Yasuhiro Sakamoto

Direct imaging of the pores and cages of three-dimensional mesoporous materials.

Mesostructured composite materials, with features ranging from 20 to 500u2009Å in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization byxa0the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (>u200910u2009µm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.

Comprehensive characterization of highly ordered MCM-41 silicas using nitrogen adsorption, thermogravimetry, X-ray diffraction and transmission electron microscopy

Highly ordered MCM-41 silicas were synthesized using a new procedure and their structures were thoroughly characterized. Using the new synthesis method and the previously reported similar one, the pore diameter of MCM-41 can be tailored from 3.1 to 4.9 nm with about 0.35 nm increments and reproducibility usually better than ±0.1 nm using surfactants of different chain length. The surfactant content and structural parameters of MCM-41 synthesized using the same single surfactant or surfactant mixture were highly similar for different silica:surfactant molar ratios in the synthesis mixture. Moreover, the silica:surfactant molar ratio in as-synthesized MCM-41 was quite independent of the chain length of the surfactant used and approximately equal to 8. This may be related to the well-defined synthesis conditions imposed by the pH adjustment procedure employed. The results indicate that the silica:surfactant ratios in starting mixtures suitable for the synthesis of high-quality MCM-41 under the present synthesis conditions should not exceed about 8 to avoid contamination with amorphous silica.

Structure analysis of mesoporous material ‘FSM-16’ Studies by electron microscopy and X-ray diffraction

High-resolution electron micrographs and X-ray powder diffraction patterns for the mesoporous material FSM-16 and for silicate organic complexes derived from the layered polysilicate kanemite are presented. HREM studies reveal information about the formation mechanism at the nanometer length scale, and X-ray powder diffraction data provides information about the averaged structure in the samples. It is demonstrated that the FSM-16 material is formed from the layered silicate kanemite through making a domain structure with hexagonal symmetry by condensation of silicate, which might be derivative of kanemite sheets, and the folded sheet mechanism should be modified.

Synthesis and characterization of europium-doped ordered mesoporous silicas

Silica mesoporous molecular sieves doped with europium were synthesized using Cab-O-Sil M5 silica and europium chloride in the presence of cetyltrimethylammonium bromide surfactant. The materials obtained with lower Eu content (Si∶Eu molar ratio of 100) in the synthesis gel exhibited two-dimensional hexagonally ordered structure of the MCM-41 type, whereas larger Eu contents resulted in lower size of hexagonally ordered porous domains (for Si∶Euxa0=xa033) or in disordered porous structures (for Si∶Euxa0=xa020). The pore size increased from 3.4 to 4.0xa0nm as the amount of Eu in the synthesis mixture increased. Pore size distributions (PSDs) for Eu-doped silicas were narrower than the PSDs of the pure-silica MCM-41 material synthesized under the same conditions. A decrease in the specific surface area and primary mesopore volume was observed for higher Eu loadings. The volume of secondary (interparticle) npores increased as the content of Eu in the synthesis gel increased, which is consistent with the transmission electron microscopy images that provided an indication of the decrease in the particle size, although the latter was not uniform throughout the materials under study. Energy dispersive X-ray fluorescence (EDX) data indicated that europium is indeed present in the structure of the materials studied, although its content tended to be somewhat lower than that in the synthesis gel and its distribution within the materials appeared to be non-uniform. The synthesis procedure reported herein was used to synthesize silicas doped with other lanthanides, and for given lanthanide loadings, the resultant materials exhibited porous structures similar to those of the Eu-doped samples.

Contribution of autophagic cell death to p53-dependent cell death in human glioblastoma cell line SF126

Apoptosis and autophagic cell death are programmed cell deaths that are involved in cell survival, growth, development and carcinogenesis. p53, the most extensively studied tumor suppressor, regulates apoptosis and autophagy by transactivating its downstream genes. It also stimulates the mitochondrial apoptotic pathway and inhibits autophagy in a transactivation‐independent manner. However, the contribution of apoptosis and autophagic cell death to p53‐dependent cell death is unclear. Using wild‐type (WT) and mutant (MT) p53 inducible cell lines in TP53‐null SF126 glioblastoma cells, we examined the apoptosis and autophagic cell death induced by p53. WT p53 expression in SF126 cells induced apoptosis and autophagy, and reduced the cell number. An autophagy inhibitor reduced autophagy, increased the S‐phase fraction, and attenuated the inhibition of cell proliferation induced by WT p53. Pan‐caspase inhibitor reduced apoptosis but showed weaker inhibition of cell proliferation than the autophagy inhibitor. We concluded that p53‐dependent cell death in SF126 cells comprises caspase‐dependent and caspase‐independent apoptosis and autophagic cell death, and the induction of autophagy as well as apoptosis could be a new strategy to treat some type of WT p53‐retaining tumors. (Cancer Sci 2011; 102: 799–807)

Overexpression of DRAM enhances p53-dependent apoptosis

Tumor suppressor p53‐dependent apoptosis is thought to be one of the most important tumor‐suppressive mechanisms in human tumorigenesis. Till date, “super p53” mutants exhibiting more potent ability to induce apoptosis than wild‐type p53 have been reported. These super p53s may provide a clue for development of novel therapeutic targets. However, the major mechanism underlying the super p53‐dependent apoptosis remains unclear. To identify critical gene(s) in this mechanism, we performed a comprehensive and comparative expression analysis in p53‐null Saos‐2 cells with conditional expression of wild‐type p53 and S121F, which was previously reported as a super p53 mutant. We identified damage‐regulated autophagy modulator (DRAM) as one of the genes that were more upregulated by S121F than wild‐type p53. Although knockdown of DRAM was not sufficient for reducing the ability of S121F to induce apoptosis, DRAM overexpression enhanced the ability in a wild‐type p53‐dependent manner. Here, we show that DRAM is an important gene for the enhancement of p53‐dependent apoptosis. Additional analysis of the mechanism of super p53‐dependent apoptosis may lead to the identification of novel drug targets for cancer therapy.

Arrayed PbI2 clusters in the spaces of zeolite LTA

Abstract Zeolite LTA has cubic symmetry with different-sized α- and β-cages arranged in a CsCl type structure. PbI 2 clusters were incorporated into the cages of LTA through a vapor phase after dehydration. The structure of this complex system was studied as a function of cluster loading by X-ray diffraction (both single crystal and powder) and by electron microscopy. The clusters were formed inside the α-cages without destroying the framework and with a maximum loading density of ca. 3.8 PbI 2 clusters per α-cage. No symmetry changes were observed except for the specimens with the maximum loading. 3.8 PbI 2 /LTA showed a domain structure, and more than two different types of superlattice reflections were observed. The major phase has tetragonal symmetry, P 4/ ncc , and the structures and the arrangements of the clusters are discussed.

Synthetic lethal interaction of CDK inhibition and autophagy inhibition in human solid cancer cell lines

Cell cycle control is a promising target in cancer treatments, and some small-molecule cyclin-dependent kinase (CDK) inhibitors have exhibited clinical effectiveness. However, no biomarkers predictive of efficacy have been developed. Recent studies have revealed that CDK inhibitor (CKI) proteins, such as p27 and p16, also induced cytoprotective autophagy in cancer cells. However, it is unclear whether small-molecule CKIs also induce autophagy in solid tumors, as induced autophagy promotes cancer cell survival. In this study, we revealed that a CDK4 inhibitor and a CKI with a broad range of targets (flavopiridol) induced autophagy in some, but not all, solid cancer cell lines. Autophagy induction by CDK4 inhibitor was observed in BT474, MDA-MB435S, SKBr3 (derived from breast cancer), A431 (derived from epidermoid cancer), and SW480 (derived from colorectal cancer) cell lines. No such autophagy was observed in MCF7, MDA-MB231 (derived from breast cancer), NCI-N87 (derived from gastric cancer), and KMST-6 (derived from a fibroblast). In the cell lines showing autophagy, which was induced by CDK4 inhibitor, the combination of CDK4 inhibitor and autophagy inhibition by either chloroquine (CQ) or knockdown of ATG5 or BECN1 induced apoptosis. However, it did not induce apoptosis in the cell lines in which autophagy was not induced by CDK4 inhibitor. These findings indicate that the autophagy induced by CDK4 inhibitor mimics stress-induced autophagy in some solid cancer cell lines. The combination of a small-molecule CKI involved in G1/S arrest and an autophagy inhibitor leads to a synthetic lethal interaction and could become a new antitumor strategy for solid tumors showing cytoprotective autophagy induced by small-molecule CKIs.

High throughput RNAi screening identifies ID1 as a synthetic sick/lethal gene interacting with the common TP53 mutation R175H

The TP53 mutation (R175H) is one of the most common mutations in human cancer. It is a highly attractive strategy for cancer therapy to find the genes that lead the R175H-expressing cancer cells. The aim of this study was to identify the synthetic sick/lethal gene interacting with R175H. Using lentiviral bar-coded comprehensive shRNA library and a tetracycline-inducible R175H expressed in the SF126 human glioblastoma cell line (SF126-tet-R175H), we conducted high-throughput screening to identify the candidate genes that induce synthetic sickness/lethality in R175H-expressing cells. We identified 906 candidate gene suppressions that may lead to accelerated cell growth inhibition in the presence of R175H. Inhibitor of differentiation 1 (ID1) was one of the candidate genes, and its suppression by siRNA resulted in the acceleration of growth inhibition in cell lines both transiently and endogenously expressing R175H but not in TP53-null cell lines or other common p53 mutants (such as R273H). Flow cytometry analysis showed that ID1 suppression resulted in G1 arrest, and the arrest was accelerated by the expression of R175H. ID1 is a synthetic sick/lethal gene that interacts with R175H and is considered to be a novel molecular target for cancer therapy in R175H-expressing cells.

Structural characterisation of micro- and mesoporous materials by electron microscopy

Abstract Zeolites are one of the most important materials currently used in the petroleum industry for a wide variety of catalytic transformations. However, they are increasingly being considered for other applications such as for designing quantum-confined materials in their spaces. With such applications in mind, precise characterisation of zeolites and related porous materials has never been more necessary. Here we show how electron diffraction coupled with high-resolution imaging can reveal the detailed fine structure in both the bulk and at the surface of these materials. A variety of case studies are considered which include ETS-10, FAU, LTL and FSM-16.