Michael D. Heagy

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 probes unique features within this class of sensors.

FLUORESCENT CHEMOSENSOR FOR CARBOHYDRATES WHICH SHOWS LARGE CHANGE IN CHELATION-ENHANCED QUENCHING

A new water-soluble saccharide receptor based on a naphthalic anhydride fluorophore was synthesized from 3-aminophenylboronic acid. The large change in fluorescence intensity (IIo=ca. 0.25) and measured pKa (7.7) make this compound a useful chemosensor at neutral pH.

Dual Fluorescent N-Aryl-2,3- naphthalimides: Applications in Ratiometric DNA Detection and White Organic Light-Emitting Devices

A ten element matrix of 5- and 6-substituted-(2,3)-naphthalimides was prepared for the appropriate placement of substituents necessary to promote dual fluorescence (DF). As prescribed by our balanced seesaw photophysical model this matrix yielded nine new DF dyes out of a possible ten compounds. From this set of nine DF dyes, 4-fluoronaphthalic amide (37) was selected as a probe for ratiometric detection of DNA and demonstration of panchromatic emission.

Highly Water-Soluble Monoboronic Acid Probes That Show Optical Sensitivity to Glucose Based on 4-Sulfo-1,8-naphthalic Anhydride

Two highly water-soluble monoboronic acid probes that display the more desirable off-on fluorescence response were synthesized based on 4-sulfo-1,8-naphthalic anhydride and a remarkable sensitivity for glucose rather than fructose and galactose was also observed.

An organic white light-emitting dye: very small molecular architecture displays panchromatic emission

The synthesis and photophysical characterization of a new white-light fluorophore is described. The optimization of excitation wavelengths allows the naphthalimide (NI) dyes to display blue, green or white light emission depending on the excitation wavelength.

Spectroscopic and Photophysical Characterization of Fluorescent Chemosensors for Monosaccharides Based on N-Phenylboronic Acid Derivatives of 1,8-Naphthalimide

Spectroscopic and photophysical properties of two fluorescent probes for monosaccharides are presented. Probes are based on the N-phenyl-1,8-naphthalimide structure having the boronic acid group [R-B(OH)2] in ortho in one case, and meta in the other case, positions of the N-phenyl group. Formation of the anionic form of the boronic acid group [R-B(OH)−3] induced a substantial decrease of the steady-state fluorescence of both compounds. Because no change in the fluorescence lifetime from the neutral to the anionic forms is observed, static quenching resulting from photoinduced electron transfer from the anionic form of the boronic acid is used to explain the decrease of the emission intensity. Both compounds show substantial decreases of their fluorescence intensity in the presence of sugars. In addition, this decrease of the fluorescence intensity is associated with an increase of the fluorescence lifetime for the ortho derivative while no effect on the lifetime is observed for the meta derivative. Both photoinduced electron transfer and steric hindrance are discussed to correlate the observed results.

An abiotic fluorescent probe for cardiac troponin I.

The first ratiometric fluorescent reporter was designed for the detection of cardiac troponin I (cTnI), a key protein elicited during cardiac muscle cell death. In designing this abiotic fluorescent probe, docking simulation studies were performed to predict the probe/protein interactions along the solvent exposed regions of cTnI. Simple cuvette titration experiments in aqueous buffered solution indicate remarkable selectivity for cardiac troponin in the clinically relevant nM region versus skeletal troponin.

A Comparative Study into Two Dual Fluorescent Mechanisms via Positional Isomers of N-hydroxyarene-1,8-naphthalimides

Three isomers of hydroxy substituted N-aryl-1, 8-naphthalimides based on N-aryl naphthalic anhydride fluorophore have been synthesized. The decrease in fluorescence intensity from ortho to para substitution of hydroxy group on N-aryl reveals that para substituted isomer undergoes ESEC (Excited State with Extended Conjugation) mechanism which is proved by low quantum yield and appearance of dual emission. The ortho isomer, however, has high quantum yield and no tautomer emission, indicating ESIPT (Excited State Intramolecular Proton Transfer) mechanism is not operating. Similarly, all these isomers show strong fluorescence quenching in presence of strong H-bonding solvents like DMSO and pyridine, but there was neither the shift of emission bands nor the appearance of new bands for proton transfer to these solvents. Thus, it also indicates the absence of excited state proton transfer mechanism. Both the ortho isomer, and to a greater degree the meta isomer, showed larger quenching constants (Kapp) with pyridine than DMSO. This trend opposes the hydrogen-bond affinity for these solvents with phenol and points to a 2-point recognition interaction. In addition, a naphthalimide derivative using 2-aminoimidazole was prepared and examined for optimal positioning of a six-membered ring hydrogen bond pattern. No dual fluorescence was observed for this compound either.

Neo-Pentoxide Precursor Synthesis, Solution Preparation, and Electronic Properties of (Ba,Sr)TiO3 Thin Films Derived from a Solution Route

We have recently isolated the neo-pentoxide (HOCH2CMe3, ONp) derivatives of Ba, Sr, and Ti as Ba4(ONp)8(HONp)6(py)2, Sr5(O)(ONp)8(Solv)5 (Solv = solvent), and Ti2(ONp)8, respectively. The combination of these precursors were found to be readily soluble in a wide range of solvents and thus were excellent candidates for preparation of barium strontium titanate ((Ba,Sr)TiO3 or BST) thin films using spin-cast deposition techniques. The highest quality BST films for this system were generated from ternary mixtures dissolved in either pyridine or pyridine/toluene. By in situ VT-GIXRD analysis it was determined that the perovskite phase of BST was readily formed at 650°C. The electronic properties of films crystallized at 700°C indicated that the thin films (300 nm) possessed a dielectric constant of 120 (tan δ = 0.03) with a tunability of 29% at ±10 V. 300 nm films (700°C) which had been generated from a standard BST solution modified with a novel tridentate ligand, had a higher dielectric constant of 180 and a tunability of 35% at ±10 V. The collective characteristics of these precursors offer an attractive alternative to the more complex, less stable sol-gel precursors currently in use.

Theme and Variation on N -Aryl-1, 8-Napthalimides: Minimal Modification to Red-Shifted Fluorescence and Applications in Fluorescent Chemosensors

Our continuing efforts into the development of N-aryl-1,8-naphthalic dicarboximides (NI) as dual fluorescent (DF) dyes for biomedical applications has led to new insights into the photophysical features that these simple dyes can be designed to display. Consequently, the development of new DF dyes with improved fluorescent properties represents a major focus of our research. The first section of this review presents results involving a “minimal modification approach” to red-shifted absorption and fluorescence in NIs and affords some key design concepts for improved DF dyes. In this section, we demonstrate the significant effect of appropriately placed charges can have on the emission properties of these unique dyes. In the next section, dual fluorescent probes for the ions of potassium and sodium are introduced with the NI framework and crown ether receptors. The ratiometric features of these dyes from absorption as well as fluorescence spectroscopy are highlighted. Finally, in the third section, we demonstrate dual fluorescence detection of saccharides with the same DF dye component as our ion probe, in this case, however, a simple phenylboronic acid is utilized as a saccharide binding component.