Near-fluorescent (NIR) dyes that absorb and emit light in the wavelength range of 650-1700 nm are well-suited for bioimaging due to the improved image contrast and increased penetration of the long-wavelength light through biological tissue. However, the imaging performance of NIR fluorescent dyes is limited by several inherent photophysical and physicochemical properties including, low fluorescence quantum yield, high chemical and photochemical reactivity, propensity to self-aggregate in water, non-specific association with off-target biological sites, and non-optimal pharmacokinetic profiles in living subjects. In principle, all these drawbacks can be alleviated by steric protection which is a structural process that surrounds the fluorophore with bulky groups that block undesired intermolecular interactions.
View Article and Find Full Text PDFThis report describes cucurbit[7]uril (CB7) complexation of azobenzene dyes that have a 4-(,'-dimethylamino) or 4-amino substituent. Absorption and NMR data show that CB7 encapsulates the protonated form of the azobenzene and that the complexed dye exists as its azonium tautomer with a azo conformation and substantial quinoid resonance character. Because CB7 complexation stabilizes the dye conjugate acid, there is an upward shift in its p, and in one specific case, the p of the protonated azobenzene is increased from 3.
View Article and Find Full Text PDFTwo new azobenzene heptamethine cyanine conjugates exist as dispersed monomeric molecules in methanol solution and exhibit near-infrared (NIR) cyanine absorption and fluorescence. Both conjugates form non-emissive cyanine H-aggregates in water, but the addition of cucurbit[7]uril (CB7) induces dye deaggregation and a large increase in cyanine NIR fluorescence emission intensity. CB7 encapsulates the protonated azonium tautomer of the 4-(,-dimethylamino)azobenzene component of each azobenzene-cyanine conjugate and produces a distinctive new absorption band at 534 nm.
View Article and Find Full Text PDFTwo new classes of near-infrared molecular probes were prepared and shown to exhibit "turn on" fluorescence when cleaved by the nitroreductase enzyme, a well-known biomarker of cell hypoxia. The fluorescent probes are heptamethine cyanine dyes with a central 4'-carboxylic ester group on the heptamethine chain that is converted by a self-immolative fragmentation mechanism to a 4'-caboxylate group that greatly enhances the fluorescence brightness. Each compound was prepared by ring opening of a Zincke salt.
View Article and Find Full Text PDFContinued advancement in bioresponsive fluorescence imaging requires new classes of activatable fluorescent probes that emit near-infrared fluorescence with wavelengths above 740 nm. Heptamethine cyanine dyes (Cy7) have suitable fluorescence properties but it is challenging to create activatable probes because Cy7 dyes have a propensity for self-aggregation and fluorescence quenching. A new synthetic strategy is employed to create a generalizable class of hydrophilic bioresponsive near-infrared fluorescent probes with appended sulfonates that provide excellent physiochemical properties.
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