(375b) Reactive Crystallization of Metal-Amino Acid Chelates and their Nucleation Kinetics

Zinc(II)-amino acid chelates have been attracted with their anti-inflammatory and even anti-tumoral activities. In the present work, zinc(II) chelate of L-methionine was produced by reactive crystallization. Since it is difficult to measure solubility of chelates sparingly soluble for water, supersaturation ratio (S) was estimated by measuring conductivity of the solution which was correlated in advance with solubility product. To evaluate nucleation kinetics, induction time defined as the time gap between the creation of supersaturation and the appearance of crystals was measured using focused beam reflectance measurement (FBRM) as a function of supersaturation. In an assumption that the formation time of a stable nucleus, t_n, is much larger than the necessary time for the nucleus to grow to a detectable size, t_g, the induction time, t_ind (t_n + t_g), can be considered as inversely proportional to the nucleation rate. From the linear regression with ln t_ind and ln^-2S, it was found that the dominant nucleation mechanism is strongly affected by degree of supersaturation.