RESUMEN
A composite consisting of CoFe2 O4 spinel nanoparticles and reduced graphite oxide (rGO) is studied as an anode material during Li uptake and release by applying synchrotron operando X-ray diffraction (XRD) and operando X-ray absorption spectroscopy (XAS), yielding a comprehensive picture of the reaction mechanisms. In the early stages of Li uptake, a monoxide is formed as an intermediate phase containing Fe2+ and Co2+ ions; this observation is in contrast to reaction pathways proposed in the literature. In the fully discharged state, metallic Co and Fe nanoparticles are embedded in an amorphous Li2 O matrix. During charge, metallic Co and Fe are oxidized simultaneously to Co2+ and Fe3+ , respectively, thus enabling a high and stable capacity to be achieved. Here, evidence is presented that the rGO acts as a support for the nanoparticles and prevents the particles from contact loss. The operando investigations are complemented by TEM, Raman spectroscopy, galvanostatic cycling, and cyclic voltammetry.
RESUMEN
In most organisms, the mitochondrial genes are transcribed by RNA polymerases related to the single-subunit RNA polymerases of bacteriophages like T3 and T7. In flowering plants, duplication(s) of the RpoTm gene coding for the mitochondrial RNA polymerase (RPOTm) led to the evolution of additional RNA polymerases transcribing genes in plastids (RPOTp) or in both mitochondria and plastids (RPOTmp). Two putative RPOTmp enzymes were previously described to be encoded by the nuclear genes RpoTmp1 and RpoTmp2 in the moss Physcomitrella patens. Here, we report on a third Physcomitrella RpoT gene. We determined the sequence of the cDNA. Comparison of the deduced amino acid sequence with sequences of plant organellar RNA polymerases suggests that this gene encodes a functional phage-type RNA polymerase. The 78 N-terminal amino acids of the putative RNA polymerase were fused to GFP and found to target the fusion protein exclusively to mitochondria in Arabidopsis protoplasts. P. patens is the only known organism to possess three mitochondrial RNA polymerases.
Asunto(s)
Bryopsida/enzimología , Bryopsida/genética , ARN Polimerasas Dirigidas por ADN/genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Mitocondrias/enzimología , Mitocondrias/genética , Secuencia de Aminoácidos , Transporte Biológico , Bryopsida/clasificación , ARN Polimerasas Dirigidas por ADN/química , Genes Mitocondriales , Datos de Secuencia Molecular , Filogenia , Plastidios/química , Plastidios/genética , ARN/química , ARN Mitocondrial , Alineación de SecuenciaRESUMEN
The physiological reaction of a membrane protein is reconstituted on a solid-supported electrode by orientational control via the position of an affinity tag. Recombinant cytochrome c oxidase (CcO) from Rhodobacter sphaeroides is immobilized on a chemically modified gold surface via the affinity of a histidine tag (His-tag) to a nickel chelating nitrilotriacetic acid surface. Control of the orientation is achieved by the adsorption of CcO through the His-tag engineered into the two opposite sites of the membrane protein surface. After reconstitution into a lipid layer, the functionality of this enzyme film electrode is probed by surface-enhanced infrared absorption spectroscopy and cyclic voltammetry. We demonstrate that cytochrome c (Cc) binds and initiates the catalytic reaction of CcO only when the latter is orientated with subunit II facing the bulk aqueous phase while Cc does not interact with the oppositely orientated CcO. We infer from the observed catalytic dioxygen reduction at potentials below 240 mV (vs a normal hydrogen electrode) that reduced Cc mediates electron input into CcO in a way similar to the physiological pathway. The quantitative analysis of the IR spectra indicates the presence of an inactive population of Cc bound to CcO at equal amounts as the redox-active population. This methodological approach demonstrates that the orientation of the membrane protein can be controlled depending on the position of the affinity tag. The approach is considered to be of general applicability as the introduction of affinity tags is routine in current biochemistry.
Asunto(s)
Complejo IV de Transporte de Electrones/química , Complejo IV de Transporte de Electrones/fisiología , Enzimas Inmovilizadas/química , Oro/química , Proteínas Recombinantes/química , Adsorción , Electroquímica , Electrodos , Complejo IV de Transporte de Electrones/aislamiento & purificación , Cinética , Membranas Artificiales , Modelos Moleculares , Rhodobacter sphaeroides/química , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de SuperficieRESUMEN
PURPOSE: Adhesive cementation reduces the need for macroretentive preparation for crowns. This study investigated the survival and clinical rating of monolithic computer-aided design/manufacturing (CAD/CAM) ceramic crowns bonded to preparations with reduced macroretention, hypothesizing that adhesion would compensate for reduced retention geometry. MATERIALS AND METHODS: Two-hundred eight posterior CAD/CAM-generated crowns from feldspar block ceramic were adhesively bonded in 136 patients in three preparation groups: classic (100% stump height, n = 70); reduced (reduced stump height or irregular stump, n = 52); and endo (absent stump but pulp chamber retention cavity, n = 86). Crowns were examined at baseline and after 55 +/- 15 months using modified USPHS criteria. Plaque and bleeding of gingiva around the crowns were assessed. RESULTS: Cumulative Kaplan-Meier survival of crowns on premolars/molars was: classic = 97.0%/94.6%; reduced = 92.9%/92.1%; and endo = 68.8%/87.1%, confirming the hypothesis for classic, reduced, and endo molars as well as for classic and reduced premolars. A significant difference was found between classic and endo premolar crowns, rejecting the hypothesis for endo preparation on premolars. Plaque and bleeding indices were significantly lower for crowned teeth than for controls. CONCLUSION: The survival of classic and reduced crowns was rated adequate for premolars and molars. Endo preparation appeared acceptable for molar crowns but inadequate for premolar crowns.
Asunto(s)
Cementación , Cerámica/química , Diseño Asistido por Computadora , Coronas , Recubrimiento Dental Adhesivo , Retención de Prótesis Dentales , Preparación Protodóncica del Diente/métodos , Silicatos de Aluminio/química , Diente Premolar , Índice de Placa Dental , Porcelana Dental/química , Fracaso de la Restauración Dental , Recubrimientos Dentinarios/química , Estudios de Seguimiento , Hemorragia Gingival/clasificación , Humanos , Ensayo de Materiales , Diente Molar , Índice Periodontal , Técnica de Perno Muñón , Compuestos de Potasio/química , Estudios Prospectivos , Análisis de SupervivenciaRESUMEN
A novel concept is introduced for the oriented incorporation of membrane proteins into solid supported lipid bilayers. Recombinant cytochrome c oxidase solubilized in detergent was immobilized on a chemically modified gold surface via the affinity of its histidine-tag to a nickel-chelating nitrilo-triacetic acid (NTA) surface. The oriented protein monolayer was reconstituted into the lipid environment by detergent substitution. The individual steps of the surface modification, including (1) chemical modification of the gold support, (2) adsorption of the protein, and (3) reconstitution of the lipid bilayer, were followed in situ by means of surface-enhanced infrared absorption spectroscopy (SEIRAS) and accompanied by normal-mode analysis. The high surface sensitivity of SEIRAS allows for the identification of each chemical reaction process within the monolayer at the molecular level. Finally, full functionality of the surface-tethered cytochrome c oxidase was demonstrated by cyclic voltammetry after binding of the natural electron donor cytochrome c.