Multiemission of Ce3+ from a Single Crystallographic Site Induced by Disordering of Ions.

White-light emission with a single activator is an attractive function of phosphors. In this work, we investigated the photoluminescence properties of Ca5.7Y1.3Si7O16.7N3.3, which is a compound denoted as Ca4+xY3-xSi7O15+xN5-x discovered by our group, with Ce-activation using optical measurements and density functional theory (DFT) calculation. Samples showed a tunable emission from purple to white under ultraviolet (UV) light. In this compound, Ca and Y as well as anions are distributed disorderly, and Ca/Y ions occupy two crystallographically distinct sites; those sites are possible sites for Ce substitution. DFT calculation and structural refinement revealed that the tunable emission was generated by Ce at the crystallographically equivalent site but with distinct local structures caused by the disordering of cations and anions. As far as we know, this is the first report about a white-light-emitting phosphor with only Ce activation.

Biophysical Properties of the Fibril Structure of the Toxic Conformer of Amyloid-ß42: Characterization by Atomic Force Microscopy in Liquid and Molecular Docking.

Alzheimer's disease is associated with the aggregation of the misfolded neuronal peptide, amyloid-ß42 (Aß42). Evidence has suggested that several reasons are responsible for the toxicity caused by the aggregation of Aß42, including the conformational restriction of Aß42. In this study, one of the toxic conformers of Aß42, which contains a Glu-to-Pro substitution (E22P-Aß42), was explored using atomic force microscopy and molecular docking to study the aggregation dynamics. We proposed a systematic model of fibril formation to better understand the molecular basis of conformational transitions in the Aß42 species. Our results demonstrated the formation of amorphous aggregates in E22P-Aß42 that are stem-based, network-like structures, while the formation of mature fibrils occurred in the less toxic conformer of Aß42, E22-Aß42, that are sphere-like flexible structures. A comparison was made between the biophysical properties of E22P-Aß42 and E22-Aß42 that revealed that E22P-Aß42 had greater stiffness, dihedral angle, number of ß sheets involved, and elasticity, compared with E22-Aß42. These findings will have considerable implications toward our understanding of the structural basis of the toxicity caused by conformational diversity in Aß42 species.

First-Principles-Based Insight into Electrochemical Reactivity in a Cobalt-Carbonate-Hydroxide Pseudocapacitor.

Cobalt carbonate hydroxide (CCH) is a pseudocapacitive material with remarkably high capacitance and cycle stability. Previously, it was reported that CCH pseudocapacitive materials are orthorhombic in nature. Recent structural characterization has revealed that they are hexagonal in nature; however, their H positions still remain unclear. In this work, we carried out first-principles simulations to identify the H positions. We then considered various fundamental deprotonation reactions inside the crystal and computationally evaluated the electromotive forces (EMF) of deprotonation (V dp). Compared with the experimental potential window of the reaction (<0.6 V (vs saturated calomel electrode (SCE)), the computed V dp (vs SCE) value (3.05 V) was beyond the potential window, indicating that deprotonation never occurred inside the crystal. This may be attributed to the strong hydrogen bonds (H-bonds) that formed in the crystal, leading to structural stabilization. We further investigated the crystal anisotropy in an actual capacitive material by considering the growth mechanism of the CCH crystal. By associating our X-ray diffraction (XRD) peak simulations with experimental structural analysis, we found that the H-bonds formed between CCH planes (approximately parallel to the ab-plane) can result in 1-D growth (stacked along the c-axis). This anisotropic growth controls the balance between the total "non-reactive" CCH phases (inside the material) and the "reactive" hydroxide (Co(OH)2) phases (surface layers); the former stabilizes the structure, whereas the latter contributes to the electrochemical reaction. The balanced phases in the actual material can realize high capacity and cycle stability. The results obtained highlight the possibility of regulating the ratio of the CCH phase versus the Co(OH)2 phase by controlling the reaction surface area.

Mechanistic insights and importance of hydrophobicity in cationic polymers for cancer therapy.

Development of molecules that can be effectively used for killing cancer cells remains a research topic of interest in drug discovery. However, various limitations of small molecules and nanotechnology-based drug-delivery systems hinder the development of chemotherapeutics. To resolve this issue, this study describes the potential application of polymeric molecules as anticancer drug candidates. We describe the design and synthesis of novel anticancer polymers containing hydrophobic groups. We established the fact that the cationic homopolymer (PAMPTMA) does not show any anticancer activity on its own; however, the insertion of hydrophobic moieties in copolymers (PAMPTMA-r-BuMA, PAMPTMA-r-HexMA, and PAMPTMA-r-OctMA) enhances their anticancer activity with a very low IC50 value (60 µg mL-1 for HepG2 cells). Mechanistic investigations were carried out using LDH leakage assay, cellular uptake, DOSY NMR and molecular dynamics to study the interaction between the polymer and the cell membrane as well as the role of hydrophobicity in enhancing this interaction. The results demonstrated that polymers are attracted by the anionic cancer cell membrane, which then leads to the insertion of hydrophobic groups inside the cell membrane, causing its disruption and ultimate lysis of the cell. This study demonstrates a novel and better approach for the rational design and discovery of new polymeric anticancer agents with improved efficacy.

Stepwise copolymerization of polybenzimidazole for a low dielectric constant and ultrahigh heat resistance.

Bio-based polymer materials having great potential due to the depletion of fossil-fuel resources have been applied as single-use and medicinal materials but their low thermomechanical resistance have limited wider applications. Here, ultrahigh thermoresistant bio-based terpolymers with a low dielectric constant, comprising polybenzimidazole and poly(benzoxazole-random-aramid), were prepared by a method involving stepwise polycondensation of three monomers, 3,4-diaminobenzoic acid for benzimidazoles, 3-amino-4-hydroxylbenzoic acid for benzoxazoles, and 4-aminobenzoic acid for aramids. For optimized monomer compositions, the obtained terpolymers exhibited dielectric constants lower than 3, and a 10% mass loss at approximately 760 °C which is a temperature higher than that for any other polymer material reported so far. The high thermal degradation temperatures of the prepared terpolymers were a result of the high interaction enthalpies of hydrogen bonding between imidazole rings in the polymer chains, which were obtained from density functional theory calculations using trimer models. Furthermore, the applicability of the prepared terpolymers as a wire-coating material for a simple motor insulation was demonstrated, indicating that it has significant potential to be used as a thermostable material with a low dielectric constant (k).

Ab Initio Evaluation of Complexation Energies for Cyclodextrin-Drug Inclusion Complexes.

We investigated the reliability of ab initio methods to predict the binding energies of molecular encapsulation complexes. Vast possibilities for the docking conformations were screened down to a couple of geometries using a semiempirical docking simulation. For the candidates, we applied density functional theory (DFT) with several exchange-correlation (XC) functionals to evaluate the binding energy. We carefully selected and compared the functionals to elucidate the role of the characteristic factors in achieving the XC effects. It is clarified that the improper combination in XC with D3 dispersion force correction leads to overbinding. For achieving a proper combination, the exchange interaction over the longer range to avoid the overbinding was found to be important.

Two-Dimensional Perovskite Oxynitride K2 LaTa2 O6 N with an H+ /K+ Exchangeability in Aqueous Solution Forming a Stable Photocatalyst for Visible-Light H2 Evolution.

Undoped layered oxynitrides have not been considered as promising H2 -evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K2 LaTa2 O6 N, as an exceptional example of a water-tolerant photocatalyst for H2 evolution under visible light. The material underwent in-situ H+ /K+ exchange in aqueous solution while keeping its visible-light-absorption capability. Protonated K2 LaTa2 O6 N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H2 evolution in the presence of I- as an electron donor and under visible light; the activity was six times higher than Pt/ZrO2 /TaON, one of the best-performing oxynitride photocatalysts for H2 evolution. Overall water splitting was also achieved using the Ir-loaded, protonated K2 LaTa2 O6 N in combination with Cs-modified Pt/WO3 as an O2 evolution photocatalyst in the presence of an I3 - /I- shuttle redox couple.

Light Absorption Properties and Electronic Band Structures of Lead-Vanadium Oxyhalide Apatites Pb5 (VO4 )3 X (X=F, Cl, Br, I).

The Pb-V oxyhalide apatite compounds Pb5 (VO4 )3 X (X=F, Cl, Br, I) were successfully synthesized using a facile solution method and studied with respect to their structural/optical characteristics and electronic band structures. UV-visible diffuse reflectance spectroscopy, electrochemical analysis and first-principles calculations showed that the synthesized apatites behaved as n-type semiconductors, with absorption bands in the UV-visible region that could be assigned to electron transitions from the valence band to a conduction band formed by hybridized V 3d and Pb 6p orbitals. Among the apatites examined, Pb5 (VO4 )3 I had the smallest band gap of 2.7 eV, due to an obvious contribution of I 5p orbitals to the valence band maximum. Based on its visible light absorption capability, Pb5 (VO4 )3 I generated a continuous anodic photocurrent under visible light (λ>420 nm) in a solution of 0.1 m NaI in acetonitrile.