Extra meridional reflections of drawn polyoxymethylene

Extra meridional reflections (00l: l = 3, 5, 13, 15, 21) were observed in drawn polyoxymethylene (POM). The 003, 0015, and 0021 x-ray diffraction intensities increase on annealing, while the 005 and 0013 intensities decrease. It is concluded that crystalline regions are of two kinds: in the first, which generates the 003, 0015, and 0021 reflections, the molecular conformation is slightly distorted from the uniform helix by intermolecular steric hindrance between the CH₂ groups; and in the second, which generates 005 and 0013 reflections, the molecular conformation is distorted in another way. The second form is converted into the first by annealing. The displacements in the c direction of the CH₂ groups and the oxygen atoms from the uniform helix in the first form are about 1.0% and 0.75% of the interval between a CH₂ group and an oxygen atom along helix axis of the POM crystal; thus the correct conformation in the stable state is known. The nature of distortion in the second region is not clarified but several characteristics are offered.     

A Single Fluorescent Probe to Visualize Hydrogen Sulfide and Hydrogen Polysulfides with Different Fluorescence Signals

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n, n>1) are endogenous regulators of many physiological processes. In order to better understand the symbiotic relationship and cellular cross‐talk between H₂S and H₂S_n, it is highly desirable to develop single fluorescent probes which enable dual‐channel discrimination between H₂S and H₂S_n. Herein, we report the rational design, synthesis, and evaluation of the first dual‐detection fluorescent probe DDP‐1 that can visualize H₂S and H₂S_n with different fluorescence signals. The probe showed high selectivity and sensitivity to H₂S and H₂S_n in aqueous media and in cells.     

Design and synthesis of highly sensitive fluorogenic substrates for glutathione S-transferase and application for activity imaging in living cells

Here we report the development of fluorogenic substrates for glutathione S-transferase (GST), a multigene-family enzyme mainly involved in detoxification of endogenous and exogenous compounds, including drug metabolism. GST is often overexpressed in a variety of malignancies and is involved in the development of resistance to various anticancer drugs. Despite the medical significance of this enzyme, no practical fluorogenic substrates for fluorescence imaging of GST activity or for high-throughput screening of GST inhibitors are yet available. So, we set out to develop new fluorogenic substrates for GST. In preliminary studies, we found that 3,4-dinitrobenzanilide (NNBA) is a specific substrate for GST and established the mechanisms of its glutathionylation and denitration. Using these results as a basis for off/on control of fluorescence, we designed and synthesized new fluorogenic substrates, DNAFs, and a cell membrane-permeable variant, DNAT-Me. These fluorogenic substrates provide a dramatic fluorescence increase upon GST-catalyzed glutathionylation and have excellent kinetic parameters for the present purpose. We were able to detect nuclear localization of GSH/GST activity in HuCCT1 cell lines with the use of DNAT-Me. These results indicate that the newly developed fluorogenic substrates should be useful not only for high-throughput GST-inhibitor screening but also for studies on the mechanisms of drug resistance in cancer cells.     

Iron hydroxide nanoparticles coated with poly(ethylene glycol)-poly(aspartic acid) block copolymer as novel magnetic resonance contrast agents for in vivo cancer imaging

PEG-coated β-FeOOH nanoparticles were prepared through electrostatic complex formation of iron oxide nanoparticles with poly(ethylene glycol)-poly(aspartic acid) block copolymer [PEG-P(Asp)] in distilled water. By dynamic light scattering (DLS) measurement, the nanopaticle size was determined to be 70 nm with narrow distribution. The FT-IR and zeta potential experimental results proved that PEG-PAsp molecules bound to the surface of the iron oxide nanoparticles via the coordination between the carboxylic acid residues in the PAsp segment of the block copolymer and the surface Fe of the β-FeOOH nanoparticles. The PEG-coated nanoparticles revealed excellent solubility and stability in aqueous solution as well as in physiological saline. In vivo MRI experiments on tumor-bearing mice demonstrated that the PEG-coated nanoparticles prepared by the current approach achieved an appreciable accumulation into solid tumor, suggesting their potential utility as tumor-selective MRI contrast agents.     

Time-resolved long-lived luminescence imaging method employing luminescent lanthanide probes with a new microscopy system

Superior fluorescence imaging methods are needed for detailed studies on biological phenomena, and one approach that permits precise analyses is time-resolved fluorescence measurement, which offers a high signal-to-noise ratio. Herein, we describe a new fluorescence imaging system to visualize biomolecules within living biological samples by means of time-resolved, long-lived luminescence microscopy (TRLLM). In TRLLM, short-lived background fluorescence and scattered light are gated out, allowing the long-lived luminescence to be selectively imaged. Usual time-resolved fluorescence microscopy provides fluorescence images with nanosecond resolution and has been used to image interactions between proteins, protein phosphorylation, the local pH, the refractive index, ion or oxygen concentrations, etc. Luminescent lanthanide complexes (especially europium and terbium trivalent ions (Eu3+ and Tb3+)), in contrast, have long luminescence lifetimes on the order of milliseconds. We have designed and synthesized new luminescent Eu3+ complexes for TRLLM and also developed a new TRLLM system using a conventional fluorescence microscope with an image intensifier unit for gated signal acquisition and a xenon flash lamp as the excitation source. When the newly developed luminescent Eu3+ complexes were applied to living cells, clear fluorescence images were acquired with the TRLLM system, and short-lived fluorescence was completely excluded. By using Eu3+ and Tb3+ luminescent complexes in combination, time-resolved dual-color imaging was also possible. Furthermore, we monitored changes of intracellular ionic zinc (Zn2+) concentration by using a Zn2+-selective luminescent Eu3+ chemosensor, [Eu-7]. This new imaging technique should facilitate investigations of biological functions with fluorescence microscopy, complementing other fluorescence imaging methodologies.     

Spectrophotometric quantification of lactose in solution with a peroxidase-based enzymatic cascade reaction system

A spectrophotometric assay was developed for the quantification of lactose in aqueous solution via a one-pot enzymatic cascade reaction at 25 °C and pH 7.2. Lactose (0.2-1.8 mM), E. coli β-galactosidase (β-Gal), Aspergillus niger glucose oxidase (GOD), horseradish peroxidase (HRP) and o-phenylenediamine (OPD) were incubated, and the increase in absorbance at 417 nm (A (417)) due to the formation of DAP (2,3-diaminophenazine), the dimeric oxidation product of OPD, was followed. The increase in A (417) was found to depend linearly on the initial lactose concentration via three consecutive but simultaneously occurring enzymatic reaction steps catalyzed by β-Gal, GOD, and HRP. No pre-incubation of lactose with β-Gal is needed with this simple lactose assay.     

Development of NIR fluorescent dyes based on Si-rhodamine for in vivo imaging

We have developed a series of novel near-infrared (NIR) wavelength-excitable fluorescent dyes, SiR-NIRs, by modifying the Si-rhodamine scaffold to obtain emission in the range suitable for in vivo imaging. Among them, SiR680 and SiR700 showed sufficiently high quantum efficiency in aqueous media. Both antibody-bound and free dye exhibited high tolerance to photobleaching in aqueous solution. Subcutaneous xenograft tumors were successfully visualized in a mouse tumor model using SiR700-labeled anti-tenascin-C (TN-C) antibody, SiR700-RCB1. SiR-NIRs are expected to be useful as labeling agents for in vivo imaging studies including multicolor imaging, and also as scaffolds for NIR fluorescence probes.     

A weighted independent even factor algorithm

An even factor in a digraph is a vertex-disjoint collection of directed cycles of even length and directed paths. An even factor is called independent if it satisfies a certain matroid constraint. The problem of finding an independent even factor of maximum size is a common generalization of the nonbipartite matching and matroid intersection problems. In this paper, we present a primal-dual algorithm for the weighted independent even factor problem in odd-cycle-symmetric weighted digraphs. Cunningham and Geelen have shown that this problem is solvable via valuated matroid intersection. Their method yields a combinatorial algorithm running in O(n ³ γ +? n ⁶ m) time, where n and m are the number of vertices and edges, respectively, and γ is the time for an independence test. In contrast, combining the weighted even factor and independent even factor algorithms, our algorithm works more directly and runs in O(n ⁴ γ?+?n ⁵) time. The algorithm is fully combinatorial, and thus provides a new dual integrality theorem which commonly extends the total dual integrality theorems for matching and matroid intersection.     

FM-AFM imaging of a commercial polyethylene film immersed in n-dodecane

The subnanometer topography of a partially crystalline polyethylene film was observed in liquid n-dodecane using a frequency-modulation atomic force microscope. Locally ordered structures were found and assigned to a (100) facet of crystalline domains.     

Stable surface termination on vicinal 6H-SiC(0 0 0 1) surfaces

Ordered nanofacet structures on vicinal 6H-SiC(0 0 0 1) surfaces, consisting of pairs of a (0 0 0 1) basal plane and a facet, are investigated in terms of stable surface stacking of the (0 0 0 1) basal planes. The surface termination of S3 (or S3*), i.e., ABC (or A*C*B*), was suggested by a structural model based on quantized step-bunching, which typically gives a one-unit-cell bunched step configuration at the facet. Here, we evaluate the surface termination at basal planes covered with a layer of silicon oxynitride by means of quantitative low-energy electron diffraction (LEED) analysis combined with scanning tunneling microscopy (STM), and show the validity of the structural model proposed.