Noble gas supported boron-pentagonal clusters B<Subscript>5</Subscript>Ng<Subscript>n</Subscript><Superscript>3+</Superscript>: exploring the structures and bonding

A novel type of trivalent BNg five-membered cational species B₅Ng_n³⁺(Ng = He~Rn, n = 1~5) has been found and investigated theoretically using the B3LYP and MP2 methods with the def2-QZVPPD and def2-TZVPPD basis sets. The geometry, harmonic vibrational frequencies, bond energies, charge distribution, bond nature, aromaticity, and energy decomposition analysis of these structures were reported. The calculated B?Ng bond energy is quite large (the averaged bond energy is in the range of 209.2~585.76 kJ mol^-1) for heavy rare gases and increases with the Ng atomic number. The analyses of the molecular wavefunction show that in the BNg compounds of heavy Ng atoms Ar~Rn, the B?Ng bonds are of typical covalent character. Nuclear independent chemical shifts display that both B₅³⁺ and B₅Ng_n³⁺(n=1~5) have obvious aromaticity. Energy decomposition analysis shows that these BNg compounds are mainly stabilized by the σ-donation from the Ng valence p orbital to the B₅³⁺ LUMO. These findings offer valuable clues toward the design and synthesis of new stable Ng-containing compounds.     

Ab initio studies on the decomposition kinetics of CF<Subscript>3</Subscript>OCF<Subscript>2</Subscript>O radical

The present study deals with the decomposition of CF₃OCF₂O radical formed from a hydrofluoroether, CF₃OCHF₂ (HFE-125), in the atmosphere. The study is performed using ab initio quantum mechanical methods. Two plausible pathways of decomposition of the titled species have been considered, one involving C-O bond scission and the other occurring via F atom elimination. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2M(CC,MP2) level of theory. Out of the two prominent decomposition channels considered, the C-O bond scission is found to be dominant involving a barrier height of 15.3 kcal mol⁻¹ whereas the F-elimination path proceeds with a barrier of 26.1 kcal mol⁻¹. The thermal rate constants for the above two decomposition pathways are evaluated using canonical transition state theory (CTST) and these are found to be 1.78 × 10⁶ s⁻¹ and 2.83 × 10⁻⁷ s⁻¹ for C-O bond scission and F-elimination respectively at 298 K and 1 atm pressure. Transition states are searched on the potential energy surfaces involved during the decomposition channels and each of the transition states is characterized. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Dynamics of <Superscript>18</Superscript>O Incorporation from H <Subscript>2</Subscript><Superscript>18</Superscript>O into Soil Microbial DNA

Heavy water (H₂¹⁸O) has been used to label DNA of soil microorganisms in stable isotope probing experiments, yet no measurements have been reported for the ¹⁸O content of DNA from soil incubated with heavy water. Here we present the first measurements of atom% ¹⁸O for DNA extracted from soil incubated with the addition of H₂¹⁸O. Four experiments were conducted to test how the atom% ¹⁸O of DNA, extracted from Ponderosa Pine forest soil incubated with heavy water, was affected by the following variables: (1) time, (2) nutrients, (3) soil moisture, and (4) atom% ¹⁸O of added H₂O. In the time series experiment, the atom% ¹⁸O of DNA increased linearly (R ² = 0.994, p < 0.01) over the first 72 h of incubation. In the nutrient addition experiment, there was a positive correlation (R ² = 0.991, p = 0.006) between the log₁₀ of the amount of tryptic soy broth, a complex nutrient broth, added to soil and the log₁₀ of the atom% ¹⁸O of DNA. For the experiment where soil moisture was manipulated, the atom% ¹⁸O of DNA increased with higher soil moisture until soil moisture reached 30%, above which ¹⁸O enrichment of DNA declined as soils became more saturated. When the atom% ¹⁸O for H₂O added was varied, there was a positive linear relationship between the atom% ¹⁸O of the added water and the atom% ¹⁸O of the DNA. Results indicate that quantification of ¹⁸O incorporated into DNA from H₂¹⁸O has potential to be used as a proxy for microbial growth in soil.     

Resolution-optimized NMR measurement of <Superscript>1</Superscript>D<Subscript>CH</Subscript>, <Superscript>1</Superscript>D<Subscript>CC</Subscript> and <Superscript>2</Superscript>D<Subscript>CH</Subscript> residual dipolar couplings in nucleic acid bases

New methods are described for accurate measurement of multiple residual dipolar couplings in nucleic acid bases. The methods use TROSY-type pulse sequences for optimizing resolution and sensitivity, and rely on the E.COSY principle to measure the relatively small two-bond ²D_CH couplings at high precision. Measurements are demonstrated for a 24-nt stem-loop RNA sequence, uniformly enriched in ¹³C, and aligned in Pf1. The recently described pseudo-3D method is used to provide homonuclear ¹H-¹H decoupling, which minimizes cross-correlation effects and optimizes resolution. Up to seven ¹H-¹³C and ¹³C-¹³C couplings are measured for pyrimidines (U and C), including ¹D_C5H5, ¹D_C6H6, ²D_C5H6, ²D_C6H5, ¹D_C5C4, ¹D_C5C6, and ²D_C4H5. For adenine, four base couplings (¹D_C2H2, ¹D_C8H8, ¹D_C4C5, and ¹D_C5C6) are readily measured whereas for guanine only three couplings are accessible at high relative accuracy (¹D_C8H8, ¹D_C4C5, and ¹D_C5C6). Only three dipolar couplings are linearly independent in planar structures such as nucleic acid bases, permitting cross validation of the data and evaluation of their accuracies. For the vast majority of dipolar couplings, the error is found to be less than ±3% of their possible range, indicating that the measurement accuracy is not limiting when using these couplings as restraints in structure calculations. Reported isotropic values of the one- and two-bond J couplings cluster very tightly for each type of nucleotide.     

Molecular properties of metal difluorides and their interactions with CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O molecules: a DFT investigation

A computational study of metal difluorides (MF₂; M = Ca to Zn) and their interactions with carbon dioxide and water molecules was performed. The structural parameter values obtained and the results of AIM analysis and energy decomposition analysis indicated that the Ca–F bond is weaker and less ionic than the bonds in the transition metal difluorides. A deformation density plot revealed the stablizing influence of the Jahn–Teller effect in nonlinear MF₂ molecules (e.g., where M= Sc, Ti, Cr). An anaysis of the metal K-edge peaks of the difluorides showed that shifts in the edge energy were due to the combined effects of the ionicity, effective nuclear charge, and the spin state of the metal. The interactions of CO₂ with ScF₂ (Scc3 geometry) and TiF₂ (Tic2 geometry) caused CO₂ to shift from its usual linear geometry to a bent geometry (η²(C=O) binding mode), while it retained its linear geometry (η¹(O) binding mode) when it interacted with the other metal difluorides. Energy decomposition analysis showed that, among the various geometries considered, the Scc3 and Tic2 geometries possessed the highest interaction energies and orbital interaction energies. Heavier transition metal difluorides showed stronger affinities for H₂O, whereas the lighter transition metal (Sc and Ti) difluorides preferred CO₂. Overall, the results of this study suggest that fluorides of lighter transition metals with partially filled d orbitals (e.g., Sc and Ti) could be used for CO₂ capture under moist conditions.

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Graphical abstract Interaction of metal difluorides with carbon dioxide and water

     

TCNE-modified graphene as an adsorbent for N<Subscript>2</Subscript>O molecule: a DFT study

Adsorption behavior of nitrous oxide (N₂O) on pristine graphene (PG) and tetracyanoethylene (TCNE) modified PG surfaces is investigated using density functional theory. A number of initial adsorbate geometries are considered on both surfaces and the most stable ones are chosen upon calculation of the adsorption energies (E_ads). N₂O is found to adsorb in a weakly exoergic process (E_ads?～??3.18 kJ mol^?1) at the equilibrium distance of 3.52 Å on the PG surface. N₂O adsorption can be greatly enhanced with the presence of a TCNE molecule (E_ads?=??87.00 kJ mol^?1). Mulliken charge analysis confirms that adsorption of N₂O is not accompanied by distinct charge transfer from the surfaces to the molecule (? 0.001 │e│ for each case). Moreover, on the basis of calculated changes in the HOMO/LUMO energy gap, it is found that electronic properties of PG and TCNE modified PG are not sensitive toward adsorption of N₂O, indicating that both surfaces are not good enough to introduce as an N₂O detector. However, the considerable amount of E_ads in TCNE modified PG can be a guide to the design of graphene-based adsorbents for N₂O capture.     

N<Subscript>2</Subscript>O and CH<Subscript>4</Subscript> emission from <Emphasis Type="Italic">Miscanthus</Emphasis> energy crop fields in the infertile Loess Plateau of China

Background

The greenhouse gas (GHG) mitigation is one of the most important environmental benefits of using bioenergy replacing fossil fuels. Nitrous oxide (N₂O) and methane (CH₄) are important GHGs and have drawn extra attention for their roles in global warming. Although there have been many works of soil emissions of N₂O and CH₄ from bioenergy crops in the field scale, GHG emissions in large area of marginal lands are rather sparse and how soil temperature and moisture affect the emission potential remains unknown. Therefore, we sought to estimate the regional GHG emission based on N₂O and CH₄ releases from the energy crop fields.

Results

Here we sampled the top soils from two Miscanthus fields and incubated them using a short-term laboratory microcosm approach under different conditions of typical soil temperatures and moistures. Based on the emission measurements of N₂O and CH₄, we developed a model to estimate annual regional GHG emission of Miscanthus production in the infertile Loess Plateau of China. The results showed that the N₂O emission potential was 0.27 kg N ha^?1 year^?1 and clearly lower than that of croplands and grasslands. The CH₄ uptake potential was 1.06 kg C ha^?1 year^?1 and was slightly higher than that of croplands. Integrated with our previous study on the emission of CO₂, the net greenhouse effect of three major GHGs (N₂O, CH₄ and CO₂) from Miscanthus fields was 4.08 t CO_2eq ha^?1 year^?1 in the Loess Plateau, which was lower than that of croplands, grasslands and shrub lands.

Conclusions

Our study revealed that Miscanthus production may hold a great potential for GHG mitigation in the vast infertile land in the Loess Plateau of China and could contribute to the sustainable energy utilization and have positive environmental impact on the region.

     

The polythiophene molecular segment as a sensor model for H<Subscript>2</Subscript>O,HCN, NH<Subscript>3</Subscript>, SO<Subscript>3</Subscript>, and H<Subscript>2</Subscript>S: a density functional theory study

Studying the interaction of some atmospheric gases (H₂O, HCN, NH₃, SO₃ and H₂S) with 3PT oligomers is important in the development of polymeric sensors for gas detection. In the present study, we studied the relaxed geometries, interaction energies, charge analysis, HOMO–LUMO orbital analysis, and UV–vis spectra of all interacted systems using first-principles density functional theory (DFT). All these analyses indicated the potential of polythiophene as an inexpensive polymeric sensor for the analytes mentioned. Interaction energy values of ?19.90, ?19.66, ?14.01, ?8.70, and ?4.76 kJ mol^?1 were achieved for adsorption of SO₃, H₂O, NH₃, HCN, and H₂S on 3PT, respectively. Consequently, clarification of their physical parameters became the major focus of this study.     

Theoretical study of the novel sandwich compound [Au<Subscript>3</Subscript>Cl<Subscript>3</Subscript>Tr<Subscript>2</Subscript>]<Superscript>2+</Superscript>

A theoretical study of a sandwich compound with a metal monolayer sheet between two aromatic ligands is presented. A full geometry optimization of the [Au₃Cl₃Tr₂]²⁺ (1) compound, which is a triangular gold(I) monolayer sheet capped by chlorines and bounded to two cycloheptatrienyl (Tr) ligands was carried out using perturbation theory at the MP2 computational level and DFT. Compound (1) is in agreement with the 18–electron rule, the bonding nature in the complex may be interpreted from the donation interaction coming from the Tr rings to the Au array, and from the back-donation from the latter to the former. NICS calculations show a strong aromatic character in the gold monolayer sheet and Tr ligands; calculations done with HOMA, also report the same aromatic behavior on the cycloheptatrienyl fragments giving us an insight on the stability of (1). The Au –Au bond lengths indicate that an intramolecular aurophilic interaction among the Au(I) cations plays an important role in the bonding of the central metal sheet. Figure (a) Ground state geometry of complex 1; (b) Top view of compound 1 and Wiberg bond orders computed with the MP2/B1 computational method; (c) Lateral view of compound 1 and NICS values calculated with the MP2/B1 method; the values in parenthesis were obtained at the VWN/TZP level     

Effect of nitrogen forms on growth,cell composition and N<Subscript>2</Subscript> fixation of <Emphasis Type="Italic">Cylindrospermopsis raciborskii</Emphasis> in phosphorus-limited chemostat cultures

The aim of this research was to test whether NH₄ ⁺ and NO₃ ⁻ affect the growth, P demand, cell composition and N₂ fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l⁻¹ PO₄-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l⁻¹ NH₄-N, 4,000 μg l⁻¹ NO₃-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH₄ ⁺ and NO₃ ⁻ supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N₂-grown culture was significantly lower. The maximum specific growth rate of N₂-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the P and energy requirement for heterocyte formation, nitrogenase synthesis and N₂ fixation. N₂ fixation was partially inhibited by NO₃ ⁻ and completely inhibited by NH₄ ⁺. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH₄ ⁺ or NO₃ ⁻ is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies. Handling editor: Luigi Naselli-Flores     

Prediction and inhibition of the N<Subscript>2</Subscript>O accumulation in the BioDeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> process for NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> removal from flue gas

BioDeNO _x process, which combines the advantages of the chemical absorption and biological reduction processes, is regarded as a promising candidate for NO removal from the flue gas. In the BioDeNO _x , N₂O was accumulated in the process of the biological reduction of Fe^II(EDTA)-NO. In this work, the pathway of the Fe^II(EDTA)-NO reduction was investigated and a mathematic model was developed to evaluate and predict the accumulation of N₂O. Furthermore, parametric tests such as the effects of the C/N ratio (molar ratio of carbon/nitrogen), electron donor, and sulfite concentrations on N₂O accumulation were investigated. Experimental results revealed that N₂O accumulation was inhibited with a high C/N ratio (2.4), sufficient electron donor, and a low sulfite concentration. In addition, compared with the inorganic electron donor (Fe^II(EDTA)), the organic electron donor (glucose) was beneficial for microorganism metabolism and N₂O accumulation inhibition. This work will provide significant insight into the inhibition of N₂O accumulation during the operation of BioDeNO _x and advance this novel process for the industrial application.     

Evidence for the possible involvement of the P2Y<Subscript>6</Subscript> receptor in Ca<Superscript>2+</Superscript> mobilization and insulin secretion in mouse pancreatic islets

Subtypes of purinergic receptors involved in modulation of cytoplasmic calcium ion concentration ([Ca²⁺]_i) and insulin release in mouse pancreatic β-cells were examined in two systems, pancreatic islets in primary culture and beta-TC6 insulinoma cells. Both systems exhibited some physiological responses such as acetylcholine-stimulated [Ca²⁺]_i rise via cytoplasmic Ca²⁺ mobilization. Addition of ATP, ADP, and 2-MeSADP (each 100 μM) transiently increased [Ca²⁺]_i in single islets cultured in the presence of 5.5 mM (normal) glucose. The potent P2Y₁ receptor agonist 2-MeSADP reduced insulin secretion significantly in islets cultured in the presence of high glucose (16.7 mM), whereas a slight stimulation occurred at 5.5 mM glucose. The selective P2Y₆ receptor agonist UDP (200 μM) transiently increased [Ca²⁺]_i and reduced insulin secretion at high glucose, whereas the P2Y_2/4 receptor agonist UTP and adenosine receptor agonist NECA were inactive. [Ca²⁺]_i transients induced by 2-MeSADP and UDP were antagonized by suramin (100 μM), U73122 (2 μM, PLC inhibitor), and 2-APB (10 or 30 μM, IP₃ receptor antagonist), but neither by staurosporine (1 μM, PKC inhibitor) nor depletion of extracellular Ca²⁺. The effect of 2-MeSADP on [Ca²⁺]_i was also significantly inhibited by MRS2500, a P2Y₁ receptor antagonist. These results suggested that P2Y₁ and P2Y₆ receptor subtypes are involved in Ca²⁺ mobilization from intracellular stores and insulin release in mouse islets. In beta-TC6 cells, ATP, ADP, 2-MeSADP, and UDP transiently elevated [Ca²⁺]_i and slightly decreased insulin secretion at normal glucose, while UTP and NECA were inactive. RT-PCR analysis detected mRNAs of P2Y₁ and P2Y₆, but not P2Y₂ and P2Y₄ receptors.     

Endogenous Expression of Adenosine A<Subscript>1</Subscript>, A<Subscript>2 </Subscript>and A<Subscript>3</Subscript> Receptors in Rat C6 Glioma Cells

Inhibitory and stimulatory adenosine receptors have been identified and characterized in both membranes and intact rat C6 glioma cells. In membranes, saturation experiment performed with [³H]DPCPX, selective A₁R antagonist, revealed a single binding site with a K _D = 9.4 ± 1.4 nM and B _max = 62.7 ± 8.6 fmol/mg protein. Binding of [³H]DPCPX in intact cell revealed a K _D = 17.7 ± 1.3 nM and B _max = 567.1 ± 26.5 fmol/mg protein. On the other hand, [³H]ZM241385 binding experiments revealed a single binding site population of receptors with K _D = 16.5 ± 1.3 nM and B _max = 358.9 ± 52.4 fmol/mg protein in intact cells, and K _D = 4.7 ± 0.6 nM and B _max = 74.3 ± 7.9 fmol/mg protein in plasma membranes, suggesting the presence of A_2A receptor in C6 cells. A₁, A_2A, A_2B and A₃ adenosine receptors were detected by Western-blotting and immunocytochemistry, and their mRNAs quantified by real time PCR assays. Giα and Gsα proteins were also detected by Western-blotting and RT-PCR assays. Furthermore, selective A₁R agonists inhibited forskolin- and GTP-stimulated adenylyl cyclase activity and CGS 21680 and NECA stimulated this enzymatic activity in C6 cells. These results suggest that C6 glioma cells endogenously express A₁ and A₂ receptors functionally coupled to adenylyl cyclase inhibition and stimulation, respectively, and suggest these cells as a model to study the role of adenosine receptors in tumoral cells.     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Theoretical study of N<Subscript>4</Subscript>X (X = O,S, Se) systems

A series of N₄X (X = O, S, Se) compounds have been examined with ab initio and density functional theory (DFT) methods. To our knowledge, these compounds, except for the C_2v ring and the C_3v towerlike isomers of N₄O, are first reported here. The ring structures are the most energetically favored for N₄X (X = O and S) systems. For N₄Se, the cagelike structure is the most energetically favored. Several decomposition and isomerization pathways for the N₄X species have been investigated. The dissociation of C_2v ring N₄O and N₄S structures via ring breaking and the barrier height are only 1.1 and −0.2 kcal mol⁻¹ at the CCSD(T)/6-311+G*//MP2/6-311+G* level of theory. The dissociation of the cagelike N₄X species is at a cost of 12.1–16.2 kcal mol⁻¹. As for the towerlike and triangle bipyramidal isomers, their decomposition or isomerization barrier heights are all lower than 10.0 kcal mol⁻¹. Although the C_S cagelike N₄S isomer has a moderate isomerization barrier (18.3–29.1 kcal mol⁻¹), the low dissociation barrier (−1.0 kcal mol⁻¹) indicates that it will disappear when going to the higher CCSD(T) level. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparison of <Superscript>13</Superscript>CH<Subscript>3</Subscript>, <Superscript>13</Superscript>CH<Subscript>2</Subscript>D,and <Superscript>13</Superscript>CHD<Subscript>2</Subscript> methyl labeling strategies in proteins

A comparison of three labeling strategies for studies involving side chain methyl groups in high molecular weight proteins, using ¹³CH₃,¹³CH₂D, and ¹³CHD₂ methyl isotopomers, is presented. For each labeling scheme, ¹H–¹³C pulse sequences that give optimal resolution and sensitivity are identified. Three highly deuterated samples of a 723 residue enzyme, malate synthase G, with ¹³CH₃,¹³CH₂D, and ¹³CHD₂ labeling in Ile δ1 positions, are used to test the pulse sequences experimentally, and a rationalization of each sequence’s performance based on a product operator formalism that focuses on individual transitions is presented. The HMQC pulse sequence has previously been identified as a transverse relaxation optimized experiment for ¹³CH₃-labeled methyl groups attached to macromolecules, and a zero-quantum correlation pulse scheme (¹³CH₃ HZQC) has been developed to further improve resolution in the indirectly detected dimension. We present a modified version of the ¹³CH₃ HZQC sequence that provides improved sensitivity by using the steady-state magnetization of both ¹³C and ¹H spins. The HSQC and HMQC spectra of ¹³CH₂D-labeled methyl groups in malate synthase G are very poorly resolved, but we present a new pulse sequence, ¹³CH₂D TROSY, that exploits cross-correlation effects to record ¹H–¹³C correlation maps with dramatically reduced linewidths in both dimensions. Well-resolved spectra of ¹³CHD₂-labeled methyl groups can be recorded with HSQC or HMQC; a new ¹³CHD₂ HZQC sequence is described that provides improved resolution with no loss in sensitivity in the applications considered here. When spectra recorded on samples prepared with the three isotopomers are compared, it is clear that the ¹³CH₃ labeling strategy is the most beneficial from the perspective of sensitivity (gains ≥2.4 relative to either ¹³CH₂D or ¹³CHD₂ labeling), although excellent resolution can be obtained with any of the isotopomers using the pulse sequences presented here.     

The nodule conductance to O<Subscript>2</Subscript> diffusion increases with high phosphorus content in the <Emphasis Type="Italic">Phaseolus vulgaris-</Emphasis>rhizobia symbiosis

Although recent studies have addressed the effects of phosphorus (P) deficiency on nodule O₂ permeability, little attention has been given to the relationship between nodule P status and nodule permeability. To study these traits, four recombinant inbred lines, namely RILs 34, 83, 115, 147 and one local variety (Concesa) of common bean (Phaseolus vulgaris) were inoculated with RhM11 (a native rhizobial strain from Haouz area of Marrakesh), and grown in hydroaeroponic culture under P-sufficiency (250 μmol P plant⁻¹ week⁻¹) versus P-deficiency (75 μmol P plant⁻¹ week⁻¹) conditions. At the flowering stage, the biomass of plants and nodules and their P contents was determined after measuring O₂ uptake by nodulated roots (Conr) and nodule conductance to O₂ diffusion (g_n). The results showed that P-deficiency significantly decreased plant growth and nodulation, though there were differences between bean genotypes. P-deficiency also induced a decrease in nodule P content (31%) in both sensitive (83, 147) and tolerant lines (34, 115), a 42 and 27% reduction in shoots of sensitive and tolerant lines, respectively. These decreases were associated with significant variations in nodule surface and O₂ permeability among bean genotypes and P-nutrition. Under P-deficiency, g_n increased more for the sensitive (39%) than for the tolerant lines (27%). This increase was linked with a rise both in the P levels in nodules and shoots, as well as in the efficiency of symbiotic nitrogen fixation as determined by nodule-dependent biomass production for the sensitive lines. Furthermore, positive correlations were found between O₂ permeability, g_n and P content both in nodules and shoots (r ² = 0.94** and r ² = 0.96**). We conclude that nodule variations in Conr and g_n are related to nodule P content, and may contribute to the adaptation of energy metabolism in N₂-fixing bean nodules to P-deficiency.     

Immobilization of glucose oxidase on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> magnetic nanoparticles

Glucose oxidase (GOD) was covalently immobilized onto Fe₃O₄/SiO₂ magnetic nanoparticles (FSMNs) using glutaraldehyde (GA). Optimal immobilization was at pH 6 with 3-aminopropyltriethoxysilane at 2% (v/v), GA at 3% (v/v) and 0.143 g GOD per g carrier. The activity of immobilized GOD was 4,570 U/g at pH 7 and 50°C. The immobilized GOD retained 80% of its initial activity after 6 h at 45°C while free enzyme retained only 20% activity. The immobilized GOD maintained 60% of its initial activity after 6 cycles of repeated use and retained 75% of its initial activity after 1 month at 4°C whereas free enzymes retained 62% of its activity.     

Structure determination of proteins in <Superscript>2</Superscript>H<Subscript>2</Subscript>O solution aided by a deuterium-decoupled 3D HCA(N)CO experiment

We developed an NMR pulse sequence, 3D HCA(N)CO, to correlate the chemical shifts of protein backbone ¹Hα and ¹³Cα to those of ¹³C′ in the preceding residue. By applying ²H decoupling, the experiment was accomplished with high sensitivity comparable to that of HCA(CO)N. When combined with HCACO, HCAN and HCA(CO)N, the HCA(N)CO sequence allows the sequential assignment using backbone ¹³C′ and amide ¹⁵N chemical shifts without resort to backbone amide protons. This assignment strategy was demonstrated for ¹³C/¹⁵N-labeled GB1 dissolved in ²H₂O. The quality of the GB1 structure determined in ²H₂O was similar to that determined in H₂O in spite of significantly smaller number of NOE correlations. Thus this strategy enables the determination of protein structures in ²H₂O or H₂O at high pH values.     

Emissions of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O from undisturbed,drained and mined peatlands in Estonia

The aim of this study is to estimate emissions of greenhouse gases CO₂, CH₄ and N₂O, and the effects of drainage and peat extraction on these processes, in Estonian transitional fens and ombrotrophic bogs. Closed-chamber-based sampling lasted from January to December 2009 in nine peatlands in Estonia, covering areas with different land-use practices: natural (four study sites), drained (six sites), abandoned peat mining (five sites) and active peat mining areas (five sites). Median values of soil CO₂ efflux were 1,509, 1,921, 2,845 and 1,741 kg CO₂-C ha^?1 year^?1 from natural, drained, abandoned and active mining areas, respectively. Emission of CH₄-C (median values) was 85.2, 23.7, 0.07 and 0.12 kg ha^?1 year^?1, and N₂O-N ?0.05, ?0.01, 0.18 and 0.19 kg ha^?1 year^?1, respectively. There were significantly higher emissions of CO₂ and N₂O from abandoned and active peat mining areas, whereas CH₄ emissions were significantly higher in natural and drained areas. Significant Spearman rank correlation was found between soil temperature and CO₂ flux at all sites, and CH₄ flux with high water level at natural and drained areas. Significant increase in CH₄ flux was detected for groundwater levels above 30 cm.