Browsing by Subject "Anions"

Now showing 1 - 5 of 5
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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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    Pd-catalyzed C(sp(3))-H functionalization/carbenoid insertion: all-carbon quaternary centers via multiple C-C bond formation
    (American Chemical Society, 2016-05-04) Gutierrez Bonet, Alvaro; Juliá Hernández, Francisco; Luis, Beatriz de; Martin, Ruben; Química Inorgánica
    A Pd-catalyzed C(sp3)-H functionalization/carbenoid insertion is described. The method allows for the rapid synthesis of bicyclic frameworks, generating all-carbon quaternary centers via multiple C–C bond-formations in a straightforward manner.
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    Site-selective catalytic carboxylation of unsaturated hydrocarbons with CO2 and water
    (American Chemical Society, 2017-08-16) Gaydou, Morgane; Moragas, Toni; Juliá Hernández, Francisco; Martin, Ruben; Química Inorgánica
    A catalytic protocol that reliably predicts and controls the site-selective incorporation of CO2 to a wide range of unsaturated hydrocarbons utilizing water as formal hydride source is described. This platform unlocks an opportunity to catalytically repurpose three abundant, orthogonal feedstocks under mild conditions.
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    Walking metals for remote functionalization
    (American Chemical Society, 2018-02-08) Sommer, Heiko; Juliá Hernández, Francisco; Martin, Ruben; Marek, Ilan; Química Inorgánica
    The distant and selective activation of unreactive C−H and C−C bonds remains one of the biggest challenges in organic chemistry. In recent years, the development of remote functionalization has received growing interest as it allows for the activation of rather challenging C−H and C−C bonds distant from the initiation point by means of a “metal-walk”. A “metal-walk” or “chain-walk” is defined by an iterative series of consecutive 1,2- or 1,3-hydride shifts of a metal complex along a single hydrocarbon chain. With this approach, simple building blocks or mixtures thereof can be transformed into complex scaffolds in a convergent and unified strategy. A variety of catalytic systems have been developed and refined over the past decade ranging from late-transition-metal complexes to more sustainable iron- and cobalt-based systems. As the possibilities of this field are slowly unfolding, this area of research will contribute considerably to provide solutions to yet unmet synthetic challenges.