Escherichia coli SdiA is a quorum-sensing (QS) receptor that responds to autoinducers produced by other bacterial species to control cell division and virulence. Crystal structures reveal that E. coli SdiA, which is composed of an N-terminal ligand-binding domain and a C-terminal DNA-binding domain (DBD), forms a symmetrical dimer. Although each domain shows structural similarity to other QS receptors, SdiA differs from them in the relative orientation of the two domains, suggesting that its ligand-binding and DNA-binding functions are independent. Consistently, in DNA gel-shift assays the binding affinity of SdiA for the ftsQP2 promoter appeared to be insensitive to the presence of autoinducers. These results suggest that autoinducers increase the functionality of SdiA by enhancing the protein stability rather than by directly affecting the DNA-binding affinity. Structural analyses of the ligand-binding pocket showed that SdiA cannot accommodate ligands with long acyl chains, which was corroborated by isothermal titration calorimetry and thermal stability analyses. The formation of an intersubunit disulfide bond that might be relevant to modulation of the DNA-binding activity was predicted from the proximal position of two Cys residues in the DBDs of dimeric SdiA. It was confirmed that the binding affinity of SdiA for the uvrY promoter was reduced under oxidizing conditions, which suggested the possibility of regulation of SdiA by multiple independent signals such as quorum-sensing inducers and the oxidation state of the cell.

Colloidal photonic crystals show structural colors yet are generally opaque due to multiple scattering. To address this problem, composite colloidal crystals with a low index mismatch were prepared to demonstrate their selective reflection color and optical transparency, which, however, show relatively low reflection intensity. Thick composite colloidal crystals may enhance the reflection intensity, which, however, causes a significant loss in optical transparency as micrometer-sized defects also increase. Herein, we prepared composite colloidal crystal films of core−shell nanospheres in a polystyrene matrix, in which the refractive index is matched by adjusting the ratio of core-to-shell volume. Therefore, we demonstrate strong reflection colors in a thick colloidal film keeping high optical transparency. Furthermore, with no deterioration of light transmission in our index-matched composite colloidal crystals, bicolored reflective films were also successfully prepared by stacking two different colloidal crystal films. Finally, by introducing photopolymerizable resin inside colloidal crystals, we fabricated patterned composite photonic crystals through selective photopolymerization and repeated photopatterning process for multicolored films. These films may potentially be useful in reflective displays, encryption, and optical identification.

Optically transparent and thermo‐mechanically stable nanocomposite films of polyethersulfone (PESU) and core–shell nanoparticles are prepared by a solvent casting and heat pressing method. As a filler, reactive ZnS‐SiO2 core–shell nanoparticles are prepared by a modified sol–gel process, of which reactive aromatic amine groups are chemically bonded with the polymer matrix. For optical transparency, the shell thickness is adjusted and the core diameter of the core–shell nanoparticles is adjusted to match the refractive index of PESU (nPESU = 1.65). For the composite film with more than 15 wt% of core–shell nanoparticles in PESU, the coefficient of thermal expansion is significantly reduced down to 12 ppm °C−1 in the temperature range of 30–90 °C, which is 80% less than the value of the bare PESU film (≈65 ppm °C−1). Furthermore, their mechanical property is also significantly improved. For 15 and 30 wt%, PESU nanocomposite films show 64 and 74 MPa of yield strength and 1.36 and 2.0 GPa of Young's modulus, respectively, while pure PESU films show only 44 MPa of the yield strength and 0.64 GPa of Young's modulus. Finally, the organic light emitting diode device is demonstrated on the PESU nanocomposite substrate.

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