ORGN 586 |
| Molecular probes derived from fluorescein are widely used as tools for studies of cellular biology. This classic green fluorophore is particularly suited for cellular analysis by confocal laser scanning microscopy and flow cytometry due to its excitation maximum at 490 nm, closely matching the 488 nm spectral line of the argon-ion laser. Under physiological conditions (pH = 7.4), fluorescein predominantly exists as a highly hydrophilic dianion exhibiting excellent quantum yield. However, protonation of fluorescein to the monoanion is observed with the relatively high pKa of 6.5, rendering this dye much less fluorescent in acidic solutions. Additionally, fluorescein is relatively susceptible to photobleaching. Oregon Green, a more acidic 2', 7'-difluoro derivative of fluorescein, was developed as a less pH-sensitive fluorophore. The appended fluorine atoms reduce the pKa of this dye to 4.8, substantially improving both photostability and fluorescence at low pH. Another more hydrophobic fluorescein analogue termed Tokyo Green was recently reported that replaces the carboxylate with a methyl group. This structural modification yields a highly fluorescent monoanion. We report a novel fluorophore termed Pennsylvania Green that combines the pH-insensitivity and photostability of Oregon Green with the hydrophobicity of Tokyo Green. To demonstrate the utility of the Pennsylvania Green fluorophore, we compared cellular membrane probes derived from 4-carboxy Tokyo Green and 4-carboxy Pennsylvania Green. Because of its lower pKa, only the Pennsylvania Green-derived probe enables facile visualization of acidic endosomes within living mammalian cells.
|
|
New Reactions and Methodology, Heterocycles and Aromatics, Bioorganic Chemistry
8:00 PM-10:00 PM, Tuesday, 12 September 2006 Moscone Center -- Hall D, Poster
Division of Organic Chemistry |
