Cyclic diarylheptanoids inhibit cell-mediated low-density lipoprotein oxidation

Two cyclic diarylheptanoids, garugamblin-3 (1) and acerogenin L (2), isolated from the MeOH extract of the fruits of Alnus japonica Steud., inhibited human low-density lipoprotein (LDL) oxidation in the thiobarbituric acid-reactive substance assay with IC50 values of 2.9 and 1.7 microM, respectively, and they also inhibited cell-mediated LDL oxidation more than five times more strongly than that of a well-known antioxidant, probucol, at a concentration of 10 microM. 1 had no effect on the anti-atherogenesis in low-density lipoprotein receptor- deficient mice.     

Novel Zn1-xMnxSe (x = 0.1-0.4) one-dimensional nanostructures: nanowires, zigzagged nanobelts, and toothed nanosaws

Novel Zn1-xMnxSe one-dimensional nanostructures-straight nanowires (x = 0.1 and 0.3), zigzagged nanobelts (x = 0.4), and toothed nanosaws (x = 0.4)-were synthesized using the chemical vapor deposition method. They all consisted of single-crystalline wurtzite ZnSe crystals, irrespective of the Mn content. In particular, the nanosaws have a unique structure in which double-sided teeth are rooted in the nanowire core and bent so as to align as two parallel rows. The long axis is parallel to the [010] direction, and all of the teeth have the [0001] growth direction. The X-ray diffraction pattern confirms the formation of wurtzite ZnSe crystal and the decrease of the lattice constant owing to Mn doping. The Mn2+ emission at 2.1 eV (appeared below 100 K), originating from the d-d (4T1 --> 6A1) transition, proves the effective substitution of Mn2+ ions at the tetrahedral coordinate sites.     

Bistable electrical switching and memory effects in a thin film of copolymer containing electron donor-acceptor moieties and europium complexes

A nonconjugated methacrylate copolymer (PCzOxEu) containing carbazole moieties (electron donors), 1,3,4-oxadiazole moieties (electron acceptors), and europium complexes in the pendant groups was synthesized via free radical copolymerization of methacrylate monomers containing the respective functional groups. The molecular structure and composition of PCzOxEu was characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, UV-vis absorption and fluorescence spectroscopies, gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CyV). The resulting copolymer exhibited a relatively high glass transition temperature (Tg approximately 125 degrees C) and good solubility in common organic solvents. It could be cast into transparent films from solutions. For a thin film of PCzOxEu sandwiched between an indium-tin oxide (ITO) electrode and an Al electrode (ITO/PCzOxEu/Al), the structure behaved as a nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and erased. The polymer memory exhibited an ON/OFF current ratio up to 10(5), switching response time of approximately 1.5 micros, more than 10(6) read cycles, retention time of more than 8 h, and write/erase voltages of about 4.4 V/-2.8 V under ambient conditions. The roles of oxadiazole moieties in improving the response time and retention time of the memory device were elucidated from the molecular simulation results.     

Photoluminescence of Cd1-xMnxS (x < or = 0.3) nanowires

Cd1-xMnxS (x = 0.1-0.3) nanowires were synthesized by using the chemical vapor deposition method. They all consist of a single-crystalline wurtzite CdS structure with a [010] or [011] growth direction. The X-ray diffraction pattern reveals the contraction of the lattice constants due to the incorporation of Mn. The Mn2+ emission at approximately 2.15 eV, originating from the d-d (4T1 --> 6A1) transition, appears below 50-80 K. Its decay time is in the range of 0.55-1 ms, showing a decrease with increasing Mn content. The Mn doping reduces significantly the decay time of band-edge emission from 590 ps to 20-30 ps. Upon applying magnetic field (up to 7 T), the Mn2+ emission is suppressed and donor-acceptor pair emission becomes dominant, suggesting the energy transfer from the band electrons to the Mn2+ ions.     

Scandium triflate catalyzed cycloaddition of imines with 1,1-cyclopropanediesters: efficient and diastereoselective synthesis of multi-substituted pyrrolidines

A tandem ring-opening-cyclization reaction of cyclopropanes with imines in the presence of 5 mol% of scandium triflate was developed for the highly diastereoselective synthesis of multi-substituted pyrrolidines.     

Crystal structures and catalytic mechanism of the Arabidopsis cinnamyl alcohol dehydrogenases AtCAD5 and AtCAD4

The cinnamyl alcohol dehydrogenase (CAD) multigene family in planta encodes proteins catalyzing the reductions of various phenylpropenyl aldehyde derivatives in a substrate versatile manner, and whose metabolic products are the precursors of structural lignins, health-related lignans, and various other metabolites. In Arabidopsis thaliana, the two isoforms, AtCAD5 and AtCAD4, are the catalytically most active being viewed as mainly involved in the formation of guaiacyl/syringyl lignins. In this study, we determined the crystal structures of AtCAD5 in the apo-form and as a binary complex with NADP+, respectively, and modeled that of AtCAD4. Both AtCAD5 and AtCAD4 are dimers with two zinc ions per subunit and belong to the Zn-dependent medium chain dehydrogenase/reductase (MDR) superfamily, on the basis of their overall 2-domain structures and distribution of secondary structural elements. The catalytic Zn2+ ions in both enzymes are tetrahedrally coordinated, but differ from those in horse liver alcohol dehydrogenase since the carboxyl side-chain of Glu70 is ligated to Zn2+ instead of water. Using AtCAD5, site-directed mutagenesis of Glu70 to alanine resulted in loss of catalytic activity, thereby indicating that perturbation of the Zn2+ coordination was sufficient to abolish catalytic activity. The substrate-binding pockets of both AtCAD5 and AtCAD4 were also examined, and found to be significantly different and smaller compared to that of a putative aspen sinapyl alcohol dehydrogenase (SAD) and a putative yeast CAD. While the physiological roles of the aspen SAD and the yeast CAD are uncertain, they nevertheless have a high similarity in the overall 3D structures to AtCAD5 and 4. With the bona fide CAD's from various species, nine out of the twelve residues which constitute the proposed substrate-binding pocket were, however, conserved. This is provisionally considered as indicative of a characteristic fingerprint for the CAD family.     

Secoisolariciresinol dehydrogenase: mode of catalysis and stereospecificity of hydride transfer in Podophyllum peltatum

Secoisolariciresinol dehydrogenase (SDH) catalyzes the NAD+ dependent enantiospecific conversion of secoisolariciresinol into matairesinol. In Podophyllum species, (-)-matairesinol is metabolized into the antiviral compound, podophyllotoxin, which can be semi-synthetically converted into the anticancer agents, etoposide, teniposide and Etopophos. Matairesinol is also a precursor of the cancer-preventative "mammalian" lignan, enterolactone, formed in the gut following ingestion of, for example, various high fiber dietary foods, as well as being an intermediate to numerous defense compounds in vascular plants. This study investigated the mode of enantiospecific Podophyllum SDH catalysis, the order of binding, and the stereospecificity of hydride abstraction/transfer from secoisolariciresinol to NAD+. SDH contains a highly conserved catalytic triad (Ser153, Tyr167 and Lys171), whose activity was abolished with site-directed mutagenesis of Tyr167Ala and Lys171Ala, whereas mutagenesis of Ser153Ala only resulted in a much reduced catalytic activity. Isothermal titration calorimetry measurements indicated that NAD+ binds first followed by the substrate, (-)-secoisolariciresinol. Additionally, for hydride transfer, the incoming hydride abstracted from the substrate takes up the pro-S position in the NADH formed. Taken together, a catalytic mechanism for the overall enantiospecific conversion of (-)-secoisolariciresinol into (-)-matairesinol is proposed.     

Determination of norfloxacin in human urine by capillary electrophoresis with electrochemiluminescence detection

A fast and sensitive approach that can be used to detect norfloxacin in human urine using capillary electrophoresis with end-column electrochemiluminescence (ECL) detection of is described. The separation column was a 75-μm i.d. capillary. The running buffer was 15 mmol L⁻¹ sodium phosphate (pH 8.2). The solution in the detection cell was 50 mmol L⁻¹ sodium phosphate (pH 8.0) and 5 mmol L⁻¹ The ECL intensity varied linearly with norfloxacin concentration from 0.05 to 10 μmol L⁻¹. The detection limit (S/N=3) was 0.0048 μmol L⁻¹, and the relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μmol L⁻¹ norfloxacin (n=11) were 2.6% and 0.8%, respectively. The method was successfully applied to the determination of norfloxacin spiked in human urine without sample pretreatment. The recoveries were 92.7–97.9%.      

Variable temperature and EPR frequency study of two aqueous Gd(III) complexes with unprecedented sharp lines

We present an EPR study of two Gd(III) complexes in aqueous solution at multiple temperatures and EPR frequencies. These two complexes, [Gd(TPATCN)] and [Gd(DOTAM)(H(2)O)](3+), display remarkably sharp lines (i.e. slow transverse electron spin relaxation) in comparison with all complexes studied in the past, especially at X-band ( approximately 9.08 GHz). These unprecedented spectra even show, for the first time in solution, a distinct influence of hyperfine coupling to two magnetically active Gd isotopes ((155)Gd 14.8%, I = 3/2, gamma = -0.8273 x 10(7) s(-1) T(-1) and (157)Gd, 15.65%, I = 3/2, -1.0792 x 10(7) s(-1) T(-1)). The hyperfine coupling splitting in [Gd(TPATCN)] was determined accurately for a (157)Gd-enriched complex, and the value A((157)Gd)/gmu(B) = 5.67 G seems to be a good estimation for most chelates of interest. Consequently, we can safely assert that neglecting the Gd isotopes in line shape studies is not a significant source of error as long as the apparent peak-to-peak width is greater than 10-20 G. This is generally the case, except at very high EPR frequencies (>150 GHz). Analyzing the spectra within the physical model of Rast et al. we find that the slow electron spin relaxation is due to a nearly zero static ZFS. We discuss some structural features that might explain this interesting electron structure.