Combinatorial synthesis of new GFP- and RFP-like chromophores and their photophysical properties

Abstract

A new synthetic methodology for the combinatorial preparation of C-terminus-modified Green and Red Fluorescent Protein chromophores is described. This method involves the modification of the previously reported [2+3] cycloaddition reaction scheme to incorporate new R2 groups in the imidate used in the final step. This is achieved through two primary routes: (a) the imidation of nitriles using hydrochloric acid gas and (b) the O-alkylation of amides using a variant of Meerwein's Salt to provide conjugated imidates. The preparation of fluorescent microcrystals and nanofibers from Green Fluorescent Protein chromophore derivatives via the reprecipitation method is also demonstrated. The properties of these microcrystals and nanofibers, especially in relation to the powder obtained from organic solvents, are also explored. Additionally, it is demonstrated that the size and shape of the microcrystals and nanofibers can be modulated with varying experimental conditions for RP. A new class of AIE-active GFP chromophores is reported. These chromophores contain a benzoxazole group on the phenyl ring and varying lengths of alkyl chains on the imidazolidinone nitrogen. These benzoxazole-based chromophores exhibit unique properties in the solid state not previously observed for GFP chromophore derivatives, namely, a broadening of the excitation spectrum and red-shifting of the emission, likely caused by excimer formation. The crystal structure also reveals a unique "hot-dog" stacking motif. Additionally, some projects which require further work are discussed at the end of the thesis. These include a stress-responsive GFP-based polymer and DNA-binding fluorophores.