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排序方式: 共有246条查询结果,搜索用时 46 毫秒
1.
Designs, Codes and Cryptography - In this paper, we give a matrix construction method for designing DNA codes that come from group matrix rings. We show that with our construction one can obtain... 相似文献
2.
The effects of polyelectrolytes on the inhibition and aggregation of calcium oxalate crystallization
The influence of polyelectrolytes with different architecture on spontaneous batch crystallization of calcium oxalate was investigated. A series of acidic acrylate block copolymers were been made, by radical polymerization, with defined molecular weight and structure. Radical polymerization of acrylic acid (AA) was carried out in the presence of α‐thiopolyethylene glycol monomethylether as a chain transfer agent to produce poly(ethylene glycolblockacrylic acid) copolymers. Poly(ethylene glycol) (PEG) block length in the copolymers was controlled by using three different molecular weight chain transfer agents (Mn = 350, 750 and 2000 g/mol). The presence of copolymers inhibited the crystal growth of calcium oxalate possibly through adsorption onto the active growth sites for crystal growth due to the charge and hydrophilic effects. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
3.
Beşli S Coles SJ Davies DB Eaton RJ Hursthouse MB Kiliç A Shaw RA Yenilmez Ciftçi G Yeşilot S 《Journal of the American Chemical Society》2003,125(16):4943-4950
A problem has arisen in using chiral shift reagents (CSR) and chiral solvating agents (CSA) to determine meso and racemic forms of diastereoisomers in which the stereogenic centers of the molecules are separated by achiral spacers. It is found that NMR signals of both meso and racemic forms of diastereoisomers may exhibit doubling on addition of CSR/CSA, which means that unequivocal assignments cannot be made without characterizing the effects for separate meso and racemic forms; this is particularly important for additions of CSR/CSA at relatively low concentrations, which always result in the splitting of some NMR signals of diastereoisomers. The phenomenon is demonstrated in the (31)P NMR spectra of meso and racemic forms of three spermine-bridged gem-disubstituted cyclotriphosphazatrienes, 1a-c, and compared with analogous achiral molecules, the per-substituted spermine-bridged cyclotriphosphazatrienes 2a-d. As expected, only one set of (31)P NMR signals was observed for the achiral compounds 2a-d, even on addition of CSA. Two sets of (31)P NMR ABX multiplets corresponding to meso and racemic diastereoisomers were observed for compounds 1a-c; on addition of CSA, the signals of at least one of the multiplets for each compound separated into more than the expected groups of three lines with an intensity distribution of 2:1:1. To understand this phenomenon, the meso and racemic forms of 1a and 1b and the meso form of 1c have been separated and characterized by X-ray crystallography. On addition of CSA to the racemic forms of 1a and 1b, the (31)P NMR spectrum shows the expected doubling of signals, but, unexpectedly, the same is observed for each of the meso forms of 1a-c. Analogous results using both CSA and CSR have been obtained for the meso and racemic forms of the diastereoisomeric piperazine-bridged macrocyclic-phosphazene compound, 3, whereas no effect was observed for the two meso forms of the doubly bridged macrocyclic-phosphazene compound 4. The phenomenon of doubling of the (31)P NMR signals of the meso form of singly bridged cyclotriphosphazatrienes, 1a-c and 3, is explained by consideration of the equilibrium in solution of independent complexation of a chiral ligand with molecules that have two chiral cyclophosphazene moieties separated by an achiral spacer group. The results show that the stereogenicity of such diastereoisomeric molecules in solution cannot be characterized unequivocally by NMR measurements on addition of either CSR or CSA. 相似文献
4.
Deniz Sinirlioglu Ali Ekrem Muftuoglu Kurtulus Golcuk Ayhan Bozkurt 《Journal of polymer science. Part A, Polymer chemistry》2014,52(13):1885-1897
This work uses a simple “grafting through” approach in the preparation of anhydrous poly(vinylidene fluoride) (PVDF)‐g‐PVTri polymer electrolyte membranes (PEMs). Alkaline‐treated PVDF was used as a macromolecule in conjunction with vinyltriazole in the graft copolymerization. The obtained polymer was subsequently doped with triflic acid (TA) at different stoichiometric ratios with respect to triazole units and the anhydrous PEMs (PVDF‐g‐PVTri‐(TA)x) were prepared. All samples were characterized by FTIR and 1H NMR. The composition of PVDF‐g‐PVTri was determined by energy dispersive spectroscopy. Thermal properties of the membranes were examined by thermogravimetric analysis and differential scanning calorimetry. The surface roughness and morphology of the membranes were studied using atomic force microscopy, X‐ray diffraction, and scanning electron microscopy. PVDF‐g‐PVTri‐(TA)3 (C3‐TA3) with a degree of grafting of 47.22% showed a maximum proton conductivity of 0.09 S cm?1 at 150 °C and anhydrous conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1885–1897 相似文献
5.
Serap Bulut 《Comptes Rendus Mathematique》2014,352(6):479-484
In this work, considering a general subclass of analytic bi-univalent functions, we determine estimates for the general Taylor–Maclaurin coefficients of the functions in this class. For this purpose, we use the Faber polynomial expansions. In certain cases, our estimates improve some of those existing coefficient bounds. 相似文献
6.
Theoretical and Mathematical Physics - The partition functions of three-dimensional N=2 supersymmetric gauge theories on different manifolds can be expressed as q-hypergeometric integrals.... 相似文献
7.
8.
Selma Bal Sedat Salih Bal Abdullah Erener Hatice Nur Halipci Seyhan Akar 《Chemical Papers》2014,68(3):352-361
Four water soluble azo dyes, 4-(isopropyl)-2-[(E)-(4-chlorophenyl)diazenyl]phenol (L 1), 4-(isopropyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L2), 4-(sec-butyl)-2-[(E)-(4-chlorophenyl) diazenyl]phenol (L 3), 4-(sec-butyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L 4), and their Cu(II) and Ni(II) complexes were synthesized and characterized using spectroscopic methods. Examination of their thermal stability revealed similar decomposition temperature of approximately 260–300°C and that they were more thermally stable than their metal complexes. Ni(II) complexes of ligands L2 and L4 were more stable than the other coordination compounds. Among the synthesized ligands, L2 and the complexes Cu(L3)2 and Ni(L4)2 showed both antimicrobial and antifungal activity. However, the other ligands and the complexes were poorly active against selected microorganisms. 相似文献
9.
2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione derivatives (DPP) are chemically stable, fluorescent molecules, known as High Performance Pigments. Preparation of the soluble derivatives of DPPs provides great advantage in designing the optic sensor for new and existing applications and overcoming aggregation problems in solid matrices. For this purpose, the synthesis of antisymmetric DPPs and the formation of new organic dyes through N,N’-dialkylation and their spectroscopic studies have been carried out both in solutions and in solid phase. 相似文献
10.
Cemil İbiş Zeliha Gökmen Nihal Yilmaz Bozkurt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2907-2914
Mono(thio)substituted dienes 1a-1b gave compounds 3a-c and 5d-g with piperazine and piperidine derivatives in dichloromethane. Compounds 8 , 9 , and 10 were obtained from the reactions of perchlorobutadiene ( 6 ) with 1,4-butanedithiol ( 7 ) in ethanol in the presence of sodium hydroxide. Compounds 12a-b , 13a-b were obtained from the reactions of perchlorobutadiene ( 6 ) with allylmercaptan (CH 2 =CH--CH 2 --SH) and mercaptoethanol (HO--CH 2 --CH 2 --SH). 相似文献