A "turn-on" fluorescent probe for the detection of permanganate in aqueous media.

A novel carbazole-based probe was synthesized and found to exhibit fluorescence upon introduction to potassium permanganate in aqueous media. Guided by a series of experimental studies and DFT calculations, the underlying mechanism is proposed to proceed through a series of tandem proton and electron transfer processes.

Turn-on and Turn-off Fluorescent Probes for Carbon Monoxide Detection and Blood Carboxyhemoglobin Determination.

Water-soluble, carbazole-based two-photon excitable fluorescent probes MPVC-I ("turn-on") and MPVC-II ("turn-off") are rationally designed and synthesized for the selective monitoring of carbon monoxide (CO). Both probes can effectively measure carboxyhemoglobin (HbCO) in the blood of the animals exposed to a CO dose as low as 100 ppm for 10 min. The palladium catalyzed azidocarbonylation reaction was optimized to improve the sensing efficiency.

Facile Synthesis of a Selective Biomolecule Chemosensor and Fabrication of Its Highly Fluorescent Graphene Complex.

A novel hydrophilic imidazolium fluorescent chemosensor has been utilized to prepare water-soluble fluorescent graphene complex via a facile ion-exchange strategy, which gives a very high quantum yield (0.87). The highly fluorescent graphene complex displays a close resemblance to the water-soluble fluorescent chemosensor, as the chemisorbed imidazolium hinders the electron transfer between the naphthalene moiety and the graphene. If the imidazolium is simply physisorbed on graphene by physical mixing, it does not show a high quantum yield because the π-π stacking between the naphthalene moiety and graphene leads to fluorescence quenching. The fluorescent chemosensor selectively detects RNA by turn-on fluorescence at physiological pH in aqueous solution. The fluorescent chemosensor as well as the fluorescent graphene complex would find potential applications as photoresponsive materials and biomedical probes.

Halides with Fifteen Aliphatic C-H···Anion Interaction Sites.

Since the aliphatic C-H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C-H (Cali-H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali-H groups. An X-ray structure of imidazolium-based scaffolds using Cali-H···A(-) interactions (A(-) = anion) shows that a halide anion is directly interacting with fifteen Cali-H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali-H···A(-) interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms.

Violation of DNA neighbor exclusion principle in RNA recognition.

DNA intercalation has been very useful for engineering DNA-based functional materials. It is generally expected that the intercalation phenomenon in RNA would be similar to that in DNA. Here we note that the neighbor-exclusion principle is violated in RNA by naphthalene-based cationic probes, in contrast to the fact that it is usually valid in DNA. All the intercalation structures are responsible for the fluorescence, where small naphthalene moieties are intercalated in between bases via π-π interactions. The structure is aided by hydrogen bonds between the cationic moieties and the ribose-phosphate backbone, which results in specific selectivity for RNA over DNA. This experimentally observed mechanism is supported by computationally reproducing the fluorescence and CD data. MD simulations confirm the unfolding of RNA due to the intercalation of probes. Elucidation of the mechanism of selective sensing for RNA over DNA would be highly beneficial for dynamical observation of RNA which is essential for studying its biological roles.

Turn-On Ratiometric Fluorescent Probe for Selective Discrimination of Cr(3+) from Fe(3+) in Aqueous Media for Living Cell Imaging.

Pyrene-based turn-on ratiometric fluorescent probe 1 demonstrates high sensitivity and exceptional selectivity toward Cr(3+) in the presence of other metals, including Fe(3+) in aqueous media. Interaction of Cr(3+) with probe 1 brings pyrene moieties close enough to have better aligned π-π stacking, thus enhancing the excimer peak many fold. On the other hand, the interaction of Fe(3+) with probe 1 brings forth a negligible difference in stacking, resulting in an insignificant change in fluorescence intensity. Exceptional selectivity of probe 1 with Cr(3+) over Fe(3+) and other metals has been confirmed by theoretical studies in addition to experimental results. Imaging of HeLa cells observed by confocal fluorescence microscopy reveals that probe 1 can be used to monitor Cr(3+) in live cells to map its subcellular distribution.

Novel ionophores with 2n-crown-n topology: anion sensing via pure aliphatic C-H···anion hydrogen bonding.

A series of novel coronands having a 2n-crown-n topology based on trioxane (6-crown-3) derivatives are designed and characterized. These neutral hosts can sense anions through pure aliphatic C-H hydrogen bonding (HB) in condensed phases due to the unusual topology of 2n-crown-n. C-H bonds are strongly polarized by two adjacent oxygen atoms in this scaffold. These hosts provide a rare opportunity to modulate anion binding strength by changing the electronic nature of aliphatic C-H bonds and offer ease of synthesis.