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991.
Effects of Matrix Porosity on the Mechanical Properties of a Porous-Matrix, All-Oxide Ceramic Composite 总被引:5,自引:0,他引:5
Michael A. Mattoni James Y. Yang Carlos G. Levi Frank W. Zok 《Journal of the American Ceramic Society》2001,84(11):2594-2602
The effects of matrix porosity on the mechanical properties of an all-oxide ceramic composite are investigated. The porosity is varied through impregnation and pyrolysis of a ceramic precursor solution. Mechanical tests are performed to assess the role of the matrix in both matrix-dominated and fiber-dominated loading configurations. The results demonstrate a loss in damage tolerance and tensile strength along the fiber direction as the porosity is reduced. Concomitantly, some improvements in interlaminar strength are obtained. The latter improvements are found to be difficult to quantify over the entire porosity range using the standard short beam shear method, a consequence of the increased propensity for tensile fracture as the porosity is reduced. Measurements of interlaminar shear strength based on the double-notched shear specimen are broadly consistent with the limited values obtained by the short beam shear method, although the former exhibit large variability. In addition, effects of precursor segregation during drying on through-thickness gradients in matrix properties and their role in composite performance are identified and discussed. An analysis based on the mechanics of crack deflection and penetration at an interphase boundary is presented and used to draw insights regarding the role of matrix properties in enabling damage tolerance in porous-matrix composites. Deficiencies in the understanding of the mechanisms that enable damage tolerance in this class of composites are discussed. 相似文献
992.
Jun-Sik Jeoung W. Howard Poisl Michael C. Weinberg Gary L. Smith Hong Li † 《Journal of the American Ceramic Society》2001,84(8):1859-1864
The effect of the oxidation state of iron on the phase separation of x Na2 O·(100 – x )SiO2 glasses, x = 18.56 and 13, containing 0.5 mol% Fe2 O3 was studied. The oxidation state of iron in the glasses was varied by changing the melting conditions, such as melting temperature and melting atmosphere. The oxidation states of the iron ion were determined using colorimetric and UV–VIS–NIR spectrophotometric methods, and a comparison was made between the results obtained using these two methods. Immiscibility temperatures of the glasses were determined using opalescence and clearing methods. The immiscibility temperature of the sodium silicate binary glasses decreased ∼25°C with the addition of 0.5 mol% Fe2 O3 . The immiscibility temperature of the doped glasses increased slightly with increased concentration of Fe2+ ion in the glass. The prediction of immiscibility tendency on the addition of a minor amount of third component was made using models proposed by Tomozawa and Obara and Nakagawa and Izumitani. The Tomozawa and Obara model showed good agreement with measured immiscibility values. 相似文献
993.
Homoionic Na+, Ca2+, Sr2+, Li+, Cu2+ and Zn2+ samples of the <2 μm fraction of a cis-vacant montmorillonite from Linden (Bavaria) were steam treated at 200°C (≈1.5 MPa), 240°C (≈3.3 MPa) and 300°C (≈8.0 MPa) after dehydroxylation at temperatures up to 630°C. Cation exchange capacity (CEC) measurements, determination of exchangeable cations and X-ray diffraction (XRD), supplemented by thermoanalytical investigations of the evolved water in a thermobalance linked to a mass spectrometer, infrared (IR) and electron spin resonance (ESR) spectroscopy were employed to obtain information about the state of expandability and structural changes of swellable montmorillonite and the sites of interlayer and octahedral cations after heating and rehydroxylation.The XRD pattern of the initial samples showed a well-defined (001) reflection according to the interlayer cation and its hydration state under laboratory atmosphere. After dehydroxylation the pattern exhibited (001) reflections between 9.6 and 9.8 Å, corresponding to a collapsed structure for all samples. The Na+-, Ca2+- and Sr2+-rich montmorillonites regained partial expandability after rehydroxylation at 200°C and full expandability after rehydroxylation at 300°C if the dehydroxylation temperature was less than 630°C. Rehydroxylation at 300°C of the Cu2+- and Zn2+-rich montmorillonites did not cause reexpansion, whereas the Li+-rich samples recovered a partial swellability after rehydroxylation at 240°C and nearly the full swellability after rehydroxylation at 300°C.The Li+-, Cu2+- and Zn2+-rich samples underwent a strong CEC reduction due to migration of the interlayer cations into the 2:1 layer before dehydroxylation started. After rehydroxylation under water steam Cu2+- and Zn2+-rich samples released 16–30 meq/100 g of Mg2+ from the structure, increasing with the steam temperature. Mg2+ release was not observed for the Li+-rich montmorillonite. 相似文献
994.
Transformation of Free and Dipeptide‐Bound Glycated Amino Acids by Two Strains of Saccharomyces cerevisiae 下载免费PDF全文
Dr. Michael Hellwig Marie Börner Falco Beer Prof. Dr. Karl‐Heinz van Pée Prof. Dr. Thomas Henle 《Chembiochem : a European journal of chemical biology》2017,18(3):266-275
The yeast Saccharomyces cerevisiae transforms branched‐chain and aromatic amino acids into higher alcohols in the Ehrlich pathway. During microbiological culturing and industrial fermentations, this yeast is confronted with amino acids modified by reducing sugars in the Maillard reaction (glycation). In order to gain some preliminary insight into the physiological “handling” of glycated amino acids by yeasts, individual Maillard reaction products (MRPs: fructosyllysine, carboxymethyllysine, pyrraline, formyline, maltosine, methylglyoxal‐derived hydroimidazolone) were administered to two strains of S. cerevisiae in a rich medium. Only formyline was converted into the corresponding α‐hydroxy acid, to a small extent (10 %). Dipeptide‐bound pyrraline and maltosine were removed from the medium with concomitant emergence of several metabolites. Pyrraline was mainly converted into the corresponding Ehrlich alcohol (20–60 %) and maltosine into the corresponding α‐hydroxy acid (40–60 %). Five specific metabolites of glycated amino acids were synthesized and characterized. We show for the first time that S. cerevisiae can use glycated amino acids as a nitrogen source and transform them into new metabolites, provided that the substances can be transported across the cell membrane. 相似文献
995.
Phylogenetic Studies,Gene Cluster Analysis,and Enzymatic Reaction Support Anthrahydroquinone Reduction as the Physiological Function of Fungal 17β‐Hydroxysteroid Dehydrogenase 下载免费PDF全文
Leon Fürtges David Conradt Dr. Michael A. Schätzle Shailesh Kumar Singh Dr. Nada Kraševec Prof. Dr. Tea Lanišnik Rižner Prof. Dr. Michael Müller Dr. Syed Masood Husain 《Chembiochem : a European journal of chemical biology》2017,18(1):77-80
17β‐Hydroxysteroid dehydrogenase (17β‐HSDcl) from the filamentous fungus Curvularia lunata (teleomorph Cochliobolus lunatus) catalyzes NADP(H)‐dependent oxidoreductions of androgens and estrogens. Despite detailed biochemical and structural characterization of 17β‐HSDcl, its physiological function remains unknown. On the basis of amino acid sequence alignment, phylogenetic studies, and the recent identification of the physiological substrates of the homologous MdpC from Aspergillus nidulans and AflM from Aspergillus parasiticus, we propose an anthrahydroquinone as the physiological substrate of 17β‐HSDcl. This is also supported by our analysis of a secondary metabolite biosynthetic gene cluster in C. lunata m118, containing 17β‐HSDcl and ten other genes, including a polyketide synthase probably involved in emodin formation. Chemoenzymatic reduction of emodin by 17β‐HSDcl in the presence of sodium dithionite verified this hypothesis. On the basis of these results, the involvement of a 17β‐HSDcl in the biosynthesis of other anthrahydroquinone‐derived natural products is proposed; hence, 17β‐HSDcl should be more appropriately referred to as a polyhydroxyanthracene reductase (PHAR). 相似文献
996.
Design of S‐Allylcysteine in Situ Production and Incorporation Based on a Novel Pyrrolysyl‐tRNA Synthetase Variant 下载免费PDF全文
Dr. Matthias P. Exner Tilmann Kuenzl Tuyet Mai T. To Zhaofei Ouyang Sergej Schwagerus Michael G. Hoesl Prof. Dr. Christian P. R. Hackenberger Prof. Dr. Marga C. Lensen Prof. Dr. Sven Panke Prof. Dr. Nediljko Budisa 《Chembiochem : a European journal of chemical biology》2017,18(1):85-90
The noncanonical amino acid S‐allyl cysteine (Sac) is one of the major compounds of garlic extract and exhibits a range of biological activities. It is also a small bioorthogonal alkene tag capable of undergoing controlled chemical modifications, such as photoinduced thiol‐ene coupling or Pd‐mediated deprotection. Its small size guarantees minimal interference with protein structure and function. Here, we report a simple protocol efficiently to couple in‐situ semisynthetic biosynthesis of Sac and its incorporation into proteins in response to amber (UAG) stop codons. We exploited the exceptional malleability of pyrrolysyl‐tRNA synthetase (PylRS) and evolved an S‐allylcysteinyl‐tRNA synthetase (SacRS) capable of specifically accepting the small, polar amino acid instead of its long and bulky aliphatic natural substrate. We succeeded in generating a novel and inexpensive strategy for the incorporation of a functionally versatile amino acid. This will help in the conversion of orthogonal translation from a standard technique in academic research to industrial biotechnology. 相似文献
997.
Synthesis,Characterization and Immunological Evaluation of Self‐Adjuvanting Group A Streptococcal Vaccine Candidates Bearing Various Lipidic Adjuvanting Moieties 下载免费PDF全文
Dr. Vincent Fagan Dr. Waleed M. Hussein Mei Su Ashwini K. Giddam Dr. Michael R. Batzloff Prof. Michael F. Good Prof. Istvan Toth Dr. Pavla Simerska 《Chembiochem : a European journal of chemical biology》2017,18(6):545-553
Four group A streptococcal glycolipopeptide vaccine candidates with different lipidic adjuvanting moieties were prepared and characterized. The immunogenicity of the compounds was evaluated by macrophage and dendritic cell uptake studies and by in vivo quantification of systemic IgG antibody by ELISA. Three of the candidates showed significant induction of the IgG response. 相似文献
998.
Cover Picture: Design of S‐Allylcysteine in Situ Production and Incorporation Based on a Novel Pyrrolysyl‐tRNA Synthetase Variant (ChemBioChem 1/2017) 下载免费PDF全文
999.
Jason Karpus Michael Bosscher Ifedayo Ajiboye Dr. Liang Zhang Prof. Chuan He 《Chembiochem : a European journal of chemical biology》2017,18(7):633-637
Effective and cheap methods and techniques for the safe removal of hexavalent chromate from the environment are in increasingly high demand. High concentrations of hexavalent chromate have been shown to have numerous harmful effects on human biology. We show that the E. coli molybdate‐binding protein ModA is a genetically encoded tool capable of removing chromate from aqueous solutions. Although previously reported to not bind chromate, we show that ModA binds chromate tightly and is capable of removing chromate to levels well below current US federal standards. 相似文献
1000.
Dr. Nadja Bertleff‐Zieschang Julian Bechold Dr. Clemens Grimm Dr. Michael Reutlinger Dr. Petra Schneider Prof. Dr. Gisbert Schneider Prof. Dr. Jürgen Seibel 《Chembiochem : a European journal of chemical biology》2017,18(15):1477-1481
Galectin‐1 is a tumor‐associated protein recognizing the Galβ1‐4GlcNAc motif of cell‐surface glycoconjugates. Herein, we report the stepwise expansion of a multifunctional natural scaffold based on N‐acetyllactosamine (LacNAc). We obtained a LacNAc mimetic equipped with an alkynyl function on the 3′‐hydroxy group of the disaccharide facing towards a binding pocket adjacent to the carbohydrate‐recognition domain. It served as an anchor motif for further expansion by the Sharpless–Huisgen–Meldal reaction, which resulted in ligands with a binding mode almost identical to that of the natural carbohydrate template. X‐ray crystallography provided a structural understanding of the galectin‐1–ligand interactions. The results of this study enable the development of bespoke ligands for members of the galectin target family. 相似文献