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991.
Circularly Polarized Luminescence from Helically Chiral N,N,O,O‐Boron‐Chelated Dipyrromethenes 下载免费PDF全文
Rua B. Alnoman Dr. Sandra Rihn Daniel C. O'Connor Fiona A. Black Dr. Bernard Costello Dr. Paul G. Waddell Prof. William Clegg Prof. Robert D. Peacock Prof. Wouter Herrebout Dr. Julian G. Knight Dr. Michael J. Hall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):93-96
Helically chiral N,N,O,O‐boron chelated dipyrromethenes showed solution‐phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λem(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5‐ortho‐phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|glum| up to 4.7 ×10?3) and fluorescence quantum yields (ΦF up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL‐based bioimaging. 相似文献
992.
Dr. Alexander R. Nödling Dr. Katarzyna Świderek Dr. Raquel Castillo Jonathan W. Hall Dr. Antonio Angelastro Dr. Louis C. Morrill Dr. Yi Jin Dr. Yu‐Hsuan Tsai Prof. Vicent Moliner Dr. Louis Y. P. Luk 《Angewandte Chemie (International ed. in English)》2018,57(38):12478-12482
There has been growing interest in performing organocatalysis within a supramolecular system as a means of controlling reaction reactivity and stereoselectivity. Here, a protein is used as a host for iminium catalysis. A pyrrolidine moiety is covalently linked to biotin and introduced to the protein host streptavidin for organocatalytic activity. Whereas in traditional systems stereoselectivity is largely controlled by the substituents added to the organocatalyst, enantiomeric enrichment by the reported supramolecular system is completely controlled by the host. Also, the yield of the model reaction increases over 10‐fold when streptavidin is included. A 1.1 Å crystal structure of the protein–catalyst complex and molecular simulations of a key intermediate reveal the chiral scaffold surrounding the organocatalytic reaction site. This work illustrates that proteins can be an excellent supramolecular host for driving stereoselective secondary amine organocatalysis. 相似文献
993.
Dr. Shaoguang Zhang Dr. Haixia Li Dr. Aaron M. Appel Prof. Michael B. Hall Dr. R. Morris Bullock 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9493-9497
Unusual cleavage of P?C and C?H bonds of the P2N2 ligand, in heteroleptic [Ni(P2N2)(diphosphine)]2+ complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P‐tridentate coordination mode. The structures of both the heteroleptic [Ni(P2N2)(diphosphine)]2+ complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single‐crystal X‐ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P?C/C?H bond cleavage, which involves C?H bond cleavage, hydride rotation, Ni?C/P?H bond formation, and P?C bond cleavage. 相似文献
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996.
A number of force fields of the molecular mechanics type have been tested for their ability to represent as an energy minimum, the observed crystal structure for three cyclic hexapeptides, cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), and cyclo-(-D-Ala-D-Ala-Gly-Gly-Gly-Gly-). The most effective force field tested was that recently proposed by Kollman and co-workers, notwithstanding its use of “united” atoms for CH, CH2, and CH3 groups. Fields proposed by Levitt, and adaptations of that of Scheraga and co-workers, were also effective. Force fields in which hydrogens bonded to electronegative atoms were not specified explicitly were less accurate in representation. 相似文献
997.
Biogenetic-type synthesis of the Calycanthaceous alkaloids 总被引:1,自引:0,他引:1
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999.
We report the observation of p-polarized guided waves that propagate confined to the surface of a two-dimensional array of silver (Ag) nanoparticles of average particle diameter and film thickness of approximately 400 and 154 nm, respectively, and comparable interparticle spacing. We interpret resonant features in the attenuated total reflection angular spectrum as arising from the excitation of guided waves in our discontinuous samples. The excitation of these waves is a direct consequence of the interaction of the light field with the localized resonance of the conduction electrons in the individual metal nanoparticles. 相似文献
1000.
The general solution for a symmetric second-order tensorX of the equationX e(a R e b cd=0 whereR is the Riemann tensor of a space-time manifold, andX is obtained in terms of the curvature 2-form structure ofR by a straightforward geometrical technique, and agrees with that given by McIntosh and Halford using a different procedure. Two results of earlier authors are derived as simple corollaries of the general theorem. 相似文献