Constant-volume combustion energy of the lead salts of 2HDNPPb and 4HDNPPb and their effect on combustion characteristics of RDX–CMDB propellant

The constant-volume combustion energies of the lead salts of 2-hydroxy-3,5-dinitropyridine (2HDNPPb) and 4-hydroxy-3,5-dinitropyridine (4HDNPPb), ΔU _c (2HDNPPb(s) and 4HDNPP(s)), were determined as –4441.92±2.43 and –4515.74±1.92 kJ mol^–1 , respectively, at 298.15 K. Their standard enthalpies of combustion, Δ_c ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K), and standard enthalpies of formation, Δ_r ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K) were as –4425.81±2.43, –4499.63±1.92 kJ mol^–1 and –870.43±2.76, –796.65±2.32 kJ mol^–1 , respectively. As two combustion catalysts, 2HDNPPb and 4HDNPPb can enhance the burning rate and reduce the pressure exponent of RDX–CMDB propellant.     

Basis of the 'duplication' strategy for enhancing the enantiomeric excess in chiral resolutions: proof of the equivalence of rate and product ratios

The 'duplication' strategy for the further enrichment of an already enantiomerically-enriched mixture consists of the formation of all the three possible 'dimeric' diastereomers, i.e., (R)–X–(R), (R)–X–(S) and (S)–X–(S), where X is an appropriate spacer that can be readily cleaved to yield the original enantiomers. The mixture of (R)–X–(R) and (S)–X–(S) thus obtained would be of higher enantiomeric excess (e.e.) as compared to the original mixture, on the basis of a simple kinetic scheme. The success of the strategy is experimentally well-established, but is apparently based on the (unproven) assumption that the theoretically-derived rate ratios are identical to the experimentally observed product ratios. Although the detailed kinetic treatment for a system such as the above is extremely complex, it is possible to show (mathematically) that the above assumption is indeed justified when all the three diastereomers are formed without chiral discrimination (as assumed in the strategy).     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

Comparison of Prediction of Phase Equilibria in the Ag–In–Sb System at 200°C with Experimental Data

Binary thermodynamic data, successfully used for phase diagram calculations of binary systems Ag–In, Ag–Sb, and In–Sb, were used for prediction of phase equilibria in ternary Ag–In–Sb system at 200°C. Symmetrical Redlich–Kister–Muggianu model for ternary thermodynamic function calculation was proved to be best valid in this ternary system. Predicted equilibria were compared with experimentally (SEM, EDX) determined composition of phases in chosen alloys after long term annealing and with the results of DTA measurements.     

Thermophysical Investigations of the Polymorphous Phases of Calcium Carbonate

1. Results of thermodynamic and kinetic investigations for the different crystalline calcium carbonate phases and their phase transition data are reported and summarized (vaterite: V; aragonite: A; calcite: C). A→C: T _tr=455±10°C, Δ_tr H=403±8 J mol^–1 at T _tr, V→C: T _tr=320–460°C, depending on the way of preparation,Δ_tr H=–3.2±0.1 kJ mol^–1 at T _tr,Δ_tr H=–3.4±0.9 kJ mol^–1 at 40°C, S _V ^Θ= 93.6±0.5 J (K mol)^–1, A→C: E _A=370±10 kJ mol^–1; XRD only, V→C: E _A=250±10 kJ mol^–1; thermally activated, iso- and non-isothermal, XRD 2. Preliminary results on the preparation and investigation of inhibitor-free non-crystalline calcium carbonate (NCC) are presented. NCC→C: T _tr=276±10°C,Δ_tr H=–15.0±3 kJ mol^–1 at T _tr, T _tr – transition temperature, Δ_tr H – transition enthalpy, S ^Θ – standard entropy, E _A – activation energy. 3. Biologically formed internal shell of Sepia officinalis seems to be composed of ca 96% aragonite and 4% non-crystalline calcium carbonate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular characteristics of poly(propylene imine) dendrimers as studied with translational diffusion and viscometry

 The generation of dendrimers based on poly(propylene imine) with CN end groups [DAB–dend–(CN) _x ] and with palmitoyl end groups [DAB–dend–(C15) _x ] was studied by methods of translational diffusion and viscometry. The volumes of the DAB–dend–(CN) _x and DAB–dend–(C15) _x dendrimers and the previously studied DAB–dend–(lacto) _x dendrimer were compared to evaluate the volumes of the end groups in hybrid dendrimers. The volume of the hybrid dendrimers compared to that of the initial dendrimers increases proportionally to the number of end groups: this means that the end groups are predominantly located on the periphery of each molecule, thus ensuring this volume will increase. It is shown that the volume of the end groups for DAB–dend–(C15) _x is 3.5 times greater, and for DAB–dend–(lacto) _x it is 5.0 times greater than that occupied by free mole- cules corresponding to the end groups. The values of the intrinsic viscosity were compared with the values of the diffusion coefficient and the chemical formula molecular weight. Received: 7 August 2001 Accepted: 2 November 2001     

Kinetic parameters determination in non-isothermal conditions for the crystallisation of a silica-soda-lead glass

Two integral isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose) and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the non-isothermal crystallisation of a silica-soda-lead glass. The objective of the paper is to show the usefulness of the IKP method to determine both the activation parameters and the kinetic model of the investigated process. Thismethod associated with the criterion of coincidence of kinetic parameters for all heating rates and some procedures of the evaluation of the parameter from Johnson–Mehl–Avrami–Erofeev–Kolmogorov (JMAEK) equation led us to the following kinetic triplet: activation energy, E=170.5±2.5 kJ mol^–1 , pre-exponential factor, A=1.178±0.350·10 10 min^–1 and JMAEK model (A _m) m=1.5.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Mixed conductivity and stability of A-site-deficient Sr(Fe,Ti)O<Subscript>3–δ</Subscript> perovskites

Deficiency in the A sublattice of perovskite-type Sr_{1– y} Fe_0.8Ti_0.2O_3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal expansion, and stability in CO₂-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures. Oxygen ion transference numbers for Sr_{1– y} Fe_0.8Ti_0.2O_3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K, increasing with temperature. The maximum ionic conductivity was observed for Sr_0.97Fe_0.8Ti_0.2O_3–δ ceramics. In the system Sr_0.97Fe_{1– x} Ti _x O_3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr_0.97(Fe,Ti)O_3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice; further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic of Sr(Fe,Ti)O_3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane permeate side. Thermal expansion coefficients of Sr_{1– y} Ti_{1– x} Fe _x O_3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10^–6 K^–1 at 350–750 K and (16.6–31.1)×10^–6 K^–1 at 750–1050 K. Electronic Publication     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Effects of fused benzene rings on tautomerizations and inversions of benzo, azabenzo, and oxabenzocycloheptatrienes at theoretical levels

Biologically important bicyclic species, including 6H-, 6H-6-aza-, and 6-oxabenzocycloheptatrienes (in which the benzene moiety is fused meta with respect to the tetrahedral constituents: –CH₂–, –NH–, and –O–, respectively), show strong shifts of tautomerizations in favor of the corresponding tricyclic benzonorcaradienes (with ΔH values of −11.49, −14.55, and −19.20 kcal mol⁻¹, respectively), at B3LYP/6-311++G**//B3LYP/6-31G*, and MP2/6-311++G**//MP2/6-31G* levels, and at 298 K. In contrast, such shifts are strongly disfavored by the isomeric bicyclic species in which the benzene moieties are fused ortho or para with respect to –CH₂–, –NH–, and –O–, respectively. Hence for species with ortho benzene rings including 5H-, 5H-5-aza- and 5-oxabenzocycloheptatrienes, tautomerization ΔH values are 30.76, 31.89, and 25.27 kcal mol⁻¹, respectively, while for species with para fused benzene moieties including 7H-, 7H-7-aza-, and 7-oxabenzocycloheptatrienes, tautomerization ΔH values are 24.12, 26.00, and 19.55 kcal mol⁻¹, respectively. NICS calculations are successfully used to rationalize these results. The calculated energy barriers for inversion of the seven-membered rings of bicyclic species predict a dynamic nature for all the structures except for the virtually planar 6H-6-aza- and 6-oxabenzocycloheptatrienes. Finally, our theoretical data are compared to the experimental results where available. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.     

Theoretical study of group 11 metal–silonyl complexes: M–SiO and M–(SiO)2 (M = Cu, Ag, or Au)

 The spectroscopic properties of M–SiO and M–(SiO)₂ (1–1 and 1–2 complexes with M = Cu, Ag, or Au) have been theoretically studied. It has been shown that both M–SiO and M–(SiO)₂ compounds in their ground state are bent with a metal–Si bonded structure. The calculated M(ns) spin density agrees well with the electron spin resonance experimental data. From a topological analysis, it has been shown that a rather large charge transfer occurs from the metal towards the SiO moiety, and that the M–Si bond energy correlates with the electron density located at the M–Si bond path (bond critical point). Received: 6 July 2000 / Accepted: 11 October 2000 / Published online: 19 January 2001     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Povarov Reaction of Glyoxylate Imines Derived from 12-Aminodehydroabietic Acid

Glyoxylate and arylglyoxal imines based on 12-aminodehydroabietic acid undergo hetero-Diels—Alder (Povarov) reaction with ethyl vinyl ether, cyclopentadiene, and indene to give, respectively, methyl (8aR,9R,12aS)-3-aroyl-5-isopropyl–9,12a-dimethyl–7,8,8a,9,10,11,12,12a-octahydronaphtho[1,2-f]quinoline-9-carboxylates, methyl (7R,10aS,10dR,13aS)-1-aroyl–3-isopropyl–7,10a-dimethyl–2,5,6,6a,7,8,9,10,10a,10d,13,13a-dodecahydro-1H-naphtho[1,2-f]cyclopenta[c]quinoline-7-carboxylates, and methyl (6aS,11bS,11eS,15R,15aR)-6-aroyl–4-isopropyl–11e,15-dimethyl–2,5,6,6a,7,11b,11e,12,13,14,15,15a-1H-dodecahydroindeno[2,1-c]-naphtho[1,2-f]quinoline-15-carboxylates.     

Crystal Structure and Conformation of a 10-Thiabilirubin

 A crystal structure determination of a bilirubin analog with a sulfur instead of a C(10)–CH₂ linking the two dipyrrinones is reported. Conformation-determining torsion angles and key hydrogen bond distances and angles are compared to those obtained from molecular dynamics calculations as well as to the corresponding data from X-ray determinations and molecular dynamics calculations of bilirubin. Like other bilirubins, the component dipyrrinones of the analog are present in the bis-lactam form with (Z)-configurated double bonds at C(4) and C(15). Despite the large differences in bond lengths and angles at –S–vs.–CH₂–, the crystal structure shows considerable similarity to bilirubin: both pigments adopt a folded, intramolecularly hydrogen-bonded ridge-tile conformation stabilized by six hydrogen bonds – although the interplanar angle of the ridge-tile conformation of the title compound is smaller (∼ 86°) than that of bilirubin (∼ 98°). The collective data indicate that even with long C–S bond lengths and a smaller C–S–C bond angle at the pivot point on the ridge-tile seam, intramolecular hydrogen bonding persists.     

Simultaneous Determination of Tramadol and Acetaminophen in Human Plasma by LC–ESI–MS

This study presents a high-performance liquid chromatography–electrospray ionization–mass spectrometric (LC–ESI–MS) method for the simultaneous determination of tramadol and acetaminophen in human plasma using phenacetinum as the internal standard. After alkalization with saturated sodium bicarbonate, both compounds were extracted from human plasma with ethyl acetate and were separated by HPLC on a Hanbon LiChrospher CN column with a mobile phase of 10 mM ammonium acetate buffer containing 0.5% formic acid–methanol (40:60, v/v) at a flow rate of 1 mL min⁻¹. Analytes were determined using electrospray ionization in a single quadrupole mass spectrometer. LC–ESI–MS was performed in the positive selected-ion monitoring (SIM) mode using target ions at [M+H]⁺ m/z 264.3 for tramadol, [M+H]⁺ m/z 152.2 for acetaminophen and [M+H]⁺ m/z 180.2 for phenacetinum. Calibration curves were linear over the range of 5–600 ng mL⁻¹ for tramadol and 0.03–16 μg mL⁻¹ for acetaminophen. The inter-run relative standard deviations were less than 14.4% for tramadol and 12.3% for acetaminophen. The intra-run relative standard deviations were less than 9.3% for tramadol and 7.9% for acetaminophen. The mean plasma extraction recovery for tramadol and acetaminophen were in the ranges of 82.7–85.9 and 83.6–85.3%. The method was applied to study the pharmacokinetics of a new formulation of tramadol/acetaminophen tablet in healthy Chinese volunteers.     

Comparison of Prediction of Phase Equilibria in the Ag–In–Sb System at 200°C with Experimental Data

Summary. Binary thermodynamic data, successfully used for phase diagram calculations of binary systems Ag–In, Ag–Sb, and In–Sb, were used for prediction of phase equilibria in ternary Ag–In–Sb system at 200°C. Symmetrical Redlich–Kister–Muggianu model for ternary thermodynamic function calculation was proved to be best valid in this ternary system. Predicted equilibria were compared with experimentally (SEM, EDX) determined composition of phases in chosen alloys after long term annealing and with the results of DTA measurements.     

Mechanism of formation of 3-methyl derivatives of imidazo[2,1-<Emphasis Type="Italic">b</Emphasis>]thiazoles and their benzo analogs in the reactions of 2-mercaptoimidazole and 2-mercaptobenzimidazole with 1,3-dichloroacetone under phase-transfer catalysis conditions

The mechanism of the unexpected formation of 3-methyl derivatives of imidazo[2,1-b]thiazoles in the system 2-mercaptoimidazole–1,3-dichloroacetone–solid K₂CO₃–solid KI–18-crown-6–toluene has been studied. The structure of 3-methyl[1,3]thiazolo[3,2-a]benzimidazole has been confirmed using X-ray structural analysis.     

Ternary phase diagrams of DNTF and TNAZ and their eutectics

The eutectic ternary phase diagrams of some typical volatilizable energetic materials have been investigated by high pressure differential scanning calorimeter (PDSC). The ternary H–X phase diagrams for TNT/TNAZ/DNTF (TTD) and TNAZ/DNTF/RDX (TDR) systems were constructed by the correlation of the apparent fusion heat with the composition (H–X method). And, the ternary T–X phase diagrams (the temperature dependence on composition) for the two ternary systems were constructed by calculating from the data of the five T–X binary phase diagrams. The eutectic compositions (mol%) of TTD and TDR ternary systems were obtained to be 52.3/27.3/20.4 (H–X method), 53.2/25.8/21.0 (T–X method) and 54.9/39.6/5.5 (H–X method), 55.1/42.2/2.7 (T–X method), respectively. The eutectic temperatures of the ternary systems were obtained by PDSC determination and T–X method calculation to be 76.5 and 76.7 °C, 47.5 and 50.2 °C, respectively. It is shown that the results obtained by two methods are in agreement and the error in measuring or calculating eutectic compositions and temperatures for the two ternary systems are within allowable ranges of ±3 mol% and ±3 °C, respectively. Moreover, by means of constructing two ternary H–X phase diagrams with different fixed composition of a component and comparing the apparent fusion heat of eutectics with calculated one, the results obtained from H–X method for TTD system were proved. The results showed that the gasification or volatilization of easy volatile materials could be efficiently restrained by high pressure atmosphere, and the perfectly and ideally H–X ternary phase diagrams can be constructed. In comparison with T–X method, H–X method has as a virtue of being quick and simple, especially on constructing ternary phase diagram.