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排序方式: 共有155条查询结果,搜索用时 46 毫秒
91.
92.
Ruth D. Rittinghaus Jakub Tremmel Prof. Dr. Ales Růžička Christian Conrads Pascal Albrecht Dr. Alexander Hoffmann Agnieszka N. Ksiazkiewicz Prof. Dr. Andrij Pich Prof. Dr. Roman Jambor Prof. Dr. Sonja Herres-Pawlis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(1):212-221
Polylactide (PLA) is a high potential bioplastic that can replace oil-based plastics in a number of applications. To date, in spite of its known toxicity, a tin catalyst is used on industrial scale which should be replaced by a benign catalyst in the long run. Germanium is known to be unharmful while having similar properties as tin. Only few germylene catalysts are known so far and none has shown the potential for industrial application. We herein present Ge complexes in combination with zinc and copper, which show amazingly high polymerization activities for lactide in bulk at 150 °C. By systematical variation of the complex structure, proven by single-crystal XRD and DFT calculations, structure–property relationships are found regarding the polymerization activity. Even in the presence of zinc and copper, germanium acts as the active site for polymerizing probably through the coordination–insertion mechanism to high molar mass polymers. 相似文献
93.
94.
We consider a class of structured cell population models described by a first order partial differential equation perturbed
by a general birth operator which describes in a unified way a wide class of birth phenomena ranging from cell division to
the McKendrick model. Using the theory of positive stochastic semigroups we establish new criteria for an asynchronous exponential
growth of solutions to such equations. 相似文献
95.
Exact closed-form solutions to Maxwell's equations are used to investigate the acceleration of electrons in vacuum driven by ultrashort and nonparaxial radially polarized laser pulses. We show that the threshold power above which significant acceleration takes place is greatly reduced by using a tighter focus. Moreover, electrons accelerated by tightly focused single-cycle laser pulses may reach around 80% of the theoretical energy gain limit, about twice the value previously reported with few-cycle paraxial pulses. Our results demonstrate that the direct acceleration of electrons in vacuum is well within reach of current laser technology. 相似文献
96.
Mixture surrogate models based on Dempster-Shafer theory for global optimization problems 总被引:2,自引:0,他引:2
Recent research in algorithms for solving global optimization problems using response surface methodology has shown that it
is in general not possible to use one surrogate model for solving different kinds of problems. In this paper the approach
of applying Dempster-Shafer theory to surrogate model selection and their combination is described. Various conflict redistribution
rules have been examined with respect to their influence on the results. Furthermore, the implications of the surrogate model
type, i.e. using combined, single or a hybrid of both, have been studied. The suggested algorithms were applied to several
well-known global optimization test problems. The results indicate that the used approach leads for all problems to a thorough
exploration of the variable domain, i.e. the vicinities of global optima could be detected, and that the global minima could
in most cases be approximated with high accuracy. 相似文献
97.
Peralta RA Bortoluzzi AJ de Souza B Jovito R Xavier FR Couto RA Casellato A Nome F Dick A Gahan LR Schenk G Hanson GR de Paula FC Pereira-Maia EC de P Machado S Severino PC Pich C Bortolotto T Terenzi H Castellano EE Neves A Riley MJ 《Inorganic chemistry》2010,49(24):11421-11438
Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear Fe(III)M(II) center (M(II) = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a variety of phosphoric acid esters. The dinuclear complex [(H(2)O)Fe(III)(μ-OH)Zn(II)(L-H)](ClO(4))(2) (2) with the ligand 2-[N-bis(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N'-(2-pyridylmethyl)(2-hydroxybenzyl) aminomethyl]phenol (H(2)L-H) has recently been prepared and is found to closely mimic the coordination environment of the Fe(III)Zn(II) active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the Fe(III) center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted Fe(III)N(2)O(4) octahedron with a dominant tetragonal compression aligned along the μ-OH-Fe-O(phenolate) direction. To probe the role of the Fe-O(phenolate) bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (-CH(3), -H, -Br, -NO(2)) in the 5-position. The effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic structural information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order -NO(2) ←Br ←H ←CH(3) when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k(cat)/k(0)) is plotted against the Hammett parameter σ. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing -NO(2) and electron-donating -CH(3) groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups. 相似文献
98.
Roger Bishop Donald C. Craig Ian G. Dance Sungho Kim Md. Aminul I. Mallick Kim C. Pich 《Supramolecular chemistry》2013,25(2):171-178
Abstract In order to be able to predict and then synthesize new lattice inclusion compounds with the helical tubuland diol host structure, the hydrogen bonding modes of a range of bicyclic and tricyclic diols have been studied using X-ray crystallography. Several distinct types of lattice structure have been recognized. Steric factors play a major role in determining which of these is produced in a given case. Establishment of a series of structural rules provides a window of opportunity for duplication of the helical tubuland host lattice by deliberate design and synthesis. New inclusion compounds resulting from this approach are presented. 相似文献
99.
100.
Yurij Stetsyshyn Joanna ZemlaОksana Zolobko Katarzyna FornalAndrzej Budkowski Andrij KostrubaVolodymyr Donchak Kristina HarhayKamil Awsiuk Jakub RyszAndrzej Bernasik Stanislav Voronov 《Journal of colloid and interface science》2012,387(1):95-105
Poly(N-isopropylacrylamide) (PNIPAM) coatings attached to glass with novel approach involving polymerization from oligoperoxide grafted to surface with (3-aminopropyl)triethoxysilane exhibit not only temperature- but also pH-dependence of wettability and protein adsorption. Wettability and composition of coatings, fabricated with different polymerization times, were determined using contact angle measurements and Time Of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), respectively. Thermal response of wettability, measured between 20 and 40 °C, was prominent at pH 9 and 7 and diminished or absent at pH 5 and 3. This indicates a transition between hydrated loose coils and hydrophobic collapsed chains that is blocked at low pH. Higher surface roughness and dramatically increased adsorption of model protein (lentil lectin labeled with fluorescein isothiocyanate) were observed with AFM and fluorescence microscopy to occur in hydrophobic phases (at pH 3, for pH varied at constant temperature of 22 °C and at ∼33 °C, for temperature varied at constant pH 9). Protein adsorption response to pH was confirmed by TOF-SIMS and Principal Component Analysis. 相似文献