145 research outputs found

    Chromophore-Protein Coupling beyond Nonpolarizable Models: Understanding Absorption in Green Fluorescent Protein

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    The nature of the coupling of the photoexcited chromophore with the environment in a prototypical system like green fluorescent protein (GFP) is to date not understood, and its description still defies state-of-the-art multiscale approaches. To identify which theoretical framework of the chromophore protein complex can realistically capture its essence, we employ here a variety of electronic-structure methods, namely, time-dependent density functional theory (TD-DFT), multireference perturbation theory (NEVPT2 and CASPT2), and quantum Monte Carlo (QMC) in combination with static point charges (QM/MM), DFT embedding (QM/DFT), and classical polarizable embedding through induced dipoles (QM/MMpol). Since structural modifications can significantly affect the photophysics of GFP, we also account for thermal fluctuations through extensive molecular dynamics simulations. We find that a treatment of the protein through static point charges leads to significantly blue-shifted excitation energies and that including thermal fluctuations does not cure the coarseness of the MM description. While TDDFT calculations on large cluster models indicate the need of a responsive protein, this response is not simply electrostatic: An improved description of the protein in the ground state or in response to the excitation of the chromophore via ground-state or state-specific DFT and MMpol embedding does not significantly modify the results obtained with static point charges. Through the use of QM/MMpol in a linear response formulation, a different picture in fact emerges in which the main environment response to the chromophore excitation is the one coupling the transition density and the corresponding induced dipoles. Such interaction leads to significant red-shifts and a satisfactory agreement with full QM cluster calculations at the same level of theory. Our findings demonstrate that, ultimately, faithfully capturing the effects of the environment in GFP requires a quantum treatment of large photoexcited regions but that a QM/classical model can be a useful approximation when extended beyond the electrostatic-only formulation

    Monographie Systematique des phyllopodes Conchostraces

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    Volume: 20Start Page: 39End Page: 33

    Freilebende S\ufcsswasser-Nemathelminthen aus der Schweiz

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    Volume: 19Start Page: 501End Page: 53

    Untersuchungen \ufcber die S\ufcsswasser-Mikrofauna Deutsch-Ost-Afrikas

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    Volume: 59Start Page: 1End Page: 31

    Untersuchungen \ufcber die S\ufcsswasser-Mikrofauna Paraguays

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    Volume: 18Start Page: 1End Page: 34

    Monographie syst\ue9matique des Phyllopodes anostrac\ue9s

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    Volume: 11Start Page: 91End Page: 48
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