Secondary Structural Preferences of Some Antibacterial Cyclooctapeptides in the Presence of Calcium(II)

Table 3

Thermodynamic parameters data for Ca²⁺ binding to COP 1–9.

Test peptide	Binding affinity^a for Ca^2+; 𝐾𝑏; (M^−1)	Change in; enthalpy; Δ𝐻 (kJ mol^−1)	Change in Gibbs free energy; Δ𝐺 (kJ mol^−1)	Change in; entropy; Δ𝑆 (J K^−1 mol^−1)
COP 1 ^b	(3.4 ± 0.6) × 10^3	−0.5 ± 0.1	−20.5 ± 0.4	65.7 ± 1.7
COP 2 ^b	(4.8 ± 1.3) × 10^3	−0.6 ± 0.04	−20.9 ± 0.8	67.8 ± 3.8
COP 3	(7.9 ± 2.8) × 10^3	−2.9 ± 1.7	−22.2 ± 1.3	63.6 ± 5.4
COP 3 in DPC^c	(3.3 ± 0.3) × 10^3	−0.8 ± 0.04	−20.5 ± 0.2	64.0 ± 0.8
COP 4	(3.1 ± 0.7) × 10^3	−11.3 ± 1.3	−20.1 ± 0.8	28.9 ± 4.6
COP 4 in DPC	(4.7 ± 1.1) × 10^3	−1.7 ± 0.1	−21.3 ± 0.8	64.9 ± 2.1
COP 5	(5.3 ± 1.4) × 10^3	−2.5 ± 1.3	−21.3 ± 0.8	62.3 ± 6.3
COP 5 in DPC	(5.4 ± 0.6) × 10^3	−2.1 ± 0.1	−21.3 ± 0.4	63.6 ± 2.1
COP 6	(6.4 ± 2.8) × 10^3	−10.0 ± 6.7	−21.8 ± 0.8	38.5 ± 23.8
COP 6 in DPC	(4.9 ± 0.7) × 10^3	−5.0 ± 2.1	−21.3 ± 0.4	54.4 ± 7.9
COP 7	(8.0 ± 1.2) × 10^3	−3.3 ± 0.8	−22.6 ± 0.4	63.6 ± 3.8
COP 7 in DPC	(4.7 ± 1.0) × 10^3	−0.8 ± 0.4	−13.8 ± 7.5	42.7 ± 7.1
COP 8	(4.9 ± 0.3) × 10^3	−2.9 ± 0.8	−21.3 ± 0.4	60.7 ± 0.8
COP 8 in DPC	(4.4 ± 0.02) × 10^3	−0.8 ± 0.1	−21.3 ± 0.04	66.5 ± 0.4
COP 9	(5.4 ± 1.2) × 10^3	−3.3 ± 0.4	−21.3 ± 0.8	59.4 ± 2.1
COP 9 in DPC	(4.1 ± 0.03) × 10^3	−1.7 ± 0.2	−20.9 ± 0.04	63.6 ± 0.4

^aValues correspond to the mean of three experiments and the standard error mean.
^bLow heat changes for this association in DPC prevented meaningful calculation of the corresponding thermodynamic parameters with certainty.
^cMicellar DPC solutions were prepared at 10 mM DPC.