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排序方式: 共有635条查询结果,搜索用时 31 毫秒
81.
Debasish Manna Basudeb Maji Soumyashree A. Gangopadhyay Kurt J. Cox Qingxuan Zhou Benjamin K. Law Ralph Mazitschek Amit Choudhary 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(19):6351-6355
Several genome engineering applications of CRISPR‐Cas9, an RNA‐guided DNA endonuclease, require precision control of Cas9 activity over dosage, timing, and targeted site in an organism. While some control of Cas9 activity over dose and time have been achieved using small molecules, and spatial control using light, no singular system with control over all the three attributes exists. Furthermore, the reported small‐molecule systems lack wide dynamic range, have background activity in the absence of the small‐molecule controller, and are not biologically inert, while the optogenetic systems require prolonged exposure to high‐intensity light. We previously reported a small‐molecule‐controlled Cas9 system with some dosage and temporal control. By photocaging this Cas9 activator to render it biologically inert and photoactivatable, and employing next‐generation protein engineering approaches, we have built a system with a wide dynamic range, low background, and fast photoactivation using a low‐intensity light while rendering the small‐molecule activator biologically inert. We anticipate these precision controls will propel the development of practical applications of Cas9. 相似文献
82.
We quantitatively investigated, by time-resolved photoluminescence (PL) spectroscopy, the shell thickness dependence of exciton trapping and its effects on the PL quantum yield (QY) in colloidal CdSe/CdS/ZnS core/shell quantum rods. The defects passivation, due to a thin shell (0.6 monolayer), leads to a 2 times reduction of the trapping from both emitting and high-energy excited states, thus explaining the observed 4.3 times increase of the PL QY. Moreover, the QY decrease in the thick shell (1.3 monolayers) sample is fully explained in terms of increased trapping from the emitting states, which is ascribed to new defects caused by the strain relaxation at the core-shell interface. 相似文献
83.
Let Cm:y2 = x3 ? m2x + p2q2 be a family of elliptic curves over ?, where m is a positive integer and p, q are distinct odd primes. We study the torsion part and the rank of Cm(?). More specifically, we prove that the torsion subgroup of Cm(?) is trivial and the ?-rank of this family is at least 2, whenever m ? 0 (mod 3), m ? 0 (mod 4) and m ≡ 2 (mod 64) with neither p nor q dividing m.
相似文献84.
Quentin Dherbassy Srimanta Manna Fabien J. T. Talbot Watcharapon Prasitwatcharakorn Gregory J. P. Perry David J. Procter 《Chemical science》2020,11(42):11380
The copper-catalyzed functionalization of enyne derivatives has recently emerged as a powerful approach in contemporary synthesis. Enynes are versatile and readily accessible substrates that can undergo a variety of reactions to yield densely functionalized, enantioenriched products. In this perspective, we review copper-catalyzed transformations of enynes, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. Particular attention is given to the regiodivergent functionalization of 1,3-enynes, and the current mechanistic understanding of such processes.The copper-catalyzed functionalization of enynes is a powerful approach to yield densely functionalized products. This review covers various transformations, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. 相似文献
85.
Dr. Sampa Maiti Dr. Saikat Manna Nicholas Banahene Lucynda Pham Zhijie Liang Jun Wang Yi Xu Reuben Bettinger John Zientko Prof. Dr. Aaron P. Esser-Kahn Prof. Dr. Wenjun Du 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(43):19105-19109
Efforts to synthesize degradable polymers from renewable resources are deterred by technical and economic challenges; especially, the conversion of natural building blocks into polymerizable monomers is inefficient, requiring multistep synthesis and chromatographic purification. Herein we report a chemoenzymatic process to address these challenges. An enzymatic reaction system was designed that allows for regioselective functional group transformation, efficiently converting glucose into a polymerizable monomer in quantitative yield, thus removing the need for chromatographic purification. With this key success, we further designed a continuous, three-step process, which enabled the synthesis of a sugar polymer, sugar poly(orthoester), directly from glucose in high yield (73 % from glucose). This work may provide a proof-of-concept in developing technically and economically viable approaches to address the many issues associated with current petroleum-based polymers. 相似文献
86.
87.
Tapan Ghosh Srikanth Birudula Kalyan Jyoti Kalita Dr. Ratheesh K. Vijayaraghavan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10501-10509
Control over the molecular packing in the solid state is of utmost importance in regulating the bulk optical properties of organic semiconductors. The electronic coupling between the molecules makes it possible to improve the properties of the bulk materials. This work reports an example of control over the selective formation of polymorphic single crystals of donor–acceptor-type small-molecule compound 25TR by 1) kinetic or 2) thermodynamic course of crystallisation to yield slipped stack (S) and cofacial (C) dimers in the single crystals. The distinct optical characteristics of the C-dimer and S-dimer are summarised. Both forms show significant excitonic interactions in the solid state, and the S-dimeric form has strong yellowish orange fluorescence, whereas the C-dimeric form is non-fluorescent in the crystalline state. DFT calculations and differential scanning calorimetric experiments revealed that the C-dimer polymorph is the thermodynamically stable form with a free energy offset of 0.43 eV in comparison with the S-dimer. Interestingly, the thermodynamically driven non-fluorescent single crystal was found to be convertible to its fluorescent form irreversibly by thermal trigger. The charge-carrier-transport characteristics of these two polymorphs were computed by using the Marcus–Hush formalism. The computations of the charge-carrier-transport behaviour revealed that the S-dimer ( 25TR(R) ) is ambipolar, whereas the C-dimer ( 25TR(Y) ) is predominantly n-type. 相似文献
88.
Total chemical and semisynthetic approaches for the preparation of ubiquitinated proteins and their applications 总被引:1,自引:0,他引:1
Protein ubiquitination is an important post-translational modification (PTM) in eukaryotic organisms that regulates a variety of cellular processes, such as protein degradation, signal transduction, apoptosis, and DNA damage tolerance. To decipher mechanistically the diverse biological functions of ubiquitination, homogeneous ubiquitinated proteins are greatly needed. Although direct isolation from cell source and in vitro enzymatic methods can be used to produce such proteins, these methods often suffer from problems of low yield or heterogeneous products. Comparably, total chemical and semisynthetic approaches offer good alternatives to produce the ubiquitinated proteins with high purity and selectivity. This review summarizes the recent developments of protein ubiquitination strategies and the use of the synthesized proteins to help garner structural and functional insight into the inner workings of the ubiquitin system. 相似文献
89.
Bikash Debnath Waikhom Somraj Singh Manik Das Sanchari Goswami Mahesh Kumar Singh Debasish Maiti Kuntal Manna 《Materials Today Chemistry》2018
Alkaloids are plant secondary metabolite. They are well known nitrogen-containing natural bioactive compounds. Cutting edge research is going on alkaloids to unravel novel therapeutic approaches. Literature reveals that alkaloids contribute multiple biological activities and some alkaloids transform into active metabolites too. In this review, we have focused on marketed and experimental alkaloids. We have summarized sources and biological activities of reported alkaloids in past decades. 相似文献
90.
o-Methyl-substituted Me-IBX is the first modified analog of IBX that oxidizes alcohols in common organic solvents at room temperature, due to a composite of two factors, that is, low solubility and hypervalent twisting-promoted rate enhancement. Furthermore, the reagent is efficient for selective oxidation of sulfides to sulfoxides, a transformation that otherwise occurs only sluggishly with standard IBX. The facile synthetic accessibility and its mild as well as non-hazardous nature render Me-IBX a stable equivalent of Dess-Martin periodinane reagent in organic oxidations. 相似文献