排序方式: 共有59条查询结果,搜索用时 19 毫秒
41.
Selina C. Wang 《Journal of organometallic chemistry》2006,691(21):4386-4392
This brief review describes experimental and theoretical data relevant to the mechanisms of transition metal promoted vinylcyclopropane-cyclopentene rearrangements. In particular, reactions utilizing Pd(0), Rh(I), and Ni(0) are highlighted and compared to analogous reactions not involving transition metals. 相似文献
42.
Selina Yo-Ping Chang Justie Su-Tzu Juan Cheng-Kuan Lin Jimmy J. M. Tan Lih-Hsing Hsu 《Annals of Combinatorics》2009,13(1):27-52
A graph G is hamiltonian connected if there exists a hamiltonian path joining any two distinct nodes of G. Two hamiltonian paths and of G from u to v are independent if u = u
1 = v
1, v = u
v(G)
= v
v(G)
, and u
i
≠ v
i
for every 1 < i < v(G). A set of hamiltonian paths, {P
1, P
2, . . . , P
k
}, of G from u to v are mutually independent if any two different hamiltonian paths are independent from u to v. A graph is k mutually independent hamiltonian connected if for any two distinct nodes u and v, there are k mutually independent hamiltonian paths from u to v. The mutually independent hamiltonian connectivity of a graph G, IHP(G), is the maximum integer k such that G is k mutually independent hamiltonian connected. Let n and k be any two distinct positive integers with n–k ≥ 2. We use S
n,k
to denote the (n, k)-star graph. In this paper, we prove that IHP(S
n,k
) = n–2 except for S
4,2 such that IHP(S
4,2) = 1.
相似文献
43.
To utilize housane-derived cation radicals as intermediates for the synthesis of the bicyclo (n.3.0) framework of natural products, a highly regioselective [1,2] shift of carbon to either a radical or an electron-deficient site is required. Herein we describe how this has been accomplished, provide a set of guidelines to assess housane oxidizability prior to its synthesis, and describe a synthesis of housane 18 that capitalizes upon the facility of [1,5] hydrogen shifts in substituted cyclopentadienes. The catalytic electrochemically mediated oxidation of 18 leads to a cation radical that engages in a rearrangement leading to the (4.3.0) adduct 23. The appearance of a catalytic current in the cyclic voltammogram of a solution containing the tris(aryl)amine and housane 18 is an excellent indicator that the amminium cation radical 14*+ is able to oxidize the housane and return the mediator to the original redox couple. DFT calculations show electron density on both the aryl and strained sigma framework in the HOMO of housane 18. From the spin density and electrostatic potential map for the cation radical, a picture where the spin resides on the side that is distal to the substituent emerges, while the hole is proximal to it. Both experiment and theory show that the rearrangement is best characterized as a [1,2] carbon shift toward an electron-deficient site and that migration toward the substituent-bearing carbon is much preferred over the alternative pathway. 相似文献
44.
A new means-discovered through quantum chemical studies (B3LYP/6-31G(d))-of selectively stabilizing the delocalized forms of unsubstituted semibullvalene and barbaralane is described. Calculations indicate that complexation of delocalized semibullvalene and barbaralane Cope rearrangement transition structures by halogen-containing molecules (homo- and heteronuclear diatomics and Lewis acids) can reduce the barrier significantly, in many cases causing it to disappear entirely. 相似文献
45.
Anastasia A. Selina Sergey S. Karlov Ekaterina V. Gauchenova Andrei V. Churakov Lyudmila G. Kuz'mina Judith A. K. Howard Jörg Lorberth Galina S. Zaitseva 《Heteroatom Chemistry》2004,15(1):43-56
Reactions of element-substituted alkynes R3MCCPh (R3M = Me3Si, Et3Si, Ph3Si, Et3Ge, n-Bu3Sn, N(CH2CH2O)3Si, N(CH2CH2O)3Ge, N(CH2-CHMeO)3Ge, and N(CH2CH2O)2(CH2CHPhO)Ge) with bromine, tetra-n-butylammonium tribromide (TBAT), and N-bromosuccinimide (NBS)/DMSO were investigated. The Z,E-ratio of isomeric dibromoalkenes formed in bromination reaction with Br2 and TBAT are discussed. The crystal structures of N(CH2CH2O)3SiCCPh and N(CH2CHMeO)3GeX (X = C CPh, C(Br)C(Br)Ph, C(Br2)C(O)Ph), and Ph3SiC(Br)C(Br)Ph are reported. © 2003 Wiley Periodicals, Inc. 15:43–56, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10211 相似文献
46.
Ronghe Lin Davide Albani Edvin Fako Selina K. Kaiser Olga V. Safonova Núria Lpez Javier Prez‐Ramírez 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(2):514-519
Single‐atom heterogeneous catalysts with well‐defined architectures are promising for deriving structure–performance relationships, but the challenge lies in finely tuning the structural and electronic properties of the metal. To tackle this point, a new approach based on the surface diffusion of gold atoms on different cavities of N‐doped carbon is presented. By controlling the activation temperature, the coordination neighbors (Cl, O, N) and the oxidation state of the metal can be tailored. Semi‐hydrogenation of various alkynes on the single‐atom gold catalysts displays substrate‐dependent catalytic responses; structure insensitive for alkynols with γ‐OH and unfunctionalized alkynes, and sensitive for alkynols with α‐OH. Density functional theory links the sensitivity for alkynols to the strong interaction between the substrate and specific gold‐cavity ensembles, mimicking a molecular recognition pattern that allows to identify the cavity site and to enhance the catalytic activity. 相似文献
47.
48.
49.
Christoph Dorn Selina Schießer Beatrix Wulkersdorfer Florian Hitzenbichler Martin G. Kees Markus Zeitlinger 《Biomedical chromatography : BMC》2020,34(6):e4820
Pharmacokinetic/pharmacodynamic indices of anti-infective drugs should be referenced to free drug concentrations. In the present study, clindamycin, flucloxacillin and tedizolid have been determined in human plasma by HPLC–UV. The drugs were separated isocratically within 3–6 min on a C18 column using mixtures of phosphate buffer–acetonitrile of pH 7.1–7.2. Sample treatment for the determination of total drug concentrations in plasma included extraction/back-extraction (clindamycin) or protein precipitation (flucloxacillin, tedizolid). The free drug concentrations were determined after ultrafiltration. An ultrafiltration device with a membrane consisting of regenerated cellulose proved to be suitable for all drugs. Maintaining a physiological pH was crucial for clindamycin, whereas maintaining body temperature was essential for tedizolid. The methods were applied to the analysis of total and free drug concentrations in clinical samples and were sufficiently sensitive for pharmacokinetic studies and therapeutic drug monitoring. 相似文献
50.
Hafeesudeen Sahabudeen Haoyuan Qi Marco Ballabio Miroslav Poloij Selina Olthof Rishi Shivhare Yu Jing SangWook Park Kejun Liu Tao Zhang Ji Ma Bernd Rellinghaus Stefan Mannsfeld Thomas Heine Mischa Bonn Enrique Cnovas Zhikun Zheng Ute Kaiser Renhao Dong Xinliang Feng 《Angewandte Chemie (International ed. in English)》2020,59(15):6028-6036
Single‐layer and multi‐layer 2D polyimine films have been achieved through interfacial synthesis methods. However, it remains a great challenge to achieve the maximum degree of crystallinity in the 2D polyimines, which largely limits the long‐range transport properties. Here we employ a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) method for the successful preparation of porphyrin and triazine containing polyimine‐based 2D polymer (PI‐2DP) films with square and hexagonal lattices, respectively. The synthetic PI‐2DP films are featured with polycrystalline multilayers with tunable thickness from 6 to 200 nm and large crystalline domains (100–150 nm in size). Intrigued by high crystallinity and the presence of electroactive porphyrin moieties, the optoelectronic properties of PI‐2DP are investigated by time‐resolved terahertz spectroscopy. Typically, the porphyrin‐based PI‐2DP 1 film exhibits a p‐type semiconductor behavior with a band gap of 1.38 eV and hole mobility as high as 0.01 cm2 V?1 s?1, superior to the previously reported polyimine based materials. 相似文献