Green fluorescence protein (GFP), which serves as an energy acceptor and emitter for bioluminescence in the sea pansy Renilla reniformis and the jellyfish Aequorea Victoria, has drawn much attention because of its applications in molecular biology and biochemistry. 1 GFP takes advantage of the presence of a chromophore that is anchored both covalently and via a hydrogen-bond network, 4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (p-HBDI, see Scheme 1), which undergoes excited-state proton transfer (ESPT) 2 via the proton relay of water molecules and a remote residue such as E222, 3 resulting in a very effective and intense anion fluorescence.Nevertheless, studies reveal a strong cutoff between the properties of wild type GFP (or certain GFP mutants) and the synthetic analogue chromophores of p-HBDI. 4 In view of photophysics, the fluorescence yield of the protein-free chromophore in fluid solvents is much weaker and strongly temperature dependent. The results suggest an efficient radiationless transition operating in p-HBDI, most probably induced by conformational relaxation along torsional deformation of the two exocyclic C-C bonds to a nonfluorescent twisted intermediate. 5 More recently, it has been proposed that the shallow potential energy surface of the intermediates may conically intersect with that of the ground state, inducing the dominant radiationless deactivation. 4c-d,6 Such a conformational relaxation is greatly suppressed in GFP by its proton relay, rigid environment.In view of chemistry, most of the research has been focused on the chemical modification of p-HBDI analogues at the C(1) position. 4c,7 Conversely, in this study, we are interested in the derivatization on the phenyl ring. As an ingenious approach, switching the hydroxyl group from the C(8) position to the C(6) position (see Scheme 1), forming 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), a structural isomer of p-HBDI may reveal several novel features with respect to p-HBDI. The geometry optimization (B3LYP/cc-pVDZ and aug-cc-pVDZ, see ESI) of o-HBDI unveils the existence of a seven-memberedring intramolecular hydrogen bond between -OH and the N(2) atom. This intramolecular hydrogen-bonding configuration should, in part, hinder the exocyclic torsional deformation such that the radiationless deactivation may be reduced. More importantly, theoretical approaches also predict that excited-state intramolecular proton transfer (ESIPT) from the OH proton to the N(2) atom is thermally favorable (vide infra), forming a zwitterionic tautomer species (see Table of Content, TOC).In light of these perspectives, we have thus expended great effort to make a facile synthesis of o-HBDI. Briefly, the o-methoxybenzaldehyde was used as a starting reactant (see Scheme 1). Because of the lack of the o-hydroxyl group and hence the intramolecular lactonation, 3 was obtained with a good yield (70%). Subsequent reaction of 3 with methylamine, followed by deprotection of the methyl group of o-MBDI by BBr 3 , afforded o-H...

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. June 14, 2007; In Final Form: August 21, 2007 Femtosecond time-resolved photoelectron spectroscopy and high-level theoretical calculations were used to study the effects of methyl substitution on the electronic dynamics of the R, -enones acrolein (2-propenal), crotonaldehyde (2-butenal), methylvinylketone (3-buten-2-one), and methacrolein (2-methyl-2-propenal) following excitation to the S 2 (ππ*) state at 209 and 200 nm. We determine that following excitation the molecules move rapidly away from the Franck-Condon region, reaching a conical intersection promoting relaxation to the S 1 (nπ*) state. Once on the S 1 surface, the trajectories access another conical intersection, leading them to the ground state. Only small variations between molecules are seen in their S 2 decay times. However, the position of methyl group substitution greatly affects the relaxation rate from the S 1 surface and the branching ratios to the products. Ab initio calculations used to compare the geometries, energies, and topographies of the S 1 /S 0 conical intersections of the molecules are not able to satisfactorily explain the variations in relaxation behavior. We propose that the S 1 lifetime differences are caused by specific dynamical factors that affect the efficiency of passage through the S 1 /S 0 conical intersection.