Perspektiven für zuckerhaltige Amphiphile mit Amid bindung

Perspektiven for Carbohydrate Containing Amphiphiles with Amide Linkages. Carbohydrate containing amphiphiles can easily be prepared by amide linkage. Reaction of the aldonic acid lactones of glucose and maltose with alkyl amines or of the N-(2-aminoethyl)aldon amides with alkanoic acids in the range of C₆-C₂₀ allows the molecular structure and the hydrophilic-hydrophobic ratio to be varied systematically. Products with one or two non-substituted amide linkages, as well as N-methylated compounds have been prepared. Strong hydrogen bonding between the amide bridges and the carbohydrate head groups of the hydrophilic part leads to the formation of highly ordered aggregates in aqueous solution: (a) Stable monolayers (C₁₂-C₂₀), suitable for the preparation of technical membranes; (b) Gels, formed from diluted solution (C₆-C₁₀), which according to electron micrographs are composed of a loose network of regularly twisted helical strands; (c) Lyotropic liquid-crystalline phases in more concentrated solutions, most pronounced with the N-methylated samples (C₁₀), or with compounds containing a disaccharide head group and a longer alkyl chain (C₁₆-C₁₈). In the latter case hydrophobic hydrocarbon interaction is dominant. These studies exemplify in which way the desired properties of compounds for different fields of application can be regulated by chemical modification. The crucial role played by the carbohydrate head groups of the glycolipids in biological systems may also be deduced.     

Dietary n-3 Fatty Acids Significantly Suppress Lipogenesis in Bovine Muscle and Adipose Tissue: A Functional Genomics Approach

Changes in fatty acid composition of longissimus muscle and subcutaneous adipose tissue of German Holstein bulls induced by a grass-silage/n-3 fatty acid based intervention diet versus a maize-silage/n-6 fatty acid based control diet were analyzed and related to shifts in lipogenic gene expression, protein expression, and enzyme activity patterns. Significantly higher amounts of n-3 fatty acids and by mean factors of 2.2–2.5 decreased n-6/n-3 fatty acid ratios in both tissues were obtained upon n-3 fatty acid intervention. In longissimus muscle, these changes of fatty acid profiles were associated with reduced SREBP1c (p = 0.02), ACC (p = 0.00), FAS (p = 0.10) and SCD (p = 0.03) gene expression, Δ6D (p = 0.03) and SCD (p = 0.03) protein expression as well as SCD enzyme activity (p = 0.03). In subcutaneous adipose tissue, significantly reduced ACC (p = 0.00) and FAS (p = 0.01) gene expression, SCD protein expression (p = 0.02) and SCD enzyme activity (p = 0.03) were detected upon n-3 fatty acid intervention, although lower degrees of correlation between gene and corresponding gene products were obtained in relation to longissimus muscle. The study elucidates tissue-specific functional genomic responses to dietary fatty acid manipulation in regard to fatty acid profile tailoring of animal tissues.     

Kinetic and stoichiometric characterisation of streptavidin-binding aptamers

Aptamers are oligonucleotide ligands that are selected for high-affinity binding to molecular targets. Only limited knowledge relating to relations between structural and kinetic properties that define aptamer-target interactions is available. To this end, streptavidin-binding aptamers were isolated and characterised by distinct analytical techniques. Binding kinetics of five broadly similar aptamers were determined by surface plasmon resonance (SPR); affinities ranged from 35-375 nM with large differences in association and dissociation rates. Native mass spectrometry showed that streptavidin can accommodate up to two aptamer units. In a 3D model of one aptamer, conserved regions are exposed, strongly suggesting that they directly interact with the biotin-binding pockets of streptavidin. Mutational studies confirmed both conserved regions to be crucial for binding. An important result is the observation that the most abundant aptamer in our selections is not the tightest binder, emphasising the importance of having insight into the kinetics of complex formation. To find the tightest binder it might be better to perform fewer selection rounds and to focus on post-selection characterisation, through the use of complementary approaches as described in this study.     

Modification of cotton fabrics with a hydrolysed organotrialkoxysilane/metal alkoxide system: multifunctionalisation and mordant dyeing

Untreated cotton fabrics and cotton samples pretreated with 1,2,3,4-butanetetracarboxylic acid were functionalised with an organotrialkoxysilane [(3-glycidyloxy)propyltrimethoxysilane] in conjunction with a metal alkoxide (aluminium isopropoxide, titanium tetraisopropoxide, or zircon tetrabutoxide). Evaluation of the physicomechanical properties revealed that the dry crease recovery angle was significantly increased in the case of aluminium isopropoxide, whereas the tensile strength and the tear strength were reduced. The application of alkyltrialkoxysilanes resulted in an enhanced contact angle. As the cotton samples were treated with hydrolysed metal alkoxides, which can function as mordants, the cotton fabrics were dyed with alizarin. The dyeing behaviour was determined from colorimetric data.     

Plasmin-Induced Activation of Human Platelets Is Modulated by Thrombospondin-1, Bona Fide Misfolded Proteins and Thiol Isomerases

Inflammatory processes are triggered by the fibrinolytic enzyme plasmin. Tissue-type plasminogen activator, which cleaves plasminogen to plasmin, can be activated by the cross-β-structure of misfolded proteins. Misfolded protein aggregates also represent substrates for plasmin, promoting their degradation, and are potent platelet agonists. However, the regulation of plasmin-mediated platelet activation by misfolded proteins and vice versa is incompletely understood. In this study, we hypothesize that plasmin acts as potent agonist of human platelets in vitro after short-term incubation at room temperature, and that the response to thrombospondin-1 and the bona fide misfolded proteins Eap and SCN⁻-denatured IgG interfere with plasmin, thereby modulating platelet activation. Plasmin dose-dependently induced CD62P surface expression on, and binding of fibrinogen to, human platelets in the absence/presence of plasma and in citrated whole blood, as analyzed by flow cytometry. Thrombospondin-1 pre-incubated with plasmin enhanced these plasmin-induced platelet responses at low concentration and diminished them at higher dose. Platelet fibrinogen binding was dose-dependently induced by the C-terminal thrombospondin-1 peptide RFYVVMWK, Eap or NaSCN-treated IgG, but diminished in the presence of plasmin. Blocking enzymatically catalyzed thiol-isomerization decreased plasmin-induced platelet responses, suggesting that plasmin activates platelets in a thiol-dependent manner. Thrombospondin-1, depending on the concentration, may act as cofactor or inhibitor of plasmin-induced platelet activation, and plasmin blocks platelet activation induced by misfolded proteins and vice versa, which might be of clinical relevance.     

Sintering behavior,microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators

The sintering behavior and the thermoelectric performance of Ca₃Co₄O₉ multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca₃Co₄O₉ green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C.     

Orthogonal Translation Meets Electron Transfer: In Vivo Labeling of Cytochrome c for Probing Local Electric Fields

Cytochrome c (cyt c), a redox protein involved in diverse fundamental biological processes, is among the most traditional model proteins for analyzing biological electron transfer and protein dynamics both in solution and at membranes. Studying the role of electric fields in energy transduction mediated by cyt c relies upon appropriate reporter groups. Up to now these had to be introduced into cyt c by in vitro chemical modification. Here, we have overcome this restriction by incorporating the noncanonical amino acid p‐cyanophenylalanine (pCNF) into cyt c in vivo. UV and CD spectroscopy indicate preservation of the overall protein fold, stability, and heme coordination, whereas a small shift of the redox potential was observed by cyclic voltammetry. The C≡N stretching mode of the incorporated pCNF detected in the IR spectra reveals a surprising difference, which is related to the oxidation state of the heme iron, thus indicating high sensitivity to changes in the electrostatics of cyt c.     

A simple intrinsic measure for rapid crack propagation in bimodal polyethylene pipe grades validated by elastic–plastic fracture mechanics analysis of data from instrumented Charpy impact test

Conventional test procedures, such as the S4 test to analyze the resistance against rapid crack propagation (RCP) of plastic pipe materials are characterized by usage of a lot of material, are far from saving of time and they are‐in need of special experimental set‐ups. Therefore, in the last decade, small‐scale accelerated reliable tests (SMART) are developed ‐ worldwide to overcome the disadvantage of such conventional tests. In this article, fracture mechanics based analysis of instrumented Charpy impact test data for a set of bimodal high‐density polyethylene pipe grades are compared with data of the conventional Charpy impact test. From this comparison the Charpy impact strength at ?30°C comes forth as a robust reproducible measure of the resistance to RCP and it is therefore proposed as a SMART method to rank materials with respect to RCP resistance. POLYM. ENG. SCI., 57:13–21, 2017. © 2016 Society of Plastics Engineers     

Toughness optimization of elastomer‐modified glass–fiber reinforced PA6 materials

To investigate the influence of moisture and EPR‐g‐MA content on the fracture behavior of glass–fiber reinforced PA6 materials, brittle‐to‐tough transition temperatures (T_btt) were determined. Water absorption was taken into account by conditioning the analyzed materials. Tensile tests could reveal the temperature range of the largest moisture dependence of mechanical properties between 10 and 50°C. J‐integral values were used to describe the fracture behavior under conditions of impact load as a function of temperature. The brittle‐to‐tough transition of reinforced polyamides was found to be less approximate than in unreinforced materials. Two different characteristic temperature points T_s and T_e were identified, which were the intercept between elastic and elastic–plastic deformation on the one hand and the starting point of dominating stable crack propagation with strong plastic deformation on the other hand. Characteristic brittle‐to‐tough transition temperatures T_btt could be calculated as the arithmetic average of these two points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013