3.4.5. Circular Dichroism (CD) Spectroscopy Measurements

The far CD spectra of HSA and the HSA-QTP complex were recorded at a wavelength between 200 and 260 nm on the spectropolarimeter with a scan speed of 100 nm min−<sup>1</sup> . HSA (5 µM) was titrated with 10 µM QTP. The measured ellipticity values were expressed as the mean residue ellipticity (MRE) in deg cm<sup>2</sup> dmol−<sup>1</sup> , defined by equation [48]:

$$\text{MRE} = \frac{\text{Observed CD (\theta obs)}}{\text{c} \times \text{n} \times \text{l} \times 10} \tag{7}$$

where θobs is the measured ellipticity in millidegree, "n" is the number of amino acids residues, "l" is the path length of the cuvette (cm), and "c" is the molar concentration of protein. The α-helical content of HSA was determined by equation [48]:

α-helical content(%) = [MRE<sup>208</sup> − 4000] [33, 000 − 4000] × 100 (8)

where MRE<sup>208</sup> is the mean residue elasticity (MRE) at 208 nm.
