RESUMEN
The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated CO bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6 F5 )3 ) is shown to catalyze the metal-free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products.
RESUMEN
High-spin Fe(1+) sites are potentially important in iron-sulfur proteins but are rare in synthetic compounds and unknown in metalloproteins. Here, we demonstrate a spectroscopically characterized example of high-spin non-heme Fe(1+) in a protein environment. Cryoreduction of Fe(2+)-substituted azurin at 77 K with (60)Co γ radiation generates a new species with a S = (3)/2 (high-spin) Fe(1+) center having D > 0 and E/D ~ 0.25. This transient species is stable in a glycerol-water glass only up to ~170 K. A combination of electron paramagnetic resonance and Mössbauer spectroscopies provides a powerful means of identifying a transient high-spin Fe(1+) site in a protein scaffold.
Asunto(s)
Azurina/química , Proteínas Bacterianas/química , Hierro/análisis , Pseudomonas aeruginosa/química , Cationes/análisis , Glicerol/química , Modelos Moleculares , Oxidación-Reducción , Temperatura , Agua/químicaRESUMEN
In light of diminishing petroleum feedstocks, there is significant interest in developing carbohydrate defunctionalization reactions. In this context we have examined the use of iridium pincer catalysts for the hydrosilylative reduction of sugars, and we report herein complete reduction of silyl-protected glucose to a mixture of hexane isomers.
Asunto(s)
Glucosa/química , Hexanos/síntesis química , Iridio/química , Silanos/química , Catálisis , Hexanos/química , Estructura MolecularRESUMEN
The apoprotein of Pseudomonas aeruginosa azurin binds iron(II) to give a 1:1 complex, which has been characterized by electronic absorption, Mössbauer, and NMR spectroscopies, as well as X-ray crystallography and quantum-chemical computations. Despite potential competition by water and other coordinating residues, iron(II) binds tightly to the low-coordinate site. The iron(II) complex does not react with chemical redox agents to undergo oxidation or reduction. Spectroscopically calibrated quantum-chemical computations show that the complex has high-spin iron(II) in a pseudotetrahedral coordination environment, which features interactions with side chains of two histidines and a cysteine as well as the CâO of Gly45. In the (5)A(1) ground state, the d(z(2)) orbital is doubly occupied. Mutation of Met121 to Ala leaves the metal site in a similar environment but creates a pocket for reversible binding of small anions to the iron(II) center. Specifically, azide forms a high-spin iron(II) complex and cyanide forms a low-spin iron(II) complex.
Asunto(s)
Azurina/química , Hierro/química , Proteínas de Hierro no Heme/química , Teoría Cuántica , Azidas/química , Sitios de Unión , Complejos de Coordinación/química , Cristalografía por Rayos X , Cianuros/química , Espectroscopía de Resonancia Magnética , Estructura Molecular , Oxidación-ReducciónRESUMEN
Studies of palladium(II) and platinum(II) binding to well-characterized proteins contribute to understanding the influence of these metals in the environment and body. The well-characterized apoprotein of azurin has a soft-metal binding site that may be exposed to solvent by mutation of a coordinating His-117 residue to glycine (H117G). Palladium(II) and platinum(II) form strong 1:1 adducts with the apo form of H117G azurin. A combination of UV-vis, circular dichroism, and inductively coupled plasma mass spectrometry techniques suggests that the metal binds specifically at His-46 and Cys-112 of the protein.
Asunto(s)
Azurina/metabolismo , Proteínas Bacterianas/metabolismo , Cobre/metabolismo , Paladio/metabolismo , Platino (Metal)/metabolismo , Pseudomonas aeruginosa/metabolismo , Apoproteínas/química , Apoproteínas/genética , Apoproteínas/metabolismo , Azurina/química , Azurina/genética , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Sitios de Unión , Cobre/química , Modelos Moleculares , Mutación , Unión Proteica , Conformación Proteica , Ingeniería de Proteínas , Pseudomonas aeruginosa/química , Pseudomonas aeruginosa/genéticaRESUMEN
Light-driven H(2) production is catalyzed by [Ni(P(2)(Ph)N(2)(Ph))(2)](BF(4))(2) when irradiated with visible light in water/acetonitrile mixed solvent in the presence of a photosensitizer (PS) and ascorbate. The catalyst gives over 2700 turnovers over 150 h, and does not degrade despite photodecomposition of the PS.