Applications of Single-site Photocatalysts to the Design of Unique Surface Functional Materials

The isolated and tetrahedrally coordinated metal oxide (Ti, V, Cr, Mo and W-oxides) moieties can be included in the silica matrixes of silica-based microporous zeolite and mesoporous silica materials and named as “single-site photocatalysts”. Under UV-light irradiation these single-site photocatalysts form the charge transfer excited state, i.e., the excited electron–hole pair state which is located quite near to each other in different from the manner observed on semiconducting materials such as TiO₂, and play a significant role in various photocatalytic reactions. These single-site photocatalysts not only can promote photocatalytic reactions but also can be utilized to synthesis of functional materials. The nano-sized metal catalyst and visible-light sensitive binary oxide photocatalyst can be synthesized on the excited single-site photocatalyst under UV-light irradiation. The transparent mesoporous silica thin film with single-site photocatalyst generates the super-hydrophilic surface. In this review, our recent applications of single-site photocatalysts to synthesis of the surface functional materials have been introduced.     

Amino acid residues in GRK1/GRK7 responsible for interaction with S-modulin/recoverin

GRK1 is a visual pigment kinase in rods and is essential for inactivation of light-activated rhodopsin. The GRK1 activity is inhibited by binding of the Ca(2+)-bound form of S-modulin/recoverin. We previously identified the S-modulin/recoverin site to interact with GRK1. In the present study, we identified its counterpart in GRK1. We synthesized 29 of GRK1 or GRK7 partial peptides that cover the entire sequence of GRK1/GRK7, and examined whether these peptides inhibit S-modulin/recoverin activity most probably by preoccupying the binding site for GRK1. The inhibition was the greatest with the N-terminal peptide (p1, aa 3-23 in GRK7). On mutation of each of eight amino acid residues highly conserved in the p1 region of more than 10 orthologs, the inhibition was significantly reduced in the mutation of Leu(6), Asn(12) and Tyr(15). We further examined the binding of the peptides, including mutated ones, to S-modulin/recoverin with a resonance mirror biosensor. The binding correlated well with the degree of the inhibition by a peptide. The inhibition, therefore, seemed to be due to a direct binding of the kinase peptide to the binding site of active S-modulin/recoverin. A GRK1 region close to its C-terminus also seemed to be the binding site for S-modulin/recoverin.     

Variation of 7Be concentration in surface air at Nagano, Japan

The concentration of ⁷Be in surface air at Nagano City has been measured during the period from August 2000 to March 2005. The average monthly concentrations of ⁷Be in surface air were in the range of 3.3–14 mBq/m³ with pronounced two peaks in spring and autumn. It took 30–40 hours to recover the ⁷Be concentrations observed before, once ⁷Be was washed out by wet precipitations. For a pronounced increase in the concentrations of ⁷Be found in winter, a low-pressure trough coming close to the Japanese Islands with high concentrations of ⁷Be is responsible under the characteristic distribution of atmospheric pressure around the Japanese Islands.     

Boosting Charge Transport in a 2D/3D Perovskite Heterostructure by Selecting an Ordered 2D Perovskite as the Passivator

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA_0.8Cs_0.2PbI₃, we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕμ), and carrier diffusion length (L_D) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of ≈1.3 μs, high ϕμ of ≈18.56 cm² V⁻¹ s⁻¹, and long L_D of ≈7.85 μm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA₂PbI₄. This carrier diffusion length is comparable to that of some perovskite single crystals (>5 μm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.     

Preparation of nano-sized Pt metal particles by photo-assisted deposition (PAD) on transparent Ti-containing mesoporous silica thin film

We have investigated a novel technique for the preparation of nano-sized Pt metals on Ti-containing mesoporous silica (TMS) thin film by photo-assisted deposition (PAD). The transparent TMS thin film was prepared on a quartz plate through sol—gel/spin coating. XRD, UV-Vis and Ti K-edge XAFS measurements revealed the formation of isolated Ti oxide species with a tetrahedral-coordination geometry in the silica framework. Deposition of Pt metal precursor on TMS thin film under UV-light irradiation, followed by reduction with molecular hydrogen, afforded a transparent thin film (Pt/TMS). The formation of highly dispersed nano-sized Pt metals having narrow size distributions was determined by Pd L_III-edge XANES and TEM analysis. The TMS and Pt/TMS thin films have been demonstrated to exhibit a strong hydrophilic property, even before UV irradiation, compared to the common mesoporous silica and TiO₂ thin films. After UV-light irradiation, the contact angle of water droplet on the TMS and Pt/TMS thin films became extremely lower, indicating the appearance of the photo-induced super-hydrophilic property.     

Selection principle for various modes of spatially nonuniform electrochemical oscillations

The pattern selection principle for various modes of spatially nonuniform oscillation was investigated by taking a current oscillation of negative differential resistance type, appearing in H2O2 reduction on platinum (Pt) ring electrodes, as a model system. In experiments, various modes of spatiotemporal oscillation, such as a spatially uniform oscillation, standing wave oscillation, and rotating wave oscillation, appeared depending on the applied potential and the distance between the Pt-ring electrode and the reference electrode. A simple mathematical model for the spatiotemporal patterns at the electrode surface was proposed. Numerical calculations and nonlinear bifurcation analysis based on the proposed model reproduced all the essential features of the experimental results and clarified the pattern selection principle.     

Spectral and theoretical studies on effective and selective non-covalent interaction between tetrahexylporphyrins and fullerenes

The host-guest interaction of zinc(II) 5,10,15,20-tetrahexylporphyrin (Zn-THP) and its free base (H2-THP) with fullerenes (C60 and C70) has been studied in toluene medium. Binding constants (K) for H2- and Zn-THP complexes of fullerenes were determined by UV-vis, fluorescence and NMR spectroscopic techniques. Large K values of C70/THP complexes (KC70 ) were obtained in the range of 1.4-2.5 x 10(4)M(-1), while those of C60/THP complexes (KC60) were smaller (1.0-3.2 x10(3)M(-1)). These results show that the KC70 is about 10 times as large as KC60 in both THPs (KC70/KC60 = 10). Enthalpies of formation (DeltaHf degrees) for various fullerene/THP complexes were estimated by ab initio calculations; DeltaHf degrees for C60/H2-THP, C70/H2-THP, C60/Zn-THP and C70/Zn-THP complexes are 5.82, 2.80, 2.31 and 1.54 kcal mol(-1), respectively. The trends in DeltaHf degrees support the experimental results of selective complexation of THPs towards C70 over C60 and fullerenes towards Zn-THP over H2-THP.     

Comparative study of the water oxidizing reactions and the millisecond delayed chlorophyll fluorescence in photosystem II at different pH

Water splitting activity, the multiline EPR signal associated with S(2)-state of the CaMn(4)-cluster and the fast and slow phases of the induction curve of the millisecond delayed chlorophyll fluorescence from photosystem II (PSII) in the pH range of 4.5-8.5 were studied in the thylakoid membranes and purified PSII particles. It has been found that O(2) evolution and the multiline EPR signal were inhibited at acidic (pK approximately 5.3) and alkaline (pK approximately 8.1) pH values, and were maximal at pH 6.0-7.0. Our results indicate that the loss of O(2) evolution and the S(2)-state multiline EPR signal associated with the decrease of the millisecond delayed chlorophyll fluorescence only in alkaline region (pH 7.0-8.5). Possible correlations of the millisecond delayed chlorophyll fluorescence components with the donor side reactions in PSII are discussed.