The Effects of pH on the Supramolecular Structure of Amino Amides.

Here, we report the determination of acidity constants of eight amino amides through the use of Nuclear Magnetic Resonance (NMR) to carry out the selective crystallization of diprotonated (a), monoprotonated (b), and neutral species (c) derived from these compounds. Crystallographic studies of compounds 2?a, 6?a, 7?a, 8?a, 2?b, 3?b, 6?b and 2?c revealed that the presence of substituents at the C8 and C10 positions determines the conformation of the molecule regardless of its degree of protonation. Although diprotonated species (a) have the same conformation and similar hydrogen bonding patterns, the supramolecular structures of these compounds are different. Furthermore, chloride ions and solvent molecules play an outstanding role in stabilizing the supramolecular structure of these compounds. This phenomenon restricts the ????? interactions between benzimidazole groups and consequently limits the possibility of aggregation in amino amides 1?8.