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131.
MM. D. Letouz J. Duflos G. Queguiner P. Pastour 《Journal of heterocyclic chemistry》1973,10(6):1075-1076
This communication describes the synthesis of 7-one (7H) cyclohepta[b]pyridine and some derivatives (6,8-dimethyl; 8-methyl; 8-ethyl….). These compounds have been obtained by condensation of ketones with 2,3-diformylpyridine. 相似文献
132.
Deformability of poly(amidoamine) dendrimers 总被引:1,自引:0,他引:1
Mecke A Lee I Baker JR Holl MM Orr BG 《The European physical journal. E, Soft matter》2004,14(1):7-16
Experimental data indicates that poly(amidoamine) (PAMAM) dendrimers flatten when in contact with a substrate, i.e. they are no longer spherical, but resemble flat disks. In order to better understand the deformation behavior of these branched polymers, a series of atomistic molecular dynamics simulations is performed. The resulting flattened dendrimer conformations are compared to atomic force microscopy (AFM) images of individual dendrimers at air/mica and water/mica interfaces. The ability of the polymers to deform is investigated as a function of dendrimer generation (2-5) and the required energies are calculated. Our modeling results show good agreement with the experimental AFM images, namely that dendrimers are highly flexible and capable of forming multiple interaction sites between most of their branch ends and the substrate. The deformation energy scales with dendrimer generation and does not indicate an increase in stiffness between generations 2 and 5 due to steric effects.PACS:
81.07.Nb Molecular nanostructures - 82.20.Wt Computational modeling; simulation - 68.37.Ps Atomic force microscopy (AFM) 相似文献
133.
Dzmitry S. Firaha Dr. Oldamur Hollóczki Prof. Dr. Barbara Kirchner 《Angewandte Chemie (International ed. in English)》2015,54(27):7805-7809
Ionic liquids (ILs), vary strongly in their interaction with CO2. We suggest simple theoretical approach to predict the CO2 absorption behavior of ILs. Strong interaction of the CO2 with the IL anions corresponds to chemical absorption whereas weak interaction indicates physical absorption. A predictive estimate with a clear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of a solvation model instead of optimizing it only in gas phase as has been done to date. The resulting Gibbs free energies compare very well with experimental values and the energies were correlated with experimental capacities. Promising anions, for ionic liquids with reversible CO2 absorption properties can be defined by a reaction Gibbs free energy of absorption in the range of ?30 to 16 kJ mol?1. 相似文献
134.
Banaszak AT 《Photochemistry and photobiology》2007,83(4):833-838
Ultraviolet (UV)-B is known to cause DNA damage, principally by the formation of thymine dimers, but little research has been conducted in coral reef environments where UV doses are high. The majority of tropical reef-dwelling corals form a mutualistic symbiosis with the dinoflagellate Symbiodinium but few studies have been conducted on in situ DNA damage in corals and none have investigated the symbiotic components separately. The aim of this research was to quantify DNA damage in both the coral host and the dinoflagellate symbiont. The first step in this investigation was to optimize the extraction of DNA from the host, Porites astreoides, as well as the symbiont. The optimization was divided into a series of steps: the preservation of the samples, separation of the coral tissue from the skeleton, separation of the host tissue from the algal cells to prevent cross contamination as well as the extraction and purification of genomic DNA from the algae that are located intracellularly within the invertebrate animal tissue. The best preservation method was freezing at low temperatures without ethanol. After scraping with a razor blade, the coral tissue can be divided into host and algal components and the DNA extracted using modifications of published techniques yielding DNA suitable for the quantification of thymine dimer formation using antibodies. Preliminary data suggest that in P. astreoides collected from 1 m depth, thymine dimers form approximately 2.8 times more frequently in the host DNA than in the DNA of its symbionts. 相似文献
135.
Hong S Leroueil PR Majoros IJ Orr BG Baker JR Banaszak Holl MM 《Chemistry & biology》2007,14(1):107-115
Dendrimer-based anticancer nanotherapeutics containing approximately 5 folate molecules have shown in vitro and in vivo efficacy in cancer cell targeting. Multivalent interactions have been inferred from observed targeting efficacy, but have not been experimentally proven. This study provides quantitative and systematic evidence for multivalent interactions between these nanodevices and folate-binding protein (FBP). A series of the nanodevices were synthesized by conjugation with different amounts of folate. Dissociation constants (K(D)) between the nanodevices and FBP measured by SPR are dramatically enhanced through multivalency ( approximately 2,500- to 170,000-fold). Qualitative evidence is also provided for a multivalent targeting effect to KB cells using flow cytometry. These data support the hypothesis that multivalent enhancement of K(D), not an enhanced rate of endocytosis, is the key factor resulting in the improved biological targeting by these drug delivery platforms. 相似文献
136.
L. Vescan M. Goryll T. Stoica P. Gartner K. Grimm O. Chretien E. Mateeva C. Dieker B. Holländer 《Applied Physics A: Materials Science & Processing》2000,71(4):423-432
The distribution of Ge islands is analysed in order to understand their optical behaviour. The Ge islands described in this
paper were deposited by low-pressure chemical vapour deposition at relatively high temperature (700 °C), therefore the diffusion
length of adatoms is high (∼100 μm) and thus, not the limiting factor for nucleation. By changing the deposition time and
the coverage, square-based pyramids, domes and relaxed domes are nucleated. Mainly domes emit light, the emission being in
the wavelength range 1.38–1.55 μm. When pyramids or relaxed domes are present, the photoluminescence broadens and decreases
in intensity. The electroluminescence of vertically correlated islands increases with the number of layers, i.e. with the
number of islands. The nucleation of islands on patterned (001) Si is changed when the deposition is performed on Si mesas
with high index facets. The size distribution becomes narrower when the mesa size is decreased. An intermixing of up to 40%
Si in the 2D layer was determined from photoluminescence data. PIN diodes fabricated on patterned wafers show an area-dependent
electroluminecence related to a different microstructure of islands on large and small mesas. Finally, the lateral ordering
on {hkl} facets is discussed.
Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000 相似文献
137.
Effects of ultraviolet radiation on plant cells 总被引:22,自引:0,他引:22
Hollósy F 《Micron (Oxford, England : 1993)》2002,33(2):179-197
Recent measurements of ozone levels have led to concern that the stratospheric ozone layer is being depleted as a result of contamination with man-made chlorofluorocarbons. Concomitantly, the amounts of solar UV-B radiation reaching the Earth's surface is increasing. UV-B radiation has been shown to be harmful to living organisms, damaging DNA, proteins, lipids and membranes. Plants, which use sunlight for photosynthesis and are unable to avoid exposure to enhanced levels of UV-B radiation, are at risk. Thus, mechanisms by which plants may protect themselves from UV radiation are of particular interest. This review will summarizes the main aspects of ultraviolet radiation on plants at physiological and biochemical level, with particular emphasis on protective structures and mechanisms. 相似文献
138.
Sascha Gehrke Dr. Oldamur Hollóczki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):10140-10151
In this work the mechanism of the aldehyde umpolung reactions, catalyzed by azolium cations in the presence of bases, was studied through computational methods. Next to the mechanism established by Breslow in the 1950s that takes effect through the formation of a free carbene, we have suggested that these processes can follow a concerted asynchronous path, in which the azolium cation directly reacts with the substrate, avoiding the formation of the carbene intermediate. We hereby show that substituting the azolium cation, and varying the base or the substrate do not affect the preference for the concerted reaction mechanism. The concerted path was found to exhibit low barriers also for the reactions of thiamine with model substrates, showing that this path might have biological relevance. The dominance of the concerted mechanism can be explained through the specific structure of the key transition state, avoiding the liberation of the highly reactive, and thus unstable carbene lone pair, whereas activating the substrate through hydrogen-bonding interactions. Polar and hydrogen-bonding solvents, as well as the presence of the counterions of the azolium salts facilitate the reaction through carbenes, bringing the barriers of the two reaction mechanisms closer, in many cases making the concerted path less favorable. Thus, our data show that by choosing the exact components in a reaction, the mechanism can be switched to occur with or without carbenes. 相似文献
139.
We prove that a.a.s. as soon as a Kronecker graph becomes connected it has a finite diameter. 相似文献
140.
We simulate ABA triblock copolymer melts using a lattice Monte Carlo method, known as cooperative motion algorithm, probing various degrees of compositional asymmetry. Selected order-disorder transition lines are determined in terms of the segment incompatibility, quantified by product χN , and the triblock asymmetry parameters, α and β. We correlate the results of the simulation with the self-consistent field theory and an experimental study of polyisoprene-polystyrene-polyisoprene triblock melt by Hamersky and coworkers. In particular, we confirm the mean-field prediction that for highly asymmetric triblocks the short A -block is localized in the middle of the B -domain due to an entropic advantage. This results in the middle block relaxation and is consistent with the experimental data indicating that as the relatively short A -blocks are grown into AB diblock, from the B -block side, the order-disorder transition temperature is considerably depressed. 相似文献