Beyond conglomerates: a minimalist model of the Viedma Deracemization of dl-amino acids

Abstract

A comprehensive kinetic rate equation model is proposed for a better understanding of the Viedma deracemization of dl-amino acids. This model includes monomer plus cluster and cluster plus cluster growth, and involves both homochiral and heterochiral interactions. Our approach employs a fully microreversible growth and dissolution kinetic scheme. It works with an irreversible cluster breaking by grinding under racemizing condition of molecules. The model which is consistent with experimental observations has been parametrized on the amplification of the enantiomeric excess during the total deracemization of a scalemic mixture of dl- and l-crystals of aspartic acid. After parametrization, numerical simulations show the possibility of spontaneous mirror symmetry breaking (SMSB). Furthermore, we identify a bifurcation scenario where it is predicted that, as long as the energy difference between racemic and enantiopure crystals is not too high, Viedma deracemization may be possible under sufficient nonequilibrium conditions. However, there are situations where the deracemization success requires an initial enantiomeric excess higher than a critical value. Our model predictions have been validated by the complete deracemization of two proteinogenic amino acids, namely dl-aspartic acid and dl-valine racemic crystals.