Sulfur and Phosphorus Oxyacid Radicals

Area of Science:

• Computational chemistry
• Radical chemistry
• Biophysical chemistry

Background:

• Neutral sulfur and phosphorus radicals are crucial in biological and chemical processes.
• Understanding their properties is essential for predicting reaction mechanisms.
• Limited data exists on the tautomeric structures and reactivity of these specific radicals.

Purpose of the Study:

• To computationally investigate the tautomeric structures and acidity (pKa) of neutral bisulfite, bisulfate, dihydro-phosphite, and dihydro-phosphate radicals.
• To explore the energetics of their microhydration clusters.
• To determine their preferred reaction pathways with a lipid model and discuss biological implications.

Main Methods:

• Density functional theory (DFT) calculations using G4 and CAM-B3LYP levels.
• Thermodynamic analysis of dissociation and microhydration.
• Investigation of reaction mechanisms including addition and hydrogen abstraction.

Main Results:

• Detailed characterization of various tautomeric forms for the studied radicals.
• Estimation of pKa values correlating with the number of hydrating water molecules.
• Identification of preferential reaction pathways: S- and P-centered radicals add to propene, while O-centered radicals abstract hydrogen.
• Energetic evaluation of microhydration effects on radical stability and reactivity.

Conclusions:

• The study provides fundamental insights into the chemistry of understudied neutral sulfur and phosphorus radicals.
• Hydration plays a significant role in the deprotonation and reactivity of these species.
• Predicted reaction mechanisms offer a basis for understanding their fate in biological systems.