Interactions between phosphate and water in solution: a natural bond orbital based analysis in a QM/MM framework

Area of Science:

• Computational chemistry
• Quantum mechanics
• Molecular dynamics

Background:

• Investigating the solvation environment of mono-methyl phosphate-ester (MMP) using combined quantum mechanical/molecular mechanical (QM/MM) methods.
• Employing self-consistent-charge density functional tight-binding (SCC-DFTB) for MMP and TIP3P for water to generate solute-solvent configurations.

Discussion:

• Utilizing natural bond orbital (NBO) and natural energy decomposition analysis (NEDA) with various QM/MM partitioning schemes at the HF/6-31+G** level.
• Observing substantial charge transfer between MMP and surrounding water molecules, irrespective of the QM region's size.

Key Insights:

• Charge-transfer interactions are found to be as significant as electrostatic (electrostatic and polarization) components in the NEDA framework.
• Demonstrating the efficacy of NBO-based analyses for characterizing intermolecular interactions in condensed-phase systems.

Outlook:

• Further application of NBO and NEDA in QM/MM studies for detailed intermolecular interaction analysis.
• Exploring the role of charge transfer in the behavior of phosphate esters in biological and chemical environments.