The intercalation of tris-chelate metal complexes into clay minerals, in particular smectite, has attracted broad attention in terms of photochemistry, catalysis, and chiral recognition. It is of interest that they exhibit different adsorption behavior between racemic and enantiopure states on natural smectite. Their adsorption structure in the interlayer space has been, however, the topic of debate. In this short review article, my approach to clarify the adsorption structure of chiral metal complexes is described. The XRD method in a transmission mode was applied for the hybrid samples of montmorillonite and racemic tris-chelate nickel complexes, which were confined in a capillary tube. When the amount of adsorbed Ni complexes exceeds the cationic exchange capacity of montmorillonite, the obtained hybrid samples exhibit anisotropic diffraction in the 2D XRD images. The newly observed peaks were attributed to the reflections from the (10), (11), and (21) planes of the hexagonal assembly of Ni complexes. Based on the results, the detailed arrangement of racemic Ni complexes in the clay interlayer space is also discussed.

Herein, the composition of lithium-exchanged natural smectite and butenediol vinyl alcohol copolymer is varied over a wide range, from 100% clay to 100% polymer. The gas permeability is measured from 40 to 160°C, and the gas permeability behavior is discussed from the perspective of activation energy. The gas permeability is considered using He, which has a gas permeability equivalent to that of hydrogen. The gas-barrier property of the lithium-exchanged smectite is one-seventh of that the purified natural smectite as a clay alone. However, the gas-barrier property of the lithium-exchanged smectite increases as it is mixed with the polymer and becomes equivalent to that of the purified natural smectite composites at some ratios. In other words, depending on the clay and polymer combination, a coating with a dramatically high barrier property can be realized by composing, even if it is not necessarily a combination of the highest-performance clay and polymer. The polymer is the dominant factor in the activation energy of the gas permeation through the composite, which is similar for composites using lithium-exchanged and purified natural smectite.

Optically induced rotation of an exfoliated fluorohectorite (FHT) in colloidal dispersion has been demonstrated. By illuminating a tightly focused circularly polarized laser beam of which power was higher than 5 mW with the wavelength at 532 nm, FHT with the in-plane area of 100 µm² was rotated. While the rotational motion, FHT was optically trapped with maintaining its center of gravity position at the focal point. As the illuminated laser power increased, the rotation speed accelerated. The direction of rotation of the FHT could be switched by alternating the handedness of polarized light.

Galacturonic acid and glucuronic acid are important constituents of polysaccharides produced by microbes and plants. To demonstrate the effect of such uronic acids on the polymorphism of calcium carbonate (CaCO₃) minerals in hot spring environments, we studied the formation of CaCO₃ minerals in the systems containing galacturonic acid or glucuronic acid at 40, 50, and 60°C for 24 h. Each system contained 5.0 mmol/L Ca²⁺ and 20.0 mmol/L total carbonate ions with 0.0, 0.01, 0.1, 1.0, 2.0, and 5.0 mmol/L galacturonic acid or glucuronic acid. Our results revealed that needle-like shaped aragonite crystals were predominantly formed in the absence of uronic acids. In the presence of uronic acids, galacturonic acid strongly inhibited aragonite formation and favored rhombohedral calcite formation as galacturonic acid concentration increased. Glucuronic acid demonstrated a similar effect on the CaCO₃ polymorphism, but the effectivity was relatively lower than that of galacturonic acid. Moreover, the aspect ratio of aragonite crystals tended to decrease more with galacturonic acid concentration than with glucuronic acid. These effects of the uronic acids on the CaCO₃ polymorphism were considered to be attributed to the higher adsorption affinity of galacturonic acid to the aragonite surface than the calcite surface. These results indicate that microbial uronic acids and organic polymers containing uronic acid residues are closely involved in the CaCO₃ polymorphism in hot spring environments.