great dependence on the R‐ratio in terms of the range of the stress‐intensity factor, the effect of the frequency may be considered to be significant in the low crack growth region. In addition, these experimental data were employed for predicting the lifetime on the basis of the crack layer (CL) theory. Only a few steps of FCG are needed to determine all necessary parameters for CL theory, and the FCG behavior can be reconstructed based on a computer program that has been developed for the application of CL theory. The predictions from this program accord with experimental data. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

A depth filtration model of straining within the void networks of stainless steel filters

A depth filtration model has been developed, based on the three‐dimensional void network model Pore‐Cor. The geometry of the void network is fitted, by means of an eight‐dimensional Boltzmann annealed amoeboid simplex, to the porosity and percolation characteristics of stainless steel sintered filters measured by mercury porosimetry. Preferential and critical flow paths through the network are calculated. Particles from an experimental size distribution are fed along these flow‐biased paths, and when straining occurs, the flow paths are re‐calculated. We show that the model usefully reproduces experimental filtration efficiencies as a function of pressure drop, measured by single pass tests. We also offer a critique of current measurements of filtration efficiency, suggesting the use of a new “alpha efficiency” rather than the standard beta efficiency. The model is currently being adapted to accept porometry as well as porosimetry data, hence avoiding the use of mercury. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Spatial and temporal variations in the occurrence of cocaine and benzoylecgonine in waste- and surface water from Belgium and removal during wastewater treatment

Estimates of cocaine consumption are currently resulting from population surveys, consumer interviews and crime statistics. A new approach (“sewage epidemiology”) based on the analysis of cocaine (COC) and its metabolite, benzoylecgonine (BE), in water samples was applied to 10 river sites and 30 wastewater treatment plants (WWTPs) in Belgium. Each river site was sampled twice, during the summer of 2007 and the winter of 2007-2008, while each WWTP was sampled on a Sunday and a Wednesday, during the summer-autumn of 2007 and the winter of 2007-2008. This sampling strategy allowed for the evaluation of spatial and seasonal variations in the occurrence of COC and BE in waste- and surface water. WWTP Brussel-Noord was sampled for 19 consecutive days to evaluate daily and weekly variations in the presence of COC and BE in wastewater. For 7 WWTPs, influent and effluent water samples were collected to investigate the removal of COC and BE during the wastewater treatment process. Analysis of water samples was performed using solid-phase extraction and liquid chromatography coupled to tandem mass spectrometry. Measured concentrations were further converted into an amount of used cocaine, called cocaine equivalents, as previously described in the literature. Results showed no significant difference in cocaine use between the investigated seasons. A constant cocaine consumption was observed during the week (Monday-Friday) with peaks during the weekend for WWTP Brussel-Noord. The COC/BE ratio in water samples was significantly higher during winter, most probably due to a slower hydrolysis of cocaine in low-temperature water. COC and BE were removed in the investigated WWTPs with a removal efficiency of >93%.