2.6. Circular Dichroism (CD) Spectroscopy Analysis

For CD analysis, peptide samples were dissolved in 5 mM phosphate buffer (pH 7.0) and RBD was in 50 mM sodium phosphate buffer (pH 7.0) containing 150 mM NaCl, with a concentration of 0.1–0.2 mg/mL. CD spectra were measured on the Chirascan Plus spectropolarimeter v.4.4.0 (Applied Photophysics Ltd., Leatherhead, Surrey, UK) by using a quartz cell of 1.0 mm thickness. The wavelengths used ranged from 190 to 260 nm. Data were collected at 1 nm intervals with a scan rate of 60 nm/min and expressed as delta epsilon (cm⁻¹M⁻¹). Delta epsilon was calculated as [θ × (MRW × 0.1)/(C × L)/3298], where θ is the ellipticity (in millidegrees), C is the concentration (in mg/mL), L is the path length (in cm), and MRW is the mean residue weight (in Da).