Primary Nucleation of Threonine Crystals from Ternary Solutions

Abstract

Primary nucleation of desired threonine enantiomer crystals occurred by changing solution compositions in a d-threonine/l-threonine/water ternary solution, and nucleation mechanisms of threonine enantiomer crystals are discussed using the ternary phase diagram for a d-threonine/l-threonine/water system. When an l-threonine mother crystal was immersed in a dl-threonine solution, the l-threonine mother crystal surfaces were dissolved, and the supersaturation in the solution with respect to d-threonine increased. Consequently, heterogeneous nucleation of d-threonine crystals occurred, and combined crystals of l- and d-threonine were formed. When an l-threonine supersaturated solution was injected into a dl-threonine supersaturated solution, the supersaturation with l-threonine in the solution became higher by mixing the two solutions, and consequently homogeneous nucleation of l-threonine crystals occurred. Controlling nucleation of desired enantiomer crystals was expected to be applied to a formation of combined crystals and preferential crystallization.