Biomineral-Inspired Colloidal Liquid Crystals: From Assembly of Hybrids Comprising Inorganic Nanocrystals and Organic Polymer Components to Their Functionalization

Abstract

Conspectus Bioinspired organic/inorganic synthetic composites have been studied as high-performance and functional materials. In nature, biominerals such as pearls, teeth, and bones are self-organized organic/inorganic composites. The inorganic components are composed of calcium carbonate (CaCO 3 ) and hydroxyapatite (HAp), while the organic components consist of peptides and polysaccharides. These composites are used as structural materials in hard biological tissues. Biominerals do not show significantly higher performances than synthetic composites such as glass-fiber- or carbon-fiber-reinforced plastics. However, biominerals consist of environmentally friendly and biocompatible components that are prepared under mild conditions. Moreover, they form elaborate nanostructures and self-organized hierarchical structures. Much can be learned about material design from these biomineral-based hierarchical and nanostructured composites to assist in the preparation of functional materials. Inspired by these biological hard tissues, we developed nanostructured thin films and bulk hybrid crystals through the self-organization of organic polymers and inorganic crystals of CaCO 3 or HAp. In biomineralization, the combination of insoluble components and soluble acidic macromolecules controls the crystallization process. We have shown that poly(acrylic acid) (PAA) or acidic peptides called polymer additives induce the formation of thin film crystals of CaCO 3 or HAp by cooperation with insoluble organic templates such as chitin and synthetic polymers bearing the OH group. Moreover, we recently developed CaCO 3 - and HAp-based nanostructured particles with rod and disk shapes. These were obtained in aqueous media using a macromolecular acidic additive, PAA, without using insoluble polymer templates. At appropriate concentrations, the anisotropic particles self-assembled and formed colloidal liquid-crystalline (LC) phases. LC materials are generally composed of organic molecules. They show ordered and mobile states. The addition of stimuli-responsive properties to organic rod-like LC molecules led to the successful development of informational displays, which are now widely used. On the other hand, colloidal liquid crystals are colloidal self-assembled dispersions of anisotropic organic and inorganic nano- and micro-objects. For example, polysaccharide whiskers, clay nanosheets, gibbsite plate-shaped particles, and silica rod-shaped particles exhibit colloidal LC states. In this Account, we focused on the material design and hierarchical aspects of biomineral-based colloidal LC polymer/inorganic composites. We describe the design and preparation, nanostructures, and self-assembled behavior of these new bioinspired and biocompatible self-organized materials. The characterization results for these self-assembled nanostructured colloidal liquid crystals found using high-resolution transm...

Unique Thermal Structural Phase Transitions Exhibited by Unsymmetrical Organometallic Gold(III)‐Dithiolene Complexes with Pentylthio and Hexylthio Groups

“…Unsymmetrical cores, unlike conventional organic materials, enable the arrangement of molecules in the solid state not only by π–π interactions but also by dipole‐dipole interactions. If flexible alkyl groups are introduced into the rigid unsymmetrical cores, the unsymmetrical complexes can be applied to new metallomesogens, which can provide various molecular liquid crystals exhibiting multifunctionalities [33–36] . Because of their unconventional electronic states, unsymmetrical metal‐dithiolene complexes with flexible alkyl groups can also be good candidates for new components that provide multifunctional liquid crystals exhibiting conducting and/or optical properties.…”

“…If flexible alkyl groups are introduced into the rigid unsymmetrical cores, the unsymmetrical complexes can be applied to new metallomesogens, which can provide various molecular liquid crystals exhibiting multifunctionalities. [33][34][35][36] Because of their unconventional electronic states, unsymmetrical metal-dithiolene complexes with flexible alkyl groups can also be good candidates for new components that provide multifunctional liquid crystals exhibiting conducting and/or optical properties. Based on this strategy, we synthesized unsymmetrical platinum(II) and gold(III) complexes coordinated by a dithiolene ligand containing the TTF moiety with flexible decylthio groups,…”

Experimental probing of dynamic self-organized columnar assemblies in colloidal liquid crystals

“…[7][8][9][10][11][12] The components with anisotropic shapes of particles form ordered and mobile assembled states. Recently we reported that biomineralization-inspired colloidal liquid crystals were formed based on calcium carbonate (CaCO 3 ) 13,14 and hydroxyapatite [15][16][17][18] particles complexed with an acidic macromolecule, poly(acrylic acid) (PAA). For hydroxyapatitebased liquid crystals, stimuli responsive properties and biofunctions, e.g., magnetic eld responsive colloidal liquid crystals composed of nanorods, were reported.…”

Molecular Complexation of Polymers and Metal Oxide Clusters for Semicrystalline, Thermoplastic Anhydrous Proton Exchange Membranes in Fuel Cells

“…25,26 In a typical biomineralization process, inorganic crystals are complexed with biomacromolecules to afford structural materials in hard biological tissues. 27 Nevertheless, a massive amount of effort is required to understand the integrating mechanism of biomineralization. On the contrary, certain functionalities, e.g., mechanical, optical, and electric properties, require the formation of highly ordered structures, which, however, is still challenging because it requires delicate tuning of interphase attractions.…”

“…The complexation of organic and inorganic components offers approaches for integrating the enriched functionalities of inorganic materials with the excellent flexibility and processability of polymers. , The covalent/noncovalent interactions between the two phases can be tuned for the controlled formation of hierarchical structures. , In a typical biomineralization process, inorganic crystals are complexed with biomacromolecules to afford structural materials in hard biological tissues . Nevertheless, a massive amount of effort is required to understand the integrating mechanism of biomineralization.…”