A Polymer To Detect Explosives : Towards An Effective Sensor Material

There are upwards of 100 million landminds in over 70 countries. Nitroaromatic vapours emanate from landmines and a need exists for a sensitive and robust sensor for their detection. It is the goal of this study to develop a thin, reusable, fluorescent film composed of ß-cyclodextrin polymer crosslinked with epichlorohydrin, for the detection of nitroaromatics. The fluorescent moiety, 2-naphthol, (sensing function) was incorporated into the ß-cyclodextrin-epichlorohydrin polymer (trapping function). Fluorimetry, FTIR and ¹H NMR were employed to characterize the polymer and examine whether 2-naphthol was covalently linked to the ß-cyclodextrin polymer network. Fluorescence quenching studies were conducted using a nitroaromatic compound, nitrobenzene, to determine the quenching efficiency. The characterization studies indicate that 2-naphthol is incorporated into ß-cyclodextrin-epichlorohydrin polymer. A difference does not seem to exist in the quenching efficiency of free 2-naphthol, 2-naphthol:ß-cyclodextrin complex and the polymers by nitrobenzene.

A Polymer To Detect Explosives : Towards An Effective Sensor Material

There are upwards of 100 million landminds in over 70 countries. Nitroaromatic vapours emanate from landmines and a need exists for a sensitive and robust sensor for their detection. It is the goal of this study to develop a thin, reusable, fluorescent film composed of ß-cyclodextrin polymer crosslinked with epichlorohydrin, for the detection of nitroaromatics. The fluorescent moiety, 2-naphthol, (sensing function) was incorporated into the ß-cyclodextrin-epichlorohydrin polymer (trapping function). Fluorimetry, FTIR and ¹H NMR were employed to characterize the polymer and examine whether 2-naphthol was covalently linked to the ß-cyclodextrin polymer network. Fluorescence quenching studies were conducted using a nitroaromatic compound, nitrobenzene, to determine the quenching efficiency. The characterization studies indicate that 2-naphthol is incorporated into ß-cyclodextrin-epichlorohydrin polymer. A difference does not seem to exist in the quenching efficiency of free 2-naphthol, 2-naphthol:ß-cyclodextrin complex and the polymers by nitrobenzene.

Study of the fluorescence and interaction between cyclodextrins and neochlorogenic acid, in comparison with chlorogenic acid

Neochlorogenic acid, a less-studied isomer of chlorogenic acid, has been seen to posses antioxidant, antifungal, anti-inflammatory and anticarcinogenic effects, which makes it an interesting candidate for incorporation in functional foods. However, its poor solubility in water and susceptibility to oxidation make such a task difficult. To overcome that, its encapsulation in cyclodextrins (CDs) is proposed. The fluorescence of neochlorogenic acid in different pH conditions was analyzed, and caffeic acid was proved to be the fluorescent moiety in the molecule. An encapsulation model whereby the ligand poses two potential complexation sites (caffeic and D-(-)-quinic moieties), showed that α-CD and HP-β-CD formed the best inclusion complexes with neochlorogenic acid, followed by M-β-CD, β-CD and γ-CD. Molecular docking with the two best CDs gave better scores for α-CD, despite HP-β-CD providing stabilization through H-bonds. The encapsulation of chlorogenic acid led to a similar CD order and scores, although constants were higher for α-CD, β-CD and M-β-CD, lower for HP-β-CD, and negligible for γ-CD. The protonation state affected these results leading to a different order of CD preference. The solubility and the susceptibility to oxidation of neochlorogenic acid improved after complexation with α-CD and HP-β-CD, while the antioxidant activity of both isomers was maintained.

Dual detection of nafcillin using a molecularly imprinted polymer-based platform coupled to thermal and fluorescence read-out

Reported here is the production of molecularly imprinted polymer (MIP) films, integrating a fluorescent moiety that serves as both, an element for template interaction and signalling, for the thermal and...

Ligand-directed covalent labelling of a GPCR with a fluorescent tag in live cells

To study the localisation of G protein-coupled receptors (GPCR) in their native cellular environment requires their visualisation through fluorescent labelling. To overcome the requirement for genetic modification of the receptor or the limitations of dissociable fluorescent ligands, here we describe rational design of a compound that covalently and selectively labels a GPCR in living cells with a fluorescent moiety. We designed a fluorescent antagonist, in which the linker incorporated between pharmacophore (ZM241385) and fluorophore (sulfo-cyanine5) is able to facilitate covalent linking of the fluorophore to the adenosine A2A receptor. We pharmacologically and biochemically demonstrate irreversible fluorescent labelling without impeding access to the orthosteric binding site and demonstrate its use in endogenously expressing systems. This offers a non-invasive and selective approach to study function and localisation of native GPCRs.

Ligand-directed covalent labelling of a GPCR with a fluorescent tag

Here, we describe rational design of a compound that covalently and selectively labels a G protein-coupled receptor (GPCR) in living cells with a fluorescent moiety. Using wild-type adenosine A2A receptor as a model system, we show fluorescent labelling without impeding access to the orthosteric binding site and demonstrate its use in endogenously expressing systems. This offers a non-invasive and selective approach to study function and localisation of native GPCRs.

Responsive fluorophore aggregation provides spectral contrast for fluorescence lifetime imaging

Fluorophores experience altered emission lifetimes when incorporated into and liberated from macromolecules or molecular aggregates; this trend suggests the potential for a fluorescent, responsive probe capable of undergoing self-assembly and aggregation and consequently altering the lifetime of its fluorescent moiety to provide contrast between the active and inactive probes. We developed a cyanobenzothioazole-fluorescein conjugate (1), and spectroscopically examined the lifetime changes caused by its reduction-induced aggregation in vitro. A decrease in lifetime was observed for compound 1 in a buffered system activated using the biological reducing agent glutathione, suggesting a possible approach for designing responsive self-aggregating lifetime imaging probes.

Molecular Dissection of dH3w, A Fluorescent Peptidyl Sensor for Zinc and Mercury

Previously, we reported that fluorescent peptide dansyl-HPHGHW-NH2 (dH3w), designed on the repeats of the human histidine-rich glycoprotein, shows a turn-on response to Zn(II) and a complex response to Hg(II) characterized by a turn-off phase at low Hg(II) concentrations and a turn-on phase at high concentrations. As Hg(II) easily displaces Zn(II), dH3w is a useful probe for the environmental monitoring of Hg(II). In order to investigate the molecular basis of the metal selectivity and fluorescence response, we characterized three variants, dH3w(H1A), dH3w(H3A), and dH3w(H5A), in which each of the three histidine residues was changed to alanine, and two variants with a single fluorescent moiety, namely dH3w(W6A), in which the tryptophan residue at the C-terminus was changed to alanine, and AcH3w, in which the N-terminal dansyl moiety was substituted by an acetyl group. These variants allowed us to demonstrate that all the histidine residues are essential for a strong interaction with Zn(II), whereas two histidine residues (in particular His5) and the dansyl group are necessary to bind Hg(II). The data reported herein shed light on the molecular behavior of dH3w, thus paving the way to the rational designing of further and more efficient fluorescent peptidyl probes for Hg(II).

A novel profluorescent paramagnetic diaza-crown ether: synthesis, characterization and alkaline metal-ion complexation

Starting from Kryptofix 22 two different branches were covalently attached through the nitrogen atoms, one containing a fluorescent moiety and the other the stable free radical TEMPO.

A new method for aldo-sugar analysis in beverages and dietary foods

Background: Carbohydrates are found in most of our everyday diet; however, sugar analysis is difficult and inconvenient in food materials such as beverages, fruits and vegetables. Here, we report a new method for labeling the sugar ingredients in beverages and plant foods. The mentioned method provides a high sensitive and efficient tool for sugar compositional analysis by labeling the aldoses in beverages and foods with 2,3-naphthalenediamine via an iodine-promoted oxidative condensation reaction to form highly fluorescent aldo-naphthylimidazole (NAIM) derivatives. We have also separated the natural glycosides from dietary foods, for instance, solanines from tomato and potato. The various types of solanines with different sugar moieties were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). The glycan is released by acidic hydrolysis, and the sugar components are subjected to NAIM labeling. These aldo-NAIM derivatives not only show enhanced mass signaling, but also provide fluorescent moiety at the reducing end of sugar to assist the detection in HPLC analysis.Objective: To develop a rapid and sensitive sugar detection method for research and commercial use, as well as to understand the sugar composition in dietary beverages and functional foods.Results: Five beverages in Taiwan were examined for the composition of six common sugars. Two Solanaceae samples extracted from the potato and tomato plants were measured by MALDI MS and ESI-MS/MS. The structures of solanines were elucidated and the glycan moieties were converted to the fluorescent NAIM derivatives to confirm their composition.Conclusions: The results suggest that the aldo-NAIM method is efficient and rapid for evaluation of sugar composition and concentration in beverages and foods.Key words: beverages, foods, potato, tomato, aldose, sugar analysis, fluorescence, NAIM kit