Role of Intact Hydrogen-Bond Networks in Multiproton-Coupled Electron Transfer

Abstract

The essential role of a well-defined hydrogen-bond network in achieving chemically reversible multiproton translocations triggered by one-electron electrochemical oxidation/reduction is investigated by using pyridylbenzimidazole−phenol models. The two molecular architectures designed for these studies differ with respect to the position of the N atom on the pyridyl ring. In one of the structures, a hydrogen-bond network extends uninterrupted across the molecule from the phenol to the pyridyl group. Experimental and theoretical evidence indicates that an overall chemically reversible two-protoncoupled electron-transfer process (E2PT) takes place upon electrochemical oxidation of the phenol. This E2PT process yields the pyridinium cation and is observed regardless of the cyclic voltammogram scan rate. In contrast, when the hydrogen-bond network is disrupted, as seen in the isomer, at high scan rates (∼1000 mV s −1 ) a chemically reversible process is observed with an E 1/2 characteristic of a one-proton-coupled electron-transfer process (E1PT). At slow cyclic voltammetric scan rates (<1000 mV s −1 ) oxidation of the phenol results in an overall chemically irreversible two-proton-coupled electron-transfer process in which the second proton-transfer step yields the pyridinium cation detected by infrared spectroelectrochemistry. In this case, we postulate an initial intramolecular proton-coupled electron-transfer step yielding the E1PT product followed by a slow, likely intermolecular chemical step involving a second proton transfer to give the E2PT product. Insights into the electrochemical behavior of these systems are provided by theoretical calculations of the electrostatic potentials and electric fields at the site of the transferring protons for the forward and reverse processes. This work addresses a fundamental design principle for constructing molecular wires where protons are translocated over varied distances by a Grotthuss-type mechanism.

Concerted Electron-Nuclear Motion in Proton-Coupled Electron Transfer-Driven Grotthuss-Type Proton Translocation

“…The differential driving force (between E1PT and E2PT states) obtained electrochemically is consistent with quantum chemical calculations performed on the full PF 15 -BIP-Pyr molecule (see section 3 of the Supporting Information and Table S2 ). Therefore, only the E2PT product is expected to be populated at thermodynamic equilibrium in these measurements, just as previously determined for BIP-Pyr in a recent study, 28 and as expected on the basis of the IRSEC results presented above.…”

“…The E 1/2 of a reference compound that can undergo only one-electron, one-proton transfer (E1PT) (BIP + -Pyr/BIP-Pyr) was measured to be 1.01 V versus SCE. 28 Assuming the center-to-center distance between the phenol and porphyrin moieties ( l ) to be 6.4 Å and the excited state (S 1 ) energy ( E 00 ) to be 1.92 eV, the driving force (Δ G ) can be estimated to be −300 and −140 meV for the E2PT and E1PT products, respectively (see section 2.1 of the Supporting Information for further details). The differential driving force (between E1PT and E2PT states) obtained electrochemically is consistent with quantum chemical calculations performed on the full PF 15 -BIP-Pyr molecule (see section 3 of the Supporting Information and Table S2 ).…”

Macrophage biomimetic nanocarriers for anti-inflammation and targeted antiviral treatment in COVID-19

“…In this study, PLGA@M manifested the talent in suppressing the formation of NETs induced by COVID-19 patient serum, suggesting that PLGA@M could play a multi-role in the treatment of COVID-19, and offer a comprehensive therapeutic benefit to patients. Meanwhile, NETs also engaged in the progression of multiple diseases including cardiovascular diseases [ 56 , 68 ], rheumatoid arthritis [ 69 ], diabetes [ 70 ], cancer [ 71 , 72 ] and so on, which meant that PLGA@M may have a potential to treat these diseases as well. However, the detailed mechanisms of how PLGA@M remove NETs and the possibility of clinical application still needed further exploration.…”

Computational investigation into intramolecular hydrogen bonding controlling the isomer formation and pKa of octahedral nickel(ii) proton reduction catalysts

“…12,13 The extensive use of DFT has allowed for notable success in the field of catalyst design, ligand modification, and enhancement of catalytic efficiency, in particular for homogeneous metal catalysts, and thus has proven to be an indispensable tool. [14][15][16][17][18][19][20] However, it is imperative to acquire a thorough knowledge of the intricacies involved in a system through a judicious survey of the molecular model that can justify the mechanistic details of the catalytic cycle in order to obtain unambiguous results.…”