The photophysics of isolated protein chromophores

Gas-phase absorption properties of chromophores of several photoactive proteins have been studied experimentally at the electrostatic heavy-ion storage ring ELISA in Aarhus. The absorption wavelength has been calculated using an augmented effective Hamiltonian technique based on the multiconfigurational quasi-degenerate perturbation theory. The results have been compared to those of widely used state-specific second-order perturbation theory formalisms and their multistate extensions and also to ground-state linear response methods. It would appear that ab initio theory is now at a stage where the intrinsic properties of the chromophore molecules may be predicted with reasonable precision. There is evidence that in terms of absorption there is almost vacuum-like conditions in the hydrophobic interior of some proteins like the green fluorescent protein (GFP). In others, like for example the visual opsins, some significant perturbations are responsible for colour tuning

On the temperature of large biomolecules in ion-storage rings

A method to determine the temperature of molecular ions in an ion-storage ring is presented. Molecular ions were repeatedly irradiated by laser pulses over several hundred milliseconds, and the rate of fragmentation was used to determine the temperature of the photoexcited ions. The initial temperature of the ions before photoabsorption was in turn found from the microcanonical caloric curve for the molecule of interest. The temperature evolution of the protonated GFP chromophore in the ELISA storage ring was found for different starting conditions by this method. We find that the initial temperature of the ions when entering the ring depends on the ion-trap temperature and the amount of buffer gas used in the trap. In particular, collisional heating during acceleration after the ion trap can be significant. Protonated GFP chromophores, produced under different conditions, were used to determine temperature effects on the gas-phase absorption spectra

Designing Red-Shifted Molecular Emitters Based on the Annulated Locked GFP Chromophore Derivatives

Bioimaging techniques require development of a wide variety of fluorescent probes that absorb and emit red light. One way to shift absorption and emission of a chromophore to longer wavelengths is to modify its chemical structure by adding polycyclic aromatic hydrocarbon (PAH) fragments, thus increasing the conjugation length of a molecule while maintaining its rigidity. Here, we consider four novel classes of conformationally locked Green Fluorescent Protein (GFP) chromophore derivatives obtained by extending their aromatic systems in different directions. Using high-level ab initio quantum chemistry calculations, we show that the alteration of their electronic structure upon annulation may unexpectedly result in a drastic change of their fluorescent properties. A flip of optically bright and dark electronic states is most prominent in the symmetric fluorene-based derivative. The presence of a completely dark lowest-lying excited state is supported by the experimentally measured extremely low fluorescence quantum yield of the newly synthesized compound. Importantly, one of the asymmetric modes of annulation provides a very promising strategy for developing red-shifted molecular emitters with an absorption wavelength of ∼600 nm, having no significant impact on the character of the bright S-S1 transition