共查询到20条相似文献,搜索用时 21 毫秒
1.
The aqueous solubilities of glycine, dl-α-alanine (2-aminopropanoic acid), dl-α-aminobutyric acid (2-aminobutanoic acid), dl-α-norvaline (2-aminopentanoic acid), dl-α-norleucine (2-aminohexanoic acid), β-alanine (3-aminopropanoic acid), γ-aminobutyric acid (4-aminobutanoic acid), 5-aminovaleric acid (5-aminopentanoic acid), and 6-aminocaproic acid (6-aminohexanoic acid) were determined from 293.15 to 323.15 K at intervals of 5.00 K using the gravimetric method. The temperature dependence of the solubility of α-amino acids and α,ω-amino acids in water is well described by the van’t Hoff equation. Linear van’t Hoff plots were used to determine the differential enthalpy of solution. The results obtained are compared with reported values in literature and are discussed in terms of the position of the ionic groups in the hydrocarbon chain. 相似文献
2.
The N-phenyl methyl esters 4 of glycine, alanine, valine, leucine, isoleucine, phenylalanine, methionine, proline, serine, threonine, tyrosine, aspartic acid, and glutamic acid have been synthesized in good to excellent yields using diphenyliodonium bromide, AgNO3, and a catalytic amount of CuBr starting from the relevant amino acid ester. The chiral integrity of the amino acids 5 was maintained during these reactions, which were confirmed by the synthesis of dipeptide for each N-phenyl amino acid. The structures of the new compounds were confirmed by the analysis of their IR, 1H, and 13C NMR spectra in addition to CHN microanalysis or high-resolution mass spectrometry for the new N-phenyl amino acids 5 and the esters 4. 相似文献
3.
《Analytical letters》2012,45(2):347-356
ABSTRACT The liquid chromatographic enantioseparation of the phenylthiohydantoin (PTH) derivatives of various amino acids on four commercial polysaccharide-derived chiral stationary phases (CSPs) is described. Chiralcel OF and Chiralpak AS showed better performance than the other CSPs for resolution of the enantiomers of PTH amino acid derivatives. The enantiomers of all amino acids as their PTH derivatives were well separated on Chiralcel OF and/or Chiralpak AS. The (-)(L) or (-)-enantiomers of all analytes examined were preferentially retained on Chiralpak AS, whereas the (+)(D) or (+)-enantiomers of most of analytes were preferentially retained on Chiralcel OF. 相似文献
4.
5.
Chiral dehydropiperidinones were synthesized in enantiopure form from α-amino acids and alkynes via azetidin-3-ones. 相似文献
6.
JianHU XiaoDaYANG KuiWANG 《中国化学快报》2004,15(10):1197-1200
The fluorescence spectra of Quin 2, (2-[(2-bis-[carboxymethyl] amino-5-methylphenoxy)methyl]-6-methoxy-8-bis [carboxymethyl] aminoquiniline), a Ca^2 probe, were investigated upon incubation with Ca^2 or La^3 . The results showed that binding of La^3 to Quin 2 resulted in different fluorescent spectrum from that of Ca^2 . Based on this observation, a fluorescent method was developed for simultaneously determination of the dissociation rates of Ca^2 and La^3 from a Ca-La- calmodulin complex (Ca2La2CaM). 相似文献
7.
Abstract The trichloroacetimidate method has been applied to the construction of α-d-galacto- and α-d-glucopyranosides. The readily available β-trichloroacetimidates of 2,3,4,6-tetra-O-benzyl-d-galacto- and glucopyranose (1-β and 3-β, respectively) have been employed in glycosidations with several monosaccharides (either A, B, C or D) under varying experimental conditions. With the galactose derivative 1-β as a donor and each of the monosaccharides A-D as acceptors, the corresponding disaccharides 1A-1D, were obtained in high yield and with good α-stereoselectivity when employing diethyl ether as solvent and either trimethylsilyl- or tert-butyldimethylsilyl trifluoro-methane sulphonate as catalyst. Glycosidations with the glucose derivative 3-β, as donor, and with the monosaccharide acceptors A, B or D, gave the corresponding disaccharides 3A, 3B and 3D, in high yield but with somewhat lower α-diastereoselectivity than observed with the galactose derivative 1-β. The stereochemical outcome of the reactions is rationalised in terms of possible reaction mechanisms. 相似文献
8.
The decarboxylation of L-threonine (2S,3R)-1, L-hydroxyproline (2S,4R)-2 and D-2-azabicyclo[3.3.0]octan-3-carboxylic acid (1R,3R,5R)-5 yield in a simple one-step procedure the corresponding optically active β-amino alcohols (R)-3 and (R)-4 and the bicyclic pyrrolidine derivative (1R,5R)-6 in 72–82% yield and >99% ee. 相似文献
9.
《液相色谱法及相关技术杂志》2012,35(6):1065-1085
Abstract An aqueous solution of α-cyclodextrin (cyclohexaamylose) is demonstrated to be a very effective mobile phase in thin-layer chromatographic separations. The chromatographic behaviors of twenty-six substituted phenolic and naphtholic compounds using polyamide thin-layer stationary sheets are described. The Rf values were found to be dependent upon both the structural features of the phenolic compounds and the concentration of α-cyclodextrin in the mobile phase. A possible mechanism that accounts for the observed chromatographic behavior is presented. The advantages and disadvantages of the aqueous α-cyclodextrin mobile phase over the traditional pure or mixed organic solvent systems typically employed are discussed. 相似文献
10.
SiO2–Al2O3 aerogels and xerogels with a Si to Al molar ratio r
Si/Al varying from 0.25 to 20, were made by sol-gel process in acidic conditions at pH 2 and respectively dried by the CO2 supercritical method and by solvent evaporation. The Al precursor was also chelated with ethylacetoacetate, which made it possible to study the structure and texture of such gels in conditions favorable to the formation of mixed Al–O–Si bonds. Nitrogen adsorption isotherms according to the Brunauer, Emmett and Teller method (BET), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR), Fourier Transformed Infrared Spectroscopy (FTIR) and Infrared absorbance spectra after Temperature Programmed Desorption (TPD) of pyridine, showed that the Si–O infrared asymmetric stretching vibration and the Bronsted acidity relative to the Lewis acidity, depended on the ratio of AlIV to Si atoms. 相似文献
11.
Standard transfer Gibbs energies $ \left( {\Updelta G_{t}^{0} (i)} \right) $ ( Δ G t 0 ( i ) ) and entropies $ \left( {\Updelta S_{t}^{0} (i)} \right) $ ( Δ S t 0 ( i ) ) of transfer of the homologous α-amino acids: glycine, dl-alanine, dl-α-amino butyric acid and dl-nor-valine (nor-val) from protic ethylene glycol (EG) to proton/cation-phobic dipolar aprotic acetonitrile (ACN) mixed solvents with 0, 20, 40, 60, 80 and 100 wt% ACN compositions have been determined at 25 °C. For this purpose solubilities of the α-amino acids were measured by “formol titrimetry” at 15, 20, 25, 30 and 35 °C. The chemical components of these Gibbs energies $ \left( {\Updelta G_{t,\rm{ch}}^{0} (i)} \right) $ ( Δ G t , ch 0 ( i ) ) and entropies $ \left( {{\rm T}\Updelta S_{t,\rm{ch}}^{0} (i)} \right) $ ( T Δ S t , ch 0 ( i ) ) of the homologous α-amino acids have been computed by subtracting the cavity effects and dipole–dipole interaction effects. The chemical contributions of transfer energetics of these homologous α-amino acids are determined by different types of interactions. The decreased acidity, basicity, H-bonding capacity, solvophilic solvation and solvophobic solvation and increased dispersion and soft–soft interaction of ethylene glycol and acetonitrile mixtures, as compared to EG, are the guiding factors. The characteristics of the solvation thermodynamics of α-amino acids in protic EG and proton/cation-philic dipolar aprotic DMF mixed solvent systems studied earlier are also discussed here for comparison. 相似文献
12.
13.
Elisabeth öhler Silvia Kanzler 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Fosmidomycin is the most active compound of a group of natural phosphonic acid antibiotics bearing a unique hydroxamic acid functionality in the γ-position1. We present here two efficient and novel routes to precursors and analogues of these compounds. 相似文献
14.
15.
Direct and indirect reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of seventeen unnatural β-amino acids, including several β-3-homo amino acids. The direct separations of the underivatized analytes were performed on chiral stationary phases containing macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T column) and teicoplanin aglycone (Chirobiotic TAG column). The indirect method involved pre-column derivatization with two new chiral derivatizing agents, (1S,2S)-1,3-diacetoxy-1-(4-nitrophenyl)-2-propylisothiocyanate, (S,S)-DANI and (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester, (S)-NIFE. The different methods were compared in systematic chromatographic examinations. The effects of organic modifier, mobile phase composition, pH and flow rate on the separation were investigated. 相似文献
16.
17.
The synthesis of O-succinimidyl-(tert-butoxycarbonylamino)methyl carbamates employing isocyanates made through the Curtius rearrangement of Boc-amino acid azides in the presence of N-hydroxysuccinimide under the influence of ultrasound is described. 相似文献
18.
《Annales de Chimie Science des Materiaux》2001,26(1):209-216
The use of high pressure and the inclusion of elements such as boron, nitrogen and fluorine increase the number of compounds that adopt the α-quartz-type structure. The α-quartz-type forms of boron phosphate (BPO4), phosphorus oxynitride (PON) and representatives of the continuous solid solution between silica and phosphorus oxynitride, including the nearly stoichiometric material SiPO3N, were prepared under high-pressure, high-temperature conditions. The crystal structures of BPO4 and PON were refined using X-ray and neutron powder diffraction data, respectively. The intertetrahedral A-X-A′ bridging angles of 140.1° and 140.6°, respectively, are slightly lower than in α-quartz as would be expected based on the higher densities of these materials. Preliminary refinements using the X-ray data from the SiO2-PON solid solutions provide no indication of Si/P order and yield fractional atomic coordinates that are very similar to those observed for the pure end members. These results indicate that one may continuously tune the unit cell and structural parameters by varying the composition of this solid solution. Other compounds, which adopt or may adopt α-quartz-type structures, are also discussed. The present work indicates that the known relationship between the intertetrahedral A-X-A′ bridging angle and the density in α-quartz-type materials also applies to boron compounds, oxynitrides and fluorides. This use of the variables composition and pressure enables structure-property relationships for α-quartz isotypes to be extended and increases the number of potential candidates for piezoelectric materials. 相似文献
19.
Canepa P Schofield E Chadwick AV Alfredsson M 《Physical chemistry chemical physics : PCCP》2011,13(28):12826-12834
Comparison and prediction of the experimental XANES spectrum is a good measurement of the quality of the electronic structure calculations employed, and their ability to predict electronic transitions in solids. Here we present a comparison between BLYP + U and hybrid-BLYP calculations regarding the geometric, magnetic and electronic structures of α-Fe(2)O(3) (hematite). Several values of U and different percentages of Fock-exchange have been screened to see how their contributions affect different properties of hematite, paying particular attention to the electronic structure. To estimate the quality of the various methods the calculated density-of-states were compared to the experimentally collected XANES spectrum of the iron K-edge, providing information about the orbitals describing the conduction band. We find that in agreement with previous studies DFT + U and hybrid-functional simulations can correctly predict the character of the valence band, but only Fock-exchange higher than 30% or U-values equal or larger than 6 eV properly reproduce the order between the t(g) and e orbitals in the conduction band, and can, therefore, be used to study and predict XANES spectra and electronic transitions in hematite. 相似文献