Non-empirical calculations and basis set effects on the inversion geometry of the aniline molecule

The geometry of the amine group and the barrier to internal conversion in aniline have been studied by single-determinantab initio SCF calculations using several basis sets from minimal to double-zeta quality. The results obtained from different types and sizes of basis sets are discussed. Calculations performed with the two most flexible basis sets yield inversion barriers of 0.9–1.1 kcal/mole and angles of pyramidalization at the nitrogen atom of 38–39 ° which are in good agreement with the experimental results (1.3 kcal/ mole and 38 °). Orbital and overlap population analyses are performed and compared with the expected mesomeric and inductive effect. The calculated dipole moment 1.48–1.49 D also agrees with the experimental values (1.48–1.50 D).Dedicated to Professor O. E. Polansky, Mülheim/Ruhr, on the occasion of his 60th birthday.     

Acid association quotients of bis-tris in aqueous sodium chloride media to 125°C

The ionic strength and temperature dependencies of the molal acid association quotients of 2,2-Bis(hydroxymethyl)-2,2,2-nitrilotriethanol (also abbreviated as bis-tris) were determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The emf was recorded for equimolal bis-tris/bis- trisHCl buffer solutions from 5 to 125°C at approximately 25°C intervals, and at nine ionic strengths from 0.05 to 5.0m (NaCl). The molal association quotients, combined with infinite dilution values from the literature, are described precisely by a seven parameter equation which yielded the following thermodynamic quantities at infinite dilution and 25°C: logK=6.481±0.003, H ^o =–28.5±0.2 kJ-mol ^–1 , S ^o =28.5±0.8 J-K ^–1 -mol ^–1 , and C _P ^o =–22±5 J-K ^–1 -mol ^–1 . The equation incorporates a simple three term expression for logK, but requires four terms to describe the rather complex ionic strength dependence despite the reaction being isocoulombic. The molal association quotients from this study and the literature were also subjected to the Pitzer ion interaction treatment.     

Synthesis of polysubstituted 1,3-cyclohexadienes from β-branched α,β-alkenals and monoesters of ylidenemalonic acids

3-Methyl- and 3-phenyl-2-butenal react with monoesters of alkylidene-, alkenylidene-, and arylmethylenemalonic acids in the presence of piperidine as the catalyst to give esters of 4,6-disubstituted 1,3-cyclohexadienecarboxylic acids in 23–96% yields. Under the same conditions cyclohexylideneacetic aldehyde reacts with the monoesters of prenylidene- and benzylidenemalonic acid to afford mixtures of 1,8a-trans- and 1,8a-cis-isomers of 1-substituted alkyl 1,5,6,7,8,8a-hexahydronaphthalene-2-carboxylates, the ratios and configurations of which were determined by means of¹H NMR spectroscopy. In some cases the formation of cyclic dienes is impeded by the competing process of decarboxylation of acidic ylidenemalonates. The derivatives of 4,6-diphenyl-1,3-cyclohexadienecarboxylic acid were shown to be convenient precursors for the preparation ofmeta-terphenyls.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 154–161, January, 1996.     

Kinetic method for the study of xylan hydrolysis by xylan hydrolases

Summary The Somogyi-Nelson colorimetric method was used in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of xylan catalyzed by xylan hydrolases. The values of the Michaelis parameters (Km=5.56 g l^–1 andV=2.94 · 10^–5 M s^–1) were determined.

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Eine kinetische Methode zur Untersuchung der Hydrolyse von Xylan durch Xylan-Hydrolase

Zusammenfassung Die kolorimetrische Methode nach Somogyi-Nelson wurde nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Xylan, katalysiert durch Xylan-Hydrolasen vonAspergillus oryzae, angewandt. Es wurden die Michaelis-Parameter (Km=5.56 g l^–1 undV=2.94 · 10^–5 M s^–1) bestimmt.

     

Electrochemical synthesis of geminal azidonitro compounds

An electrochemical method for the synthesis of geminal azidonitro compounds was developed. The method involves electrooxidative coupling of azide anions with salts of nitro compounds and affords geminal azidonitroalkanes, azidonitrocycloalkanes, and diazidodinitrocycloalkanes in 45–92% yields.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2452–2457, November, 2004.     

Solvation and dissociation of the carbanionic barium salt of the double 1,1′diphenylethylene in tetrahydrofuran

Mono- and dicarbanionic derivatives of 4,4bis(1-phenylethylene)1,1-biphenyl) (BPB): are prepared by addition of cumyl-barium or polystyryl-barium to BPB in tetrahydrofuran (THF). Spectroscopic and conductimetric measurements on monoadduct solutions were carried out in a temperature range from –105 to 25°C. At low temperature these solutions show a large spectral shift, due to the equilibrium between tight and solvent separated ion pairs. The thermodynamic parameters of this two step ion pair solvation were determined and the corresponding dissociation constant was found to be K _d =1×10^–6 mol-dm^–3 at 20°C. Once the first addition completed, the remaining double bond of the monoadduct seems to be less reactive than those of the original BPB. The diadduct has been prepared in the presence of an excess of cumyl-barium, and characterized spectroscopically.     

Spectroscopic detection of theendo-enol form of 2-acetylcyclopentane-1,3-dione

According to vibrational spectroscopic data, in the gas phase at 280 °C and in crystals prepared by sublimation, 2-acetylcyclopentane-1,3-dione was established to exist not as trione 1 but as the enol-form 2 with an exo-cyclic C=C bond (v(C=C) = 1593 cm^–1) and an intramolecular hydrogen bond. The enol 3 prepared by crystallization from CCl₄ is also stabilized by an intramolecular H-bond but has anendo-cyclic C=C bond (v(C=C) = 1545 cm^–1). In a trichloroethylene solution, both theexo- andendo-enol forms co-exist, and the percentage of the latter is 11 %. The frequencies in the vibrational spectra have been assigned using the normal coordinate calculation of2, 3, and their OD-analogs. The mechanism of tautomer transfer is discussed in terms of PMO theory.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 57–62, January, 1994.The authors are grateful to professor J. G. Ramos (Madrid Institute of Optics) for making it possible to record the far IR and Raman spectra in his laboratory, to Dr. V. Z. Kurbako for the registration of spectra and its discussion, and to Dr. N. A. Kubasova for recording the Raman spectra with a Coderg Ar-300 instrument.     

Reaction of α-(trialkylstannyl) acetylenes with metallic sodium

-Trialkylstannylacetylenes react under mild conditions with metallic sodium at the Sn-C(sp) bond to give hexaalkyldistannanes and sodium acetylalkynides inca. 65–85 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1109–1110, June, 1994.     

Effect of urea on the structure and functional activity of proteins. Chymotrypsinogen A and α-chymotrypsin

The effect of urea on the structural stability and functional activity of globular proteins,viz., chymotrypsinogen A (ChtG) and -chymotrypsin (Cht), was studied over a wide range of concentrations (0.5–6 rnol L-1), and the existence of two different mechanisms of the action of urea on these proteins was demonstrated. No changes in the spatial structure of ChtG were observed in the concentration range from 0,5 to 3 mol L^–1 (region 1). Differential UV spectroscopy shows tile redistribution of aromatic groups between the inner volume and the outer surface of a protein molecule (protein denaturation) at concentrations >3 mol L^–1 (regionII), In regionI, urea changes the kinetic parameters of enzymatic reactions involving Cht, which is explained on the basis of millimeter spectroscopy data by its action on the structure and nucleophilic reactivity of water.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 998–1002, April, 1996.     

Quantum-chemical study of the molecular and electronic structure of 2,2′-dithiodi(2-methyl-2,3-dihydro-1,4-thiazino[2,3,4-i,j]quinolinium)

Conformational isomerism of 2,2-dithiodi(2-methyl-2,3-dihydro-1,4-thiazino[2,3,4-i,j]quinolinium) has been studied by semiempirical MNDO and AM1 methods. Six symmetrical and unsymmetrical stationary states have been found. Optimum intramolecular rotations around single bonds have been considered. The possibility of the inversion of the reaction centers in nucleophilic and electrophilic reactions depending on the conformational state of the molecule has been shown. The spatial structure of one of the conformers found is similar to that typical of (–)-cystine. The observed constancy of some geometric and electronic parameters makes it possible to study the principal physicochemical properties of dithiazinoquinolinium compounds by the most sophisticatedab initio methods using small model structures, which are constructed by taking into account the variability of other geometric parameters, as an example.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2359–2364, December, 1995.The work was supported by the Russian Foundation for Basic Research (Project No. 93-03-18400).     

1H NMR studies on intermolecular association of amphiphilic cationic polyelectrolyte micelles induced by hydrophobic counteranions in water

Interactions of a series of amphiphilic cationic polyelectrolytes with various kinds of organic counteranions have been investigated in water by one- and two-dimensional ¹H NMR spectroscopy at 20 °C. The cationic polyelectrolytes were prepared by micellar homopolymerization of tail-type cationic surface-active monomers with a cationic charge with -end, (ST–C_m–AB, m=5, 7, and 9, where ST is a styrenic group, C_m, an alkylene chain at the 4-position of styrene, and AB, alkyltrimethylammonium bromide). Aliphatic monosodium salt of maleic acid (MAS) and its stereoisomer, fumaric acid (FAS), sodium benzoate (NaB), potassium hydrogen phthalate (PHK), and sodium salicylate (NaSal) were added to a salt-free aqueous solution of the polyelectrolytes and ¹H NMR measurements were carried out. Amphiphilic P(ST–C_m–AB) polyelectrolytes act as efficient hosts to strongly capture the hydrophobic counteranions B^–, PH^–, and Sal^–, but not MA^– and FA^–. The ¹H NMR signals of these hydrophobic counteranions remarkably shift upfield and broaden in water in the presence of the amphiphilic polyelectrolytes. The nuclear Overhauser effect (NOE) signals between the cationic group of the polymer and aromatic benzoate counteranion protons are clearly observed to imply cation– interaction. The capturing of hydrophobic counterions by the polyelectrolytes is likely due to electrostatic, hydrophobic, and cation– interactions between them. The reduced viscosity, _sp/C_p, for the solution at [PHK]/[P(ST–C₇–AB)]=1.0 steeply increases with increasing polymer concentration (C_p) above ca. 0.9 g/dL to show pronounced viscoelasticity.     

Polyimides from complexes of benzophenonetetracarboxylic acid diesters with diamines. 5. Mechanism of thermal cyclization of H-complexes

The results of a study, by thermal mass spectrometric analysis and NMR spectroscopy, of the polycondensation of H-complexes are presented from which it is possible to propose a mechanism for the reaction. It is shown that conversion of the H-complexes into polyimides takes place through the formation of intermediate zwitterions with an amino acid bond after initial separation of methanol, following which elimination of water commences in one stage to form an imide ring. The role of theortho position of the functional groups in the acid ester during the formation of the hydrogen bond is discussed.Institute of Macromolecular Compounds, Russian Academy of Sciences, 199004 St. Petersburg. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2517–2524, November, 1992.     

Organomineral sorbents based on clinoptilolite-containing tuffs

The anion-exchange properties of a new organomineral sorbent obtained by modification of clinoptilolite-containing tuffs by polyhexamethyleneguanidine have been studied after different periods of storage (time after synthesis) and numbers of sorption-regeneration cycles. The sorbent can be used as a cation- and an anion-exchanger simultaneously. Selectivity coefficients (exchange constants) for F^–, SO₄ ^2–, and HPO₄ ^2– ionsvs. Cl^– ions on modified clinoptilolite-containing tuffs have been determined. The modification improves the mechanical properties of clinoptilolite tuffs.For part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1554–1556, September, 1994.     

Photoredox properties of Kojic acid and its derivatives complexed to Iron(III)

Summary Iron(III) complexes of the formcis-[Fe(SB(X - K)] in whichSB ^2– are open-chain tetradentateSchiff base N₂O₂-ligands ofacacen,benacen orsalen type, andX - K ^– are bidentate anions of kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) or other -pyranones undergo photoredox transformations when being irradiated in methanol into intraligand orLMCT bands. The quantum yields of the photoredox reactions depend on the peripheral constitution of the N₂O₂ ligands, the substituentsA andB of the ligandsX - K ^–, and the wavelength of irradiation _irr. The proposed mechanism involves the population of photoredox reactiveLMCT states by photophysical deactivation steps, primary photoredox formation ofX - K radicals and Fe(II), and subsequent dark redox processes giving back the anionsX - K ^– and the final products Fe(II) and formaldehyde formed in the molar ratio 2:1.

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Photoredoxeigenschaften von Fe(III)-Komplexen von Kojic Acid und ihren Derivaten

Zusammenfassung Eisen(III)-Komplexe der Formcis-[Fe(SB)(X - K)] mitSB ^2–=offenkettige tetradentateSchiff-Basen-N₂O₂-Liganden undX - K ^–=bidentate Anionen von 5-Hydroxy 2-hydroxymethyl-4H-pyran-4-on oder andere -Pyranone unterliegen bei Bestrahlung in Methanol Photoredoxumwandlungen, was durch Intraligand- oderLMCT-Banden belegt wird. Die Quantenausbeuten der Reaktionen hängen von der Konstitution der N₂O₂-Liganden, den SubstituentenA undB und dem LigandenX - K ^– sowie der Anregungswellenlänge _irr ab. Der vorgeschlagene Mechanismus beinhaltet die Population photoredoxreaktiverLMCT-Zustände durch photophysikalische Deaktivierungsschritte, die Bildung vonX - K*-Radikalen und Fe(II) und-Über Dunkelprozesse — die Rückbildung der AnionenX - K ^– sowie die Reaktion zu den Endprodukten Fe(II) und Formaldehyd im molaren Verhältnis 2:1.

     

The analysis of carbide and intermetallic phase γ′ isolates in nickel alloys by means of injection method of flame atomic absorption spectrometry

The determination of the chemical composition of intermetallic phase and carbide isolates is of a great importance for estimating the properties of the high-temperature nickel-base alloys. This paper presents the examination of the application of these isolates for the chemical analysis; a modernized variant of the injection technique of flame atomic absorption is described. It is based on constructing the teflon crater manifold together with a portable capillary bearing. The precision of the determination of the given elements in phase isolates was as follows: Al 3.5–4.2%, Ti 4.1–4.6%, Mo 3.8–4.2%, Co 2.5–2.8%, W 8.6–8.8%, Nb 11.2–11.6%, Cr 3.1–3.4%, Ta 10.2–10.6%.     

Catalytic decomposition of organic peroxides by 4,4′-diamino-trans-stilbene (DTS)/montmorillonite complex: II.p-nitro andp-methyl dibenzoyl peroxide

The kinetics of the induced decomposition ofp-NO₂- andp-CH₃-dibenzoyl peroxide in the presence of 4,4-diamino-trans-stilbene (DTS) were studied in ethanol under both homogenous and heterogeneous conditions. The heterogeneous reaction was carried out in the presence of the DTS/montmorillonite complex. The decomposition reaction was found to be second order and three-halves order for the peroxide concentration in homogeneous and heterogeneous systems, respectively. The reaction was first order for the amine concentration in the homogeneous system. The activation energies for the decomposition reaction were obtained as 54.7±2 and 59.5±3 kJ mol^–1 forp-NO₂- andp-CH₃-dibenzoyl peroxides, respectively, in the homogeneous systems and are higher than the corresponding values of 41±1.5 and 47.6±1 kJ mol^–1 for thep-NO₂ andp-CH₃ derivatives in heterogeneous media.     

Synthesis and properties of 2,2′-dipyridyl and 4,4′-dipyridyl complexes with thulium salts

Summary New complexes of 2,2-dipyridyl and 4,4-dipyridyl with thulium salts TmX ₃ (whereX=Cl^–, Br^–, NO ₃ ^– , NCS^–, and ClO ₄ ^– ) have been prepared and their solubilities in water at 21 °C were determined. The IR spectra of these compounds are discussed. The conditions of thermal decomposition of the complexes were also studied.

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Synthese und Eigenschaften von 2,2-Dipyridyl- und 4,4-Dipyridylkomplexen mit Thuliumsalzen

Zusammenfassung Es wurden neue 2,2-Dipyridyl- und 4,4-Dipyridyl-Komplexen mit Thuliumsalzen TmX ₃ (X=Cl^–, Br^– No ₃ ^– , NCS^–, ClO ₄ ^– ) dargestellt und ihre Wasserlöslihkeit bei 21 °C bestimmt. Die IR-Spektren werden diskutiert. Das thermische Verhalten der erhaltenen Komplexe wurde untersucht.

     

Synthesis and sorption properties of new hybrid chelating sorbents with β-alanine functional groups

A series of -aminopropylsilylated sorbents was obtained from different oxide supports (silica gels, silica fillers, macroporous glasses, alumina) and by the direct synthesis (hydrolytic polycondensation of tetraalkoxysilanes with -aminopropyltriethoxysilane). The highest degree of immobilization was achieved for silicas, while the most convenient solvent was methanol. Sorbents with -alanine functional groups were obtained by the subsequent reaction with acrylic acid. The degree of -carboxyethylation was 1.3–1.9, and the highest content of functional groups (v_COOH = 3.23 mmol g^–1) was achieved for carboxyethylated xero gel synthesized by the copolycondensation of tetraethoxysilane with -aminopropyltriethoxysilane. The sorbents containing -alanine possess a higher selectivity of Cu²⁺ ion sorption than the initial -aminopropylsilylated sorbents.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2620–2625, December, 2004.     

Application of solvent extraction and synchronous spectrofluorimetry to the determination of the formation constant for a 1:1 complex of carbazole withβ-cyclodextrin in water-dimethyl sulfoxide medium

Extraction of carbazole in heptane was performed at 25±1°C with an aqueous dimethyl sulfoxide (DMSO) medium containing -cyclodextrin (CD) at consecutive concentrations in the range of 0–10 mM. The fluorescence intensity of carbazole remaining in the heptane phase was measured by synchronous scanning fluorimetry. The apparent formation constant (K _f) for a 1:1 carbazole: CD inclusion complex in water-DMSO medium was determined by using a linear plot of the distribution ratio calculated from the fluorescence intensities vs. the -CD concentration. The values thus obtained ranged from 477 M^–1 in a 10% v/v DMSO medium to 12.1 M^–1 in a 60% v/v medium. Good linear relationships were observed between logK _f and the DMSO concentration ([DMSO]), and also between logK _f and the logarithm of the distribution coefficient (K _d) for carbazole. The formation constant in 100% water was estimated to be approximately 1.0×10³ M^–1 on the basis of the logK _f vs. [DMSO] and the logK _f vs. logK _d correlations.     

Theoretical studies on the conformation of saccharides

Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (⁴ C ₁) and equatorial (¹ C ₄) conformer, G = 2.9–3.7 kJ/mol, and the dipole moment, = 1.20 ± 0.05 D (1D = 3.33 10^–30mAs) agree well with the calculated values E = 3.18 kJ/mol and <> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22.