Table 2. Effects of C-Terminal Modifications and N-Terminal Modifications on the Association of Compound 1, Determined from the Concentration Dependence of the UV–vis Absorption and ITCa.
| pK(hex-mon) |
|||||||
|---|---|---|---|---|---|---|---|
| compound | sequence | ITC | UV–vis | λmax(hex) (nm) | λmax(mon) (nm) | Δλmax (nm) | ΔH(hex-mon) (cal/mol) |
| C-Terminal Modifications | |||||||
| 1 | H2N-(Lys-Sal)4-CONH2 | 18.8 | 19.3 | 318.1 | 303.5 | 14.6 | 14100 |
| 2 | H2N-(Lys-Sal)4-COOH | 302 | |||||
| 3 | H2N-(Lys-Sal)4-COOCH3 | 17.9 | 315.1 | 304.4 | 10.7 | ||
| 4 | H2N-(Lys-Sal)4-CONH-(CH2)2-COOH | 21.0 | 21.8 | 317.6 | 303.1 | 14.5 | 13800 |
| N-Terminal Modifications | |||||||
| 8 | (Lys-Sal)3-CONH2 | <15 | 304.0 | ||||
| 5 | Sal-(Lys-Sal)3-CONH2 | 20.3 | 21.1 | 323.3 | 305.7 | 17.6 | 15700 |
| 6 | Ac-Sal-(Lys-Sal)3-CONH2 | 21.7 | 21.5 | 319.8 | 305.1 | 14.7 | 15600 |
| 1 | Lys-Sal-(Lys-Sal)3-CONH2 | 18.8 | 19.3 | 318.1 | 303.5 | 14.6 | 14100 |
a
Δλmax is the difference between the λmax values of the hexameric and monomeric species, determined from the fits. The association of compound 2 was too weak for UV–vis data fitting. ITC heats of formation were too small to accurately determine dissociation constants for compounds 2 and 3.