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This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure-property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.
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The uterine tube is an essential conduit for the gametes and zygote during reproduction. The necessary bidirectional conveyance occurs through peristalsis and ciliary activity, but unlike in respiratory tract, little is known about mucociliary transport in the uterine tube, and the direction of transport and the alignment of oviductal cilia have not been conclusively characterized. This study aimed to determine the uniformity in the axonemal orientation of motile cilia in the bovine uterine tube, to identify the direction of mucociliary transport and to relate the presumptive beating plane and the mucociliary transport direction to the long axis of the uterine tube. The angular spread of oviductal motile cilia was determined by electron microscopy, and by maintaining the accurate alignment of the samples throughout the processing steps, axonemal orientation was determined relative to the long axis of the oviduct. The direction of the effective mucociliary transport was determined by the analysis of video microscopic data recorded on explants. Vector-based analysis of electron micrographs yielded the mean angle of deviation between the 'effective ciliary stroke', as derived from axonemal orientation, and the tubal longitudinal axis pointing towards the uterus to be 0.8°, with a standard deviation of 35.2°. The corresponding angular deviation of the short-wave propagation was -6.8° (SD 34.6°). These results show that oviductal motile cilia are rigorously aligned, that the beating plane of the cilia is parallel to the long axis of the uterine tube and that the 'effective stroke' and mucociliary transport are directed towards the uterus.
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Transporte Biológico/fisiologia , Cílios/fisiologia , Tubas Uterinas/metabolismo , Espermatozoides/metabolismo , Animais , Bovinos , Feminino , Masculino , Microscopia Eletrônica , ReproduçãoRESUMO
We report a method based on density functional theory molecular dynamics that allows us to calculate the plasmonic properties of liquid metals and metal alloys from first principles with no a priori knowledge of the system. We show exceptional agreement between the simulated and measured optical constants of liquid Ga and the room temperature liquid In-Ga eutectic alloy (T(m) = 289 K). We then use this method to analyze the plasmonic properties of various alloy concentrations in the In-Ga system. The plasmonic performance of the In-Ga system decreases with increasing In concentration. However, the benefits of a room-temperature plasmonic liquid are likely to outweigh the minor reduction in plasmonic performance when moving from pure Ga to the eutectic composition. Our results show that density functional theory molecular dynamics can be used as a predictive tool for studying the optical properties of liquid metal systems amenable to plasmonics.
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Multiple vibrational modes have been observed for copper phthalocyanine (CuPc) adlayers on Ag(111) using ultrahigh vacuum (UHV) tip-enhanced Raman spectroscopy (TERS). Several important new experimental features are introduced in this work that significantly advance the state-of-the-art in UHV-TERS. These include (1) concurrent sub-nm molecular resolution STM imaging using Ag tips with laser illumination of the tip-sample junction, (2) laser focusing and Raman collection optics that are external to the UHV-STM that has two cryoshrouds for future low temperature experiments, and (3) all sample preparation steps are carried out in UHV to minimize contamination and maximize spatial resolution. Using this apparatus we have been able to demonstrate a TERS enhancement factor of 7.1 × 10(5). Further, density-functional theory calculations have been carried out that allow quantitative identification of eight different vibrational modes in the TER spectra. The combination of molecular-resolution UHV-STM imaging with the detailed chemical information content of UHV-TERS allows the interactions between large polyatomic molecular adsorbates and specific binding sites on solid surfaces to be probed with unprecedented spatial and spectroscopic resolution.
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The translocation of proteins across membranes usually requires specific transport systems composed of membrane-bound and soluble components. A combination of biochemical and genetic approaches has led to the identification and preliminary characterization of some of these components.
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Membranas Intracelulares/metabolismo , Mitocôndrias/metabolismo , Peptídeos/metabolismo , Proteínas/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Transporte Biológico/fisiologia , HumanosRESUMO
The import of proteins into mitochondria occurs in several steps. At least three of these steps require ATP and involve molecular chaperones. This energy requirement has served as a useful tool for elucidating the import pathways into the four mitochondrial compartments.
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Metabolismo Energético/fisiologia , Mitocôndrias/metabolismo , Proteínas/metabolismo , Trifosfato de Adenosina/fisiologia , Compartimento Celular/fisiologia , Citoplasma/fisiologia , Mitocôndrias/ultraestruturaRESUMO
Surface plasmon polaritons (SPPs) and Rayleigh anomalies (RAs) are two characteristic phenomena exhibited by periodic grating structures made of plasmonic materials. For Au subwavelength hole arrays, SPPs and RAs from opposite sides of the film can interact under certain conditions to produce highly intense, narrow spectral features called RA-SPP resonances. This paper reports how RA-SPP effects can be achieved in subwavelength hole arrays of Pd, a weak plasmonic material. Well-defined resonances are observed in measured and simulated optical transmission spectra with RASPP peaks as narrow as 45 nm (FWHM). Dispersion diagrams compiled from angle-resolved spectra show that RA-SPP resonances in Pd hole arrays shift in wavelength but do not decrease significantly in amplitude as the excitation angle is increased, in contrast with RA-SPP peaks in Au hole arrays. The apparent generality of the RA-SPP effect enables a novel route to optimize resonances in non-traditional plasmonic media.
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Artefatos , Ouro/química , Modelos Químicos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Paládio/química , Refratometria/métodos , Simulação por Computador , PorosidadeRESUMO
Although mitochondria and chloroplasts synthesize some of their own proteins, they must import most of them from the cytosol. Import is mediated by molecular chaperones in the cytosol, receptors and channels in the organelle membranes and ATP-driven 'import motors' inside the organelles. Many of these components are now known, allowing informed guesses on how they might work.
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Mitochondria can import proteins from the cytoplasm at sites where the two mitochondrial membranes are closely apposed. However, each of these membranes contains a distinct protein translocation channel. Recent evidence suggests that the two types of channel are not permanently coupled, but may dissociate in a reversible manner. This reversible interaction is probably essential for intramitochondrial sorting proteins.
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Bovine pancreatic trypsin inhibitor (which contains three intramolecular disulfide bridges) was chemically coupled to the COOH terminus of a purified artificial mitochondrial precursor protein. When the resulting chimeric precursor was presented to energized isolated yeast mitochondria, its trypsin inhibitor moiety prevented the protein from completely entering the organelle; the protein remained stuck across both mitochondrial membranes, with its NH2 terminus in the matrix and its trypsin inhibitor moiety still exposed on the mitochondrial surface. The incompletely imported protein appeared to "jam" mitochondrial protein import sites since it blocked import of three authentic mitochondrial precursor proteins; it did not collapse the potential across the mitochondrial inner membrane. Quantification of the inhibition indicated that each isolated mitochondrial particle contains between 10(2) and 10(3) protein import sites.
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Membranas Intracelulares/metabolismo , Mitocôndrias/metabolismo , Precursores de Proteínas/metabolismo , Álcool Desidrogenase/metabolismo , Transporte Biológico , Dissulfetos , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Técnicas In Vitro , ATPases Translocadoras de Prótons/metabolismo , Proteínas Recombinantes de Fusão/metabolismo , Saccharomyces cerevisiae , Relação Estrutura-AtividadeRESUMO
A purified, artificial precursor protein was used as a transport vehicle to test the tolerance of the mitochondrial protein import system. The precursor was a fusion protein consisting of mouse dihydrofolate reductase linked to a yeast mitochondrial presequence; it contained a unique cysteine as its COOH-terminal residue. This COOH-terminal cysteine was covalently coupled to either a stilbene disulfonate derivative or, with the aid of a bifunctional cross-linker, to one of the free amino groups of horse heart cytochrome c. Coupling to horse heart cytochrome c generated a mixture of branched polypeptide chains since this cytochrome lacks a free alpha-amino group. Both adducts were imported and cleaved by isolated yeast mitochondria. The mitochondrial protein import machinery can thus transport more complex structures and even highly charged "membrane-impermeant" organic molecules. This suggests that transport occurs through a hydrophilic environment.
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Membranas Intracelulares/metabolismo , Mitocôndrias/metabolismo , Precursores de Proteínas/metabolismo , Transporte Biológico , Grupo dos Citocromos c/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Técnicas In Vitro , Cinética , Precursores de Proteínas/ultraestrutura , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes de Fusão/ultraestrutura , Saccharomyces cerevisiae , Estilbenos/metabolismo , Relação Estrutura-Atividade , Tetra-Hidrofolato Desidrogenase/metabolismoRESUMO
Import of precursor proteins into the yeast mitochondrial matrix can occur directly across the inner membrane. First, disruption of the outer membrane restores protein import to mitochondria whose normal import sites have been blocked by an antibody against the outer membrane or by a chimeric, incompletely translocated precursor protein. Second, a potential- and ATP-dependent import of authentic or artificial precursor proteins is observed with purified inner membrane vesicles virtually free of outer membrane components. Third, import into purified inner membrane vesicles is insensitive to antibody against the outer membrane. Thus, while outer membrane components are clearly required in vivo, the inner membrane contains a complete protein translocation system that can operate by itself if the outer membrane barrier is removed.
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Membranas Intracelulares/metabolismo , Mitocôndrias/metabolismo , Precursores de Proteínas/metabolismo , Saccharomyces cerevisiae/metabolismo , Anticorpos/imunologia , Quimera , Endopeptidase K , Membranas Intracelulares/imunologia , Membranas Intracelulares/fisiologia , Mitocôndrias/fisiologia , Mitocôndrias/ultraestrutura , Serina Endopeptidases/farmacologiaRESUMO
To identify the membrane regions through which yeast mitochondria import proteins from the cytoplasm, we have tagged these regions with two different partly translocated precursor proteins. One of these was bound to the mitochondrial surface of ATP-depleted mitochondria and could subsequently be chased into mitochondria upon addition of ATP. The other intermediate was irreversibly stuck across both mitochondrial membranes at protein import sites. Upon subfraction of the mitochondria, both intermediates cofractionated with membrane vesicles whose buoyant density was between that of inner and outer membranes. When these vesicles were prepared from mitochondria containing the chaseable intermediate, they internalized it upon addition of ATP. A non-hydrolyzable ATP analogue was inactive. This vesicle fraction contained closed, right-side-out inner membrane vesicles attached to leaky outer membrane vesicles. The vesicles contained the mitochondrial binding sites for cytoplasmic ribosomes and contained several mitochondrial proteins that were enriched relative to markers of inner or outer membranes. By immunoelectron microscopy, two of these proteins were concentrated at sites where mitochondrial inner and outer membranes are closely apposed. We conclude that these vesicles contain contact sites between the two mitochondrial membranes, that these sites are the entry point for proteins into mitochondria, and that the isolated vesicles are still translocation competent.
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Trifosfato de Adenosina/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Proteínas Fúngicas/metabolismo , Membranas Intracelulares/metabolismo , Mitocôndrias/metabolismo , Saccharomyces cerevisiae/metabolismo , Tetra-Hidrofolato Desidrogenase/metabolismo , Transporte Biológico , Citoplasma/metabolismo , Hexoquinase/metabolismo , Membranas Intracelulares/ultraestrutura , Microscopia Eletrônica , Proteínas Recombinantes de Fusão/metabolismo , Ribossomos/metabolismo , Partículas Submitocôndricas/metabolismo , Partículas Submitocôndricas/ultraestruturaRESUMO
By screening a collection of Saccharomyces cerevisiae mutants temperature sensitive for growth on a nonfermentable carbon source, we have isolated a gene (termed MAS37) which encodes a novel receptor for protein import into mitochondria. Mas37p is a 37-kD outer membrane protein with two putative membrane-spanning regions. Inactivation of the MAS37 gene renders cells temperature-sensitive for respiration-driven growth, inhibits import of precursors into isolated mitochondria, and is synthetically lethal with a deletion of one of the genes encoding the import receptors Mas70p or Mas20p. Inactivation of Mas37p with specific antibodies inhibits import of different precursors to different extents; the precursor specificity of Mas37p resembles that of the previously described import receptor Mas70p. Mas70p and Mas37p form a 1:1 complex in detergent extracts of mitochondria and overexpression of one protein enhances that of the other. We suggest that the Mas37p/Mas70p heterodimer functions as a receptor for protein import into yeast mitochondria and that the mitochondrial receptor system consists of hetero-oligomeric subcomplexes with distinct binding activities, but overlapping precursor specificities.
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Proteínas de Membrana/biossíntese , Mitocôndrias/metabolismo , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Citosol/metabolismo , Expressão Gênica , Genes Fúngicos , Substâncias Macromoleculares , Proteínas de Membrana/química , Proteínas de Membrana/metabolismo , Modelos Estruturais , Dados de Sequência Molecular , Mutação , Conformação Proteica , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/crescimento & desenvolvimento , Sulfatos/metabolismo , Radioisótopos de Enxofre , TemperaturaRESUMO
Many newly synthesized proteins must be translocated across a membrane to reach their final destinations. Translocation requires a signal on the protein itself, a loose conformation of the protein, energy, and receptor-like components in the cytosol and on the target membrane.
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Membrana Celular/metabolismo , Membranas Intracelulares/metabolismo , Proteínas de Membrana , Proteínas/metabolismo , Serina Endopeptidases , Animais , Transporte Biológico , Compartimento Celular , Endopeptidases/fisiologia , Biossíntese de Proteínas , Processamento de Proteína Pós-Traducional , Sinais Direcionadores de Proteínas/fisiologia , Receptores de Superfície Celular/fisiologiaRESUMO
Most major systems that transport proteins across a membrane share the following features: an amino-terminal transient signal sequence on the transported protein, a targeting system on the cis side of the membrane, a hetero-oligomeric transmembrane channel that is gated both across and within the plane of the membrane, a peripherally attached protein translocation motor that is powered by the hydrolysis of nucleoside triphosphate, and a protein folding system on the trans side of the membrane. These transport systems are divided into two families: export systems that export proteins out of the cytosol, and import systems that transport proteins into cytosol-like compartments.
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Membrana Celular/metabolismo , Membranas Intracelulares/metabolismo , Proteínas/metabolismo , Sequência de Aminoácidos , Bactérias/metabolismo , Transporte Biológico , Cloroplastos/metabolismo , Citosol/metabolismo , Retículo Endoplasmático/metabolismo , GTP Fosfo-Hidrolases/metabolismo , Proteínas de Membrana/metabolismo , Microcorpos/metabolismo , Mitocôndrias/metabolismo , Chaperonas Moleculares/metabolismo , Dados de Sequência Molecular , Dobramento de Proteína , Sinais Direcionadores de Proteínas/metabolismoRESUMO
The role of protein degradation in mitochondrial homeostasis was explored by cloning of a gene from Saccharomyces cerevisiae that encodes a protein resembling the adenosine triphosphate (ATP)-dependent bacterial protease Lon. The predicted yeast protein has a typical mitochondrial matrix-targeting sequence at its amino terminus. Yeast cells lacking a functional LON gene contained a nonfunctional mitochondrial genome, were respiratory-deficient, and lacked an ATP-dependent proteolytic activity present in the mitochondria of Lon+ cells. Lon- cells were also impaired in their ability to catalyze the energy-dependent degradation of several mitochondrial matrix proteins and they accumulated electron-dense inclusions in their mitochondrial matrix.
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Genes Fúngicos , Proteínas de Choque Térmico/genética , Mitocôndrias/metabolismo , Consumo de Oxigênio , Saccharomyces cerevisiae/genética , Serina Endopeptidases/genética , Proteases Dependentes de ATP , Adenosina Trifosfatases/genética , Adenosina Trifosfatases/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Proteínas Fúngicas/metabolismo , Proteínas de Choque Térmico/metabolismo , Microscopia Eletrônica , Mitocôndrias/ultraestrutura , Dados de Sequência Molecular , Saccharomyces cerevisiae/metabolismo , Serina Endopeptidases/metabolismoRESUMO
In order to reach the inner membrane of the mitochondrion, multispanning carrier proteins must cross the aqueous intermembrane space. Two essential proteins of that space, Tim10p and Tim12p, were shown to mediate import of multispanning carriers into the inner membrane. Both proteins formed a complex with the inner membrane protein Tim22p. Tim10p readily dissociated from the complex and was required to transport carrier precursors across the outer membrane; Tim12p was firmly bound to Tim22p and mediated the insertion of carriers into the inner membrane. Neither protein was required for protein import into the other mitochondrial compartments. Both proteins may function as intermembrane space chaperones for the highly insoluble carrier proteins.
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Proteínas de Transporte/metabolismo , Proteínas Fúngicas/metabolismo , Membranas Intracelulares/metabolismo , Proteínas de Membrana/metabolismo , Proteínas de Membrana Transportadoras , Mitocôndrias/metabolismo , Proteínas de Saccharomyces cerevisiae , Transporte Biológico , Clonagem Molecular , Proteínas Fúngicas/genética , Genes Fúngicos , Temperatura Alta , Potenciais da Membrana , Proteínas de Membrana/genética , Translocases Mitocondriais de ADP e ATP/metabolismo , Proteínas de Transporte da Membrana Mitocondrial , Proteínas do Complexo de Importação de Proteína Precursora Mitocondrial , Modelos Biológicos , Chaperonas Moleculares/metabolismo , Mutagênese , Proteínas de Ligação a Fosfato , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , SolubilidadeRESUMO
Computational studies of basic chemical processes not only provide numbers for comparison with experiment or for use in modeling complex chemical phenomena such as combustion, but also provide insight into the fundamental factors that govern molecular structure and change which cannot be obtained from experiment alone. We summarize the results of three case studies, on HCO, OH + H(2), and O + C(2)H(2), which illustrate the range of problems that can be addressed by using modern theoretical techniques. In all cases, the potential energy surfaces were characterized by using ab initio electronic structure methods. Collisions between molecules leading to reaction or energy transer were described with quantum dynamical methods (HCO), classical trajectory techniques (HCO and OH + H(2)), and statistical methods (HCO, OH + H(2), and O + C(2)H(2)). We can anticipate dramatic increases in the scope of this work as new generations of computers are introduced and as new chemistry software is developed to exploit these computers.