High quality protein crystals are necessary to realize three-dimensional structure analysis of proteins. However, protein crystallization, which involves nucleation and crystal growth, remains a major bottleneck in the structural determination process. In this decade, the authors have been developing innovative crystallization techniques to solve the problem. In this review, we first introduce our recent development of spatio-temporal control of protein crystal growth by femtosecond laser ablation, which enables us to promote protein crystal growth. We also explain the molecular mechanism from the viewpoint of crystal growth mode and its relevance to our past studies of protein crystal growth under flow. In addition, we also describe new methods for selective crystallization of the metastable phase of pharmaceutical compounds with cavitation bubbles induced by femtosecond laser irradiation or ultrasonic irradiation. Surprisingly, the metastable phase obtained by the methods was extremely stable and thus can potentially be applied to producing new medicines. These polymorphic control technologies are applicable to other materials, thus they have possibility to be practical applications in the future.
The results of various genome projects have shown that up to 30% of human proteins occur in cell membranes. Membrane proteins play crucial roles in many biological functions and are of key importance for medicine. Over 50% of commercially available drugs target membrane proteins. However, crystallization of membrane proteins still remains extremely difficult and many scientists are developing new techniques to conquer the problem. Here I will discuss three current topics of membrane protein crystallization: (1) crystallization in lipidic cubic phase, (2) crystallization using antibody fragments and (3) crystallization for X-ray free electron laser experiments.
The crystal growth mechanism of polymer has been investigated for a long period but has not been fully understood. In order to understand the crystal growth mechanism, we have investigated the melt-crystallization of poly(buthylene terephthalate) (PBT) by optical microscopy, differential scanning calorimetry and small angle X-ray scattering and have clarified the crystallization temperature dependences of growth rate and lamellar thickness, and the relation between the melting temperature and the lamellar thickness. Since these results cannot be interpreted by the conventional model that polymer crystallized directly from the melt, we have introduced the crystallization model through the mesophase. The attempt clarifies that the crystallization proceeds through the mesophase below 208℃ and directly from the melt above 208℃ in PBT.
The lateral growth rate and growth shape morphology of isotactic polybutene-1 (iPB1) tetragonal crystals were investigated for crystallization from the melt over the temperature range 68–101℃. The growth rate of tetragonal crystals shows supercooling dependence predicted by surface nucleation theory, and a regime II-III transition is observed at temperatures of 77–82℃. The morphology of single crystals is rounded below temperatures of 77–80℃, while the growth shape has a faceted morphology at higher crystallization temperatures. The kinetic roughening transition occurs between 77 and 80℃. The regime II growth mode is observed above 82℃ and proceeds by multiple nucleation on the faceted growth front, while the regime III growth mode is observed below 77℃ and proceeds by rough surface growth on the kinetically roughened growth front. The observed regime II-III transition can therefore be explained by the morphology transition of crystal growth shape.
The hard sphere/disk systems are one of the simplest models and have been playing a crucial role to investigate the fundamental problems, especially in the field of statistical physics. The pioneering numerical works on the solid-fluid phase transition by using Monte Carlo (MC) and molecular dynamics (MD) methods on the electronic computer was published in 1957. As historical milestones, those works have had a significant influence on the development of computer algorithms and provide novel tools to analyze a broad range of the physical phenomena from the microscopic points of view. This article reviews that (i) historical aspects of the study of hard sphere/disk systems from the viewpoints of computer simulation and (ii) modern methodologies especially for "Hybrid Scheme" between Event-Chain MC and Event-Driven MD. We also addressed (iii) recent applications of the novel methods in the study of melting/crystallization and the phase transition including the binary mixture systems as the simple glass model.