posted on 2024-02-02, 22:43authored byMuhamed Amin, Divya Kaur, Gary W. Brudvig, Bernard R. Brooks
The
oxygen-evolving complex (OEC) of Photosystem II catalyzes the
water-splitting reaction using solar energy. Thus, understanding the
reaction mechanism will inspire the design of biomimetic artificial
catalysts that convert solar energy to chemical energy. Conceptual
Density Functional Theory (CDFT) focuses on understanding the reactivity
of molecules and the atomic contribution to the overall nucleophilicity
and electrophilicity of the molecule using quantum descriptors. However,
this method has not been applied to the OEC before. Here, we use Fukui
functions and the dual descriptor to provide quantitative measures
of the nucleophilicity and electrophilicity of oxygens in the OEC
for different models in different S states. Our results show that
the μ-oxo bridges connected to terminal Mn4 are nucleophilic,
and those in the cube formed by Mn1, Mn2, and Mn3 are mostly electrophilic.
The dual descriptors of the bridging oxygens in the OEC showed a similar
reactivity to that of bridging oxygens in Mn model compounds. However,
the terminal water W1, which is bound to Mn4, showed very strong reactivity
in some of the S3 models. Thus, our calculations support
the model that proposes the formation of the O2 molecule
through nucleophilic attack by a terminal water.