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Stoichiometry between Humate Unit Molecules and Metal Ions in Supramolecular Assembly Induced by Cu2+ and Tb3+ Measured by Gel Electrophoresis Techniques
journal contribution
posted on 2021-11-03, 19:46 authored by Sumika Nakano, Kazuki Marumo, Rintaro Kazami, Takumi Saito, Tomoko Haraga, Yuiko Tasaki-Handa, Shingo SaitoHumic acid (HA), a fraction of humic
substances, can strongly complex
with metal ions to form a supramolecular assembly via coordination
binding and other intermolecular forces. However, determining the
supramolecular size distribution and stoichiometry between small HA
unit molecules constituting HA supramolecules and metal ions has proven
to be challenging. Here, we investigated the changes in the size distributions
of HAs induced by Cu2+ and Tb3+ ions using unique
PAGE for the separation and quantification of HA complexes and metal
ions bound, followed by UV–vis spectroscopy and excitation–emission
matrix–parallel factor analysis. By determining the concentrations
of HA and metal ions, it was possible to estimate the stoichiometry
of the HA unit molecule to metal ions in supramolecular complexes.
It was found that the supramolecular behaviors of Cu2+ and
Tb3+ complexes with HA collected from peat (PAHA) and deep
groundwater (HHA) differed. For example, two HHA unit molecules form
a supramolecule via cross-linking by a Cu2+ ion in the
case of Cu2+–HHA. Our results suggest that this
supramolecular stoichiometry is related to the abundance of sulfur
atoms in the elemental composition of HHA. Our experimental results
and analysis provide new insights into HA supramolecules formed via
metal complexation.
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supramolecule via crosshumate unit molecules3 + sup2 + supmetal ions boundha unit moleculesupramolecular size distributionsupramolecular assembly inducedmetal ionssize distributionssupramolecular behaviorssupramolecular complexessulfur atomsstrongly complexresults suggestintermolecular forceshumic substancesha collectedha ),experimental resultselemental compositiondeep groundwater