Solid–liquid equilibrium,thermal and physicochemical studies of organic eutectics

The solid–liquid phase equilibrium data of two binary organic systems, namely, urea (U)–3-aminophenol (AP) and 3-hydroxybenzaldehyde (HB)–β-napthaol (BN) show formation of a eutectic in each case. The enthalpies of fusion of the pure components and binary eutectics have been determined using differential scanning calorimeter (Mettler DSC-4000) system. The thermal properties of the materials such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were computed using the enthalpy of fusion values. The microstructures of eutectics were developed using unidirectional thermal gradient and interested region were photographed.     

Solid–liquid equilibrium and thermochemical studies of organic analogue of metal–nonmetal system: Succinonitrile–pentachloronitrobenzene

The phase diagram of an organic analogue of a metal–nonmetal system, involving succinonitrile–pentachloronitrobenzene, shows the formation of a eutectic and a monotectic. The two immiscible liquid phases are in equilibrium with a single liquid phase and the consolute temperature being 53.5 °C above the monotectic horizontal. The phase equilibrium study confirms the alloy composition of monotectic and eutectic at 0.150 and 0.985 mol fractions of succinonitrile, respectively. The solidification behaviour shows the validity of Hilling–Turnbull equation. The thermal properties such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy, grain boundary energy and excess thermodynamic functions for parent components, monotectic and eutectic have been studied using their enthalpy of fusion values. The effects of solid–liquid interfacial energy on morphological change of monotectic have also been discussed. The microstructure of monotectic shows the lamellar growth along with droplets, however, eutectic infers the vertical growth of lamella.     

Solid–liquid equilibrium,thermal, crystallization and microstructural studies of organic monotectic alloy

A monotectic and a eutectic organic alloy have been synthesized with the help of phase diagram study. The phase diagram of an organic analogue of a metal–nonmetal system involving succinonitrile–1,4-diiodobenzene shows two immiscible liquid phases are in equilibrium with a single liquid phase. Growth behaviour of the eutectic, the monotectic and the pure components, studied at different undercooling temperatures, suggests that the data obey the square relationship between growth velocity and undercoolings. The thermal study such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated via the enthalpy of fusion values, determined using differential scanning calorimeter (DSC) method. The effects of solid–liquid interfacial energy on morphology of monotectic have also been discussed. The microstructures of monotectic, eutectic and pure components show their peculiar characteristic features.     

Synthesis of chlorin–phorbin dimer with carborane fragment

A chlorin–phorbin dimer with the carborane fragment attached to the dimer via amide bond has been synthesized. The obtained boronated dimer is of interest for a further study as a promising agent for combined application in boron neutron capture and photodynamic therapy of oncological diseases.     

Quantum chemical studies on solvent effects,ligand–water complexes and dimer structure of 2,2ʹ-dipyridylamine

In this work, optimised structures, structural and spectroscopic properties of 2,2?-dipyridylamine (DPA) in solvent media have been investigated. Conformational structures of DPA were determined and relative population distributions of the conformations were obtained. Vibrational modes were calculated for each environment and they were compared with the experimental values. The effects of the changing solvent environments on the molecular structures were investigated and hydrogen bonded complex structures that DPA could form with water molecules were studied. As a result of this study, the effects of solvent environments on the molecular structure of DPA have been determined. Chemical reactivities of DPA which have not been studied previously have been determined. When the solid phase infrared spectrum of pure DPA was examined, it was seen that N-H stretching mode was observed at 3250 cm^?1. Since it will mean that there is bonded N-H in the structure, the dimer structure of DPA has been investigated.     

Thermal studies of chitin–chitosan derivatives

New poly(azo) amino-chitosan compounds were obtained from the azo coupling reaction of N-benzyl chitosan and diazonium salts. The thermal behavior of these compounds was studied by thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), TG coupled with a Fourier-transform infrared, and differential scanning calorimetry (DSC). TG/DTG curves of chitin–chitosan polymer showed two thermal events attributed to water loss and decomposition of the polysaccharide after cross-linking reactions. Thermal analysis of the poly(azo) amino-chitosan compounds showed that the decomposition temperatures decreased when compared to the starting chitin–chitosan and N-benzyl chitosan. DSC results showed an agreement with the TG/DTG analyses. Thermal behavior of poly(azo) amino-chitosans suggest that these compounds could be considered as potential thermal sensors.     

Ternary phase equilibrium studies of the water—ethanol—1,8-cineole system

Ternary liquid—liquid equilibrium data at 25°C were obtained for the water—ethanol—1,8-cineole system, 1,8-cineole being the main component of eucalyptus oil. This study formed one aspect of a project utilizing solar energy stored in plants as liquid fuel components. Experimental results confirmed the absence of phase separation problems in the use of this system as a liquid fuel. The tie-line data for the system were well correlated by the methods of Hand and Othmer—Tobias. The solubility of 1,8-cineole in water was determined over a range of temperatures.     

Molecular thermodynamics of salt effect in vapor–liquid equilibrium of ethanol–water systems

Scaled particle theory was used to derive a general expression for the salt effect parameter, K, of isobaric vapor–liquid equilibrium for ethanol–water-1-1 type electrolytic systems, which appears in the Furter equation. This expression was essentially a sum of two terms: 1, the hard sphere interaction term calculated by Masterton–Lee's equation, 2, the soft sphere interaction term calculated by Y. Hu's molecular thermodynamical model, in which the diameters of nacked ions were replaced by that of solvated ions, the solvation coefficients (i.e., in the radio of the latter to the former) were taken to be adjustable parameters, their magnitude implies the ionic solvation rules. A correlation equation for the local dielectrical constant around central ions with liquid concentration was obtained by mapping out experimental points. The calculated salt effect parameters of 9 ethanol–water-1–1 type electrolytic systems were in good agreement with the literature values within the wide range of liquid concentration.     

Ab initio studies of push–pull systems

Twelve push–pull ethylene derivatives, NH₂CH=CHX, NH₂C≡CCH=CHX, and ⁻OCHX=CHX (with X=BH₂, C≡N, NO₂, and CH₂ ⁺) have been studied by ab initio calculations. The rotational barrier around the central double bond was chosen as a probe for push–pull effects, as push–pull effects would remove electron density from the central double bond. The amount of reduction of double bond character will increase with the contribution of the zwitterionic resonance hybrid structure. Complete geometry optimizations and calculations of vibrational frequencies were performed for all minima and transition state structures of these 12 systems. The calculations were carried out with the B3LYP and MP2 methods using the 6-311+G(d,p) and the 6-311++G(d,p) basis sets. All the systems investigated exhibited properties consistent with push–pull effects such as elongated C=C double bonds, dipolar electronic structures, and reduced barriers to internal rotation.     

Modeling of gas–solid equilibrium of binary systems aided by Frankenstein PSO

Binary systems containing supercritical CO₂ + hydrocarbons were used for modeling gas–solid equilibrium by a combined method including a thermodynamic model and a meta-heuristic algorithm. The Peng–Robinson (PR) equation of state was used in the classical solubility equation. In addition, Wong–Sandler (WS) mixing rules were used, and the van Laar model (VL) was included in order to evaluate the excess Gibbs free energy that appears in these mixing rules. Then, a variant of particle swarm optimization (PSO), called Frankenstein PSO (FPSO) was implemented for minimizing the difference between calculated and experimental solubility values. The results showed that the FPSO algorithm is a very powerful tool for parameter estimation on the PR-WS-VL model with good performance and accuracy, and considerably low deviations. Therefore, values calculated by the combined method (PR-WS-VL + FPSO) are considered accurate enough for physical and engineering calculations, among other uses.     

Critical parameters of liquid–vapor equilibrium and its geometric interpretation

Expressions are derived for the Gibbs and free energies of a liquid–vapor system. The critical parameters of the liquid are determined, and the character of the relationship between them is found. The temperature dependence of the vaporization heat is found. The analytical expression of the empirical Tait rule is substantiated. General patterns of subcritical and critical equilibria were revealed. A geometric definition of a critical state is proposed, and the existence of two critical states is proven.     

Thermal studies of sodium tetrahydroborate–potassium tetrafluoroborate mixtures

The results of DSC studies of NaBH₄–KBF₄ mixtures are presented. It is shown by chemical analysis, XRD analysis, IR spectroscopy, and ¹¹B and ⁹F MAS NMR that the decomposition of the mixtures starts at ~563 K to yield polyhedral borohydride compounds (predominantly B₁₂H₁₂^2-) in the solid residue. This temperature is much lower than the decomposition temperature of pure NaBH₄ (749 K). The mechanism of formation of the B₁₂H₁₂^2- anion has been proposed and confirmed. According to this mechanism, boron atoms from KBF₄ are involved in the formation of this anion.     

Thermodynamic modelling of liquid-vapour equilibrium and thermophysical properties of molten Pb–Bi systems

A lead–bismuth alloy is an advanced coolant for nuclear power plants. The study of this alloy is of current importance. However, performing high-temperature experiments involves many problems. In this work, to study evaporation of a lead–bismuth alloy in the presence of intermetallic compounds in the condensed phase and dimers and trimers of metals in the vapour phase, a method of thermodynamic modelling was used. The investigations were carried out at temperatures from 400 to 3000 K with the lead content from 0.1 to 0.9 weight fractions in the lead–bismuth alloy. In the method of thermodynamic modelling a software package TERRA and a model of an ideal solution of interaction products were applied. Concentration and temperature dependencies of the content of components in the melt and in the gaseous phase over the melt were calculated. Temperatures, enthalpies, entropies of the melt–vapour transition and various thermophysical properties were defined.     

Application of LA–ICP–MS in polar ice core studies

The direct determination of element signatures in polar ice core samples from Greenland by laser ablation with subsequent inductively coupled plasma mass spectrometry analysis has been investigated. A cryogenic sample chamber enables the element determination in ice directly from the solid (frozen) state. A procedure was developed to analyse up to 38 elements (traces: Mg, Al, Fe, Zn, Cd, Pb and rare earth elements; minor constituents: Na) in ice samples from Greenland with a previously unachievable spatial resolution of 4 mm along the core axis. This resolution is helpful to detect seasonal variations of element concentration in thin annual layers of deep ice. We report operating conditions and analytical performance of the experimental set up, the improvement of signal stability by (17)OH internal standardisation and application of a desolvation unit. Calibration of the system was performed with frozen multielement standard solutions along a special preparation procedure. Detection limits for the tracers Na, Mg (sea salt), Al (mineral dust) and Zn (anthropogenic source) are 0.1-1 microg kg(-1). Best detection limits in the range of 0.001-0.01 microg kg(-1 )were reached for Co, Pb and all rare earth elements. To validate the method, frozen standard reference materials were measured. The recovery is about +/-10%. Greenland ice core samples from different ages were analysed with the new technique. The results obtained by laser ablation were compared with values from solution analysis, available published data and the particle content. Most elements have shown good correlation with the particle content in the Greenland samples; however, differences could be seen between the values obtained by laser ablation and solution bulk analysis after a tri-acid digestion. The influence of particles is discussed. The high spatially resolved 2D mapping of element concentrations shows strong inhomogeneities along the core axis most probably due to seasonal variations of element deposition.     

Analytical and statistical studies of Rodriguez–Velazquez indices

Journal of Mathematical Chemistry - In this work we perform analytical and statistical studies of the Rodríguez–Velázquez (RV) indices on graphs G. The topological RV(G) indices,...     

Spectroscopic and electrochemical studies of cocaine–opioid interactions

The drugs of abuse cocaine (C), heroin (H), and morphine (M) have been studied to enable understanding of the occurrence of cocaine–opioid interactions at a molecular level. Electrochemical, Raman, and NMR studies of the free drugs and their mixtures were used to study drug–drug interactions. The results were analyzed using data obtained from quantum-mechanical calculations. For the cocaine–morphine mixture (C–MH), formation of a binary complex was detected; this involved the 3-phenolic group and the heterocyclic oxygen of morphine and the carbonyl oxygen and the methyl protons of cocaine’s methyl ester group. NMR studies conducted simultaneously also revealed C–MH binding geometry consistent with theoretical predictions and with electrochemical and vibrational spectroscopy results. These results provide evidence for the occurrence of a cocaine–morphine interaction, both in the solid state and in solution, particularly for the hydrochloride form. A slight interaction, in solution, was also detected by NMR for the cocaine–heroin mixture. Figure "Schematic representation of the proposed model for cocaine:morphine salt interaction"