Participation of strong charge-assisted hydrogen bonds in interactions of dissolved organic matter represented by Suwannee River Humic Acid

• Published in: Water research (Oxford) 2024-11, Vol.265, p.122274, Article 122274
• Main Authors: Wang, Zhengyang, Nagata, Mayu, Murano, Hirotatsu, Pignatello, Joseph J.
• Format: Article
• Language: English
• Subjects: Chromatography, Gel; Humic Substances; Hydrogen Bonding; Hydrogen-Ion Concentration; Low-barrier hydrogen bond; Macromolecular model; Microscopy, Electron, Transmission; Natural organic matter; Organic Chemicals - chemistry; Phosphate binding; Rivers - chemistry; Size-exclusion chromatography; Supramolecular model
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2024.122274

•The results support a two-tiered state of aggregation for DOM•Evidence for CAHB is gained through zeta potential changes and pH drift experiments•CAHB-capable co-solutes can disrupt intra-aggregate CAHB and react to form new ones•Molecular weight distribution is shifted upon addition of CAHB-capable co-solutes•Phosphate causes the greatest shifts in molecular weight distribution Terrestrial dissolved organic matter (DOM) plays critical roles in many biotic and abiotic environmental reactions as well as in water treatment. Its structure is therefore of great interest. We examined dissolved Suwannee River Humic Acid (HA) to probe the potential participation of exceptionally strong, negative charge-assisted hydrogen bonds, (−)CAHB, in DOM cohesion and interaction with small weak acids using high performance size exclusion chromatography (HPSEC), transmission electron microscopy, zeta-pH curves, and pH drift experiments. The results support a previously proposed two-tier state of aggregation, in which tightly-knit primary particles (≤ ∼10 kDa) form larger secondary aggregates (up to micrometer in size). Evidence for (−)CAHB is gained through zeta potential changes and pH drift experiments. The primary particles interact with (−)CAHB-capable solutes (simple carboxylic acids and phosphate) but not (−)CAHB-incapable solutes. We identified disruption of intra-segmental and inter-molecular (−)CAHB leading to swelling and disaggregation, as well as formation of nouveau (−)CAHB with free groups on HA. The effects were solute-concentration dependent and greater at pH 5 than pH 6, consistent with CAHB theory. Phosphate induced the greatest shifts in the HPSEC molecular size distribution curves. The shifts were unaffected by prior stripping of innate polyvalent metals. We conclude that the (−)CAHB contributes to the cohesion of DOM, affecting its size and charge, and provides a means by which weak acid pollutants, nutrients, and natural compounds can interact with DOM. Such interactions have implications for the behavior of DOM in the environment, the fate and transport of anthropogenic pollutants, and the roles DOM play in water treatment technologies. [Display omitted]