Quantitative structure and energetics of pyrophosphate protonation microstates in implicit water
- 1Chemistry
- 2Stanford Online High School, Stanford University
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.
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BibTeX
@misc{tsai2026quantitative,
title = {{Quantitative structure and energetics of pyrophosphate protonation microstates in implicit water}},
author = {Aris Tsai},
howpublished = {ChemRxiv},
year = {2026},
month = aug,
doi = {10.26434/chemrxiv.15008119/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008119/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Quantitative structure and energetics of pyrophosphate protonation microstates in implicit water
AU - Aris Tsai
PY - 2026
DA - 2026/08/31
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008119/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008119/v1
AB - 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.
ER -