Simultaneous chiral resolution of monosaccharides as 8-aminonaphthalene-1,3,6-trisulfonate derivatives by ligand-exchange CE using borate as a central ion of the chiral selector

Six reducing monosaccharides (mannose, galactose, fucose, glucose, xylose, and arabinose) were derivatized with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS). Based on the chiral ligand-exchange principle using borate as a central ion of the chiral selector and (S)-3-amino-1,2-propanediol (SAP) as a chiral selector ligand, all of the six ANTS-monosaccharides were simultaneously enantioseparated using absorbance at 245 nm for detection. The optimum conditions for both high resolution and moderately short migration time consisted of 200 mM SAP-200 mM borate buffer (pH 9.2) containing 10% ACN as a BGE at 30 degrees C with an applied voltage of +30 kV. It was revealed that the proposed chiral ligand-exchange CE using the SAP-borate system was applicable to enantioseparation of not only diols but also polyols.     

Spectroscopic investigation of cationic comb-type copolymers/DNA interaction: interpolyelectrolyte complex enhancement synchronized with DNA hybridization

We have demonstrated that cationic comb-type copolymers consisting of a polycation backbone and abundant grafts of water-soluble polymers stabilize DNA hybrids. Furthermore, the copolymers were found to accelerate strand exchange reaction between a double-stranded DNA and its complementary single-stranded DNA. In this article, we investigated the effects of PLL-g-Dex on base pairs of a self-complementary DNA octamer, d(GGAATTCC). The soluble interpolyelectrolyte complex (IPEC) between the DNA and copolymer allowed us to characterize the complex by using spectroscopic methods under physiological ionic condition. Chemical shifts of nucleobase proton signals were not changed by PLL-g-Dex. Furthermore, the copolymer slightly changed the von't Hoff DeltaH accompanying the helix-coil transition of the octamer. These results indicated that the base pairs of the duplex DNA in the IPEC were not perturbed by the polycationic copolymer. It was obviously shown by temperature dependencies of proton and phosphorus NMR spectra that DNA/copolymer interaction was considerably enhanced in response to ds DNA formation. An increase in the density and total number of DNA negative charges upon hybrid formation likely caused the higher affinity of the copolymer with the ds form over that of the copolymer with the ss form. The IPEC formation of CCCs with DNA, however, seems highly sensitive to the coil-helix transition of the DNA.     

Heterogeneous Pd/C-catalyzed ligand-free, room-temperature Suzuki-Miyaura coupling reactions in aqueous media

A mild and efficient ligand-free Suzuki-Miyaura coupling reaction catalyzed by heterogeneous Pd/C was developed. Aryl bromides and triflates undergo the cross-coupling with aryl boronic acids in excellent yields without the presence of any additives in aqueous media at room temperature. Aryl vinyl boronic acids are also applicable to this coupling reaction and provide the trans-stilbene derivatives in high yields. The application of wet-type Pd/C to the coupling reaction was achieved without any loss of activity under aerobic conditions, and the reuse of Pd/C is feasible for a fifth run without significant loss of activity. Inductively coupled plasma (ICP) mass-spectrometric analysis of the filtrate from the reaction mixture of 4-bromonitrobenzene with phenylboronic acid demonstrated that the palladium metal hardly leached into the solution within the limits of the detector (<1 ppm), thus suggesting that the present Suzuki-Miyaura reaction proceeded by heterogeneous catalysis.     

Possible mechanism of proton transfer through peptide groups in the H-pathway of the bovine cytochrome c oxidase

The peptide group connecting Tyr440 and Ser441 of the bovine cytochrome c oxidase is involved in a recently proposed proton-transfer path (H-path) where, at variance with other pathways (D- and K-paths), a usual hydrogen-bond network is interrupted, thus making this proton propagation rather unconventional. Our density-functional based molecular dynamics simulations show that, despite this anomaly and provided that a proton can reach a nearby water, a multistep proton-transfer pathway can become a viable pathway for such a reaction: a proton is initially transferred to the carbonyl oxygen of a keto form of the Tyr440-Ser441 peptide group [-CO-NH-], producing an imidic acid [-C(OH)-NH-] as a metastable state; the amide proton of the imidic acid is then transferred, spontaneously to the deprotonated carboxyl group of the Asp51 side chain, leading to the formation of an enol form [-C(OH)=N-] of the Tyr440-Ser441 peptide group. Then a subsequent enol-to-keto tautomerization occurs via a double proton-transfer path realized in the two adjacent Tyr440-Ser441 and Ser441-Asp442 peptide groups. An analysis of this multistep proton-transfer pathway shows that each elementary process occurs through the shortest distance, no permanent conformational changes are induced, thus preserving the X-ray crystal structure, and the reaction path is characterized by a reasonable activation barrier.     

Subdiffraction imaging through the selective donut-mode depletion of thermally stable photoswitchable fluorophores: numerical analysis and application to the fluorescent protein Dronpa

The fast and reversible on/off switching of the fluorescence emission of the GFP-like fluorescent protein Dronpa has attracted considerable interest for applications in subdiffraction imaging. In this paper we study the use of a donut-mode beam in combination with two more overlapping laser beams to increase the imaging resolution through selective switching to the nonfluorescent photoswitched state. We devise and run a series of numerical simulations to determine suitable photophysical parameters of prospective, thermally stable photoswitchable molecules, in terms of photoswitching quantum yields, fatigue resistance, and possible presence of transient nonfluorescent states. Many of our findings are applicable to other measurements that make use of donut beams, and these guidelines can be used in the synthesis and screening of novel photoswitchable compounds. We experimentally demonstrate the possibility of obtaining increased resolution by making use of the efficient and thermally stable Dronpa photoswitching, using equipment that is commonly available.     

Conformation and location of membrane-bound salinomycin-sodium complex deduced from NMR in isotropic bicelles

An ionophore antibiotic salinomycin was studied in a membrane environment consisting of isotropic bicelles, a better model for biological membranes than micelles, and its conformation and topological orientation in bicelles was determined. 2D NMR measurements and restrained conformational search revealed that salinomycin-sodium salt in bicelles adopts an open conformation in which the orientation of the E-ring is significantly different from that in crystal and solution structures. This conformational alteration breaks an intramolecular hydrogen bond between 28-OH and 1-O, dislocates the ether oxygen of the E-ring from a coordinated position to the sodium ion observed in the crystal, and consequently weakens the complexation between salinomycin and the sodium ion. Paramagnetic relaxation experiments using doxyl-phospholipids reveal that salinomycin is embedded shallowly in bicelles, with both terminals being closer to the water interface and the olefin portion facing the bicelle interior. Measurements of intermolecular NOEs between salinomycin and phospholipids further supported this orientation. Weaker complexation with sodium ion and positional preference in the membrane polar region may facilitate the catch-and-release of metal ions at the polar/nonpolar interface of bilayers. On the basis of these findings, a model for salinomycin-assisted transport of metal ions across biological membranes is proposed.     

A hetero-core structured fiber optic pH sensor

Novel spectroscopic sensor based on a hetero-core structured fiber optic is described in this paper. The hetero-core structured fiber optic consists of multi mode fibers and a short piece of single mode fiber which was inserted in the multi mode fibers. Phenol red and/or cresol red as pH sensitive dyes were immobilized on the surface of the hetero-core portion by using sol-gel method, and the pH change detection was performed by immersing the hetero-core portion into the solution. In the case that the cresol-red immobilized fiber was immersed in the alkaline and/or acidic solution, the peak wavelength of the propagating loss spectra were about 575 and 545 nm, respectively. These propagating loss spectra were similar to that of the absorbance spectra of the dye solution. In the propagating loss spectra of phenol-red immobilized fiber, these spectra were similar to that of the dye solution. The colorimetric change of the dye in the support matrix was reversible, and the response time of the sensor was within 30 s.     

Structural development of liver X receptor (LXR) antagonists derived from thalidomide-related glucosidase inhibitors

Following our previous discovery of LXR antagonistic activity of 2'-substituted phenylphthalimides derived from thalidomide-related glucosidase inhibitors, structure-activity studies and further structural development led to 5-chloro-N-2'-n-pentylphenyl-1,3-dithiophthalimide (5CPPSS-50), with IC50 values of about 10 and 13 microM for LXRalpha and LXRbeta, respectively.     

Adsorption behaviors of high-valence metal ions on desferrioxamine B immobilization nylon 6,6 chelate fiber under highly acidic conditions

Adsorption behaviors of the high-valence metal ions Zr(IV), Hf(IV), Ti(IV), V(V), Nb(V), Ta(V), and Mo(IV) on desferrioxamine B (DFB) immobilization nylon 6,6 chelate fiber was investigated under highly acidic conditions. Though the complexes of DFB and the high-valence metal ions were extracted without selectivity by solvent extraction, the only zirconium ions showed higher adsorption percentages than that of other high-valence metal ions on the DFB immobilization nylon 6,6 chelate fiber. Adsorption properties were caused that limited the freedom of DFB by chemical immobilization. Especially, hafnium ions and zirconium ions, which have similar chemical properties, showed different adsorption behavior in highly acidic aqueous solutions. Zirconium ions were quantitatively adsorbed up to 13.5 micromol/g.