Kazuki Murai

Enhancement of activity and stability of the formaldehyde dehydrogenase by immobilizing onto phenyl-functionalized mesoporous silica.

Formaldehyde dehydrogenase (FDH, molecular size of 8.6 nm × 8.6 nm × 19.0 nm) was immobilized on seven types of mesoporous silica (MPS), whose pores were from 2.4 to 31.2 nm sized, and their catalytic activities were evaluated by oxidation of formaldehyde. Among MPSs, FDH immobilized on MPS-4 (pore size of 12.3 nm) showed the best catalytic activity. Enhancement of catalytic activity was obtained by immobilizing onto MPS, whose pore (mesopore) size was similar to the molecular size of FDH. In addition, FDH was immobilized on five types of organo-functionalized MPS-4. Results from assays of enzyme activity showed that FDH immobilized on phenyl-functionalized MPS-4 (MPS-4-Ph) had higher activity than FDH immobilized on non-functionalized one. Immobilized FDH on MPS-4-Ph was active for low formaldehyde concentration form 6.0 μM and more sensitive than conventional formaldehyde detectors. Stability of FDH activity was also evaluated under the various conditions, in which protein denaturation could occur by solvent treatment, such as methanol or sodium dodecyl sulfate. As a result, FDH stability was strongly improved by the immobilization on MPS materials. Further investigation using tryptophan fluorescence and circular dichroism (CD) indicated that the high-order structure of the FDH did not alter upon binding to the non-functionalized MPS surface. On the other hand, FDH immobilized on functionalized-MPS was changed by hydrophobic interaction or covalent binding. Consequently, substrate affinity was improved by the change in the structure of FDH and then the orientation of the active site.

Enzyme structure and catalytic properties affected by the surface functional groups of mesoporous silica

The enzyme subtilisin from Bacillus licheniformis (4.1 nm × 7.8 nm × 3.7 nm) was easily immobilized onto a mesoporous silica (MPS) surface by a direct one-step method and the amount of subtilisin immobilized on each functionalized MPS surface was similar (approximately 0.30 mg of enzyme/mg of MPS support). The catalytic performance (hydrolytic activity and enantioselectivity) of the immobilized subtilisin was found to depend on the properties of the organofunctional group on the MPS surface. In particular, the hydrolytic activity of enzyme immobilized on ethyl-group-modified MPS increased relative to the behavior of free subtilisin (relative activity 143%). The activity of subtilisin immobilized on the modified MPS was improved by facilitation of contact between enzyme and hydrophobic substrate by increase in hydrophobicity with an immobilized carrier. On the other hand, the enantioselectivity of subtilisin immobilized on 3-mercaptopropyl-group-modified MPS significantly decreased (enantioselectivity of 2.6 compared to 4.3 for free subtilisin). This decrease in enantioselectivity indicated that the mercapto group on the MPS surface was changed in the secondary structure of enzyme by interacting between enzyme and immobilized support. The denaturation temperature of subtilisin immobilized on no-substituted MPS increased (65 °C compared with 57 °C for free subtilisin). The denaturation temperature of immobilized subtilisin was dependent on the absorbed fraction of thermal energy by functional groups on the MPS surface.

Mineralization of Calcium Carbonate on Multifunctional Peptide Assembly Acting as Mineral Source Supplier and Template

Crystal phase and morphology of biominerals may be precisely regulated by controlled nucleation and selective crystal growth through biomineralization on organic templates such as a protein. We herein propose new control factors of selective crystal growth by the biomineralization process. In this study, a designed β-sheet Ac-VHVEVS-CONH2 peptide was used as a multifunctional template that acted as mineral source supplier and having crystal phase control ability of calcium carbonate (CaCO3) during a self-supplied mineralization. The peptides formed three-dimensional nanofiber networks composed of assembled bilayer β-sheets. The assembly hydrolyzed urea molecules to one carbonate anion and two ammonium cations owing to a charge relay effect between His and Ser residues under mild conditions. CaCO3 was selectively mineralized on the peptide assembly using the generated carbonate anions on the template. Morphology of the obtained CaCO3 was fiber-like structure, similar to that of the peptide template. The mineralized CaCO3 on the peptide template had aragonite phase. This implies that CaCO3 nuclei, generated using the carbonate anions produced by the hydrolysis of urea on the surface of the peptide assembly, preferentially grew into aragonite phase, the growth axis of which aligned parallel to the direction of the β-sheet fiber axis.

Catalytic performance of subtilisin immobilized without covalently attachment on surface-functionalized mesoporous silica materials

Mesoporous silica (MPS) materials were synthesized using cetyltrimethylammonium bromide or amphiphilic pluronic polymer P123 (EO20PO70EO20) as structure-directing agent. MPS samples were characterized by FE-SEM and N2 adsorption-desorption isotherms, respectively. Subtilisin from Bacillus licheiformis (4.1 × 7.8 × 3.7 nm) was easily immobilized by a direct one-step immobilization process onto MPS with different organo-functinalized surfaces. However, enzyme immobilized on MPS modified with 3-mercaptopropyl group strongly reduced its enantioselectivity. Denaturation temperature of immobilized subtilisin shifted to a high temperature compared to free-enzyme. These biocatalysts on MPS particles retained about 30% of original activity even after 5 cycles of recycle use.

Superhydrophobic Surfaces on Phase-separated Nanostructures of Polystyrene/Polymethyl Methacrylate Films Fabricated by the Double-spray Technique

Rapid large-area printing techniques are required to fabricate superhydrophobic surfaces of polymer films on solid substrates. Here, we report a double-spray technique for fabrication of mixed phase-separated films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS-b-PMMA. The surface wettability of the films changes to superhydrophobic by immersing the samples in cyclohexane, which is a good solvent for only PS. The rinsing process forms nanostructures in the remaining PMMA films that have flat surfaces before the rinsing treatment. The highest contact angle is about 150° on the film with a PMMA ratio of 0.2. X-ray photoelectron spectroscopy shows that a small amount of PS remains on the surface of the PMMA films, making the films superhydrophobic. Addition of PS-b-PMMA to the PS/PMMA films forms smaller phase-separated structures than those in the original PS/PMMA films because of an increase in the compatibility between PS and PMMA. The contact angle hysteresis in the films decreases with increasing PS-b-PMMA ratio, indicating an increase in the homogeneity of the phase-separated structures.

Monte carlo simulations for blue-phase structure in liquid crystals

ABSTRACT Blue-phase liquid crystals form three-dimensional structures in a self-organizing manner and are similar to living tissue structures such as the teeth of mice and collagen tissues. This study presents numerical results regarding the conditions under which blue-phase liquid crystals occur. The Monte Carlo simulations are performed by employing an improved Lennard–Jones potential that considers anisotropy and chirality. The conditions for the formation of the blue phase, which vary with respect to the chirality, are examined first. The relationship between the anisotropic parameters and the chiral parameter for the formation of the blue phase is discussed. Identical blue-phase structures are obtained, even when the cell size and molecular number are varied drastically. This discussion is useful for considering the scale-up problem, which is almost always a difficult issue for molecular-scale simulations.

Self-bonding and the electrochemical properties of silica-coated nanowires composed of cobalt-coordinated peptide bundles

We propose a method for self-bonding between electrodes using the self-organizational processes of a silica-coated peptide hybrid nanowire. We designed and synthesized a 23-mer α-helical peptide having functional sites that serve as catalytic sites for silica mineralization (glutamic acid [Glu] and lysine [Lys]) and binding (serine [Ser]), as well as for the formation of a Co(II) ion complex. The peptides formed nanowires composed of α-helical bundles that showed axial connection because of complexation between Co(II) and the histidine (His) residues, and macro-dipole interactions of the α-helical peptides. The nanowires self-bonded between the electrodes, and the surface of the nanowires was coated with silica using mineralization. The silica coating of the surface of the Co(II)-coordinated peptide nanowires induced two kinds of phenomena: (1) structural stabilization of the peptide nanowire component in the composite and (2) an increase in conductivity compared with that of the non-coated peptide nanowires.

Regulated Drug Release Abilities of Calcium Carbonate-Gelatin Hybrid Nanocarriers Fabricated via a Self-Organizational Process

In this study, we investigated the drug‐releasing behavior of a calcium carbonate (CaCO3)–gelatin hybrid nanocarrier, fabricated through a single process using biomimetic mineralization. The organic scaffold (gelatin) of the fabricated nanocarrier is responsible for its capacity to load anionic drugs and for controlling the morphology of the inorganic matrix (CaCO3). We studied the drug‐releasing properties of the nanocarrier by investigating the response of the CaCO3 matrix to acidic conditions. We found that under neutral conditions, drug release from the nanocarrier was inhibited, whereas under acidic conditions, the drug was efficiently released. Therefore, drug release from the nanocarrier is largely dependent on the surrounding pH.