10.1021/acs.est.7b06281.s001
Jinling Xu
Jinling
Xu
Luuk K. Koopal
Luuk K.
Koopal
Linchuan Fang
Linchuan
Fang
Juan Xiong
Juan
Xiong
Wenfeng Tan
Wenfeng
Tan
Proton
and Copper Binding to Humic Acids Analyzed
by XAFS Spectroscopy and Isothermal Titration Calorimetry
American Chemical Society
2018
XAFS
Isothermal Titration Calorimetry Proton
Humic Acids Analyzed
deprotonated phenolic-type sites
deprotonated carboxylic-type sites
NICA model calculations
yields molecular-scale mechanisms
ITC
HA
lignite-based humic acid
Cu binding
2018-03-09 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Proton_and_Copper_Binding_to_Humic_Acids_Analyzed_by_XAFS_Spectroscopy_and_Isothermal_Titration_Calorimetry/6007499
Proton and copper (Cu) binding to
soil and lignite-based humic
acid (HA) was investigated by combining X-ray absorption fine structure
(XAFS) spectroscopy, isothermal titration calorimetry (ITC), and nonideal-competitive-adsorption
(NICA) modeling. NICA model calculations and XAFS results showed that
bidentate and monodentate complexation occurred for Cu binding to
HA. The site-type-specific thermodynamic parameters obtained by combining
ITC measurements and NICA calculations revealed that copper binding
to deprotonated carboxylic-type sites was entropically driven and
that to deprotonated phenolic-type sites was driven by entropy and
enthalpy. Copper binding to HA largely depended on the site-type and
coordination environment, but the thermodynamic binding mechanisms
for Cu binding to the specific site-types were similar for the different
HAs studied. By comparing the site-type-specific thermodynamic parameters
of HA–Cu complexation with those of low molar mass organic
acids, the Cu coordination could be further specified. Bidentate carboxylic–Cu
complexes made the dominating contributions to Cu binding to HA. The
present study not only yields molecular-scale mechanisms of ion binding
to carboxylic- and phenolic-type sites of HA but also provides the
new insight that the universal nature of site-type-specific thermodynamic
data enables quantitative estimation of the binding structures of
heavy metal ions to humic substances.