Liquid chromatography on carbosilochrom and carbosilica gel-silica adsorbents with a modified carbon surface

Summary The silica adsorbent Silochrom C-120 which is homogeneous, macroporous and thermally stable, and Spherisorb S20W which is a wide-pore silica gel have been modified by the deposition on them of carbon formed by the pyrolysis of benzene. The adsorbent structures before and after modification have been studied. Columns packed with the Carbosilochrom and Carbosilica gel so obtained were used for studies of their selectivity in the liquid chromatography of an homologous series of polymethyl-and monoalkylsubstituted benzenes, alkylnaphthalenes, methylphenols and benzoic esters on elution with solutions of methanol + water of different concentrations. An increase in the amount of carbon deposited on the adsorbent and an increase in solvent polarity results in an increase in adsorbent selectivity. In the case of polymethylsubstituted benzenes this increase is greater than in the case of isomeric monoalkylsubstituted benzenes. For phenols this increase is less than that for the corresponding hydrocarbons. The separating power of the column can be controlled by changing the degree of specificity of the carbosilica and the polarity of the eluent.     

A Convenient Mannich-Type One-Pot Synthesis of Pyrimido[6,1-b][1,3,5]thiadiazines

Summary. 3-(Het)aryl-2-cyanoprop-2-enethioamides easily reacted with primary amines and excessive formaldehyde under mild conditions to afford pyrimido[6,1-b][1,3,5]thiadiazine derivatives in moderate yields. Furthermore, 2-cyano-2-cyclohexylideneethanethioamide reacted in the similar Mannich-type manner to give spiro-conjugated pyrimido-1,3,5-thiadiazines. The structure of 3,7-dibenzyl-8-(fur-2-yl)-3,4,7,8-tetrahydro-2H,6H-pyrimido[6,1-b][1,3,5]thiadiazine-9-carbonitrile was determined by X-ray diffraction analysis.     

Precise calculation of coulomb binding energies of mesomolecules

The best variational energies obtained to date for the ground states of all -mesomolecules are presented. The results are of rather high accuracy and can serve as a theoretical basis for the experimental study of three-body systems. The energies of thee ^– e ⁺ e ^–,H^– and 1¹ S, 2³ S, 2³ P, 2³ P states ofHe are calculated using the same method.     

Peculiarities in the evolution of the BUM of stimulated radio emission of the ionosphere

We present measured spectral and dynamic characteristics of the broad upshifted maximum (BUM) in the spectrum of artificial ionospheric radio emission (AIRE). It is shown that BUM is already formed starting from pump-wave frequencies that are smaller by at least 10 kHz than the values of electron gyrofrequency harmonic nf_He determined by the disappearance of the principal downshifted maximum (DM) in AIRE spectrum. The characteristics of additional maxima in BUM spectrum, which are a multiple of its principal maximum, are studied. It is shown that the frequency of BUM intensity maximum does not depend on the pump-wave frequency and the characteristic times of its evolution increase sharply for f_PW close to nf_He. We discuss the possibility of existence of the fast and slow components in BUM spectrum, which have significantly different evolution times. Experimental results on BUM behavior for different regimes of ionosphere modification are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 3, pp. 352–371, March, 1996.The authors thank the staff of the Sura heating facility for assistance in organizing and running the experiments. The Russian authors also thank the Russian Foundation for Fundamental Research (grants 94-02-03253a and 96-02-18659), Soros Foundation (grants R87000 and 020623), and Ministry of Science for financial support of this paper and the Sura heating facility.     

Quantum-Chemical Analysis of Coordination of Dimethylsulfoxide Molecules to Sodium and Potassium Cations

Coordination of dimethylsulfoxide molecules to the sodium and potassium cations was investigated by HF/6-31G(d)//HF/6-31G(d) and DFT(B3LYP/6-31G(d)) quantum-chemical methods. The coordination numbers of Na⁺ and K⁺ are found to be five and six, respectively. Thermal effects of complexation were calculated for each stage of the process; these were found to be 197.8, 160.1, 106.9, 88.0, 53.9 [HF/6-31G(d)] and 195.0, 158.5, 108.9, 95.7, 60.0 kJ/mole [B3LYP/6-31G(d)] for Na⁺ (one to five DMSO molecules, respectively); 146.6, 118.7, 90.2, 68.9, 70.0, 49.0 [HF/6-31G(d)] and 144.0, 117.4, 91.7, 78.9, 78.6, 56.4 kJ/mole [B3LYP/6-31G(d)] for K⁺ (one to six DMSO molecules, respectively). Structural parameters and charge distributions are given for the complexes. It is shown that solvation of sodium and potassium cations by DMSO molecules is preferable to solvation by water molecules.     

Estimate for the spectrum of an operator bundle and its application to stability problems

Simple estimates are obtained for the spectrum of the operator bundle \(R(\lambda ) = \sum\nolimits_{i = 0}^n {A_{n - i} \lambda ^i }\) in terms of estimates of the maximum and minimum eigenvalues of the operators \(\frac{1}{2}(A_{n - i} - A_{n - i}^* )(i = 0,1,2, \ldots n)\) and the norms of the operators \(\frac{1}{2}(A_{n - i} - A_{n - i}^* )(i = 0,1,2, \ldots n)\) We formulate a criterion of the asymptotic stability of the differential equations $$\sum\nolimits_{i = 1}^n {A_{n - i} } \frac{{d^{(i)} x}}{{dt^i }} = 0.$$ We present examples of the stability conditions for equations with n=2 and n=3.     

Calculation of the characteristics of ethanol and methanol adsorbed in a pore of activated carbon by the density functional method

Density functional theory was used to perform quantum-chemical calculations of changes in the energy and structure characteristics of methanol and ethanol molecules caused by their adsorption in model slitlike pores of activated carbon. The conclusion was made that changes in these characteristics (bond lengths, angles, charges on atoms, and harmonic vibration frequencies) is additional evidence of the validity of the Tolmachev thermodynamic model, in which adsorption is treated as a quasi-chemical reaction of the addition of adsorbate molecules to adsorption centers of an adsorbent. It was shown that the arrangement of alcohol molecules, when the C-O and C-C bonds were approximately parallel to pore walls and the hydrogen atom was directed toward a nearer pore wall, was most favorable energetically. Two adsorbed alcohol molecules are also arranged parallel to pore walls and form a hydrogen bond.     

Investigation of electronic structure of allenyl ethers by means of photoelectron and UV spectroscopy

A study of the photoelectron spectra of alkyl allenyl ethers has demonstrated their similarity to spectra of alkyl vinyl ethers, with the exception of a band in the 10.0–10.3 eV interval due to ionization of the -orbital of the allenyl fragment C=C. According to data obtained by photoelectron spectroscopy and MNDO quantum-chemical calculations, alkyl allenyl ethers with straightchain substituents exist primarily in the s-cis conformation. The stable conformation of allenyl tert-butyl ether is the s-trans form. The long-wave absorption bands in the UV spectra of alkyl allenyl ethers at 255–275 and 208–213 nm are assigned to electronic transitions of the ^* and ^{* *} types; these are quite insensitive to s-cis/s-trans isomerism.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 81–88, January, 1990.The authors are extremely grateful to V. K. Turchaninov for assistance in interpreting the spectra.