The origin of the red shift of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si14.svg"><mml:mrow><mml:msub><mml:mrow><mml:mi>Q</mml:mi></mml:mrow><mml:mrow><mml:mi>y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> band of chlorophylls d and f

Poddubnyy, Vladimir V.; Kozlov, Maxim I.; Glebov, I. O.

doi:10.1016/j.cplett.2021.138792

Cited by 5 publications

(6 citation statements)

References 31 publications

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“…Overall, the minimal (4,4) AS can provide a reasonable qualitative description of the Q-band if at least 4 states are included in the orbital optimization, but it is insufficient to reproduce the energy difference between the states contributing to the Qband. Interestingly, the (4,4) AS has been considered insufficient for Chl a, 76 but the present results show that it can still provide a reasonable description if SA-CASSCF is performed including more roots. It is not obvious at this point whether these deficiencies of the Gouterman space can be fully compensated when the (4,4) AS is used as the RAS2 subspace in the context of a RASSCF approach.…”

Section: Rational Selection Of the Minimal Asmentioning

confidence: 60%

“…Large differences between the excitation energies derived from CASSCF and NEVPT2 are observed in all calculations carried out in this work (see Tables S1 and S2 for comparison of CASSCF and NEVPT2 energies for the (4,4) AS). This shows that accounting for dynamic correlation effects is crucial for obtaining meaningful results for porphyrin derivatives, 70,72,75,76 thus in the remainder of this work we report and discuss only the NEVPT2 energies (complete results from all calculations are provided as Supporting Information). Importantly, in many cases NEVPT2 even changes the order of the CASSCF states, which implies that the number of roots to be included in the initial CASSCF procedure must be treated with utmost care to ensure that the number of states is sufficient to produce stable final (NEVPT2) results.…”

Section: Rational Selection Of the Minimal Asmentioning

confidence: 99%

“…Multireference methods have been previously employed for the study of electronic spectra of highly symmetric parent compounds of (magnesium) chlorin, i.e. (magnesium) porphyrin (Figure 1), 52,70−74 and comparatively less on chlorophylls 61,63,75,76 and bacteriochlorophylls. 33,65,77,78 Technical choices such as the size and composition of the active space (AS) and the number of states included in the stateaveraged orbital optimization significantly affect the predicted energies and nature of the calculated states.…”

Section: Introductionmentioning

confidence: 99%

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Combined Multireference–Multiscale Approach to the Description of Photosynthetic Reaction Centers

Drosou,

Bhattacharjee,

Pantazis

2024

J. Chem. Theory Comput.

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A first-principles description of the primary photochemical processes that drive photosynthesis and sustain life on our planet remains one of the grand challenges of modern science. Recent research established that explicit incorporation of protein electrostatics in excited-state calculations of photosynthetic pigments, achieved for example with quantum–mechanics/molecular–mechanics (QM/MM) approaches, is essential for a meaningful description of the properties and function of pigment–protein complexes. Although time-dependent density functional theory has been used productively so far in QM/MM approaches for the study of such systems, this methodology has limitations. Here we pursue for the first time a QM/MM description of the reaction center in the principal enzyme of oxygenic photosynthesis, Photosystem II, using multireference wave function theory for the high-level QM region. We identify best practices and establish guidelines regarding the rational choice of active space and appropriate state-averaging for the efficient and reliable use of complete active space self-consistent field (CASSCF) and the N-electron valence state perturbation theory (NEVPT2) in the prediction of low-lying excited states of chlorophyll and pheophytin pigments. Given that the Gouterman orbitals are inadequate as a minimal active space, we define specific minimal and extended active spaces for the NEVPT2 description of electronic states that fall within the Q and B bands. Subsequently, we apply our multireference–QM/MM protocol to the description of all pigments in the reaction center of Photosystem II. The calculations reproduce the electrochromic shifts induced by the protein matrix and the ordering of site energies consistent with the identity of the primary donor (ChlD1) and the experimentally known asymmetric and directional electron transfer. The optimized protocol sets the stage for future multireference treatments of multiple pigments, and hence for multireference studies of charge separation, while it is transferable to the study of any photoactive embedded tetrapyrrole system.

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Section: Rational Selection Of the Minimal Asmentioning

confidence: 60%

Section: Rational Selection Of the Minimal Asmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combined Multireference–Multiscale Approach to the Description of Photosynthetic Reaction Centers

Drosou,

Bhattacharjee,

Pantazis

2024

J. Chem. Theory Comput.

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“…Great care must be taken in the selection of active spaces for multi-configurational approaches. Previous theoretical investigations have achieved reasonable results with small, 70 medium-sized 71,72 and very large 22,23 active spaces. After initial testing, we settled on an active space of six electrons in six orbitals (Fig.…”

Section: Methodsmentioning

confidence: 85%

Q-Band relaxation in chlorophyll: new insights from multireference quantum dynamics

Reiter

Bäuml

Hauer

et al. 2022

Phys. Chem. Chem. Phys.

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“…This observation suggests that the pretreatments effectively cleaved the acetyl groups, aligning with the xylan removal results exhibited in Table 1. A redshift in the band of pretreated reed was observed, indicative of changes in the reed structure [39]. The bands at 1245 cm − 1 , associated with C-O within lignin and hemicellulose [40], were signi cantly weakened in pretreated reed samples compared to untreated feedstock (Fig.…”

Section: Ftir Analysismentioning

confidence: 91%

Efficient production of fermentable sugars from common reed biomass through hydrothermal and citric acid pretreatment processes

Wang,

You,

Gui

et al. 2024

Preprint

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Producing fermentable sugars from lignocellulosic biomass could provide renewable substrate for biofuel production by microbial fermentation. However, the structure of lignocellulose hinders enzymatic saccharification efficiency to obtain sugars, thus development of efficient pretreatment methods to reduce the biomass recalcitrance is an important issue. In this study, the effects of two typical processes including hydrothermal (HTP) and citric acid pretreatments (CAP) on the enzymatic hydrolysis yield of reed biomass were investigated. The results indicate that a higher glucose yield of 87.1% was achieved using cellulase of 10 FPU/g substrate following HTP conducted at 180 ℃ for 120 min. Subsequently, a yield of 63.4% glucose was realized after enzymatic hydrolysis with cellulase when subjected to reed pretreatment with 6% (w/v) CA at 150 ℃ for 60 min. The enhancement in enzymatic yield to 84.2% was also achieved by adding Tween-80 of 100 mg/g substrate. The mechanism of enhanced enzymatic hydrolysis by HTP and CAP processes was elucidated through physicochemical characterization techniques. Overall, this study offers valuable insights for the production of fermentable sugars from renewable lignocellulose.

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The origin of the red shift of Qy band of chlorophylls d and f

Cited by 5 publications

References 31 publications

Combined Multireference–Multiscale Approach to the Description of Photosynthetic Reaction Centers

Combined Multireference–Multiscale Approach to the Description of Photosynthetic Reaction Centers

Q-Band relaxation in chlorophyll: new insights from multireference quantum dynamics

Efficient production of fermentable sugars from common reed biomass through hydrothermal and citric acid pretreatment processes

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