Photoiniferter surface grafting of poly(methyl acrylate) using xanthates

The UV‐induced and catalyst‐free photoiniferter surface grafting using xanthate RAFT agents is studied. First, a novel silane containing a xanthate RAFT agent moiety is synthesized and successfully grafted onto a silicon wafer as confirmed by secondary ion mass spectrometry (SIMS). Next, using only methyl acrylate, solvent and UV light (365 nm) polymer brushes are grafted rapidly from the surface with film thicknesses up to 25 nm reached within half an hour. The obtained polymer films are thoroughly analyzed by X‐ray photoelectron spectroscopy (XPS), ToF‐SIMS, and AFM. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2002–2007     

Singularity in the density of states of quasi-one-dimensional disordered systems

We have calculated the correction to the density-of-states in two-dimensional weakly disordered systems. It is shown that the electron-electron interaction gives rise to a singularity in the density-of-states at the Fermi level, the form of which is very sensitive to the width of the sample. The transition from a two-dimensional behaviour to the quasi-one-dimensional regime is discussed. The effects should be observable by electron tunnelling measurements.     

Monofunctionally trans-diammine platinum(II)-modified peptide nucleic acid oligomers: a new generation of potential antisense drugs

A solid-phase approach is described that provides facile access to monofunctionally trans-PtII-modified PNA oligomers of arbitrary sequence for potential use both in antigene and antisense strategies. The approach includes the synthesis of a platinated building block 1 and its subsequent incorporation into three different PNA oligomers 5-7 by solid-phase synthesis. In a model cross-linking reaction one of the latter is found to recognize sequence-specifically a target oligonucleotide 8 and to cross-link to it. The resulting structure is the trans-PtII-cross-linked PNA/DNA duplex 9 as revealed by mass spectrometry in combination with a Maxam-Gilbert sequencing experiment.     

Two novel yellow pigments natronochrome and chloronatronochrome from the natrono(alkali)philic sulfur-oxidizing bacterium Thialkalivibrio versutus strain ALJ 15

Two novel membrane-bound yellow pigments natronochrome (1) and chloronatronochrome (2) were isolated from the obligately chemolithoautotrophic sulfur-oxidizing natrono(alkali)philic bacterium Thialkalivibrio versutus strain ALJ 15. They were derivatives of fully unsaturated fatty acids with a phenyl group, and their structures were determined by spectral data.     

Removal of Small Particles from a Porous Material by Ultrasonic Irradiation

A study has been made of the removal of small particles from a porous material by means of ultrasonic irradiation. To that purpose a microscopic theoretical model has been developed to calculate the force of a traveling acoustic wave on a spherical particle attached to the wall of a smooth, cylindrical pore inside the porous material. This force was compared with the adhesion force between a small particle and a pore wall. From the comparison between the two forces the conditions were found, at which particles are detached from pore walls and removed from the porous material. The transformation of the results gained from the microscopic model to macroscopic property (permeability) of the porous material was made by means of the Kozeny relation. The aim is to be able to understand and predict qualitatively the influence of relevant parameters on the ultrasonic cleaning process. Predictions made with the theoretical model were compared with data from experiments carried out with ultrasound to remove particles from Berea sandstone. The agreement is reasonable.     

Removal of Particle Bridges From a Porous Material by Ultrasonic Irradiation

Particle bridge formation during the flow of a liquid with particles through a porous material is a fouling mechanism that can block the pores and, hence, decrease the permeability of the material. Ultrasonic irradiation of the material is a cleaning method that can restore the permeability. We make a numerical study of this cleaning method using the lattice-Boltzmann method. We start from a pore blocked by two spherical particles attached to the pore wall by colloidal adhesion forces, thus forming a particle bridge. Next we calculate the hydrodynamic force exerted by a high-frequency acoustic wave on the two particles. By comparing the hydrodynamic force and the adhesion force we investigate, whether the particle bridge will be removed by the ultrasonic irradiation. A sensitivity study is carried out to investigate the influence of some relevant parameters, such as the acoustic wave amplitude, the acoustic frequency, the fluid flow velocity and the ratio of particle diameter and pore diameter. An upscaling procedure is applied to translate the microscopic results for the removal of the particles at the pore level to the permeability improvement of the material at the macroscopic level. A comparison is made between numerical results and experimental data. The agreement is reasonable.     

Mixing of peptides and electrophilic traps gives rise to potent, broad-spectrum proteasome inhibitors

The synthesis and evaluation of hybrid proteasome inhibitors that contain structural elements of the known inhibitors bortezomib, epoxomicin and peptide vinyl sulfones is described. From the panel of 15 inhibitors some structure activity relationships can be deduced with regard to inhibitory activity in relation to peptide recognition element, inhibitor size and nature of the electrophilic trap. Further, the panel contains one of the most potent peptide-based pan-proteasome inhibitors reported to date.     

(Automated) Synthesis of Well-defined Staphylococcus Aureus Wall Teichoic Acid Fragments

Wall teichoic acids (WTAs) are important components of the cell wall of the opportunistic Gram-positive bacterium Staphylococcus aureus. WTAs are composed of repeating ribitol phosphate (RboP) residues that are decorated with d -alanine and N-acetyl-d -glucosamine (GlcNAc) modifications, in a seemingly random manner. These WTA-modifications play an important role in shaping the interactions of WTA with the host immune system. Due to the structural heterogeneity of WTAs, it is impossible to isolate pure and well-defined WTA molecules from bacterial sources. Therefore, here synthetic chemistry to assemble a broad library of WTA-fragments, incorporating all possible glycosylation modifications (α-GlcNAc at the RboP C4; β-GlcNAc at the RboP C4; β-GlcNAc at the RboP C3) described for S. aureus WTAs, is reported. DNA-type chemistry, employing ribitol phosphoramidite building blocks, protected with a dimethoxy trityl group, was used to efficiently generate a library of WTA-hexamers. Automated solid phase syntheses were used to assemble a WTA-dodecamer and glycosylated WTA-hexamer. The synthetic fragments have been fully characterized and diagnostic signals were identified to discriminate the different glycosylation patterns. The different glycosylated WTA-fragments were used to probe binding of monoclonal antibodies using WTA-functionalized magnetic beads, revealing the binding specificity of these WTA-specific antibodies and the importance of the specific location of the GlcNAc modifications on the WTA-chains.     

HPLC-ICP-MS method development to monitor arsenic speciation changes by human gut microbiota

Inorganic arsenic (iAs) has been classified as a type 1 carcinogen and has also been linked to several noncancerous health effects. Prior to 1995, the As^V methylation pathway was generally considered to be a detoxification pathway, but cellular and animal studies involving MMA^III (mono metyl arsonous acid) and DMA^III (dimethyl arsinous acid) have indicated that their toxicities meet or exceed that of iAs, suggesting an activation process. In addition, thiolated arsenic metabolites were observed in urine after oral exposure of inorganic arsenic in some studies, for which the toxicological profile was not yet fully characterized in human cells. Studies have revealed that microorganisms from the gut environment are important contributors to arsenic speciation changes. This presystemic metabolism necessitates the development of protocols that enable the detection of not only inorganic arsenic species, but also pentavalent and trivalent methylated, thiolated arsenicals in a gastrointestinal environment. We aim to study the biotransformation of arsenic (As) using a Simulator of the Human Intestinal Microbial Ecosystem (SHIME). To be able to analyze the arsenicals resulting from biotransformation reactions occurring in this system, a method using liquid chromatography hyphenated to an inductively coupled plasma mass spectrometer (HPLC‐ICP‐MS) was developed. A Hamilton PRP‐X100 anion exchange column was used. The method allowed separation, identification and quantification of As^III(arsenite), As^V(arsenate), DMA^V(dimethylarsinicacid), MMA^V(monomethylarsonicacid) and MMMTA (monomethylmonothioarsenate). Attempts to optimize the same method for also separating MMA^III and DMA^III did not succeed. These compounds could be successfully separated using a method based on the use of a Zorbax C₁₈ column. The properties of the column, buffer strength, pH and polar nature of mobile phase were monitored and changed to optimize the developed methods. Linearity, sensitivity, precision, accuracy and resolution of both methods were checked. The combination of the two methods allowed successful quantification of arsenic species in suspensions sampled in vitro from the SHIME reactor or in vivo from the human colon and feces. Copyright © 2011 John Wiley & Sons, Ltd.