The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Helene Bertrand - One of the best experts on this subject based on the ideXlab platform.
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Understanding the g -tensors of perchlorotriphenylmethyl and Finland-type trityl radicals
Physical Chemistry Chemical Physics, 2020Co-Authors: Paul Demay-drouhard, H. Ching, Christophe Decroos, Régis Guillot, Leandro Tabares, Clotilde Policar, Helene BertrandAbstract:The 285 GHz EPR spectra of perchlorotriphenylmethyl and tetrathiatriarylmethyl radicals in frozen solution have been accurately measured. The relationship between their molecular structures and their g-tensors has been investigated with the aid of DFT calculations, revealing that the degree of spin density delocalization away from the central Methylene Carbon is an important determining factor of the g-anisotropy. In particular, the small amount of spin densities on the Cl or S heteroatoms at the 2 and 6 positions with respect to the central Carbon have the strongest influence. Furthermore, the amount of spin densities on these heteroatoms and thus the anisotropy can be modulated by the protonation (esterification) state of the carboxylate groups at the 4 position. These results provide unique insights into the g-anisotropy of persistent trityl radicals and how it can be tuned.
Bhisma K. Patel - One of the best experts on this subject based on the ideXlab platform.
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Generation of bis-acyl ketals from esters and benzyl amines under oxidative conditions.
The Journal of organic chemistry, 2015Co-Authors: Ganesh Majji, Suresh Rajamanickam, Nilufa Khatun, Sourav Kumar Santra, Bhisma K. PatelAbstract:Treatment of benzylamines with esters at an elevated temperature are expected to give amides. However, in the presence of TBAI/TBHP, esters possessing a Methylene Carbon α-to oxygen with benzylamines provide bis-esters rather than the expected amides. Benzylamines under oxidative conditions generate less nucleophilic carboxylates, which couples at the sp3 C–H bonds of esters and cyclic ethers to give bis-acyl ketals and α-acyloxy ethers, respectively.
Toshihide Okajima - One of the best experts on this subject based on the ideXlab platform.
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The Radical S-Adenosyl-L-methionine Enzyme QhpD Catalyzes Sequential Formation of Intra-protein Sulfur-to-Methylene Carbon Thioether Bonds.
The Journal of biological chemistry, 2015Co-Authors: Tadashi Nakai, Hiroto Ito, Kazuo Kobayashi, Yasuhiro Takahashi, Hiroshi Hori, Motonari Tsubaki, Katsuyuki Tanizawa, Toshihide OkajimaAbstract:The bacterial enzyme designated QhpD belongs to the radical S-adenosyl-l-methionine (SAM) superfamily of enzymes and participates in the post-translational processing of quinohemoprotein amine dehydrogenase. QhpD is essential for the formation of intra-protein thioether bonds within the small subunit (maturated QhpC) of quinohemoprotein amine dehydrogenase. We overproduced QhpD from Paracoccus denitrificans as a stable complex with its substrate QhpC, carrying the 28-residue leader peptide that is essential for the complex formation. Absorption and electron paramagnetic resonance spectra together with the analyses of iron and sulfur contents suggested the presence of multiple (likely three) [4Fe-4S] clusters in the purified and reconstituted QhpD. In the presence of a reducing agent (sodium dithionite), QhpD catalyzed the multiple-turnover reaction of reductive cleavage of SAM into methionine and 5′-deoxyadenosine and also the single-turnover reaction of intra-protein sulfur-to-Methylene Carbon thioether bond formation in QhpC bound to QhpD, producing a multiknotted structure of the polypeptide chain. Homology modeling and mutagenic analysis revealed several conserved residues indispensable for both in vivo and in vitro activities of QhpD. Our findings uncover another challenging reaction catalyzed by a radical SAM enzyme acting on a ribosomally translated protein substrate.
Motomu Kanai - One of the best experts on this subject based on the ideXlab platform.
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directing activator assisted regio and oxidation state selective aerobic oxidation of secondary c sp3 h bonds in aliphatic alcohols
Organic and Biomolecular Chemistry, 2016Co-Authors: Jizhi Ni, Kounosuke Oisaki, Jun Ozawa, Motomu KanaiAbstract:The regioselective conversion of an unactivated C(sp3)–H bond of a Methylene Carbon (CH2) into a C–O single bond is an attractive reaction in organic synthesis. Herein, we present a strategy for a regio- and oxidation state-selective aerobic C–H oxidation based on an N-hydroxyamide-derived directing activator (DA), which is attached to a hydroxy group in alcohol substrates. The DA reacts with NOx species generated in situ from NaNO2, a Bronsted acid, and aerobic oxygen, and effectively generates an amidoxyl radical from the N-hydroxy moiety of the DA. Then, the amidoxyl radical promotes site-selective intramolecular C–H abstraction from Methylenes with γ- (or δ-) selectivity. The thus-generated Methylene radicals are trapped by molecular oxygen and NO. This process results in the predominant formation of nitrate esters as products, which suppresses undesired overoxidation. The products can be easily converted into alcohols after hydrogenolysis.
Paul Demay-drouhard - One of the best experts on this subject based on the ideXlab platform.
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Understanding the g -tensors of perchlorotriphenylmethyl and Finland-type trityl radicals
Physical Chemistry Chemical Physics, 2020Co-Authors: Paul Demay-drouhard, H. Ching, Christophe Decroos, Régis Guillot, Leandro Tabares, Clotilde Policar, Helene BertrandAbstract:The 285 GHz EPR spectra of perchlorotriphenylmethyl and tetrathiatriarylmethyl radicals in frozen solution have been accurately measured. The relationship between their molecular structures and their g-tensors has been investigated with the aid of DFT calculations, revealing that the degree of spin density delocalization away from the central Methylene Carbon is an important determining factor of the g-anisotropy. In particular, the small amount of spin densities on the Cl or S heteroatoms at the 2 and 6 positions with respect to the central Carbon have the strongest influence. Furthermore, the amount of spin densities on these heteroatoms and thus the anisotropy can be modulated by the protonation (esterification) state of the carboxylate groups at the 4 position. These results provide unique insights into the g-anisotropy of persistent trityl radicals and how it can be tuned.