Quantitative structure and energetics of pyrophosphate protonation microstates in implicit water
Year: 2026
Type: preprint
Abstract: Pyrophosphate is a minimal phosphoanhydride whose protonation microstates can reorganize local electrostatics and bridge geometry. We optimized 24 structures spanning five protonation states at B3LYP/ def2-SVPD with SMD water and quantified within-charge energy landscapes, structural asymmetry, Mulliken populations and orbital gaps. Most states were shallow, whereas H2P2O72- spanned 13.37 kcal mol-1. Its lowest sampled structure redistributed the two protons, contracted the P–O–P angle to 120.29°, formed two 1.89 Å intramolecular hydrogen-bond contacts and nearly equalized the phosphorus charges. Persistent asymmetric minima were 13.23–14.81 kcal mol-1 higher across B3LYP, PBE0 and ωB97X-D/ def2-TZVPD calculations; quasi-RRHO thermochemistry retained an 11.10 kcal mol-1 preference. These results identify proton placement as a major determinant of the static aqueous pyrophosphate landscape and motivate microstate screening before more expensive explicit-solvent simulations.
Source: ChemRxiv
Author: Aris Tsai
Institution: Stanford University
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204938954