Gas-liquid chromatography of thioesters of perfluorocarboxylic acids 1. Characteristics of retention

Retention of thioesters of perfluoropentanoic acid C₄F₉C(O)SR was studied by GLC on packed and capillary columns using stationary phases SE-30, SKTFT-50X, XE-60, and Carbowax 20M. The retention indices of these compounds were calculated, and their relationship with the structure of the compounds and the conditions of the analysis were established. Translated fromIzvestiya Akademii, Nauk. Seriya Khimicheskaya, No. 5, pp. 984–986, May, 1997.     

Thermodynamic characteristics of sorption of heterocyclic compounds m capillary gas chromatography

Dependences of sorption energies of sulfur-, oxygen-, and nitrogen-containing heterocyclic compounds on the nature of heteroatoms, structure of substituents and their position in the ring were studied. The contributions of heteroatoms, functional and alkyl groups to the energy of dispersive interaction of position isomers with nonpolar stationary phases were determined for imidazoles, piperidines, morpholines, thiomorpholines, dioxalanes, oxathiolanes, dithiolanes, thiophenes, and furans. The nonequivalence of contributions of the same substituents to the sorption energy of each of the heterocyclic compounds, depending on the nature of the heteroatom and position of the substituent, was shown. The obtained values of contributions of heteroatoms and substituents can be used for apriori calculation of retention indices of position isomers of five- and six-membered heterocycles containing one or two heteroatoms in the ring.Translated from lzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2033–2038, August, 1996.     

Cotrimerization of mono- and dinitriles of perfluorocarboxylic acids under high pressures

Cotrimerization of mono- and dinitriles of perfluorocarboxylic acids under high pressures affords oligoperfluoroalkylenetriazines. These oligomers are highly efficient stabilizers of thermooxidative destruction of perfluoropolyethers, when they are contacting with metals at elevated temperatures.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1814–1816, September, 1995.     

Sorption characteristics of polyfluorocarboxamides

The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides R_FC(O)NR₂ (R_F = CF₃(CF₂) _i ,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 868–871, May, 1994.We are grateful to R. V. Golovnya and D. N. Grigor'eva (Institute of Food Substances of the RAS, Moscow) for their participation in the discussion of the results obtained.     

Complexes of crown ethers with perfluorocarboxylic acids and their thermal decarboxylation

Crown ethers form strong proton-acceptor complexes with CF₃COOH or C₄F₉COOH that undergo thermal decarboxylation at 200–260 °C which results in 60–80% of CF₃H or C₄F₉H (including up to 20 % of a mixture of C₄F₈). Critical parameters of the process were determined in relation to the temperature and amount of crown ether. The relative activities of different crown ethers in decarboxylation were also established. A scheme is proposed that explains the effect of the structure of crown ethers on this reaction. The data obtained substantiate the view that the topological correspondence concept is insufficient to explain the ability of crown ethers to form complexes with cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1098–1101, June, 1993.     

Gas-liquid chromatography of isopropylidene monosaccharides and their trimethylsilyl derivatives

Summary This paper describes the gas chromatographic separation of the mixture of isopropylidene monosaccharides, and their trimethylsilyl derivatives. Based on the total analysis time and resolution the best stationary phase was SF-96 using Chromosorb G as the solid support and temperature programming.     

Gas-liquid chromatography of isopropylidene-glucose and glucose as their trimethylsilyl derivatives

Summary This paper describes the gas chromatographic separation of the mixture of di- and mono-O-isopropylidene-D-glucose and D-glucose as their trimethylsilyl derivatives. The use of OV-101 as liquid phase provides a complete separation for the all components in the mixture. Quantative analysis was performed using xylitol as the internal standard for di- and mono-O-isopropylidene-D-glucose, and sorbitol as the internal standard for -and -glucose.     

Solid-phase synthesis of peptide and glycopeptide thioesters through side-chain-anchoring strategies

An efficient new strategy for the synthesis of peptide and glycopeptide thioesters is described. The method relies on the side-chain immobilization of a variety of Fmoc-amino acids, protected at their C-termini, on solid supports. Once anchored, peptides were constructed using solid-phase peptide synthesis according to the Fmoc protocol. After unmasking the C-terminal carboxylate, either thiols or amino acid thioesters were coupled to afford, after cleavage, peptide and glycopeptide thioesters in high yields. Using this method a significant proportion of the proteinogenic amino acids could be incorporated as C-terminal amino acid residues, therefore providing access to a large number of potential targets that can serve as acyl donors in subsequent ligation reactions. The utility of this methodology was exemplified in the synthesis of a 28 amino acid glycopeptide thioester, which was further elaborated to an N-terminal fragment of the glycoprotein erythropoietin (EPO) by native chemical ligation.     

气液色谱法研究双-(O,0′-二正辛基二硫代磷酸酯)合镍(Ⅱ)与酮类加合反应的热力学性质

二烷基二硫代磷酸酯及其过渡金属配合物具有强杀菌性能及抑制酶水解作用,可以用作石油添加剂和高聚物防老剂,又是一类优良的萃取剂,用于钴镍、钴锰等的萃取分离^[1-2]。二硫代磷酸酯的金属盐与含氮、含氧的有机碱形成的加合物在液-液萃取中起着重要作用^[3],因此这类配物合的加合作用受到了广泛的注意。     

Synthesis of phosphonocinnamic thioesters, substrate analogues of cinnamoyl-CoA reductase, a key enzyme in the lignification process

The one-pot transesterification of diethylarylvinylphosphonates with N-acetylcysteamine has been achieved using phosphonochloridates as intermediates. Reaction of phosphonodiesters with (COCl)₂ gave the corresponding chlorinated compounds, which were coupled with N-acetylcysteamine in presence of Et₃N.     

Choice of procedures for preparative chromatography

Quantitative criteria, necessary and sufficient, were developed basing on the analysis of asymtotic solutions of border equations in elution sorption dynamics for realization of selectivity inversion for components in a chromatographic system due to the effect of kinetic selectivity. Analysis is suggested for experiments, where the new approach to realization of chromatographic processes using effect of kinetic selectivity allows optimization of preparative separation of biologically active substances. The approach suggested implies shortening of the experiment duration for separation processes, which can be crucial in most systems where components to be isolated are labile, or the process economics suffers considerably due to mobile phase, or energy consumption.     

Stationary-phase swelling and its consequences in capillary gas-liquid chromatography

Sample introduction using the solvent effect can lead to significant swelling of the stationary phase. The phenomenon has been studied theoretically and experimentally. The longitudinal profile of the swollen phase has been established. Swelling can affect the retention time of solutes, the shape of solute bands emerging from the inlet, and the maximum permissible sample size.     

Efficient synthesis of thioesters and amides from aldehydes by using an intermolecular radical reaction in water

The combination of the water-soluble radical initiator, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) and the surfactant, cetyltrimethyl-ammonium bromide (CTAB), was found to be the most suitable condition for the effective and direct synthesis of useful active thioesters (pentafluorophenyl thioesters) in water. In addition, the direct amidation of aldehydes was achieved by the addition of the amines to the thioesterification reaction mixture in water.     

Influence of the chemical nature of siloxanes on the thermodynamic characteristics of sorption for a series of linear and cyclic saturated hydrocarbons

The thermodynamic characteristics of sorption (Henry’s constants of sorption equilibrium K _sorp, heats of sorption q, and standard entropies of sorption ΔS°) were studied by gas chromatography to describe the behavior of linear and cyclic saturated hydrocarbons on phenylmethylsiloxane HP-5, fluoromethylsiloxane OV-210, and methylsiloxane OV-1. The K _sorp and q values and, correspondingly, the energy of dispersion interactions decrease in the series HP-5 > OV-1 > OV-210. The difference in structures of adamantane, trans-decalin, and decane molecules has almost no effect on the heats of sorption. Henry’s constants increase on going from decane to trans-decalin and, further, to adamantane. This effect becomes more pronounced with an increase in the sorbent polarity (OV-1 < HP-5 < OV-210). The entropy factor can play a key role in sorption processes on siloxanes.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 140–143, January, 2005.     

Gas-liquid chromatography of serum bile acids using glass capillary columns

The proposed combination of a rather simple procedure for sample preparation with capillary gas-liquid chromatography using a barium carbonate/polyethyleneglycol 20,000 column and a Grob-type on-column injector permits measurement of bile acids in serum with high separation efficiency, short analysis time and complete separation of bile acids from cholesterol. The method can be adapted to combined capillary gas-liquid chromatography - mass spectrometry.     

辛基苯酚的气相色谱

本文用高温液晶芳香羧酸酯作固定相, 经气相色谱法直接分离了2-辛醇与苯酚的反应产物, GC-MS及合成的标准样品证明为1-甲基庚基本酚、1-乙基己基本酚及1-丙基戊基苯酚的邻位和对位异构体组成。研究了柱温对调整保留时间和柱效能的影响, 讨论了“过冷"现象, 并对不同催化体系的反应产物进行了定量分析。     

The reaction of thioesters with nitriles. A new synthetic approach to the preparation of substituted 4-alkylthio- and 4-arylthiopyrimidine derivatives

S-Alkyl and S-aryl thioesters react with nitriles in the presence of triflic anhydride to form substituted 4-alkylthio- and 4-arylthiopyrimidines. However, when methyl thiocyanate is used as nitrile, dithioimidocarbonates are formed. A mechanism to explain these differences is postulated.     

The formation of open-chain thioesters in the reaction of 2-lithio-2-methyl- and 2-lithio-2-phenyl-1,3-dithiane with chlorodiphenylphosphane followed by oxidation

The unexpected formation of open-chain thioesters (3) and (6) from the reaction of 2-lithio-r-2-t-4-t-6-trimethyl (1-Li) and 2-lithio-r-2-phenyl-t-4-t-6-dimethyl-1,3-dithiane (4-Li), respectively, with chlorodiphenylphosphane followed by oxidation was observed instead of the anticipated gem-derivatives. The X-ray diffraction analysis of (6) and the trapped intermediate (10) confirmed the structure and the proposed mechanism of formation of the open-chain products.