Peptide cation-radicals. A computational study of the competition between peptide N?C? bond cleavage and loss of the side chain in the [GlyPhe-NH2 + 2H]+? cation-radical

2003 ◽  
Vol 38 (10) ◽  
pp. 1093-1104 ◽  
Author(s):  
Franti?ek Ture?ek ◽  
Erik A. Syrstad ◽  
Jennifer L. Seymour ◽  
Xiaohong Chen ◽  
Chunxiang Yao
Keyword(s):  
Computational Study ◽  
Bond Cleavage ◽  
Cation Radical ◽  
Side Chain ◽  
Cation Radicals

scholarly journals Computational study on the mechanism of metal-free photochemical borylation of aryl halides

2021 ◽  
Author(s):  
Chenhao Tu ◽  
Nana Ma ◽  
Qingli Xu ◽  
Wenyue Guo ◽  
Lanxin Zhou ◽  
...  
Keyword(s):  
Density Functional ◽  
Uv Light ◽  
Computational Study ◽  
Halogen Bond ◽  
Bond Cleavage ◽  
Aryl Halides ◽  
Homolytic Cleavage ◽  
Functional Theory ◽  
Aryl Radicals

C-radical borylation is an significant approach for the construction of carbon−boron bond. Photochemical borylation of aryl halides successfully applied this strategy. However, precise mechanisms, such as the generation of aryl radicals and the role of base additive(TMDAM) and water, remain controversy in these reactions. In this study, photochemical borylation of aryl halides has been researched by density functional theory (DFT) calculations. Indeed, the homolytic cleavage of the C−X bond under irradiation with UV-light is a key step for generation of aryl radicals. Nevertheless, the generation of aryl radicals may also undergo the process of single electron transfer and the heterolytic carbon-halogen bond cleavage sequence, and the latter is favorable during the reaction.

scholarly journals Methyl-Eliminierung aus dem metastabilen Homoadamantan-Radikalkation / Methyl Loss from Metastable Homoadamantane Cation Radical

1980 ◽  
Vol 35 (2) ◽  
pp. 207-211 ◽  
Author(s):  
Helmut Schwarz ◽  
Chrysostomos Wesdemiotis ◽  
Thomas Weiske ◽  
Helmut Schwarz ◽  
Chrysostomos Wesdemiotis ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Cation Radical ◽  
Model Calculations ◽  
Direct Ionization ◽  
Cation Radicals

Abstract It is demonstrated that methyl loss from ionized homoadamantane (1) yields exclusively the 1-adamantyl cation (4); there is no experimental evidence for the formation of the secondary adamantyl cation (5). From both model calculations and the investigation of [4-13C]-homoadamantane (1a) and 1(13C-methyl)adamantane (2a) it is concluded, that 24% of the metastable homoadamantane cation radicals dissociate after one isomerization (1→2); the remaining 76% are able to undergo at least a second (degenerate) isomerization cycle (2→1→2) prior to methyl loss. 78% of metastable 1-methyl-adamantane cation radical, obtained upon direct ionization of the corresponding neutral hydrocarbon, dissociate directly, whereas the loss of methyl from the remaining 22% is preceded by an isomerization 2 →1 →2.

The Mechanism of NO Bond Cleavage in Rhodium-Catalyzed CH Bond Functionalization of QuinolineN-oxides with Alkynes: A Computational Study

2015 ◽  
Vol 21 (28) ◽  
pp. 10131-10137 ◽  
Author(s):  
Yingzi Li ◽  
Song Liu ◽  
Zisong Qi ◽  
Xiaotian Qi ◽  
Xingwei Li ◽  
...  
Keyword(s):  
Computational Study ◽  
Bond Cleavage ◽  
Bond Functionalization

scholarly journals Steroid Hydroxylation by Basidiomycete Peroxygenases: a Combined Experimental and Computational Study

2015 ◽  
Vol 81 (12) ◽  
pp. 4130-4142 ◽  
Author(s):  
Esteban D. Babot ◽  
José C. del Río ◽  
Marina Cañellas ◽  
Ferran Sancho ◽  
Fátima Lucas ◽  
...  
Keyword(s):  
Computational Study ◽  
Biological Activities ◽  
Side Chain ◽  
Enzymatic Reactions ◽  
Fungal Enzymes ◽  
Content Type ◽  
Protein Energy ◽  
Esterified Sterols ◽  
Ligand Diffusion ◽  
Protein Energy Landscape

ABSTRACTThe goal of this study is the selective oxyfunctionalization of steroids under mild and environmentally friendly conditions using fungal enzymes. With this purpose, peroxygenases from three basidiomycete species were tested for the hydroxylation of a variety of steroidal compounds, using H2O2as the only cosubstrate. Two of them are wild-type enzymes fromAgrocybe aegeritaandMarasmius rotula, and the third one is a recombinant enzyme fromCoprinopsis cinerea. The enzymatic reactions on free and esterified sterols, steroid hydrocarbons, and ketones were monitored by gas chromatography, and the products were identified by mass spectrometry. Hydroxylation at the side chain over the steroidal rings was preferred, with the 25-hydroxyderivatives predominating. Interestingly, antiviral and other biological activities of 25-hydroxycholesterol have been reported recently (M. Blanc et al., Immunity 38:106–118, 2013,http://dx.doi.org/10.1016/j.immuni.2012.11.004). However, hydroxylation in the ring moiety and terminal hydroxylation at the side chain also was observed in some steroids, the former favored by the absence of oxygenated groups at C-3 and by the presence of conjugated double bonds in the rings. To understand the yield and selectivity differences between the different steroids, a computational study was performed using Protein Energy Landscape Exploration (PELE) software for dynamic ligand diffusion. These simulations showed that the active-site geometry and hydrophobicity favors the entrance of the steroid side chain, while the entrance of the ring is energetically penalized. Also, a direct correlation between the conversion rate and the side chain entrance ratio could be established that explains the various reaction yields observed.

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