Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 8 de 8
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nat Rev Chem ; 8(6): 405, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38720118
3.
Chem Rev ; 122(17): 13883-13914, 2022 09 14.
Artigo em Inglês | MEDLINE | ID: mdl-35970513

RESUMO

Electron crystallography has a storied history which rivals that of its more established X-ray-enabled counterpart. Recent advances in data collection and analysis have sparked a renaissance in the field, opening a new chapter for this venerable technique. Burgeoning interest in electron crystallography has spawned innovative methods described by various interchangeable labels (3D ED, MicroED, cRED, etc.). This Review covers concepts and findings relevant to the practicing crystallographer, with an emphasis on experiments aimed at using electron diffraction to elucidate the atomic structure of three-dimensional molecular crystals.


Assuntos
Elétrons , Cristalografia por Raios X
4.
Org Lett ; 23(2): 454-458, 2021 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-33406362

RESUMO

Advances in radical-based catalytic reactions have created a demand for understanding their mechanistic underpinnings. Here, we present the isolation, structural elucidation, and theoretical analysis of a catalytically relevant charge-transfer species formed between the azidyl radical and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). The unusual bond angles and pancake bonding between these two fragments highlight the weak bonding interactions present in this complex. This X-ray structure validates computational predictions as well as mechanistic proposals of TEMPO-mediated radical azidation reactions.

5.
Methods Mol Biol ; 2215: 329-348, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33368013

RESUMO

Structural elucidation of small macromolecules such as peptides has recently been facilitated by a growing number of technological advances to existing crystallographic methods. The emergence of electron micro-diffraction (MicroED) of protein nanocrystals under cryogenic conditions has enabled the interrogation of crystalline peptide assemblies only hundreds of nanometers thick. Collection of atomic or near-atomic resolution data by these methods has permitted the ab initio determination of structures of various amyloid-forming peptides, including segments derived from prions and ice-nucleating proteins. This chapter focuses on the process of ab initio structural determination from nano-scale peptide assemblies and other similar molecules.


Assuntos
Amiloide/química , Microscopia Eletrônica de Transmissão/métodos , Peptídeos/química , Microscopia Eletrônica de Transmissão/instrumentação , Nanopartículas/química
6.
ACS Cent Sci ; 5(9): 1507-1513, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31572777

RESUMO

Here we apply microcrystal electron diffraction (MicroED) to the structural determination of transition-metal complexes. We find that the simultaneous use of 300 keV electrons, very low electron doses, and an ultrasensitive camera allows for the collection of data without cryogenic cooling of the stage. This technique reveals the first crystal structures of the classic zirconocene hydride, colloquially known as "Schwartz's reagent", a novel Pd(II) complex not amenable to solution-state NMR or X-ray crystallography, and five other paramagnetic and diamagnetic transition-metal complexes.

7.
J Am Chem Soc ; 140(39): 12511-12520, 2018 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-30160949

RESUMO

We report a mild and efficient electrochemical protocol to access a variety of vicinally C-O and C-N difunctionalized compounds from simple alkenes. Detailed mechanistic studies revealed a distinct reaction pathway from those previously reported for TEMPO-mediated reactions. In this mechanism, electrochemically generated oxoammonium ion facilitates the formation of azidyl radical via a charge-transfer complex with azide, TEMPO-N3. DFT calculations together with spectroscopic characterization provided a tentative structural assignment of this charge-transfer complex. Kinetic and kinetic isotopic effect studies revealed that reversible dissociation of TEMPO-N3 into TEMPO• and azidyl precedes the addition of these radicals across the alkene in the rate-determining step. The resulting azidooxygenated product could then be easily manipulated for further synthetic elaborations. The discovery of this new reaction pathway mediated by the TEMPO+/TEMPO• redox couple may expand the scope of aminoxyl radical chemistry in synthetic contexts.


Assuntos
Azidas/química , Óxidos N-Cíclicos/química , Técnicas de Química Sintética , Técnicas Eletroquímicas , Cinética , Espectrofotometria Ultravioleta
8.
Science ; 357(6351): 575-579, 2017 08 11.
Artigo em Inglês | MEDLINE | ID: mdl-28798126

RESUMO

Vicinal diamines are a common structural motif in bioactive natural products, therapeutic agents, and molecular catalysts, motivating the continuing development of efficient, selective, and sustainable technologies for their preparation. We report an operationally simple and environmentally friendly protocol that converts alkenes and sodium azide-both readily available feedstocks-to 1,2-diazides. Powered by electricity and catalyzed by Earth-abundant manganese, this transformation proceeds under mild conditions and exhibits exceptional substrate generality and functional group compatibility. Using standard protocols, the resultant 1,2-diazides can be smoothly reduced to vicinal diamines in a single step, with high chemoselectivity. Mechanistic studies are consistent with metal-mediated azidyl radical transfer as the predominant pathway, enabling dual carbon-nitrogen bond formation.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...