Comparing the Heterogeneity of Copper-Binding Characteristics for Two Different-Sized Soil Humic Acid Fractions Using Fluorescence Quenching Combined with 2D-COS

Table 2

Copper-binding parameters¹ calculated by the Ryan-Weber model.

HA size fractions	Peak wavelength (nm)	𝑟	𝐹ML(%)	log𝐾M	𝐶𝐶M(mmol (g C)^−1)
1–10 K	357^2	0.996*	40.0±2.4	4.91±0.06	0.63±0.29
	451^2	1.000*	7.2±6.3	5.70±0.03	1.33±0.14
	462^3	0.999*	6.3±0.7	5.86±0.07	1.17±0.09
	467^2	0.999*	5.6±0.5	5.86±0.05	1.56±0.29
>100 K	376^2	0.953*	59.7±1.5	6.48±0.52	0.67±1.22
	460^3	0.999*	15.7±0.9	5.96±0.08	1.12±0.32
	464^2	0.999*	14.5±0.8	5.97±0.07	1.12±0.27

¹Correlation coefficients of predicted versus observed fluorescence intensity (𝑟), relative percentage of fluorescence intensity for copper-saturated complexes (𝐹_ML (%)), conditional stability constants (log𝐾_M), and complexing capacities (𝐶𝐶_M) and fraction of the initial fluorescence corresponding to binding sites (𝑓).
²The peak wavelengths were selected based on peaks observed in the synchronous and asynchronous maps of 2D-COS in Figure 2.
³The peak wavelengths were selected based on the apparent shapes of the synchronous fluorescence spectra in Figure 1.
* 𝑃 value < 0.001.