Analogues synthesis of the GFP chromophore. Precursors of a new family of polymers without metallic components

Abstract

In this research study, the synthesis of a new set of organic molecules that present an analogous structure to the Green Fluorescent Protein’s chromophore is described. This protein,has nowadays a paramount importance in several areas of scientific knowledge, because it ismainly used as a biological marker. The analogous structures are formed by two aromatic rings bonded through an exocycliccarbon bridge. The first one is, in all the synthetized molecules, an electron-withdrawing heterocycle (imidazolone), whereas the electron delocalization in the other π-system depends onthe different substituents (R), that have been selected. In the specific case of GFP chromophore, the R substituent is an -OH group, located in thepara position respect to the carbon bridge. Consequently, this second heterocycle forms anelectron-donor system. As a result, the final structure of the GFP chromophore is 4-(phydroxybenzylidene) imidazolidin-5-one showed in the following figure.Previous studies disclose that this chromophore, and some synthetized analogues, showedan unexpected magnetic behaviour, being non-diamagnetic molecules. This behaviour is due tothe fact that there is a thermal equilibrium between the closed-shell singlet state and the excitedtriplet state, that is more stable when this type of molecule loss its planarity. This conformational equilibrium is called valence tautomerism.The formation of a stable diradical in the triplet excited state, can be understood with theresonance stabilization of the two unpaired electrons found, each one, in both aromatic rings,through the carbon bridge. The main objective of this study is to increase the existent family of this analogues withdifferent substituents, in para position, to see the impact on the stable formation of the diradical triplet. Subsequent studies will use these molecules to enable the anchoring in polymeric supports to check their magnetic response, and observe if a response amplification is produced by magnetic cooperativity between vicinal molecules. This fact could provide interesting advances in the development of new polymeric materials without metallic nor radical components in its structure