Kinetic and Thermodynamic Parameters of the Thermal Decomposition of Some Metal Complexes of 4‐Benzamido‐3‐Thiosemicarbazone Derivatives

The kinetic and thermodynamic parameters such as reaction order, activation energy, enthalpy, free energy and entropy change related to the thermal decomposition of Co(II), Ni(II) and Cu(II) hydrazone complexes of 4‐benzamido‐1‐(4‐actylpyridine)‐3‐thiosemicarbazone (BACPT) and 4‐benzamido‐1‐(pyridine‐3‐aldehye)‐3‐thiosemicarb‐azone (BAPT) were evaluated from differential thermal analysis (DTA) curves using Thomas‐Clarke's method. The thermal stability of these complexes are discussed in relation to the nature of the metalion and of the ligand present. A suitable mechanism for the thermal decomposition process of the complexes based on the data of the thermogravimetric analysis (TGA) was suggested.     

Chiral stationary phases for LC and SFC obtained by “Polymer coating”

Summary Chirally substituted Si–H-containing polysiloxanes were synthesized, which can be immobilized on small particle silica gel as well as on the smooth surfaces of fused silica capillaries. Immobilization is achieved either by crosslinking or by chemical bonding to the surfaces via silanol groups; both reactions can only be performed by addition of H₂PtCl₆, which acts as catalyst for hydrosilylation and as stoichiometric reagent for crosslinking. Chiral substituents of systematically varied chemical structure were introduced into the polysiloxanes by hydrosilylation. The mechanism of immobilization was investigated by spectroscopic methods, notably²⁹Si-NMR. Homogenous stationary-phase coatings of variable film thickness and corresponding retentivity can easily be achieved. The enantioselectivity of the phase systems was characterized in dependency on the chemical structure of the chiral selectors attached to the polysiloxane chain of the chiral stationary phases and also in terms of the functional groups introduced into the solutes by derivatisation.     

Synthese von „Dithio-Oxolinsäure“

5-Amino-benzo-1,3-dithiol, available by reduction of 5-amino-benzo-1,3-dithiol-2-thion, was elaborated into dithio-oxolinic Acid (6 a).

     

Microcalorimetric investigation of influence of cancerogenic and anticancerogenic compounds on nuclear chromatin of tumor cells

The influence of mitoxantron (M) and benz(a)pyrene (BP) on chromatin DNA in composition of spleen and liver tissues and cells of BALB/c mice were studied using a high-sensitive differential scanning microcalorimeter. It was established that BP can cause a) the specific breaks in inactive chromatin DNA chain and unfolding of the whole domain (a loop of chromatin) which should lead to uncontrolled genome activation; b) the breaks in the DNA double-helix creating short duplexes.M at low doses, interacting with naked linker DNA of tumor restores the chromatin structure, at high doses or at repeated injections,M causes the disturbance of chromatin structure.     

HPLC determination of urinary 2,4- and 2,6-toluendiamines as potential degradation products of polyurethane breast implants

Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples was by liquid/liquid extraction and urine specimens of patients after surgury were analysed.     

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.     

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.     

Bias in modal parameters due to aliasing in the time domain

This paper deals with some aliasing effects in the time domain that can lead to unacceptable misestimations of modal parameters. When a frequency response function of a vibrating system is sampled and inverse Fourier transformed, the resulting impulse response is given by an infinite geometric series, the single term of which is the impulse response itself shifted in time. For this reason, some modal parameters, if estimated in the time domain, are biased; in particular, while the damping factor and the natural frequency are not influenced by the aliasing phenomenon, the magnitude and phase of the residue can be highly biased. Corrective terms are theoretically evaluated and their efficiency is shown in numerical simulations.

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Sommario In questo articolo e' presentato un metodo per correggere gli errori che si compiono nella stima di alcuni parametri modali, quando essi vengono ricavati nel dominio del tempo. Infatti se la funzione di risposta in frequenza e' ottenuta con eccitazioni particolari—quali ad esempio lo pseudo-random, lo stepped-sine a passo costante o lo sweep in frequenza-la risposta impulsiva, ottenuta per mezzo dell'antitrasformata discreta di Fourier, risulta periodica, con periodo pari all'inverso della spaziatura tra le righe spettrali. Cio' comporta un errore nella stima dell'ampiezza e della fase del residuo, mentre nessuna conseguenza si ha sulla frequenza naturale e sul fattore di smorzamento. L'errore sulle stime risulta tanto piu' grande, quanto meno smorzata e' la risposta impulsiva all'interno dell'intervallo di osservazione.Partendo dall'inviluppo e dalla fase istantanea dei segnali complessi, ottenibili per mezzo della trasformata di Hilbert, si sono ricavati i termini correttivi sia per il modulo, che per la fase del residuo. La validita' delle correzioni e' mostrata con esempi numerici.

     

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.