Mechanism of resonant electron emission from the deprotonated GFP chromophore and its biomimetics

Abstract

By uncovering the mechanism of UV resonant electron emission, we show that the GFP biomimetics are more stable to photooxidation.

The Effect of Conjugation on the Competition between Internal Conversion and Electron Detachment: A Comparison between Green Fluorescent and Red Kaede Protein Chromophores

“…4) and contrasts with pHBDI -for which calculations have determined that ADE ≈ VDE. 24,26,[31][32]37 At the optimized D 0 minimum, the main structural changes with respect to S 0 are found in the imidazole ring (see bond lengths in Figure 2), which is consistent with the ring having a formal negative charge in the N(-)-1 anion.…”

“…In pHBDI -, the S 1 , S 2 and S 3 states are shape, Feshbach and excited-shape resonances, respectively, with respect to the D 0 continuum. 37 Thus, in pHBDI -the S 3 state that is accessible at 315 nm is so strongly coupled to the D 0 electronic continuum that it will undergo rapid autodetachment, resulting in a broadening of the photoelectron spectrum to lower eKEs (higher eBE) but not to a continuum at very low eKE.…”

“…Although there are many excited states and competing non-adiabatic decay pathways, the electron emission is dominated by a single, optically bright, excited state shape resonance that is strongly coupled to the electronic continuum. 24,37 The rKaede chromophore has two deprotonation states: the O(-) form which is deprotonated at revealed the chromophore in the protein to be deprotonated at the phenolic oxygen. 21,23 The pK a of unsubstituted imidazole in water (14.52) 38 is higher than that of phenol (9.95), suggesting that the phenoxy form might be the more stable form of the deprotonated isolated chromophore in the gas phase; however, MP2 calculations on seven N(-) and O(-) rKaede isomers with different side chain conformations indicate that the N(-) form is more stable in the gas phase (see Computational Details and Table S1 in the Supporting Information).…”

Chromophores of chromophores: a bottom-up Hückel picture of the excited states of photoactive proteins

“…The S 1 state of HDBI -has been the focus of a large number of gas-phase studies. 13,19,31,[33][34][35][36][37] A very insightful picture of the electronic structure of the S 1 state was provided by Bravaya et al, who rationalised the energetic shifts in different coloured photoactive proteins using a 3-centre allyl radical in a simple Hückel framework and a particle in the box model. 38 More recently, experimental and computational work has been directed to the higher-lying excited states in the UV spectral region.…”

“…[5][6][7] Gas-phase spectroscopy has been particularly valuable as it provides an unperturbed view of the excited states of the chromophores and of their dynamics. [8][9][10][11][12] Additionally, the gas-phase environment is tractable by highlevel electronic structure theory, [13][14][15][16] which when combined with experiment, provides a detailed understanding of the excited state dynamics. However, the reliance on very high level computational methods can mask some of the simple physical principles that are the foundation of the overall electronic structure of the chromophores.…”