Atomic and bond properties in functionalized esters and amides

The properties of various atomic groups of molecules containing a carbonyl unit (XCOY) consisting of an ester (Y=OR) or amide function (Y=NHR) in different molecular environments (X=H, Me, Et, OH, OMe, NH₂, NHMe, F, Cl), as well as their influence on the properties of the alkyl chain (R=C₈H₁₇) in the molecule, were analyzed by use of the theory of atoms in molecules (AIM). To this end, the main atomic and bond properties for each atom in 18 carbonyl compounds of the aforementioned types were determined on the basis of 6-31++G**//6-31G* wave functions. The properties of the C and O atoms in the carbonyl group, and those of their bonds, are directly related to the nature and electronegativity of the X substituent and to the character of the Y group. The nature of the C Y bond and the properties of the Y group are also dependent on the proximity of the X group. Based on the precision with which integrated properties were determined, assessed by L(Ω), the properties of the methylene groups of the R chain located in α and β with respect to Y are essentially dependent on the nature of Y and, to a lesser extent, on that of X. The methylene group in γ with respect to Y exhibits a dependence on the nature of the latter that vanishes in more distinct groups; therefore, the methylene in ε can be assimilated to one in an alkane. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1444–1454, 1999     

Singlet-triplet splitting of divalent five-membered fused rings C<Subscript>12</Subscript>H<Subscript>8</Subscript>M (M = C,Si, Ge,Sn, and Pb): Application in nanocomplex synthesis

Energy differences, ΔX _s−t (X = E, H, and G) (ΔX _s−t = X(singlet) − X(triplet)) between singlet (s) and triplet (t) states of C₁₂H₈M were calculated at B3LYP/6-311+G*. The DFT calculations indicated that the ΔG _s−t between singlet (s) and triplet (t) states of C₁₂H₈M were increased from M = C to M = Pb. The ΔG _s−t of C₁₂H₈M was compared with its analogue C₄H₄M through replacement of heavy atoms from M = C to M = Pb. Configurations of the electrons in orbitals (σ² or π²) for the singlet state of C₁₂H₈M were discussed.     

Thermodynamic analysis of polymer‐solid adhesion: Sticker and receptor group effects

Adhesion of dense linear polymer chains containing a small number of randomly distributed sticker groups (?_X) to a solid substrate containing receptor groups (?_Y) has been analyzed by a single‐chain scaling approach. An entanglement sink probability (ESP) model motivated by vector percolation explains the nonmonotonic influences of sticker concentration (?_X), receptor concentration (?_Y), and their interaction strength (χ) on the adhesion strength G_IC of the polymer‐solid interface. The ESP model quantifies the degree of interdigitation between adsorbed and neighboring chains on the basis of the adsorbed chain domain with an extension of the scaling treatment of de Gennes. Here, the adsorbed chain domain changes thermodynamically with respect to the energy of interaction parameter, r = χ?_X?_Y. This model considers the situation of a blend consisting of a small volume fraction of adhesive molecules as a compatibilizer at the interface, where these molecules promote adhesion by adsorbing to the surface via sticker‐receptor interactions. The percolation model scales solely with r = χ?_X?_Y, and this parameter can be related to both the adhesive potential (G_A) and the cohesive potential (G_C). G_A describes adhesive failure between adsorbed chains and the solid surface and linearly behaves as G_A ～ r = χ?_X?_Y. The cohesive strength between adsorbed and neighboring chains corresponds to G_C ～ r^?0.5～?1.0 = (χ?_X?_Y)^?0.5～?1.0. When the fracture stresses for cohesive and adhesive failure are equal, the model predicts maximum adhesion strength at an optimal value of r* = (χ?_X?_Y)*. Thus, for a given χ value, optimal values ? and ? exist for the sticker and receptor groups, above or below which the fracture energy will not be optimized. Alternatively, if the X‐Y interaction strength χ increases, then the number of sticker groups required to achieve the optimum strength decreases. Significantly, the optimum strength is not obtained when the surface is completely covered with receptor groups (?_Y = 1) but is closer to 30%. For polybutadiene, the optimum value of r* was determined experimentally (Lee, I.; Wool, R. P. J Adhesion 2001, 75, 299), and typically ? ≈ 1–3%, ? ≈ 25–30%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2343–2353, 2002     

Composition and structure of complexes formed in the reaction of uranyl di(2-ethylhexyl)phosphate and tributyl phosphate or di-N-octyl sulfoxide in benzene solutions

This paper reprots of³¹P NMR and IR studies of the interaction of tributyl phosphate (TBP) and di-n-octyl sulfoxide (DOSO) with polymer molecules of uranyl di-2-ethylhexyl phosphate (UO₂X₂)_p (I) in C₆H₆ sulutions. Detailed interpretations of the³¹P NMR spectra and the v_as(POO) IR bands and determination of the fraction of nonequivalent phosphorus atoms of X⁻ anions and uranium (VI) atoms as well as the concentration of U(VI)-bonded TBP in I have shown that only a single TBP or DOSO molecule is coordinated to the uranium atoms of polymer I at C_TBP=0.1–2 M or C_DOSO=0.1–0.5 M. In the case of 100% TBP, two TBP molecules are coordinated to some U(VI) atoms. Distribution of TBP (DOSO) molecules along the polymer chain agrees with the mean statistical value. The portion of terminal chalate POO-groups of X⁻ anions is determined. The dependence of the degree of (UO₂X₂)_p·nL (L=TBP, DOSO) polymerization on C_L is obtained. Saturation of solutions with water only slightly affects the terminal POO-groups and has no effects on the distribution of L along the polymer chain of I. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 66–73, November–December, 1994. Translated by K. Shaposhnikova     

A method for phenomenological calculations in series of substituted benzenes

The methodology of calculations of the physicochemical properties of substituted benzenes C₆H_{6 − p} X _p , C₆H_{6 − p − q} X _p Y _q , ... (X and Y are univalent substituents) and C₆H₅A, where A = OH (phenol), NH₂ (aniline), etc. by the phenomenological methods of chemical structure theory is discussed.     

Thermodynamic investigation of room temperature ionic liquid

The molar heat capacities of the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature X by polynomial equations, C _P,m (J K^–1 mol^–1)= 195.55+47.230 X–3.1533 X ²+4.0733 X ³+3.9126 X ⁴ [X=(T–125.5)/45.5] for the solid phase (80~171 K), and C _P,m (J K^–1 mol^–1)= 378.62+43.929 X+16.456 X ²–4.6684 X ³–5.5876 X ⁴ [X=(T–285.5)/104.5] for the liquid phase (181~390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BMIBF₄ relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass translation of BMIBF₄ was observed at 176.24 K. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BMIBF₄ was determined to be Δ_c H _m ^o= – 5335±17 kJ mol^–1. The standard molar enthalpy of formation of BMIBF₄ was evaluated to be Δ_f H _m ^o= –1221.8±4.0 kJ mol^–1 at T=298.150±0.001 K.     

The effect of CH<Subscript>3</Subscript>, F and NO<Subscript>2</Subscript> substituents on the individual hydrogen bond energies in the adenine–thymine and guanine–cytosine base pairs

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The electron withdrawing (EW) substituents (F and NO₂) increase the total binding energy (ΔE) of X–G–C derivatives and the electron donating (ED) substituent (CH₃) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH₃ in the 1 position and F in the 5 position, which in both cases the ΔE value decreases negligibly small. With minor exceptions (X=8–CH₃, 8–F, and 9–NO₂), both ED and EW substituents increase slightly the ΔE values of X–A–T derivatives. The individual HB energies (∆E _HBs) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the role of atoms entered H-bonding. The remarkable change is observed for NO₂ substituted derivative in each case.     

Micellar and associated thermodynamic properties of binary mixtures of alkyl triphenyl phosphonium bromides in ethylene glycol and water mixtures

Micellar properties of binary combinations of a family of cationic alkyl triphenyl phosphonium bromides with varying chain length (C₁₀–C₁₆) were investigated in aqueous and aqueous ethylene glycol mixtures employing conductometric technique. The results of the mixed systems were analyzed in the light of the Regular Solution Theory and the Gibbs–Duhem equation to evaluate the composition of the mixed micelle, the activity coefficients, and the interaction parameter (β). The excess free energy and the other related thermodynamic parameters of mixing were calculated and discussed in terms of the stability of the mixed micelles in the presence of an ethylene glycol additive. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

D-xylose Derivative Liquid Crystals

We studied the phase transition temperatures of a series of amphiphilic D-xylopyranose and D-xylofuranose derivatives in which the lipophilic part is an alkyl chain R (n-C_nH_2n+1), regiospecifically linked to D-xylose, at different positions, by Z which is an atom or a functional group (O, S, O–(CH₂)₃–S). The alkyl chain was moved from the C-1 to the C-5 position in the xylose moiety, thereby allowing us to compare directly the phase transition temperatures of the individual materials. These compounds give thermotropic and/or lyotropic liquid crystals. In some cases, we also observed solid–solid phase transitions. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Thermodynamics of C70 fullerence in the 0–390 K temperature range

The temperature dependence of heat capacity of C₇₀ fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic characteristics were determined. From the experimental data obtained, the thermodynamic functionsH ^o (T)-H ^o(0),S ^o(T),G ^o(T)-H ^o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δ_f S ^o, Δ_f G ^o, and logK _f ^o for the formation of C₇₀ from graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998.     

Radical addition reactions: factors determining the transition-state geometry

Interatomic distances in the reaction centers of the addition reactions of (i) H^· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ^·CH₃ radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the type X^· + Y=Z → X— Y—Z^· the r ^# _X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined for seventeen classes of radical addition reactions. The bond elongation, Δr ^# _X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the reaction center, and the force constant of the attacked multiple bond increase. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005.     

Types of rotary crystal state of solid solutions of paraffins

Thermal deformations and polymorphous transformations of solid solutions of paraffins in C₁₇–C₁₉, C₁₉–C₂₁, C₂₁–C₂₃, C₂₂–C₂₄, and C₂₃–C₂₄ systems are investigated by thermal X-ray diffractometry using a temperature step of several tenths of a degree. It is examined how the length of a molecular chain of a homolog (n) and the difference in length (Δn) between the chains as well as the molecular composition of a solid solution affect these transitions, and the data are compared with those for the individual homologs of paraffins. St. Petersburg University. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 3, pp. 380–394, May–June, 1998. This work was supported by RFFR grant No. 97-05-65534 and ISSEP grants No. 156p and a97-2633.     

Anab initio quantum-chemical study of proton addition to F-, Ch3-, and CF3-substituted ethylene derivatives

Protonated forms of the molecules of ethylene derivatives with the general formula C₂X₂Y₂ (X=Y=H) (1), F (2), CH₃ (3) CH₃ (4); X=F, Y=H:cis-(5)trans- (6)) were calculated by theab initio MP2/6-31 G^* method with full geometry optimization. The minima and saddle points located on the potential energy surface (PES) of the protonated ethylene molecule correspond to the stationary states and transition states of proton migration, respectively. The stationary states are characterized by a nonclassical geometry of carbocations similar to that of π-complexes, whereas the transition states have a classical structure. Unlike1, the carbocations of molecules2–6 have the classical structure. The saddle points on the PES of the ethylene derivatives correspond to the structures of the π-complex type, which are the transition states of proton migration between the C atoms of the ethylene bond. The barrier to rotation about, the C−C bond depends essentially on the substituent nature. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1333–1337, August, 2000.     

Molecular and electronic structure of some binary polyhedral clusters

The molecular and electronic structures of some polyhedral alternate molecules X_nY_n, where n=12, 16; X=B, Al, Si; Y=N,P,C, and of homoatomic clusters C₂₄, Si₂₄, C₃₂, and Si₃₂ are calculated in a valence approximation by the MNDO method. It is suggested that the σ-frameworks of these molecules are formed of four- and six-membered rings, with each X atom having only Y atoms as neighbors. The singlet states of all these systems have local minima on the corresponding potential energy surfaces with T_h symmetry for n=12 and T_d symmetry for n=16. The main structural parameters, heats of formation, ionization potentials, and effective charge distributions are given. It is concluded that the X_nY_n heteroatomic clusters can exist when X and Y are atoms of Group III and V elements, respectively, or both are atoms of Group IV elements. A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp.976–982, November–December, 1995. Translated by L. Smolina     

Non-debye nature in thermal relaxation and thermal properties of lithium borate glasses studied by modulated DSC

Complex heat capacity, C _p ^*=C _p ^'–iC _p ^', of lithium borate glasses xLi₂O·(1–x)B₂O₃ (molar fraction x=0.00–0.30) has been investigated by Modulated DSC. We have analyzed the shape of C _p ^* by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation, and then determined the parameters related to the non-Debye nature of thermal relaxation. Moreover, the concentration dependence of the thermal properties has been investigated. Glass transition temperatures become higher with the increase of molar fraction of Li₂O and shows the board peak around x=0.26. Temperature ranges of glass transitions become narrower with the increase of Li₂O concentration.     

Optimization of process variables and corrosion properties of a multi layer silica sol gel coating on AZ91D using the Box–Behnken design

Anti-corrosion silica coating was prepared via the sol–gel method for AZ91D magnesium alloy using tetraethoxysilane and methyltriethoxysilane as precursors. Silica coating was deposited on fluorinated magnesium alloy substrates by dip coating. The surface morphology of the silica coating was characterized by scanning electron microscope (SEM). The corrosion properties were studied by electrochemical impedance measurements and polarisation technique in 3.5 wt% Sodium chloride solution. The results showed an improvement in the corrosion performance from these coatings. A three-factor, three-level design of experiment (DOE) with response surface methodology including a Box–Behnken design was run to evaluate the main and interaction effects of several independent formulation variables, which included precursor ratios MTES/TEOS (X₁), sintering temperature (X₃) and sol dilution (X₂) which measured the volume of the diluted sol divided by the initial volume of sol. The dependent variables included the corrosion current derived from the polarisation curve (i_cor = Y₁) and the coating resistance derived from the Nyquist curve (R_coat = Y₂). Optimizations were predicted to yield Y₁ and Y₂ values of 1.57018E–7A cm⁻² and 14279 Ω cm², when X₁, X₂, and X₃ were 3.36, 1.52 and 222, respectively.     

Electronic spectra of the linear cationic chains NC<Subscript>2<Emphasis Type="Italic">n</Emphasis></Subscript>N<Superscript>+</Superscript> (<Emphasis Type="Italic">n</Emphasis> = 1–7): an ab initio study

The ground-state equilibrium geometries of the linear carbon chain cations NC_2n N⁺ (n = 1–7) have been investigated with B3LYP, CAM-B3LYP, and RCCSD(T) calculations. The ground state (X²П_g/u) and excited state (1²П_u/g) have been optimized by using the complete active space self-consistent field method. The present study reveals that these linear cations generally have the characteristic of bond length alternation in both electronic states. The vertical excited energies for the dipole-allowed (1, 2, 3)²П_u/g ← X²П_g/u transitions as well as the dipole-forbidden 1²Φ_u/g ← X²П_g/u transitions have been computed with the complete active space second-order perturbation theory. The calculated transition energies of 1²П_u/g ← X²П_g/u for NC_2n N⁺ (n = 1–6) in the gas phase are 2.26, 2.09, 1.91, 1.72, 1.56, and 1.39 eV, respectively, which mutually agree well with the available experimental values of 2.11, 2.07, 1.88, 1.67, 1.49, and 1.34 eV. Moreover, the corresponding absorption wavelengths are predicted to have the significant nonlinear size dependence, which is different from the bands origin in NC_2n N (n = 1–7).     

Self-association of n -hexyltrimethyl-ammonium bromide in aqueous electrolyte solution

 The self-association of n-hexyltrimethylammonium bromide (C₆TAB) in aqueous solution has been studied by static and dynamic light scattering and NMR spectroscopy at 25 °C in the presence of added electrolyte, and critical aggregation concentrations, aggregation numbers and the degree of ionization have been calculated. Aggregation numbers determined from light scattering and from the application of mass-action theory to the concentration dependence of ¹H NMR chemical shifts of four protons along the alkyl chain of C₆TAB, were between three and four over the range of electrolyte concentration studied (0.2–0.7  molkg⁻¹ NaBr). A structure for the small aggregates has been proposed from the NMR chemical shift data. Received: 4 June 2001 Accepted: 17 September 2001     

Study of the Alkyl Chain Length on Laccase Stability and Enzymatic Kinetic with Imidazolium Ionic Liquids

The activity and stability of laccase and their kinetic mechanisms in water soluble ionic liquids (ILs): 1-butyl-3-methyl imidazolium chloride [C₄mim][Cl], 1-octyl-3-methyl imidazolium chloride [C₈mim][Cl], and 1-decyl-3-methyl imidazolium chloride [C₁₀mim][Cl] were investigated. The results show that an IL concentration up to 10% is satisfactory for initial laccase activity at pH 9.0. The laccase stability was well maintained in [C₄mim][Cl] IL when compared to the control. The inactivation of laccase increases with the length of the alkyl chain in the IL: [C₁₀mim][Cl] > [C₈mim][Cl] > [C₄mim][Cl]. The kinetic studies in the presence of ABTS as substrate allowed calculating the Michaelis–Menten parameters. Among the ILs, [C₄mim][Cl] was the suitable choice attending to laccase activity and stability. Alkyl chains in the ions of ILs have a deactivating effect on laccase, which increases strongly with the length of the alkyl chain.