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51.
The systematic integration of the small 2π- and 4π-electron systems cyclopropenylium ion, cyclopropenone, oxo-cyclobutenylium ion, and cyclobutadiene into phane chemistry was initiated only a few years ago. [n2]Cyclopropenylophanes, [n2]cyclopropenonophanes, metal-capped [n4]cyclobutadienosuperphanes, and other new families of double-decker phane species became available from cycloalkydiynes through special methods of double [2+1]cycloaddition with carbenes and metal complex induced dimerization by double [2+2]cycloaddition. Phane-specific structural features were elucidated by X-ray structural analyses. Cyclic voltammetry and PE spectroscopy as well as MO calculations reealed considerable interactions between closely spaced π-electron systems. Decapping cyclobutadienosuperphanes formally extended the synthetic principle to threefold [2+2]cycloadditions resulting in [n4]-bridged tricyclo-[4.2.0.03, 5]octa-3,7-dienes, which represent a new type of cage compounds. Moreover, completion to fourfold [2+2]addition was achieved with the photoinduced transformation of [34]bridged tricyclo[4.2.0.03, 5]octa-3,7-diene into propella[34]cubane. 相似文献
52.
53.
总结了近年来用于不对称催化羟醛缩合反应的各种有机小分子催化剂, 简要阐述了每种类型的催化剂的催化机理以及它们的优缺点, 同时对有机小分子催化反应的发展进行了展望. 相似文献
54.
M. Nierlich L.L.B. F. Boue L.L.B. A. Lapp L.L.B. R. Oberthür I.L.L. 《Colloid and polymer science》1985,263(12):955-964
We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS
1(q) and the structure factorS
2(q). Two lengths are deduced from these two factors: the persistence lengthb
t which characterizes the electrostatic interactions along the chain by a fitting ofS
1(q) with calculation of the scattering function for a wormlike chain, and fromS
2(q),q
m
–1
which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b
t C
p
–1/2
,q
m
–1
C
p
–1/2
) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS. 相似文献
55.
V. Sankara Sastry S. Kalavathy B. K. Guha R. Baskaran U. De J. Janaki 《Phase Transitions》2013,86(1-2):97-105
Electrical resistance measurements at low temperatures and high quasihydrostatic pressures on superconducting and non-superconducting varieties of Y0.8Ba1.2Cu2O5 (obtained by annealing in oxygen and air respectively) show striking anomalies in the vicinity of 100K and 40K. Arguments are presented to show that these anomalies as also the occurrence of T 's in the oxide superconductors either in the vicinity of 100K or of 40K are connected with their layered structure containing planes of Cu-O otahedral complexes. 相似文献
56.
Shuyang Liu Miao Tian Dr. Xiubin Bu Dr. Hua Tian Prof. Xiaobo Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(28):7738-7744
Photoactive two-dimensional covalent organic frameworks (2D-COFs) have become promising heterogenous photocatalysts in visible-light-driven organic transformations. Herein, a visible-light-driven selective aerobic oxidation of various small organic molecules by using 2D-COFs as the photocatalyst was developed. In this protocol, due to the remarkable photocatalytic capability of hydrazone-based 2D-COF-1 on molecular oxygen activation, a wide range of amides, quinolones, heterocyclic compounds, and sulfoxides were obtained with high efficiency and excellent functional group tolerance under very mild reaction conditions. Furthermore, benefiting from the inherent advantage of heterogenous photocatalysis, prominent sustainability and easy photocatalyst recyclability, a drug molecule (modafinil) and an oxidized mustard gas simulant (2-chloroethyl ethyl sulfoxide) were selectively and easily obtained in scale-up reactions. Mechanistic investigations were conducted using radical quenching experiments and in situ ESR spectroscopy, all corroborating the proposed role of 2D-COF-1 in photocatalytic cycle. 相似文献
57.
58.
W.J. Walker 《Applicable analysis》2013,92(2):121-131
In this paper we replace uniformly convex (or reflexive and normal structure) as required by Browder and Kirk, by uniformly normal structure to obtain a fixed point theorem for non-expansive self mappings. Examples are given to show that spaces with uniformly normal structure are not all uniformly convex and spaces with normal structure do not all have uniformly normal structure. AMS (MOS) subject classification (1970) Primary 47410. 相似文献
59.
A milestone in probability theory is the law of the iterated logarithm (LIL), proved by Khinchin and independently by Kolmogorov in the 1920s, which asserts that for iid random variables with mean 0 and variance 1 In this paper we prove that LIL holds for various functionals of random graphs and hypergraphs models. We first prove LIL for the number of copies of a fixed subgraph H. Two harder results concern the number of global objects: perfect matchings and Hamiltonian cycles. The main new ingredient in these results is a large deviation bound, which may be of independent interest. For random k‐uniform hypergraphs, we obtain the Central Limit Theorem and LIL for the number of Hamilton cycles. 相似文献
60.
Tianming Dai Weifan Jiang Zizheng Guo Zhenyu Wang Mingping Huang Guorui Zhong Chuxin Liang Xuzhe Pei Renke Dai 《Biomedical chromatography : BMC》2019,33(9)
Withaferin A (WA) is one of the major bioactive steroidal lactones with extensive pharmacological activities present in the plant Withania somnifera. The absolute oral bioavailability of WA remains unknown and human‐related in vitro data are not available. Therefore, in the present study, the absolute oral bioavailability of WA in male rats and the in vitro screening of absorption factors by Q‐trap and LC–MS/MS analysis were conducted to explore possible clinical properties of WA. The developed and validated analytical methods were successfully applied to the pharmacokinetic studies and in vitro measurement of WA. The oral bioavailability was determined to be 32.4 ± 4.8% based on intravenous (5 mg/kg) and oral (10 mg/kg) administrations of WA in male rats. The in vitro results showed that WA could be easily transported across Caco‐2 cells and WA did not show as a substrate for P‐glycoprotein. Moreover, the stability of WA was similar between male rat and human in simulated gastric fluid (stable), in intestinal microflora solution (slow decrease) and in liver microsomes (rapid depletion, with a half‐life of 5.6 min). As such, the first‐pass metabolism of WA was further verified by rat intestine‐liver in situ perfusion, revealing that WA rapidly decreased and 27.1% remained within 1 h, while the content of three major metabolites (M1, M4, M5) identified by Q‐trap increased. This perfusion result is consistent with the oral bioavailability results in vivo. The first‐pass metabolism of WA might be the main barrier in achieving good oral bioavailability in male rats and it is predicted to be similar in humans. This study may hold clinical significance. 相似文献