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Methods for the Self-integration of Megamolecular Biopolymers on the Drying Air-LC Interface

Living organisms that use water are always prone to drying in the environment. Their activities are driven by biopolymer-based micro- and ...

Japan Advanced Institute of Science and Technology

By using a thermo-sensitive polymer network in which the sensitizer and the catalyst are immobilized, novel hydrogen generating gel systems capable of temperature control of photoreaction have been realized.

Temperature control of photoreaction for hydrogen generating gel systems.

Here we report a novel biomimetic gel that efficiently converts photoenergy and the water inside into H(2). By immobilizing a photosensitizer into the polymer network, the gel system involving an electronic transmission circuit generates H(2) with a high quantum efficiency of over 10%, significantly higher than the conventional solution system.

Role of copolymerized photosensitizer in hydrogen-generating gel systems for higher quantum efficiency.

Photoinduced hydrogen-generating nanogel systems.

The nanointegration mechanism for photoinduced hydrogen nanogenerators using nanogels is described. By spatially integrating poly(N-isopropylacrylamide-co-Ru(bpy)(3)) nanogels as a photosensitizer and Pt nanoparticles as a catalyst, a mechanism using electrostatic interactions and the shrinking behavior of the thermosensitive polymer network is revealed. In addition, to evaluate the sensitivity to exterior energy, light, and heat, the integrated nanospace is controlled by using thermosensitive nanogels, which drastically shrink above the volume phase transition temperature. Such nanospatial control of multiple kinds of functional molecules in a photochemical reaction is important for the realization of artificial photosynthetic systems.

Effect of nanointegration on photoinduced hydrogen-generating nanogel systems.

Here we show a comb-type self-oscillating gel that exhibits spontaneous swelling-deswelling oscillation without on-off switching of external stimuli. The redox oscillation of the polymerized catalyst of the BZ reaction is converted to mechanical oscillation of the polymer. By introducing grafted polymer chains, self-oscillation with faster and larger swelling-deswelling changes was achieved.

Design of a comb-type self-oscillating gel.

Several strategies for controlling microtubule patterns are developed because of the rigidity determined from the molecular structure and the geometrical structure. In contrast to the patterns in co-operation with motor proteins or associated proteins, microtubules have a huge potential for patterns via their intrinsic flexural rigidity. We discover that a microtubule teardrop pattern emerges via self-assembly under hydrodynamic flow from the parallel bundles without motor proteins. In the growth process, the bundles ultimately bend according to the critical bending curvature. Such protein pattern formation utilizing the intrinsic flexural rigidity will provide broad understandings of self-assembly of rigid rods, not only in biomolecules, but also in supramolecules.

Microtubule teardrop patterns.

Internal microscopic structures of poly(N-isopropylacrylamide-co-tris(2,2'-bipyridyl))ruthenium(II) complex microgels were investigated using small-angle X-ray scattering (SAXS) in the extended q-range of 0.07 ≤ q/nm(-1) ≤ 20. The microgels were prepared by aqueous free-radical precipitation polymerization, resulting in formation of monodispersed, submicrometer-sized microgels, which was confirmed by transmission electron microscopy and dynamic light scattering. To reveal the changes in the microscopic structures of the microgels during swelling/deswelling or dispersing/flocculating oscillation, the redox state of Ru(bpy)3 complexes was fixed in the microgels using Ce(IV) or Ce(III) ions under high ionic strength (1.5 M) during the SAXS measurements. The scattering intensity of the microgels manifested five different structural features. In particular, the correlation length (ξ), which was obtained from the fitting analysis using the Ornstein-Zernike equation, of the microgels both in the reduced and oxidized Ru(bpy)3 states exhibited divergent-like behavior. In addition, a low-q peak centered at q ≈ 5 nm(-1) did not appear clearly in both the reduced [Ru(bpy)3](2+) and oxidized [Ru(bpy)3](3+) states, indicating that the formation of a polymer-rich domain was suppressed; thus, Ru(bpy)3 complexes can be active even though the microgels are deswollen or flocculated during the oscillation reaction.

Small-Angle X-ray Scattering Study on Internal Microscopic Structures of Poly(N-isopropylacrylamide-co-tris(2,2'-bipyridyl))ruthenium(II) Complex Microgels.

Herein we report a novel reaction field for photoinduced H2 generation by using microtubules as a medium. By controlling the tubulin/microtubule hierarchical structure, synergistic effects by which the Ru(bpy)3(2+)-conjugated microtubule network causes suppression of energy loss by collision are clarified.

Effect of microtubule polymerization on photoinduced hydrogen generation.

Many strategies have been explored to achieve artificial photosynthesis utilizing mediums such as liposomes and supramolecules. Because the photochemical reaction is composed of multiple functional molecules, the surrounding microenvironment is expected to be rationally integrated as observed during photosynthesis in chloroplasts. In this study, photoinduced electronic transmission surrounding the microenvironment of Ru(bpy)3(2+) in a polymer network was investigated using poly(N-isopropylacrylamide-co-Ru(bpy)3), poly(acrylamide-co-Ru(bpy)3), and Ru(bpy)3-conjugated microtubules. Photoinduced energy conversion was evaluated by investigating the effects of (i) Ru(bpy)3(2+) immobilization, (ii) polymer type, (iii) thermal energy, and (iv) cross-linking. The microenvironment surrounding copolymerized Ru(bpy)3(2+) in poly(N-isopropylacrylamide) suppressed quenching and had a higher radiative process energy than others. This finding is related to the nonradiative process, i.e., photoinduced H2 generation with significantly higher overall quantum efficiency (13%) than for the bulk solution. We envision that useful molecules will be generated by photoinduced electronic transmission in polymer networks, resulting in the development of a wide range of biomimetic functions with applications for a sustainable society.

Design of Polymer Networks Involving a Photoinduced Electronic Transmission Circuit toward Artificial Photosynthesis.

A drying environment is always a proposition faced by dynamic living organisms using water, which are driven by biopolymer-based micro- and macrostructures. Here, we introduce a drying process for aqueous liquid crystalline (LC) solutions composed of biopolymer with extremely high molecular weight components such as polysaccharides, cytoskeletal proteins, and DNA. On controlling the mobility of the LC microdomain, the solutions showed milliscale self-integration starting from the unstable gas-LC interface during drying. In particular, we first identified giant rod-like microdomains (∼1 μm diameter and more than 20 μm length) of the mega-molecular polysaccharide, sacran, which is remarkably larger than other polysaccharides. These microdomains led to the formation of a single milliscale macrodomain on the interface. In addition, the dried polymer films on a solid substrate also revealed that such integration depends on the size of the microdomain. We envision that this simple drying method will be useful not only for understanding the biopolymer hierarchization at the macroscale level but also for preparation of surfaces with direction controllability, as seen in living organisms, for use in various fields such as diffusion, mechanics, and photonics.

Milliscale Self-Integration of Megamolecule Biopolymers on a Drying Gas-Aqueous Liquid Crystalline Interface.

We propose a self-similar assembly to generate planar orientation of megamolecular polysaccharides on the nanometer scale and submicron scale. Evaporating the aqueous liquid crystalline (LC) solution on a planar air-LC interface induces polymer layering by self-assembly and rational action of macroscopic capillary forces between the layers. To clarify the mechanisms of nanometer- and submicron-scale layering, the polymer films are investigated by electron microscopy.

Kosuke Okeyoshi

Japan Advanced Institute of Science and Technology

Methods for the Self-integration of Megamolecular Biopolymers on the Drying Air-LC Interface