Comparison of the performance of different “local reactive descriptors” in 3D-QSAR analysis of enantioselective molecules

Structural Chemistry - The interaction between Ligand-Receptor (L-R) to solve the pharmacological and toxicological problems of enantioselective molecules was studied as 3D Quantitative...     

Wilhelm Ostwald’s energetics 3: energetic theory and applications,part II

This is the third of a series of essays on the development and reception of Wilhelm Ostwald’s energetics. The first essay described the chemical origins of Ostwald’s interest in the energy concept and his motivations for seeking a comprehensive science of energy. The second essay and the present one discuss his various attempts, beginning in 1891 and extending over almost 3 years, to develop a consistent and coherent energetic theory. A final essay will consider reactions to this work and Ostwald’s replies, and will also seek to evaluate his program of research. Ostwald’s project—to reconstruct physics and chemistry “as a pure energetics”—is worth attending to for several reasons: first, because Ostwald did ground-breaking work in chemistry (he was awarded a Nobel Prize in 1909 for his studies in catalysis and rates of reaction); second, because an important school of physical chemistry formed around him at Leipzig, a school that promoted his ideas; and, finally, because he was a prominent and vigorous participant in debates at the end of the nineteenth century concerning the proper course of physical theory.

Perspective on “Semiclassical theory of atom–diatom collisions: path integrals and the classical S matrix”

Miller's papers on classical S-matrix theory had a profound influence on the understanding of inelastic atom–molecule collisions. This perspective discusses the historical background, the content, some applications, and new developments. Received: 26 February 1999 / Accepted: 5 April 1999 / Published online: 21 June 1999     

A critical analysis of the effect of crosslinking on the linear viscoelastic behavior of styrene–butadiene rubber and other elastomers

The linear viscoelastic behavior in dynamic shear and tensile creep at temperatures from −30 to 70 °C is measured for an styrene–butadiene rubber (SBR) elastomer cured with dicumyl peroxide to crosslinking densities between 0 and 23.5 × 10⁻⁵ mol/cm³. The G′, G″, and tan δ isotherms are analyzed by time–temperature superposition (TTS), where the tan δ master curves are consistent with those of Mancke and Ferry. However, to achieve the TTS in the lightly crosslinked SBR systems, an anomalous vertical shift is required in the narrow temperature region from 10 to 30 °C. The vertical shift factor in this temperature region is not the standard from rubber elasticity. No anomalous behavior is detected in the equilibrium modulus, which is a linear function of temperature in accordance with the classical theory of rubber elasticity. In contrast to SBR, standard vertical shifts are required to effect TTS for uncrosslinked polybutadiene and an ethylene propylene diene monomer elastomer. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Study and 3D modeling of the phase diagram of the Ag–Ge–Se system

In view of the contradictoriness of the literature data, phase equilibria in the Ag–Ge–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and an isothermal section at room temperature of the phase diagram were constructed, and so was the projection of the liquidus surface. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was shown that, in the system, a single ternary compound, Ag₈GeSe₆, forms, which undergoes congruent melting at 1175 K and a polymorphic transformation at 321 K. The formation of the compounds Ag₂GeSe₃ and Ag₈GeSe₅, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Use of biopartitioning micellar chromatography and RP-HPLC for the determination of blood–brain barrier penetration of α-adrenergic/imidazoline receptor ligands,and QSPR analysis

For this study, 31 compounds, including 16 imidazoline/α-adrenergic receptor (IRs/α-ARs) ligands and 15 central nervous system (CNS) drugs, were characterized in terms of the retention factors (k) obtained using biopartitioning micellar and classical reversed phase chromatography (log k_BMC and log k_wRP, respectively). Based on the retention factor (log k_wRP) and slope of the linear curve (S) the isocratic parameter (φ₀) was calculated. Obtained retention factors were correlated with experimental log BB values for the group of examined compounds. High correlations were obtained between logarithm of biopartitioning micellar chromatography (BMC) retention factor and effective permeability (r(log k_BMC/log BB): 0.77), while for RP-HPLC system the correlations were lower (r(log k_wRP/log BB): 0.58; r(S/log BB): –0.50; r(φ₀/P_e): 0.61). Based on the log k_BMC retention data and calculated molecular parameters of the examined compounds, quantitative structure–permeability relationship (QSPR) models were developed using partial least squares, stepwise multiple linear regression, support vector machine and artificial neural network methodologies. A high degree of structural diversity of the analysed IRs/α-ARs ligands and CNS drugs provides wide applicability domain of the QSPR models for estimation of blood–brain barrier penetration of the related compounds.     

Experimental Study and 3D Modeling of the Phase Diagram of the Ag–Sn–Se System

In connection with the contradictoriness of literature data, phase equilibria in the Ag–Sn–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and the isothermal section at room temperature of the phase diagram were constructed, and a projection of the liquidus surface was built. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was demonstrated that, in the system, two ternary compounds, Ag₈SnSe₆ and Ag_xSn_{2 – x}Se₂ (0.84 < x < 1.06), form. The former melts congruently at 1015 K and undergoes a polymorphic transformation at 355 K, and the latter melts with decomposition by a peritectic reaction at 860 K. The formation of the compound Ag₂SnSe₃, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a limited number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

A Novel 2D→3D Network with the Coexistence of Polythreading and Inclined Polycatenation Constructed by the Tripodal Linker

A new cadmium(II) coordination polymer with unique structure was synthesized under diffusion process by employing triangular N-containing ligand tris(4-(pyridyl) phenyl) amine(Tppa). Complex 1 crystallizes in the space group Pbcn, with a = 28.906(3), b = 13.5294(14), c = 17.8727(18), V = 6989.7(12) 3, C66H48 Cd Cl2N8, Mr = 1136.42, Dc = 1.080 g/cm3, F(000) = 2328, μ = 0.428 mm-1 and Z = 4. Complex 1 features a 2D → 3D framework with the coexistence of inclined polycatenation and polythreading. In addition, the luminescent property of complex 1 was studied.     

Thermal analysis of the oxide–chloride systems GdCl3–Gd2O3 and GdCl3–KCl–Gd2O3

Journal of Thermal Analysis and Calorimetry - The thermal analysis of the oxide–chloride systems GdCl3–Gd2O3 and GdCl3–KCl–Gd2O3 with the Gd2O3 content up to...     

Twinkling fractal theory of the glass transition: Rate dependence and time–temperature superposition

The twinkling fractal theory (TFT) of the glass transition temperature T_g provides a new method of analyzing rate effects and time–temperature superposition in amorphous materials. The rate dependence of T_g was examined in the light of new experimental and theoretical evidence for the nature of the dynamic heterogeneity near T_g. As T_g is approached from above, dynamic solid fractal clusters begin to form and eventually percolate rigidity at T_g. The percolation cluster is a solid fractal and to the observer, appears to “twinkle” as solid and liquid clusters interchange in dynamic equilibrium with a vibrational density of states g(ω) ∼ ω. The solid-to-liquid twinkling frequencies ω_TF are controlled by the Boltzmann population of intermolecular oscillators in excited energy levels of their anharmonic potential energy functions U(x) such that ω_TF = ω exp −B(T*² − T²)/kT in which T* ≈ 1.2T_g. An oscillator changes from a solid to a liquid when a thermal fluctuation causes it to expand beyond its inflection point in the anharmonic potential. This leads to a continuous solid fraction P_s near T_g given by P_S ≈ 1−[(1 − p_c) T/T_g] where p_c ≈ 1/2 is the rigidity percolation threshold. Since g(ω) is continuous from very low to very high frequencies, the complex twinkling dynamics existing near T_g produces a continuous relaxation spectrum with many different length scales and times associated with the fractal clusters. The twinkling frequencies control the kinetics of T_g such that for a given observation time t when the rate γ > 1/t, only those parts of the twinkling spectrum with ω > γ can contribute to relaxation or percolation upto time t. The most important results in this article are as follows: The TFT describes the rate dependence of T_g, both for DSC thermal heating/cooling rates and DMA frequencies as the classic T_g − lnγ law as T_g(γ) = T_go + (k/2B) ln γ/γ_o in which the constant B = 0.3 cal/mol K². The constant B appears quite universal for the 17 thermoset polymers investigated in this study and 18 linear polymers investigated by others. Many other amorphous metal and ceramic glass materials exhibited the same rate law but required a new B value approximately half that for polymers. The same B = 0.3 value was also used to successfully describe the TTS shift factors using the twinkling fractal frequencies ω_TF = ωexp −B(T*² − T²)/kT, as ln a_T(TFT) = exp B(T_R² − T²)/kT, which gave comparable results with the classical WLF equation, log a_T = [−C₁(T − T_R)]/[C₂ + (T − T_R)]. The advantage of the TFT over the WLF is that C₁ and C₂ are not universal constants and must be determined for every material, whereas the TFT uses one known constant B which appears to be the same for all polymers. The TFT has also been found to describe the strong and fragile nature of the viscosity behavior of liquids and the rate and temperature dependence of the yield stress in polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2578–2590, 2009     

Relativity and the Jahn–Teller,Berry pseudorotations of TBP clusters: group theory,spin–orbit and combinatorial nuclear spin statistics of TBP Desargues–Levi isomerization graph

Jahn–Teller and Berry pseudorotations in transition metal and main group clusters such as Hf₅, Ta₅, W₅ and Bi₅ are interesting because of the competition between relativistic effects and pseudorotations. Topological representations of various isomerization pathways arising from the Berry pseudorotation of pentamers constitute the edges of the Desargues–Levi graph. We have computed the combinatorics for multinomial colorings of the vertices, edges and 10-faces of the Desargues–Levi isomerization graph for all irreducible representations and the nuclear spin statistics of spin-7/2 ¹⁸¹Ta₅ as well as the TBP composite cluster particles. Topological insights into Jahn–Teller and Berry pseudorotations and relativistic effects are provided.     

Electrical conductivity of sodium polystyrenesulfonate in acetonitrile–water-mixed solvent media: experiment and data analysis using the Manning counterion condensation model and the scaling theory approach

Precise measurements on the electrical conductivity of sodium polystyrenesulfonate in acetonitrile–water-mixed solvent media containing 20 and 40 vol.% of acetonitrile at 308.15, 313.15, and 318.15 K are reported. The mobility of the polyelectrolyte solute was found to be influenced by the polyelectrolyte concentration, the relative permittivity of the medium, and the temperature. The Manning counterion condensation theory for salt-free polyelectrolyte solution failed to describe the experimental results. The data have, therefore, been analyzed on the basis of a new model for semidilute polyelectrolyte conductivity which takes into account the scaling arguments to obtain the fractions of uncondensed counterions which were found to depend on the polyelectrolyte concentration. The effects of the temperature and the relative permittivity of the medium on the equivalent conductivity as well as on the fraction of uncondensed counterions have also been discussed.     

Synthesis and Characterization of a Novel 3D Organic–Inorganic Hybrid Framwork Templated by Keggin Anions

A novel 3D compound, {K₃H₂[Cu(Gly)₂]₃BW₁₂O₄₀}·10H₂O 1 (Gly = glycine), has been synthesized and characterized by elemental analyses, IR, TG analyses, cyclic voltammetry, and single-crystal X-ray diffraction. Compound 1 contains square-grid layers constructed by potassium cations and copper-glycine coordination complexes, the [BW₁₂O₄₀]^4? anions as templates are accommodated in the square grids by connecting with the K atoms. The K atoms link [BW₁₂O₄₀]^4? anions from different layers together to yield a 3D novel structure. The crystal data for compounds 1: monoclinic, space group p2(1)/n, a = 18.832(4) Å, b = 16.488(3) Å, c = 20.570(4) Å, β = 106.21(3)°, V = 6133(2) Å³, Z = 4.     

IR Study of Monomer–Dimer Self-association of 2,2-Dimethyl-3-ethyl-3-pentanol in n-Octane: Determination of the Molar Absorptivities of Monomer and Dimer Bands, and Dimerization Constants Using Novel Equations

The monomer–dimer self-association equilibrium of 2,2-dimethyl-3-ethyl-3-pentanol in n-octane has been studied by IR spectroscopy at four temperatures (288, 298, 308, and 318 K). The solute was chosen to restrict the self-association between solute molecules to dimerization only, owing to steric hindrance of the bulky chains in the vicinity of the OH group. Two linear equations have been derived for the treatment of the experimental data. One of these equations was used to treat the data of the concentration dependent integrated absorbance of the monomer bands for each temperature to obtain the monomer molar absorptivity, ε _m, and dimerization constant, K. The other equation was used to treat the data of concentration-dependent dimer bands to obtain the dimer molar absorptivity, ε _d, and K. Thus, the dimerization constant was determined by two methods. Since the same thermodynamic quantity K is obtained from either the monomer bands or the dimer bands, the difference between them at a given temperature can serve as an assessment of the quality of the experiment. The standard enthalpy and entropy of dimerization were also obtained from a van’t Hoff plot.     

A Novel,Convenient Synthesis of the 3‐O‐β‐D‐ and 4′‐O‐β‐D‐Glucopyranosides of trans‐Resveratrol

Abstract

trans‐Resveratrol‐3‐O‐β‐D‐glucupyranoside (trans‐piceid, 2) and trans‐resveratrol‐4′‐O‐β‐D‐glucupyranoside (trans‐resveratroloside 3) are the naturally occurring O‐glucoside conjugates of the polyphenolic stilbenoid trans‐resveratrol 1. Recently, attention has been drawn towards the interesting biological properties of the glucoside conjugates 2 and 3 as well as those of the aglycone 1. The fact that only limited quantities can be obtained by extraction from natural sources has prompted the development of novel syntheses of 2 and 3, based on a convergent Heck‐coupling strategy, which now conveniently allows for the preparation of multi‐milligram to gram quantities of each.