*2.3. Chelation Properties of Hesperidin*

Hesperidin and copper(II) acetate were dissolved in methanol and mixed to obtain hesperidin-copper complex. Likewise, with other compounds with a similar structure, HSD possesses chelation potential when it is mixed with metal(II) ions [33]. Figure 2 presents the FT-IR spectra of hesperidin, copper(II) acetate, and hesperidin–copper complex.

**Figure 2.** Fourier transform infrared (FT-IR) spectra of hesperidin (HSD, dotted line), copper(II) acetate (Cu(II), dashed line), and HSD–Cu(II) complex (full line) on a Cary 630 FT-IR spectrometer equipped with a monolithic design diamond Attenuated Total Reflectance (ATR) accessory (Agilent Technologies Inc.). Hesperidin is a chelating agen<sup>t</sup> of metal multivalent ions (Me<sup>2</sup>+). The creation of the complex involves -OH groups in ortho- positions that coordinate with divalent cations [1].

The FT-IR spectra of HSD, copper(II) acetate, and the HSD–Cu(II) complex showed HSD band shift upon complexation with a metal ion [33]. For example, the vibration stretching for -C=O in HSD at 1644 cm<sup>−</sup><sup>1</sup> was shifted to 1515 cm<sup>−</sup><sup>1</sup> in the HSD–Cu(II) complex, due to the coordination with the metal ion. The absorption bands in HSD for C-O at 1297, 1275, 1242, 1206, 1184, 1154, 1132, 1095, 1054, 1037, and 1009 cm<sup>−</sup><sup>1</sup> were suppressed, probably because of the Cu(II) bonding with -OH groups. Therefore, there is a strong indication that hesperidin formed a complex with Cu(II) ions.
