共查询到20条相似文献,搜索用时 31 毫秒
1.
Eight hemicellulosic fractions were obtained by sequential treatment of dewaxed barley straw with 0.1 M NaOH at 45 °C for 3 h, 0.25, 0.5, 1.0, 1.5, 2.0, and 3.0% H 2O 2 at 45 °C for 3 h at pH 11.5, and 10% KOH–1% Na 2B 4O 7·10H 2O at 28 °C for 15 h under continuous agitation. The yields of the fractions were 8.0, 3.1, 3.3, 3.3, 2.2, 2.0, 2.0, and 9.9%, respectively, of the initial amount of barley straw, corresponding to the dissolution of 21.6, 8.4, 8.9, 8.9, 5.9, 5.4, 5.4, and 26.7% of the original hemicelluloses. Meanwhile, the successive treatment also solubilized 29.1, 15.8, 14.6, 10.8, 4.5, 3.2, 2.7, and 3.7% of the original lignin, respectively. This sequential extraction together resulted in dissolution of 91.1% of the original hemicelluloses and 84.8% of the original lignin. The 0.1 M NaOH-soluble hemicellulosic fraction contained mainly xylose, glucose, and arabinose, 44.2, 15.7, and 15.2%, respectively, while the 10% KOH–1% Na 2B 4O 7·10H 2O-soluble fraction predominated in xylose, 75.0%. The six alkaline peroxide-soluble fractions were composed of 50.3–54.4% xylose, 14.7–16.9% arabinose, 6.8–10.7% glucose, 6.8–8.5% glucuronic acid or 4- O-methyl-
-glucuronic acid, 0.4–1.5% mannose, and 0.3–1.2% rhamnose. All the hemicellulosic fractions contained substantial amounts of glucuronoarabinoxylans and noticeable quantities of β-glucans. In comparison, the six hemicellulosic fractions, isolated with alkaline peroxide, had much higher molecular weights (56,890–63,810 g mol −1) than those of the two hemicellulosic preparations (28,000–29,080 g mol −1), isolated with alkali in the absence of hydrogen peroxide. The thermal stability of the hemicelluloses increased with an increment of their molar mass. 相似文献
2.
人类活动显著增加了氮沉降,对森林生态系统产生了不同程度的影响;凋落物在其分解过程中输入的大量有机碳、氮也会影响土壤碳氮的形成、稳定及转化.本研究选择亚热带常绿阔叶林,对样地进行8年氮添加[对照(0)、低氮(75 kg·hm -2·a -1)、高氮(150 kg·hm -2·a -1)]和控制凋落物处理(保留凋落物、去除凋落物),之后采集土壤样品,通过K 2SO 4、Na 2B 4O 7、Na 4P 2O 7、NaOH、H 2SO 4、Na 2S 2O 4、HF等化学试剂逐级浸提土壤,测定各浸提液和残渣中的碳、氮含量,研究凋落物及氮添加对土壤矿物结合态碳、氮的影响.结果表明: 整体上,胡敏素(humin,H)组分的土壤碳、氮含量均为最高,分别占土壤全量的33.5%和33.3%.Na 2B 4O 7溶液提取的土壤可溶性碳、氮含量最高,其次是NaOH和Na 4P 2O 7溶液,3种试剂提取的土壤可溶性总碳、可溶性总氮以及可溶性有机氮分别占提取总量的46.2%、47.9%和76.5%.与对照相比,氮添加增加了Na 2S 2O 4和H组分碳、氮含量;与保留凋落物比较,去除凋落物降低了Na 2B 4O 7、H 2SO 4、Na 2S 2O 4和H组分的碳含量,以及NaOH、HF和H组分的氮含量.保留凋落物和氮添加显著增加了K 2SO 4组分氮含量.可见,保留凋落物和外源氮通过影响化学稳定性不同的土壤组分的碳氮变化来改变土壤碳氮过程. 相似文献
3.
A new mild alkaline/oxidative pretreatment of wheat straw prior to enzymic hydrolysis was carried out. It consists of a first alkaline (1% NaOH for 24 h) step, which mainly solubilises hemicellullose and renders the material more accessible to further chemical attack, and a second alkaline/oxidative step (1% NaOH and 0·3% H 2O 2 for 24 h), which solubilises and oxidises lignin to minor polluting compounds. The entire process was carried out at low temperature (25–40°C) using a low concentration of chemicals, resulting in a relatively low cost and waste liquors containing only trace amounts of dangerous pollutants derived from lignin. Recovery of cellulose after the double pretreatment reached 90% of that contained in the starting material, with a concomitant 81% degradation of lignin. The action of a commercial cellulase on the cellulose obtained produced a syrup with a high concentration of reducing sugars (220 mg/ml), of which a large percentage was glucose. 相似文献
4.
Three fractions containing hemicellulosic material were obtained by sequential extraction of barley residue (left after removal of water-extractable polysaccharides) with saturated barium hydroxide [Ba(OH) 2 fraction], distilled water [ Ba( OH) 2/ H2O fraction], and 1 m sodium hydroxide [NaOH fraction]. The yields of the fractions were 1.6, 1.7, and 2.6% (w/w), respectively, of the dry barley grist. The Ba(OH) 2 fraction contained mainly arabinose and xylose, 35.8% and 60.9%, respectively. The Ba( OH) 2/ H2O fraction in addition to 26.7% Ara and 36.6% Xyl contained also 34.8% Glc. The NaOH fraction was composed of 14.2% Ara, 44.0% Xyl, and 40.9% Glc. The Ba( OH) 2/ H2O and NaOH extracts were further fractionated by stepwise (NH 4) 2SO 4 precipitation into several subfractions with varying amounts of β-glucans and arabinoxylans. β-Glucans in Ba( OH) 2/ H2O and NaOH fractions were characterized by high ratios of β-(1→4)/β-(1→3) linkages, large amounts of contiguously linked β-(1→4) segments, and high ratios of cellotriosyl/cellotetraosyl units. The alkali-extractable arabinoxylans, especially those NaOH-extractable, were characterized by a very low degree of substitution, high xylose/arabinose ratio, and a small content of doubly substituted xylose residues. Some populations of arabinoxylans displayed structural features that would enable them to self-associate or to interact with β-glucans. 相似文献
5.
In this study, Ecklonia cava was enzymatically hydrolyzed to prepare water-soluble extracts, using five carbohydrases (Viscozyme, Celluclast, AMG, Termamyl, and Ultaraflo) and five proteases (Protamex, Kojizyme, Neutase, Flavourzyme, and Alcalase), and the potential antioxidant activity of each was assessed. The Celluclast and Viscozyme extracts of E. cava evidenced good hydrogen peroxide (H 2O 2) scavenging activities (73.25% and 72.92%, respectively) as compared to those of other enzymatic extracts. Therefore, the Celluclast enzymatic extract was selected for use in further experiments, and separated into four different molecular weight fractions (<1, 1–10, 10–30 and >30 kDa). Among these fractions, the >30 kDa fraction manifested the most profound H 2O 2 scavenging activity, with a measured IC 50 of 13 μg/ml. The >30 kDa fraction also strongly enhanced cell viability against H 2O 2-induced oxidative damage, and evidenced relatively good lipid peroxidation inhibitory activity in a Chinese hamster lung fibroblast (V79-4) cell line. This fraction also effected a reduction in the proportion of cells undergoing H 2O 2-induced apoptosis, as was demonstrated by a decreased quantity of sub-G 1 hypodiploid cells and decreased apoptotic body formation on the flow cytometry assay. These results clearly indicate that the >30 kDa fraction of E. cava possesses good antioxidant activity against H 2O 2 mediated cell damage in vitro. 相似文献
6.
β-Amyloid peptide (Aβ) 1–42, involved in the pathogenesis of Alzheimer’s disease, binds copper ions to form Aβ · Cu n complexes that are able to generate H 2O 2 in the presence of a reductant and O 2. The production of H 2O 2 can be stopped with chelators. More reactive than H 2O 2 itself, hydroxyl radicals HO (generated when a reduced redox active metal complex interacts with H 2O 2) are also probably involved in the oxidative stress that creates brain damage during the disease. We report in the present work a method to monitor the effect of chelating agents on the production of hydrogen peroxide by metallo-amyloid peptides. The addition of H 2O 2 associated to a pre-incubation step between ascorbate and Aβ · Cu n allows to study the formation of H 2O 2 but also, at the same time, its transformation by the copper complexes. Aβ · Cu n peptides produce but do not efficiently degrade H 2O 2. The reported analytic method, associated to precipitation experiments of copper-containing amyloid peptides, allows to study the inhibition of H 2O 2 production by chelators. The action of a ligand such as EDTA is probably due to the removal of the copper ions from Aβ · Cu n, whereas bidentate ligands such as 8-hydroxyquinolines probably act via the formation of ternary complexes with Aβ · Cu n. The redox activity of these bidentate ligands can be modulated by the incorporation or the modification of substituents on the quinoline heterocycle. 相似文献
7.
The effect of a range of iron chelates on the cytotoxicity of H 2O 2 was studied on a mammalian epithelial cell line. Iron complexes which were internalised enhanced the cytotoxicity of H 2O 2 measured by delayed thymidine incorporation. Iron complexed to 8-hydroxyquinoline (Fe/8-HQ) potentiated the cytotoxicity of 50 µM by 38% and Fe/dextran by 23%. Pre-exposure of cells to Fe/dextran at 4°C did not result in any potentiation of H 2O 2-induced cytotoxicity which we ascribe to failure of the Fe/dextran to be endocytosed at low temperature. Iron complexes which are slowly taken up or remain extracellular protected the cells from H 2O 2-induced cytotoxicity. Thus, Fe/EDTA inhibited the cytotoxicity of 50 µM H 2O 2 by 33%; Fe/ADP by 80% and Fe/ATP by 88%, suggesting mutual extracellular detoxification. 相似文献
8.
1. Single reduced methyl viologen (MV .+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ max 600 nm; MV .+, = 1.3 · 10 4 M −1 · cm −1; oxidised form of methyl viologen (MV 2+), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques. 2. A convenient electrochemical preparation of large amounts of MV.+ has been developed. 3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity. 4. The reaction of MV.+ with O2 produced H2O2 (k > 5 · 106 M−1 · s−1, pH 7.5, 25 °C). H2O2 subsequently reacted with excess MV.+ (k = 2.3 · 103 M−1 · s−1, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations. 5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H2O2 (or radicals derived from H2O2) induced damage of plant cell membrane. 相似文献
9.
Two new multi-cobalt-containing polyoxotungstates K 4Na 6Co 2(H 2O) 12{Co(H 2O) 4[Co 2(H 2O) 10Co 4(H 2O) 2( B--SiW 9O 34) 2] 2} · 40H 2O (1) and K 10Na 2[Co 4(H 2O) 2(GeW 9O 34) 2] · 20H 2O (2) have been obtained by the routine synthetic reactions in aqueous solution. The polyoxoanion framework of 1 consists of two sandwich-type polyoxoanions [Co 4(H 2O) 2( B--SiW 9O 34) 2] 12− connected together by a [CoO 2(H 2O) 4] cluster to constitute the sandwich dimer, and then, four isolated Co(H 2O) 5 cations coordinate to the dimer through four μ2-O atoms. The polyoxoanion 2 is isomorphic to the sandwich-type polyoxoanion [Co 4(H 2O) 2( B--SiW 9O 34) 2] 12− in 1. The magnetic property of compound 1 has been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0 K, indicating the existence of intramolecular ferromagnetic Co–Co interactions, and, the electrochemical properties of 1 and 2 are detected in the pH 4 buffer solution. 相似文献
10.
The present work analyzes the activity in decomposition of H 2O 2 using magnetite-immobilized catalase. The support of catalase is a glutaraldehyde-treated magnetite (Fe 3O 4). The data obtained in the H 2O 2 decomposition are analyzed. The fitting of the initial rate of the H 2O 2 decomposition versus hydrogen peroxide concentration data is discussed using a specific program for enzyme kinetics modeling (Leonora). The free catalase from Aspergillus niger (3.5 or 10 U/mL) does not show substrate inactivation up to 0.4 M H 2O 2. The immobilized catalase at low catalyst concentration shows substrate inhibition. Using 1 mg/mL of supported catalase the predicted maximum activity is higher than in the case of the free catalase at similar catalase concentration, although the optimum temperature is lower (40 °C versus 60 °C). 相似文献
11.
The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H 2L and Ln(NO 3) 3 · 6H 2O give rise to three mononuclear lanthanide complexes Ln(H 2L)(NO 3) 3 [H 2L = N, N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N, N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O 2O 2 set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac) 2 · H 2O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO 3) 3 · H 2O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N 2O 2 cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes. 相似文献
12.
For staining in toto, planarians are fixed in a mixture of 10 ml of commercial formalin, 45 ml of 95% ethanol and 2 ml of glacial acetic acid. After treatment with 70% ethanol 3-10 days, they are washed in distilled water and immersed in 10% CuSO 4. 5H 2O for 3 hr at 50° C, transferred without washing to 1% AgNO 3 for 1.0-1.5 hr at 50° C; and then developed in: 10 ml of 1% pyrogallol, 100 ml of 56% ethanol and 1 ml of 0.2% nitric acid. Gold toning, 5% Na 2S 2O 3 and dehydration follow as usual. For staining sections, material is fixed in the same fixative, embedded in paraffin and sectioned at 10 μ. After bringing sections to water, they are immersed in 20% CuSO 4. 5H 2O for 48 hr at 37° C; then rinsed briefly in distilled water and placed in 7% AgNO 3 for 24 hr at 37° C. They are washed briefly in distilled water and reduced in: hydroquincne, 1 gm; Na 2SO 3, 5 gm and distilled water 100 ml. Gold toning, followed by 5% Na 2S 2O 3 and dehydration completes the process. Any counterstaining may follow. 相似文献
13.
The action of K 2Cr 2O 7, Ag 2O, KMnO 4, HgO and NaIO 3 in polychroming methylene blue is explored. The last two have no action in neutral or acid methylene blue solutions. With the other three reagents the amount of polychroming, as measured by the shift in the absorption spectrum, is roughly proportional to the amount of oxidant used. Various lots of methylene blue produce similar products with similar proportions of K 2Cr 2O 7. With similar quantities of this reagent similar products are produced by polychroming at 100°, 80°, 70° or 60° C. At 100° C. the action of K 2Cr 2O 7 or of Ag 2O appears to be completed in 15 minutes. In K 2Cr 2O 7 polychroming, H 2SO 4 can be substituted for HCl, and subsequent BaCO 3 neutralization removes the salts formed and prevents accidental alkali polychroming. K 2Cr 2O 7 polychroming produces products with narrower absorption bands than alkali polychroming. 相似文献
14.
Hydrogen peroxide activation of MMb with and without the presence of BSA gave rise to rapid formation of hyper-valent myoglobin species, myoglobin ferryl radical (·MbFe(IV)=O) and/or ferrylmyoglobin (MbFe(IV)=O). Reduction of MbFe(IV)=O showed first-order kinetics for a 1-2 times stoichiometric excess of H 2O 2 to MMb while a 3-10 times stoichiometric excess of H 2O 2 resulted in a biphasic reaction pattern. Radical species formed in the reaction between MMb, H 2O 2 and BSA were influenced by [H 2O 2] as measured by electron spin resonance (ESR) spectroscopy and resulted in the formation of cross-linking between BSA and myoglobin which was confirmed by SDS-PAGE and subsequent amino acid sequencing. Moreover, dityrosine was formed in the initial phases of the reaction for all concentrations of H 2O 2. However, initially formed dityrosine was subsequently utilized in reactions employing stoichiometric excess of H 2O 2 to MMb. The observed breakdown of dityrosine was ascribed to additional radical species formed from the interaction between H 2O 2 and the hyper-valent iron-center of H 2O 2-activated MMb. 相似文献
15.
Trypanosoma cruzi trypanothione reductase (TR) was irreversibly inhibited by peroxidase/H 2O 2/phenothiazine (PTZ) systems. TR inactivation depended on (a) time of incubation with the phenothiazine system; (b) the peroxidase nature and (c) the PTZ structure and concentration. With the most effective systems, TR inactivation kinetics were biphasic, with a relatively fast initial phase during which about 75% of the enzyme activity was lost, followed by a slower phase leading to total enzyme inactivation. GSH prevented TR inactivation by the peroxidase/H 2O 2/PTZ +· systems. Production of PTZ +· cation radicals by PTZ peroxidation was essential for TR inactivation. Horseradish peroxidase, leukocyte myeloperoxidase (MPO) and the pseudo-peroxidase myoglobin (Mb) were effective catalysts of PTZ +· production. Promazine, thioridazine, chlorpromazine, propionylpromazine prochlorperazine, perphenazine and trimeprazine were effective constituents of the HRP/H 2O 2/PTZ system. The presence of substituents at the PTZ nucleus position 2 exerted significant influence on PTZ activity, as shown by the different effects of 2-trifluoromethyl and 2-H or 2-chlorophenothiazines. The PTZ +· cation radicals disproportionation regenerated the non-radical PTZ molecule and produced the PTZ sulfoxide that was inactive on TR. Thiol compounds including GSH interacted with PTZ +· cation radicals transferring an electron from the sulfide anion to the PTZ +·, thus nullifying the PTZ +· biological and chemical activities. 相似文献
16.
Two compounds, [Eu(H 2O) 7][Al(OH) 6Mo 6O 18] · 4H 2O (1) and {(C 2H 5NO 2) 2[Eu(H 2O) 5]}[Al(OH) 6Mo 6O 18] · 10H 2O (2), have been synthesized by conventional solution method and determined by single-crystal X-ray diffraction. Compound 1 shows a 1D chain structure built up of alternating Anderson-type polyanions [Al(OH) 6Mo 6O 18] 3− and hydrated rare-earth ions Eu 3+. Compound 2 displays a 3D supramolecular network structure containing 1D sandglass-like channels along c axis, which were occupied by repetitive array of (H 2O) 8 clusters. Extensive hydrogen bonds play an important role in the formation of the 3D structures of 1 and 2. Luminescence measurements reveal that 1 and 2 exhibit intense red and orange fluorescent emission at room temperature, respectively. Origin of the distinct emission can be assigned to the different site symmetries of Eu 3+ centers in the two compounds. These results are consistent with the crystal structures of the two compounds. 相似文献
17.
The hydrothermal reactions of (Ph 4P)[VO 2Cl 2] and H 2C 2O 4 at 150 and 125°C yield (Ph 4P) 2[V 2O 2(H 2O) 2(C 2O 4) 3]·4H 2O (1) and (Ph 4P)[VOCl(C 2O 4)] (2), respectively. The structure of the molecular anion of 1 consists of a binuclear unit of oxovanadium(IV) octahedra bridged by a bisbidentate oxalate group. The VO 6 coordination geometry at each vanadium site is defined by a terminal oxo group, an aquo ligand, and four oxygen donors — two from the bisbidentate bridging oxalate and two from the terminal bidentate oxalate. The structure of 2 consists of discrete Ph 4P + cations occupying regions between [VOCl(C 2O 4)] −∞ spiral chains. The structure of the one-dimensional anionic chain exhibits V(IV) octahedra bridged by bisbidentate oxalate groups. Crystal data: 1·4H 2O, monoclinic P2 1/ n, A = 12.694(3), B = 12.531(3), C = 17.17(3) Å, β = 106.32(2)°, V = 2621.3(13) Å 3, Z = 2, Dcalc = 1.501 g cm −3, structure solution and refinement converged at a conventional residual of 0.0518; 2, tetragonal P4 3, A = 12.145(2), C = 15.991(3) Å, V = 2358.7(12) Å 3, Z = 4, R = 0.0452. 相似文献
18.
The aqueous chemistry of vanadium with physiologically relevant ligands constitutes a subject of burgeoning research, extending from bacterial metalloenzymic functions to human-health physiology. Vanadium, in the form of VCl 3 and V 2O 5, reacted expediently with citric acid, in a 1:2 molar ratio in water at pH4, and, in the presence of various cations, afforded crystalline materials bearing the general formula (Cat) 2[V 2O 4(C 6H 6O 7) 2]· nH 2O (A) (Cat +=Na +, NH 4 +, n=2; Me 4N +, K +, n=4). Exploration of the reactivity of A toward H 2O 2 yielded the peroxo-containing complexes (Cat) 2[V 2O 2(O 2) 2(C 6H 6O 7) 2]·2H 2O (B) (Cat +=K +, NH 4 +). Both classes of compounds were characterized analytically and spectroscopically. The X-ray structures of complexes A and B emphasize the exceptional stability of the dimeric rhombic unit V V 2O 2, which is retained upon H 2O 2 reaction, and the preserved mode of coordination of the citrate ligand as a doubly deprotonated moiety. In these complexes, typical six and eight coordination numbers were observed for the Na + and K + counter-ions, respectively. The variety of synthetic approaches leading to A, along with the stepwise and direct assembly and isolation of peroxo-compounds (B), denotes the significance of reaction pathways and intermediates in vanadium(III–V)–citrate synthetic chemistry. Hence, a systematic investigation of reactivity modes in aqueous vanadium–citrate systems emerges as a crucial tool for the establishment of chemical interconnectivity among low MW complex species, potentially participating in the intricate biodistribution of that metal ion in biological fluids. 相似文献
19.
The reaction of H 2[PtCl 6] · 6H 2O and (H 3O)[PtCl 5(H 2O)] · 2(18C6) · 6H 2O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH) 2[PtCl 6] · 2H 2O (1).The same compound was obtained from the reaction of Na 2[PtCl 6] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H 3O)[PtCl 5(H 2O)] · 2(18C6) · 6H 2O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl 5(GuaH)] · 1.5(18C6) · H 2O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl 3(GuaH)] · (18C6) · 2Me 2CO (3).H 2[PtCl 6] · 6H 2O and guanosine was found to react in water, yielding (GuoH) 2[PtCl 6] (4) and in ethanol at 50 °C, yielding [PtCl 5(GuoH)] · 3H 2O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl 5(DMSO)] −.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H 2[PtCl 6] · 6H 2O and(H 3O)[PtCl 5(H 2O)] · 2(18C6) · 6H 2O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH) 2[PtCl 6] · 2H 2O (6) and (CydH) 2[PtCl 6] (7), respectively. Identities of all complexes were confirmed by 1H, 13C and 195Pt NMR spectroscopic investigations, revealing coordination of GuoH + in complex 5 through N7 whereas GuaH + in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH +) 2, whereas in complex 6 non-base-paired MeCytH + cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules. 相似文献
20.
Trehalose is known to protect membranes and macromolecules. Its accumulation has been implicated in allowing plants to tolerate stress, including heat-shock. However, under heat-shock, it is not clear whether trehalose eliminates reactive oxygen species (ROS) directly or indirectly by protecting antioxidant enzymes. In this study, we initially examined the effects of trehalose on the activities of key antioxidant enzymes, including superoxide dismutases (SODs), ascorbate catalases (CATs), and ascorbate peroxidases (APX) from wheat ( Triticum aestivum L.), and then measured the ability of trehalose to scavenge hydrogen peroxide (H 2O 2) and superoxide anions (O 2−). Our results indicated that trehalose protected SOD activity slightly. However, it inhibited CAT and APX activities under heat stress, with a little protection of CAT activity (only about 7% promotion) at 22 °C. Moreover, trehalose scavenged H 2O 2 and O 2− greatly in a concentration-dependent manner, reaching the maximal scavenging H 2O 2 rate of 95% and O 2− rate of 78%, respectively, at 50 mM trehalose. These results suggest that trehalose plays a direct role in eliminating H 2O 2 and O 2− in wheat under heat stress. 相似文献
|