2026-10-14T08:18:58Z https://api.figshare.com/v2/oai

oai:figshare.com:article/33872460 2026-09-17T06:08:21Z category_1 category_4 category_146 category_8 category_14 category_272 category_873 category_69 portal_63 item_type_3 month_year_09_2026

Second-Sphere Protonation Imparts a Biologically Relevant Potential Shift in a Chlorophyll Model Compound Oscar Reid Kelly (21805486) David Emanuel Elcock (25002420) Katie Murphy (10083781) Brendan Twamley (1267278) Marcel Swart (639109) Aidan R. McDonald (2245723) Biophysics Biochemistry Space Science Microbiology Molecular Biology Environmental Sciences not elsewhere classified Chemical Sciences not elsewhere classified Inorganic Chemistry proximal charged substituents protonated amino acids local protein electrostatics protonated complex yielded cation radical complex electronic absorption spectroscopy sphere protonation imparts electron transfer chemistry coupled electron transfer porphyrin complex electron oxidation electronic structure vivo </ strong analogy significant increase redox potential ray diffraction probe directly potential chlorophyll postulated influence porphyrin ring porphyrin macrocycle porphyrin framework pigment interactions oxidized chlorophyll limited proton experimental techniques experimental data cyclic voltammetry crystal x corresponding π based oxidants achieving high >; however Electrostatic protein-pigment interactions have been implicated in tuning the electron transfer chemistry of chlorophylls <i>in vivo</i>; however, these effects are difficult to probe directly, leading to a dearth of experimental data that limits our understanding. Herein, we report a chlorophyll model compound based on a Mg-porphyrin framework with a secondary coordination sphere designed to probe isolated electrostatic interactions with the porphyrin macrocycle. Protonation of two second-sphere amine groups led to a significant increase in the redox potential of the porphyrin ring, drawing a strong analogy to the postulated influence of protonated amino acids on the properties of chlorophylls <i>in vivo</i>. Experimental techniques (electronic absorption spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry) were complemented by density functional theory calculations to uncover the impact of the proximal charged substituents on the electronic structure of the Mg-porphyrin complex. 1-electron oxidation of the protonated complex yielded the corresponding π-cation radical complex, which mimicked the reaction between photo-oxidized chlorophyll and tyrosine during photosynthesis by rapidly oxidizing phenolic substrates to yield phenoxyl radicals via electron-transfer-limited proton-coupled electron transfer. Overall, this work lends strong experimental support for the role of local protein electrostatics in achieving high-potential chlorophyll-based oxidants in Nature. 2026-09-17T00:00:00Z Dataset Dataset 10.1021/jacs.6c12109.s002 https://figshare.com/articles/dataset/Second-Sphere_Protonation_Imparts_a_Biologically_Relevant_Potential_Shift_in_a_Chlorophyll_Model_Compound/33872460 CC BY-NC 4.0