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G protein-coupled receptors (GPCRs) mediate diverse signaling in part through interaction with arrestins, whose binding promotes receptor internalization and signaling through G protein-independent pathways. High-affinity arrestin binding requires receptor phosphorylation, often at the receptor's C-terminal tail. Here, we report an X-ray free electron laser (XFEL) crystal structure of the rhodopsin-arrestin complex, in which the phosphorylated C terminus of rhodopsin forms an extended intermolecular ß sheet with the N-terminal ß strands of arrestin. Phosphorylation was detected at rhodopsin C-terminal tail residues T336 and S338. These two phospho-residues, together with E341, form an extensive network of electrostatic interactions with three positively charged pockets in arrestin in a mode that resembles binding of the phosphorylated vasopressin-2 receptor tail to ß-arrestin-1. Based on these observations, we derived and validated a set of phosphorylation codes that serve as a common mechanism for phosphorylation-dependent recruitment of arrestins by GPCRs.
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Arrestinas/química , Rodopsina/química , Sequência de Aminoácidos , Animais , Arrestinas/metabolismo , Cromatografia Líquida , Humanos , Camundongos , Modelos Moleculares , Fosforilação , Ratos , Rodopsina/metabolismo , Alinhamento de Sequência , Espectrometria de Massas em Tandem , Raios XRESUMO
In the PDF version of this Article, owing to a typesetting error, an incorrect figure was used for Extended Data Fig. 5; the correct figure was used in the HTML version. This has been corrected online.
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G-protein-coupled receptors comprise the largest family of mammalian transmembrane receptors. They mediate numerous cellular pathways by coupling with downstream signalling transducers, including the hetrotrimeric G proteins Gs (stimulatory) and Gi (inhibitory) and several arrestin proteins. The structural mechanisms that define how G-protein-coupled receptors selectively couple to a specific type of G protein or arrestin remain unknown. Here, using cryo-electron microscopy, we show that the major interactions between activated rhodopsin and Gi are mediated by the C-terminal helix of the Gi α-subunit, which is wedged into the cytoplasmic cavity of the transmembrane helix bundle and directly contacts the amino terminus of helix 8 of rhodopsin. Structural comparisons of inactive, Gi-bound and arrestin-bound forms of rhodopsin with inactive and Gs-bound forms of the ß2-adrenergic receptor provide a foundation to understand the unique structural signatures that are associated with the recognition of Gs, Gi and arrestin by activated G-protein-coupled receptors.
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Microscopia Crioeletrônica , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/ultraestrutura , Rodopsina/metabolismo , Rodopsina/ultraestrutura , Arrestina/química , Arrestina/metabolismo , Sítios de Ligação , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/química , Subunidades alfa Gs de Proteínas de Ligação ao GTP/química , Subunidades alfa Gs de Proteínas de Ligação ao GTP/metabolismo , Humanos , Modelos Moleculares , Receptores Adrenérgicos beta 2/química , Receptores Adrenérgicos beta 2/metabolismo , Rodopsina/química , Transdução de Sinais , Especificidade por SubstratoRESUMO
Although many bacterial species do not possess proteasome systems, the actinobacteria, including the human pathogen Mycobacterium tuberculosis, use proteasome systems for targeted protein removal. Previous structural analyses of the mycobacterial proteasome ATPase Mpa revealed a general structural conservation with the archaeal proteasome-activating nucleotidase and eukaryotic proteasomal Rpt1-6 ATPases, such as the N-terminal coiled-coil domain, oligosaccharide-/oligonucleotide-binding domain, and ATPase domain. However, Mpa has a unique ß-grasp domain that in the ADP-bound crystal structure appears to interfere with the docking to the 20S proteasome core particle (CP). Thus, it is unclear how Mpa binds to proteasome CPs. In this report, we show by cryo-EM that the Mpa hexamer in the presence of a degradation substrate and ATP forms a gapped ring, with two of its six ATPase domains being highly flexible. We found that the linkers between the oligonucleotide-binding and ATPase domains undergo conformational changes that are important for function, revealing a previously unappreciated role of the linker region in ATP hydrolysis-driven protein unfolding. We propose that this gapped ring configuration is an intermediate state that helps rearrange its ß-grasp domains and activating C termini to facilitate engagement with proteasome CPs. This work provides new insights into the crucial process of how an ATPase interacts with a bacterial proteasome protease.
Assuntos
Adenosina Trifosfatases/metabolismo , Mycobacterium tuberculosis/enzimologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Adenosina Trifosfatases/química , Modelos Moleculares , Domínios Proteicos , Multimerização Proteica , Estrutura Quaternária de ProteínaRESUMO
Surface defects influence the dye adsorption on TiO2 used as a substrate in dye-sensitized solar cells (DSSCs). In this study, we have used different Ar+ sputtering doses to create a controlled density of defects on a TiO2 surface exposed to different pre-heating temperatures in order to analyse the influence of defects on the N719 dye adsorption. TiO2 was pre-treated using two different treatments. The first treatment involved heating to 200 °C with subsequent sputtering at different doses. The second treatment included heating only, but at four different temperatures starting at 200 °C. After the pre-treatments, the TiO2 samples were immersed into an N719 dye solution for 24 hours at room temperature to dye the TiO2 substrates. The amount of Ti3+ surface defects introduced by the different pre-treatments and their influence on dye adsorption onto the TiO2 surface were examined by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES). Neutral impact collision ion scattering spectroscopy (NICISS) was used to determine the coverage of the TiO2 surface by adsorbed dye molecules. It was found that Ti3+ surface defects were formed by Ar+ sputtering but not by pre-treatment through heating alone. MIES analysis of the outer-most layer and density of states calculations show that the thiocyanate ligand of the N719 dye becomes directed away from the TiO2 surface. Both XPS and NICISS results indicate that the amount of adsorbed N719 dye decreases with increasing density of Ti3+ surface defects. Thus, the generation of surface defects reduces the ability of the TiO2 surface to adsorb the dye molecules. Heating alone as pre-treatment of the TiO2 substrates instead increases the dye adsorption, without causing detectable defects on the TiO2 surface.
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The properties of semiconductor surfaces can be modified by the deposition of metal clusters consisting of a few atoms. The properties of metal clusters and of cluster-modified surfaces depend on the number of atoms forming the clusters. Deposition of clusters with a monodisperse size distribution thus allows tailoring of the surface properties for technical applications. However, it is a challenge to retain the size of the clusters after their deposition due to the tendency of the clusters to agglomerate. The agglomeration can be inhibited by covering the metal cluster modified surface with a thin metal oxide overlayer. In the present work, phosphine-protected Au clusters, Au9(PPh3)8(NO3)3, were deposited onto RF-sputter deposited TiO2 films and subsequently covered with a Cr2O3 film only a few monolayers thick. The samples were then heated to 200 °C to remove the phosphine ligands, which is a lower temperature than that required to remove thiolate ligands from Au clusters. It was found that the Cr2O3 covering layer inhibited cluster agglomeration at an Au cluster coverage of 0.6% of a monolayer. When no protecting Cr2O3 layer was present, the clusters were found to agglomerate to a large degree on the TiO2 surface.
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Dimensional engineering of perovskite solar cells has attracted significant research attention recently because of the potential to improve both device performance and stability. Here, a novel 2D passivation scheme for 3D perovskite solar cells is demonstrated using a mixed cation composition of 2D perovskite based on two different isomers of butylammonium iodide. The dual-cation 2D perovskite outperforms its single cation 2D counterparts in surface passivation quality, resulting in devices with an impressive open-circuit voltage of 1.21 V for a perovskite composition with an optical bandgap of ≈1.6 eV, and a champion efficiency of 23.27%. Using a combination of surface elemental analysis and valence electron spectra decomposition, it is shown that an in situ interaction between the 2D perovskite precursor and the 3D active layer results in surface intermixing of 3D and 2D perovskite phases, providing an effective combination of defect passivation and enhanced charge transfer, despite the semi-insulating nature of the 2D perovskite phase. The demonstration of the synergistic interaction of multiple organic spacer cations in a 2D passivation layer offers new opportunities for further enhancement of device performance with mixed dimensional perovskite solar cells.
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The glucagon receptor (GCGR) belongs to the secretin-like (class B) family of G protein-coupled receptors (GPCRs) and is activated by the peptide hormone glucagon. The structures of an activated class B GPCR have remained unsolved, preventing a mechanistic understanding of how these receptors are activated. Using a combination of structural modeling and mutagenesis studies, we present here two modes of ligand-independent activation of GCGR. First, we identified a GCGR-specific hydrophobic lock comprising Met-338 and Phe-345 within the IC3 loop and transmembrane helix 6 (TM6) and found that this lock stabilizes the TM6 helix in the inactive conformation. Disruption of this hydrophobic lock led to constitutive G protein and arrestin signaling. Second, we discovered a polar core comprising conserved residues in TM2, TM3, TM6, and TM7, and mutations that disrupt this polar core led to constitutive GCGR activity. On the basis of these results, we propose a mechanistic model of GCGR activation in which TM6 is held in an inactive conformation by the conserved polar core and the hydrophobic lock. Mutations that disrupt these inhibitory elements allow TM6 to swing outward to adopt an active TM6 conformation similar to that of the canonical ß2-adrenergic receptor complexed with G protein and to that of rhodopsin complexed with arrestin. Importantly, mutations in the corresponding polar core of several other members of class B GPCRs, including PTH1R, PAC1R, VIP1R, and CRFR1, also induce constitutive G protein signaling, suggesting that the rearrangement of the polar core is a conserved mechanism for class B GPCR activation.
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Modelos Moleculares , Receptor Tipo 1 de Hormônio Paratireóideo/agonistas , Receptores de Hormônio Liberador da Corticotropina/agonistas , Receptores de Glucagon/agonistas , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/agonistas , Receptores Tipo I de Polipeptídeo Intestinal Vasoativo/agonistas , Sequência de Aminoácidos , Substituição de Aminoácidos , Sítios de Ligação , Linhagem Celular , Sequência Conservada , Humanos , Interações Hidrofóbicas e Hidrofílicas , Ligantes , Mutagênese Sítio-Dirigida , Mutação , Fragmentos de Peptídeos/agonistas , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/metabolismo , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Estabilidade Proteica , Receptor Tipo 1 de Hormônio Paratireóideo/química , Receptor Tipo 1 de Hormônio Paratireóideo/genética , Receptor Tipo 1 de Hormônio Paratireóideo/metabolismo , Receptores de Hormônio Liberador da Corticotropina/química , Receptores de Hormônio Liberador da Corticotropina/genética , Receptores de Hormônio Liberador da Corticotropina/metabolismo , Receptores de Glucagon/química , Receptores de Glucagon/genética , Receptores de Glucagon/metabolismo , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/química , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/genética , Receptores de Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/metabolismo , Receptores Tipo I de Polipeptídeo Intestinal Vasoativo/química , Receptores Tipo I de Polipeptídeo Intestinal Vasoativo/genética , Receptores Tipo I de Polipeptídeo Intestinal Vasoativo/metabolismo , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Sistemas do Segundo Mensageiro , Homologia Estrutural de ProteínaRESUMO
G protein-coupled receptors (GPCRs) from the secretin-like (class B) family are key players in hormonal homeostasis and are important drug targets for the treatment of metabolic disorders and neuronal diseases. They consist of a large N-terminal extracellular domain (ECD) and a transmembrane domain (TMD) with the GPCR signature of seven transmembrane helices. Class B GPCRs are activated by peptide hormones with their C termini bound to the receptor ECD and their N termini bound to the TMD. It is thought that the ECD functions as an affinity trap to bind and localize the hormone to the receptor. This in turn would allow the hormone N terminus to insert into the TMD and induce conformational changes of the TMD to activate downstream signaling. In contrast to this prevailing model, we demonstrate that human class B GPCRs vary widely in their requirement of the ECD for activation. In one group, represented by corticotrophin-releasing factor receptor 1 (CRF1R), parathyroid hormone receptor (PTH1R), and pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R), the ECD requirement for high affinity hormone binding can be bypassed by induced proximity and mass action effects, whereas in the other group, represented by glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), the ECD is required for signaling even when the hormone is covalently linked to the TMD. Furthermore, the activation of GLP-1R by small molecules that interact with the intracellular side of the receptor is dependent on the presence of its ECD, suggesting a direct role of the ECD in GLP-1R activation.
Assuntos
Receptor do Peptídeo Semelhante ao Glucagon 1/química , Receptor do Peptídeo Semelhante ao Glucagon 1/metabolismo , Receptores Acoplados a Proteínas G/química , Receptores Acoplados a Proteínas G/metabolismo , Receptores de Glucagon/química , Receptores de Glucagon/metabolismo , Sequência de Aminoácidos , Substituição de Aminoácidos , Glucagon/metabolismo , Peptídeo 1 Semelhante ao Glucagon/metabolismo , Receptor do Peptídeo Semelhante ao Glucagon 1/genética , Células HEK293 , Humanos , Modelos Moleculares , Mutagênese Sítio-Dirigida , Domínios Proteicos , Receptores Acoplados a Proteínas G/classificação , Receptores de Glucagon/genética , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Homologia de Sequência de Aminoácidos , Transdução de SinaisRESUMO
A robust solution phase ligand exchange system for lead sulfide (PbS) quantum dots (QDs) in the presence of Pb-thiolate ligands is presented that can better preserve the excitonic absorption and emission features as compared to the conventional ligands. The photoluminescence after ligand exchange of PbS QDs with Pb-thiolate ligand is preserved up to 78% of the original oleate capped PbS QDs.
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AIM: Dominant negative mutant G proteins have provided critical insight into the mechanisms of G protein-coupled receptor (GPCR) signaling, but the mechanisms underlying the dominant negative characteristics are not completely understood. The aim of this study was to determine the structure of the dominant negative Gαi1ß1γ2 G203A/A326S complex (Gi-DN) and to reveal the structural basis of the mutation-induced phenotype of Gαi1ß1γ2. METHODS: The three subunits of the Gi-DN complex were co-expressed with a baculovirus expression system. The Gi-DN heterotrimer was purified, and the structure of its complex with GDP was determined through X-ray crystallography. RESULTS: The Gi-DN heterotrimer structure revealed a dual mechanism underlying the dominant negative characteristics. The mutations weakened the hydrogen bonding network between GDP/GTP and the binding pocket residues, and increased the interactions in the Gα-Gßγ interface. Concomitantly, the Gi-DN heterotrimer adopted a conformation, in which the C-terminus of Gαi and the N-termini of both the Gß and Gγ subunits were more similar to the GPCR-bound state compared with the wild type complex. From these structural observations, two additional mutations (T48F and D272F) were designed that completely abolish the GDP binding of the Gi-DN heterotrimer. CONCLUSION: Overall, the results suggest that the mutations impede guanine nucleotide binding and Gα-Gßγ protein dissociation and favor the formation of the G protein/GPCR complex, thus blocking signal propagation. In addition, the structure provides a rationale for the design of other mutations that cause dominant negative effects in the G protein, as exemplified by the T48F and D272F mutations.
Assuntos
Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/química , Subunidades beta da Proteína de Ligação ao GTP/química , Subunidades gama da Proteína de Ligação ao GTP/química , Sequência de Aminoácidos , Animais , Baculoviridae/genética , Sítios de Ligação , Bovinos , Cristalografia por Raios X , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/genética , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Subunidades beta da Proteína de Ligação ao GTP/genética , Subunidades beta da Proteína de Ligação ao GTP/metabolismo , Subunidades gama da Proteína de Ligação ao GTP/genética , Subunidades gama da Proteína de Ligação ao GTP/metabolismo , Humanos , Simulação de Dinâmica Molecular , Mutação , Ligação Proteica , Conformação Proteica , Receptores Acoplados a Proteínas G/metabolismo , Alinhamento de Sequência , Células Sf9 , SpodopteraRESUMO
Cesium-lead-bromide (CsPbBr3) has shown promise in thin film photovoltaics due to its desirable energy band gap, charge mobility and chemical and thermal stability. The low solubility of its single crystal in organic solvents has driven development of the two-step spin-coating technique. In this work, precursor solutions of different PbBr2 and CsBr concentrations were spin-coated and investigated via Photoelectron Spectroscopy. The properties of the CsxPbyBrz film in cross-section demonstrate this method leads to varying stoichiometries, work functions and band gaps through the thickness. This anisotropy of the perovskite thickness has ramifications for design of photovoltaic devices.
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To understand the impact of binary doping in ZnO, nanosized Zn(Ag, Ni)O systems were synthesized by the sol-gel method. The amount of Ag was fixed at 2 at%, and that of Ni was varied from 1 to 15 at%. Ni incorporation equal to or beyond 3 at% gave rise to the development of the NiO phase. The presence of Ag and Ni did not have much influence on the lattice constants of ZnO. However, a larger addition of Ni impacted the unit cell of NiO, as indicated by the reduction of the lattice constant of NiO. The increase in NiO and Ag contents in ZnO reduced the second and third harmonic intensities under non-linear investigations. X-ray photoelectron spectroscopy analysis indicated that initial Ni addition varied randomly along with Ag, and it stabilized itself at higher concentration. Field emission scanning electron microscopy revealed that interlinked particles and chains with tamarind shapes were formed, closely matching the rod-like structures under high resolution. Ag and Ni addition altered the structures slightly and randomly till 5 at% Ni; thereafter they deviated from the particle shape to flat disc-shapes. Interestingly, the magnetic response of the sample was determined by the NiO phase, and the effect of Ni and Ag substitution in the ZnO host matrix was almost irrelevant at low temperatures toward magnetic contribution. Weak ferromagnetism at low temperatures (≤50 K) with superparamagnetic-like behavior (cusp in ZFC magnetization) was observed in all the samples. This could be attributed to the finite nano-size effect and uncompensated spins at the surface of the particle.
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The NACHT-, leucine-rich-repeat-, and pyrin domain-containing protein 3 (NLRP3) is a critical intracellular inflammasome sensor and an important clinical target against inflammation-driven human diseases. Recent studies have elucidated its transition from a closed cage to an activated disk-like inflammasome, but the intermediate activation mechanism remains elusive. Here we report the cryo-electron microscopy structure of NLRP3, which forms an open octamer and undergoes a ~ 90° hinge rotation at the NACHT domain. Mutations on open octamer's interfaces reduce IL-1ß signaling, highlighting its essential role in NLRP3 activation/inflammasome assembly. The centrosomal NIMA-related kinase 7 (NEK7) disrupts large NLRP3 oligomers and forms NEK7/NLRP3 monomers/dimers which is a critical step preceding the assembly of the disk-like inflammasome. These data demonstrate an oligomeric cooperative activation of NLRP3 and provide insight into its inflammasome assembly mechanism.
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Inflamassomos , Proteína 3 que Contém Domínio de Pirina da Família NLR , Humanos , Proteína 3 que Contém Domínio de Pirina da Família NLR/metabolismo , Inflamassomos/metabolismo , Microscopia Crioeletrônica , Quinases Relacionadas a NIMA/genética , Quinases Relacionadas a NIMA/metabolismo , ProteínasRESUMO
Damaged DNA-binding protein-1 (DDB1)- and CUL4-associated factor 12 (DCAF12) serves as the substrate recognition component within the Cullin4-RING E3 ligase (CRL4) complex, capable of identifying C-terminal double-glutamic acid degrons to promote the degradation of specific substrates through the ubiquitin proteasome system. Melanoma-associated antigen 3 (MAGEA3) and T-complex protein 1 subunit epsilon (CCT5) proteins have been identified as cellular targets of DCAF12. To further characterize the interactions between DCAF12 and both MAGEA3 and CCT5, we developed a suite of biophysical and proximity-based cellular NanoBRET assays showing that the C-terminal degron peptides of both MAGEA3 and CCT5 form nanomolar affinity interactions with DCAF12 in vitro and in cells. Furthermore, we report here the 3.17â Å cryo-EM structure of DDB1-DCAF12-MAGEA3 complex revealing the key DCAF12 residues responsible for C-terminal degron recognition and binding. Our study provides new insights and tools to enable the discovery of small molecule handles targeting the WD40-repeat domain of DCAF12 for future proteolysis targeting chimera design and development.
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Chromium oxide (Cr2O3) is a beneficial metal oxide used to prevent the backward reaction in photocatalytic water splitting. The present work investigates the stability, oxidation state, and the bulk and surface electronic structure of Cr-oxide photodeposited onto P25, BaLa4Ti4O15, and Al:SrTiO3 particles as a function of the annealing process. The oxidation state of the Cr-oxide layer as deposited is found to be Cr2O3 on the surface of P25 and Al:SrTiO3 particles and Cr(OH)3 on BaLa4Ti4O15. After annealing at 600 °C, for P25 (a mixture of rutile and anatase TiO2), the Cr2O3 layer diffuses into the anatase phase but remains at the surface of the rutile phase. For BaLa4Ti4O15, Cr(OH)3 converts to Cr2O3 upon annealing and diffuses slightly into the particles. However, for Al:SrTiO3, the Cr2O3 remains stable at the surface of the particles. The diffusion here is due to the strong metal-support interaction effect. In addition, some of the Cr2O3 on the P25, BaLa4Ti4O15, and Al:SrTiO3 particles is reduced to metallic Cr after annealing. The effect of Cr2O3 formation and diffusion into the bulk on the surface and bulk band gaps is investigated with electronic spectroscopy, electron diffraction, DRS, and high-resolution imaging. The implications of the stability and diffusion of Cr2O3 for photocatalytic water splitting are discussed.
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Radio frequency (RF) magnetron sputtering allows the fabrication of TiO2 films with high purity, reliable control of film thickness, and uniform morphology. In the present study, the change in surface roughness upon heating two different thicknesses of RF sputter-deposited TiO2 films was investigated. As a measure of the process of the change in surface morphology, chemically -synthesised phosphine-protected Au9 clusters covered by a photodeposited CrOx layer were used as a probe. Subsequent to the deposition of the Au9 clusters and the CrOx layer, samples were heated to 200 â to remove the triphenylphosphine ligands from the Au9 cluster. After heating, the thick TiO2 film was found to be mobile, in contrast to the thin TiO2 film. The influence of the mobility of the TiO2 films on the Au9 clusters was investigated with X-ray photoelectron spectroscopy. It was found that the high mobility of the thick TiO2 film after heating leads to a significant agglomeration of the Au9 clusters, even when protected by the CrOx layer. The thin TiO2 film has a much lower mobility when being heated, resulting in only minor agglomeration of the Au9 clusters covered with the CrOx layer.
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The M. tuberculosis (Mtb) ClpB is a protein disaggregase that helps to rejuvenate the bacterial cell. DnaK is a protein foldase that can function alone, but it can also bind to the ClpB hexamer to physically couple protein disaggregation with protein refolding, although the molecular mechanism is not well understood. Here, we report the cryo-EM analysis of the Mtb ClpB-DnaK bi-chaperone in the presence of ATPγS and a protein substrate. We observe three ClpB conformations in the presence of DnaK, identify a conserved TGIP loop linking the oligonucleotide/oligosaccharide-binding domain and the nucleotide-binding domain that is important for ClpB function, derive the interface between the regulatory middle domain of the ClpB and the DnaK nucleotide-binding domain, and find that DnaK binding stabilizes, but does not bend or tilt, the ClpB middle domain. We propose a model for the synergistic actions of aggregate dissolution and refolding by the Mtb ClpB-DnaK bi-chaperone system.
Assuntos
Proteínas de Bactérias/metabolismo , Endopeptidase Clp/metabolismo , Proteínas de Escherichia coli/metabolismo , Mycobacterium tuberculosis/genética , Modelos Moleculares , Redobramento de ProteínaRESUMO
Graphene supported transition metal clusters are of great interest for potential applications, such as catalysis, due to their unique properties. In this work, a simple approach to deposit Au101(PPh3)21Cl5 (Au101NC) on reduced graphene oxide (rGO) via an ex situ method is presented. Reduction of graphene oxide at native pH (pH ≈ 2) to rGO was performed under aqueous hydrothermal conditions. Decoration of rGO sheets with controlled content of 5 wt% Au was accomplished using only pre-synthesised Au101NC and rGO as precursors and methanol as solvent. High resolution scanning transmission electron microscopy indicated that the cluster size did not change upon deposition with an average diameter of 1.4 ± 0.4 nm. It was determined that the rGO reduction method was crucial to avoid agglomeration, with rGO reduced at pH ≈ 11 resulting in agglomeration. X-ray photoelectron spectroscopy was used to confirm the deposition of Au101NCs and show the presence of triphenyl phosphine ligands, which together with attenuated total reflectance Fourier transform infrared spectroscopy, advocates that the deposition of Au101NCs onto the surface of rGO was facilitated via non-covalent interactions with the phenyl groups of the ligands. Inductively coupled plasma mass spectrometry and thermogravimetric analysis were used to determine the gold loading and both agree with a gold loading of ca. 4.8-5 wt%. The presented simple and mild strategy demonstrates that good compatibility between size-specific phosphine protected gold clusters and rGO can prevent aggregation of the metal clusters. This work contributes towards producing an agglomeration-free synthesis of size-specific ligated gold clusters on rGO that could have wide range of applications.
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A polymer made from equal masses of sulfur and canola oil was carbonised at 600 °C for 30 minutes. The resulting material exhibited improved uptake of mercury from water compared to the polymer. The carbonisation could also be done after using the polymer to clean up oil spills, which suprisingly improved mercury uptake to levels rivaling commercial carbons.