The recent progress in the understanding of the melting kinetics of polymer crystals was reviewed. The melting behavior of folded-chain crystals (FCC) of polymers becomes seriously complicated due to the metastability of FCC causing melting-recrystallization cycles and reorganization of crystals. Conventional calorimetry of the melting under constant rate of heating suggested a heating rate dependence of melting peak temperature, which is understood as a superheated melting kinetics. A morphological observation of melting of single crystals supported this behavior. Recent progress of chip-sensor fast scanning calorimetry (FSC) also confirmed the behavior and enabled the examination of isothermal melting kinetics. The results suggested an exponential dependence of melting rate on superheating, which can be interpreted as a consequence of inhomogeneous stability of crystalline stems derived from broad variations of chain-folding conformations. As a further application of FSC to organic crystals, melting kinetics of sucrose is also reviewed.

  I would like to introduce the particle image diffusometry (PID) as its inventor. PID enables the visualization of pre-nucleation solutes through their Brownian motion. The hardware setup is a standard optical microscope and a camera to capture the movie data. PID does not assume fluorescent labeling of solute molecules, but the data analysis is of the central importance in this methodology. The fundamental theoretical principle roots back to the statistical physics of well-known dynamic light scattering (DLS), but the visualization of spatio-temporal patterns is realized by the invention of a simple algorithm. In contrast to the single molecule/particle tracking (SMT/SPT), PID does not track the bright points but evaluates the spatio-temporal fluctuation of time-series images. This is more advantageous for the analysis of crystallization phenomena, where high concentration of solutes often hinders the SMT/SPT approach. Looking back the long histories of SMT/SPT and DLS, there will be plenty of room on the avenue opened by PID.

  Understanding of crystallization and crystal growth of organic crystals is essential for promoting the development of techniques for controlling crystallization and morphology. We are investigating the crystal growth mechanism of organic crystals from a viewpoint of hydration structure at an organic crystal surface-solution interface using three-dimensional (3D) force distribution measurement by atomic force microscopy (AFM). In this article, it is revealed that hydration structures of acetaminophen crystals are different between polymorphs and that those of α-glycine crystals are different between crystal planes. Then, the influence of the different hydration structures on crystal growth of polymorph and morphology is discussed.

  Protein crystals are attracting attention as solid biomaterials because of their porous structure formed by the regular assembly of proteins. Protein crystals are functionalized as templates to immobilize foreign molecules such as metal nanoparticles, metal complexes, and proteins. These hybrid crystals have been used as functional materials for catalytic reactions and structural analysis. In addition, in-cell protein crystals have been extensively studied with the development of rapid protein crystallization and crystal structure analysis. This review shows the recent advances in crystal engineering for protein crystallization and the generation of solid-state functional materials used in cell crystals.

  The three-dimensional (3D) structure of a protein molecule is usually solved by using crystals grown with copious amounts of precipitants. The obtained structure could be significantly different from those in vivo because the precipitant concentration in vivo is much less than those under normal crystallization conditions. For the first time, we have developed novel precipitant-free protein crystallization methods by centrifugal concentration and drying. For both methods, atomic-level 3D structures were successfully obtained. 3D molecular structure of hen egg-white lysozyme (HEWL) obtained without precipitants was significantly different from that obtained with precipitants, whereas the precipitant-free molecular structure of glucose isomerase (GI) was similar to those obtained with precipitants.