Sorption properties of TEMPO-oxidized natural and man-made cellulose fibers

Cotton and lyocell fibers were oxidized with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), under various conditions. Water-insoluble fractions, collected after TEMPO-mediated oxidation, were analyzed and characterized in terms of weight loss, aldehyde and carboxyl contents, and sorption properties. Aldehyde and carboxyl groups were introduced into the oxidized cotton up to 0.321 and 0.795 mmol/g, and into the oxidized lyocell up to 0.634 and 0.7 mmol/g, respectively, where weight loss was generally lower than 12% for cotton and 27% for lyocell. Oxidized cotton and lyocell were shown to exhibit 1.55 and 2.28 times higher moisture sorption than the original fibers, respectively, and water retention values up to about 85% for cotton and 335% for lyocell, while iodine sorption values of oxidized fibers were lower up to 35% for cotton and up to 18% for lyocell than the original fibers.     

Novel alginates prepared by independent control of chain stiffness and distribution of G-residues: Structure and gelling properties

The study of alginate hydrogels is of increasing interest, given their potential applications as biomaterials for tissue engineering and for encapsulating drugs and living cells. In this study, we present a new strategy for tailoring alginates on the basis of homopolymeric mannuronan, where the chain stiffness and the content of G-residues could be varied independently. Partial periodate oxidation (0–8%) followed by borohydride reduction, introducing flexible linkages through C2–C3 cleavage and ring opening, was combined with in vitro epimerization, introducing either alternating (MG) sequences (in the case of enzyme AlgE4) or G-blocks (in the case of enzyme AlgE6). Both enzymes are recombinantly expressed from Azotobacter vinelandii. Two strategies were followed: (a) oxidation/reduction followed by epimerization (b) epimerization to 90% G followed by oxidation/reduction. The resulting alginates were characterised by NMR spectroscopy and size-exclusion chromatography (SEC) with multi angular laser light scattering (MALLS) and viscosity detectors. Gels were prepared using the ‘internal setting’ method with either 10 mM or 20 mM Ca²⁺ present, and studied by small-strain oscillatory measurements. It was found that periodate oxidation, in the range P₀ = 0.02–0.06, had a pronounced influence on the gelling properties. The decrease in dynamic storage modulus (G′) could mainly be attributed to increased local flexibility and not only a decrease in G-block lengths as a consequence of oxidation. The new alginate gels are easily degradable in a mild acidic environment and the degradation is easier to control than gels made of unoxidized alginate.     

Molecular structure and catechol oxidase activity of a new copper(I) complex with sterically crowded monodentate N-donor ligand

The attempted alkylation of 1,3-bis(2′-pyridylimino)isoindoline (indH) by the use of n-BuLi and subsequent alkyl halides led to quaternization of the pyridine nitrogens and the zwitterionic monodentate N-ligand (Me₂ind)I was formed. By the use of the ligand the copper(I) complex [Cu^I(Me₂ind)I₂] was prepared and its structure determined. It was found to be good catalyst for the oxidation of 3,5-di-tert-butylcatechol (DTBCH₂) to 3,5-di-tert-butyl-1,2-benzoquinone (DTBQ) and H₂O₂ by dioxygen. Detailed kinetic studies revealed first-order dependence on the catalyst and dioxygen concentration and saturation type behavior with respect to the substrate.     

Lipid droplets interact with mitochondria using SNAP23

Triglyceride-containing lipid droplets (LD) are dynamic organelles stored on demand in all cells. These droplets grow through a fusion process mediated by SNARE proteins, including SNAP23. The droplets have also been shown to be highly motile and interact with other cell organelles, including peroxisomes and the endoplasmic reticulum. We have used electron and confocal microscopy to demonstrate that LD form complexes with mitochondria in NIH 3T3 fibroblasts. Using an in vitro system of purified LD and mitochondria, we also show the formation of the LD-mitochondria complex, in which cytosolic factors are involved. Moreover, the presence of LD markers in mitochondria isolated by subcellular fractionations is demonstrated. Finally, ablation of SNAP23 using siRNA reduced complex formation and beta oxidation, which suggests that the LD-mitochondria complex is functional in the cell.     

The inhibition of mitochondrial metabolic activity in etiolated pea seedlings under water stress

In the present work, we studied the influence of water (osmotic) stress on mitochondrial metabolic activity in etiolated pea (Pisum sativum L.) seedlings. Three-day-old pea seedlings were subjected to stress by placing their roots in 0.6 M mannitol for 48 h. Epicotyl growth was severely suppressed, and tissue water content was decreased. We revealed the negative influence of the water stress on mitochondrial metabolic activity of seedlings, which effect was retained also after organelle isolation. In particular, in the mitochondria of stressed seedlings, the rate of oxidation of malate and other respiratory substrates (in state 3) was severely decreased, as well as respiratory control ratio. The rate of proline oxidation was reduced most seriously (by 70%). The efficiency of oxidative phosphorylation, according to the ADP/O ratio was not changed or was increased as compared to mitochondria in control plants. Activation of CN-resistant oxidase and other alternative pathways of electron transport in the mitochondrial electron-transport chain in stressed plants were not observed. In the epicotyl tissues under water stress, no MDA was accumulated and proline accumulation was insignificant. The role of mitochondria in adaptation responses of young seedlings is discussed.     

Responses from freshwater sediment during electricity generation using microbial fuel cells

In a two-electrode system, freshwater sediment was used as a fuel to examine the relationship between current generation and organic matter consumption with different types of electrode. Sediment microbial fuel cells using porous electrodes showed a superior performance in terms of generating current when compared with the use of non-porous electrodes. The maximum current densities with thicker and thin porous electrodes were 45.4 and 37.6 mA m⁻², respectively, whereas the value with non-porous electrodes was 13.9 mA m⁻². The amount of organic matter removed correlated with the current produced. The redox potential in the anode area under closed-circuit conditions was +246.3 ± 67.7 mV, while that under open-circuit conditions only reached −143.0 ± 7.18 mV. This suggests that an application of this system in organic-rich sediment could provide environmental benefits such as decreasing organic matter and prohibiting methane emission in conjunction with electricity production via an anaerobic oxidation process.     

Proteomic analysis of changes in mitochondrial protein expression during fruit senescence

Fruit senescence has been reported to be an oxidative phenomenon, but the detailed mechanisms by which ROS regulate this process remain largely unknown. Here we show that senescence process of apple fruit was concomitant with the dynamic alterations in the mitochondrial proteome. Mitochondrial proteins involved in tricarboxylic acid cycle, electron transport chain, carbon metabolism, and stress response were found to be differentially expressed during fruit senescence. Alleviating oxidative stress by lowering the ambient oxygen concentration noticeably decreased the number of changed proteins and delayed fruit senescence, indicating the involvement of ROS in this process. To further investigate the regulatory effect of ROS on senescence process, we analyzed the mitochondrial proteome variations upon exposure to high oxygen (100%), which induces oxidative stress and accelerates fruit senescence. High oxygen treatment led to a further identification of differentially expressed proteins such as mitochondrial manganese superoxide dismutase, an antioxidant scavenging superoxide radicals produced in the mitochondria. Activity of manganese superoxide dismutase was reduced after high oxygen exposure, accompanied by an increase in oxidative protein carbonylation (damaged proteins). These data suggest that ROS may regulate fruit senescence by changing expression profiles of specific mitochondrial proteins and impairing the biological function of these proteins.     

Modeling the noncovalent interactions at the metabolite binding site in purine riboswitches

We present gas phase quantum chemical studies on the metabolite binding interactions in two important purine riboswitches, the adenine and guanine riboswitches, at the B3LYP/6-31G(d,p) level of theory. In order to gain insights into the strucutral basis of their discriminative abilities of regulating gene expression, the structural properties and binding energies for the gas phase optimized geometries of the metabolite bound binding pocket are analyzed and compared with their respective crystal geometries. Kitaura-Morokuma analysis has been carried out to calculate and decompose the interaction energy into various components. NBO and AIM analysis has been carried out to understand the strength and nature of binding of the individual aptamer bases with their respective purine metabolites. The Y74 base, U in case of adenine riboswitch and C in case of guanine riboswitch constitutes the only differentiating element between the two binding pockets. As expected, with W:W cis G:C74 interaction contributing more than 50% of the total binding energy, the interaction energy for metabolite binding as calculated for guanine (-46.43 Kcal/mol) is nearly double compared to the corresponding value for that of adenine (-24.73 Kcal/mol) in the crystal context. Variations in the optimized geometries for different models and comparison of relative contribution to metabolite binding involving four conserved bases reveal the possible role of U47:U51 W:H trans pair in the conformational transition of the riboswitch from the metabolite free to metabolite bound state. Our results are also indicative of significant contributions from stacking and magnesium ion interactions toward cooperativity effects in metabolite recognition.     

圆柏属常绿木本植物叶片抗氧化系统季节变化与抗冷冻的关系

测定分析圆柏属2种常绿木本植物叶抗氧化系统在冷冻适应过程中的季节变化。结果表明,叶能在组织结冰状况下生存与其具备完善的抗氧化保护系统有关,该系统能及时清除氧自由基、抑制膜脂过氧化、维持膜的完整性;冷适应期积累的活性氧可能诱导了抗氧化保护系统使叶片获得抗冻性。祁连圆柏的抗氧化系统比圆柏在抗冻性诱导中具有更广泛的适应策略。