Browsing by Subject "Alkyls"

Now showing 1 - 3 of 3
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    Kinetically-controlled ni-catalyzed direct carboxylation of unactivated secondary alkyl bromides without chain walking
    (American Chemical Society, 2024-01-09) Davies, Jacob; Lyonnet, Julien R.; Carvalho, Bjorn; Sahoo, Basudev; Day, Craig S.; Juliá Hernández, Francisco; Duan, Yaya; Obst, Marc; Norrby, Per-Ola; Velasco-Rubio, Álvaro; Hopmann, Kathrin H; Martin, Ruben; Obst, Marc; Per-OLa, Norrby; Química Inorgánica
    Herein, we report the direct carboxylation of unactivated secondary alkyl bromides enabled by the merger of photoredox and nickel catalysis, a previously inaccessible endeavor in the carboxylation arena. Site-selectivity is dictated by a kinetically controlled insertion of CO2 at the initial C(sp3 )−Br site by the rapid formation of Ni(I)−alkyl species, thus avoiding undesired β-hydride elimination and chain-walking processes. Preliminary mechanistic experiments reveal the subtleties of stereoelectronic effects for guiding the reactivity and site-selectivity.
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    Occupancy of nonannular lipid binding sites on KcsA greatly increases the stability of the tetrameric protein
    (American Chemical Society, 2010-05-19) Triano García, Irene; Barrera Olivares, Francisco Nicolás; Renart Pérez, María Lourdes; Molina Gallego, María Luisa; Fernández Ballester, Gregorio; Poveda Larrosa, José Antonio; Fernández Carvajal, Asia María; Encinar Hidalgo, José Antonio; Ferrer Montiel, Antonio Vicente; Otzen, Daniel; González Ros, José Manuel; Bioquímica y Biología Molecular B e Inmunología
    KcsA, a homotetrameric potassium channel from prokaryotes, contains noncovalently bound lipids appearing in the X-ray crystallographic structure of the protein. The binding sites for such high-affinity lipids are referred to as “nonannular” sites, correspond to intersubunit protein domains, and bind preferentially anionic phospholipids. Here we used a thermal denaturation assay and detergent−phospholipid mixed micelles containing KcsA to study the effects of different phospholipids on protein stability. We found that anionic phospholipids stabilize greatly the tetrameric protein against irreversible, heat-induced unfolding and dissociation into subunits. This occurs in a phospholipid concentration-dependent manner, and phosphatidic acid species with acyl chain lengths ranging 14 to 18 carbon atoms are more efficient than similar phosphatidylglycerols in protecting the protein. A docking model of the KcsA−phospholipid complex suggests that the increased protein stability originates from the intersubunit nature of the binding sites and, thus, interaction of the phospholipid with such sites holds together adjacent subunits within the tetrameric protein. We also found that simpler amphiphiles, such as alkyl sulfates longer than 10 carbon atoms, also increase the protein stability to the same extent as anionic phospholipids, although at higher concentrations than the latter. Modeling the interaction of these simpler amphiphiles with KcsA and comparing it with that of anionic phospholipids serve to delineate the features of a hydrophobic pocket in the nonannular sites. Such pocket is predicted to comprise residues from the M2 transmembrane segment of a subunit and from the pore helix of the adjacent subunit and seems most relevant to protein stabilization.
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    Reductive Elimination Reactions in Gold(III) Complexes Leading to C(sp3)–X (X = C, N, P, O, Halogen) Bond Formation: Inner-Sphere vs SN2 Pathways
    (American Chemical Society, 2023-01-19) Portugués Rodríguez, Alejandro; Martínez-Nortes, Miguel Ángel; Bautista, Delia; González Herrero, Pablo; Gil Rubio, Juan; Química Inorgánica
    The reactions leading to the formation of C–heteroatom bonds in the coordination sphere of Au(III) complexes are uncommon, and their mechanisms are not well known. This work reports on the synthesis and reductive elimination reactions of a series of Au(III) methyl complexes containing different Au–heteroatom bonds. Complexes [Au(CF3)(Me)(X)(PR3)] (R = Ph, X = OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br; R = Cy, X = Me, OTf, Br) were obtained by the reaction of trans-[Au(CF3)(Me)2(PR3)] (R = Ph, Cy) with HX. The cationic complex cis-[Au(CF3)(Me)(PPh3)2]OTf was obtained by the reaction of [Au(CF3)(Me)(OTf)(PPh3)] with PPh3. Heating these complexes led to the reductive elimination of MeX (X = Me, Ph3P+, OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br). Mechanistic studies indicate that these reductive elimination reactions occur either through (a) the formation of tricoordinate intermediates by phosphine dissociation, followed by reductive elimination of MeX, or (b) the attack of weakly coordinating anionic (TfO– or ClO4–) or neutral nucleophiles (PPh3 or NEt3) to the Au-bound methyl carbon. The obtained results show for the first time that the nucleophilic substitution should be considered as a likely reductive elimination pathway in Au(III) alkyl complexes.