The combination of resonance Raman, electron paramagnetic resonance and M?ssbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes. 相似文献
Hindered Amine Light Stabilizers (HALS), N-methylated and O-alkylhydroxylamine, were successfully anchored onto an ethylene-co-butyl acrylate (BA) by a transesterification reaction in the molten state. The content of HALS bonded to the EBA was calculated from the atomic ratio (N/C) determined by X-ray Photoelectron Spectroscopy (XPS). After reaction times of 5–30 min in the molten state the content of bonded HALS attained values from 0.17 to 0.63%. The modified EBA with HALS were studied by Chemiluminescence emission and the photostabilization effect was evaluated under accelerated ageing in the presence of pesticides. The antioxidant effect of HALS bonded to EBA was evaluated by determination of Carbonyl Index (CI) and retention of elongation at break as a function of exposure time and pesticide treatment. The stability of the EBA with anchored HALS exhibited higher performance as shown by low CI-values and correlated with the content of bound HALS and the thermal history of the materials. Also, mechanical properties correlated well with the CI results and the photostabilization of bound HALS was effective until 3150 h of exposure time using pesticides. 相似文献
The defect accumulation mechanism of amorphization has been studied for the La2Zr2O7 pyrochlore by means of classical molecular dynamic simulations. Present calculations show that the accumulation of cation Frenkel pairs is the main driving parameter for the amorphization process, while the oxygen atoms simply rearrange around cations. Under Frenkel pair accumulation, the structure follows the pyrochlore-fluorite-amorphous sequence. Present results consequently provide atomic-level interpretation to previous experimental irradiation observations of the two-step phase transition. 相似文献
We give an algorithm to determine a finite set of generators of the unit group of an order in a non-split classical quaternion algebra over an imaginary quadratic extension K of the rationals. We then apply this method to obtain a presentation for the unit group of . As a consequence a presentation is discovered for the orthogonal group . These results provide the first examples of a characterization of the unit group of some group rings that have an epimorphic image that is an order in a non-commutative division algebra that is not a totally definite quaternion algebra. 相似文献
The effect of iron and calcium stearates on the degradation of polyethylene (LDPE and LLDPE), under natural and artificial exposure, has been studied. The activity of stearates has been evaluated by chemiluminescence and FTIR of polyethylenes. The analysis of the molecular weight changes and content of degradation products identified by GC-MS during ageing process confirmed their pro-degrading activity. Films containing stearates exhibited lower CL emission, and revealed the higher efficiency of Fe-Stearate compared to Ca-Stearate in decomposing hydroperoxides, leading to higher degradation during processing. The results were confirmed by TGA analysis, where the weight loss onset and Tmax shifted to lower temperatures in polyethylenes with incorporation of Fe- and Ca-stearates compared to pure polymers.Polyethylenes were outdoor and accelerated exposed, and CL measured at different period of times. Chemiluminescence temperature-ramping tests under nitrogen showed the formation of a peroxide peak at lower temperature, and a significant increase in carbonyl index for PE containing stearates was found by FTIR. The results were supported by GC-MS, where the concentration of extracted products identified in the polyethylenes containing Fe-stearate was significant, and a much greater decrease in molecular weight was determined by GPC, which confirmed the development of degradation for polyethylenes with Fe-Stearates in comparison to pure or Ca-stearate polyethylenes. 相似文献
SEBS block copolymers were treated under mild conditions in an ozone atmosphere, producing very slightly chemically-modified surfaces. The thermal stability was analysed by chemiluminescence and related to morphological changes observed by AFM. The intrinsic thermal stability was diminished by ozone exposure, but the oxidation induction times were delayed which indicates an enhancement of thermal stability under oxidative conditions. Also, chemiluminescence analysis showed the presence of a typical order-disorder transition at temperatures around 120 °C. Two different sets of samples which showed different morphological patterns were imaged by AFM. The effects of micro-domain separation and inter-domain structure on thermal properties are discussed and explained by a coarsening of the internal interface induced by ozone. A detailed 2D Fourier transformed analysis of AFM images allowed us to identify a regular wrinkled nano-pattern induced by uniaxial strain combined with ozone treatment, offering new opportunities in applications ranging from organic electronics to bio-patterning. 相似文献
The incorporation of cyclodextrins (CDs) to nonviral cationic polymer vectors is very attractive due to recent studies that report a clear improvement of their cytocompatibility and transfection efficiency. However, a systematic study on the influence of the CD derivatization is still lacking. In this work, the relevance of β‐CD permethylation has been addressed by preparing and evaluating two series of copolymers of the cationic N‐ethyl pyrrolidine methacrylamide (EPA) and styrenic units bearing pendant hydroxylated and permethylated β‐CDs (HCDSt and MeCDSt, respectively). For both cell lines, CDs permethylation shows a strong influence on plasmid DNA complexation, “in vitro” cytocompatibility and transfection efficiency of the resulting copolymers over two murine cell lines. While the incorporation of the hydroxylated CD moiety increased the cytotoxicity of the copolymers in comparison with their homopolycationic counterpart, the permethylated copolymers have shown full cytocompatibility as well as superior transfection efficiency than the controls. This behavior has been related to the different chemical nature of both units and tentatively to a different distribution of units along the polymeric chains. Cellular internalization analysis with fluorescent copolymers supports this behavior.