Aqueous (ET1) and alcoholic (ET2) extracts from Mactra veneriformis were studied for their antioxidant potentials using various in?vitro assays. The ET2 was fractioned into four parts according to the polarity of the extractive medium, viz. ET2-p (petroleum ether), ET2-e (ethyl acetate), ET2-n (n-butanol) and ET2-w (water). Among the four fractions, ET2-w showed the strongest reducing power, and highest 2,2 diphenyl-1-picrylhydrazyl (DPPH) scavenging and metal chelating activities, while the ET2-p possessed higher hydroxyl radical scavenging activities. It was found that ET2-w had large amounts of free amino acids and oligosaccharides, while ET2-p contained a large amount of unsaturated fatty acids. We conclude that amino acids, oligosaccharides and unsaturated fatty acids all contribute to the antioxidant activity of M. veneriformis. In order to elucidate the above, antioxidative components involved in the antioxidant activities were also detected. It was found that amino acids and carbohydrates were the major components of ET2-w. The amino acids were Tau (0.26%), Tyr (0.38%), Met (0.31%), Cys (0.38%), Arg (1.79%) and so on, while carbohydrates were oligosaccharides that were composed of disaccharides and trisaccharides. The unsaturated fatty acids were the major components of ET2-p, which contained a high amount of docosahexaenoic acid (9.03%) and eicosapentaenoic acid (18.49%). 相似文献
Eucalyptus cellulose is usually pre-treated by oxidation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), NaBr and NaClO at pH 10.5 and 25 °C before the mechanical process required to obtain cellulose nanofibers (CNFs). In this study, different aspects to improve the effectiveness and sustainability of the TEMPO-mediated oxidation are analyzed. The optimization was carried out at different reaction times by modifying both the concentration of the NaClO and the amount of the catalysts (TEMPO and NaBr). Results show that the carboxyl groups increased up to 1.1 mmol/g with 5 mmol NaClO/g after 50 min, and that the catalyst concentration can be reduced to 0.025 mmol TEMPO/g and 0.5 mmol NaBr/g to minimize costs while maintaining the high fibrillation degree of the CNFs. The kinetic of the reaction can be considered as zero-order with respect to NaClO, and as first order with respect to cellulose. As a result of this work, the catalyst doses are reduced up to 75% compared to the most widely used catalyst doses (0.1 mmol/g TEMPO and 1 mmol/g NaBr), obtaining highly fibrillated CNFs with a lower environmental impact. This reduction of catalyst doses will reduce the costs and facilitate the implementation of CNF production at industrial scale.
The reorientation of one small paramagnetic molecule (spin probe) in glassy polystyrene (PS) is studied by high-field electron paramagnetic resonance spectroscopy at two different Larmor frequencies (190 and 285 GHz). Two different regimes separated by a crossover region are evidenced. Below 180 K the rotational times are nearly temperature independent with no apparent distribution. In the temperature range of 180-220 K a large increase of the rotational mobility is observed with the widening of the distribution of correlation times which exhibits two components: (i) a deltalike, temperature-independent component representing the fraction of spin probes w which persist in the low-temperature dynamics; (ii) a strongly temperature-dependent component, to be described by a power distribution, representing the fraction of spin probes 1-w undergoing activated motion over an exponential distribution of barrier heights g(E). Above 180 K a steep decrease of w is evidenced. The shape and the width of g(E) do not differ from the reported ones for PS within the errors. For the first time the large increase of the rotational mobility of the spin probe at 180 K is ascribed to the onset of the fast dynamics detected by neutron scattering at T(f)=175+/-25 K. 相似文献
The effect of exogenous hydroxyl, carboxyl groups and/or Sn~(2+) on pyrolysis reactions of poly(L-lactide)(PLLA) was investigated by thermogravimetric analysis(TGA). The activation energy(E_a) of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose method. The kinetic models were also explored by the Malek method, and the random degradation behavior was determined by comparing the plots of ln{-ln[1-(1-w)~(0.5)]} versus 1/T for experimental data from TGA with model reactions. The pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65-70 mg·kg~(-1) but increased appreciably in the presence of extraneous Sn~(2+), ―COOH/Sn~(2+), or ―OH/Sn~(2+). The E_a values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn~(2+) in different chemical environments because Sn~(2+) can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups, which were different in steric hindrance for the formation of activated complex between Sn~(2+) and PLLA. Under the catalysis of Sn~(2+), a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains, and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of lactide. However, it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol~(-1). 相似文献
A novel 3D porous reduced graphene oxide/montmorillonite composite hydrogel (rGO–MMT) was prepared by solvent method, where the MMT nanosheets were homogenously dispersed in 3D rGO hydrogel. The porous 3D structure and the high dispersion of MMT nanosheets can promote the adsorption capacity. The effects of MMT content (wt%), the initial concentration of Cr(VI) solution (C0), pH value (pH0), the adsorption dose and temperatures on the adsorption capacity of rGO–MMT for Cr(VI) ions have been investigated. The optimum pH value for Cr(VI) adsorption is 2, and the adsorption capacity increases with MMT content and adsorption temperature. The rGO–MMT composite hydrogel displays the excellent adsorption property for both the heavy metal and organic pollutants. The adsorption capacity of rGO–MMT composite hydrogel is obviously higher than those of single rGO hydrogel and MMT due to the synergistic adsorption of rGO hydrogel and MMT. The adsorption of Cr(VI) ions on the rGO–MMT composite hydrogel follows linear pseudo-second-order kinetics, and the Langmuir model describes the adsorption process much better. Thermodynamic parameters indicate that adsorption is spontaneous, favorable and endothermic in nature.
In this work, a separation and purification process of U(VI), Zr(IV) and I2 from various fission products in nitric acid solution by 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][NTf2]) and dibutyl-3-(3-methylimidazolium)propylphosphoramide bis(trifluoromethanesulfonyl)imide-task specific ionic liquid (phosphoramide-TSIL) was investigated. The phosphoramide-TSIL was found to reduce ligand loss compared to dibutyl propylphosphoramidate by total organic carbon testing (TOC). The stripping of U(VI), Zr(IV) and I2 could be achieved by guanidine carbonate solution, oxalic acid solution and sodium hydroxide solution, respectively. The phosphoramide-TSIL/[C4mim][NTf2] showed good irradiation stability and recyclability. Phosphoramide-TSIL has the potential to be applied for separation and purification in the actual radioactive environment.
