共查询到20条相似文献,搜索用时 15 毫秒
1.
Yu. G. Kuraeva L. A. Onuchak M. A. Evdokimova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(8):1698-1701
The thermodynamic characteristics of sorption of 24 organic compounds of various classes from the gas phase on the binary stationary phase based on polyethylene glycol 400 and permethylated β-cyclodextrin were determined. The influence of geometrical structure and optical activity of organic compounds on the possibility of forming sorbate–macrocycle complexes was examined. It was found that the studied stationary phase shows the enantioselectivity towards low-polar terpenes under the conditions of gas chromatography. 相似文献
2.
CHEN Li-Tao CHEN Guang-Ju FU Xiao-YuanChemistry Department Beijing Normal University Beijing China 《中国化学》1995,13(1):10-18
The dehydrohalogenation mechanism of 2-haloacetic acids (XCH2CO2H, X=F, Cl and Br) has been studied theoretically by HF/3-21G and AM1 methods. The results indicate that these reactions are most probably proceeded in terms of a polar five-membered cyclic transition state in the gas phase. Their microscopic processes are beleived to be a stepwise reaction and the rate-determining step is the first one. By comparing the energy barriers of different 2-haloacetic acids, it can be realized that 2-fluoroacetic acid is easier to react than 2-chloroacetic and 2-bromoacetic acids. 相似文献
3.
Calculated vertical ionization energies of the common α-amino acids in the gas phase and in solution
Close DM 《The journal of physical chemistry. A》2011,115(13):2900-2912
The vertical ionization energies of the low-lying conformers of the α-amino acids found in proteins have been calculated. Geometry optimizations were first performed at the B3LYP/6-311G(d,p) level of theory, and then reoptimized at the MP2/6-311G(d,p) level of theory. Vertical ionization energies were then computed by three methods, electron propagator in the partial third-order (P3) approximation, Outer-Valence-Green's Functions, and by evaluating the difference in the total energy between the cation radical and the neutral amino acid in the geometry of the neutral species. When available, the results are compared to the experimental vertical ionization energies. The vertical ionization energies calculated using the MP2/P3 method gave the best overall agreement with the experimental results. Next, the ionization energies in solution are calculated for the zwitterionic forms of the α-amino acids by using IEFPCM methods. To obtain the vertical ionization energy in solution, it is necessary to use the nonequilibrium polarizable continuum model (NEPCM), the results of which are reported here for the α-amino acids. 相似文献
4.
Keunchkarian S Padró JM Gotta J Nardillo AM Castells CB 《Journal of chromatography. A》2011,1218(23):3660-3668
The natural alkaloid quinine (QN) was immobilized on porous silica particles, and part of the material was subsequently endcapped with n-hexyl hydrocarbon chains. Two synthetic strategies for silanization of the support were first compared. These columns were thoroughly evaluated in order to study the influence of endcapping in the enantiorecognition features. Enantioseparations of twenty N-derivatized 2,4-dinitrophenyl α-amino acids (DNP-amino acids) were studied by changing mobile phase pH, buffer concentration, type of organic solvent in the mobile phase, and column temperature. Maximum retention factors were observed at pH ≈6, at this intermediate pH the tertiary amine of the quinine is protonated to a high degree and therefore available for strong electrostatic interactions with unprotonated anionic DNP-amino acids. The enantioselectivity factors, however, increased as the pH did in the range between 5 and 7. The increase in ionic strength had influence on retention, but not on enantioselectivity, allowing the use of this variable for optimization of retention factors. Finally, the thermodynamic transfer parameters of the enantiomers from the mobile to both CSPs (with and without endcapping, QN-CSP(EC) and QN-CSP, respectively) were estimated from van't Hoff plots within the range of 10-40 °C. Thus, the differences in the transfer enthalpy, Δ(ΔH°), and transfer entropy, Δ(ΔS°), enabled an investigation of the origin of the differences in interaction energies. 相似文献
5.
Angelo Carotti Cosimo Altomare Saverio Cellamare AnnaMaria Monforte Giancarlo Bettoni Fulvio Loiodice Nicola Tangari Vincenzo Tortorella 《Journal of computer-aided molecular design》1995,9(2):131-138
Summary The HPLC resolution of a series of racemic -substituted -aryloxy acetic acid methyl esters I on a -acid chiral stationary phase containing N,N-(3,5-dinitrobenzoyl)-trans-1,2-diaminocyclohexane as chiral selector was modelled by linear free energy-related (LFER) equations and comparative molecular field analysis (CoMFA). Our results indicate that the retention process mainly depends on solute lipophilicity and steric properties, whereas enantioselectivity is primarily influenced by electrostatic and steric interactions. CoMFA provided additional information with respect to the LFER study, allowed the mixing of different subsets of I and led to a quantitative 3D model of steric and electrostatic factors responsible for chiral recognition. 相似文献
6.
《Tetrahedron letters》1986,27(27):3173-3176
Various types of fluorine-containing α,β-unsaturated acids and their esters were synthesized from 2-trilfuoromethylacrylic acid as a sole starting material. 相似文献
7.
D. L. Kotova E. G. Davydova T. A. Krysanova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(13):2255-2259
The dynamics of sorption of pure imino acids (proline and hydroxyproline) and imino acids in the presence of aromatic amino
acid, phenylalanine, on KU-2 × 8 sulfocation exchanger in the H form was studied. Mutual influence of amino acids on the dynamic
characteristics of sorption was observed. This influence changed the shape of elution curves and decreased the working exchange
capacity. Both competitive and synergistic sorption mechanisms governed sorption of amino acids from binary solutions. 相似文献
8.
Mingkun Fu Sen Li Enada Archibold Michael J. Yurkovich John J. Nash Hilkka I. Kenttämaa 《Journal of the American Society for Mass Spectrometry》2010,21(10):1737-1752
Gas-phase reactivity of a positively charged aromatic σ,σ-biradical (N-methyl-6,8-didehydroquinolinium) was examined toward six aliphatic amino acids and 15 dipeptides by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) and laser-induced acoustic desorption (LIAD). While previous studies have revealed that H-atom and NH2 abstractions dominate the reactions of related monoradicals with aliphatic amino acids and small peptides, several additional, unprecedented reaction pathways were observed for the reactions of the biradical. For amino acids, these are 2H-atom abstraction, H2O abstraction, addition — CO2, addition — HCOOH, and formation of a stable adduct. The biradical reacts with aliphatic dipeptides similarly as with aliphatic amino acids, but undergoes also one additional reaction pathway, addition/C-terminal amino acid elimination (addition — CO — NHCHRC). These reactions are initiated by H-atom abstraction by the biradical from the amino acid or peptide, or nucleophilic addition of an NH2 or a HO group of the amino acid or peptide at the radical site at C-6 in the biradical. Reactions of the unquenched C-8 radical site then yield the products not observed for related monoradicals. The biradical reacts with aromatic dipeptides with an aromatic ring in N-terminus (i.e., Tyr-Leu, Phe-Val, and Phe-Pro) similarly as with aliphatic dipeptides. However, for those aromatic dipeptides that contain an aromatic ring in the C-terminus (i.e., Leu-Tyr and Ala-Phe), one additional pathway, addition/N-terminal amino acid elimination (addition — CO — NHCHRN), was observed. This reaction is likely initiated by radical addition of the biradical at the aromatic ring in the C-terminus. Related monoradicals add to aromatic amino acids and small peptides, which is followed by Cα-Cβ bond cleavage, resulting in side-chain abstraction by the radical. For biradicals, with one unquenched radical site after the initial addition, the reaction ultimately results in the loss of the N-terminal amino acid. Similar to monoradicals, the C-S bond in amino acids and dipeptides was found to be especially susceptible to biradical attack. 相似文献
9.
Elena Reshetova 《液相色谱法及相关技术杂志》2016,39(3):145-153
The effect of the pH of aqueous–ethanol mobile phases on the retention and adsorption thermodynamics of the optical isomers of several α-phenylcarboxylic acids on a chiral stationary phase “Nautilus-E” with a grafted antibiotic, eremomycin, was studied. It was determined that ionic interactions dominated in the retention of α-phenylcarboxylic acid enantiomers. It was revealed that the Nautilus-E adsorbent was most selective to acids, the adsorption of which is an enthalpy-controlled process. It was found that the nature of adsorption was changed by varying the eluent pH. The dissociation constants of α-phenylcarboxylic acids have been determined by chromatographic method in aqueous–ethanol solution. A statistical analysis of the phenomenon of enthalpy-entropy compensation was performed, and a manifestation of the false compensation effect was established. It was shown that the spatial configuration of the molecule and the presence of polar groups on a chiral carbon atom in its structure have a greater influence on the chiral recognition mechanism of acid enantiomers using the Nautilus-E CSP. 相似文献
10.
A. S. Blinov E. N. Reshetova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(10):1778-1784
Regularities of the chromatographic retention and thermodynamics of the adsorption of enantiomers of α-phenylcarboxylic acids on a chiral stationary phase with immobilized macrocyclic antibiotic eremomycin under conditions of reversed-phase liquid chromatography with aqueous-ethanol mobile phases are studied. Relationships between the retention characteristics of the acids, the enantioselectivity of their separation, and the concentration of organic modifier in the mobile phase are found. It is shown that the sterical structure of substituents on the chiral atoms of the acids affect the mechanism of retention. The compensation effect in the studied systems is considered. 相似文献
11.
Mihlbachler K Kaczmarski K Seidel-Morgenstern A Guiochon G 《Journal of chromatography. A》2002,955(1):35-52
The binary isotherms of the two enantiomers of Tr?ger's base were measured on a system made of pure 2-propanol as the mobile phase and of Chiralpak AD, a chiral stationary phase (CSP) based on amylose tri-(3,5-dimethylphenyl carbamate). The experimental data were acquired using both frontal analysis and the perturbation method. The results obtained are most unusual. The adsorption of the more-retained (-)-enantiomer is not competitive: the amount adsorbed onto the CSP at equilibrium with a constant concentration of the (-)-enantiomer is independent of the concentration of the (+) enantiomer. On the other hand, the adsorption of the less-retained enantiomer is cooperative: the amount of this (+)-enantiomer adsorbed by the CSP at equilibrium with a constant concentration of this enantiomer increases with increasing concentration of the (-)-enantiomer. Such a phenomenon has hardly ever been reported. A model equation is proposed that accounts well for all these isotherm data. 相似文献
12.
The Kováts retention indices (I) of 1-nitroalkanes and alkanenitriles were determined on polydimethylsiloxane and Innowax (polyethylene glycol) columns in a wide temperature range. The temperature dependence of the retention indices exhibits a definite minimum for the early members of the homologous series. The position of the minimum shifts to lower temperatures with increasing carbon atom number of the solute. The thermodynamic explanation of an extreme in the I vs. T function is the higher solvation heat capacities of nitroalkanes and alkanenitriles relative to those of the reference n-alkanes, owing to the deviation from the ideal state in the solution. A novel equation was derived which describes the minimum in the I vs. T function, too. 相似文献
13.
Tao Hong Li Chuan Ming Wang Shi Wen Yu Xiang Yi Liu Hui Fu Xiao Guang Xie 《中国化学快报》2009,20(8):1010-1014
The reaction of Os~+(~6D,~4F) with N_2O has been investigated at B3LYP/TZVP and CCSD(T)/6-311+G~* levels of theory.The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed.It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism,leading to the formation of OsO~+ and OsN~+,whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism.The calculated energ... 相似文献
14.
M. Isabel García-Aranda M. Teresa García-LópezM. Jesús Pérez de Vega Rosario González-Muñiz 《Tetrahedron letters》2014
1,3,5-Trisubstituted tetramic acids and 2,3-disubstituted indole derivatives were prepared from β-keto esters derived from amino acids by their reaction with iodophenyl-2-trifluoroacetylamine under Cu-catalysis. Both heterocyclic systems were generated from the same starting materials by choice of the appropriate reaction conditions. 相似文献
15.
V. N. Artem'eva V. V. Kudryavtsev E. M. Nekrasova V. P. Skilizkova L. A. Shibaev N. G. Stepanov Yu. N. Sazanov G. N. Fedorova O. P. Shkurko V. P. Borovik 《Russian Chemical Bulletin》1992,41(10):1797-1800
The thermocyclization of polypyromellitamido acids based on 2,5-bis(p-aminophenyl)pyrimidine and 4,4-diaminoterphenyl was investigated by thermogravimetric and mass spectrometric analysis. Characteristics of the thermocyclization of pyrimidine-containing polyamido acids due to the presence of a basic nitrogencontaining ring in the main macrochain were revealed. The hypothesis advanced in Part 1, that the pyrimidine ring displaces solvent molecules bound to the polyamido acid, was confirmed. The hypothesis of the presence of shift packing in a pyrimidine-containing polyamido acid was confirmed by its greater kinetic homogeneity in comparison with the completely aromatic analog.Institute of High-Molecular-Weight Compounds Russian Academy of Sciences, 199004 St. Petersburg. Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2297–2301, October, 1992. 相似文献
16.
Dias C Dias M Borges C Almoster Ferreira MA Paulo A Nascimento J 《Journal of mass spectrometry : JMS》2003,38(12):1240-1244
The chemical composition of Autonoë madeirensis bulbs was characterized as part of a systematic phytochemical study of this species. The compounds reported were mainly identified on the basis of gas chromatography/electron ionization, electrospray ionization and tandem mass spectrometry. The structures of the pure compounds were also characterized by means of other physical and spectroscopic data (m.p., IR, UV, NMR). The compounds identified were 2‐hydroxy di‐ and tricarboxylic acids and esters (malic acid, citric acid and their methyl and ethyl esters), cis‐ and trans‐hydroxycinnamic esters (methyl and ethyl p‐coumarate and methyl ferulate) and a new flavone diglucoside, 7‐O‐[β‐glucosyl‐(1→2)‐O‐β‐glucosyl]apigenin, the interglucosidic linkage (1→2) of which is, to the best of our knowledge, reported for the first time in a diglucoside of apigenin. The results may contribute to the chemotaxonomy of the Autonoë genus and lead to a rapid tool for the systematic characterization of these compounds in plant extracts. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
17.
A. B. Terent'ev T. T. Vasil'eva N. A. Kuz'mina E. I. Mysov N. S. Ikonnikov N. Yu. Kuznetsov Yu. N. Belokon 《Russian Chemical Bulletin》1999,48(6):1121-1127
Reformatsky-type addition of esters of α-halogeno carboxylic acids to aldehydes and ketones in the presence of Fe(CO)5 and an activating agent (CBrCl3 or I2) afforded the corresponding esters of β-hydroxy acids in good yields. Possible reaction mechanisms are discussed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1132–1138, June, 1999. 相似文献
18.
We present a systematic study of 1:1 glycine-water complexes involving all possible glycine conformers. The complex geometries are fully optimized for the first time both in the gas phase and in solution using three DFT methods (B3LYP, PBE1PBE, X3LYP) and the MP2 method. We calculate the G3 energies and use them as the reference data to gauge hydrogen bond strength in the gas phase. The solvent effects are treated via the integral equation formalism-polarizable continuum model (IEF-PCM). Altogether, we loca... 相似文献
19.
K. Videnská Š. Palágyi K. Štamberg H. Vodičková V. Havlová 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):547-554
The sorption of 2 × 10?5 mol/dm3 Na2SeO4 and Na2SeO3 dissolved in synthetic granitic water (SGW) were investigated in columns of crushed granite and fracture infill (clay minerals) of various grain sizes. Desorption was studied using pure SGW. The goal of study was the quantification of the effect of grain size on the retardation and distribution coefficients of SeO4 2? and SeO3 2?, as well as on the other transport parameters (Peclet number and hydrodynamic dispersion coefficient). A model based on the erfc-function, assuming a non-linear reversible equilibrium sorption/desorption isotherm, was used for evaluation of sorption/desorption and transport parameters. The determination of selenium was performed using an ICP-MS technique. The experimental breakthrough curves were fitted using non-linear regression procedure, in the course of which the parameters mentioned were sought. Summing up, no sorption was recorded in the case of SeO4 2? under these conditions. The values of retardation coefficients were practically one for all studied grain sizes. On the other hand, significant sorption was found for SeO3 2?: depending on the grain size, the retardation coefficients varied between 1.6–8.7 in pure granite and 1.8–37.2 in infill materials. These values correspond to distribution coefficients of 0.2–2.5 and 0.2–12.7 cm3/g, respectively. The both parameters have similar values in a case of desorption which reflects the reversible character of sorption process. It was found that retardation and distribution coefficients and sorption capacity for SeO3 2? also increase with decreasing grain size. 相似文献