Inclusion complexes of selected amines with pillar[5]arenes: experimental and molecular dynamics study

Abstract

Selected amines were allowed to form inclusion complexes with selected synthesized pillar[5]arenes. Formation of inclusion complexes were confirmed by MALDI–TOF, ESI–MS analyses and 1H NMR spectroscopy. The complexation was supported by molecular dynamics calculations. Various pillar[5]arenes have been synthesized by BF3·OEt2 (Lewis acid) catalyzed cyclization of 1,4-disubstitutedbenzenes with paraformaldehyde. Selected synthesized host macrocycles; DMpillar[5]arene (7), DPpillar[5]arene (8a), DPGpillar[5]arene (8b) were allowed to form inclusion complexes with N-containing guests; hexamethylenediamine (GA), di-n-octyl amine (GB) and diethyl amine (GC). Host–guest complex formation of the selected pillar[5]arenes with the N-containing guests has been confirmed by MALDI–TOF, ESI–MS analyses and 1H NMR spectroscopy. ESI–MS revealed highly intense ion peaks that correspond to [pillar[5]arene@GA+Na]+ for inclusion complexes of pillar[5]arenes with hexamethylenediamine (GA). ESI–MS confirmed formation of inclusion complexes between pillar[5]arenes with di-n-octyl amine (GB) and diethyl amine (GC) as evidenced by intense peaks that corresponds to [pillar[5]arene@GB+H]+ and [pillar[5]arene@GC+H]+, respectively. Performed molecular dynamics (MD) simulations provided supportive results that indicate the formation of stable complexes between the three pillar[5]arene hosts and the guests included in this study. Hydrogen bonding and CH–π interactions were found amongst the factors that contribute significantly to the stability of these complexes.