Thermodynamic characteristics of L-histidine polymorphs and effect of ethanol on the crystallization

L-Histidine(L-His) has two polymorphs of FormA and FormB. It is known that the crystallization of polymorphs is influenced by antisolvents. In this study, crystal morphology of polymorph was considered from prediction of crystal structures. Next, the effects of ethanol on polymorphs and morphology of L-His were studied by evaluating crystals obtained from saturated aqueous solutions by cooling or adding of ethanol. From the prediction of crystal structures, It is suggested that FormA crystal tend to grow in the long side direction. Experiments show that FormA tends to be obtained from aqueous solvent, on the other hands, FormB tends to be obtained from ethanol existing solution. However, FormB were found to dissolve gradually and transited to FormA. Furthermore, results show high concentration of ethanol change the morphology along its thickness direction, so it suggests that the effect of antisolvents has a big influence on crystallization. Moreover, the results of Thermogravimeter-Differential Thermal Analyzer (TG-DTA) and Differential Scanning Calorimetry (DSC) analysis demonstrate that FormB, which is thought as a metastable form, is possibly favorable in term of thermal stability and suggests the behavior of melting and decomposition of L-His.