Investigation of Phase Transition inLa1–xPrxGaO3 and La1–xNdxGaO3 Crystals

The solid solution crystals, La_1–xNd_xGaO₃ and La_1–xPr_xGaO₃ have been studied by differential scanning calorimetry method; the crystals exhibit the first order phase transition, the temperature of the transition linearly increases with the concentration of Pr or Nd. The structure of the crystals has been determined by X-ray diffraction. The correlation between the phase transition temperature and crystalline structure at the temperature of the phase transition in both solid solution families is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,Optical and Electrochemical Properties of D1–A–D2–A–D1 Type Conjugated Donor-Acceptor Assemblies of Five-Membered Aromatic Heterocycles

Chemistry of Heterocyclic Compounds - Novel conjugated systems of the D1–A–D2–A–D1 type were synthesized based on...     

Reduction of 1-Deoxy -13–oxotaxanes

Numerous reports have described the semisynthesis of paclitaxel and its anologues from different taxoids 1. However, to the best of our knowledge almost all taxoids have a C-1-hydroxyl. Heretofore, the semisynthesis from taxinine, an abundant natural taxoid lacking of C-1-hydroxyl, has only reached the point of C-13 ketone intermediate 2. We have also encountered difficulties in reducing C-13 ketone to corresponding α- hydroxy group using the same conditions as in total synthesis of paclita…     

TG/DSC studies of modified 1–vinyl-2-pyrrolidone–divinylbenzene copolymers

In this paper, the synthesis and characterization of porous copolymers of 1-vinyl-2-pyrrolidone with divinylbenzene are presented. They were obtained by suspension polymerization as pure polymers or composite materials with different inorganic fillers. The influence of the type of filler on the textural and thermal properties was investigated in detail. It was found that the value of the porous surface area and the degree of double bonds’ conversion of composites are much lower than in the case of pure copolymers. Thermal properties of the obtained materials were investigated by the means of thermogravimetry and differential scanning calorimetry.     

Electrochemical performance of Mg–9Al–1Zn alloy in aqueous medium

A systematic study on the corrosion and passivation behavior of AZ91D alloy in relation to the influence of concentration, temperature, pH, and immersion time was made in aqueous sulfate solution using electrochemical techniques including open-circuit potential, potentiodynamic polarization and impedance spectroscopy. It was found that the corrosion and pitting potentials (E _corr and E _pit) of the alloy drift to more active values with increasing either concentration (0.01–1.0 M) or temperature (278–338 K) of the test solution, suggesting that sulfate solution enhances the alloy dissolution, particularly at higher temperatures. On the other hand, values of the total film resistance (R _T) indicate that neutral solution (pH 7.0) supports the formation of a better protective layer on AZ91D surface than alkaline (pH 12.5) or acidic (pH 1.0) medium. The growth of a protective film on the alloy surface at short immersion times (up to ∼50 h) is evinced by a rapid positive evolution of E _corr and fast decrease in the corrosion rate (i _corr). However, for a long-term exposure (up to 500 h) E _corr drifts negatively and i _corr increases due to breakdown of the protective film, which causes a decrease in the alloy stability. Fitting the impedance data to equivalent circuit models suitable to each behavior assisted to explore the mechanism for the attack of the sample surface at various testing times. The results obtained from the three studied electrochemical techniques are in good agreement.     

High-pressure phase equilibria for the carbon dioxide–2-methyl-1-butanol,carbon dioxide–2-methyl-2-butanol,carbon dioxide–2-methyl-1-butanol–water,and carbon dioxide–2-methyl-2-butanol–water systems

High-pressure vapor–liquid equilibria for the binary carbon dioxide–2-methyl-1-butanol and carbon dioxide–2-methyl-2-butanol systems were measured at 313.2 K. The phase equilibrium apparatus used in this work is of the circulation type in which the coexisting phases are recirculated, on-line sampled, and analyzed. The critical pressure and corresponding mole fraction of carbon dioxide for the binary carbon dioxide–2-methyl-1-butanol system at 313.2 K were found to be 8.36 MPa and 0.980, respectively. The critical point of the binary carbon dioxide–2-methyl-2-butanol was also found 8.15 MPa and 0.970 mole fraction of carbon dioxide. In addition, the phase equilibria of the ternary carbon dioxide–2-methyl-1-butanol–water and carbon dioxide–2-methyl-2-butanol–water systems were measured at 313.2 K and several pressures. These ternary systems showed the liquid–liquid–vapor phase behavior over the range of pressure up to their critical point. The binary equilibrium data were all reasonably well correlated with the Redlich–Kwong (RK), Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), and Patel–Teja (PT) equations of state with eight different mixing rules the van der Waals, Panagiotopoulos–Reid (P&R), and six Huron–Vidal type mixing rules with UNIQUAC parameters.     

Ignition limits of hydrogen–methane–air mixtures over metallic Rh at a pressure of 1–2 atm

The ignition temperatures and effective activation energies of the ignition limits of mixtures (40–70% H₂ + 60–30% CH₄)_stoich + air over Rh were experimentally determined at a pressure of 1 atm in the temperature range 20–300 °C. Over an ignition-treated Rh surface, the ignition temperature of a mixture of 70% H₂ + 30% methane + air is 62 °C. This indicates the potential of using Rh to markedly lower the ignition temperature of fuels based on hydrogen–methane mixtures.     

Liquid–Liquid Equilibrium Data for 1-Ethyl-3-methylimidazolium Acetate–Thiophene–Diesel Compound: Experiments and Correlations

Extraction of thiophene from cyclohexane, isooctane and toluene were performed using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) at T=298.15 K. The liquid?Cliquid equilibrium (LLE) experiments were performed on three systems, namely: [EMIM][OAc]?Cthiophene?Ccyclohexane, [EMIM][OAc]?Cthiophene?Cisooctane and [EMIM][OAc]?Cthiophene?Ctoluene. The LLE data showed that [EMIM][OAc] has a higher selectivity at low concentration of thiophene and also showed that the hydrocarbon-rich phase is free of ionic liquid. This implies that there will be no cross contamination and the ionic liquid will be a non-pollutant in fuel after extraction. Further, the amount of hydrocarbon in the ionic-liquid-rich phase is very small. This implies that ionic liquid can be regenerated with negligible loss of fuel. LLE data was then correlated using the NRTL and UNIQUAC models. These showed root mean square deviation (RMSD) values of 0.82?% and 1.46?% for the isooctane system, 1.37?% and 1.57?% for the cyclohexane system and 1.39?% and 1.53?% for the toluene system.     

Stereoselective synthesis of C12–C21 common fragment of thermolides 1–5

A highly stereoselective synthesis of C12–C21 common fragment of thermolides 1–5 has been described. The salient features of the synthesis are the utilization of desymmetrization protocol, Barton-McCombie reaction, Brown’s asymmetric allylation and Wacker oxidation.     

Thermal Synthesis of the Zn1–xCOxO Pigments

In our laboratory, the synthesis of new inorganic pigments is followed by thermal analysis using a derivatograph apparatus. First information about the temperature region of the formation of the pigments investigated is provided by thermal analysis. The attention was directed to the preparation of the pigments based on zinc oxide in new green hues which can be used as medium colour pigments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase diagram of the selenium–sulfur system in the pressure range 1 × 10<Superscript>–5</Superscript>–1 × 10<Superscript>–1</Superscript> MPa

The partial pressures of the components in the saturated vapor of the Se–S system were determined and presented as the temperature–concentration dependences. Based on these data, the boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum (1350, 100, and 10 Pa) were calculated. A complete phase diagram was constructed, which included the vapor–liquid equilibrium fields at atmospheric and low pressures, whose boundaries allowed us to determine the behavior of sulfur and selenium during distillation separation.     

Structural Stability Among Hybrid Antimicrobial Peptide Cecropin A(1–8)–Magainin 2(1–12) and Its Analogues: A Computational Approach

Cecropin A–Magainin 2 (CA–MA) hybrid antimicrobial peptide (AMP), a combination of two naturally occurring AMPs, cecropin A and magainin 2 is preferred widely in biotechnological, nano and pharmaceutical applications. It exhibits a strong antibacterial activity with a characteristic reduced cytotoxic effect towards mammalian cells. In this study, three AMP structures native CA–MA hybrid and its tryptophan substitutes CA–MA L2 and CA–MA A2 was computationally studied to analyze their structural stability and functionality. Computational analysis like, intra-molecular interactions (25), relative stability (3.22) and instability index (?14.28) showed an increase in structural stability of native CA–MA hybrid. Additionally, the generated peptide ensembles showed a RMSD (3.98 Å), RMSF (0.202 Å), radius of gyration (11.98 Å), ovality (3.33) and hydrophobicity (69.7%) supporting native CA–MA along with hydrogen bond strength (?4.212 kcal/mol) and distribution comparatively. The distribution of secondary structure in native CA–MA hybrid showed the sequential maintenance of stable helical content along with helical stability (52.25%) and computed free energy (?1.74 kcal/mol) in membrane mimicking environment proving its functional activity comparatively. This study aids in designing stable AMP biodrugs with low cytotoxicity in future, the result can be potentially extended to other AMPs to assist in their exploitation as peptide and nano drugs.     

The influence of the temperature on the liquid–liquid equilibrium of the ternary system 1-pentanol–ethanol–water

Liquid–liquid equilibrium data for the ternary system 1-pentanol–ethanol–water have been determined experimentally at 25, 50, 85 and 95°C. These results have been correlated simultaneously by the uniquac method obtaining two sets of interaction parameters: one of them independent of the temperature and the other with a linear dependence. Both sets of parameters fit the experimental results well.     

High Performance Liquid Chromatographic Separation of Bryostatins 1–12

Abstract

A reversed-phase high performance liquid chromatographic (RP-8; acetonitrile-water gradient) separation procedure was developed for detecting bryostatins 1–12, using a photodiode array detector system. While bryostatins 6 and 9 were found to co-elute they were easily separated using a silica gel column with 9:1 n-hexane-n-propanol as eluent.     

The Alkylidenphthalan–1-Alkylisobenzofuran Equilibrium: A Computational Study

Semiempirical (AM1, PM3) and density functional theoretical studies (B3LYP/6-31G*) are reported for the tautomerism of 2-methylidene-2,5-dihydrofurans (3a–e) and the corresponding 2-methylfurans (4a–e) and of benzannulated derivatives (5a–e, 6a–e, 7–14).