Chirality in Bare and Passivated Gold Nanoclusters

Chiral structures have been found as the lowest-energy isomers of bare (Au$_{28}$ and Au$_{55}) and thiol-passivated (Au$_{28}(SCH$_{3})$_{16}$and Au$_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in the chiral clusters was calculated using the Hausdorff chirality measure. We found that the index of chirality is higher in the passivated clusters and decreases with the cluster size. These results are consistent with the observed chiroptical activity recently reported for glutahione-passivated gold nanoclusters, and provide theoretical support for the existence of chirality in these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR

Aromaticity in a Surface Deposited Cluster: Pd4_4 on TiO2_2 (110)

We report the presence of \sigma-aromaticity in a surface deposited cluster, Pd$_4$ on TiO$_2$ (110). In the gas phase, Pd$_4$ adopts a tetrahedral structure. However, surface binding promotes a flat, \sigma-aromatic cluster. This is the first time aromaticity is found in surface deposited clusters. Systems of this type emerge as a promising class of catalyst, and so realization of aromaticity in them may help to rationalize their reactivity and catalytic properties, as a function of cluster size and composition.Comment: 4 pages, 3 figure

Green electrochemical template synthesis of CoPt nanoparticles with tunable size, composition, and magnetism from microemulsions using an ionic liquid (bmimPF6)

Altres ajuts: Substrates have been prepared in IMB-CNM (CSIC),supported by the (CSIC) NGG-258 project.Electrodeposition from microemulsions using ionic liquids is revealed as a green method for synthesizing magnetic alloyed nanoparticles, avoiding the use of aggressive reducing agents. Microemulsions containing droplets of aqueous solution (electrolytic solution containing Pt(IV) and Co(II) ions) in an ionic liquid (bmimPF) define nanoreactors in which the electrochemical reduction takes place. Highly crystalline hcp alloyed CoPt nanoparticles, in the 10-120 nm range with a rather narrow size distribution, have been deposited on a conductive substrate. The relative amount of aqueous solution to ionic liquid determines the size of the nanoreactors, which serve as nanotemplates for the growth of the nanoparticles and hence determine their size and distribution. Further, the stoichiometry (PtCo) of the particles can be tuned by the composition of the electrolytic solution inside the droplets. The control of the size and composition of the particles allows tailoring the room-temperature magnetic behavior of the nanoparticles from superparaparamagnetic to hard magnetic (with a coercivity of H = 4100 Oe) in the as-obtained state. © 2014 American Chemical Society

High activity redox catalysts synthesized by chemical vapor impregnation

The use of precious metals in heterogeneous catalysis relies on the preparation of small nanoparticles that are stable under reaction conditions. To date, most conventional routes used to prepare noble metal nanoparticles have drawbacks related to surface contamination, particle agglomeration, and reproducibility restraints. We have prepared titania-supported palladium (Pd) and platinum (Pt) catalysts using a simplified vapor deposition technique termed chemical vapor impregnation (CVI) that can be performed in any standard chemical laboratory. These materials, composed of nanoparticles typically below 3 nm in size, show remarkable activity under mild conditions for oxidation and hydrogenation reactions of industrial importance. We demonstrate the preparation of bimetallic Pd–Pt homogeneous alloy nanoparticles by this new CVI method, which show synergistic effects in toluene oxidation. The versatility of our CVI methodology to be able to tailor the composition and morphology of supported nanoparticles in an easily accessible and scalable manner is further demonstrated by the synthesis of Pdshell–Aucore nanoparticles using CVI deposition of Pd onto preformed Au nanoparticles supported on titania (prepared by sol immobilization) in addition to the presence of monometallic Au and Pd nanoparticles

The CDK-Activating Kinase (CAK) Csk1 Is Required for Normal Levels of Homologous Recombination and Resistance to DNA Damage in Fission Yeast

BACKGROUND: Cyclin-dependent kinases (CDKs) perform essential roles in cell division and gene expression in all eukaryotes. The requirement for an upstream CDK-activating kinase (CAK) is also universally conserved, but the fission yeast Schizosaccharomyces pombe appears to be unique in having two CAKs with both overlapping and specialized functions that can be dissected genetically. The Mcs6 complex--orthologous to metazoan Cdk7/cyclin H/Mat1--activates the cell-cycle CDK, Cdk1, but its non-redundant essential function appears to be in regulation of gene expression, as part of transcription factor TFIIH. The other CAK is Csk1, an ortholog of budding yeast Cak1, which activates all three essential CDKs in S. pombe--Cdk1, Mcs6 and Cdk9, the catalytic subunit of positive transcription elongation factor b (P-TEFb)--but is not itself essential. METHODOLOGY/PRINCIPAL FINDINGS: Cells lacking csk1(+) are viable but hypersensitive to agents that damage DNA or block replication. Csk1 is required for normal levels of homologous recombination (HR), and interacts genetically with components of the HR pathway. Tests of damage sensitivity in csk1, mcs6 and cdk9 mutants indicate that Csk1 acts pleiotropically, through Cdk9 and at least one other target (but not through Mcs6) to preserve genomic integrity. CONCLUSIONS/SIGNIFICANCE: The two CAKs in fission yeast, which differ with respect to their substrate range and preferences for monomeric CDKs versus CDK/cyclin complexes as substrates, also support different functions of the CDK network in vivo. Csk1 plays a non-redundant role in safeguarding genomic integrity. We propose that specialized activation pathways dependent on different CAKs might insulate CDK functions important in DNA damage responses from those capable of triggering mitosis

Genetics of photoreceptor degeneration and regeneration in zebrafish

Zebrafish are unique in that they provide a useful model system for studying two critically important problems in retinal neurobiology, the mechanisms responsible for triggering photoreceptor cell death and the innate stem cell–mediated regenerative response elicited by this death. In this review we highlight recent seminal findings in these two fields. We first focus on zebrafish as a model for studying photoreceptor degeneration. We summarize the genes currently known to cause photoreceptor degeneration, and we describe the phenotype of a few zebrafish mutants in detail, highlighting the usefulness of this model for studying this process. In the second section, we discuss the several different experimental paradigms that are available to study regeneration in the teleost retina. A model outlining the sequence of gene expression starting from the dedifferentiation of Müller glia to the formation of rod and cone precursors is presented

CD133+ adult human retinal cells remain undifferentiated in Leukaemia Inhibitory Factor (LIF)

<p>Abstract</p> <p>Background</p> <p>CD133 is a cell surface marker of haematopoietic stem and progenitor cells. Leukaemia inhibitory factor (LIF), sustains proliferation and not differentiation of embryonic stem cells. We used CD133 to purify adult human retinal cells and aimed to determine what effect LIF had on these cultures and whether they still had the ability to generate neurospheres.</p> <p>Methods</p> <p>Retinal cell suspensions were derived from adult human post-mortem tissue with ethical approval. With magnetic automated cell sorting (MACS) CD133⁺retinal cells were enriched from post mortem adult human retina. CD133⁺retinal cell phenotype was analysed by flow cytometry and cultured cells were observed for proliferative capacity, neuropshere generation and differentiation with or without LIF supplementation.</p> <p>Results</p> <p>We demonstrated purification (to 95%) of CD133⁺cells from adult human postmortem retina. Proliferating cells were identified through BrdU incorporation and expression of the proliferation markers Ki67 and Cyclin D1. CD133⁺retinal cells differentiated whilst forming neurospheres containing appropriate lineage markers including glia, neurons and photoreceptors. LIF maintained CD133⁺retinal cells in a proliferative and relatively undifferentiated state (Ki67, Cyclin D1 expression) without significant neurosphere generation. Differentiation whilst forming neurospheres was re-established on LIF withdrawal.</p> <p>Conclusion</p> <p>These data support the evidence that CD133 expression characterises a population of cells within the resident adult human retina which have progenitor cell properties and that their turnover and differentiation is influenced by LIF. This may explain differences in retinal responses observed following disease or injury.</p