Do homochiral aggregates have an entropic advantage?

The present work seeks to illuminate the underlying principles which control the aggregation of chiral building blocks into larger aggregates by examining the role that entropy plays in this process. Entropic effects are first examined within the confines of a simple model system, and the results are then compared to experimental data on clusters of amino acids. The model system predicts that the formation of a specific structure is more likely to occur from an enantiopure solution because forming a particular structure from a racemic solution is hindered by significant entropic barriers. These predictions are in good agreement with the experimental results. In our examination of clusters of all of the amino acids, clusters which are unusually abundant are found only when enantiopure solutions are sampled. Furthermore, the majority of all clusters exhibit no preference for chiral composition, suggesting that entropic effects negate any changes in enthalpy. Although the experimental data are not comprehensive, our results strongly suggest that specificity in homochiral clusters is entropically advantageous compared to specificity in racemic clusters.