Fig. 2: Comformational transition studies of hepta-peptide with Ca²⁺.

Three-dimensional structures of DDDEEKC before (a) and after binding with five Ca²⁺ ions (b), obtained by molecular dynamic calculation. c Circular dichroism (CD) spectra of the hepta-peptide (0.5 mM) upon additions of a gradient concentration of CaCl₂ from 0.5 to 2.5 mM in H₂O. d Graphic illustration of the secondary conformation changes of the hepta peptide interacting with Ca²⁺. e Fluorescence spectra of fluorescein-labeled CF₃-PT (5 × 10⁻⁶ mol L⁻¹) upon the addition of hepta-peptide in a Tris–HCl buffer solution (pH = 7.4, 10 mM) at 20 °C. The inset shows the fluorescence intensity change (at 517 nm) upon the addition of the hepta-peptide. [G]/[H] is an abbreviation of the molar ratio of guest to host, and the red line in the inset is a nonlinear-fitted curve for calculating the association constant (K_a). f Fluorescence spectra of a mixture of fluorescein-labeled CF₃-PT (5 × 10⁻⁶ mol L⁻¹) and equimolar amount of hepta-peptide upon the addition of CaCl₂ in a Tris–HCl buffer solution at 20 °C. Recovery of fluorescence intensity indicated that the addition of Ca²⁺ ions destroyed the complexation between CF₃-PT and the hepta-peptide copolymer