Estimates of electronic coupling for excess electron transfer in DNA

Area of Science:

• Computational chemistry
• Molecular biophysics
• DNA charge transport

Background:

• Electronic coupling V(da) is crucial for DNA charge transfer rates.
• Previous studies focused on hole transfer, leaving excess electron transfer (ET) unquantified.
• Accurate V(da) calculations are needed for understanding DNA's electronic properties.

Purpose of the Study:

• To develop an efficient computational strategy for calculating ET matrix elements V(da) in DNA base pairs.
• To compare V(da) values obtained using the diabatic-state (DS) method and LUMO-based approaches.
• To investigate the influence of base pairing and structural changes on excess electron transfer couplings.

Main Methods:

• Employed the diabatic-state (DS) method using radical anions of adenine-thymine (AT) and guanine-cytosine (GC) base pairs.
• Utilized generalized Mulliken-Hush and fragment charge methods based on lowest unoccupied molecular orbitals (LUMOs) of neutral systems.
• Calculated V(da) using different basis sets (6-31G(*), 6-31++G(**)) and with/without diffuse functions.

Main Results:

• The DS method and LUMO-based approaches yielded similar V(da) values when diffuse functions were omitted in neutral calculations.
• LUMOs of neutral base pairs without diffuse functions accurately represent radical-anion states for V(da) estimation.
• Intrastrand thymine and cytosine bases showed larger V(da) than interstrand pyrimidine bases.
• Excess electron transfer couplings are significantly smaller than hole transfer couplings and highly sensitive to structural variations.

Conclusions:

• The developed strategy provides reliable estimates for electronic couplings in excess electron transfer through DNA.
• Excess electron transfer in DNA is weaker and more structurally dependent than hole transfer.
• Findings offer insights into DNA's charge transport mechanisms and electronic behavior.