title: Ground state isomerization of a model green fluorescent protein chromophore.
abstract: The relationship between ground state cis-trans isomerization and protonation state is explored for a model green fluorescent protein chromophore, 4-hydroxybenzylidene-1,2-dimethylimidazolinone (HBDI). We find that the protonation state has only a modest effect on the free energy differences between cis and trans isomers and on the activation energies for isomerization. Specifically, the experimental free energy differences are 3.3, 8.8, and 9.6 kJ/mol for cationic, neutral, and anionic forms of HBDI, respectively, and the activation energies are 48.9, 54.8, and 54.8 kJ/mol for cationic, neutral, and anionic forms, respectively. Furthermore, these activation energies are much smaller than might be expected based on comparison with similar systems. These results suggest that there may be a sub-population of the chromophore, which is nearly equally accessible to all three protonation states, through which thermal isomerization may proceed.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: He
authors.forename: Alasdair F
authors.initials: AF
authors.lastname: Bell
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Tonge
mesh_terms: D049452:Green Fluorescent Proteins; D007477:Ions; D007536:Isomerism; D008164:Luminescent Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D013816:Thermodynamics
chemical_list: D007477:Ions; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins