The Anionic States of Ubiquinone Characterized by Second-Order Approximate Coupled-Cluster Theory

Area of Science:

• Computational Chemistry
• Biochemistry
• Quantum Chemistry

Background:

• Ubiquinone's role in cellular respiration involves critical electron transfer.
• Ubiquinone exhibits two anionic states: valence and dipole-bound.
• Dipole-bound states are potential doorways for electron transfer.

Purpose of the Study:

• Investigate anionic states of ubiquinone analogues (Q0 and Q1) using computational methods.
• Characterize conformational energy, molecular dipole, and binding energies.
• Analyze the influence of molecular conformation and intermolecular interactions on electron affinity.

Main Methods:

• Employed the electron-attachment variant of the second-order approximate coupled-cluster (CC2) method.
• Studied Q0 and Q1 ubiquinone analogues.
• Performed cluster scans with small molecules (H2O, HF, NH3, CH4) and larger models of bacterial reaction center QA.

Main Results:

• Valence state electron affinity varies with conformation; dipole-bound state appears discontinuously.
• Intermolecular interactions significantly modulate valence state electron affinity (up to ~0.6 eV).
• Simulated mutations in bacterial reaction center QA reproduced experimental findings on electron affinity changes.

Conclusions:

• Biological and chemical environments profoundly modulate ubiquinone's electron-accepting properties.
• Interplay between conformation, intermolecular interactions, and electronic structure dictates redox properties.
• Findings contribute to understanding dipole-bound anions in biological systems.