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Continuous flow chemistry is used to trap the nucleation and growth stages of platinum-nickel nano-octahedra with second time resolution and high throughputs to probe their properties ex situ. The growth starts from poorly crystalline particles (nucleation) at 5 seconds, to crystalline 1.5 nm particles bounded by the {111}-facets at 7.5 seconds, followed by truncation and further growth to octahedral nanoparticles at 20 seconds.

Engineering the surface ligands of metal nanoparticles is critical in designing unique arrangements of metal atoms. Here, we report the synthesis and total structure determination of a large box-shaped Ag 67 nanocluster (NC) protected by a mixed shell of thiolate (2,4-dimethylbenzenethiolate, SPhMe 2 ) and phosphine (triphenylphosphine, PPh 3 ) ligands. Single crystal X-ray diffraction (SCXRD) and electrospray ionization mass spectrometry (ESI-MS) revealed the cluster formula to be [Ag 67 (SPhMe 2 ) 32 (PPh 3 ) 8 ] 3+ . The crystal structure shows an Ag 23 metal core covered by a layer of Ag 44 S 32 P 8 arranged in the shape of a box. The Ag 23 core was formed through an unprecedented centered cuboctahedron, i.e., Ag 13 , unlike the common centered Ag 13 icosahedron geometry. Two types of ligand motifs, eight AgS 3 P and eight bridging thiols, were found to stabilize the whole cluster. The optical spectrum of this NC displayed highly structured multiple absorption peaks. The electronic structure and optical spectrum of Ag 67 were computed using time-dependent density functional theory (TDDFT) for both the full cluster [Ag 67 (SPhMe 2 ) 32 (PPh 3 ) 8 ] 3+ and a reduced model [Ag 67 (SH) 32 (PH 3 ) 8 ] 3+ . The lowest metal-to-metal transitions in the range 500-800 nm could be explained by considering the reduced model that shows almost identical electronic states to 32 free electrons in a jellium box. The successful synthesis of the large box-shaped Ag 67 NC facilitated by the combined use of phosphine and thiol paves the way for synthesizing other metal clusters with unprecedented shapes by judicious choice of thiols and phosphines.

Hybrid organic/inorganic perovskites have recently emerged as an important class of materials and have exhibited remarkable performance in photovoltaics. To further improve their device efficiency, an insightful understanding of the interfacial charge transfer (CT) process is required. Here, we report the first direct experimental observation of the tremendous effect that the shape of perovskite nanocrystals (NCs) has on interfacial CT in the presence of a molecular acceptor. A dramatic change in CT dynamics at the interfaces of three different NC shapes, spheres, platelets, and cubes, is recorded. Our results clearly demonstrate that the mechanism of CT is significantly affected by the NC shape. More importantly, the results demonstrate that complexation on the NC surface acts as an additional driving force not only to tune the CT dynamics but also to control the reaction mechanism at the interface. This observation opens a new venue for further developing perovskite NCs-based applications.

Controlling the rate of softening to extend shelf life was a key target for researchers engineering genetically modified (GM) tomatoes in the 1990s, but only modest improvements were achieved. Hybrids grown nowadays contain 'non-ripening mutations' that slow ripening and improve shelf life, but adversely affect flavor and color. We report substantial, targeted control of tomato softening, without affecting other aspects of ripening, by silencing a gene encoding a pectate lyase.

Chiral mixed ligand silver nanoclusters were synthesized in the presence of a chiral and an achiral ligand. While the chiral ligand led mostly to the formation of nanoparticles, the presence of the achiral ligand drastically increased the yield of nanoclusters with enhanced chiral properties.

Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV(2+)) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs.

The canonical action of the p85α regulatory subunit of phosphatidylinositol 3-kinase (PI3K) is to associate with the p110α catalytic subunit to allow stimuli-dependent activation of the PI3K pathway. We elucidate a p110α-independent role of homodimerized p85α in the positive regulation of PTEN stability and activity. p110α-free p85α homodimerizes via two intermolecular interactions (SH3:proline-rich region and BH:BH) to selectively bind unphosphorylated activated PTEN. As a consequence, homodimeric but not monomeric p85α suppresses the PI3K pathway by protecting PTEN from E3 ligase WWP2-mediated proteasomal degradation. Further, the p85α homodimer enhances the lipid phosphatase activity and membrane association of PTEN. Strikingly, we identified cancer patient-derived oncogenic p85α mutations that target the homodimerization or PTEN interaction surface. Collectively, our data suggest the equilibrium of p85α monomer-dimers regulates the PI3K pathway and disrupting this equilibrium could lead to disease development.

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.

Sedimentation equilibrium (analytical ultracentrifugation) is one of the most inherently suitable methods for the determination of average molecular weights and molecular weight distributions of polymers, because of its absolute basis (no conformation assumptions) and inherent fractionation ability (without the need for columns or membranes and associated assumptions over inertness). With modern instrumentation it is also possible to run up to 21 samples simultaneously in a single run. Its application has been severely hampered because of difficulties in terms of baseline determination (incorporating estimation of the concentration at the air/solution meniscus) and complexity of the analysis procedures. We describe a new method for baseline determination based on a smart-smoothing principle and built into the highly popular platform SEDFIT for the analysis of the sedimentation behavior of natural and synthetic polymer materials. The SEDFIT-MSTAR procedure - which takes only a few minutes to perform - is tested with four synthetic data sets (including a significantly non-ideal system), a naturally occurring protein (human IgG1) and two naturally occurring carbohydrate polymers (pullulan and λ-carrageenan) in terms of (i) weight average molecular weight for the whole distribution of species in the sample (ii) the variation in "point" average molecular weight with local concentration in the ultracentrifuge cell and (iii) molecular weight distribution.

Rrp6 is a key catalytic subunit of the nuclear RNA exosome that plays a pivotal role in the processing, degradation, and quality control of a wide range of cellular RNAs. Here we report our findings on the assembly of the complex involving Rrp6 and its associated protein Rrp47, which is required for many Rrp6-mediated RNA processes. Recombinant Rrp47 is expressed as a non-globular homodimer. Analysis of the purified recombinant Rrp6·Rrp47 complex revealed a heterodimer, suggesting that Rrp47 undergoes a structural reconfiguration upon interaction with Rrp6. Studies using GFP fusion proteins show that Rrp6 and Rrp47 are localized to the yeast cell nucleus independently of one another. Consistent with this data, Rrp6, but not Rrp47, is found associated with the nuclear import adaptor protein Srp1. We show that the interaction with Rrp6 is critical for Rrp47 stability in vivo; in the absence of Rrp6, newly synthesized Rrp47 is rapidly degraded in a proteasome-dependent manner. These data resolve independent nuclear import routes for Rrp6 and Rrp47, reveal a structural reorganization of Rrp47 upon its interaction with Rrp6, and demonstrate a proteasome-dependent mechanism that efficiently suppresses the expression of Rrp47 in the absence of Rrp6.

Mucins are the key macromolecular component of mucus, nature's natural lubricant, and one of the most important physical properties is their molecular weight distribution. A new approach for polydisperse polymers was recently published based on sedimentation velocity in the analytical ultracentrifuge and converts a distribution of sedimentation coefficient g(s) vs. s plot into a distribution of molecular weight utilising the power-law or scaling relationship between the sedimentation coefficient and molecular weight, s=κsMw(b) where s is the sedimentation coefficient, Mw is the weight average molecular weight and κs and b are characteristic coefficients related to conformation. We investigate the possibility of using a large database of previously published values of s an M to define κs and b for both aqueous solution and aqueous solution supplemented by 6M guanidine hydrochloride (a solvent which helps to minimise sample degradation). These values are then applied to a study of the molecular weight distributions of preparations of human gastric mucin in the different solvents and at different stages of purification., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

This investigation establishes a likely order of magnitude for the zero-time correction factor governing the effective time of centrifugation that is pertinent in the analysis of boundary spreading in sedimentation velocity experiments. This correction is shown to be too small to unduly affect the magnitudes of sedimentation and diffusion coefficients deduced from the application of computer software incorporating the printout value of ω²t and an effective position of the air-solution meniscus that is obtained as an additional parameter in the analysis involving nonlinear least-squares curve-fitting of sedimentation velocity distributions to the Lamm equation. Although this procedure slightly underestimates the actual meniscus position (r(a)), uncertainty about its exact location precludes adoption of the alternative approach with r(a) fixed and the correction to ω²t regarded as the additional curve-fitting parameter., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Hydrodynamic studies of miniagrin indicate a molar mass that is 20% larger than the value calculated from the sequence of this genetically engineered protein. Consistent with this finding is the negative sign and also the magnitude of the second virial coefficient obtained from small-angle X-ray scattering measurements. The inference that miniagrin reversibly self-associates is confirmed by a sedimentation equilibrium study that yields an equilibrium constant of 0.24 L/g for a putative monomer-dimer interaction. Finally, Guinier analysis of the small-angle X-ray scattering (SAXS) results yields concentration-dependent values for the radius of gyration that may be described by the monomer-dimer model and respective R(g) values of 40 and 105 Å for the monomeric and dimeric miniagrin species. Although intermolecular protein interactions are endemic in the events leading to acetylcholine receptor aggregation by agrin, the matrix proteoglycan of which miniagrin is a miniaturized model, this investigation raises the possibility that agrin may itself self-associate., (© 2011 American Chemical Society)

Ubiquitin specific protease 15 (USP15) functions in COP9 signalosome mediated regulation of protein degradation and cellular signaling through catalyzing the ubiquitin deconjugation reaction of a discrete number of substrates. It influences the stability of adenomatous polyposis coli, IκBα, caspase-3, and the human papillomavirus type 16 E6. USP15 forms a subfamily with USP4 and USP11 related through a shared presence of N-terminal "domain present in ubiquitin specific proteases" (DUSP) and "ubiquitin-like" (UBL) domains (DU subfamily). Here we report the 1.5 Å resolution crystal structure of the human USP15 N-terminal domains revealing a 80 Å elongated arrangement with the DU domains aligned in tandem. This architecture is generated through formation of a defined interface that is dominated by an intervening β-hairpin structure (DU finger) that engages in an intricate hydrogen-bonding network between the domains. The UBL domain is closely related to ubiquitin among β-grasp folds but is characterized by the presence of longer loop regions and different surface characteristics, indicating that this domain is unlikely to act as ubiquitin mimic. Comparison with the related murine USP4 DUSP-UBL crystal structure reveals that the main DU interdomain contacts are conserved. Analytical ultracentrifugation, small-angle X-ray scattering, and gel filtration experiments revealed that USP15 DU is monomeric in solution. Our data provide a framework to advance study of the structure and function of the DU subfamily., (© 2011 American Chemical Society)