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The first catalytic enantioselective isomerization of secondary allylic alcohols to access ketones with a α-tertiary stereocenter is presented. The racemic allylic alcohol substrates can be converted to the enantioenriched ketone products in a stereoconvergent fashion. The use of commercially available catalysts and mild reaction conditions makes this an attractive method in stereoselective synthesis. [ABSTRACT FROM AUTHOR]

Domain swapping creates protein oligomers by exchange of structural units between identical monomers. At present, no unifying molecular mechanism of domain swapping has emerged. Here we used the protein Cyanovirin-N (CV-N) and 19F-NMR to investigate the process of domain swapping. CV-N is an HIV inactivating protein that can exist as a monomer or a domain-swapped dimer. We measured thermodynamic and kinetic parameters of the conversion process and determined the size of the energy barrier between the two species. The barrier is very large and of similar magnitude to that for equilibrium unfolding of the protein. Therefore, for CV-N, overall unfolding of the polypeptide is required for domain swapping. [ABSTRACT FROM AUTHOR]

The prion protein (PrP) takes up 4-6 equiv of copper in its extended N-terminal domain, composed of the octarepeat (OR) segment (human sequence residues 60-91) and two mononuclear binding sites (at His96 and His111; also referred to as the non-OR region). The OR segment responds to specific copper concentrations by transitioning from a multi-His mode at low copper levels to a single-His, amide nitrogen mode at high levels (Chattopadhyay et al. J. Am. Chem. Soc.2005, 127, 12647-12656). The specific function of PrP in healthy tissue is unclear, but numerous reports link copper uptake to a neuroprotective role that regulates cellular stress (Stevens, et al. PLoS Pathog.2009, 5 (4), e1000390). A current working hypothesis is that the high occupancy binding mode quenches copper's inherent redox cycling, thus, protecting against the production of reactive oxygen species from unregulated Fenton type reactions. Here, we directly test this hypothesis by performing detailed pH-dependent electrochemical measurements on both low and high occupancy copper binding modes. In contrast to the current belief, we find that the low occupancy mode completely quenches redox cycling, but high occupancy leads to the gentle production of hydrogen peroxide through a catalytic reduction of oxygen facilitated by the complex. These electrochemical findings are supported by independent kinetic measurements that probe for ascorbate usage and also peroxide production. Hydrogen peroxide production is also observed from a segment corresponding to the non-OR region. Collectively, these results overturn the current working hypothesis and suggest, instead, that the redox cycling of copper bound to PrP in the high occupancy mode is not quenched, but is regulated. The observed production of hydrogen peroxide suggests a mechanism that could explain PrP's putative role in cellular signaling. [ABSTRACT FROM AUTHOR]

As the population ages, the need to develop methods to understand and intercept the processes responsible for protein aggregation diseases is becoming more urgent. The aggregation of the protein β-amyloid (Aβ) has been implicated in Alzheimer's Disease (AD); however, whether the toxic species is a large, insoluble aggregate or some lower order form is not yet known. Agents that can modulate the aggregation state of Aβ could resolve this controversy by facilitating our understanding of the consequences of aggregation and its underlying mechanism. To date, however, ligands that bind to specific forms of Aβ have not been identified. To address this deficiency, we tested whether phage display could yield such ligands by screening libraries against Aβ in two different states: monomeric or highly aggregated. Intriguingly, the peptides selected had different effects on Aβ aggregation. Peptides selected for binding to monomeric Aβ did not perturb aggregation, but those selected using highly aggregated Aβ increase the rate of aggregation drastically. The latter also alter the morphology of the resulting aggregate. The ability of a peptide to promote aggregation correlated with its affinity for the N-terminal 10 residues of Aβ. This result indicates that the mechanism by which the peptides influence aggregation is related to their affinity for the Aβ N-terminus. Thus, the identification of compounds that bind to this Aβ section can afford agents that affect aggregation. Moreover, the data suggest that endogenous ligands that interact with the N-terminal region can influence the propensity of Aβ to form aggregates and the morphology of those that form. Our data highlight the utility of phage display for identifying ligands that bind to target proteins in different states, and they indicate that such agents can be used to perturb protein aggregation. [ABSTRACT FROM AUTHOR]

We report a highly enantioselective Morita-Baylis-Hillman (MBH) reaction of isatins and acrolein to provide enantiomerically enriched 3-substituted 3-hydroxyoxindoles, which could serve as valuable synthetic building blocks. This is also the first time that a ketone has been used as the electrophile and acrolein as the nucleophile in a highly enantioselective catalytic asymmetric MBH reaction. Hatakeyama's catalyst, β-isocupreidine (1), turned out to be a powerful catalyst for this transformation. [ABSTRACT FROM AUTHOR]

Discusses the catalytic growth and characterization of gallium nitride nanowires. Systematic optimization of GaN nanowire growth; Vapor-liquid-solid growth of GaN nanowires; Structural characterization; Photoluminescence spectroscopy; Raman spectroscopy.

The article presents a study which examines the self-assembly approach for the ternary semiconducting tellurium-iron-copper (Te-Fe-Cu) carbonyl polymers. The construction of supramolecules has been a common focus of the research, but the ternary CuFeE2 are the most commonly known semiconducting materials. It concludes that Te-Fe-Cu polymers displays semiconductor properties, but needs further studies.