Combinatorial Fluorescent Probes

Scientists develop a range of full-color tunable fluorescent molecules in one-pot reactions with a single core skeleton structure.

Fig. 1: The emissive properties of some of the new fluorescent probes along with their molecular structure and ability to label cells in vitro.

Fluorescent molecules are used extensively as research tools in biology and biomedicine, as well as being of interest for potential application as organic light emitting diodes. However, in spite of the great demand for these materials, the availability of different core molecules—critical components of new fluorescent probes—is limited. Now scientists from Korea¹ have used computational studies and combinatorial methods to develop a library of full-color tunable fluorescent molecules based on one new core fluorescent molecule.

Seung Bum Park and colleagues used a recently reported synthetic development pathway to identify the novel core skeleton known as 1,2-dihydropyrrolo(3,4-ß)indolizin-3-one. The researchers calculated the positions where substituents could be added to the molecule to tune its emissive properties.

One-pot reactions involving several chemical manipulations of combinations of different aldehydes and pyridines with different electronic properties resulted in a library of 24 novel fluorescent molecules with different colour emissions all with a consistent core skeleton molecular structure.

The library of molecules generated showed dramatic changes in their fluorescent properties simply by having different substituents at two different points on the core molecular framework as a result of using different combinations of pyridines and aldehydes. They also demonstrated the significant correlation of emission wavelength with the electronic properties of substituent, confirmed by experimental data as well as computational study. Compared with the well known molecule Fluorescein, the new molecule was more resistant to photobleaching and its emission was not affected by pH, unlike Fluorescein.

Next, the researchers investigated whether their probes could be used as tools for biological investigations. The molecules were lipophilic enabling cell membrane permeability. Hydroxy groups present on the new fluorescent probes were easily converted to azides or amines without affecting their photochemical properties. The researchers then charged the molecules with a maleimide group which enabled conjugation with thiol groups in cysteine residues of proteins. In this way Park and colleagues demonstrated direct in vitro labelling of several different proteinaceous species present in HeLa cells.