Dynamic Electron Correlation Effects on the Ground State Potential Energy Surface of a Retinal Chromophore Model

We investigate the origin of the excitation energy shifts induced by the apoprotein in the active site of the bacterial photoreceptor BLUF (Blue Light sensor Using Flavin adenine dinucleotide). In order to compute the vertical excitation energies of three low-lying electronic states, including two π-π* states of flavin (S1 and S2) and a π-π* tyrosine-flavin electron-transfer state (ET), with respect to the energy of the closed-shell ground state (S0), we prepared alternative quantum mechanical (QM) cluster and quantum mechanics/molecular mechanics (QM/MM) models. We found that the excitation energies computed with both types of models correlate with the magnitude of the charge transfer character of the excitation. Accordingly, we conclude that the small charge transfer character of the light absorbing S0-S1 transition and the substantial charge transfer character of the nonabsorbing but redox active S0-ET transition explain the small color changes but substantial redox tuning in BLUF and also in other flavoproteins. Further analysis showed that redox tuning is governed by the electrostatic interaction in the QM/MM model and transfer of charge between the active site and its environment in the QM cluster. Moreover, the wave function polarization of the QM subsystem by the MM subsystem influences the magnitude of the charge transfer, resulting in the QM/MM and QM excitation energies that are not entirely consistent.

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“…A similar MS-CASPT2 artifact was previously reported elsewhere 89 (see for instance Figure 2A in ref. 89).…”

Section: ሺ1ሻsupporting

confidence: 86%

Role of the Molecular Environment in Flavoprotein Color and Redox Tuning: QM Cluster versus QM/MM Modeling

Udvarhelyi

Olivucci

Domratcheva

2015

J. Chem. Theory Comput.

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“…Larger active spaces are demonstrated to palliate this effect but cannot be presently considered in this work to properly validate the MS-CASPT2 result, so we expect future results employing larger active spaces to be placed in between the estimates here given for the CASPT2 and MS-CASPT2 methods [81]. More accurate estimates are expected from the extended multistate (XMS) approach of Granovsky [82] and its related implementations [83][84][85][86][87][88].…”

Section: Type Of Calculationmentioning

confidence: 89%

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

et al. 2016

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Abstract:The present study provides new insights into the topography of the potential energy hypersurfaces (PEHs) of the thymine nucleobase in order to rationalize its main ultrafast photochemical decay paths by employing two methodologies based on the complete active space self-consistent field (CASSCF) and the complete active space second-order perturbation theory (CASPT2) methods: (i) CASSCF optimized structures and energies corrected with the CASPT2 method at the CASSCF geometries and (ii) CASPT2 optimized geometries and energies. A direct comparison between these strategies is drawn, yielding qualitatively similar results within a static framework. A number of analyses are performed to assess the accuracy of these different computational strategies under study based on a variety of numerical thresholds and optimization methods. Several basis sets and active spaces have also been calibrated to understand to what extent they can influence the resulting geometries and subsequent interpretation of the photochemical decay channels. The study shows small discrepancies between CASSCF and CASPT2 PEHs, displaying a shallow planar or twisted 1 (ππ*) minimum, respectively, and thus featuring a qualitatively similar scenario for supporting the ultrafast bi-exponential deactivation registered in thymine upon UV-light exposure. A deeper knowledge of the PEHs at different levels of theory provides useful insight into its correct characterization and subsequent interpretation of the experimental observations. The discrepancies displayed by the different methods studied here are then discussed and framed within their potential consequences in on-the-fly non-adiabatic molecular dynamics simulations, where qualitatively diverse outcomes are expected.

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“…To enhance sensitivity, quantum yields must be maximized, whereas thermal rates, which create the "background noise" in the signal, must be minimized. Although Rh quantum yield computations have been reported (48), their significance is limited by the affordable numbers of semiclassical trajectories and, most importantly, by the cost of accurate MCQC energy gradients (49). To avoid these limitations, here we discuss the relative quantum yields of hMeOp, sqRh, and Rh using the correlation proposed by Weiss and Warshel (50) and Mathies and coworkers (25) who also provided supporting experimental evidence (51).…”

Section: Significancementioning

confidence: 95%

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Rinaldi

Melaccio

Gozem

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260 (5553):679-683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol −1 higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131-6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412-415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsincontaining cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates.F or a long time it was assumed that the human retina contains only two types of photoreceptor cells: the rods and cones responsible for dim-light and daylight vision, respectively. However, recent studies have revealed the existence of a small number of intrinsically photosensitive retinal ganglion cells (ipRGCs) that regulate nonvisual photoresponses (1). ipRGCs express an atypical opsin-like protein named melanopsin (2, 3) which plays a role in the regulation of unconscious visual reflexes and in the synchronization of endogenous physiological responses to the dawn/dusk cycle (circadian rhythms) (4, 5).Melanopsins are unique among vertebrate photoreceptors because their amino acid sequence shares greater similarity to invertebrate than vertebrate rhodopsin (i.e., the photoreceptor of rods) (6, 7). Like rhodopsins, melanopsins feature an up-down bundle architecture of seven transmembrane α-helices incorporating the 11-cis isomer of retinal as a covalently bound protonated Schiff base (PSB11 in Fig. 1A). Light-induced (i.e., photochemical) isomerization of PSB11 to its all-trans isomer (PSBAT) triggers an opsin conformational change that, ultimately, activates the receptor and signaling cascade (8, 9). However, similar to invertebrate and in contrast to vertebrate rhodopsins, melanopsins are bistable ...

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Dynamic Electron Correlation Effects on the Ground State Potential Energy Surface of a Retinal Chromophore Model

Cited by 161 publications

References 56 publications

Role of the Molecular Environment in Flavoprotein Color and Redox Tuning: QM Cluster versus QM/MM Modeling

Role of the Molecular Environment in Flavoprotein Color and Redox Tuning: QM Cluster versus QM/MM Modeling

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

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