A versatile synthesis of meyers' bicyclic lactams from furans: singlet-oxygen-initiated reaction cascade

All in one: Meyers' bicyclic lactams were synthesized in high yield from furans using a new and powerful method that involves a one-pot singlet-oxygen-initiated reaction cascade (see scheme; TFA=trifluoroacetic acid). This method has broad synthetic potential because of the ease of access to a wide range of furans with a variety of substituents.     

Cyclodextrin cavity size effect on the complexation and rotational dynamics of the laser dye 2,5-diphenyl-1,3,4-oxadiazole: from singly occupied complexes to their nanotubular self-assemblies

The general complexation scheme as well as the dynamic features of the supramolecular structures resulting from the interaction of the laser dye 2,5-diphenyl-1,3,4-oxadiazole (PPD) with the naturally occurring alpha-, beta-, and gamma-cyclodextrins in water are studied by means of fluorescence spectroscopy, both steady-state (SS) and time-resolved (TR). PPD interacts weakly, from a thermodynamic point of view, with alpha-cyclodextrin (alpha-CD), forming 1:1 complexes with an association constant of K(11) = 85 +/- 4 M(-1). However, the local motion of the substrate (PPD) with respect to the ligand (CD) in the complexed form is hindered; namely, dynamically, they are strongly coupled and only a global tumbling motion, = 370 +/- 30 ps, of the whole adduct is observed. The next homologue beta-CD also forms 1:1 entities with PPD, but although the binding strength of reactants (K(11) = 682 +/- 60 M(-1)) is almost an order of magnitude greater than the former case with the alpha-CD, these are dynamically weakly coupled. In fact, two independent motions are detected: one is that of the whole nanostructure motion (1:1, PPD/beta-CD) with a global rotational relaxation time of = 480 +/- 30 ps, and the other is an internal librational motion of the dye inside the host cavity with an average angular displacement of theta approximately 27 degrees . Finally, the interaction of PPD with the wider and more flexible cavity of the gamma-CD "triggers" a self-associative scheme of the initially formed supramolecular building blocks, namely, singly occupied complexes, leading to the formation of nanotubular superstructures. It is found that these linear arrays are constituted from more than 17 gamma-CD units which are held together with the aid of dimers of PPD. Interestingly, our results supported that two distinct dimeric forms of PPD play the role of the "shaft" between adjacent cyclodextrin units. The topology of the dimers in the interlinking space of gamma-CD units is such that PPD molecules are held in suitable proximity, resulting, upon excitation, in the observation of dual excimer emission.     

Advancing Hydrovoltaic Energy Harvesting from Wood through Cell Wall Nanoengineering

Converting omnipresent environmental energy through the assistance of spontaneous water evaporation is an emerging technology for sustainable energy systems. Developing bio-based hydrovoltaic materials further pushes the sustainability, where wood is a prospect due to its native hydrophilic and anisotropic structure. However, current wood-based water evaporation-assisted power generators are facing the challenge of low power density. Here, an efficient hydrovoltaic wood power generator is reported based on wood cell wall nanoengineering. A highly porous wood with cellulosic network filling the lumen is fabricated through a green, one-step treatment using sodium hydroxide to maximize the wood surface area, introduce chemical functionality, and enhance the cell wall permeability of water. An open-circuit potential of ≈140 mV in deionized water is realized, over ten times higher than native wood. Further tuning the pH difference between wood and water, due to an ion concentration gradient, a potential up to 1 V and a remarkable power output of 1.35 µW cm⁻² is achieved. The findings in this study provide a new strategy for efficient wood power generators.     

An intelligent agent negotiation strategy in the electronic marketplace environment

E-commerce will strongly penetrate the market if coupled with appropriate technologies and mechanisms. Mobile agents may enhance the intelligence and improve the efficiency of systems in the e-marketplace. We propose a dynamic multi-lateral negotiation model and construct an efficient negotiation strategy based on a ranking mechanism that does not require a complicated rationale on behalf of the buyer agents. This strategy can be used to extend the functionality of autonomous intelligent agents, so that they quickly reach to an agreement aiming to maximise their owner’s utility. The framework proposed considers both contract and decision issues, is based on real market conditions, and has been empirically evaluated. Moreover, it is shown that in a linear framework like the one we employ, more elaborate ranking mechanisms do not necessarily improve efficiency.     

Controlled free‐radical polymerization of 2‐vinylpyridine in the presence of nitroxides

Bulk free‐radical polymerization of 2‐vinylpyridine (2VP) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was studied under different conditions (temperature and presence of additives). Linear poly‐(2‐vinylpyridine) with a narrow molecular weight distribution and controllable molecular weight was prepared in the presence of acetic anhydride at 95 °C up to a conversion of 66%. At higher conversions side reactions became very important (pseudoliving polymerization). By applying this procedure, well‐defined random copolymers of 2VP with styrene or tert‐butylmethacrylate as well as block copolymers of 2VP with styrene were synthesized. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2889–2895, 2001     

-bounds for spectral multipliers on graphs

We prove that certain spectral multipliers associated with the discrete Laplacian on graphs satisfying the doubling volume property and the Poincaré inequality are bounded on the Hardy space .

     

Discovery and Biosynthesis of Bolagladins: Unusual Lipodepsipeptides from Burkholderia gladioli Clinical Isolates**

Two Burkholderia gladioli strains isolated from the lungs of cystic fibrosis patients were found to produce unusual lipodepsipeptides containing a unique citrate-derived fatty acid and a rare dehydro-β-alanine residue. The gene cluster responsible for their biosynthesis was identified by bioinformatics and insertional mutagenesis. In-frame deletions and enzyme activity assays were used to investigate the functions of several proteins encoded by the biosynthetic gene cluster, which was found in the genomes of about 45 % of B. gladioli isolates, suggesting that its metabolic products play an important role in the growth and/or survival of the species. The Chrome Azurol S assay indicated that these metabolites bind ferric iron, which suppresses their production when added to the growth medium. Moreover, a gene encoding a TonB-dependent ferric-siderophore receptor is adjacent to the biosynthetic genes, suggesting that these metabolites may function as siderophores in B. gladioli.     

Density functional study of structural, electronic, and optical properties of small bimetallic ruthenium-copper clusters

The structural, electronic, bonding, magnetic, and optical properties of bimetallic [Cu(n)Ru(m)](+/0/-) (n + m ≤ 3; n, m = 0-3) clusters were computed in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) using the full-range PBE0 nonlocal hybrid GGA functional combined with the Def2-QZVPP basis sets. Several low-lying states have been investigated and the stability of the ground state spinomers was estimated with respect to all possible fragmentation schemes. Molecular orbital and population analysis schemes along with computed electronic parameters illustrated the details of the bonding mechanisms in the [Cu(n Ru(m)](+/0/-) clusters. The TD-DFT computed UV-visible absorption spectra of the bimetallic clusters have been fully analyzed and assignments of all principal electronic transitions were made and interpreted in terms of contribution from specific molecular orbital excitations.     

Dual reactivity disulfide bridging reagents; enabling new approaches to antibody fragment bioconjugation

Disulfide bridging, also known as disulfide stapling, is a powerful strategy for the construction of site-selective protein bioconjugates. Here we describe the first examples of a new class of such reagents, containing a ‘stable-labile’ design. These dual-reactive reagents are designed to form a stable bond to one cysteine and a labile bond to the second; resulting in a robust attachment to the protein with one end of the bridge, whilst the other end serves as a reactive handle for subsequent bioconjugation. By incorporating thioesters into these bridges, we demonstrate that they are primed for native chemical ligation (NCL) with N-terminal cysteines; offering an alternative to the requirement for C-terminal thioesters for use in such ligations. Alternatively, the use of hydrazine as the ligating nucleophile enables a separate cargo to be attached to each cysteine residue, which are exploited to insert variably cleavable linkers. These methodologies are demonstrated on an antibody fragment, and serve to expand the scope of disulfide bridging strategies whilst offering a convenient route to the construction of multifunctional antibody fragment conjugates.

Here we describe the first examples of a new class of disulfide bridging reagents, designed to insert a ‘stable-labile’ linkage; which can then be exploited to generate dual functional antibody fragment conjugates.