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31.
32.
α-Aspartame (L-α-aspartyl-L-phenylalanine methyl ester) is increasingly being used in wide variety of commonly consumed food products. This structure contains ester and peptide bonds. The ester linkage may hydrolyze to produce L-α-aspartyl-L-phenylalanine or cyclohydrolyze to produce the corresponding diketopiperazine ring. This ring can open to form L-α-aspartyl-L-phenylalanine and ultimately this compound can hydrolyze to L-phenylalanine and L-aspartic acid. The pH, buffer type, concentration, the presence of water and temperature are other important factors affecting its stability. Because α-aspartame can lose its sweetness under these conditions determination of aspartame and its breakdown products is extremely important for diet foods quality. The optimum mobile phase for the chromatographic separation was found to be acetonitrile-water (20:80, ν/ν) with 5.10?3 M hexanesulfonic acid and a pH of 2.6. 相似文献
33.
H. Yücel H. Karadeniz M. A. Çetiner H. Demirel Ş. Turhan 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(2):445-447
The sorption behavior of 235U fission fission products 99Mo and 132Te was studied through batch and dynamic experiments when they were dissolved in 1 to 7M HNO3 solutions. It was found that 99Mo is always totally adsorbed on hydrated SnO2, while 132Te is rather weakly adsorbed, therefore they can be separated from each other although 132Te in the solution still remains contaminated with other radionuclides as well as 99Mo does in the solid. 相似文献
34.
Jalal A.?Zahra Bassam Abu?Thaher Mustafa M.?El-Abadelah Hans-Hartwig?OttoEmail author 《Monatshefte für Chemie / Chemical Monthly》2005,136(4):567-570
Summary. Nitrilimines prepared from N-arylhydrazono chlorides reacted with 2-mercaptonicotinic acid yielding the corresponding addition products, 2-[(2-oxo-1-arylhydrazonopropan-1-yl)mercapto] nicotinic acids, which were treated with 1,1-carbonyldiimidazole in THF affording by cyclocondensation the corresponding hitherto unknown 2-arylhydrazono-3-oxothieno[2,3-b]pyridines. 相似文献
35.
36.
Serkan Erdemir Mustafa Tabakci Mustafa Yilmaz 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):197-202
Herein the synthesis and extraction abilities of new d-/l-phenylalaninol substituted p-tert-butylcalix[4]arene triamide derivatives (3 and 4) towards amino acids are reported. These compounds (3 and 4) have been easily synthesized via aminolysis of p-tert-butylcalix[4]arene trimethylester (2) with d-/l-phenylalaninol in methanol-toluen solvent system at one step. The extraction properties of the prepared chiral calix[4]arene
triamide derivatives (3 and 4) towards some selected amino acid methylesters are studied by liquid–liquid extraction. Results show that these chiral calix[4]arene
triamide derivatives (3 and 4) exhibited a good affinity towards all amino acid species without any remarkably discrimination. 相似文献
37.
Serdar Karabcek Ismail Degirmencioglu Nevin Karabcek Mustafa Er Kerim Serbest 《Journal of heterocyclic chemistry》2003,40(4):639-643
The synthesis and structural properties of three novel imidates, 11,13‐bis‐(2‐amino‐ethylimino)‐1,10‐dioxa‐4,7‐dithiacyclotridecane ( 2 ), 11,13‐bis‐(3‐aminopropylimino)‐1,10‐dioxa‐4,7‐dithiacyclotridecane, ( 3 ) and 2,11‐dioxa‐5,8‐dithia‐13,16,19,22‐tetraazabicyclo[10.10.1]tricosa‐1(22),12‐diene, ( 4 ) have been described. These compounds were synthesized by treating 1,10‐dioxa‐4,7‐dithiacyclotridecane‐11,13‐diester ( 1 ) with the appropriate diamine under N2 and their structures have been characterised by elemental analyses, 1H‐ and 13C‐nmr, ir, and mass spectral studies. Elemental analyses and spectroscopic data support the proposed imidate structures. In addition, total energy and heat of formation (Figure 2) calculated for imidates 2a‐4a and 2b‐4b by the semiempirical AM1 calculations have shown that imidates 2b‐4b having intramolecular hydrogen bonds are more stable (5‐10 kcal/mol) than compounds 2a‐4a . 相似文献
38.
The Claisen rearrangement of the N‐protected, silylated allyl glycinates 11 and 12 led to the formation of allyl/silyl‐functionalized amino acids 13 and 14 in yields up to 80%. The diastereoisomer ratio varied from 2 : 1 to 29 : 1 for 11mb , and from 2 : 1 to 46 : 1 (syn/anti) for 12mb , depending on reaction conditions, as shown by X‐ray crystallographic analysis of 14mb . The relationship between the size of the alkyl groups on the chlorosilane reagent (Me2R″SiCl, R″=Cl, Me, t‐Bu, Ph) used as an enolate trap and the observed stereoselectivity was investigated in the case of the Ireland–Claisen variant. Me3SiCl gave the best results. However, the size of the alkyl groups on the silylated ester (Me2R″Si, R=Me, t‐Bu, Ph, i‐Pr) did not exert a significant effect on the diastereoselectivity or yield of the rearrangement. 相似文献
39.
U. Çevik A. I. Kopya H. Karal Y. Sahin 《Journal of Radioanalytical and Nuclear Chemistry》1995,201(3):241-249
Sea-bed sediments from Eastern Black Sea have been analyzed for their Fe, Ba and Sr contents using the methods of standard addition and energy dispersive X-ray fluorescence (EDXRF). Samples were prepared from powder sifted by a 200 mesh sieve. An annular 100 mCi241Am radioactive source emitting 59.543 keV photons was used for excitation and a Ge(Li) detector, which has a 190 eV FWHM for 5.9 keV photons was used for intensity measurements. 2048 channels of the MCA are employed for 20 or 30 min. Dried and ground sea-bed sediments are found to contain 2.95–7.50% Fe, 0.032–0.268% Ba and about 73–273 ppm Sr. These results agree with those obtained via atomic absorption methods. 相似文献
40.
The adsorption of two different molecular weights of polyvinylpyrrolidone (PVP) (M(w)=44,000 and M(w)=360,000 g mol(-1)) from water on kaolinite saturated with sodium chloride has been studied. The adsorption of PVP increases slowly as temperature increases. The adsorption of PVP on the kaolinite was studied by considering Fourier transform infrared (FTIR) spectra, X-ray diffraction patterns, and dielectric constants. During the adsorption process, PVP interacts with saturating sodium cations and possibly forces some of them onto the edges of the kaolinite; thus, the dielectric constant of saturated kaolinite is reduced after PVP adsorption. Copyright 2001 Academic Press. 相似文献