Dispersion interaction of conjugated molecules: One- and many-electron models

A scheme for calculating van der Waals constants C₆, C₈, and C₁₀ in terms of the full configuration interaction for π-shells is suggested. The required imaginary frequency dynamic polarizabilities are also investigated with one-electron schemes. The variational perturbation theory of the Hartree-Fock method considerably exaggerates the constant C_2l the conjugated variant of perturbation theory is preferable. The additive scheme for estimating the Σ-contribution allows one to calculate the energy of dispersion attraction in real conjugated systems, as demonstrated by semiempirical estimates of evaporation heat in butadiene, benzene, naphthalene, and phenylacetylene. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1029–1037, November–December, 1997. Original article submitted December 14, 1996.     

Zirconyl-containing microspheric silica gel surfaces

The adsorption properties of two samples of zirconyl-containing silica gels derived from zirconium oxychloride, polyetoxysiloxane oligomer 3% ZrOCl₂/SiO₂ (composite 1) and tetraetoxysilane 5% ZrOCl₂/SiO₂ (composite 2) were investigated by gas chromatography at low surface coverages. n-Alkanes and n-alkenes (C₆–C₈), C₆H₆ were used as test adsorbates, along with polar compounds whose molecules had different donor-acceptor interaction abilities. The dispersion and specific (electron-donor and electronacceptor) components of the energy of intermolecular interactions for the studied systems were determined from the experimental data on chromatographic retention. It was shown that composite 2 had a higher dispersion potential and higher surface energy characteristics of the surface’s electron-donating and electronacceptor centers, as compared to composite 1.     

Endohedral chemical shifts in higher fullerenes with 72–86 carbon atoms

For all isolated pentagon isomers of the fullerenes C₆₀–C₈₆ with nonzero HOMO–LUMO gap and for one nonclassical C₇₂ isomer (C_{2 v} ), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental ³He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C₆₀, C₇₀ and C₇₆). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental ³He chemical shifts, the assignments of the observed ³He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C₈₂ and one C₈₆ isomer (C₈₂:3 and C₈₆:17). The calculated helium chemical shifts also suggest the reassignment of the δ(³He) resonances of two C₇₈ isomers. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

Thermal Stability of Some Textile Dyes

The effect of thermal treatment at 25–800°C on the structure of some textile dyes (rhodanine' derivatives) has been investigated. The general formula of these dyes are;[(R)–C₆H₄–C₃NS₂O–C₅H₄N–CH=CH–C₆H₄N(CH₃)₂]; 2-[p-dimethylamino-styryl]-6-[5-(3-aryl)-rhodanine]-1,2-dihydropyridine and its derivatives, R=H (I), o-OCH₃ (II), p-OCH3 (III) and p-OH (IV). The techniques employed were TG, IR, UV, NMR and elemental analysis. The results showed that the thermal stability of these dyes depends on the nature of the substituent (R) alkyl radical present and its position in the benzene ring. On the basis of the application of a non-isothermal kinetic equation, it was found to be a first order reaction. Some kinetic and thermodynamic parameters for the thermal decomposition process in each stage have been evaluated by the application of two different calculation methods. To support the above results a simple quantum study was reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Organophosphoryl polyoxotungstates α-[R2PW9O34]5− [R = PhP(S), C6H11P(O), H2NCH(n-Pr)P(O)]

Tetrabutylammonium salts of organophosphoryl derivatives of tungstophosphate of formula α-[R₂PW₉O₃₄]⁵⁻ [R = PhP(S), C₆H₁₁P(O), H₂NCH(n-Pr)P(O)] have been prepared, purified and characterized by elemental analysis, i.r., ³¹P- and ¹⁸³W-n.m.r. spectroscopy. These anions consist of an α-[PW₉O₃₄]⁹⁻ framework on to which are grafted two equivalent organophosphoryl groups through P–O–W bridges; these new species still retain the ‘unsaturated’ Keggin structure. The five-line ¹⁸³W spectra indicates that the hybrid anions possess C _s symmetry in acetonitrile. This revised version was published online in June 2006 with corrections to the Cover Date.     

Theoretical and experimental study of fullerenol molecules and ions C60(OH)24 ? n(OL)n and C60(OH)24 ? n(OL)nL+ successively substituted by Alkali Metal atoms L (n = 1?24)

The equilibrium geometric parameters and the energetic characteristics of fullerenol molecules and ions C₆₀(OH)_{24 − n} (OL) _n and C₆₀(OH)_{24 − n} (OL) _n L⁺ successively substituted by alkali metal atoms L with the number of substitutions n = 1–24 have been calculated by the density functional theory B3LYP/6-31G* method. For all compounds, the structure of the covalent [C₆₀O₂₄] cage in which the oxygen atoms are bound to the C atoms of the six-membered [C₆] rings of the fullerene cage, six O atoms per [C₆] ring. The lithium derivatives have been considered in most detail. Computations have shown that the first four single substitutions of Li for H in the OH groups attached to the same C₆ ring require very low energy inputs, no more than 1 kcal/mol, and can spontaneously occur under common conditions. The further fifth and sixth single substitutions in the same C₆ ring are endothermic, but the required energy inputs are also modest (on the order of few kcal/mol). The first and second cooperative substitutions of Li for H simultaneously in all four hydroxylated C₆ rings require energy inputs of ∼3 and 11.6 kcal/mol, respectively; in the third and fourth fourfold substitutions, the energies increase by ∼15–16 kcal/mol. The mean partial energy per single substitution of Li for H in this series (n = 1−6) is ∼2 kcal/mol. Calculations have predicted that all C₆₀(OH)_{24 − n} (OLi) _n molecules with intermediated degrees of substitution (n = 1−16) can be obtained under the conditions of relatively low energy inputs (for example, under the conditions of the MALDI experiment) and can exist in the isolated state. For the sodium- and potassium-substituted analogues, the qualitative pattern persists, but the H/Na and H/K substitutions are somewhat more endothermic. The computational results are compared with the MALDI mass spectrum of the [C₆₀(OH) _x (ONa) _y -CH₃COONa) system.     

Modeling the electronic structure of graphite intercalation compounds with lithium by metal complexes with polybenzene systems

The electronic structure of intercalation compounds obtained by inclusion of an alkali metal in graphite is considered using molecular complexes C₆H₆Li₂, (C₆H₆)₂Li, and (C₆H₆)₃Li₂ in the lowest energy states as examples. Modeling the electron distributions of the intercalates requires inclusion of metal d-orbitals in the basis set of AOs and rejection of purely ionic models. It was found that exclusion of the lithium d-AO from the basis set significantly increases the ionic character of the distributions. Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 450–457, May–June, 1996.     

Mathematical modelling of enzyme kinetics reaction mechanisms and analytical solutions of non-linear reaction equations

The boundary value problem in basic enzyme reactions is formulated and approximate expressions for substrate and product concentrations are presented. He’s variational iteration method is used to give approximate and analytical solutions of non-linear reaction equations containing a non-linear term related to enzymatic reaction. The relevant analytical solutions for the substrate, enzyme, substrate-enzyme and product concentration profiles are discussed in terms of dimensionless reaction diffusion parameters K, λ and e{\varepsilon}.     

Molecular structures and electronic properties of helical thiophene carbon–sulfur oligomers, H2(C2S)nC2H2 (n?=?1–20)

Structure optimizations of the thiophene carbon–sulfur H₂(C₂S) _n C₂H₂ (n = 1–20) were carried out using density functional theory calculations at the B3LYP/6-31G(d) level. The B3LYP/6-31G(d) geometrical data for heptamer H₂(C₂S)₇C₂H₂ and undecamer H₂(C₂S)₁₁C₂H₂ are in good agreement with the X-ray crystallographic data for the helical (C₂S)_n β-heptathiophene and β-undecathiophene, respectively. Structural and electronic properties of helical oligothiophenes obtained at the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level are reported. The strain energy formula of n oligothiophenes as a linear function of their molecular length was obtained.     

Specific low-shear viscosity of a liquid dispersion of solid particles from variational theory for the Fuchs stability ratio

The contribution of a solid phase to the low-shear viscosity of a solid–liquid dispersion, i.e., the specific viscosity, η_SP, is investigated theoretically by applying a variational procedure. The Fuchs stability ratio has been interpreted as a general steady-state equilibrium constant for aggregation and has been extended to a functional form which describes the motion of two Brownian units in a dispersion. Application of the Euler–Lagrange equation under the validity of an adiabatic-like approximation for the Hamiltonian (approximately Brownian kinetic energy and inertial potential field) yields a constraint that involves specific viscosity, solid volume fraction, φ, interparticle energy and correlation functions of the dispersed phase. The Einstein formula is found as the limit of the Saito equation when an infinitely dilute hard-sphere suspension is considered, while a general closed form expression, η_SP=η_SP(φ), is proposed for a concentrated suspension. It depends on the particle coordination number and affinity, returns the low density expansion predicted by effective-medium-type theories for the viscosity, and can be represented as the sum of two dominant contributions, associated respectively with the first peak of the radial distribution function and the second peak of the total correlation function. Application to experimental data, concerning latex particles in cis-decalin and interacting silica–water systems, is presented and discussed. Received: 31 March 2000/Accepted: 13 July 2000     

Algorithm for variational calculations of molecular symmetry in solving anharmonic vibrational problems

A universal program for variational calculations of molecular symmetry in solving anharmonic vibrational problems, realized by the author, is described. The program uses the group-theoretical method. Symmetrized basis wave functions are constructed with the aid of the generalized KJebsch-Gordan series suggested by the author. The method of constructing symmetrized basis wave functions and the program for adequate calculations of molecular symmetry were verified for many molecules of different symmetry groups: O_h, O, T_d, T_h, T, D_∞h, C_t8v, D_nd, D_nh, D_n, C_nv, C_nh, S_2n, C_n, C_i, C_s, and C₁ where 2 ≤n ≤6. It was confirmed that the program provides correct results and high-speed operation. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1146–1153, November–December, 1997.     

Application of He’s variational iteration method in nonlinear boundary value problems in enzyme– substrate reaction diffusion processes: part 1. The steady-state amperometric response

A mathematical model of amperometric biosensors has been developed. In this paper, He’s variational iteration method is implemented to give approximate and analytical solutions of non-linear reaction diffusion equations containing a non linear term related to Michaelis–Menten kinetic of the enzymatic reaction. The variational iteration method which produces the solutions in terms of convergent series, requiring no linearization or small perturbation. These analytical results are compared with available limiting case result and are found to be in good agreement.     

Thermodynamics of the interaction of liquid-crystalline polypropyleneimine dendrimer with low-molecular-weight compounds studied by reversed-phase gas chromatography

The thermodynamic functions of dissolution of n-alkanes (C₇–C₉) and n-alkanols (C₅–C₈) in the liquid-crystalline and isotropic phases of polypropyleneimine dendrimer of the first generation at infinite dilution were determined by the reversed-phase gas chromatography. The dependences of the thermodynamic parameters of sorbates on the phase state of the dendrite solvent, hydrocarbon chain length, and polarity of low-molecular-weight components of mesogenic—nonmesogenic binary systems were considered. The role of dispersion forces and specific intermolecular interactions in the solutions under study was estimated. Saturated hydrocarbons are more compatible with columnar phases of the dendrimer than alcohols.     

Impact of Transition Metal Substituents on Polysilane Properties: Iron versus Ruthenium

Summary. The previously unknown ruthenio disilanes Rp–Si₂Me₄–C₆H₄X (Rp = η⁵-C₅H₅Ru(CO)₂; X = H, Br, –CHO, CH=C(CN)₂) were synthesized from ClSi₂Me₄C₆H₄X (X = H, Br) and Rp⁻ using conventional chemical methods. Trends in the UV/Vis absorption spectra indicate strong electronic coupling within the Rp–Si–Si–C_aryl fragment and, therefore, closely resemble the ones observed for the corresponding iron complexes. The four compounds however, were shown to be less sensitive towards UV irradiation. The crystal structure of Rp–Si₂Me₄–C₆H₄CH=C(CN)₂ was determined by X-ray diffraction and exhibits an all-trans-array of the Ru–Si–Si–C_aryl moiety, what is a basic requirement for optimal through-bond interaction.     

Phase transformations and cation mobility in Li3 ? 2xNbxIn2 ? x(PO4)3 complex phosphates

Cation mobility in Li_{3 − 2x} Nb _x In_{2 − x} (PO₄)₃ complex phosphates was studied by impedance spectroscopy, calorimetry, and ⁷Li NMR spectroscopy. A phase transition at ≈273 K is suggested for compositions containing ≈1 mol lithium per formula unit. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, N.A. Zhuravlev, I.V. Arkhangel’skii, A.I. Rebrov, A.B. Yaroslavtsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 4, pp. 552–557.     

Simulation of molecular and electronic structure of polyhydrogenated (n,0)-tubulenes and their analogs intercalated with lithium

Molecular and electronic structure of four polyhydrogenated (n,0)-tubulenes, namely, [−C₂₄H₄−] _m (1), two isomers of composition [−C₂₈H₄−] _m (2 and3), and [−C₃₂H₄−] _m (4) withn benzene rings in the cross section (n=6, 7, 7, and 8, respectively), was simulated atm>1 (m is the number of repeating fragemnts). It was assumed that hydrogen atoms are attached to all carbon atoms lying on the two most distant elements of the cylinders of the corresponding tubulenes. The energy band structures of macromolecules1–4 and their Li-intercalated analogs [−C₂₄H₄Li−] _m (5) [−C₂₈H₄Li−] _m (two isomers,6 and7), and [−C₃₂H₄Li−] _m (8), containing one Li atom per repeating unit at each center, were obtained in the EHT approximation by the crystal orbital method. Geometric parameters of repeating units of structures1–8 were found after MNDO/PM3 optimization of the energies of hydrocarbon molecules C₇₂H₂₄, C₈₄H₂₆ (two geometric isomers), and C₉₆H₂₈, containing three repeating units of corresponding tubulenes1–4 each. The conductivity types of polyhydrogenated tubulenes1–4 are the same as those of their precursors, (6,0)-, (7,0)-, and (8,0)-tubulenes. Dispersion curves of systems5–8 are much the same as those of macromolecules1–4; however, electron energy spectra of5–8 possess metallic conductivity type and the positions of Fermi levels for these systems are higher than for compounds1–4. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2061–2067, November, 1999.     

Crystal structure and spectral characteristics of {[(C6H5)NH]2C=NH(C6H5)}[B(C6H5)4]·C2H5OH

A novel compound of {[(C₆H₅)NH]₂C=NH(C₆H₅)}[B(C₆H₅)₄]·C₂H₅OH is prepared and examined by single crystal X-ray diffraction. Crystal data: C₄₅H₄₄BN₃O, M = 653.64, monoclinic, space group P2₁/c, unit cell parameters: a = 24.375(2) Å, b = 17.5829(15) Å, c = 18.090(1) Å, β = 105.277(2)°, V = 7479.0(11) ų, Z = 8, d _calc = 1.161 g/cm³, T = 293 K, R ₁ = 0.064. The structure contains two crystallographically independent cations, two anions, and two solvate ethanol molecules. Three types of interactions occur between them: interionic N-H(N)⋯π and N(H)⋯π⋯H(C), π-delocalized system of Ph rings of the anions, and interaction of ions with ethanol molecules N-H⋯O-H(O)⋯π. The compound is characterized by IR and luminescence spectra. At room temperature, the emission intensity grows with time of exposure to UV irradiation. Original Russian Text Copyright ? 2008 by T. M. Polyanskaya, E. A. Il’inchik, V. V. Volkov, M. K. Drozdova, O. P. Yur’eva, and G. V. Romanenko __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 3, pp. 512–521, May–June, 2008.     

Synthesis and physicochemical study of nanocrystalline magnesium-containing calcium hydroxylapatites and chitosan

The interaction in the CaCl₂-MgCl₂-(NH₄)₂HPO₄-NH₃-H₂O and CaCl₂-MgCl₂-(NH₄)₂HPO₄-(C₆H₁₁NO₄) _n -NH₃-H₂O systems at 25°C has been investigated by the solubility (Tananaev’s residual concentration) method and by pH measurements. Magnesium-containing calcium hydroxylapatites with the general formula Mg _x Ca_{10 − x} (PO₄)₆(OH)₂ · nH₂O (x = 0.05, 0.1, 0.2, 0.3; n = 6–7.3) and magnesium- and chitosan-containing calcium hydroxylapatites with the general formula Mg _x Ca_{10 − x} (PO₄)₆(OH)₂ · y(C₆H₁₁NO₄) · nH₂O (x = 0.05, 0.1, 0.2, 0.3; y = 0.1, 0.3, 0.46; n = 6–8.3) have been isolated in the nanocrystalline state. The solids have been characterized by chemical and thermogravimetric analyses, X-ray diffraction, and IR spectroscopy.     

Preparation and Thermal Decomposition of Solid-state Cinnamates of Lighter Trivalent Lanthanides

Some new compounds of cinnamic acid with lighter trivalent lanthanides were prepared in the solid state. The compounds have general formula ML₃ H₂ O, where L is cinnamate (C₆ H₅ –CH=CH–COO^– ) and M is La, Ce, Pr, Nd or Sm. Thermogravimetry, derivative thermogravimetry, differential scanning calorimetry, infrared absorption spectra and X-ray diffraction powder patterns were used to characterize and to study the thermal stability and thermal decomposition of these compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dependence of the dispersion behavior of [60]fullerene in aqueous media on the chain length of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) as a dispersing agent

We have investigated the effect of the chain length of temperature-sensitive poly(N-isopropylacrylamide) (PIPAAm) on the dispersion of [60]fullerene (C₆₀) in aqueous media through an interaction between PIPAAm and C₆₀ below the lower critical solution temperature (LCST) of PIPAAm. UV–vis absorption spectral measurements showed that the saturated amount of the dispersed C₆₀ increased in proportion to the chain length of the PIPAAm. Additionally, an absorption band at around 430 nm was observed in the dispersed C₆₀ solution and was assigned to a C₆₀/PIPAAm complex. The complex formed an amorphous molecular assembly between C₆₀ molecules and PIPAAm chains, the structure of which was confirmed in a transmission electron microscopy image. Dynamic light scattering measurements indicated that the particle size of the C₆₀/PIPAAm complex increased with the chain length of the PIPAAm. From electrophoretic laser light scattering measurements, the zeta potential of the C₆₀/PIPAAm complex was found to be shifted from a negative value to zero with an increase in the chain length of PIPAAm. Longer PIPAAm chains, however, gave rise to a higher dispersion stability of the complex. Similar to the dispersion behavior of PIPAAm-C₆₀ conjugates in aqueous solutions, the aqueous C₆₀ dispersion with PIPAAm exhibited rapid, and reversible dispersion–aggregation changes in response to temperature alternation across the LCST.