Study on the interaction mechanism between keratin and dyes under surfactant regulation

To elucidate the molecular interactions between synthetic dyes and hair keratin, the structural protein constituting 90 % of hair fibers was isolated via optimized aqueous ammonolysis (120 °C, 2 h). Comprehensive characterization using FT-IR, UV–vis, XRD, TGA, SDS-PAGE, and SEM confirmed the preserved α -helical structure (characteristic amide I band at 1,650 cm −1 ) and molecular weight distribution (45–60 kDa) of the extracted keratin. Fluorescence spectral analysis revealed pH-dependent quenching mechanisms: Disperse Blue 7 induced static quenching (Stern-Volmer constant K sv = 1.8 × 10 4 M −1 ) under acidic conditions (pH 4–6), transitioning to composite quenching (static + dynamic) at physiological pH (7–9) with increased bimolecular quenching rate ( k q = 2.3 × 10 12 M −1 s −1 ). Notably, surfactant modulation studies demonstrated that gemini cationic surfactants maintained stable quenching efficiency (Δ F / F 0 < 5 % variation), whereas nonionic alkyl polyglucoside (APG) enhanced quenching by 38 % under pH 6–7 conditions through synergistic hydrophobic interactions (ΔG = −25.6 kJ/mol).