Synthesis and Investigation of Derivatives of 1,8-Naphthalimide with a Red Emission via an Aromatic Nucleophilic Substitution Reaction.

1,8-Napthalimides (NIs) have been widely used as fluorescent molecules in biological, chemical, and medical fields because NIs shows high stability and various fluorescence properties under different conditions. However, NIs typically display a fluorescence emission wavelength in the range of 350 - 550 nm which can be notably interfered with by autofluorescence in living cells, significantly limiting their bio-applications. Moreover, low solubility in aqueous media is another major limitation for NIs. In this project, four derivatives of NIs (1-4) have been synthesized via an aromatic nucleophilic substitution reaction and their photophysical properties have been investigated in various media (water, MeOH, MeCN, DMSO, EtOAc, and THF). All of these derivatives (1-4) show a long emission wavelength around 600 nm and high solubility in polar solvents. Particularly molecules (1-4) show the longest emission (624-629 nm) in water and the fluorescence intensity is not significantly varied in the range of pH 4-11. These unique features, long emission wavelength, high solubility, and high stability in difference pH media, will allow these derivative (1-4) to be used as excellent labeling reagents in the biological system.

Investigation of a Sensing Strategy Based on a Nucleophilic Addition Reaction for Quantitative Detection of Bisulfite (HSO3-).

A reaction-based sensor (NAS-1) showed a high affinity and sensitivity to HSO3- via a nucleophilic addition reaction in the aqueous media, giving dual signals from absorption and emission spectra. NAS-1 was successfully applied in RK13 epithelial cells to detect HSO3- in a cellular environment.

Analysis of Bisulfite Via a Nitro Derivative of Cyanine-3 (NCy3) in the Microfluidic Channel.

NCy3, a derivative of Cyanine 3 with a nitro substituent, showed a high reactivity to bisulfite in aqueous media, instantly leading to ratiometric change of absorption spectra and significant fluorescence quenching. Applied in the microfluidic channel, NCy3 functionalize as a sensitive approach for quantitative detection of bisulfite, particularly for samples with a small volume.

Investigation of a sensing approach based on a rapid reduction of azide to selectively measure bioavailability of H2S.

A new reaction-based sensor (AHS) was synthesized for quantitative detection of H2S. AHS showed a high selectivity and sensitivity toward H2S over other thio-containing molecules, or reducing reagents with high abundance in living cells. In the presence of H2S, significant fluorescence enhancement (17-fold) was observed due to the reduction of the azide on AHS. The absorption (362 nm) and fluorescence emission (557 nm) of reduced AHS showed a highly linear correlation to H2S level, which were used to measure concentration of H2S in the range of 0-100 µM.

Reduction of nitro group on derivative of 1,8-napthalimide for quantitative detection of hydrogen sulfide.

A fluorescence "turn-on" sensor (HSS) for detection of H2S was developed on the basis of NO2-NH2 reduction. HSS showed a high affinity and sensitivity to H2S over other reducing reagents, particularly for biothiols. Also, the short responding time and high linear dependence between fluorescence enhancement and H2S concentration had HSS behave as a rapid sensor for quantitatively detection of H2S in the biological level.

Investigation of desilylation in the recognition mechanism to fluoride by a 1,8-naphthalimide derivative.

A reaction-based chemosensor (AF-1) was designed, synthesized and applied as an optical approach for quantitative measurement of F(-) in MeCN. In the presence of F(-), selective fluoride-assisted desilylation instantly gave colorimetric and fluorogenic signals, providing a dual-optical channel for the detection of F(-). (1)H NMR titration was carried out to investigate the desilylation process, revealing F(-) triggered rapid cleavage of Si-O bond in trimethylsilyl ether. AF-1 exhibited high sensitivity and selectivity to F(-) over other anions. The detection limit to F(-) was calculated to be 0.05 ppm.

Excimer-monomer switch: a reaction-based approach for selective detection of fluoride.

A N-aryl-1,8-naphthalimide based sensor (ES-1) bearing a trimethylsilyl ether has been synthesized by a two-step reaction for quantitative detection of fluoride (F(-)). ES-1 exhibited monomer/excimer emissions at 410 and 524 nm respectively in CH2Cl2. In the presence of F(-), the desilylation of trimethylsilyl ether caused decay of the excimer emission as well as enhancement of the monomer emission to give a ratiometric signal. The fluoride-triggered desilylation showed a high reaction rate and high affinity to F(-) over nine other interfering anions. ES-1 provided a novel fluorescence assay based on excimer-monomer switch of N-aryl-1,8-naphthalimide to quantitatively measure F(-) with a detection limit of 0.133 ppm.

A new N-imidazolyl-1,8-naphthalimide based fluorescence sensor for fluoride detection.

A chemosensor is reported with high sensitivity and selectivity for detection of fluoride anion. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bond between imidazole and naphthalimide moieties, resulting in a noncoplanar geometry with low fluorescence.

Identification of an orthogonal peptide binding motif for biarsenical multiuse affinity probes.

Biarsenical multiuse affinity probes (MAPs) complexed with ethanedithiol (EDT) permit the selective cellular labeling of proteins engineered with tetracysteine motifs, but are limited by the availability of a single binding motif (i.e., CCPGCC or PG tag) that prevents the differential labeling of coexpressed proteins. To overcome this problem, we have used a high-throughput peptide screen to identify an alternate binding motif (i.e., CCKACC or KA tag), which has a similar brightness to the classical sequence upon MAP binding, but displays altered rates and affinities of association that permit the differential labeling of these peptide sequences by the red probe 4,5-bis(1,3,2-dithiarsolan-2-yl)-resorufin (ReAsH-EDT2) or its green cognate 4',5'-bis(1,3,2-dithoarsolan-2-yl)fluorescein (FLAsH-EDT2). The utility of this labeling strategy was demonstrated following the expression of PG- and KA-tagged subunits of RNA polymerase in E. coli. Specific labeling of two subunits of RNA polymerase in cellular lysates was achieved, whereby ReAsH-EDT2 is shown to selectively label the PG-tag on RNA polymerase alpha-subunit prior to the labeling of the KA-tag sequence of the beta-subunit of RNA polymerase with FlAsH-EDT2. These results demonstrate the ability to selectively label multiple individual proteins with orthogonal sequence tags in complex cellular lystates with spectroscopically distinct MAPs, and indicate the absolute specificity of ReAsH to target expressed proteins with essentially no nonspecific binding interactions.

CrAsH: a biarsenical multi-use affinity probe with low non-specific fluorescence.

CrAsH is a tetracysteine-binding probe which has improved properties in terms of signal-to-noise ratio and pH dependence of fluorescence compared to the parent compound.

Matrix screening of substituted N-aryl-1,8-naphthalimides reveals new dual fluorescent dyes and unusually bright pyridine derivatives.

A 3 x 14 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence. Because of their unique photophysical properties, these dual fluorescent systems represent an exception to the widely studied TICT (Twisted Internal Charge Transfer) fluorescent dyes or tautomeric benzofluorescein class of two-color dyes. The matrix library was designed to investigate the effects of heterocycles, particularly pi-excessive and pi-deficient systems. Of the 42 compounds surveyed, five displayed well-resolved two-color emission in solvents as nonpolar as hexane. Based on the observed trends in fluorescence lambda(max) and quantum yield, a new model is proposed that predicts LW and SW emission for these systems. In addition, this model provides potential design features for the synthesis of new dual fluorescent species.

Fluorescent chemosensors for carbohydrates: a decade's worth of bright spies for saccharides in review.

This review provides a chronological survey of over fifty fluorescent chemosensors for carbohydrates from the period between 1992 to the present. The survey contains only those sensors that are synthetic or chemosensory, utilize boronic acids and display a fluorescence response in the form of intensity changes or shifts in wavelength. With each compound listed, a description of the saccharide probe is given with regard to concentration, excitation and emission wavelengths, pH and solvent mixture proportions. In addition, the selectivity of each chemosensor is provided as well as the trends in binding constants. Where possible, a description of the fluorescence signaling mechanism is given as well as commentary on the probe's unique features within this class of sensors.

Substituent effects on monoboronic acid sensors for saccharides based on N-phenyl-1,8-naphthalenedicarboximides.

In the course of our investigations on new monoboronic acid saccharide sensors with C(0) spacers, a series of probes 1-6 based on 1,8-naphthalenedicarboximide were synthesized. Sensor 1 displays features typical of PET monoboronic acid sensors and shows high selectivity to fructose. Sensor 2 exhibits a novel dual emission and remarkable sensitivity for glucose relative to fructose and galactose through subtle changes in pH. Sensor 3 displays significantly enhanced fluorescence in the presence of galactose at low pH. Although probes 4-6 exhibit unique properties such as high quantum yield (Phi(F) = 0.407) and excellent solubility in water, they did not show significant change in fluorescence intensity in the presence of monosaccharides. The effects of substituent on all six probes lend support to the proposed photoelectrochemical model.

Enhanced photostability of ICG in close proximity to gold colloids.

Photobleaching of fluorophores frequently limits their detectability or observation time. We examined Indocyanine green (ICG) which is widely used in medical testing and is highly unstable. We showed that spatial localization of ICG near metallic gold colloids resulted in increased photostability. This suggests the use of fluorophore-metal conjugates in situations adversely affected by photobleaching.

Metal-Enhanced Fluorescence (MEF) Due to Silver Colloids on a Planar Surface: Potential Applications of Indocyanine Green to in Vivo Imaging.

We examined the effects of metallic silver colloids on the fluorescence spectral properties of indocyanine green (ICG), which is a dye widely used for in vivo medical testing. Silver colloids from a suspension bind spontaneously to amine-coated surfaces. These colloid-coated surfaces were found to cause a 30-fold increase in the intensity of ICG, which was held close to the metal surface by adsorbed albumin. The increased intensities of ICG were also associated with decreased lifetimes and increased photostability, which are indicative of modifying the fluorophores radiative decay rate. These results suggest the use of metal colloid-enhanced ICG for applications to retinal angiography and vascular imaging and as a contrast agent for optical tomography.

Monoboronic acid sensor that displays anomalous fluorescence sensitivity to glucose.

[reaction: see text]. A monoboronic acid fluorescent sensor was conveniently synthesized from 3-nitronaphthalic anhydride and 3-aminophenylboronic acid. This novel saccharide probe exhibits dual emission suitable for ratiometric sensing and displays a remarkable sensitivity for glucose relative to fructose and galactose.