Silica Transfer in Ternary Rubber Blends: Calculation and Experimental Determination

A novel model is presented for predicting the phase selective filler localization in an equilibrium state for ternary rubber blends of SBR, NBR, and NR. It is based on surface tension data of the rubber components and the filler. Phase‐selective filler localization in ternary rubber blends is determined experimentally by means of FTIR spectroscopy on the basis of the wetting concept. It is found that by preparation of ternary blends with certain silica loadings, pre‐mixed in each blend phase using the masterbatch technology, silica transfer processes between blend phases take place until the equilibrium filler distribution is reached. The sequence of the silica transfer processes can be explained by taking into consideration the formation of a phase‐in‐phase morphology of the ternary blend.

     

Experimental analysis and modeling of local ageing effects during laser sintering of polyamide 12 in regard to individual thermal histories

Polymer laser sintering (LS) is an important additive manufacturing (AM) technology. Individual and complex parts are directly produced from CAD data without the need of specific tools. The raw material is a polymer powder, which is deposited layerwise and melted selectively with a laser. Built parts are embedded in residual unmolten powder, the so‐called part cake, which undergoes thermal ageing effects due to the exposure to high temperatures for long times during the manufacturing process. Hence, the recyclability of the unmolten powder is limited. This article focuses on a fundamental analysis of the ageing kinetics dependent on time, temperature, and oxygen content in the gas atmosphere. A model is developed and applied to measured, position‐dependent process temperature histories to successfully predict the ageing distribution within a part cake. The results can be used to optimize the thermal process management in LS and to develop new efficient powder recycling methods. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45435.     

Polar Hinges as Functionalized Conformational Constraints in (Bi)cyclic Peptides

Two polar hinges for cyclization of peptides have been developed, leading to bicyclic peptides and cyclized peptides with improved solubility and biological activity. Increasingly, we note that a good aqueous solubility of peptides is an absolute prerequisite, not only to allow handling and purification of our target peptides but also being crucial for biological activity characteristics. Compared to earlier hinges, the 1,1′,1“‐(1,3,5‐triazinane‐1,3,5‐triyl)tris(2‐bromoethanone) (TATB) and 2,4,6‐tris(bromomethyl)‐s‐triazine (TBMT), each containing three nitrogen atoms are structurally similar but chemically very different. Both were accessible in a one‐step fashion from bromoacetonitrile. TATB and TBMT are very suitable for the preparation of more soluble bicyclic peptides. Azide‐modified TATB and TBMT derivatives provide hinges for the preparation of cyclized peptides for incorporation on scaffolds to afford protein mimics.     

INFLUENCE OF THE PARTICLE SIZE AND SUPERFICIAL GAS VELOCITY ON THE SUBLIMATION OF PURE SUBSTANCES IN FLUIDIZED BEDS OF DIFFERENT SIZES

In the present study the sublimation of large solid carbon dioxide particles inside fluidized beds of fine particles is investigated. A model which takes the surface area of the sublimable particles into account is used to describe the sublimation kinetics. Based on this model, the results of different experiments, namely single particle experiments using a precision scale, batch experiments in a laboratory-scale fluidized bed and continuous experiments in a larger circulating fluidized bed are compared. The main focus of the study is to evaluate the influences of the particle size, of the inert bed material, of the bed temperature and of the superficial gas velocity, respectively.     

Structural characterization of the oligomeric constituents of petroleum pitches

The separation of petroleum pitch into its oligomeric fractions via dense-gas extraction (DGE), followed by the application of both new and conventional analytical techniques to those fractions, has given us unique capabilities for identifying both the specific molecular structures that exist in petroleum pitches and their concentration. Specifically, pitch fractions containing 98% monomer or 97% dimer were isolated by DGE and characterized using MALDI, MALDI-PSD, and FD mass spectrometry (MS); and ¹H NMR, UV-Vis, and FT-IR spectroscopy. Results indicate that the molecular weight distribution (MWD) of the 98% monomer pitch fraction is approximately Gaussian, with the dominant species being methylated derivatives of the polycyclic aromatic hydrocarbons (PAH) benzofluorene (216.4 m/z), chrysene, (228.3 m/z), benzofluoranthene (252.3 m/z), and their isomers. The distribution of methyl substituents per molecule is also approximately Gaussian, with a maximum at 2. The MWD of the 97% dimer pitch fraction is also approximately Gaussian, and the most prevalent species (m/z = 454.6, 468.7, and 482.8) are consistent with condensation reactions of the most common monomer species with an accompanying loss of 4-6 hydrogens. As mesophase pitches that contain up to 25% dimer were previously identified, herein are proposed specific molecular structures that are significant constituents in mesophase pitch.     

Mites as Matchmakers: Semiochemicals from Host-associated Mites Attract Both Sexes of the Parasitoid Lariophagus distinguendus

The role of volatile chemicals used for mate finding was studied for males of Lariophagus distinguendus (Först.), a parasitoid of the granary weevil Sitophilus granarius (L.). In bioassays that used a static four-chamber olfactometer, males were attracted by host feces, hexane extracts from host feces, and volatile extracts of the feces obtained by closed-loop stripping (CLS). On the other hand, volatiles emitted by unmated females did not elicit any preferences in males. Both sexes of L. distinguendus responded to a synthetic mixture of neral, geranial, neryl formate, and tridecane occurring in the investigated extracts. All compounds are common constituents of astigmatid mites that are often associated with possible hosts of L. distinguendus. In the system investigated, all main compounds found in CLS extracts from larval feces of S. granarius are due to the mold mite Tyrophagus putrescentiae (Schrank) that uses neral, geranial, and neryl formate as an alarm pheromone. The possible role of host-associated astigmatid mites in mate and host finding of L. distinguendus is discussed.     

Chemicals Used for Host Recognition by the Granary Weevil Parasitoid Lariophagus distinguendus

In order to develop methods for mass rearing of the parasitic wasp Lariophagus distinguendus, we characterized and identified chemicals used by this parasitoid to recognize wheat grains infested by its host, larvae of the granary weevil, Sitophilus granarius, a major pest of stored grain worldwide. Bioassays revealed that drumming and drilling behavior of the parasitoids on grain models of filter paper treated with host feces was as intense as on host-infested grains. Thus, chemicals from feces are highly important to recognize infested grains. Extracts of the feces with hexane or dichloromethane applied on grain models were able to provoke drumming and drilling activity. Hexane extract of feces was as active as infested grain itself. Subsequent fractionation of the hexane extract by adsorption chromatography revealed that highest activity was recovered in the dichloromethane fraction. This fraction was characterized by the presence of -tocopherol, -tocopherol, -tocotrienol, cholesterol, ergostenol, and -sitosterol. Synthetic chemicals in proportions found in the active dichloromethane fraction stimulated drumming behavior in bioassays. The significance of these results with respect to the mass propagation of L. distinguendus as natural enemies for the control of the granary weevil is discussed.     

Cis-Configured aziridines are new pseudo-irreversible dual-mode inhibitors of Candida albicans secreted aspartic protease 2

A series of cis-configured epoxides and aziridines containing hydrophobic moieties and amino acid esters were synthesized as new potential inhibitors of the secreted aspartic protease 2 (SAP2) of Candida albicans. Enzyme assays revealed the N-benzyl-3-phenyl-substituted aziridines 11 and 17 as the most potent inhibitors, with second-order inhibition rate constants (k(2)) between 56,000 and 121,000 M(-1) min(-1). The compounds were shown to be pseudo-irreversible dual-mode inhibitors: the intermediate esterified enzyme resulting from nucleophilic ring opening was hydrolyzed and yielded amino alcohols as transition-state-mimetic reversible inhibitors. The results of docking studies with the ring-closed aziridine forms of the inhibitors suggest binding modes mainly dominated by hydrophobic interactions with the S1, S1', S2, and S2' subsites of the protease, and docking studies with the processed amino alcohol forms predict additional hydrogen bonds of the new hydroxy group to the active site Asp residues. C. albicans growth assays showed the compounds to decrease SAP2-dependent growth while not affecting SAP2-independent growth.     

Rational Design of Pseudozyma antarctica Lipase B Yielding a General Esterification Catalyst

Pseudozyma antarctica lipase B (CALB) shows activity in the acrylation of hydroxypropylcarbamate, a racemic mixture of enantiomers of primary and secondary alcohols. However, full conversion is hampered by the slowly reacting S enantiomer of the secondary alcohol. The same is true for a wide range of secondary alcohols, for example, octan‐2‐ and ‐3‐ol. In order to get high conversion in these reactions in a short time, the stereospecificity pocket of CALB was redesigned by using predictions from molecular modeling. Positions 278, 104, and 47 were targeted, and a library for two‐site saturation mutagenesis at positions 104 and 278 was constructed. The library was then screened for hydrolysis of acrylated hydroxypropylcarbamates. The best mutants L278A, L278V, L278A/W104F, and L278A/W104F/S47A showed an increased conversion in hydrolysis and transesterification of more than 30 %. While the wild‐type showed only 73 % conversion in the acrylation of hydroxypropylcarbamate after 6 h, 97 % conversion was achieved by L278A in this time. Besides this, L278A/W104F reached >96 % conversion in the acrylation of octan‐2‐ and ‐3‐ol within 48 h and showed a significant decrease in stereoselectivity, while the wild‐type reached only 68 and 59 % conversion, respectively. Thus the new biocatalysts can be used for efficient transformation of racemic alcohols and esters with high activity when the high stereoselectivity of the wild‐type hampers complete conversion of racemic substrates in a short time.     

Multivalent Display and Receptor‐Mediated Endocytosis of Transferrin on Virus‐Like Particles

The structurally regular and stable self‐assembled capsids derived from viruses can be used as scaffolds for the display of multiple copies of cell‐ and tissue‐targeting molecules and therapeutic agents in a convenient and well‐defined manner. The human iron‐transfer protein transferrin, a high affinity ligand for receptors upregulated in a variety of cancers, has been arrayed on the exterior surface of the protein capsid of bacteriophage Qβ. Selective oxidation of the sialic acid residues on the glycan chains of transferrin was followed by introduction of a terminal alkyne functionality through an oxime linkage. Attachment of the protein to azide‐functionalized Qβ capsid particles in an orientation allowing access to the receptor binding site was accomplished by the Cu^I‐catalyzed azide–alkyne cycloaddition (CuAAC) click reaction. Transferrin conjugation to Qβ particles allowed specific recognition by transferrin receptors and cellular internalization through clathrin‐mediated endocytosis, as determined by fluorescence microscopy on cells expressing GFP‐labeled clathrin light chains. By testing Qβ particles bearing different numbers of transferrin molecules, it was demonstrated that cellular uptake was proportional to ligand density, but that internalization was inhibited by equivalent concentrations of free transferrin. These results suggest that cell targeting with transferrin can be improved by local concentration (avidity) effects.