A dual-selective fluorescent probe for GSH and Cys detection: Emission and pH dependent selectivity.

A novel fluorescent probe 1 based on acridine orange was developed for the selective detection and bioimaging of biothiols. The probe exhibits higher selectivity and turn-on fluorescence response to cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) than to other amino acids. Importantly, the probe responds to GSH and Cys/Hcy with distinct fluorescence emissions in PBS buffer at pH of 7.4. The Cys/Hcy-triggered tandem SNAr-rearrangement reaction and GSH-induced SNAr reaction with the probe led to the corresponding amino-acridinium and thio-acridinium dyes, respectively, which can discriminate GSH from Cys/Hcy through different emission channels. Interestingly, Cys finishes the tandem reaction with the probe and subsequently forms amino-acridinium and Hcy/GSH induces SNAr reaction with the probe to form thio-acridiniums at weakly acidic conditions (pH 6.0), enabling Cys to be discriminated from Hcy/GSH at different emissions. Finally, we demonstrated that probe 1 can selectively probe GSH over Cys and Hcy or Cys over GSH and Hcy in HeLa cells through multicolor imaging.

A dual-response fluorescent probe for Zn2+ and Al3+ detection in aqueous media: pH-dependent selectivity and practical application.

A Schiff base-type fluorescent probe (1) consist of 2-hydroxynaphthaldehyde and glutamide moieties has been designed and synthesized for detection Zn2+ and Al3+. The probe shows pH dependent dual-selectivity for Zn2+ and Al3+ in Tris-HCl buffer, viz. that can selectively recognized Zn2+ at pH 7.4 and Al3+ at pH 6.0, respectively. From Job's plots and MS data, the stoichiometric ratios of the probe with Zn2+ and Al3+ appeared to be 1:1 and 2:1, respectively. The probe can detect as low as 5.5 × 10-8 M-1 Zn2+ and 1.27 × 10-7 M-1 Al3+, whereas respective association constants are 4.27 × 104 M-1 and 3.50 × 109 M-1. Furthermore, it is also confirmed that the probe has good cell-permeability and could thus be used to selectively sense intracellular Zn2+ and Al3+ by bioimaging in different pH environment. Finally the probe has been used successfully for determination of the analytes in real drug samples.

T-shaped monopyridazinotetrathiafulvalene-amino acid diad based chiral organogels with aggregation-induced fluorescence emission.

A series of pyridazine coupled tetrathiafulvalene T-shaped derivatives with varying amino acid moieties have been synthesized and their gelation properties were studied in various organic solvents. Among these derivatives, two gelators bearing glycine or phenylalanine units display efficient gelation in aromatic and polar solvents. Interestingly, these gelators, except for the gelator containing two tryptophan units, are able to gel DMF via a solution-to-gel transformation when triggered with sonication for less than 20 s or cooled below zero. A number of experiments revealed that these gelator molecules self-assembled into elastically interpenetrating three-dimensional chiral fibrillar aggregates. Importantly, all of the resulting gels result in a dramatic enhancement of the fluorescence intensity compared with their hot solution in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by the introduction of C60. Moreover, the gelators can be utilized for the removal of different types of toxic molecules, such as aromatic solvents and cationic dyes, from wastewater.

MPTTF-containing tripeptide-based organogels: receptor for 2,4,6-trinitrophenol and multiple stimuli-responsive properties.

A series of monopyrrolotetrathiafulvalene-tripeptide conjugates have been synthesized and investigated as new low-molecular mass organogelators. It was found that most of these compounds could immobilize low-polarity solvents readily and the gelation behaviors of these gelators showed a dependence on the amino acid residues. These organogels were thoroughly studied using various techniques including atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), circular dichroism (CD) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, (1)H NMR spectroscopy, UV-Vis absorption spectroscopy and X-ray diffraction (XRD). The results showed that the cooperative interplay of hydrogen bonding, π-π stacking and SS interactions were the main driving force for the formation of the gels. Of all the organogels, the aromatic solvent gels, such as toluene gel, exhibited multiple-stimulus responsiveness towards heating, shaking, chemical redox activity and the presence of anions, thus leading to reversible sol-gel phase transitions. Most interestingly, gelation in the presence of 2,4,6-trinitrophenol (TNP) in organic solvents could be observed visually with a concomitant color change through donor-acceptor interactions. The strength of the charge-transfer interaction between gelators and TNP was proportional to the incubation time and increasing critical gelation concentration (CGC). The gels could function as efficient absorbents for potential application in removal of crystal violet and rhodamine B dyes from water.

Coordination-induced gelation of an L-glutamic acid Schiff base derivative: the anion effect and cyanide-specific selectivity.

By rational assembly of Zn(2+) and Cu(2+) with G, three metallogels (ZnG, CuG and Zn-CuG) were prepared. The gelation was controlled by the presence of specific anions, with their efficacy linked to the Hofmeister series. Zn-CuG could fluorescently detect CN(-) with specific selectivity over S(2-) and Cys through the competitive coordination of CN(-) and G with Cu(2+).

Poly(aryl ether) Dendrons with Monopyrrolotetrathiafulvalene Unit-Based Organogels exhibiting Gel-Induced Enhanced Emission (GIEE).

A series of poly(aryl ether) dendrons with a monopyrrolo-tetrathiafulvalene unit linked through an acyl hydrazone linkage were designed and synthesized as low molecular mass organogelators (LMOGs). Two of the dendrons could gelate the aromatic solvents and some solvent mixtures, but the others could not gel all solvents tested except for n-pentanol. A subtle change on the molecular structure produces a great influence on the gelation behavior. Note that the dendrons could form the stable gel in the DMSO/water mixture without thermal treatment and could also form the binary gel with fullerene (C60 ) in toluene. The formed gels undergo a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. A number of experiments (SEM, FTIR spectroscopy, (1) H NMR spectroscopy, and UV/Vis absorption spectroscopy, and XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional fibrillar aggregates and maintain rectangular molecular-packing mode in organogels. The hydrogen bonding, π-π, and donor-acceptor interactions were found to be the main driving forces for formation of the gels. Moreover, the gel system exhibited gel-induced enhanced emission (GIEE) property in the visible region in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by introduction of C60 .

A colorimetric and ratiometric fluorescent probe for selective detection and cellular imaging of glutathione.

A new colorimetric and ratiometric fluorescent probe 1 based on a chlorinated coumarinyl aldehyde was developed for selective detection and cellular imaging of glutathione (GSH) over cysteine (Cys) and homocysteine (Hcy). Probe 1 exhibits a dramatic colorimetric and ratiometric fluorescence responses toward biothiols Cys, Hcy and GSH with high selectivity over other amino acids. Cys (or Hcy) induces a tandem SNAr-rearrangement reaction to form the corresponding amino-coumarins (2a or 2b), which result in about 75 nm and 35 nm blue-shifts in absorption and emission, respectively. By comparison, the thio-coumarin (3') derived from the SNAr reaction with GSH, which does not occur rearrangement because of steric hindrance, undergoes an intramolecular aldimine condensation lead to a cyclic iminium cation (3) with 47 nm and 39 nm red-shifts in absorption and emission, respectively. The significantly difference of photophysical properties enable excellent selectivity towards GSH over Cys and Hcy. Further application to cellular imaging indicates that the probe has appreciable cell permeability and is highly responsive to the changes of GSH level. As a result, it is applicable to monitor GSH level in living cells.

Colorimetric and fluorometric dual-modal probes for cyanide detection based on the doubly activated Michael acceptor and their bioimaging applications.

In this study, we synthesized CTB and CB probes based on doubly activated Michael acceptors to selectively detect cyanide (CN(-)) anions through a one-step condensation reaction of coumarinyl acrylaldehyde with the corresponding derivatives of malonyl urea (thiourea). Through the conjugated addition of CN(-) to the ß-site of the Michael acceptor, both probes displayed colorimetric and fluorometric dual-modal responses that were highly reactive and selective. CTB generates an active fluorescent response, whereas CB displays a ratiometric fluorescent response. The fluorescent signal of the probes reached its maximum given only 1 CN(-) equivalent and the signal change was linearly proportional to CN(-) concentrations ranging from 0 to 5 µM with the detection limits 18 and 23 nM, respectively. The reaction rate of the probes is highly dependent on the methylene acidity of malonyl urea derivatives. Thus, the response rate of CTB to CN(-) is 1.2-fold faster than that of CB, and the response rate of CB to CN(-) is 1.2-fold faster than that of the previously examined CM. We then verified the highly reactive nature of the ß-site of the probes through density functional reactivity theory calculations. In addition, according to proof-of-concept experiments, these probes may be applied to analyze CN(-) contaminated water and biomimetic samples. Finally, cell cytotoxicity and bioimaging studies revealed that the probes were cell-permeable and could be used to detect CN(-) with low cytotoxicity.

Monopyrrolotetrathiafulvalene-succinamide conjugates and their TCNQ charge transfer complex based supramolecular gels with multiple stimulus responsiveness.

A series of monopyrrolotetrathiafulvalene-succinamide conjugates and their 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) charge transfer (CT) complexes have been synthesized and investigated as new low-molecular mass organogelators. The gelation capability of these conjugates is highly dependent on the length of the alkyl chain of the terminal amide. Thus, only the short alkyl chain derivatives and could efficiently gelate cyclohexane and methylcyclohexane (MCH). Surprisingly, these gelators react with TCNQ to form stable CT complex gels in both cyclohexane and MCH. The FE-SEM images of the native gels reveal the characteristic gelation morphologies of microporous or fibrous structures, whereas the morphologies of CT complex gels show the fibrillar and globular aggregates in cyclohexane and MCH, respectively. SAXS study of the native gel and the CT complex gel of in cyclohexane suggests that the molecules maintain rectangular and hexagonal columnar molecular packing models in the gel phase, respectively. The native gels undergo a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. Alternatively, the corresponding CT complex gels exhibit a complicated response to external stimuli. Chemical oxidation by I2 results in the destruction of the gel state. However, neither Fe(3+) nor Cu(2+) can induce the collapse of the gel phase. Interestingly, all the gels show an irreversible gel-sol transition on successively triggering with trifluoroacetic acid and triethylamine. The reformation of the gel from the sol state is achieved just by the addition of water, showing the phase-selective gelation of the solvents from their mixtures with water.

A regeneratable and highly selective fluorescent probe for sulfide detection in aqueous solution.

A novel fluorescent probe based on a coumarin-dipicolylamine-Cu(2+) complex was synthesized and characterized. The probe is able to highly sensitively and selectively sense sulfide over other common anionic analytes including thiols followed by releasing ligand 1 to give a remarkable change of fluorescent intensity in aqueous solution. The probe could be regenerated by the addition of Cu(2+), and therefore the probe could be utilized repetedly to sense sulfide anions with Cu(2+) and S(2-), in turn, increased. The detection limit of the fluorescent assay for sulfide is as low as 14 nM with a rapid response time (a few seconds). Importantly, the displacement mechanism for sensing of sulfide anions was clarified through single-crystal X-ray diffraction analysis and DFT calculations. Based on this probe, a rapid, selective and sensitive fluorescence method for the detection of sulfide anions in environmental samples was established.

Synthesis and properties of T-shaped organic conjugates based on 3,6-diarylpyridazine-fused tetrathiafulvalene.

A facile synthetic approach to the π-expanded tetrathiafulvalene derivatives is described. The Suzuki reaction of 3,6-dichloropyridazine-fused tetrathiafulvalenes with phenyl boronic acid or biphenyl boronic acid gave a series of novel T-shaped organic π-conjugates. The electronic properties of the conjugates were studied experimentally by the combination of cyclic voltammetry and UV-vis spectroscopy. Their HOMO and LUMO energy levels are estimated to be about -5 eV and -3.2 eV, which are the air operating stability ranges in the p-channel and n-channel field effect transistors, respectively. Only one conjugate bearing the longer alkyl chain (n = 1, R = n-C18H37) was verified to self-assemble into lamellar structures in the mesogenic phase and the best measured charge carrier mobility of its thin-film devices was 4.5 × 10(-5) cm(2) V(-1) s(-1).

A coumarin-Meldrum's acid conjugate based chemodosimetric probe for cyanide.

A highly reactive and selective chemodosimetric probe for cyanide was synthesized based on alkylidene Meldrum's acid as a novel cyanide reaction site. A theoretical study was conducted to rationalize the high reactivity and the photophysical properties of probe 1 and the 1-CN adduct.

2,2,2-Trifluoro-N-(4-methyl-2-oxo-2H-chromen-7-yl)acetamide.

In the title mol-ecule, C(12)H(8)F(3)NO(3), the trifluoro-methyl group is rotationally disordered over three orientations in a 0.5:0.3:0.2 ratio. In the crystal, N-H⋯O hydrogen bonds link the mol-ecules related by translation into chains along the c axis. The crystal packing exhibits π-π inter-actions between the pyran rings of neighboring mol-ecules [centroid-centroid distance = 3.462 (4) Å] and short C⋯O contacts of 3.149 (4) Å.

5-(4-Methyl-phenyl-sulfon-yl)-1,3-dithiolo[4,5-c]pyrrole-2-thione.

The asymmetric unit of the title compound, C(12)H(9)NO(2)S(4), contains one half-mol-ecule with the N, two S amd four C atoms lying on a mirror plane. The mol-ecule exhibits a V-shaped conformation, with a dihedral angle of 87.00 (7)° between the benzene and dithiol-opyrrole rings. The methyl group was treated as rotationally disordered between two orientations in a 1:1 ratio. In the crystal, weak C-H⋯O hydrogen bonds link the mol-ecules into chains in [010].

7-Diethyl-amino-2-oxo-2H-chromene-3-carbaldehyde.

In the title compound, C(14)H(15)NO(3), all non-H atoms except for those of the methyl and the disordered ethyl groupare approximately co-planar, the largest deviation from the mean plane being 0.0223 (13) Šat the N atom. In the crystal, the packing of mol-ecules through weak inter-molecular C-H⋯O hydrogen-bonding inter-actions leads to the formation of layers parallel to bc plane. Within these layers, there exist slipped π-π stacking inter-actions between symmetry-related fused rings [centroid-centroid distances = 3.527 (3) and 3.554 (3), slippage = 0.988 and 1.011 Å, respectively]. One ethyl group is disordered over two sets of sites with site-occupation factors of 0.54 and 0.46.

4-(Diethyl-amino)-salicyl-aldehyde azine.

The title compound, C(22)H(30)N(4)O(2), has a crystallographic inversion center located at the mid-point of the N-N single bond. Apart from the four ethyl C atoms, the non-H atoms are nearly coplanar with a mean deviation of 0.0596 (2) Å. An intra-molecular O-H⋯N hydrogen bond occurs. In the crystal, weak inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into layers parallel to (100).

7-Diethyl-amino-2-oxo-2H-chromene-3-carbohydrazide.

The asymmetric unit of the title compound, C(14)H(17)N(3)O(3), contains two independent mol-ecules with different conformations of the ethyl groups. In the crystal, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into ribbons extending along the a axis.

6,7-Bis(methyl-sulfan-yl)-2,3-[(3,6,9-trioxaundecane-1,11-di-yl)bis-(sulfanediylmethyl-ene)]-1,4,5,8-tetra-thia-fulvalene.

In the title compound, C(18)H(26)O(3)S(8), the two five-membered rings exhibit envelope conformations. The two S atoms in the 17-membered macrocycle deviate from the plane of the fused five-membered ring by 1.429 (3) and -1.434 (3) Šin opposite directions.

4,6,7,9,10,12,13,15,16,18-Decahydro-1,3-dithiolo[4,5-l][1,4,7,10,15]trioxadithia-cyclo-hepta-decine-2-thione.

The title compound, C(13)H(20)O(3)S(5), is bis-ected by a crystallographic twofold rotation axis, which relates the two halves of the mol-ecule to one another: one S, one C and one O atom lie on the axis. The thione S atom lies in the plane of the five-membered rings with an r.m.s. deviation of 0.0042 (5) Å. Parts of the 17-membered macrocycle were refined using a two-part disorder model [occupancies of 0.553 (14) and 0.447 (14)]. There are no noteworthy inter-molecular inter-actions.

2,3-(3,6,9-Trioxaundecane-1,11-diyl-disulfan-yl)-1,4,5,8-tetra-thia-fulvalene-6,7-dicarbonitrile.

In the title compound, C(16)H(16)N(2)O(3)S(6), the two five-membered rings form a dihedral angle of 7.86 (9)°. Weak C-H⋯N hydrogen bonds link the mol-ecules to form a chain along c; the chains are further connected by weak C-H⋯O hydrogen bonds to form a three-dimensional supra-molecular network.