New fluorescein adds to cellular probe arsenal

Pennsylvania Green is a newly synthesized fluorescein derivative reported to improve the pH range and photostability of the classical green fluorophore (Org. Lett. 2006, 8, 581). Switching key fluorescein substituents has already proven useful to optimize fluorescein to function under a broader range of pH conditions and light intensity. For example, commercially available Oregon Green has two fluorine substituents on the molecule's xanthene core, improving fluorescence at lower pH. Tokyo Green replaces the carboxylate group with a methyl group, increasing hydrophobicity to facilitate monitoring of intracellular activity. Pennsylvania Green, synthesized by Laurie F. Mottram in Blake R. Peterson's research group at Pennsylvania State University, is a hybrid of Oregon Green and Tokyo Green, incorporating both the fluorine and methyl substituents and reaping the benefits of both probes. Pennsylvania Green is less polar than Oregon Green and has better photostability than Tokyo Green, making it a potentially ideal probe for investigating cellular biology, Peterson says.