Constructing molecular polygons using halogen bonding and bifurcated N-oxides

Bifurcated halogen bonds constructed from N-oxides and complementary halogen-bond donors provide the basis for a synthetic strategy for the deliberate assembly of molecular polygons in the solid state. The donor- and acceptor sites were located on different molecular components and a co-crystallization approach furnished the desired architectures

Visualizing the complex morphology of fatigue cracks in voxel-based 3D datasets

The synthetic vanadinites (Pb(x)Ca(10-x))(VO4)6F2delta, 1 < x < 9, adopt a P6(3)/m apatite structure with 9.7590 (1) < or = a < or = 10.1179 (1) A and 7.0434 (3) < or = c < or = 7.4021 (1) A. The partitioning of calcium and lead over the AI(4f) and AII(6h) positions is nonstoichiometric with lead preferentially entering the larger AII site. High-resolution electron microscopy showed that samples annealed for 10 h at 1073 K are in disequilibrium with calcium- and lead-rich microdomains co-existing at unit-cell scales. For (Pb5Ca5)(VO4)6F2delta, sintering in excess of 2 weeks is required for the metals to order macroscopically. As annealing progresses, c/a, the partitioning coefficient kPb(AI/AII) and the AIO6 metaprism twist angle (phi) adjust cooperatively to enlarge the apatite channel, and thereby accommodate higher lead content. These results demonstrate that phi is a sensitive measure of disequilibrium and a useful device for monitoring changes in apatite topology as a function of composition

SWEET17, a facilitative transporter, mediates fructose transport across the tonoplast of Arabidopsis roots and leaves

Fructose (Fru) is a major storage form of sugars found in vacuoles, yet the molecular regulation of vacuolar Fru transport is poorly studied. Although SWEET17 (for SUGARS WILL EVENTUALLY BE EXPORTED TRANSPORTERS17) has been characterized as a vacuolar Fru exporter in leaves, its expression in leaves is low. Here, RNA analysis and SWEET17-β-glucuronidase/-GREEN FLUORESCENT PROTEIN fusions expressed in Arabidopsis (Arabidopsis thaliana) reveal that SWEET17 is highly expressed in the cortex of roots and localizes to the tonoplast of root cells. Expression of SWEET17 in roots was inducible by Fru and darkness, treatments that activate accumulation and release of vacuolar Fru, respectively. Mutation and ectopic expression of SWEET17 led to increased and decreased root growth in the presence of Fru, respectively. Overexpression of SWEET17 specifically reduced the Fru content in leaves by 80% during cold stress. These results intimate that SWEET17 functions as a Fru-specific uniporter on the root tonoplast. Vacuoles overexpressing SWEET17 showed increased [14C]Fru uptake compared with the wild type. SWEET17-mediated Fru uptake was insensitive to ATP or treatment with NH4Cl or carbonyl cyanide m-chlorophenyl hydrazone, indicating that SWEET17 functions as an energy-independent facilitative carrier. The Arabidopsis genome contains a close paralog of SWEET17 in clade IV, SWEET16. The predominant expression of SWEET16 in root vacuoles and reduced root growth of mutants under Fru excess indicate that SWEET16 also functions as a vacuolar transporter in roots. We propose that in addition to a role in leaves, SWEET17 plays a key role in facilitating bidirectional Fru transport across the tonoplast of roots in response to metabolic demand to maintain cytosolic Fru homeostasis

Evaluation of the in vitro Inhibitory Impact of Hypericin on Placental Glutathione S-Transferase pi

St John's Wort (SJW) extracts are herbal products which are available without prescription in most countries and widely used in the treatment of mild to moderate depression. Since it is a herbal product and available without prescription, use of SJW is common among pregnant and/or lactating woman. The principal of the study was to clarify the effects of hypericin, one of the components of SJW, on glutathione S-transferase-pi (GST-pi) purified from human placenta. The K (m) values of GST-pi were 0.21 +/- A 0.03 mM for glutathione (GSH) and 2.29 +/- A 0.54 mM for 1-chloro-2,4-dinitrobenzene (CDNB). At fixed [GSH], the V (m) value calculated was about 3 times higher than the conditions in which [CDNB] was fixed; 201 +/- A 30 U/mg protein versus 74 +/- A 3 U/mg protein. At constant substrate concentrations (1 mM), an average IC (50) value of 0.70 +/- A 0.02 mu M was obtained. Hypericin inhibited GST-pi competitively with respect to both substrates. When GSH was the varied substrate a K (i) value of 0.31 +/- A 0.05 mu M was found; when CDNB was the varied substrate, a K (i) value of 0.85 +/- A 0.02 mu M was obtained. On the basis of these data considering transplacental transfer of hypericin and immature hepatic clearance of the baby, using this herbal product may cause abnormalites due to the inhibition of one of the most important placental detoxification enzymes, GST-pi

Exploitation of the Menshutkin reaction for the controlled assembly of halogen bonded architectures incorporating 1,2-diiodotetrafluorobenzene and 1,3,5-triiodotrifluorobenzene

1,4-Diazabicyclo[2.2.2]octane (DABCO) forms well-defined co-crystals with 1,2-diiodotetrafluorobenzene (1,2-DITFB), [(1,2-DITFB) DABCO], and 1,3,5-triiodotrifluorobenzene, [(1,3,5-TITFB) DABCO]. Both systems exhibited lowerthan-expected supramolecular connectivity, which inspired a search for polymorphs in alternative crystallization solvents. In dichloromethane solution, the Menshutkin reaction was found to occur, generating chloride anions and quaternary ammonium cations through the reaction between the solvent and DABCO. The controlled in situ production of chloride ions facilitated the crystallization of new halogen bonded networks, DABCO-CH Cl[(1,2-DITFB)Cl] (zigzag X-bonded chains) and (DABCO-CH Cl) [(1,3,5-TITFB) Cl ] ·CHCl3 (2D pseudo-trigonal X-bonded nets displaying Borremean entanglement), propagating with charge-Assisted C-I⋯Cl-halogen bonds. The method was found to be versatile, and substitution of DABCO with triethylamine (TEA) gave (TEA-CH Cl) [(1,2-DITFB)Cl ] ·4(H O) (mixed halogen bond hydrogen bond network with 2D supramolecular connectivity) and TEA-CH Cl[(1,3,5-TITFB)Cl] (tightly packed planar trigonal nets). The co-crystals were typically produced in high yield and purity with relatively predictable supramolecular topology, particularly with respect to the connectivity of the iodobenzene molecules. The potential to use this synthetic methodology for crystal engineering of halogen bonded architectures is demonstrated and discussed