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1.
Summary Amino acids have been esterified with n-butanol and isobutanol in the presence of perchloric acid. It has been established that in the concentration range of [H2O]/[n-BuOH]=0.10–0.40 esterification can be utilized for the determination of alanine, glycine, valine, leucine, proline, methionine, aspartic acid, phenylalanine, tyrosine, glutamic acid, lysine, arginine, histidine and cystine. In the case of [H2O]/[i-BuOH] =0.05–0.20 the esterification yield decreases from 100% to 70%, in proportion to the water content. 相似文献
2.
Summary Racemic resolution of aromatic and aliphatic amino acid esters into L-amino acid and D-amino acid ester via LC and HPLC is
achieved by using enzyme reactors as chromatographic columns. For this purpose α-chymotrypsin and trypsin are immobilized
on Eupergit C, Sepharose 4B and Lichrosorb-Diol. 相似文献
3.
Volatile fatty acids in aqueous media were esterfied in situ with phenyldiazomethane (PDM). Complete esterification was achieved in 3 h at 40°C under continuous stirring of an ether/water system. The process involved immediate transfer of benzyl esters into the organic phase. The separation of benzyl esters mixtures was carried out in glass capillary GC columns. The retention data and FID molar responses were determined for C1 to C6 acid benzyl esters, including 2-methylpropionic, 3-methylbutyric, 2-methylvaleric, and 2-ethylbutyric acid. An unusual relationship was observed between benzyl ester relative molar responses and carbon atom number. 相似文献
4.
Krishna Chaitanya NadimpallyKishore Thalluri Nani Babu PalakurthyAbhijit Saha Bhubaneswar Mandal 《Tetrahedron letters》2011,52(20):2579-2582
A catalyst free procedure for the preparation of amides from inactive esters of N-protected amino acids and various amines is demonstrated under mild reaction conditions. Our effort to recover excess amine and generated alcohol is an approach towards environment friendly and cost effective synthesis under easy operational conditions. 相似文献
5.
De-Ming Liu 《Chromatographia》1988,25(5):393-396
Summary D,L-amino acids were derivatized with (+), (±)-2-butanol or N-trifluoroacetyl-L-prolyl chloride (L-TPC) and then chromatographed.
Four optical isomers were separated on a Chirasil-Val capillary column. By this method, the concentration of optical impurities
arising from the commercial optically active reagents can be determined. The observed abnormal elution orders of enantiomeric
amino acid esters may be caused by a selective intermolecular force. 相似文献
6.
K. Iwaki M. Yamazaki N. Nimura T. Kinoshita R. Matsuda Y. Hayashi 《Chromatographia》1993,37(3-4):156-158
Summary Naphthylethylurea multiple-bonded chiral stationary phases prepared for the optimal resolution of p-bromophenylcarbamyl derivatives of enantiomeric amino acids are examined from the viewpoint of information theory. The criterion used is the function of mutual information (FUMI) which describes the precision of analysis as a function of peak shape (area and width), overlap and noise level. The length of the polyethyleneamine spacer in the chiral stationary phases is evaluated by the precision (FUMI) calculated from the peak shape and overlap. The best column is defined as the one which gives the highest precision. The temperature effect on the precision is also examined. 相似文献
7.
B. Shtrumfs J. Hermane I. Kalvinsh P. Trapencieris 《Chemistry of Heterocyclic Compounds》2007,43(2):169-174
A series of N-substituted amides and esters of aziridine-2-carboxylic acids have been prepared and have been subjected to
deprotonation with lithium diisopropylamide. The intermediate carbanions reacted more readily with the carbonyl groups of
the substrates than with methyl iodide. So, in place of the expected amides or esters of methylaziridine-2-carboxylic acids,
amides or esters of 2-aziridinylcarbonylaziridine-2-carboxylic acids were isolated.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 220–225, February, 2007. 相似文献
8.
E. P. Promyshlennikova V. E. Kirichenko K. I. Pashkevich D. N. Grigor'eva R. V. Golovnya 《Russian Chemical Bulletin》1993,42(12):1963-1967
The contributions of methylene and difluoromethylene units of six homologous and six pseudohomologous series of esters ofn-perfluoroalkanoic acids to the differential molar free energy, enthalpy, and entropy of sorption on stationary phases of different polarities in glass capillary columns under isothermal conditions were calculated. The features observed characterize the peculiarities of the sorption of esters of polyfluorinated carboxylic acids on phases of different polarities and make it possible to estimate the enthalpy and entropy contributions to the energy of sorption of the esters, the effect of the temperature of the analysis and the length of the alkyl or polyfluoroalkyl chain on the retention parameters of the compound analyzed. The inversion of the retention order of trifluoroacetates and pentafluoropropionates in XE-60 nitrile-containing phase was found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2051–2055, December, 1993. 相似文献
9.
10.
The preparation of novel 3-, 4-, 6-, and 13-amino-tetradecanoic acid methyl esters (2a–d) obtained by the reduction of 3-, 4-, 6-, and 13-oximino-tetradecanoic acid methyl esters (1a–d), was investigated. Oximino esters were reduced to afford the corresponding amino esters using NaBH4–ZrCl4 reducing system with good yields (58–82%). However, the reduction of oximino esters with LiAlH4 and BH3. Tetrahydrofuran gave the corresponding novel 3-, 4-, 6-, and 13-oximino alcohols (3a–d), and 3-, 4-, 6-, and 13-amino alcohols (4a–d) respectively with good chemical yields. 相似文献
11.
12.
Summary An experimental design has been used to study the effect of column temperature on the gas chromatographic retention of eightpara-hydroxy benzoic esters. A rapid procedure has been developed to reduce the number of experiments compared with traditional methods. Capacity factors were determined and the enthalpy and entropy of transfer from the mobile phase to the stationary phase, Ho and So, respectively, were calculated using the linear Van't Hoff equation (dependence of ln k on 1/T). A retention prediction system (RPS) for these compounds in GC was investigated. The molecular connectivity index was used to describe the quantitative structure relationships. Enthalpy — entropy compensation revealed that the mechanism was similar for all the compounds studied. 相似文献
13.
Summary The retention of 14 dansylated amino acid derivatives was determined using aqueous LiCl, NaCl, KCl, RbCl and CsCl solutions as eluents in reversed-phase thinlayer chromatography. The salts exerted typical salting-out effects, the retention of each dansylated amino acid increased with increasing concentration of salt in the eluent. This effect has been tentatively explained by the suppression of the dissociation of the polar groups in the solute molecules resulting in increased apparent lipophilicity. The correlation between the increased retention of dansyl amino acids and the salt concentration was found to be linear. The hydrated radii and energy of hydration of cations as well as the hydrophobicity of free amino acids and the pK value of the -amino groups simultaneously influenced the retention. 相似文献
14.
A. V. Makarycheva-Mikhailova E. A. Tronova V. Yu. Kukushkin 《Russian Chemical Bulletin》2005,54(3):610-614
The reaction of the nitrile platinum(IV) complex trans-[PtCl4(EtCN)2] with amino acid esters H2NC(R1)(R2)CO2Me (R1 = R2 = H, H-Me, Me-Me, H-Ph) and H2NCH2CH2CO2Me in CH2Cl2 produces the amidine complexes trans-[PtCl4{ Z-NH=C(Et)NHC(R1)(R2)CO2Me}2] and trans-[PtCl4{ Z-NH=C(Et)NHCH2CH2CO2Me}2], which were isolated in 70–80% yields and characterized by elemental analysis, mass spectrometry, IR spectroscopy, and 1H and 13C{1H} NMR spectroscopy. The structures of the complexes with R1 = R2 = H (1), R1 = H, R2 = Me (2), and R1 = H, R2 = Ph (4) were established by X-ray diffraction analysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 601–605, March, 2005. 相似文献
15.
16.
Correlation method for comparison of selectivity and retention on different chiral stationary phases
Summary The main chromatographic properties: selectivity and retention of two chiral stationary phases: (R)-3,5-dinitrobenzoylphenylglycine
(CSP I) and (S)-3,5-dinitro-benzoylleucine (CSP II) have been compared on the basis of correlation of retention factors of
derivatized esters of amino acids and derivatized aminoalcohols. The differences in retention and selectivity for the two
CSPs can be easily estimated from the correlation equation. It is shown that in the case of the correlation for two sets of
retention factors obtained on two different CSPs, it is mainly the intercept that decides which CSP has the better selectivity.
It is demonstrated that the correlation method provides more informations on the selectivity and retention than comparison
of the chromatographic data of single pairs of enantiomers. Additionally, the possible influence of the polar modifier mixed
with n-hexane as diluent on the constants in the correlation equation is demonstrated. 相似文献
17.
I.L. Borisov E.A. Grushevenko T.S. Anokhina D.S. Bakhtin I.S. Levin G.N. Bondarenko V.V. Volkov A.V. Volkov 《Materials Today Chemistry》2021
We have synthesized a number of comb-like polysiloxanes with linear, branched, cyclic and silicon-containing substituents; most of them are new and previously not studied polymers. The physicochemical properties of comb-like polysiloxanes have been systematically investigated. Differential-scanning calorimetry and wide-angle X-ray scattering data revealed the side-chain microphase assembly for polymers with linear aliphatic substituents, while the polymers with bulky substituents did not form a microphase. It is shown that the ratio of microphase in the polymer is greater, the closer the values of the thickness of the microphase layer and the length of the cross-link. The effect of the side-chain substituent on the hydrocarbon transport properties of comb-like polysiloxanes was studied. All synthesized polymers are promising as membrane materials for a vital process of hydrocarbon separation. This is associated with an increase in the solubility selectivity of n-butane/methane because the solubility coefficient of methane sharply decreases when long side chains are introduced into the polysiloxane. It was shown for the first time that microphase forming polymers have a significantly higher butane/methane selectivity (23.2–27.5) than polysiloxanes not forming a microphase (selectivity 12.3–20.0). The effect is demonstrated on polysiloxanes with various types of side substituents. It was revealed that for the comb-like polysiloxanes, the diffusivity selectivity and permselectivity are proportional to the fraction of the side-chain microphase in the polymer. With the increase in the hydrocarbon microphase share, the diffusion coefficient of the permanent gas methane is decreasing more rapidly than n-butane, which dissolves well in hydrocarbons and plasticizes polymer. Consequently, the polymers forming the microphase have a higher selectivity C3+/CH4 in the separation of a multicomponent hydrocarbons mixture. 相似文献
18.
Summary A GC method has been elaborated for the separation of enantiomers of some amino acid methyl esters after derivatization with activated (S)-(+)-naproxen. Nine amino acid ester paris were completely resolvede in a single run on a fused silica capillary column. 相似文献
19.
Summary The esterification of C1–C8 fatty acid in aqueous solutions and in the presence of sulfuric or hydrochloric acid and with n-butanol is described. It has been established that the esterification can be used for the quantitative determination of these fatty acids in the concentration ratio range of [H2O]/[n-BuOH]=0.01–5.3. In the concentration ratio range of 0.01–0.8 the water present does not interfere. In the concentration range of above 0.8 anhydrous sodium sulfate is used for binding the water, in the amount of [Na2SO4.anh.]/[H2O]0.2. 相似文献
20.
The retention behavior of components analyzed by chromatography varies with instrumental settings. Being able to predict how changes in these settings alter the elution pattern is useful, both with regards to component identification, as well as with regards to optimization of the chromatographic system. In this work, it is shown how experimental designs can be used for this purpose. Different experimental designs for response surface modeling of the separation of fatty acid methyl esters (FAME) as function of chromatographic conditions in GC have been evaluated. Full factorial, central composite, Doehlert and Box-Behnken designs were applied. A mixture of 38 FAMEs was separated on a polar cyanopropyl substituted polysilphenylene-siloxane phase capillary column. The temperature gradient, the start temperature of the gradient, and the carrier gas velocity were varied in the experiments. The modeled responses, as functions of chromatographic conditions, were retention time, retention indices, peak widths, separation efficiency and resolution between selected peak pairs. The designs that allowed inclusion of quadratic terms among the predictors performed significantly better than factorial design. Box-Behnken design provided the best results for prediction of retention, but the differences between the central composite, Doehlert and Box-Behnken designs were small. Retention indices could be modeled with much better accuracy than retention times. However, because the errors of predicted tR of closely eluting peaks were highly correlated, models of resolution (Rs) that were based on retention time had errors in the same range as corresponding models based on ECL. 相似文献