Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives

A series of 2,5‐distyrylfuran derivatives bearing pentafluorophenyl‐ and cyanovinyl units have been synthesized for aggregation‐induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X‐ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single‐crystal X‐ray diffraction analysis confirmed that C?H???F, F???F, C?H???nitrile, Ar???Ar_F (Ar=aryl, Ar_F=fluoroaryl), and nitrile???Ar_F intra‐ and intermolecular interactions drive the topology of the molecule and that solid‐state supramolecular contacts favor AIE of the furan derivatives.     

Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates: Inversion and Enhanced Chirality Based on Spatial Arrangements and Self-Assembly

We synthesized two bichromophoric difluoroboron-β-diketonates (DFB) connected in para and meta positions by using cyclohexane diamine as a chiral bridge ( para and meta (R/S)-CyDFB ). TD-DFT calculations revealed that the variation in connectivity of the DFB units leads to different spatial arrangements and a chirality inversion of the bichromophoric DFB. Higher g_abs values were obtained in (R/S)-CyDFB connected in para as compared to meta position. Aggregation of para (R/S)-CyDFB in mixture of solvents increase the g_lum values as compared to its monomeric form. Ultrasonication and heating induced the formation of highly ordered nano-helical wires of para (R/S)-CyDFB that increased the g_lum values to 0.015. On the other hand, meta (R/S)-CyDFB failed to form highly ordered self-assembled wires due to hindered H-binding sites. These observations indicate that the chiroptical properties of DFB bi-chromophore system can be modulated with self-assembly and spatial arrangement of the chromophores.     

Decreased optical nonlinearities upon CF3 substitution on tricyanofuran acceptors

Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3-TCF results in decreased second-order optical nonlinearities in merocyanines bearing a proaromatic 1,3-dithiole donor. The TCF-containing derivatives display exceptionally high mu beta values up to 31,000 x 10(-48) esu, unprecedented for 1,3-dithiole-based NLO-phores.     

Iminium salts of omega-dithiafulvenylpolyenals: an easy entry to the corresponding aldehydes and doubly proaromatic nonlinear optic-phores

A short, high-yielding route to omega-dithiafulvenylpolyenals (1) via the corresponding iminium salts (2) and starting from trimethyl-1,3-dithiolium tetrafluoroborate is reported. The Knoevenagel reactions of either 1 or 2 with isoxazolone-containing acceptors afford merocyanines 7 and 9, in a process that is often accompanied by a vinylene-shortening side reaction. Experimental and theoretical studies reveal that compounds 7 and 9, featuring two proaromatic end groups, are strongly polarized and show good second-order nonlinear optical responses.     

Elongated Bacterial Pili as a Versatile Alignment Medium for NMR Spectroscopy

In NMR spectroscopy, residual dipolar couplings (RDCs) have emerged as one of the most exquisite probes of biological structure and dynamics. The measurement of RDCs relies on the partial alignment of the molecule of interest, for example by using a liquid crystal as a solvent. Here, we establish bacterial type 1 pili as an alternative liquid-crystalline alignment medium for the measurement of RDCs. To achieve alignment at pilus concentrations that allow for efficient NMR sample preparation, we elongated wild-type pili by recombinant overproduction of the main structural pilus subunit. Building on the extraordinary stability of type 1 pili against spontaneous dissociation and unfolding, we show that the medium is compatible with challenging experimental conditions such as high temperature, the presence of detergents, organic solvents or very acidic pH, setting it apart from most established alignment media. Using human ubiquitin, HIV-1 TAR RNA and camphor as spectroscopic probes, we demonstrate the applicability of the medium for the determination of RDCs of proteins, nucleic acids and small molecules. Our results show that type 1 pili represent a very useful alternative to existing alignment media and may readily assist the characterization of molecular structure and dynamics by NMR.     

Changes in dynamics of SRE-RNA on binding to the VTS1p-SAM domain studied by 13C NMR relaxation

RNA recognition by proteins is often accompanied by significant changes in RNA dynamics in addition to conformational changes. However, there are very few studies which characterize the changes in molecular motions in RNA on protein binding. We present a quantitative (13)C NMR relaxation study of the changes in RNA dynamics in the pico-nanosecond time scale and micro-millisecond time scale resulting from interaction of the stem-loop SRE-RNA with the VTS1p-SAM domain. (13)C relaxation rates of the protonated carbons of the nucleotide base and anomeric carbons have been analyzed by employing the model-free formalism, for a fully (13)C/(15)N-labeled sample of the SRE-RNA in the free and protein-bound forms. In the free RNA, the nature of molecular motions are found to be distinctly different in the stem and the loop region. On binding to the protein, the nature of motions becomes more homogeneous throughout the RNA, with many residues showing increased flexibility at the aromatic carbon sites, while the anomeric carbon sites become more rigid. Surprisingly, we also observe indications of a slow collective motion of the RNA in the binding pocket of the protein. The observation of increased motions on binding is interesting in the context of growing evidence that binding does not always lead to motional restrictions and the resulting entropy gain could favor the free energy of association.     

FRET templated by G-quadruplex DNA: a specific ternary interaction using an original pair of donor/acceptor partners

G-quadruplex represents a suitable scaffold for FRET (fluorescence resonance energy transfer) since its two external quartets offer two well-defined binding sites for concomitant trapping of donor/acceptor partners. Combining selective G-quadruplex binders (macrocyclic bis(quinacridine) BOQ(1) or monomeric quinacridine MMQ(1), donor) with a highly fluorescent DNA probe (thiazole orange, acceptor), we designed a structure-specific FRET-system based on an unprecedented noncovalent ternary complex. This system could be potentially usable as a signature for quadruplex-DNA conformation in solution, but also might offer a unique means for observing cation and ligand binding influence on quadruplex topology.     

Imbibition, desiccation and mechanical deformations of zein pills in relation to their porosity

This paper deals with the interaction between zein (the main protein component of corn grain) and water. It induces macroscopic properties changes and may allow for the understanding of the basis of zein endosperm structure: vitreous endosperm is compact and floury endosperm is porous, giving the endosperm its hard and soft textures, respectively. In that aim porous pills made by compaction of zein powder submitted to different hydration/dehydration processes have been prepared and studied. In particular, imbibition measurements of a pure-water drop deposited onto a zein pill were performed. Also, desiccation of a zein pill previously imbibed induces strong mechanical stresses leading to crack formation and/or large deformations.     

Distributed caching over heterogeneous mobile networks

Sharing content over a mobile network through opportunistic contacts has recently received considerable attention. In proposed scenarios, users store content they download in a local cache and share it with other users they meet, e.g., via Bluetooth or WiFi. The storage capacity of mobile devices is typically limited; therefore, identifying which content a user should store in her cache is a fundamental problem in the operation of any such content distribution system. In this work we propose Psephos, a novel mechanism for determining the caching policy of each mobile user. Psephos is fully distributed: users compute their own policies individually, in the absence of a central authority. Moreover, it is designed for a heterogeneous environment, in which demand for content, access to resources, and mobility characteristics may vary across different users. Most importantly, the caching policies computed by our mechanism are optimal: we show that Psephos maximizes the system’s social welfare. To the best of our knowledge, our work is the first to address caching with heterogeneity in a fully distributed manner.