Special features of the hydration of siderophores of the ferrichrome family

An investigation of the hydration of the siderophore ferrichrome A has been carried out by the Monte-Carlo method. It has been shown that the ligands and the iron atom interact weakly with water. The four carbonyl groups of the peptide ring of the molecule, with which hydrogen bonds are formed by six water molecules, and the side-chain carboxyl groups, with each of which a hydrogen bond is formed by one water molecule, interact most strongly with the aqueous phase. Evaluations of the free energy of hydration of the molecule have been carried out. The different activities of the siderophores of the ferrichrome family have been explained on the basis of the calculations. It has been postulated that the bonding of ferrichromes to a membrane receptor is effected by means of the peptide ring of the molecule. The transport of ferrichrome A through the interior of a membrane is energetically considerably more difficult than that of ferrichrome, since it is associated with dehydration of the side-chain carboxyl groups of the molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 167–172, March–April, 1988.     

Solute–solvent interactions of acid–1,4-dioxane mixtures—By dielectric, FTIR, UV–vis and 13C NMR spectrometric methods

Results of the dielectric studies carried out on the binary mixture of n-butyric and caprylic acids with 1,4-dioxane over the entire composition range and at temperatures 303 K, 308 K, 313 K and 318 K, and FTIR, UV–vis and 13C NMR spectral studies are presented in this paper. The excess permittivity and excess free energy were fitted with the Redlich–Kister polynomial. The variation of Kirkwood correlation factors, excess permittivity and excess free energy of mixing with the concentration and temperature has been investigated in view of understanding the ordering of dipoles of solute and solvent molecules. The FTIR, UV–vis and 13C NMR spectral analysis reveals the formation of complex between solute and solvent molecules. The parallel alignment of electric dipoles of the complex predicted by dielectric studies is well supported by UV–vis spectral analysis. The structure of the complex molecule present in the clusters has been deduced.     

Molecular ozone-water complex.ab initio calculation with inclusion of electron correlation

The geometrical and electronic structure of different molecular O₃–H₂O complexes has been calculated by the ab initio method in the 4–31G (d, p) basis set with inclusion of electron correlation according to the Möller-Plesset fourth-order perturbation theory (MP4). It has been shown that the geometrical structure of the experimentally observed hydrogen-bonded complex is mainly determined by the entropy (rather than energy) effect, and is characterized by an almost free internal rotation of the H₂O molecule.Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Ruberzhansk Department of Dnepropetrovsk Chemical Technological Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 3, pp. 26–30, May–June 1993.Translated by L. Smolina     

Nonempirical calculations of potential-energy surfaces for nucleophilic addition of H− and F− to an acetylene molecule

The minimal energy paths for the nucleophilic addition of a hydride ion (H^–) and a fluoride ion (F^–) to a molecule of acetylene (A) have been calculated with the use of 3–21++G and 3–21+G double basis sets in the framework of the Hartree-Fock-Roothaan method. The values of the total energies of the reactants, transition states, and products have been refined by means of calculations with more complete basis sets [6–31++G// 3–21++G and 6–31++G*//3–21++G for reaction (1); 6–31+G*//3–21+G and 6–31++G**//3–21+G for reaction (2)] and by taking into account the correlation energy for reaction (1) in the framework of the SCEP/6–31++*//3–21++G method. It has been established that the activation energy of reaction (2) is 15.94 kJ/mole lower than that for reaction (1), that reaction (1) is exothermic, and that the enthalpy change accompanying reaction (2) is close to zero. The character of the distribution of the electron density along the minimal energy paths of both reactions has been analyzed, and the differences appearing as a result of the replacement of the soft nucleophile H^– by the harder nucleophile F^– have been ascertained. The results of the calculations have been compared with the results available in the literature for reaction (1).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 149–155, March–April, 1989.     

Determination of the effective concentration of free charge carriers in solid proton-conducting electrolytes

A method for the theoretical determination of the effective concentration of free charge carriers in solid proton-conducting electrolytes with the use of experimentally measured values of the electrical conductivity has been proposed. Polyantimonic acid has been considered as an example. It has been shown that the high electrical conductivity of solid proton-conducting electrolytes in comparison to other compounds with hydrogen bonds is due to the high concentration of effective free charge carriers and the low activation energy for the mobility of a proton.Translated from Teoreticheskaya i éxperimental'naya Khimiya, Vol. 24, No. 1, pp. 111–114, January–February, 1988.     

Spatial and electronic structure of the BEDT-TTF molecule

The spatial structure of the molecule of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) has been determined by the semiempirical SCF-MO-LCAO method in the all-valence-electron MNDO approximation with the use of the formalism of the restricted Hartree-Fock method, and its principal energy and charge characteristics have been calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 352–355, May–June, 1986.We thank I. I. Ukrainskii for taking an interest in the work and V. A. Zaits for providing the program and helping in the performance of the calculations.     

Calculation of the structure and evaluation of the reactivity of N-methyl-N-(β-d-xylopyranosyl)-N-nitrosourea under acid-base catalysis conditions

An investigation of N-methyl-N-(-D-xyloxyl)urea (I) and its nitroso derivative (II) has been carried out in the MINDO/3 approximation by the MO-LCAO method. It has been shown that the very significant difference between the energies of molecule I in the free state and in a crystal is due to the potential energy of the crystal field and intermolecular hydrogen bonds. An analysis of the distribution of the charges on the atoms showed that the most probable site for protonation and nucleophilic attack in I and II is the carbonyl group. A picture of the changes in the electronic structure and properties of the reaction centers in I and II under model acid-base catalysis conditions has been obtained.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 596–599, September–October, 1985.     

Theoretical investigation of the stereochemical structure of valinomycin and its hydration

The stereochemical structure of the A and B forms of valinomycin and their hydration were investigated by theoretical conformational analysis and by the Monte Carlo method. It was found that the aqueous phase has a predominant role in the stabilization of the B form. An analytical method is proposed for calculation of the conformational energy gradient of a random molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 360–365, May–June 1987.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling lignin. III. Quinones and quinone methides

An investigation has been made by the CNDO/S method with allowance for configurational interaction (the lowest six vacant and the highest eight occupied MMOs) of the electronic structure of a number of quinones and quinone methides forming component parts of the structural unit of lignin. The energies of the first singlet-singlet and singlet-triplet transitions and the redistribution of charges on excitation have been obtained, and the dependence of the energy of the transitions on the chromophores present in the molecule has been discussed. The change in the donor-acceptor properties of the fragments in excited states, leading to a change in the pathways in nucleophilic and electrophilic reactions has been shown.A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 858–865, November–December, 1988.     

Spectrophotometric determination of cadmium(II) using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

The complex of cadmium with the reagent 2-(-5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been studied. The composition, stability constant, and free energy change of formation of the complex have been determined. A sensitive spectrophotometric method for the determination of cadmium has been developed and applied for a range of concentration of 0.4–4.0 μg/ml cadmium using the complex Cd-5-Br-PADAP. The optimum conditions for maximum sensitivity of determination such as standing time, pH, wavelength, and order of addition have been determined. The effect of foreign ions on this method has been also studied.     

Spatial structure of akiferin from Ferula akitschkensis

The spatial structure of the carotane ester akiferin has been established by the x-ray structural method (diffractometer, CuK radiation, 1109 reflections, direct method, R=0.084). Using the method of molecular mechanics, possible conformational states of the free akiferin molecule have been calculated by rotating the para-methoxybenzoate [sic] moiety of the molecule relative to the C6-O axis.Institute of Chemistry of Plant Substances, Uzbekistan Republic Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedeninii, No. 1, pp. 96–100, January–February, 1993.     

Mean value of the electric field gradient in a molecule

The relationship between the mean value of the second derivative of the electrostatic potential of the electronic shell of a molecule on its axis and the first derivative of the energy of the molecule with respect to the internuclear distance has been established.Scientific-Research Institute of Physics, Leningrad State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 47–50, March–April, 1991.     

Solute-solute-solvent interactions in dilute aqueous solutions of aliphatic diols. Excess enthalpies and gibbs free energies

The heats of dilution and the osmotic coefficients for some aliphatic diols (1,3-propanediol; 1,2-butanediol; 1,3-butanediol; 1,4-butanediol; 2,3-butanediol; 1,5-pentanediol; 1,6-hexanediol) in water at 25°C are reported. The experimental free energy and enthalpy pairwise interaction coefficients were evaluated and are discussed in terms of the hydrophobic-hydrophilic properties of the solutes. The effect of the mutual position of the polar hydrophilic groups in the molecule on the experimental interaction coefficients transposed to the McMillan-Mayer (MM) state is emphasized. The Sawage-Wood additivity of groups (SWAG) approach has been used and critically discussed.Paper presented at J.C.A.T. '86-Ferrara 27–30 Ottobre 1986.     

Chemical modification of the tryptophan residues of the L-asparaginase of E. coli with N-bromosuccinimide

Summary The role of the tryptophan residues in the L-asparaginase molecule has been studied by the method of chemical modification with N-bromosuccinimide, and it has been established that in an acid medium this reagent modifies all four tryptophan residues present in the molecule, completely suppressing the activity of the enzyme.The substrate — L-asparagine — and a competing inhibitor — S-benzyl-N-benzyloxycarbonyl-L-cysteine — protect the L-asparaginase from the action of N-bromosuccinimide, which shows the role of the tryptophan in the catalytic center of the L-asparaginase.Institute of Organic Synthesis, Academy of Sciences of the Latvian SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 228–231, March–April, 1975.     

XANES Determination of Intraatomic Potentials

A new scheme has been developed for determining the parameters of the local one-electron potential in molecules and solids. The scheme is based on interpretation of the experimental X-ray absorption near edge struucture. The scheme is an extension of the method for solving the inverse problem of XANES theory suggested by one of the authors. In this scheme, oscillator strengths and maximum heights are considered along with the energy and half-width of spectral maxima. The scheme is used for determining the intraatomic potential in the nitrogen molecule.Original Russian Text Copyright © 2004 by Yu. F. Migal and O. M. Kholodova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 986–989, November–December, 2004.     

Conformational analysis and vibrational spectroscopic investigation of 3-phenylpropylamine

The possible stable forms of 3-phenylpropylamine (3-PPA) molecule were experimentally and theoretically studied by infrared and Raman spectroscopy. FT-IR and Raman spectra of 3-PPA were recorded in the regions of 4000–400 cm⁻¹ and 3700–60 cm⁻¹, respectively. The potential energy surface corresponding to the internal rotations of the molecule was investigated by semi-empirical quantum mechanical methods, and appropriate conformers defined with B3LYP hybrid density functional theory method along with the basis sets of different size and type. Results from experimental and theoretical data showed the trans–trans–gauche (TTG) to be the most stable form of a 3-PPA molecule.     

Properties of the TDAE Molecule Within Density-Functional Theory

Density-functional-based methodologies have been used to calculate the geometric, electronic, and vibrational properties of the TDAE molecule. The molecule has a low first-ionization energy but, in contrast to alkali atoms, releases the electron without appreciably changing the effective molecular size. In addition to ionization energies and geometries we present the vibrational spectrum of the molecule and determine the infrared (IR) and Raman intensities as well. A discussion of some of the energetics that impact the ionicity and subsequent magnetism of TDAE–C₆₀ is presented. Further, we identify one Raman active mode, at 1682 cm^–1, which is particularly interesting since it may be used to probe the TDAE charge state experimentally.     

Bisindoles. 18. Some electrophilic substitution reactions in the 1,2-di(indol-5-yl)ethane series

A quantum-chemical calculation has been made and the laws of the electron-density distribution in the molecule of 1,2-di(indol-5-yl)ethane have been determined. The electrophilic substitution reactions most characteristic for it have been studied.For communications 15–17, see [1–3].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 73–77, January, 1984.     

Quantum-chemical simulation of the active center of vitamin B12

The electronic structure of porphin and corrin complexes of cobalt differing with respect to the oxidation state of the central ion has been investigated by the MO-LCAO-SCF-CNDO method with the Kai-Nishimoto parameters for transition metals. On the basis of an analysis of the distribution of the electron density and the structure of the energy spectrum, it has been shown that the oxidation-reduction processes of the complexes are accompanied by restructuring of the energy spectrum, and the differences between the electronic structures of porphin and corrin complexes have been discussed. It has been established that cobalt(I) porphin has stronger nucleophilic properties than does cobalt(I) corrin. The electronic structure of hexacoordinate complexes in which an imidazole molecule and a molecule of L (L = H₂O, CH₃ ⁺, CN^–) are axially coordinated has been calculated. The mechanisms of the dissociation of cobalt alkyl complexes and the differences between the processes of the heterolytic dissociation of porphin and corrin complexes have been discussed. It has been shown that the elimination of a CH₃ ⁺ cation, which plays an important role in biomethylation reactions, is more favorable in corrin complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 400–409. July–August, 1986.     

Field determination of iodide in water

A simple, fast and sensitive spectrophotometric method for the quantification of iodine and iodide in waters is described. Firstly iodide has been oxidised by sodium nitrite to iodine in HCl medium and the resulting I₂Cl^– has been preconcentrated into toluene. This can be subsequently determined in the extract with brilliant green. A ten-fold preconcentration is obtained, the molar absorptivity is (4.2×10⁴) I mol^–1 cm^–1 at 635 nm. A detection limit of 4 ng/ml iodide in water can be reached. The effect of common anions and cations have been investigated. The method has been applied to the determination fo free iodine, total iodine and iodide in river, pond and well water.