Fig. 2: HSAL shows a metal chelating capability.

a Representative images of HSAL powder and HSAL chelated with FeSO₄, FeCl₃ or CaCl₂ respectively. b X-ray photo electron spectrometer (XPS) spectra of HSAL and HSAL chelated with FeSO₄ or FeCl₃. The positions of Fe(2p_1/2) and Fe(2p_3/2) peak were located 723.3–723.9 eV and 709.7–710.6 eV respectively. c XPS spectra of HSAL and HSAL chelated with CaCl₂. The positions of Ca(2p_1/2) and Ca(2p_3/2) peak were 349.5–350.0 eV and 346.5–347.0 eV respectively. d FT-IR spectra comparisons of HSAL, HSAL chelated with FeSO₄ or FeCl₃. The FT-IR spectra at 3360 cm⁻¹ for the O-H band of HSAL was shifted to 3320 cm⁻¹ and 3410 cm⁻¹ for the chelated complexes of HSAL with FeSO₄ and FeCl₃ respectively. Two prominent bands at 665 cm⁻¹ and 1220 cm⁻¹ for the chelated complexes of HSAL with FeSO₄ and FeCl₃ were corresponding to Fe–O stretching vibrations and C–O of the guaiacol stretching respectively. e FT-IR spectra comparisons of HSAL and HSAL chelated with CaCl₂. The FT-IR spectra of the O-H band at 3360 cm⁻¹ for HSAL was shifted to 3400 cm⁻¹ for the chelated complexes of HSAL with CaCl₂. Two new bands at 1200 cm⁻¹ and 3640 cm⁻¹ were likely assigned to C–O of the guaiacol stretching and the calcium hydroxide stretching respectively. f Comparisons of metal chelating capability of HSAL and EDTA using complexometric titration analysis. The graphs depict mean and standard deviation (error bars). Statistically significant differences between the means were analyzed with Student’s t-test (n = 3 independent experiments).