A solid solution Mg5Sn1-xTixO4(BO3)2(x=0.2), showing 430 nm light emission under irradiation of 270 nm light with a high quantum efficiency of 0.89, crystallizes in a triclinic cell of a new ludwigite-type superstructure. Mg5MO3(BO3)3(M=Nb, Ta) have superstructures of the warwickite-type structure in which Nb or Ta and Mg atoms are ordered. A photoluminescence peak of 470 nm was observed for Mg5NbO3(BO3)3 by 270 nm light excitation.
Polymer nucleation is the process of disentanglement and chain sliding diffusion along the chain axis due to the topological nature of chain-like polymers. Although the large “melt elongation” of polymers should significantly affect crystallization that controls the structure and properties of solids, it has been difficult due to technical reasons. We showed that nucleation and morphology changed under large elongational strain field: they discontinuously changed from heterogeneous to homogeneous nucleation and from spherulite to new morphology of “nano-oriented crystals (NOCs)”, respectively, when the elongational strain rate increased larger than a critical elongational strain rate. NOCs showed ultra-high performance such as high tensile strength, high thermal resistance and high transparency.
To develop high performance piezoelectric materials, a new method called at “nanodomain engineering” was proposed and investigated in this study. The nanodomain engineering means a method, which can produce high density nanodomain configurations by control of chemical composition, i.e., to develop an intermediate state between relaxor ferroelectrics and normal ferroelectrics. To confirm the concept, ternary system ceramics of BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3(BT-BMT-BF) was prepared and characterized. As the results, a formation of nanodomain configurations was confirmed by a transmission electron microscopy. Moreover, for the ceramics with the nanodomain configurations, high apparent piezoelectric constants over 500 pC/N was clearly obtained, which suggested that the concept of “nanodomain engineering” might work good.
This review article reports on the results of recent transmission electron microscopy studies about the complex magnetic domain structures produced in transition metal oxides. Cryogenic Lorentz microscopy and electron holography studies have revealed the nucleation and growth process of the ferromagnetic metal phase in a colossal magnetoresistive manganite La0.25Pr0.375Ca0.375MnO3. The in situ microscopy observations provide useful information for deeper understanding of the magnetic anomaly in a spinel-type compound MnV2O4, in which the micrometer-scale magnetic domains are lost below 42 K.
Using scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS), we have investigated the charge-discharge mechanism in the first cycle and the origin of its high charge-discharge capacity for Li1.2Mn0.4Fe0.4O2(0.5Li2MnO3·0.5LiFeO2) positive electrode material of lithium ion batteries. Results revealed that local valence states of Mn ions, behaviors of extraction and insertion of Li ions, and the contribution of oxide ions into charge compensation in the entire region of the Li1.2Mn0.4Fe0.4O2 particles composed of Mn-rich and Fe-rich nanodimains during the first charge. The high charge-discharge capacity can be attributed to extraction and insertion of the partial oxide ions. The origin of the irreversible capacity can be related to the irreversible loss of oxygen during the charge.
Evectin-2 is a recycling endosomal protein and plays an essential role in retrograde transport from recycling endosomes to the trans-Golgi network. The pleckstrin homology (PH) domain of Evectin-2 can specifically binds to phosphatidylserine (PS), which is enriched in recycling endosomes. To elucidate the molecular mechanism how it specifically binds to PS, we solved the crystal structures of human Evectin-2 PH domain for apo and O-phospho-L-serine complexed forms at 1.75 and 1.00 Å resolution, respectively. These structural analyses clearly show that PS-induced conformational change of Evectin-2 PH domain effectively explains the strict phospholipid binding specificity.
The human malaria parasite Plasmodium falciparum is responsible for the death of more than a million people each year. Fosmidomycin has proved to be efficient in the treatment of P. falciparum malaria through the inhibition of 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), an enzyme of the non-mevalonate pathway of isoprenoid biosynthesis, which is absent in humans. Crystal structure analyses of P. falciparum DXR (PfDXR) revealed that (i) an intrinsic flexibility of the PfDXR molecule accounts for the induced-fit movement to accommodate the bound inhibitor in the active site, and (ii) a cis arrangement of the oxygen atoms of the hydroxamate group of the bound inhibitor is essential for tight binding of the inhibitor to the active site metal. We believe that our study will serve as a useful guide to develop more potent PfDXR inhibitors.
Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.