The effect of the structure of bonded cyanoalkyl stationary phases on their selectivity in the liquid chromatographic separation of polynuclear aromatic hydrocarbons

Summary The paper discusses the effect of the length and structure of the hydrocarbon chain connecting the nitrile group to the silica gel surface on the chromatographic properties of cyanoalkyl phases.When using non-polar and polar mobile phases, the selectivity of the cyanodecyl phases toward PAHs is higher than of the cyanopropyl phase and of hydroxylated silica gel.Polar additives to the mobile phase drastically decrease the retention on silica gel and on the cyanopropyl phase while affect the properties of cyanodecyl phases only to a considerably less degree. Newly synthesized phases with different structures of the hydrocarbon chain are compared with the commerical cyano-and ODS-phases. The retention mechanism on the cyanoalkyl phases is discussed.     

Study of a Catalytic Mechanism in Additive Differential Pulse Techniques

The new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t₂?t₁, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV).     

Determination by LC of Polyphenols in Italian Red Wine

A reversed-phase liquid chromatographic method, optimised for the separation of trans-, and cis-resveratrol, catechin, epicatechin, quercetin and rutin, is reported. Separation was achieved using a C18 column and a gradient elution with acetonitrile and 5% formic acid aqueous solution. The analyses required an equilibration period of 10 min and a run time of 25 min for completion. Identification was based on retention characteristics and by relative UV spectra, obtained by photodiode array detector and were compared with commercial standards. Analyses were performed without any sample pre-treatment. Detection was carried out by UV–Vis detector at three different wavelengths. The detection limit ranged from 0.16 μgm L⁻¹ (cis-resveratrol) to 1.5 μgm L⁻¹ (+)-catechin. Investigation was extended to quantitative determination of phenol compounds in Italian red wine and to investigate the stability of the six antioxidants.     

GC–MS analysis of phenolic compounds in fuels after conversion to trifluoroacetate esters

The GC–MS characteristics of trifluoroacetate esters of phenolic compounds are discussed. Linear temperature programmed retention indices and total ion current MS response factors of over 120 phenolic esters are reported. The main GC advantages from analysis of trifluoroacetate esters as compared to plain phenols are enhanced volatility and improved resolution. For example, the elution temperature of a given phenol is typically 50 °C greater than that of the corresponding trifluoroacetate ester. Also, while retention of compounds with two trifluoroacetate groups is only moderately greater than mono esters, underivatized dihydroxy compounds are very difficult to elute from any GC column. Complete resolution of isomeric C₀-, C₁- and C₂-alkylphenol esters is readily achieved on conventional fused silica GC columns; resolution of the corresponding underivatized compounds requires specialized GC columns with low temperature limits. In general, mass spectra of trifluoroacetate esters are more characteristic of a given structure than those of the corresponding phenols and may be more rigorously interpreted towards structural elucidation. A table in the report summarizes some of the more important spectral features used in compound identification. Example applications in analysis of coal-, shale- and petroleum-derived materials are presented. Selected ion monitoring is used to determine individual phenolic components in whole distillates; reconstructed ion chromatograms are used to illustrate distributions of selected species as a function of fuel storage and thermal stress.     

Stoichiometric and catalytic methods of asymmetric synthesis of nonproteinogenic α-and β-amino acids via transition metal coordination compounds

The complexes of glycine, -alanine, and -alanine with (S)-[N-(N-benzylprolyl)amino] benzophenone formed by Ni(II) and Cu(II) ions and Schiff bases enter into different nucleophilic and electrophilic reactions with the formation of diastereoisomeric complexes which decompose into proteinogenic and nonproteinogenic L-amino acids with a high chemical yield and elevated optical purity (70–90%). Optically pure amino acids can be obtained from diastereoisomerically pure complexes after the complexes are separated by recrystallization of the mixture of diastereoisomeric complexes formed. A new type of interphase catalysts of C-alkylation of achiral Schiff bases was proposed. The catalysts are positively charged Ni(II) and Cu(II) complexes of Schiff bases of chiral diamines. In some cases, these complexes have a higher activity and capacity to execute asymmetric alkylation than traditional chiral interphase catalysts based on cinchonidine.Based on materials in the section report by Yu. N. Belokon' to the 7th European Symposium on Organic Chemistry, ESOC-7.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1106–1127, May, 1992.     

Convexlike and concavelike conditions in alternative,minimax, and minimization theorems

Convexlike and concavelike conditions are of interest for extensions of the Von Neumann minimax theorem. Since the beginning of the 80's, these conditions also play a certain role in deriving generalized alternative theorems of the Gordan, Motzkin, and Farkas type and Lagrange multiplier results for constrained minimization problems.In this paper, we study various known convexlike conditions for vector-valued functions on a set and investigate convexlike and concavelike conditions for real-valued functions on a product setC×D, where we are mainly interested in the relationships between these conditions. At the end of the paper, we point out several conclusions from our results for the above-mentioned mathematical fields.The author is indebted to Dr. R. Reemtsen and Dr. V. Jeyakumar for their helpful comments during the preparations of this paper.     

X-ray and IR spectroscopic studies of specific intermolecular interactions inN′-substituted isonicotinohydrazides

_N-Thenylidene- andN-(o-nitrobenzylidene)hydrazides of isonicotinic acid have been studied by X-ray structural analysis and IR spectroscopy. In the crystalline state, these molecules are linked through intermolecular N—H ... Np_y hydrogen bonds. Carbonyl groups are not involved in intermolecular hydrogen bonds. However, it was found that the C=O group participates in an attractive interaction with the sulfur atom of the thiophene group. The energy of this interaction is comparable with the energies of intermolecular C=O ... H—N hydrogen bonds in amides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 896–900, April, 1996.     

Thermal Decomposition of Bi(III), Cd(II), Pb(II) and Cu(II) Thiocyanates

Thermal decomposition of Bi(SCN)₃, Cd(SCN)₂, Pb(SCN)₂ and Cu(SCN)₂ has been studied. The thermal analysis curves and the diffraction patterns of the solid intermediate and final products of the pyrolysis are presented. The gaseous products of the decomposition (SO₂ and CO₂) were detected and quantitatively determined. Thermal, X-ray and chemical analyses have been used to establish the nature of the reactions occurring at each stage in the decomposition.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effect of medium on the rate constant of decomposition of di(tert-butyl)trioxide

It was found that the medium affects the rate constant of the thermal decomposition of di(tert-butyl)trioxide. In all solvents studied, the decomposition occurred according to the first-order law. The effect of the solvent on the rate constant was analyzed within the framework of the Koppel-Palm equation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1167–1168, June, 1995.The authors are grateful to O. N. Makarova for help in this work.This study was financially supported by the Russian Foundation for Basic Research (Grant No. 93-03-5231).     

Determination of acidic sites and binding toxic metal ions on cumin surface using nonideal competitive adsorption model

A fundamental study of the application of cumin biomass in the recovery of Cu and Zn metal ion uptake from food and drinks is carried out at different pH's and at fixed ionic strength. The chemical characteristics of protein in cumin seeds were investigated. Results showed that cumin contains 18.25% crude protein, which includes 18 amino acids. The main reactive groups on protein cumin are amino and carboxylic groups of dicarboxylic amino acids, leading to a pH-dependent charge. Therefore, the cumin surface is considered as a heterogeneous system. To describe protonation behavior in a heterogeneous cumin biomass (cumin/0.1 M NaNO(3)) system, acid-base titrations have been performed with conductometric and potentiometric titration. Measurement of the reactivity of cumin surface in the adsorption of Cu and Zn metal ions and determination of metal binding at different pH's were also carried out. To solve broad and ill-defined titration curves, a simplified version of nonideal competitive analysis (NICA) by Plette et al.) was applied. The results show that the sorption of the bivalent metal ions onto the whole surface of cumin could be attributed to a monodentate binding to one site mainly carboxylic-type site.