Structure-chiroptical property relationship of kinetically labile camphor-derivative beta-diketone Yb(III) complexes: do the adducts coexist as diastereomers or not?

The present work examines the relationship between the crystal structures and chiroptical properties of four chiral Yb(III) complexes with camphor-derivative beta-diketone ligands by means of solid-state circular dichroism (CD) spectroscopy. For the seven-coordinate complexes, [Yb(H(2)O)(d-hfc)(3)] (I) and [Yb(H(2)O)(l-hfc)(3)] (II) (d/l-hfc(-) = 3-heptafluorobutyryl-(+)/(-)-camphorate), the Lambda- and Delta-diastereomers coexist in their crystals and no apparent bisignate couplets are observed in their solid-state CD spectra. A theoretical study indicates that the ground-state energy difference between the two diastereomers I and II is only 0.913 kcal mol(-1), which explains why they could coexist in a crystal environment with the ratio of 1:1. While, eight-coordinate complexes Delta-[Yb(TPPO)(2)(d-hfc)(3)]center dot CHCl(3)center dot 3C(6)H(12) (III) and Lambda-[Yb(TPPO)(2)(l-hfc)(3)]center dot CHCl3 center dot 3C(6)H(12) (IV) (TPPO = triphenylphosphine oxide) are enantiopure in the solid-state, and typically negative and positive exciton splitting patterns around 330 nm are observed in their solid-state CD spectra. The solid-state CD spectra of these four complexes are in accordance with their X-ray single-crystal analyses. Besides, their solution CD spectra show that no particular isomer predominates in solution.NSFC[20973136, 20773098, 20673069]; NSF of Shanxi province[2007011021

Azospirillum brasilense Chemotaxis Depends on Two Signaling Pathways Regulating Distinct Motility Parameters

The genomes of most motile bacteria encode two or more chemotaxis (Che) systems, but their functions have been characterized in only a few model systems. Azospirillum brasilense is a motile soil alphaproteobacterium able to colonize the rhizosphere of cereals. In response to an attractant, motile A. brasilense cells transiently increase swimming speed and suppress reversals. The Che1 chemotaxis pathway was previously shown to regulate changes in the swimming speed, but it has a minor role in chemotaxis and root surface colonization. Here, we show that a second chemotaxis system, named Che4, regulates the probability of swimming reversals and is the major signaling pathway for chemotaxis and wheat root surface colonization. Experimental evidence indicates that Che1 and Che4 are functionally linked to coordinate changes in the swimming motility pattern in response to attractants. The effect of Che1 on swimming speed is shown to enhance the aerotactic response of A. brasilense in gradients, likely providing the cells with a competitive advantage in the rhizosphere. Together, the results illustrate a novel mechanism by which motile bacteria utilize two chemotaxis pathways regulating distinct motility parameters to alter movement in gradients and enhance the chemotactic advantage

Chiral phosphoproline-catalyzed asymmetric Michael addition of ketones to nitroolefins: an experimental and theoretical study

A novel pyrrolidine-based chiral phosphoproline is an effective bifunctional organocatalyst for the asymmetric Michael addition of ketones to nitroolefins giving high levels of diastereo- and enantio-selectivities (up to >99:1 dr and 96% ee). anti-SR Transition state has the lowest barrier which controls the stereoselectivity, in agreement with experimental results.National Natural Science Foundation of China[20732004, 20805037, 20972130

Specific Release of Bacteriochlorophylls B800 of LH2 from Rhodobacter azotoformans Induced by Sodium Dodecyl Sulfate

The release behaviors of bacteriochlorophylls of peripheral light-harvesting complex LH2 from Rhodobacter azotoformans induced by sodium dodecyl sulfate (SDS) were investigated using absorption spectroscopy. The results indicated that bacteriochlorophylls of B800 band are released from their binding sites and transformed into free bacteriochlorophylls by incubating LH2 sample in 10 mmol.L-1 Tris-HCl (pH 8.0) buffer containing SDS of low concentration at room temperature. However, the bacteriochlorophylls of B850 band are not released. The dynamics of B800 release and free BChl formation induced by 0.08% (w/V) SDS can be well fitted by the monoexponential model. The rate constant of B800 release is nearly equal to that of free BChls formation. The release of both B800 and B850 of LH2 can be induced by high concentration SDS, simultaneously. The bacteriochlorophylls of B800 band can be completely transformed into free BChls, but not for B850. Although both of their release processes show monoexponential models in 1% SDS solution, the release rate constant of B850 is remarkably lower than that of B800 and close to that of free BChls formation.国家自然科学基金(No. 30970068)、国家科技基础条件平台建设(No. 2005DKA21209)、厦门大学近海海洋环境科学国家重点实验室高级访问学者基 金(No. MELRS0907)和山西省回国留学人员科研(No. 200713)资助项目

Chirality at phosphorus in pentacoordinate spirophosphoranes: stereochemistry by X-ray structure and spectroscopic analysis

Two pairs of enantiomers of stable chiral pentacoordinate spirophosphoranes with two bonds from the amino and two bonds from the carboxyl groups of amino acids have been synthesized and analysed. The results show that differences in chirality at phosphorus are linked to distinct differences in physical properties.NSFC [20732004, 20572061, 20773098]; International Cooperation MOST [2006DFA43030

Nitric oxide enhances salt secretion and Na+ sequestration in a mangrove plant, Avicennia marina, through increasing the expression of H+-ATPase and Na+/H+ antiporter under high salinity

Modulation of nitric oxide (NO) on ion homeostasis, by enhancing salt secretion in the salt glands and Na+ sequestration into the vacuoles, was investigated in a salt-secreting mangrove tree, Avicennia marina (Forsk.) Vierh. The major results are as follows: (i) under 400 mM NaCl treatment, the application of 100 mu M sodium nitroprusside (SNP), an NO donor, significantly increased the density of salt crystals and salt secretion rate of the leaves, along with maintaining a low Na+ to K+ ratio in the leaves. (ii) The measurement of element contents by X-ray microanalysis in the epidermis and transversal sections of A. marina leaves revealed that SNP (100 mu M) significantly increased the accumulation of Na+ in the epidermis and hypodermal cells, particularly the Na+ to K+ ratio in the salt glands, but no such effects were observed in the mesophyll cells. (iii) Using non-invasive micro-test technology (NMT), both long-term SNP (100 mu M) and transient SNP (30 mu M) treatments significantly increased net Na+ efflux in the salt glands. On the contrary, NO synthesis inhibitors and scavenger reversed the effects of NO on Na+ flux. These results indicate that NO enhanced salt secretion by increasing net Na+ efflux in the salt glands. (iv) Western blot analysis demonstrated that 100 mu M SNP stimulated protein expressions of plasma membrane (PM) H+-ATPase and vacuolar membrane Na+/H+ antiporter. (v) To further clarify the molecular mechanism of the effects of NO on enhancing salt secretion and Na+ sequestration, partial cDNA fragments of PM H+-ATPase (HA1), PM Na+/H+ antiporter (SOS1) and vacuolar Na+/H+ antiporter (NHX1) were isolated and transcriptional expression of HA1, SOS1, NHX1 and vacuolar H+-ATPase subunit c (VHA-c1) genes were analyzed using real-time quantitative polymerase chain reaction. The relative transcript abundance of the four genes were markedly increased in 100 mu M SNP-treated A. marina. Moreover, the increase was reversed by NO synthesis inhibitors and scavenger. Taken together, our results strongly suggest that NO functions as a signal in salt resistance of A. marina by enhancing salt secretion and Na+ sequestration, which depend on the increased expression of the H+-ATPase and Na+/H+ antiporter.Natural Science Foundation of China (NSFC) [30930076, 30770192, 30670317, 30271065, 39970438]; Foundation of the Chinese Ministry of Education [209084]; Xiamen University [NCETXMU X071l5]; Changjiang Scholarship [X09111