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101.
Thorsten?Fiedler Thomas?Moritz Lothar?W.?KrohEmail author 《European Food Research and Technology》2006,223(6):837-842
The correlations between formation of melanoidins and the content of α-dicarbonyl compounds and colour formation were studied in Maillard reaction model sucrose solutions at high treating temperatures (130 °C) corresponding to the industrial sucrose processing. Molecular weight distribution was determined by gel permeation chromatography (GPC) and α-dicarbonyls as high reactive intermediates of the Maillard reaction were detected by RP-HPLC and GC/MS. Referring to formation of melanoidins, new knowledge could be gained. The investigations clearly point out, that individual α-dicarbonyls are involved in formation of specific molecular weight fractions. 3-Deoxyhexosulose (3-DH) and methylglyoxal are the important α-dicarbonyl compounds in thermal-treated sucrose solutions. A low molecular weight fraction with a molecular weight range of <5,800 g/mol preferably occurs when 3-DH is formed in high concentrations. The high increase in intensity of a low molecular weight fraction is combined with a strong colour formation. In contrast to 3-DH, methylglyoxal promotes the formation of high molecular weight fractions between 6,600 g/mol and approximately 17,000 g/mol. Furthermore, model solutions with a high intensity of high molecular weight fractions show an early colour formation during the starting period of the reaction. Indeed, this early browning is not as intensive as the colour formation caused by the low molecular weight fraction during the later stage of the browning reaction. Out of this, 3-DH can be regarded as the most important intermediate for an intensive colour formation in sucrose solutions. 相似文献
102.
Incorporation of catalyst atoms during the growth process of semiconductor nanowires reduces the electron mean free path and degrades their electronic properties. Aberration-corrected scanning transmission electron microscopy (STEM) is now capable of directly imaging single Au atoms within the dense matrix of a GaAs crystal, by slightly tilting the GaAs lattice planes with respect to the incident electron beam. Au doping values in the order of 10(17-18) cm(3) were measured, making ballistic transport through the nanowires practically inaccessible. 相似文献
103.
The 3D structure reconstruction of gold core-silver shell nanoparticles by electron tomography is combined with optical dark-field spectroscopy. Electron tomography allows segmentation of the particles into core and shell subvolumes and facilitates avoiding Bragg diffraction artifacts inherent in 2D images. This advantage proves essential for accurate correlation of plasmon spectra and structure. We find that for the nanoparticles of near-spherical shape studied here the plasmon resonances depend on the relative size of the core and shell, rather than on their exact shapes and concentricity. A remarkable dependence of the spectral shape on the permittivity of the surrounding medium is also demonstrated, suggesting that core-shell nanoparticles can be used as ratiometric sensors with a very high dynamic range. 相似文献
104.
Schipani P Noethe L Arcidiacono C Argomedo J Dall'Ora M D'Orsi S Farinato J Magrin D Marty L Ragazzoni R Umbriaco G 《Journal of the Optical Society of America. A, Optics, image science, and vision》2012,29(7):1359-1366
The wavefront sensor in active and adaptive telescopes is usually not in the optical path toward the scientific detector. It may generate additional wavefront aberrations, which have to be separated from the errors due to the telescope optics. The aberrations that are not rotationally symmetric can be disentangled from the telescope aberrations by a series of measurements taken in the center of the field, with the wavefront sensor at different orientation angles with respect to the focal plane. This method has been applied at the VLT Survey Telescope on the ESO Paranal observatory. 相似文献
105.
Spudat C Müller M Houben L Maultzsch J Goss K Thomsen C Schneider CM Meyer C 《Nano letters》2010,10(11):4470-4474
We study collective vibrational breathing modes in the Raman spectrum of a multiwalled carbon nanotube. In correlation with high-resolution transmission electron microscopy, we find that these modes have energies differing by more than 23% from the radial breathing modes of the corresponding single-walled nanotubes. This shift in energy is explained with intershell interactions using a model of coupled harmonic oscillators. The strength of this interaction is related to the coupling strength expected for few-layer graphene. 相似文献
106.
Zinc supplementation induces regulatory T cells by inhibition of Sirt‐1 deacetylase in mixed lymphocyte cultures
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107.
Roberto Köferstein Lothar Jäger Mandy Zenkner Hans-Peter Abicht 《Journal of Materials Science》2008,43(3):832-838
The formation of solid solutions of the type [Ba(HOC2H4OH)4][Ti1−x
Ge
x
(OC2H4O)3] as Ba(Ti1−x
/Ge
x
)O3 precursors and the phase evolution during thermal decomposition of [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) are described herein. The 1,2-ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO3 and BaGeO3. A heating rate controlled calcination procedure, up to 730 °C, leads to a nm-sized Ba(Ti0.9/Ge0.1)O3 powder (1a) with a specific surface area of S = 16.9 m2/g, whereas a constant heating rate calcination at 1,000 °C for 2 h yields a powder (1b) of S = 3.0 m2/g. The shrinkage and sintering behaviour of the resulting Ba(Ti0.9/Ge0.1)O3 powder compacts in comparison with nm-sized BaTiO3 powder compacts (2a) has been investigated. A two-step sintering procedure of nm-sized Ba(Ti0.9/Ge0.1)O3 compacts (1a) leads, below 900 °C, to ceramic bodies with a relative density of ≥90%. Furthermore, the cubic ⇆ tetragonal phase transition
temperature has been detected by dilatometry, and the temperature dependence of the dielectric constant (relative permittivity)
has also been measured. 相似文献
108.
Sergey Sirotkin Robert Meszaros Lothar Wondraczek 《International Journal of Applied Glass Science》2012,3(1):44-52
We report on chemical stability and corrosion behavior of highly depolymerized sulfophosphate glasses from the system ZnO–Na2O–SO3–P2O5 in aqueous solution, providing data on weight loss, ion release rates, and modifications of surface topology as a function of time, temperature and pH value. Observations seem consistent with the previously developed structural model of chemical heterogeneity, where cations Na+ and Zn2+ cluster selectively in the vicinity of sulfate and phosphate anions, respectively. 相似文献
109.
Influence of the chemical structure on the thermal degradation of the glucosinolates in broccoli sprouts 总被引:1,自引:0,他引:1
Glucosinolates are secondary plant metabolites occurring in Brassica vegetables. Food processing significantly reduces glucosinolate content, among other things due to thermal degradation. As there is only little information about thermal glucosinolate breakdown, the influence of the chemical structure as well as the influence of different pH to thermal degradation of individual glucosinolates was studied by analysing desulphoglucosinolates with HPLC-DAD. Thermal degradation was forced by heating broccoli sprouts at 130 °C in dry medium, whereas the influence of the pH was studied by cooking at 100 °C in aqueous medium. Within each group of glucosinolates differences in thermal degradation were revealed. Within the sulphur containing aliphatic glucosinolates the oxidative state of the sulphur atom as well as the side chain length influenced the reactivity. Among the indole glucosinolates great differences in stability were observed. A hydroxyl function in the side chain generally seems to destabilise glucosinolates. Glucosinolates were most stable towards thermal treatment in neutral and slightly acidic medium, whereas they degraded more rapidly in basic medium. 相似文献
110.
Bettina?C?mmererEmail author Katharina?Chodakowski Claudia?Gienapp Laura?Wohak Andrea?Hartwig Lothar?W.?Kroh 《European Food Research and Technology》2012,234(4):663-670
High molecular weight Maillard reaction products (melanoidins) are described to possess metal-chelating properties. Whereas
in food systems, this ability contributes to antioxidant properties, the consequences on biological systems are not quite
clear. The study was aimed to evaluate the implication of metal complexation by melanoidins on DNA damage. Melanoidins prepared
with d-glucose and different l-amino acids under water-free reaction conditions were charged with cupric ions. The effect on isolated DNA was investigated
by the PM2 assay and on cellular systems in the human colon carcinoma cell line HCT-116 by alkaline unwinding. Independent
of the amino acid composition, pure melanoidins (MW >14 kDa) did not cause significant DNA damage. By charging melanoidins
with Cu2+ ions, a considerable DNA strand breaking activity was detectable, which was again amplified in an oxidative milieu (addition
of hydrogen peroxide). Since Cu2+ normally does not provoke the formation of reactive oxygen species (ROS) via Fenton-type reaction, the results obtained have
to be attributed to reducing properties of melanoidins. Thus, in melanoidin–copper complexes redox cycling may take place
leading to Cu+ which subsequently undergoes Fenton-type and Haber–Weiss reactions. As a consequence, ROS are formed, which may explain the
generation of DNA strand breaks. 相似文献