Impact of chirality in the amorphous state of conglomerate forming systems: case study of N-acetyl-α-methylbenzylamine

Bienvenu Atawa (1, 2) , Nicolas Couvrat (2) , Frederic Affouard (3) , Natália T. Correia (3) , Gérard Coquerel (2) , Allisson Saiter (1)

1 GPM - Groupe de physique des matériaux
2 SMS - Sciences et Méthodes Séparatives
3 UMET - Unité Matériaux et Transformations - UMR 8207

The present work aims at addressing the issue of molecular handedness in the glassy and liquid states and its impact on heterogeneous equilibrium. For this purpose we evaluated the glass forming ability (GFA), the crystallization propensity, the molecular mobility and the hydrogen bonding structure of a chiral conglomerate forming system N-acetyl-α-methylbenzylamine (Nac-MBA) at various enantiomeric excess (ee) by mean of experimental and computational techniques. We revealed that the rich relaxational landscape (Debye (D), α, βJG and ϒ) and the temperature dependence of the time scale of each process was insensitive to chirality. The most remarkable impact of chirality was expressed on the GFA and the recrystallization of heterochiral arrangements. In fact the GFA increases with decreasing ee while the crystallization propensity increases with increasing ee. The counter enantiomer acts as a disruptor of crystallization and favored the glass formation upon cooling. The Molecular Dynamic Simulation (MDS) results on the architecture of chiral sequences showed that homochiral sequences were most favorable when compared to heterochiral in the liquid state. However, this predisposition to form homochiral sequences in the liquid state was not precursor of the future crystalline structure since the liquid or the glassy system recrystallizes as heterochiral sequences. At our understanding the crystallization was mostly controlled by the mean free migration path of an enantiomer to build homochiral or heterochiral sequences. In the present case, it seems that the mean free migration path achieved by an enantiomer for heterochiral sequences is lower compared to homochiral arrangements in such a way that the crystallization of the metastable racemic compound is kinetically more favorable.

Domaines: Matériaux; Science des matériaux [cond-mat.mtrl-sci]; Matériaux

Bienvenu Atawa, Nicolas Couvrat, Frederic Affouard, Natália T. Correia, Gérard Coquerel, et al.. Impact of chirality in the amorphous state of conglomerate forming systems: case study of N-acetyl-α-methylbenzylamine. Physical Chemistry Chemical Physics, 2021, 23 (42), pp.24282-24293. ⟨10.1039/D1CP03843E⟩. ⟨hal-03365079⟩