Modeling near-edge fine structure x-ray spectra of the manganese catalytic site for water oxidation in photosystem II

• The Mn 1s near-edge absorption fine structure (NEXAFS) has been computed by means of transition-state gradient-corrected density functional theory (DFT) on four Mn 4Ca clusters modeling the successive S 0 to S 3 steps of the oxygen-evolving complex (OEC) in photosystem II (PSII). The model clusters were obtained from a previous theoretical study where they were determined by energy minimization. They are composed of Mn(III) and Mn(IV) atoms, progressing from Mn(III) 3Mn(IV) for S 0 to Mn(III) 2Mn(IV) 2 for S 1 to Mn(III)Mn(IV) 3 for S 2 to Mn(IV) 4 for S 3, implying an Mn-centered oxidation during each step of the photosynthetic oxygen evolution. The DFT simulations of the Mn 1s absorption edge reproduce the experimentally measured curves quite well. By the half-height method, the theoretical IPEs are shifted by 0.93 eV for the S 0 → S 1 transition, by 1.43 eV for the S 1 → S 2 transition, and by 0.63 eV for the S 2 → S 3 transition. The inflection point energy (IPE) shifts depend strongly on the method used to determine them, and the most interesting result is that the present clusters reproduce the shift in the S 2 → S 3 transition obtained by both the half-height and second-derivative methods, thus giving strong support to the previously suggested structures and assignments.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

Absorption edges

Absorption fine structure

Catalytic sites

Clusters modeling

Energy minimization

Fine structures

Gradient-corrected density functional theory

Inflection points

Oxygen evolution

Oxygen-evolving complexes

Photosystem II

Theoretical study

Transition-state

Water oxidation

X-ray spectra

Catalytic oxidation

Density functional theory

Manganese

oxygen

water

article

catalysis

chemical structure

energy

molecular model

oxidation

photosynthesis

roentgen spectroscopy

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