排序方式: 共有20条查询结果,搜索用时 15 毫秒
1.
Thawatchai Tuntulani Praput Thavornyutikarn Sirilux Poompradub Nongnuj Jaiboon Vithaya Ruangpornvisuti Narongsak Chaichit Zouhair Asfari Jacques Vicens 《Tetrahedron》2002,58(52):10277-10285
Tripodal aza crown ether calix[4]arenes, 5a, 5b, 6a and 6b, have been synthesized. The structure of protonated 5a was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of 5a and 5b towards anions using Na+ as countercation were carried out by 1H NMR titration in dimethylsulfoxide-d6 and the mixture of chloroform-d and methanol-d4, respectively. Ligands 5a and 5b were able to form 1:1 complexes with Br−, I− and NO3− and the complexation stability varied as follows: NO3−>I−>Br−. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of 5a towards Br− in the presence of various cations varied as K+>Bu4N+>Na+. The enhancement in anion complexation ability of 5a may result from the rearrangement of the tripodal ammonium unit in the presence of K+. The neutral forms, 6a and 6b, were able to form complexes with transition metal ions such as Co2+, Ni2+, Cu2+ and Zn2+. The stability of the complexes followed the sequence: Ni2+2+Cu2+Zn2+. Compounds 6a and 6b may, therefore, potentially be used as either transition metal ion or anion receptors that can be controlled by pH of the solution. 相似文献
2.
3.
Sophon Roegsumran Nongnuj Jaiboon Narongsak Chaichit Damrong Sommit Duangpen Pattamadilok Chaiyo Chaichantipyuth Amorn Petsom 《Journal of chemical crystallography》2002,32(12):511-517
Two labdane diterpenoids, labda-7,12(E),14-triene-17-oic acid (1) and labda-12(Z),14,17-triene-18-oic acid (2), C20H30O2, have been isolated from Croton oblongifolius. Both 1 and 2 crystallized in the monoclinic system, space group C2, with cell dimensions of a = 21.912(1) Å, b = 7.4002(4) Å, c = 11.5079(7) Å, = 101.999(1)o and a = 21.308(2) Å, b = 11.9067(9) Å, c = 7.5606(6) Å, = 100.763(1)o, respectively. Compound 1, a rare example of carboxylic group bound to a cyclohexene ring, forms an infinite intermolecular hydrogen-bonded polymer [O1 O2(–x + 1/2, y + 1/2, –z + 2) 2.697(2) Å], whereas molecules of compound 2 are linked to form an asymmetric hydrogen-bonded dimer [O1 O2(–x, y, –z) 2.657(3) Å]. 相似文献
4.
The purpose of this paper is to investigate the problem of finding the common element of the set of common fixed points of a countable family of nonexpansive mappings, the set of an equilibrium problem and the set of solutions of the variational inequality prob- lem for a relaxed cocoercive and Lipschitz continuous mapping in Hilbert spaces. Then, we show that the sequence converges strongly to a common element of the above three sets under some parameter controlling conditions, which are connected with Yao, Liou, Yao[17], Takahashi[12] and many others. 相似文献
5.
Nongnuch Rueangjitt Chalermrat Akarawitoo Sumaeth Chavadej 《Plasma Chemistry and Plasma Processing》2012,32(3):583-596
The aim of this research work was to evaluate the possibility of upgrading the simulated biogas (70?% CH4 and 30?% CO2) for hydrogen-rich syngas production using a multi-stage AC gliding arc system. The results showed that increasing stage number of plasma reactors, applied voltage and electrode gap distance enhanced both CH4 and CO2 conversions, in contrast with the increases in feed flow rate and input frequency. The gaseous products were mainly H2 and CO, with small amounts of C2H2, C2H4 and C2H6. The optimum conditions for hydrogen-rich syngas production using the four-stage AC gliding arc system were a feed flow rate of 150?cm3/min, an input frequency of 300?Hz, an applied voltage of 17?kV and an electrode gap distance of 6?mm. At the minimum power consumption (3.3?×?10?18?W?s/molecule of biogas converted and 2.8?×?10?18?W?s/molecule of syngas produced), CH4 and CO2 conversions were 21.5 and 5.7?%, respectively, H2 and CO selectivities were 57.1 and 14.9?%, respectively, and H2/CO (hydrogen-rich syngas) was 6.9. The combination of the plasma reforming and partial oxidation provided remarkable improvements to the overall process performance, especially in terms of reducing both the power consumption and the carbon formation on the electrode surface but the produced syngas had a much lower H2/CO ratio, depending on the oxygen/methane feed molar ratio. The best feed molar ratio of O2-to-CH4 ratio was found to be 0.3/1, providing the CH4 conversion of 81.4?%, CO2 conversion of 49.3?%, O2 conversion of 92.4?%, H2 selectivity of 49.5?%, CO selectivity of 49.96?%, and H2/CO of 1.6. 相似文献
6.
7.
8.
In this paper, we introduce and analyze a new general iterative scheme by the viscosity approximation method for finding the common element of the set of equilibrium problems, the set of fixed points of an infinite family of nonexpansive mappings and the set solutions of the variational inequality problems for an ξ-inverse-strongly monotone mapping in Hilbert spaces. We show that the sequence converge strongly to a common element of the above three sets under some parameters controlling conditions. The result extends and improves a recent result of Chang et al. (Nonlinear Anal. 70:3307–3319, 2009) and many others. 相似文献
9.
Nongnuch Rueangjitt Chalermrat Akarawitoo Thammanoon Sreethawong Sumaeth Chavadej 《Plasma Chemistry and Plasma Processing》2007,27(5):559-576
The objective of the present work was to study the reforming of simulated natural gas via the nonthermal plasma process with
the focus on the production of hydrogen and higher hydrocarbons. The reforming of simulated natural gas was conducted in an
alternating current (AC) gliding arc reactor under ambient conditions. The feed composition of the simulated natural gas contained
a CH4:C2H6:C3H8:CO2 molar ratio of 70:5:5:20. To investigate the effects of all gaseous hydrocarbons and CO2 present in the natural gas, the plasma reactor was operated with different feed compositions: pure CH4, CH4/He, CH4/C2H6/He, CH4/C2H6/C3H8/He and CH4/C2H6/C3H8/CO2. The results showed that the addition of gas components to the feed strongly influenced the reaction performance and the
plasma stability. In comparisons among all the studied feed systems, both hydrogen and C2 hydrocarbon yields were found to depend on the feed gas composition in the following order: CH4/C2H6/C3H8/CO2 > CH4/C2H6/C3H8/He > CH4/C2H6/He > CH4/He > CH4. The maximum yields of hydrogen and C2 products of approximately 35% and 42%, respectively, were achieved in the CH4/C2H6/C3H8/CO2 feed system. In terms of energy consumption for producing hydrogen, the feed system of the CH4/C2H6/C3H8/CO2 mixture required the lowest input energy, in the range of 3.58 × 10−18–4.14 × 10−18 W s (22.35–25.82 eV) per molecule of produced hydrogen. 相似文献
10.
Wendy I. Cross Mohjat Z. Dahalan Stephen M. Godfrey Nongnuch Jaiboon Charles A. McAuliffe Robin G. Pritchard Graeme M. Thompson 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):140-141
The title molecule, (iodobromo)triphenylarsenic(III), [As(BrI)(C6H5)3], has a dart shape, with the phenyl rings arranged in a propeller conformation [I—As—C—C 61.3 (4), 43.8 (4) and 54.1 (4)°]. There is no indication that the halogen atoms have mixed site occupancies. Packing forces displace the I atom away from one phenyl ring [I—As—C 117.3 (2)°] towards the other two [I—As—C 109.8 (2) and 108.3 (2)°] and produce an even more pronounced leaning of the terminal bromine [As—I—Br 174.78 (2)°]. 相似文献