When a host becomes a guest—competition between decreasing hydrophobic spaces and supramolecular synthon propagation

Abstract

The presented results of racemic resolution of N-(4-nitrobenzoyl)-DL-asparagine by fractional crystallization of brucinium diastereomeric salts (at 5 °C) reveal a molecular recognition as a competition between decreasing of hydrophobic spaces by a hydrophobic recognition on a surface of a brucinium self-assembly (brucinium N-(4-nitrobenzoyl)-D-asparaginate heptahydrate (1)—first fraction) and formation by anions of the resolved acid a strong hydrogen bonds network mediated by characteristic supramolecular synthon (brucinium N-(4-nitrobenzoyl)-L-asparaginate methanol trisolvate (2)). Comparison of 1 with result of its recrystallization at abient conditions, brucinium N-(4-nitrobenzoyl)-D-asparaginate methanol disolvate 0.73 hydrate (1a), shows that in lower temperature the system favors hydrophobic recognition while higher temperature encourages it to formation, defined by other than in 2 supramolecular synthon, a strong hydrogen bonds network. Presence of the nitro group bonded to the phenyl ring of N-(4-nitrobenzoyl)-amino acid derivative plays an important role decreasing enantiospecifity and enantioselectivity of brucine driving brucinium cations to be assembled in a way suitable for interactions with this group.