Non‐stochastic behavior in sodium chlorate crystallization

Abstract

AbstractNaClO3 is achiral in solution. If crystallization is performed under a static set‐up, it is recognized that the stochastic nucleation probability results in a racemic mixture of the conglomerate. In this paper, we report a reexamination of the crystallization of NaClO3 from static solution in petri dishes that was conducted over a number of years and is based on the count and analysis of several thousand d‐ vs. l‐NaClO3 crystals. Remarkably, instead of an expected nearly 50/50 coin‐tossing situation for the d/l crystal frequency, in most of our experiments a statistically significant bias in favor of d‐ over l‐NaClO3 crystals was found. The experiments also showed that the NaClO3 system was relatively insensitive regarding the intentional addition of a variety of optically active agents. Only in some cases, the persisting d‐bias observed in the unseeded experiments slightly increased upon the presence of such additives. Nevertheless, experiments in plastic petri dishes or in presence of fungal spores were able to reverse this bias. A literature survey shows that mainly d‐directed non‐stochastic behavior in the NaClO3 system has been previously observed in other laboratory settings and by the application of different crystallization techniques. So far, the kind of chiral influence that could be at the origin of the observed bias remains unknown. After the examination of several possible chiral influences of physical, chemical and biological origin, we carefully consider the presence of bio‐contaminants as most likely for the cause of this effect.