| 1. |
- Guo, X. W., et al.
(författare)
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Effects of SiO2/Al2O3, MgO modification and hydrothermal treatment on the catalytic activity of HZSM-5 zeolites in the methylation of 4-methylbiphenyl with methanol
- 2004
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 261:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to study the effects Of SiO2/Al2O3 of HZSM-5, MgO modification and hydrothermal treatment on methylation of 4-methylbiphenyl (4-MBP) with methanol under fixed-bed down-flow conditions. The results show that, with an increase in the SiO2/Al2O3 of HZSM-5 (from 50 to 150, molar ratio), the selectivity to 4,4'-dimethylbiphenyl (4,4'-DMBP) increases from 25 to 79%. MgO modification also increases the selectivity to 4,4'-DMBP, but leads as well to low catalyst activity and rapid deactivation. Hydrothermal treatment not only increases the selectivity, but also improves the stability. When CBV1502 (SiO2/Al2O3 = 150) catalyst was hydrothermally treated at 500degreesC, the selectivity to 4,4'-DMBP increased to 85%. The selectivity to 4,4'-DMBP was further improved to about 90% by the increasing in the amount of mesitylene in the feed as solvent.
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| 2. |
- Guo, X. W., et al.
(författare)
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Methylation of 4-methylbiphenyl with methanol over metal oxide-modified HZSM-5 zeolite catalysts
- 2003
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Ingår i: Cuihuà xuébào. - 0253-9837 .- 1872-2067. ; 24:5, s. 333-337
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Tidskriftsartikel (refereegranskat)abstract
- A series of HZSM-5 zeolite catalysts modifed with metal oxides (MgO, CaO, SrO, BaO, ZnO, La2O3 and CeO2) were prepared by impregnation method and characterized by XRD, TPD and N-2-adsorption. Methylation of 4-methylbiphenyl (4-MBP) with methanol to 4,4'-dimethylbiphenyl (4,4'-DMBP) was carried out over the prepared catalysts under fixed-bed down-flow conditions. The results showed that the MgO-modified HZSM-5 can significantly improve the selectivity for target product 4,4'-DMBP (up to 80 % vs only 13 % over the parent HZSM-5). The effects of metal oxides on 4,4'-DMBP selectivity are arranged in the following order: MgO>SrOapproximate toZnOapproximate toCaOapproximate toLa(2)O(3)>BaO>CeO2. The effects of MgO contents, precursor-salt types, and loading methods were further investigated, and the results revealed that during 4-MBP conversion, proper MgO loading (5.6 %) can be more effective, and the ion-exchange methed is much better than the impregnation method. However, it is difficult to get higher metal oxide loading by using the ion-exchange method. The high selectivity over HZSM-5 modified with MgO largely results from the depression of 4,4-DMBP second reactions such as isomerization, dealkylation and alkylation, as demonstrated by the reaction of 4,4'-DMBP as reactant over MgO/ZSM-5 catalyst and HZSM-5 zeolite.
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| 3. |
- Guo, X. W., et al.
(författare)
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Shape-selective methylation of 4-methylbiphenyl to 4,4 '-dimethylbiphenyl over zeolite HZSM-5 modified with metal oxides of MgO, CaO, SrO, BaO, and ZnO
- 2003
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Ingår i: Catalysis Letters. - 1011-372X .- 1572-879X. ; 87:02-jan, s. 25-29
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Tidskriftsartikel (refereegranskat)abstract
- A series of ZSM-5 samples modified with metal oxides MO(M = Mg, Ca, Sr, Ba and Zn) were employed for the alkylation of 4-methylbiphenyl (4-MBP) with methanol to 4,4'-dimethylbiphenyl (4,4'-DMBP) under fixed-bed down-flow conditions. The methylation results showed that the use of basic metal oxides can effectively enhance the selectivity to the target product 4,4'-DMBP. MgO is the most effective modifier among the metal oxides used and it can improve selectivity to 4,4'-DMBP up to 80% as compared to only 13% over the parent zeolite HZSM-5. The modi. cation effectiveness of metal oxides on 4,4'-DMBP selectivity can be arranged in the order MgO> SrO similar to ZnO similar to CaO> BaO. The optimization of MgO modi. cation through the content, salt types and loading methods revealed that proper MgO loading (5.6 wt%) can be more effective, and the impregnation method is much better than ion exchange. The correlation of physicochemical properties (TPD, TGA, chemical analysis and chemical adsorption, etc.) of the modified HZSM-5 with the catalytic data showed that the high selectivity over ZSM-5 modified with MgO largely results from the effective suppression of 4,4'-DMBP secondary reactions such as isomerization, dealkylation and alkylation.
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| 4. |
- Lee, W. N., et al.
(författare)
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Metabolic sensitivity of pancreatic tumour cell apoptosis to glycogen phosphorylase inhibitor treatment
- 2004
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Ingår i: Br J Cancer. - 0007-0920. ; 91:12, s. 2094-100
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Tidskriftsartikel (refereegranskat)abstract
- Inhibitors of glycogen breakdown regulate glucose homeostasis by limiting glucose production in diabetes. Here we demonstrate that restrained glycogen breakdown also inhibits cancer cell proliferation and induces apoptosis through limiting glucose oxidation, as well as nucleic acid and de novo fatty acid synthesis. Increasing doses (50-100 microM) of the glycogen phosphorylase inhibitor CP-320626 inhibited [1,2-(13)C(2)]glucose stable isotope substrate re-distribution among glycolysis, pentose and de novo fatty acid synthesis in MIA pancreatic adenocarcinoma cells. Limited oxidative pentose-phosphate synthesis, glucose contribution to acetyl CoA and de novo fatty acid synthesis closely correlated with decreased cell proliferation. The stable isotope-based dynamic metabolic profile of MIA cells indicated a significant dose-dependent decrease in macromolecule synthesis, which was detected at lower drug doses and before the appearance of apoptosis markers. Normal fibroblasts (CRL-1501) did not show morphological or metabolic signs of apoptosis likely due to their slow rate of growth and metabolic activity. This indicates that limiting carbon re-cycling and rapid substrate mobilisation from glycogen may be an effective and selective target site for new drug development in rapidly dividing cancer cells. In conclusion, pancreatic cancer cell growth arrest and death are closely associated with a characteristic decrease in glycogen breakdown and glucose carbon re-distribution towards RNA/DNA and fatty acids during CP-320626 treatment.
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| 5. |
- Wang, W, et al.
(författare)
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Stimulatory activity of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptors.
- 2000
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Ingår i: Chinese medical journal. - 0366-6999. ; 113:10, s. 867-71
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To study the activity of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptors on cAMP production and inward calcium currents (Ica) in guinea pig ventricular myocytes. A comparison was also made with those of a muscarinic receptor agonist. METHODS: cAMP content was determined by radioimmunoassay and the Ica in guinea pig single ventricular cells were recorded by the whole-cell patch clamp technique. RESULTS: Both the muscarinic receptor agonist, carbachol (Carb 10 mumol/L), and anti-peptide antibodies (Abs 100 nmol/L) could decrease basal cAMP levels (by 46.9% +/- 4.2% and 60.2% +/- 4.6%, respectively) and basal Ica. Both Carb (10 mumol/L) and Abs (100 nmol/L) could also inhibit the isoprenaline-induced (Iso 0.8 mumol/L) increases in cAMP production (from 108.2 +/- 7.0 to 88.4 +/- 7.2 pmol/mg.protein/min for Carb and 88.6 +/- 5.1 pmol/mg.protein/min for Abs, respectively) and the increases in Ica. The muscarinic receptor antagonist atropine (Atr) was able to prevent these effects of Carb and Abs. CONCLUSIONS: Anti-peptide antibodies against an epitope located in the second extracellular loop of human M2 muscarinic receptors, similar to muscarinic receptor agonist, could decrease the basal Ica and beta-receptor agonist stimulated increase of Ica by decreasing the basal and beta-receptor agonist stimulated increase of cAMP production, and therefore could have an effect on their target receptor. These results further suggest that autoimmunity may participate in the pathogenesis of human cardiomyopathy and the second extracellular loop of human M2 muscarinic receptor could be the main immunodominant region.
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| 6. |
- Zheng, W.T., et al.
(författare)
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Chemical bonding in carbon nitride films studied by X-ray spectroscopies
- 2001
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Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:9-10, s. 1897-1900
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride films are deposited using dc magnetron sputtering in a N2 discharge. The nature of chemical bonding of the films is investigated using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and X-ray emission spectroscopy. X-Ray photoelectron spectroscopy spectra show that N1s binding states depend on substrate temperature, in which two pronounced peaks can be observed. The near edge X-ray absorption fine structure at C1s and N1s exhibits a similar absorption profile in the p* resonance region, but the s* resonance is sharper in the N1s spectra. Resonant N K-emission spectra show a strong dependence on excitation photo energies. Compared XPS N1s spectra with recent theoretical calculations by Johansson and Stafstrom, two main nitrogen sites are assigned in which N bound to sp3 hybridized C and sp2 hybridized C, respectively. The correlation of X-ray photoelectron, X-ray absorption, and X-ray emission spectra for N in carbon nitride films is also discussed. © 2001 Elsevier Science B.V. All rights reserved.
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