Fluorescent Chemosensors Based on Spiroring-Opening of Xanthenes and Related Derivatives

New fluorescent probes for sulfane sulfurs and the application in bioimaging

A sulfane sulfur mediated benzodithiolone formation was developed. Based on this reaction, two fluorescent probes (SSP1 and SSP2) for the detection of sulfane sulfur species (persulfide, polysulfide, and elemental sulfur) were prepared and evaluated. The probes showed high selectivity and sensitivity to sulfane sulfurs. Moreover, SSP2 was successfully applied for bioimaging sulfane sulfurs in living cells.

Turn-on fluorescent chemosensor for Hg²⁺ based on multivalent rhodamine ligands

Rhodamine-based fluorescent chemosensors 1 and 2 exhibit selective fluorescence enhancement to Fe3+ and Hg2+ over other metal ions at 580 nm in CH(3)CN/H(2)O (3/1, v/v) solution. Bis(rhodamine) chemosensor 1, under optimized conditions (CH(3)CN/HEPES buffer (0.02 M, pH = 7.0) (95/5, v/v)), shows a high selectivity and sensitivity to Hg2+, with a linear working range of 0-50 μM, a wide pH span of 4-10, and a detection limit of 0.4 μM Hg2+.

Through bond energy transfer: a convenient and universal strategy toward efficient ratiometric fluorescent probe for bioimaging applications

Fluorescence resonance energy transfer (FRET) strategy has been widely applied in designing ratiometric probes for bioimaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. The through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of the classical FRET system. It seems to be more favorable for designing ratiometric probes for bioimaging applications. In this paper, we have designed and synthesized a coumarin-rhodamine (CR) TBET system and demonstrated that TBET is a convenient strategy to design an efficient ratiometric fluorescent bioimaging probe for metal ions. Such TBET strategy is also universal, since no spectral overlap between the donor and the acceptor is necessary, and many more dye pairs than that of FRET could be chosen for probe design. As a proof-of-concept, Hg(2+) was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well-separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency, and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg(2+). Moreover, by employing an Hg(2+)-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg(2+). All these unique features make it particularly favorable for ratiometric Hg(2+) sensing and bioimaging applications. It has been preliminarily used for a ratiometric image of Hg(2+) in living cells and practical detection of Hg(2+) in river water samples with satisfying results.

Colorimetric chemodosimeter based on diazonium-gold-nanoparticle complexes for sulfite ion detection in solution

A fast and simple colorimetric detection system for sulfite, based on diazonium-gold-nanoparticle(AuNP) complexation, has high selectivity and sensitivity in aqueous media. The positively charged diazonium has affinity for the AuNP surface due to an electrostatic effect, which prevents AuNPs from aggregating in highly saline solutions. Upon addition of sulfite, the AuNPs are free to aggregate due to the formation of a neutral and insoluble phenylhydrazine derivative.

A selective, sensitive, colorimetric, and fluorescence probe for relay recognition of fluoride and Cu(II) ions with "off-on-off" switching in ethanol-water solution

Anion to cation relay recognition was designed and realized for the first time with sequence specificity (F(-)→Cu(2+)) via a fluorescence "off-on-off" mechanism. Probe 1 was a highly selective, sensitive, and turn-on chemodosimeter for F(-) through a specific cyclization reaction triggered by the strong affinity of fluoride toward silicon with a significant change of fluorescence color in both ethanol and ethanol-water (1:1, v/v) solution. Fluorescence enhancement factors were dramatic: 833-fold in ethanol and 164-fold in ethanol-water (1:1, v/v) solution, respectively. The in situ system generated from the sensing of F(-) showed good relay recognition ability for Cu(2+) via fast fluorescence quenching by the formation of a 1:1 complex in ethanol-water (1:1, v/v) solution. The isolated pure compound 2 also exhibited high selectivity toward Cu(2+) in PBS buffer (pH = 7.0) solution. The origin of this sequence specificity of fluorescence recognition was disclosed through the crystal or optimized structures and DFT calculations of corresponding compounds.

2-Amino-5-nitro-N-[(E)-thio-phen-2-yl-methyl-idene]aniline

In the title mol-ecule, C(11)H(9)N(3)O(2)S, the thio-phene and benzene rings form a dihedral angle of 17.68 (9)°. The thio-phene S atom and the imine N atom are syn with respect to each other. In the crystal, N-H⋯O and N-H⋯N hydrogen bonds connect mol-ecules, forming a two-dimensional network parallel to (10-1).

Tricolor emission of a fluorescent heteroditopic ligand over a concentration gradient of zinc(II) ions

The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2'-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn(ClO(4))(2) in acetonitrile. Coordination of Zn(2+) stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn(ClO(4))(2), the nonfluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn(2+)-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e., from blue to green to orange as [Zn(2+)] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn(2+) coordination under pH neutral aqueous conditions.

Iron(III) selective molecular and supramolecular fluorescent probes

Iron is one of the most important elements in metabolic processes, being indispensable for all living systems and therefore it is extensively distributed in environmental and biological materials. However, both its deficiency and excess from the normal permissible limit can induce serious disorders. Therefore, several analytical techniques have been adopted for the detection of iron. Among the various techniques used for its detection, the method based on fluorescent sensors has received considerable interest in recent years because of its ability to provide online monitoring of very low concentrations without any pre-treatment of the sample together with the advantages of spatial and temporal resolution. In this article, efforts have been made to review the various molecular and supramolecular fluorescent sensors that have been developed for the selective detection of iron(III).

Design and synthesis of a ratiometric fluorescent chemosensor for Cu(II) with a fluorophore hybridization approach

A new ratiometric fluorescent sensor for Cu(2+), WLN, has been developed via integrating a 1,8-naphthalimide fluorophore with 8-aminoquinoline. WLN exhibits a highly selective ratiometric response to Cu(2+) over other transition metal ions in aqueous media. Moreover, its practical ratiometric imaging ability for intracellular Cu(2+) has been confirmed in human breast adenocarcinoma cells (MCF-7 cells) using a confocal microscope.

Sensing performance enhancement via acetate-mediated N-acylation of thiourea derivatives: a novel fluorescent turn-on Hg(2+) chemodosimeter

A Hg(2+) chemodosimeter P3 derived from a perylenebisimide scaffold and thiourea fragments was systematically studied with focus on the photophysical, chemodosimetric mechanistic, as well as fluorogenic behaviors toward various metal cations for the sake of improving selectivity to Hg(2+). As demonstrated, Hg(2+) can promote a stepwise desulfurization and N-acylation of P3 with the help of an acetate anion (OAc(-)), resulting in an N-acylated urea derivative. Interestingly, OAc(-) has the effect of improving the selectivity of P3 to Hg(2+) among other metal ions; that is, in an acetone/Britton-Robinson buffer (9:1, v/v; pH 7.0) upon excitation at 540 nm, the relative fluorescence intensity is increased linearly with increasing concentration of Hg(2+) in the range of 2.5-20 μM with a detection limit of 0.6 μM, whereas the fluorescence intensity of P3 to other metal ions, including Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Ni(2+), Co(2+), Zn(2+) Ag(+), Cd(2+), Pb(2+), and Cu(2+), is negligible. The fluorescent bioimaging of chemodosimeter P3 to detect Hg(2+) in living cells was also reported.

A fluorescein-based probe with high selectivity to cysteine over homocysteine and glutathione

A fluorescent probe based on fluorescein displays excellent selectivity and sensitivity for cysteine and its application for bio-imaging is described.