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991.
992.
Mike Jörges Dr. Alexander Kroll Leif Kelling Dr. Richard Gauld Dr. Bert Mallick Prof. Dr. Stefan M. Huber Prof. Dr. Viktoria H. Gessner 《ChemistryOpen》2021,10(11):1089-1094
α-Metallated ylides have revealed themselves to be versatile reagents for the introduction of ylide groups. Herein, we report the synthesis of the thiophosphinoyl and piperidyl (Pip) substituted α-metallated ylide [Ph2(Pip)P=C−P(S)Ph2]M (M=Li, Na, K) through a four-step synthetic procedure starting from diphenylmethylphosphine sulfide. Metallation of the ylide intermediate was successfully accomplished with different alkali metal bases delivering the lithium, sodium and potassium salts, the latter isolable in high yields. Structure analyses of the lithium and potassium compounds in the solid state with and without crown ether revealed different aggregates (monomer, dimer and hexamer) with the metals coordinated by the thiophosphoryl moiety and ylidic carbon atom. Although the piperidyl group does not coordinate to the metal, it significantly contributes to the stability of the yldiide by charge delocalization through negative hyperconjugation. 相似文献
993.
Gregory B. Kharas Yesenia L. Soto Emily L. Divino Mikaela Donovan Mike D. Dotson Deena Kishawi 《高分子科学杂志,A辑:纯化学与应用化学》2017,54(1):1-5
Novel trisubstituted ethylenes, ring-disubstituted propyl 2-cyano-3-phenyl-2-propenoates, RPhCH?C(CN)CO2C3H7 (where R is 2-fluoro-5-methoxy, 2-fluoro-6-methoxy, 3-fluoro-4-methoxy, 4-fluoro-3-methoxy, 5-fluoro-2-methoxy, 2-fluoro-6-methyl, 3-fluoro-2-methyl, 4-fluoro-2-methyl, 4-fluoro-3-methyl, 5-fluoro-2-methyl) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and propyl cyanoacetate and characterized by CHN elemental analysis, IR, 1H- and 13C-NMR. All the ethylenes were copolymerized with styrene (M1) in solution with radical initiation (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR, GPC, DSC, and TGA. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (1.4–3.0% wt.), which then decomposed in the 500–800°C range. 相似文献
994.
Laurell F. Kessler Ashwin Balakrishnan Nina S. Deußner-Helfmann Yunqing Li Maximilian Mantel Marius Glogger Hans-Dieter Barth Marina S. Dietz Mike Heilemann 《Angewandte Chemie (International ed. in English)》2023,62(39):e202307538
Super-resolution techniques like single-molecule localisation microscopy (SMLM) and stimulated emission depletion (STED) microscopy have been extended by the use of non-covalent, weak affinity-based transient labelling systems. DNA-based hybrid systems are a prominent example among these transient labelling systems, offering excellent opportunities for multi-target fluorescence imaging. However, these techniques suffer from higher background relative to covalently bound fluorophores, originating from unbound fluorophore-labelled single-stranded oligonucleotides. Here, we introduce short-distance self-quenching in fluorophore dimers as an efficient mechanism to reduce background fluorescence signal, while at the same time increasing the photon budget in the bound state by almost 2-fold. We characterise the optical and thermodynamic properties of fluorophore-dimer single-stranded DNA, and show super-resolution imaging applications with STED and SMLM with increased spatial resolution and reduced background. 相似文献
995.
Martin Wozniak Stefan Sander Dr. Beatrice Cula Dr. Mike Ahrens Prof. Dr. Thomas Braun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(33):e202200626
S−F-bond activation of sulfur tetrafluoride at [Rh(Cl)(tBuxanPOP)] ( 1 ; tBuxanPOP=9,9-dimethyl-4,5-bis-(di-tert-butylphosphino)-xanthene) led to the formation of the cationic complex [Rh(F)(Cl)(SF2)(tBuxanPOP)][SF5] ( 2 a ) together with trans-[Rh(Cl)(F)2(tBuxanPOP)] ( 3 ) and cis-[Rh(Cl)2(F)(tBuxanPOP)] ( 4 ) which both could also be obtained by the reaction of SF5Cl with 1 . In contrast to that, the conversion of SF4 at the methyl complex [Rh(Me)(tBuxanPOP)] ( 5 ) gave the isolable and room-temperature stable cationic λ4-trifluorosulfanyl complex [Rh(Me)(SF3)(tBuxanPOP)][SF5] ( 6 ). Treatment of 6 with the Lewis acids BF3 or AsF5 produced the dicationic difluorosulfanyl complex [Rh(Me)(SF2)(tBuxanPOP)][BF4]2 ( 8 a ) or [Rh(Me)(SF2)(tBuxanPOP)][AsF6]2 ( 8 b ), respectively. Refluorination of 8 a was possible with the use of dimethylamine giving [Rh(Me)(SF3)(tBuxanPOP)][BF4] ( 9 ). A reaction of 6 with trichloroisocyanuric acid (TClCA) gave the fluorido complex [Rh(F)(Cl)(SF2)(tBuxanPOP)][Cl] ( 2 b ) together with chloromethane and SF5Cl. 相似文献
996.
Gerald De Leeuw John S. Field Raymond J. Haines Beth McCullouch Elsie Meintjies Christiaan Monberg Kandasamy G. Moodley Gillian M. Olivier Clifford N. Sampson Nick D. Steen 《Journal of organometallic chemistry》1982,228(3):C66-C70
Bis- and, in particular, tetra-substituted ditertiary phosphine and diphosphazane derivatives of [Fe2(CO)9] and [Ru2(CO)9], readily synthesised by reaction of the appropriate bidentate ligand with [Fe2(CO)9] and [Ru3(CO)12], respectively, are very susceptible to electrophilic attack by reagents such as halogens and protons; the solid state structure of one of the products [Fe2(μ-Br)(CO)4 {μ-(PhO)2PN(Et)P(OPh)2}2]PF6 has been determined by X-ray crystallography. 相似文献
997.
We develop a new nonlinear mean field dynamo theory that couples field growth to the time evolution of the magnetic helicity and the turbulent electromotive force, E. We show that the difference between kinetic and current helicities emerges naturally as the growth driver when the time derivative of E is coupled into the theory. The solutions predict significant field growth in a kinematic phase and a saturation rate/strength that is magnetic Reynolds number dependent/independent in agreement with numerical simulations. The amplitude of early time oscillations provides a diagnostic for the closure. 相似文献
998.
We propose an atomistic model for the nucleation of aluminum oxide on the Al(111) surface derived from first principles molecular dynamics simulations. The process begins with the dissociative adsorption of O2 molecules on the metal surface, which occurs via a "hot-atom" mechanism driven by the partial filling of the sigma* antibonding molecular orbital of O2. During the subsequent hyperthermal motion, O atoms can be spontaneously incorporated underneath the topmost Al surface layer, initiating the nucleation of the oxide far below the saturation coverage of one (1 x 1) O adlayer. 相似文献
999.
Kelly C. Goss Wenying Zheng Geoffrey G. Messier Mike E. Potter 《Optics Communications》2007,271(1):30-39
This paper presents an intersymbol interference (ISI) and system noise analysis of the P-SLAM (parallel-sub-lambda) optical data storage system. Data are stored in sub-wavelength features accessed by transmitting light through the structure and collecting optical power measurements in the near-field. The non-linear ISI caused by the interactions of light between these features is characterized using finite-difference time-domain (FDTD) simulations. A system noise analysis is also presented that quantifies the effects of imperfections in fabrication and material properties. Previously, the authors proposed a detection scheme that dealt with the non-linear ISI by physically reducing it with air gaps. In this paper a signal processing method, the Viterbi algorithm, is proposed to overcome ISI. A modification is proposed to the Viterbi algorithm that is designed to deal with both the non-linear ISI and system noise. System simulations are used to show the uncoded bit error rate of the system is similar to current technologies. Conservative predictions estimate a data density of 5 Gbits/cm2 for the system which exceeds densities achievable by current optical technologies. 相似文献
1000.
A Framework for Representing Reticulate Evolution 总被引:1,自引:0,他引:1
Acyclic directed graphs (ADGs) are increasingly being viewed as more appropriate for representing certain evolutionary relationships, particularly in biology, than rooted trees. In this paper, we develop a framework for the analysis of these graphs which we call hybrid phylogenies. We are particularly interested in the problem whereby one is given a set of phylogenetic trees and wishes to determine a hybrid phylogeny that embeds each of these trees and which requires the smallest number of hybridisation events. We show that this quantity can be greatly reduced if additional species are involved, and investigate other combinatorial aspects of this and related questions.Received November 12, 2003 相似文献