Effects of hydrostatic pressure on amorphous chiral materials: Impact on homochiral or heterochiral H-bond sequences

Abstract

High pressure effects on static dielectric permittivity of homochiral and heterochiral N-acetyl-α-methyl-benzylamine (Nac-MBA) were investigated. For homochiral composition, the static permittivity increases of 178% with pressure at T = 388 K. Interestingly, as pressure continued increasing, εS drastically collapsed to reach ε∞=3±0.3. In the case of heterochiral composition, the static permittivity increases with pressure (in the same magnitude order as the pure enantiomer), and reaches a constant value depending on the isothermal temperature. Thus, the size of the H-bond aggregates is highly pressure sensitive, increasing up to a level that crystallization becomes unavoidable. For heterochiral composition, this process may be kinetically time consuming since the initial heterochiral H-bond aggregates need to be surrounded by their suitable neighbors in order to fulfilled the crystalline packing. The initial H-bond sequences are the precursors of the future crystalline arrangement under pressure application.