Quinoxaline derivatives (1−4) bearing two imidazolium moieties are found to strongly bind anions and show unique charge-transfer fluorescent responses to pyrophosphate and acetate, whereas they show excimer formation with other anions. Anion-binding studies are investigated with fluorescence and 1 H NMR analysis, single-crystal X-ray analysis, and theoretical calculations.Anions play a fundamental role in a wide range of chemical and biological processes, and numerous efforts have been devoted to the development of abiotic receptors for anionic species. 1 Sensors based on anion-induced changes in fluorescence 2 and intramolecular/intermolecular excimer formation 3 appear to be particularly attractive. On the other hand, given that carboxylic acids (or carboxylates) are a common functional group in biological and synthetic organic molecules, the development of simple to sophisticated receptors for carboxylates has attracted immense attention. 4 The imidazolium group can make a strong interaction with anions through the (C-H) + -X --type ionic hydrogen bond-ing involving the dominating charge-charge electrostatic interaction 5 which is in contrast to well-known neutral receptors involving typical hydrogen bonding for the anion

No abstract

Golden reactivity: A new gold(I)‐catalyzed cycloisomerization of 3‐methoxy‐1,6‐enynes was discovered. Structurally simple 3‐methoxy‐1,6‐enynes engage in a tandem cyclization/[3,3]‐sigmatropic rearrangement to deliver a variety of 1‐methoxy‐1,4‐cycloheptadienes (see scheme). Notably, the reaction can be performed under very mild conditions and the synthetic utility of this reaction was demonstrated by facile conversion of the product into various cyclohept‐4‐en‐1‐ones.

By linking the urea moiety at the 1,8 positions of the carbazole fragment, we synthesized host systems 1, 2, and 3 having both chromogenic and fluorogenic signaling subunits. The spectral changes in both the signaling subunits could be easily analyzed via a simple 2-dimensional (2D) analytic approach described here, which enables us to differentiate the given set of anions. Structural studies are also reported.

No abstract

Graphene has been studied intensively in opto-electronics, and its transport properties are well established. However, efforts to induce intrinsic optical properties are still in progress. Herein, we report the production of micron-sized sheets by interconnecting graphene quantum dots (GQDs), which are termed ‘GQD solid sheets’, with intrinsic absorption and emission properties. Since a GQD solid sheet is an interconnected QD system, it possesses the optical properties of GQDs. Metal atoms that interconnect the GQDs in the bottom-up hydrothermal growth process, induce the semiconducting behaviour in the GQD solid sheets. X-ray absorption measurements and quantum chemical calculations provide clear evidence for the metal-mediated growth process. The as-grown graphene quantum dot solids undergo a Forster Resonance Energy Transfer (FRET) interaction with GQDs to exhibit an unconventional 36% photoluminescence (PL) quantum yield in the blue region at 440 nm. A high-magnitude photocurrent was also induced in graphene quantum dot solid sheets by the energy transfer process.

Mass-balanced (1)H/(2)H isotope dipeptide tags (MBITs) are presented for simultaneous protein quantitation and identification. MBIT is derived from N-acetyl-Ala-Ala dipeptide and conjugated to primary amines of target peptides. (1)H/(2)H isotopes are encoded in the methyl groups of N-acetylated dipeptide: one tag deuterated on the N-acetyl group and another on the C-terminal alanine. MBIT-linked peptides comigrate in reversed-phase liquid chromatography without significant (1)H/(2)H isotope effects and provide 2-plex quantitation signals at 114 and 117 Th as well as peptide sequence information upon MS/MS analysis with MALDI TOF/TOF. MBIT shows good quantitation linearity in a concentration range of 20-250 fmol. The performance of MBIT on protein quantitation and identification is further tested with yeast heat-shock protein (Hsp82p) obtained from three different physiological states. MBIT using nanogram-scale samples produces the relative abundance ratios comparable to those obtained from optical imaging of microgram-scale samples visualized with SYPRO Ruby stain. The MBIT strategy is a simple and low-cost alternative for 2-plex quantitation of proteins and offers possibilities of tuning the 2-plex signal mass window by replacing the N-terminal alanine with other amino acid residues.

No abstract