| Nucleation in a crystallization process is a critical step in determining properties of crystals produced. However, the nucleation mechanism of small and macro organic molecules is not clearly understood. In this work, novel methods were applied to explore nucleation of protein and small organic molecule crystals and to provide a better idea for producing crystals of desired properties.;First, non-photochemical Laser Induced Nucleation (NPLIN) was used for studying nucleation of model proteins. Small droplets of supersaturated lysozyme and trypsin solution were exposed to irradiation of intense linearly polarized laser light with different wavelengths and duration rates of laser pulses. The number of droplets in which crystals were observed in a given period time significantly increased with laser irradiation compared with samples in the absence of irradiation. Moreover, it was established that the efficiency of NPLIN for lysozyme crystals is strongly dependent on the aging time and wavelength of the laser. It is proposed that the nucleation of protein proceeds by a two-step mechanism and that the polarized electric field generated by intense laser irradiation can aid the protein molecules in the disordered liquid-like cluster to reorganize into a crystalline structure, in turn, enhancing the nucleation rate of lysozyme and trypsin crystals. Therefore, NPLIN has high potential for controlling nucleation of proteins.;Second, patterned Self Assembled Monolayers (SAMs) were employed to discover concomitant nucleation phenomenon of small organic molecules and to generate different crystal forms of model drug compounds. Arrays of small solution droplets on the nano- and pico liter scale were generated using patterned substrates of SAMs. As the solvent evaporated from the droplets, crystals were formed within each droplet. The solid state form of each crystal produced was characterized using Raman and optical microscopy. With mefenamic acid and sulfathiazole as model drug compounds, two and four different polymorphic forms of mefenamic acid and sulfathiazole, respectively, were observed under identical conditions. Furthermore, it is established that the polymorphic distribution of the crystals obtained is highly dependent on the evaporation rate of solvent and the concentration of solution. These results imply that different polymorphic forms competitively nucleate in a solution, and the probability of each polymorph form nucleating is strongly dependent on the supersaturation of the solution. This technology complements current polymorph screening approaches, in that very small amount of drug substance and short times are required and large numbers of experiments can be conducted. |
