Influence of the Solvent and the Enantiomeric Purity on the Transition between Different Supramolecular Polymers

Abstract

The self-assembly of two enantiomerically pure hexa(oligo(p-phenylene vinylene))-substituted benzenes having 24 stereocenters was studied in pure methylcyclohexane (MCH) and in a mixture of MCH/toluene (4:1). Irrespective of the solvent a cooperative supramolecular polymerization mechanism was determined for these star-shaped molecules by using temperature-dependent CD and UV/Vis spectroscopy. Quite remarkably, a transition from one helical supramolecular state (A) to a second more thermodynamically stable supramolecular helical assembly (B) was observed. The rate of the A→B transition was strongly dependent on the nature of the solvent; being faster in the solvent mixture than in pure MCH. By using size exclusion chromatography we could relate the increased rate to a decreased stability of the supramolecular A state in the solvent mixture. Next, we mixed the two enantiomerically pure hexa-substituted benzene derivatives in a so-called majority-rules experiment, which lead to the anitcipated chiral amplification in the A state. More importantly it appeared that the A→B transition was significantly hampered in these mixed systems. Furthermore, the absence of chiral amplification in the B state revealed the formation of separated enantiomerically pure assemblies. Therefore, by using a wide variety of spectroscopic and chromatographic techniques we determined the influence of solvent and enantiomeric purity on the transition between different supramolecular states.

Model-driven optimization of multicomponent self-assembly processes

“…3D). In agreement with previous chiral amplification studies (22,23), the ee has a large effect on the annealing kinetics. Slower rates are obtained for less enantiopure compositions, as predicted by the model.…”

Chiral recognition and selection during the self-assembly process of protein-mimic macroanions

“…Small chiral organic molecules (for example, lactic acid) are found to selectively suppress the self-assembly process of the enantiomers of Ba-Fe 28 . As weak acids, lactic acids partially exist as anions in aqueous solution 44 .…”

“…Current research on the mechanism of homochirality mainly focuses on chiral recognition and chiral selection through studies of chirality transfer and amplification induced by chemical reactions, force fields 3,[6][7][8][9][10][11][12] , physical properties of solid samples (including crystallization) [13][14][15] , amino-acid clustering in gas phase 16 , molecular interaction on surfaces [17][18][19][20] and supramolecular assemblies of chiral molecules in bulk and solutions [21][22][23][24][25][26][27][28][29][30] . A few sketchy theories have been developed to explain how homochirality originated, was amplified in macromolecules and supramolecular assemblies and was transmitted to other biomolecules/assemblies during the evolution of life 2,31 .…”

“…The limitation of stereoselective synthetic technology and the rare examples of the natural biomacromolecule enantiomers make it difficult to study chiral recognition/selection. Through manipulating intermolecular hydrogen bonding and aromatic stacking interactions, Aida and Meijer et al observed the self-sorted behaviour in the solution of organic enantiomers during their formation of one-dimensional supramolecular structure [27][28][29] . However, the investigation of physical interactions (for example, electrostatic interaction) and spherical supramolecular assemblies (good analogues of virus capsid) in chiral recognition and selection is still rare.…”

“…Here two inorganic chiral macroions, [Fe 28 (m 3 -O) 8 (Tart) 16 28 ), are used as simple models, for the first time, to study the role of one type of universal physical interaction, electrostatic interaction, in chiral recognition and selection behaviour of biomolecules in solution. The kinetics study of the self-assembly indicates that the two enantiomers recognize each other and form their individual 'blackberry' structures.…”