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191.
具反馈控制和无穷时滞单种群模型周期正解 总被引:15,自引:0,他引:15
利用重合度理论和Liapunov泛函方法讨论了具反馈控制的无穷时滞单种群模型周期正解的存在性和全局吸引性,得到了周期正解存在和全局吸引的充分条件,推广并改进了某些已知相关结果。 相似文献
192.
Presence or absence of electron-accepting dye chromophores is the key function for ON/OFF switching of fluorescence from the dihydrodibenzo[c,g]phenanthrene skeleton in 22+/3. The helical fluorophore in 22+ could be generated stereoselectively upon electrolysis of binaphthylic donor 1 through intramolecular chirality transmission. Huge chiroptical signals are easily detected by circular dichroism (CD) and fluorescence-detected CD (FDCD) techniques to realize novel four-way-output response. 相似文献
193.
Vladimir A. Alfonsov Alexander A. Bredikhin Zemfira A. Bredikhina Rimma M. Eliseenkova Olga N. Kataeva Igor A. Litvinov Michael A. Pudovik 《Structural chemistry》2008,19(6):873-878
The first three examples of the cocrystallization of covalent diastereomers of phosphorus compounds containing different chiral
elements (centres of chirality on carbon and phosphorus, and an axis of chirality) are reported. The phenomenon can be attributed
to the complementarity of the molecular shapes of the diastereomers. The X-ray data of all the crystals exhibit centrosymmetric
statistics regardless of their very different natures.
Dedicated to the memory of Professor Viktor Naumov (1932–2007). 相似文献
194.
Dr. Guogang Liu Yujian Liu Dr. Chengxi Zhao Prof. Yan Li Prof. Zhaohui Wang Prof. He Tian 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202214769
Despite the great progress in research on molecular carbons containing multiple helicenes around one core, realizing the stereoselectivity of carbons containing multiple helicenes around more cores is still a great challenge. Herein, molecular carbon C204 featuring 12-fold [5]helicenes around four cores was successfully constructed by using nine perylene diimide (PDI) units, and exhibits good solubility and stability. Despite 256 possible stereoisomers caused by the 12-fold [5]helicenes, we only obtained one pair of enantiomers with D3 symmetry. There are four possible pairs of enantiomers with D3 symmetry, namely 7A, 7B, 7C and 7D. Theoretical and experimental results verify that the obtained structure belongs to 7C, which has the lowest energy. The enantiomers can also be separated by chiral HPLC. These results suggest that choosing PDIs as building blocks can not only improve the solubility and stability but also realize the stereoselectivity and chirality of molecular carbons. 相似文献
195.
Baohua Cai Yuan Cui Jian Zhou Dr. Yong-Bin Wang Prof. Dr. Limin Yang Prof. Dr. Bin Tan Prof. Dr. Jun Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202215820
A Cu/CPA co-catalytic system has been developed for achieving the direct hydrophosphinylation of alkynes with phosphine oxides in delivering novel axially chiral phosphorus-containing alkenes in high yields and excellent enantioselectivities (up to 99 % yield and 99 % ee). DFT calculations were performed to elucidate the reaction pathway and the origin of enantiocontrol. This streamlined and modular methodology establishes a new platform for the design and application of new axially chiral styrene-phosphine ligands. 相似文献
196.
Dr. Weichao Xue Dr. Kai Wu Nianfeng Ouyang Dr. Thierry Brotin Prof. Dr. Jonathan R. Nitschke 《Angewandte Chemie (International ed. in English)》2023,62(18):e202301319
Self-assembly of a flexible tritopic aniline and 3-substituted 2-formylpyridine subcomponents around iron(II) templates gave rise to a low-spin FeII4L4 capsule, whereas a high-spin FeII3L2 sandwich species formed when a sterically hindered 6-methyl-2-formylpyridine was used. The FeII4L4 cage adopted a new structure type with S4 symmetry, having two mer-Δ and two mer-Ʌ metal vertices, as confirmed by NMR and X-ray crystallographic analysis. The flexibility of the face-capping ligand endows the resulting FeII4L4 framework with conformational plasticity, enabling it to adapt structurally from S4 to T or C3 symmetry upon guest binding. The cage also displayed negative allosteric cooperativity in simultaneously binding different guests within its cavity and at the apertures between its faces. 相似文献
197.
Yong Zuo Xiaoning Liu Enguang Fu Shaodong Zhang 《Angewandte Chemie (International ed. in English)》2023,62(14):e202217225
Without chiral induction the emergence of homochirality from achiral molecules is rather serendipitous, as the rationale is somewhat ambiguous. We herein provide a plausible solution. From achiral precursors are formed a pair of interconverting cage conformers that exhibit a C3-axis as the only symmetry element. When their interconversion is impeded with intramolecular H-bonding, each conformer self-sorts into a homochiral crystal, which is driven by a helical network of multivalent intermolecular interactions during the self-assembly of homochiral cage conformers. As no chiral induction is involved throughout, we believe our study could enlighten the rational design for the emergence of homochirality with several criteria: 1) formation of a molecule without inversion center or mirror plane; 2) suppression of the enantiomeric interconversion, and introduction of multivalent interactions along the helical trajectory of screw symmetry within the resulting superstructure. 相似文献
198.
Zongshang Li Dr. Ke Xiao Dr. Qingyun Wan Rui Tang Dr. Kam-Hung Low Prof. Xiaodong Cui Prof. Chi-Ming Che 《Angewandte Chemie (International ed. in English)》2023,62(10):e202381061
Introduction of multiple kinetic aggregation states (Aggs) into the self-assembly pathway could bring complexity and flexibility to the self-assemblies, which is difficult to realize due to the delicate equilibria established among different Aggs bonded by weak noncovalent interactions. Here, we describe a series of chiral and achiral d10 AuI bis(N-heterocyclic carbene, NHC) complexes, and the achiral complex could undergo self-assembly with multiple kinetic Aggs. Generation of multiple kinetic Aggs was realized by applying chiral or achiral seeds exhibiting large differences in elongation temperatures for their respective cooperative self-assembly processes. We further showed that the chiral AuI self-assemblies having non-centrosymmetric packing forms exhibit nonlinear optical response of second harmonic generation (SHG), while the SHG signal is absent in the achiral analogue. The crystalline achiral AuI self-assemblies could function as optical waveguides with strong emission polarization. 相似文献
199.
Ting Zhao Jigao Yi Chunhong Liu Xiaotong Liang Yanling Shen Lingling Wei Xiangyu Xie Prof. Dr. Wanhua Wu Prof. Dr. Cheng Yang 《Angewandte Chemie (International ed. in English)》2023,62(22):e202302232
Perylene diimide tethered pillar[5]arene derivatives form aggregates in non-polar organic solvents, and the complexation of cationic amino acid ethyl ester (cAA-OEt) with the aggregates induce a central-to-planar-to-helical chirality transfer, leading to intensive circular dichroism (CD) signals having dissymmetric factors (gabs) of up to 3.67×10−2. The hierarchical chiral induction exhibited an intriguing threshold dose effect, namely, the chiral induction does not occur in the low concentration range of cAA-OEt but is triggered when cAA-OEt exceeds a threshold concentration. The inhibited interconversion between the Rp and Sp conformers of pillar[5]arene, which is further restricted in the aggregation, plays a crucial role in the threshold effect. When adding enantiopure cAA-OEt first to the threshold concentration and then adding an equal amount of the antipodal cAA-OEt to give cAA-OEt in racemic form, CD spectra having the same sign as the CD induced by first adding pure cAA-OEt were induced, thus showing an unprecedented “first come, first served” effect. 相似文献
200.
Chao Ren Wenjing Sun Dr. Tonghan Zhao Dr. Chengxi Li Chengyu Jiang Prof. Pengfei Duan 《Angewandte Chemie (International ed. in English)》2023,62(50):e202315136
The helical twisting tendency of liquid crystals (LCs) is generally governed by the inherent configuration of the chiral emitter. Here, we introduce the multistage inversion of supramolecular chirality as well as circularly polarized luminescence (CPL) by manipulating the ratio of single enantiomeric emitters (R-PCP) to LC monomers (5CB). Increasing the content of R-PCP from 1 wt % to 3 wt % inverted the helix of LCs from left-handed to right-handed, accompanying a CPL sign changed from positive to negative. The biaxiality of chiral emitters, as well as the steric effect of chiral-chiral and chiral-achiral interaction, were identified as the reasons for helical sense inversion. Due to the strong helical twisting power, 4 wt % R-PCP drove the photonic band gap (PBG) of chiral LCs to match up with their emission range, leading to an inversion of the CPL again with a high dissymmetry factor (≈1.2). Directly adjusting the PBG using chiral emitters is seldom achieved in cholesteric LCs. On this basis, an achiral sensitizer PtTPBP was assembled into the helical superstructure. The generation of triplet-triplet annihilation-induced upconverted CPL from R-PCP and the downshifting CPL from PtTPBP with opposite rotation was achieved in a single chiral LC system by tuning the position of the PBG. 相似文献