Switching of optical-resolution selectivity through the Onsager's reaction field: Chiral recognition of dl-amino acids by hydrophilic/hydrophobic chitosans

Unusual switching of optical-resolution selectivity in chitosan resins is reported. While in hydrophilic chitosan resins, the l -form of amino acids are selectively adsorbed, and in hydrophobic chitosan resins, the d -form was preferred. We found that the adsorption selectivity of the amino acids in the optical-resolution agents is controlled by the hydrophilicity/hydrophobicity or permittivity of the resins, through the Onsager's reaction field. This intriguing selectivity switching is supported by the polarized continuum model calculations. This method provides a promising strategy for switching of optical-resolution preferences by controlling the permittivity of the resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48317.     

Self-healing bio-based furan polymers cross-linked with various bis-maleimides

A series of bio-based self-healing polymers was prepared by cross-linking a furan polymer, poly(2,5-furandimethylene succinate), with bis-maleimide compounds by means of Diels–Alder reactions. In addition to the amount of the bis-maleimide linker, the molecular structure of the bis-maleimide played a key role in determining the extent of the Diels–Alder reaction and the mechanical and healing properties of the polymers. Bis-maleimides with phenylene rings markedly enhanced the tensile strength of the network polymers but hindered healing. In contrast, bis-maleimides with a flexible molecular structure tended to improve the polymer elongation, affording polymers with excellent healing ability. The efficiencies of self-healing (=healing without any external stimulus) and healing with an assistance of solvent (CHCl₃) were over 70% and 80%, respectively, for the network polymer crosslinked by bis-maleimide with flexible long-alkyl segment. Thus, our results indicate that the choice of bis-maleimide linker is an important factor for designing furan-maleimide–based self-healing polymers.     

Fluorescent superlattices of gold nanoparticles: A new class of functional materials

Fluorescent three-dimensional (3-D) superlattices of dansyl glutathione protected gold nanoparticles, with potential applications in molecular detection, have been synthesized at an air/water interface by controlling the pH of the nanoparticle suspension. The number of fluorophores per nanoparticle was calculated to be ∼127. Morphologies of the superlattice crystals were examined using scanning electron microscopy (SEM). Most of the crystals observed were triangular in shape. High-resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS) were used to study the packing of nanoparticles in these crystals. Both these studies showed that the nanoparticles were arranged in a face-centered cubic (fcc) pattern with a particle-particle distance (center-center) of ∼10.5 nm. Evolution of the crystal morphologies with time was also examined. The fluorescence properties of these triangles were studied using confocal fluorescence imaging and confocal Raman mapping, which were in good agreement with the morphologies observed by SEM. The superlattice exhibits near-infrared (NIR) absorption in the range 1100–2500 nm. Easy synthesis of such functional nanoparticle-based solids makes it possible to use them in novel applications. We utilized the fluorescence of dansyl glutathione gold superlattice crystals for the selective detection of bovine serum albumin (BSA), the major protein constituent of blood plasma, based on the selective binding of the naphthalene ring of the dansyl moiety with site I of BSA. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Oxygen toxicity induces apoptosis in neuronal cells

1. A high oxygen atmosphere induced apoptosis in cultured neuronal cells including PC12 cells and rat embryonic cortical, hippocampal, and basal forebrain neurons associated with DNA fragmentation and nuclear condensation. 2. The sensitivity of CNS neurons to a high-oxygen atmosphere was the following order; cortex > basal forebrain > hippocampus. 3. Cycloheximide and actinomycin-D inhibited the apoptosis, indicating that it depends on new macromolecular synthesis. In contrast, cultured postnatal CNS neurons were resistant to oxidative stress. 4. Neurotrophic factors such as nerve growth factor (NGF), fibroblast growth factor (FGF), and epidermal growth factor (EGF) blocked the apoptosis induced by a high-oxygen atmosphere.     

Memory array architecture and decoding scheme for 3 V only sectorerasable DINOR flash memory

A memory array architecture and row decoding scheme for a 3 V only DINOR (divided bit line NOR) flash memory has been designed. A new sector organization realizes one word line driver per two word lines, which is conformable to tight word line pitch. A hierarchical negative voltage switching row decoder and a compact source line driver have been developed for 1 K byte sector erase without increasing the chip size. A bit-by-bit programming control and a low threshold voltage detection circuit provide a high speed random access time at low V_cc and a narrow program threshold voltage distribution. A 4 Mb DINOR flash memory test device was fabricated from 0.5 μm, double-layer metal, triple polysilicon, triple well CMOS process. The cell measures 1.8×1.6 μm² and the chip measures 5.8×5.0 mm ². The divided bit line structure realizes a small NOR type memory cell     

Structural analysis of nucleic acids by using fluorescence resonance energy transfer (FRET)

We examined changes in the extent of fluorescence resonance energy transfer (FRET) between two different fluorochromes attached to a single oligonucleotide in the presence or absence of target nucleic acids with a specific sequence and a higher-ordered structure. In our system, FRET was maximal when probes were free in solution and a decrease in FRET was evidence of successful hybridization. Incubation of the probe with a single-stranded complementary oligonucleotide reduced the FRET. While, a small change in FRET was also observed when the probe was incubated with an oligonucleotide in which the target site had been embedded in a stable hairpin structure. These results indicate that this spectrofluorometric method and FRET probes can be used to estimate the efficacy of hybridization between a probe and its target site within highly ordered structures. It should help us to estimate the suitability of designed functional molecules, such as antisense DNA and RNA and ribozymes, that target to specific sites.     

Effects of firing temperature on morphology and crystal structure of zirconiumbis(monohydrogen phosphate) and its alkali salts

In zirconiumbis(monohydrogen phosphate)monohydrate, the stability of water of crystallization and of the crystal form was strongly influenced by its crystal size. The water of crystallization of a smaller crystal was completely released on heating to 200° C while a part of this water was held at 300° C in a larger crystal with a diameter of several micrometres. While a smaller crystal was decomposed by heating to 900° C and cubic zirconium pyrophosphate was formed, for a larger crystal,-layered zirconium pyrophosphate was formed instead of cubic zirconium pyrophosphate and a layered structure was held. For the Na₂-, K₂- and Rb₂-forms, good layer structure was retained even by heating to 1000° C. For the Li₂-form, the layer structure was decomposed on heating at or above 900° C. The thermal stability of the layered structure increased with increasing crystal size and ionic radii of the alkali cation.     

A novel hetero-junction Tunnel-FET using Semiconducting silicide–Silicon contact and its scalability

A new type of silicon-based Tunneling FET (TFET) using semiconducting silicide Mg₂Si/Si hetero-junction as source-channel structure is proposed and the device simulation has been presented. With narrow bandgap of silicide and the conduction and valence band discontinuous at the hetero-junction, larger drain current and smaller subthreshold swing than those of Si homo-junction TFET can be obtained. Structural optimization study reveals that low Si channel impurity concentration and the alignment of the gate electrode edge to the hetero-junction lead to better performance of the TFET. Scaling of the gate length increases the off-state leakage current, however, the drain voltage (V_d) reduction in accordance with the gate scaling suppresses the phenomenon, keeping its high drivability.