[Effects of soil water stress and atmospheric CO2 concentration on photosynthetic and post-photosynthetic fractionation].

Analysis of plant photosynthesis and post-photosynthetic fractionation can improve our understanding of plant physiology and water management. By measuring δ13C in the atmosphere, and δ13C of soluble compounds in leaves and branch phloem of Platycladus orientalis, we examined discrimination pattern, including atmosphere-leaf discrimination during photosynthesis (ΔCa-leaf) and leaf-twig discrimination during post-photosynthesis (ΔCleaf-phlo), in response to changes of soil water content (SWC) and atmospheric CO2 concentration (Ca). The results showed that ΔCa-leaf reached a maximum of 13.06‰ at 95%-100% field water-holding capacity (FC) and Ca 400 µmol·mol-1, and a minimum of 8.63‰ at 35%-45% FC and Ca 800 µmol·mol-1. Both stomatal conductance and mesophyll cell conductance showed a significant linear positive correlation with ΔCa-leaf, with a correlation coefficient of 0.43 and 0.44, respectively. ΔCleaf-phlo was not affected by SWC and Ca. Our results provide mechanism of carbon isotopes fractionation and a theoretical basis for plant survival strategies in response to future climate change.

Molecular characterization of multidrug-resistant Mycobacterium tuberculosis isolated from south-central in China.

Rifampicin (RIF) and isoniazid (INH) Mycobacterium tuberculosis isolates were characterized from south-central China and transmission patterns within the Beijing genotype were detected in multidrug-resistant isolates. Six genetic regions, including rpoB for RIF, and katG, inhA, ahpC, mabA-inhA promoter and oxyR-ahpC intergenic region for INH were analyzed by DNA sequencing in 60 multidrug-resistant isolates, including 7 extensively drug-resistant isolates. The genomic deletion RD105 was characterized by genotyping. The results showed that 91.7% of MDR isolates carried mutations in the rpoB gene and 85.0% of the MDR isolates had at least one mutation in the INH resistance-associated loci detected. In total, these six genetic regions are responsible for 95.0% of MDR isolates. Mutations in the XDR isolates were focused on rpoB 531 or rpoB 526, and katG 315, correlating to a higher frequency level of resistance to RIF MIC ⩾8 µg ml⁻¹ and INH MIC ⩾4 µg m⁻¹. Three novel katG mutants (G273S, I266T and P232S) and three new alleles (E458A, S509R and P535S) in the rpoB gene were identified. Among the 85 clinical isolates, 78 are Beijing genotypes and the other 7 are non-Beijing genotypes. The results present the identification of genetic markers in M. tuberculosis isolates, some of which may be unique to this particular geographic niche. An understanding of the mutations in these drug-resistant strains may aid in choosing the appropriate chemotherapy regimens on the pharmacogenetic properties of the mutations for the prevention and control of tuberculosis.

Pillared-layer microporous metal-organic frameworks constructed by robust hydrogen bonds. Synthesis, characterization, and magnetic and adsorption properties of 2,2'-biimidazole and carboxylate complexes.

Two new isostructural complexes [M(H2biim)3][M(btc)(Hbiim)].2H2O (M = Co, (1); M = Ni, (2)) (btc = 1,3,5-benzenetricarboxylate; H2biim = 2,2'-biimidazole) have been synthesized and characterized by single-crystal X-ray diffraction. They present a unique structure consisting of two distinct units: the monomeric cations [M(H2biim)3]2+ and the two-dimensional (2D) anionic polymer [M(Hbiim)(btc)]2-. In the anionic moiety, the Hbiim- monoanion is simultaneously coordinated to one metal atom in a bidentate mode and further to another metal atom in a monodentate mode. The imidazolate groups bridge the two adjacent metal ions into a helical chain which is further arranged in left- and right-handed manners. These chains are bridged by btc ligands into a 2D brick wall structure. The most interesting aspect is that the [M(H2biim)3]2+ cations act as pillars and link the anionic layers via robust heteromeric hydrogen-bonded synthons (9) and (7) formed by the uncoordinated oxygen atoms of carboxylate groups and the H2biim ligands, resulting in a microporous metal-organic framework with one-dimensional (1D) channels (ca. 11.85 angstroms x 11.85 angstroms for 1 and 11.43 angstroms x 11.43 angstroms for 2). Magnetic properties of these two complexes have also been studied in the temperature range of 2-300 K, and their magnetic susceptibilities obey the Curie-Weiss law in the temperature range of 20-300 K (for 1) and 2-300 K (for 2), respectively, showing anti-ferromagnetic coupling through imidazolate bridging. Taking into consideration the Heisenberg infinite chain model as well as the possibility of chain-to-chain and chain-to-cation interactions, the anti-ferromagnetic exchange of 2 is analyzed via a correction for the molecular field, giving the values of g(cat) = 2.296, g(Ni) = 2.564, J = -13.30 cm(-1), and zJ' = -0.017 cm(-1). The microporous frameworks are stable at ca. 350 degrees C. They do not collapse after removal of the guest water molecules in the channels, and they adsorb methanol molecules selectively.

Formation of one-dimensional metal-water chain containing cyclic water hexamers.

Cyclic water hexamers containing 1-D metal--water chains have been observed in the complexes of [M(H(2)biim)(2)(OH(2))(2)](ina)(2) x 4H(2)O [M = Zn (1) and Co (2), H(2)biim = 2,2'-biimidazole, ina = isoniconate]. The water clusters are trapped by the cooperative association of coordination interactions as well as hydrogen bonds.