Substrate-independent dip-pen nanolithography based on reactive coatings

We report that nanostructuring via dip-pen nanolithography can be used for modification of a broad range of different substrates (polystyrene, Teflon, stainless steel, glass, silicon, rubber, etc.) without the need for reconfiguring the underlying printing technology. This is made possible through the use of vapor-based coatings that can be deposited on these substrates with excellent conformity, while providing functional groups for subsequent spatially directed click chemistry via dip-pen nanolithography. Pattern quality has been compared on six different substrates demonstrating that this approach indeed results in a surface modification protocol with potential use for a wide range of biotechnological applications.     

Structural and mechanistic information on c<Subscript>1</Subscript> ion formation in collision-induced fragmentation of peptides

The formation of c₁ ions during collision-induced fragmentation of peptides with asparagine, ornithine, or glutamine at the N-terminal position 2 has been studied. For this purpose, the corresponding fragment ion spectra of a large set of synthetic peptides were investigated. It is demonstrated that the c₁ ion intensity depends on the nature of the second residue in the N-terminal dipeptide motif as well as on the peptide length. It is shown that the formation of c₁ ions proceeds by two competing mechanisms. One mechanism is the secondary fragmentation of the b₂ ion, the efficiency of which shows only a minor dependency on the complete peptide sequence. The other mechanism is the direct formation from the molecular ion, which is identified to be connected with sequence-specific c₁ ion intensities. A model for this latter mechanism is proposed based on the analysis of the formation and secondary fragmentation of the z_max-1 ion, which is the complementary ion to the c₁ ion. Additional evidence is obtained by investigation of peptides with ornithine in N-terminal position 2, which in general exhibit c₁ ion intensities intermediate between the asparagine- and glutamine-containing species. The data presented support the reliable assignment of N-terminal dipeptide motifs using collision-induced dissociation.     

Analysis of autophosphorylation sites in the recombinant catalytic subunit alpha of cAMP-dependent kinase by nano-UPLC–ESI–MS/MS

The catalytic subunit of recombinant wild-type cyclic adenosine monophosphate-dependent protein kinase A (PKA) has been analyzed by a combination of 1D gel electrophoresis, in-gel digestion by trypsin, chymotrypsin, or endoproteinase AspN, and nano-ultraperformance liquid chromatography–MS/MS. The MS/MS spectra were annotated by MASCOT and the annotations were manually controlled. Using Ga(III)-immobilized metal ion affinity chromatography (IMAC), in addition to the four established autophosphorylation sites of the catalytic subunit of recombinant PKA, pSer10, pSer139, pThr197, and pSer338, six new phosphorylated residues have been characterized–pSer14, pThr48, pSer53, pSer212, pSer259, and pSer325. The established phosphorylation sites all are part of a PKA consensus motif and were found to be almost completely modified. In contrast, the newly detected sites were only partially phosphorylated. For estimation of their degree of phosphorylation, a method based on signal intensity measurements was used. For this purpose, signal intensities of all phospho- and non-phosphopeptides containing a particular site were added for estimation of site-specific phosphorylation degrees. This addition was performed over all peptides observed in the different digestion experiments, including their different charge states. pThr48 and pSer259 are located within PKA consensus motifs and were observed to be phosphorylated at 20% and 24%, respectively. pSer14 and pSer53 are located within inverted PKA consensus motifs and were found to be phosphorylated around 10% and 15%, respectively. The sequence environments of pSer212 and pSer325 have no similarity to the PKA consensus motif at all and were observed to be phosphorylated at about 5% or lower. All newly observed phosphorylation sites are located at the surface of the native protein structure of the PKA catalytic subunit. The results add new information on the theme of site-specific (auto)phosphorylation by PKA.      

Effect of clay modification on the structure and mechanical properties of polyamide-6 nanocomposites

Polyamide-6 nanocomposites were prepared from a new phosphonium organoclay obtained at pilot scale in supercritical carbon dioxide (scCO₂) and a commercially available ammonium modified-silicate. The composites were homogenised by twin-screw extrusion, then specimens for testing were prepared by injection moulding. The clay content of the composites was varied from 0 to 7 vol.% in 7 steps. The clays were characterised in detail; they differed in their surface coverage and gallery structure, while their particle size was similar and their surface energy differed only slightly. X-ray diffraction, electronic microscopy and rheology were used for the characterisation of composite structure. Different gallery structure of the clays led to dissimilar extent of exfoliation. The phosphonium organoclay exfoliated better in PA than the silicate treated with the ammonium salt in spite of its smaller surface coverage. The nanocomposites showed the usual complex structure: besides individual platelets and intercalated stacks, large particles were also present and the development of a silicate network could be shown at large clay contents. Quantitative determination of the extent of reinforcement revealed two determining factors: contact surface and strength of interaction. The first increases with exfoliation, but the latter decreases as an effect of organophilisation. The extent of exfoliation was also estimated quantitatively, and the calculation confirmed the results of qualitative evaluation showing larger extent of exfoliation for the scCO₂-prepared phosphonium clay.     

Competition of ester, amide, ether, carbonate, alcohol and epoxide ligands in the dirhodium experiment (chiral discrimination by NMR spectroscopy)

Thirty-eight derivatives of 3-hydroxy-2-methylpropanoic acid, each with two different oxygen functionalities, were synthesized and subjected to the standard dirhodium experiment (1H NMR in the presence of an equimolar amount of the chiral dirhodium tetracarboxylate complex Rh*). Their structures represent ester, amide, carbonate, ether, alcohol and/or epoxy groups. Significant selectivity in the binding of those oxygen groups to the complex were determined. From these results, a priority list in binding to a rhodium atom of Rh* was established: epoxides > primary alcohols > ethers > or = esters > or = amides > carbonates > tertiary alcohols. This sequence allows the prediction of the preferred binding site of oxygen-containing groups in polyfunctional compounds, which frequently occur among natural products, and, particularly, in asymmetric synthesis of such compounds. Differentiation of the enantiomers by the dirhodium experiment is easily accomplished due to numerous signal dispersions in nearly all cases.     

Differentially Degradable Janus Particles for Controlled Release Applications

Janus particles with differentially degradable compartments were prepared by electrohydrodynamic (EHD) co‐jetting and subsequent controlled crosslinking. These bicompartmental particles are composed of an interpenetrating polymer network of poly(ethylene oxide) and poly(acrylamide‐co‐acrylic acid) in one hemisphere and a crosslinked copolymer of dextran and poly(acrylamide‐co‐acrylic acid) segments in the second compartment. The compositional anisotropy caused differential hydrolytic susceptibility: Although both compartments were stable at pH 3.0, selective degradation of the PEO‐containing compartment pH 7.4 was observed wtihin 5 days. Janus particles with differentially degradable polymer compartments may be of interest for a range of oral drug delivery applications because of their propensity for decoupled release profiles.     

Heterobifunctional Poly(ethylene glycol) Derivatives for the Surface Modification of Gold Nanoparticles Toward Bone Mineral Targeting

Heterobifunctional poly(ethylene glycol)s can be used for many biomedical applications ranging from solubility enhancement of hardly soluble compounds to surface modification of medical devices. In order to modify gold nanoparticles as model particles for drug targeting applications, PEG derivatives are synthesized that possess a high affinity for gold surfaces, namely a thioalkyl function, known to form stable monolayers on gold. Additionally a bisphosphonate function is introduced in the PEG molecule to allow targeting of hydroxyapatite rich tissues, like bone. Gold nanoparticles are modified using the synthesized bifunctional PEG and investigated for their stability in biological fluids and their ability to bind to hydroxyapatite granules in these fluids.

     

Preparation of core-shell and hollow fibers using layer by layer (LbL) self-assembly of polyelectrolytes on electrospun submicrometer-scale silica fibers

Herein, fabrication of hollow fibers made of polyelectrolyte multilayers is reported. Silica submicrometer-scale fibers were fabricated by electrospinning and layer by layer deposition of polyelectrolytes were performed to coat silica fibers with polyelectrolyte multilayers, which were prepared by consecutive deposition of poly(ethyleneimine) and poly(styrene sulfonate sodium salt)/sodium dodecyl sulfate onto the surface of the silica fibers. In order to obtain hollow fibers, the core removal was carried out by introducing the core-shell fibers to a hydrofluoric acid solution. The hollow fibers were stable in hydrofluoric acid solution and displayed pH-dependent structural changes. SEM microscopy indicated the formation of the glass fibers and the fibers coated with polyelectrolyte multilayers (Silica—polyelectrolyte multilayers (PEM) fibers). The diameter of the core-shell fibers was increased after layer-by-layer coating. ATR-FTIR was performed for characterization of the glass fibers before and after layer-by-layer coating as well as after selective core removal. IR spectrum of the Silica-PEM fibers indicates C-H stretching modes of saturated hydrocarbons, confirming multilayers formation. Core removal was also confirmed by IR spectroscopy as Si-O-Si band disappears for the IR spectrum of the fibers after core-removal.     

Nucleon axial charge in full lattice QCD

The nucleon axial charge is calculated as a function of the pion mass in full QCD. Using domain wall valence quarks and improved staggered sea quarks, we present the first calculation with pion masses as light as 354 MeV and volumes as large as (3.5 fm)3. We show that finite volume effects are small for our volumes and that a constrained fit based on finite volume chiral perturbation theory agrees with experiment within 7% statistical errors.     

Liquid chromatographic determination of deoxynivalenol in baby food and animal feed: interlaboratory study

An interlaboratory study was conducted for the determination of deoxynivalenol in baby food and animal feed by high-performance liquid chromatography with UV detection. The study included 14 participants representing a cross section of industry, official food control, and research facilities. Mean recoveries reported ranged from 89% (at 120 microg/kg) to 85% (at 240 microg/kg) for baby food and from 100% (at 200 microg/kg) to 93% (at 400 microg/kg) for animal feed. On the basis of the results for spiked samples (blind duplicates at 2 levels), as well as those for naturally contaminated samples (blind duplicates at 3 levels), the relative standard deviation for repeatability (RSDr) in analyses of baby food ranged from 6.4 to 14.0% and in analyses of animal feed, from 6.1 to 16.5%. The relative standard deviation for reproducibility (RSDR) in analyses of baby food ranged from 9.4 to 19.5% and in analyses of animal feed, from 10.5 to 25.2%. The HorRat values ranged from 0.4 to 1.0 and from 0.7 to 1.3, for baby food and animal feed, respectively. The method showed acceptable performance for within-laboratory and between-laboratory precision for each matrix, as required by European legislation.