Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns

Summary The retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH₂PO₄ mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.     

Quantum-chemical study of the mechanism of the influence of cations of d metals on the rate of the oxidation of phosphine by Cu(II) halides

A hypothesis concerning the formation of associates between intermediate complexes and cations has been introduced in order to account for the experimental dependence of the rate constant of the oxidation of phosphine by Cu(II) halides on the nature of the cation in the salt MCl₂ (M = Mn, Co, Ni). The quantum-chemical characteristics of the systems formed have been calculated by the Mulliken—Wolfsberg—Helmholz-SCCC method. It has been shown that the correct correlation between the electronic properties of the intermediates and the rate constant of the reaction upon the variation of M can be obtained only for a specific mechanism for the addition of M²⁺ to the complex.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 6, pp. 718–722, November–December, 1985.     

Electronic Structure, Chemical Bonding, and Properties of Binary Carbides Mx M′y Cz in the Crystalline and Molecular States: XES, XPS, and Quantum-Chemical Studies

This paper reviews the results of electronic structure studies and investigations of the nature of chemical bonding and properties of binary d-metal carbides in the crystalline and molecular states. X-ray emission and X-ray photoelectron spectroscopy as well as quantum-chemical data are analyzed, and variations of the electronic properties and interatomic interactions are discussed for carbides of high-melting metals doped on the metal sublattice and a series of their reciprocal solid solutions: NbC–TaC, TiC–VC_0.87, TiC–NbC, and NbC–MoC_0.67 over a wide range of compositions. Prospects are discussed for application of quantum-chemical methods to structure and property modeling and forecasting for a new class of molecular clusters — binary metallocarbohedrenes M_8-n M_n C₁₂ and related metal–carbon nanoparticles of mixed composition.     

Synthesis and spectroscopic properties of soluble aza analogs of phthalocyanine and naphthalocyanine

The syntheses of aryl-substituted octaaza analogs of phthalocyanine — tetra-2,3-(4,5-diphenylpyrazino)porphyrazin and its vanadyl complex — and also of the vanadyl complex of tetra-2,3-(4-phenylquinolino)porphyrazin — a tetraaza analog of naphthalocyanine — are described. A modified singlestage method for the synthesis of the previously reported tetra-2,3-(5-tert-butylpyrazino)porphyrazin is put forward. The electronic absorption spectra of the compounds synthesized have been studied in organic solvents and acid media — in sulfuric acid solution and in organic solvents with the addition of phenol or trichloroacetic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 58–63, January, 1993.     

Über das Kriechen kristallisierender Salze, 11. Mitt.: Über Besonderheiten zweier Methoden zur Darstellung reiner kristalliner Salze: Die kriechende Kristallisation und das Zonenschmelzen

Zusammenfassung Die kriechende Kristallisation wird als Methode zur weitgehenden Reinigung kristalliner Salze der Methode des Zonenschmelzens gegenübergestellt. Zwischen der Verteilung der Verunreinigung in der Grundkristallmasse bei der kriechenden Kristallisation und der beim Zonenschmelzen existiert ein direkter Zusammenhang, welcher vom Verteilungskoeffizienten bestimmt wird.Gemeinsame Besonderheiten, wie auch einige Unterschiede dieser beiden Methoden, werden behandelt.

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In the present work, the creeping crystallization—as a highly purifying method applied for crystalline salts—is juxtaposed to the zonal melting method for preparing substances of high purification grade. A direct relationship exists between the distribution of impurities in the basic mass of crystalline salt during creeping crystallization and their distribution during zonal melting, which is controlled by the distribution coefficient.Some peculiarities, common to both methods, as well as some differences, provoked by the nature of the methods, are treated.

     

Retention of organic ligands on anionic and nonionic resins: Application to the separation and preconcentration of metal ions

Complexing resins obtained by retention of an organic compound on anionic and nonionic conventional exchangers have been reviewed. The influence of different parameters—nature of fixed ligand, kind and chemical form of the conventional resin, and pH of the aqueous solution—on characteristics and applications of this type of resin has been discussed. Results from the literature have been tabulated to simplify their presentation.     

Optical Alignment of Organic Dopants in a Solid Gel Matrix: Dispersed and Grafted Rhodamine B Molecules

We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment.     

Alanto- and isoalantolactones

Literature information (up to 1989) on two typical representatives of the eudesmane series of sesquiterpene lactones — alanto- and isoalantolactones — has been generalized for the first time. Questions of their occurrence in nature, their ecological role, isolation, and synthesis, and also their chemical and biological properties, are considered. The possibility has been shown of passing by a series of successive chemical transformations to other naturai sesquiterpene lactones with the same or a different type of skeieton.Institute of Organic Synthesis, Latvian SSR Academy of Sciences, Riga. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 307–320, May–June, 1990.     

Structures and conformational behavior of phosphorothioites and their complexes with transition metals obtained from X-ray diffraction analysis

The data on the structures, conformational behavior, and coordination properties of phosphorothioites are summarized. Their complexes with transition metals are characterized by different modes of coordination depending on the nature of the metal atom, the substituents at the sulfur atoms, reaction conditions, and conditions of single-crystal growth. The principal differences in properties of phosphorothioites and their analogs containing the P—O and P—N bonds are analyzed.     

Structures and reactivities of benzo-1,2,3-dithiazolium salts and their selenium analogs

A number of benzo-1,2,3-dithiazolium chlorides (I) and their selenium analogs — benzo-1,2,3-thiaselenazolium, benzo-2,1,3-thiaselenazolium, and benzo-1,2,3-diselenazolium salts — were synthesized. The electronic structures and reactivities of the I cation and salts I–IV are discussed on the basis of a quantum-chemical calculation of cation I and the PMR spectra of salts I–IV. Successive substitution of the sulfur atoms in the I cation by selenium atoms, particularly in the 2 position, substantially increases the degree of transfer of positive charge to the condensed benzene ring. The trend of the nucleophilic reactivities of 6-methoxy derivatives of salts I–IV in the reaction with aromatic amines is the same as the trend of the degree of localization of the positive charge in the 6 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 912–916, July, 1978.     

Anode volt-amperometry of aminopyridines and aminopicolines

The electrochemical behavior of amino derivatives of pyridine — 2-, 3-, and 4-aminopyridines, 2-amino-3-methylpyridine, 2-amino-4-methylpyridine, 4-amino-3-methylpyridine, and 2,6-diaminopyridine — during their oxidation on a rotating platinum microanode in acetonitrile and aqueous alcohol was investigated. Differences associated with the electronic effect of the substituent were uncovered during the electrical oxidation of the indicated compounds. The data obtained make it possible to conclude that the magnitude of the current strength in the oxidation of aminopyridines is determined by the rate of diffusion of the depolarizer to the electrode.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1654–1657, December, 1977.     

Functional Polyoxometalate Thin Films via Electrostatic Layer-by-Layer Self-Assembly

Polyoxometalates (POMs) comprise a structurally diverse class of inorganic transition metal oxygen clusters which—owing to their unique electronic properties—hold promise for a host of technological applications such as electrochromic windows, sensors, or heterogeneous catalysts, prototypic examples of which will be briefly exemplified. The integration of POMs into functional architectures and devices, however, necessitates the development of general methods that allow positioning these clusters in well-defined supramolecular architectures, thin films, or mesophases. This short review highlights recent advances in the preparation of composite multilayers fabricated by electrostatic layer-by-layer self-assembly (ELSA) of POMs and a variety of water-soluble cationic species, including transition metal complexes, cationic surfactants, polycations and bipolar pyridine.     

An extension of the CNDO/2 formalism for the study of transition metal complexes

The electronic structure and the conformational analysis of some Ni(PX₃)₄ (X = F, OCH₃, Cl, CH₃, H) complexes are investigated within the framework of the previously described extended CNDO/2 method in order to interpret their magneto-optical behaviour and to propose a suitable scheme for the electronic content of a metal-ligand ( + ) dative bond. Chatt and Wilkinson's pattern, used up to now, is criticized and a new scheme is proposed which — taking accurately the role of electronegativity into account and abiding by Pauling's principle of electroneutrality — fits well the sets of available physico-chemical data and allows us to understand whyab initio bonds overlap populations as well as IR force constants are low for any metal-ligand ( + ) dative bond.     

Ab initio study of the structure and conformations of 2-fluoroethanal in the ground and lowest excited electronic states

The structure of the conformationally flexible 2-fluoroethanal molecule (CH₂FCHO, FE) in the ground (S₀) and lowest excited triplet (T₁) and singlet (S₁) electronic states was investigated by ab initio quantum-chemical methods. The FE molecule in the S₀ state was found to exist as two conformers, viz., as cis (the F—C—C—O angle is 0°) and trans (the F—C—C—O angle is 180°) conformers. On going both to the T₁ and S₁ states, the FE molecule undergoes substantial structural changes, in particular, the CH₂F top is rotated with respect to the core and the carbonyl CCHO fragment becomes nonplanar. The potential energy surfaces for the T₁ and S₁ states are qualitatively similar, viz., six minima in each of the excited states of FE correspond to three pairs of mirror-symmetrical conformers. Based on the potential energy surfaces calculated for the FE molecule in the T₁ and S₁ states, the one-dimensional problems on the torsion and inversion nuclear motions as well as the two-dimensional torsion-inversion problems were solved.     

Insight on Structural Change in Sol–Gel-Derived Silica Gel with Aging under Basic Conditions for Mesopore Control

Structural rearrangement of sol–gel-derived silica gel by aging under basic conditions was investigated using small angle X-ray scattering (SAXS) and ²⁹Si nuclear magnetic resonance (NMR). A wet silica gel prepared under acidic conditions had a fractal nature, and many unreacted silanols remained on the surface. During aging of the gel in ammonia solution, additional Si—O—Si bonds rapidly formed, whereas the change in mesoscale structure gradually proceeded. This result was compared with that of simulation modeling the Ostwald ripening, i.e. dissolution from positive curvature and reprecipitation on negative curvature. In the simulation, structural change in a cluster from fractal nature to particle aggregates was well visualized in 2-dimmensional square lattice. Both scattering profiles calculated from the model clusters and the change in average coordination number of monomers in the cluster well agreed with the experimental SAXS and NMR results, respectively. This agreement strongly ensures us that structural change by aging under basic conditions proceeds through the Ostwald ripening. The mesopore size as well as mesopore volume in calcined silica gel is determined by the shrinkage degree during drying and calcination. The sample aged in basic solution restrains the shrinkage because of the growth of particulate structure, and retains large size and volume of pores.     

Experimental Studies on Isonicotinato Cadmium(II) Complex [Cd(C<Subscript>6</Subscript>H<Subscript>4</Subscript>NO<Subscript>2</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>] and Density Functional Calculations

Isonicotinato cadmium(II) complex [Cd(C₆H₄NO₂)₂(H₂O)₄] has been synthesized by hydrothermal method and characterized by elemental analysis, electronic-spectra and thermogravimetric analysis. Density functional theory (DFT) method calculations of the structure, atomic charges distribution, electronic spectra, natural population analysis and the thermodynamic properties at different temperatures have been performed. The calculated results show the electronic transitions are mainly derived from the contribution of bands π → π^* and the decomposition of the title compound should first occur at the bond of Cd—O, then at the bond of Cd—N, which agrees very well with the experimental data.     

Synthesis and spectral-luminescence properties of hetarylethylene derivatives of 2,5-diphenyloxazole and 2,5-diphenyl-1,3,4-oxadiazole

A number of new organic luminophores was synthesized by PO olefination from 2- (4-bromomethylphenyl)-5-phenyloxazole and -1,3,4-oxadiazole and various heterocyclic aldehydes that contain a furan ring. The absorption and fluorescence spectra of the products in toluene, as well as their scintillation characteristics, were measured. The effect of the electronic nature of the substituents on the spectral-luminescence properties of the luminophores is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 617–621, May, 1982.     

Die Untersuchung der Pyrolyseprodukte von Tabak-Zusatzstoffen als Grundlage ihrer gesundheitlichen Beurteilung

Zusammenfassung Die gsundheitliche Beurteilung eines Tabak-Zusatzstoffes erfordert die Kenntnis seines eigenen toxikologischen Verhaltens und das seiner Schwelprodukte. Eine neu entwickelte Versuchsanordnung gestattet — bei dem Rauchvorgang angenäherten Bedingungen — alle Zusatzstoffe zu verschwelen und die Schwelprodukte — vor allem die cancerogen und cocancerogen verdächtigen — nach Art und Menge zu bestimmen. Als Leitsubstanz für die Cancerogenität dient das 3,4-Benzpyren. Bei den Untersuchungen wurden bemerkenswerte Zusammenhänge zwischen Struktur, Kettenlänge und Kondensationsgrad des Zusatzstoffes und Art und Menge der Polycyclen im Schwelprodukt beobachtet. Außer auf die primär durch Pyrolyse entstandenen Aromaten erstrecken sich die Untersuchungen auch auf die durch Sekundärreaktionen gebildeten ebenfalls cancerogen wirksamen Nitrosamine und die Lactone.

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Summary The hygienic judgment of tobacco additives requires the knowledge of his own toxicological effect and that of his smouldering products. A newly developed testing arrangement allows (approximately under smoking conditions) the smouldering of all additives and the determination of their smouldering products — especially those suspected to be carcinogenic and cocarcinogenic — according to their nature and quantity. 3,4-Benzopyrene has been taken as prototype of carcinogenity. The tests revealed remarkable relations between structure, chain length and grade of condensation of the additive and the nature and quantity of polycycles in the smouldering product. Besides the aromatics formed primarily by pyrolysis also carcinogenic substances were examined which are formed by secondary reactions, for example nitrosamines and lactones.

     

Proton magnetic shielding in H2O and (H2O)2

The proton magnetic shielding constants in the water molecule and its linear perpendicular dimer are computed from SCF-MO-LCGO wave functions by using the uncoupled Hartree-Fock variation-perturbation procedure due to Karplus and Kolker. The convergence of the calculated shielding constants as well as their gauge dependence is studied. The final results for 17-term polynomial variation function indicate that the best choice for the gauge origin corresponds to the molecular electronic centroid.The calculated proton magnetic shielding constant in the water molecule is in remarkable agreement with experimental data and favourably compares with the best coupled Hartree-Fock results. It follows from the calculations for the water dimer that the H-bond NMR-shift amounts in this case —1.0 ppm and qualitatively agrees with the experimental data for the liquid water.     

Electrosynthesis of N-Arylazoles by Electrolyzing a Mixture of Azole and 1,4-Dimethoxybenzene in a Diaphragmless Cell

An analysis is performed and data are compared on the electrosynthesis of N-arylazoles and regularities of this process in conditions of a diaphragmless galvanostatic electrolysis (Pt, MeCN, Bu₄NClO₄) of a mixture of 1,4-dimethoxybenzene (DMB) with azoles (pyrazole, triazole, their derivatives, tetrazole). Electrolysis of an azole/DMB mixture leads to the formation of products of an ortho-substitution—1,4-dimethoxy-2-(azolyl-1)benzenes—and, simultaneously, hydrolytically unstable products of an ipso-bis-attachment—1,4-dimethoxy-1,4-di-(azolyl-1)cyclohexa-2,5-dienes. The overall yield of these compounds increases upon adding a base (collidine) or an acid (AcOH) into the initial mixture, and the basicity of initial azoles substantially affects the electrosynthesis results. New notions on the nature of nucleophilic species interacting with radical cation of DMB are considered. The species in question are complexes of azoles with one another or with collidine generated at the expense of the hydrogen bond, rather than azolate ions. Furthermore, the cathodic process is largely connected not with the generation of azolate ions (as a result of the reduction of initial azoles) but with the deprotonation of onium compounds (BH⁺)—products of the interaction of azoles or collidine with protons. The mechanism of electrosynthesis of N-arylazoles is discussed. The key stages of the synthesis are the attack of a nucleophile on the ipso- and, possibly, ortho-positions of the benzene ring of radical cation of DMB, as well as the rearrangement of the intermediate cation of 1,4-dimethoxy-1-(azolyl-1)arenonium into the cation of 1-(azolyl-1)-2,5-dimethoxyarenonium, which affects both the yield and ratio of final products of the reaction mixture.