C4Cn behaviour in solution and interaction with basic amino acids.

(A) Effects of increasing C4C1, C4C3, C4C7 and C4C12 concentrations on the surface tension of aqueous solution. The surface tension is measured as described in Methods. Each value is the mean of three experiments ± the standard error. C4C1, C4C3, C4C7 and C4C12 are indicated by circles, diamonds, triangles and squares, respectively. (B) Dynamic light scattering of C4Cn in aqueous solution. Experiments were carried out as described in Methods. Mean size values are indicated in nm for the corresponding compound. (C) Effect of pH on the surface tension generated by C4C7. Experiments have been carried out as in (A), neutralizing C4C7 at pH 9.0, 8.0 and 6.0, and measuring the resulting surface tension by increasing the concentration of the compound, as indicated by circles, triangles and squares, respectively. The values result from triplicate experiments. (D) Interaction of C4C7 with amino acids probed by surface tension. C4C7 diluted to 10 µM was incubated with increasing concentrations of either glutamate (circles), lysine (triangles), arginine (squares) or proline (diamonds), measuring the resulting surface tension, as described in Methods. (E) Chemical shifts of the αH and εH protons of lysine in the presence of C4C1. The ¹H NMR spectra of L-Lysine (10 mM) was recorded as described in Methods in the presence of increasing C4C1 concentrations as indicated in the Figure, resulting in chemical shifts of αH and εH protons of lysine which were plotted as a function of C4C1 concentration. (F). Dissociation of the L-lysine - C4C1 complex, each added at 10 mM, induced by increasing the salt concentration as indicated and probed by measuring the chemical shift of lysine αH protons.