Exploring abiotic non-catalytic polyphenol-Maillard humification in light-limited environment

Abiotic humification involving polyphenol-maillard precursors leads to the formation of Humic-like substances (HLSs). Previous research has been conducted on catalytic or mineral-associated pathways, although the physicochemical role of noncatalytic abiotic pathway in light-limited environments remains unexplored. Current study investigates the noncatalytic polycondensation reaction between catechol (free polyphenol) and Maillard precursors (glucose & glycine) to synthesize HLSs. In the presence of catechol, singlet oxygen (¹O₂) production solely derived the reaction at mild temperature and light-limited conditions, independent of photochemical or Fenton-type reactions. Spectroscopic analyses revealed a dominant presence of aliphatic moieties, consistent with ultra-high-resolution mass spectrometry (UHRMS) data. Polycondensation reaction released elevated CO₂ levels and decline in pH, indicating aromatic ring cleavage, carboxyl group formation and transformation of aromatics into aliphatic fragments. Additionally, Van Krevelen analysis showed increased O/C ratio in HLS. Notably, the key components included acidic and glucose oxidation products, along with some Maillard reaction intermediates (confirmed with Kendrick Mass analysis). This study provides a novel noncatalytic abiotic humification pathway, corroborating with environments where light-assisted and photochemical processes are minimal such as subsurface soils and underground water.