@article{oai:kanazawa-u.repo.nii.ac.jp:00044974,
 author = {長谷川, 浩 and Begum, Zinnat A. and Rahman, Ismail M.M. and Tate, Yousuke and Ichijo, Toshiharu and Hasegawa, Hiroshi},
 journal = {Journal of Molecular Liquids},
 month = {Mar},
 note = {The bioavailability of trivalent iron (Fe3+) to plants can be enhanced using fertilizer solutions containing humic acids (HA) as manifested from the increased crop yield at an iron stress conditions. The lignite-derived HA (HAlignite) facilitates higher diffusion of Fe3+ between the soil layers as attributable to more number of reactive sites in the assemblage compared to those from other origins. In the current work, the proton-binding of HAlignite size-fractions (5–10, 10–30, 30–100, and >100 kDa), as segmented based on the molecular weight distribution, and their complexation with Fe3+ have been studied at varying pH ranging from low to high. The protonation or formation of Fe3+-complexes exhibited a comparable pattern despite the differences in the conformational distribution of HAlignite size-fractions. The protonation behavior specified that the behavior of HAlignite size-fractions has similarity with that of a dibasic acid. The results are interpreted using reactive structural units (RSU) concept to show that the carboxyl and phenolic-hydroxyl groups in the HAlignite size-fractions simultaneously available as the Fe3+-binding sites. The stability constants for larger MW fractions of HAlignite (>100 kDa) was the lowest, as attributed to the increased aggregation rate in an aqueous matrix. The trend in conditional stability constants of HAlignite-size fractions and other Fe-chelators point to a better Fe-binding capability of HAlignite (30–100 kDa) size-fraction than the biodegradable alternatives (GLDA, HIDS, EDDS, IDSA, or NTA), while the Fe-interaction was stronger with classical synthetic chelators (EDTA, DTPA, or EDDHA). © 2018 Elsevier B.V., Embargo Period 12 months, 金沢大学理工研究域物質化学系},
 pages = {241--247},
 title = {Binding of proton and iron to lignite humic acid size-fractions in aqueous matrix},
 volume = {254},
 year = {2018}
}