Predominance zone diagrams and their application to solvent extraction techniques

Predominance zone diagrams have been useful tools in solving problems in analytical chemistry. They can be used to establish the best conditions for separation of mixtures or to optimize recovery procedures for a given species. The few reports on predominance zone diagrams for the participant species in liquid-liquid extraction systems, describe their construction as diagrams of the Pourbaix type (epsilon/pH). With the generalized species and equilibria method (GSEM) it is possible to elaborate Predominance zone diagrams for extraction (PZDE) in proper spaces and with parameters strictly related to these processes such as pH and the volume ratio, r. Therefore, using the GSEM, PZDE that allow us to determine the best conditions for the extraction of a given substance have been elaborated. The stoichiometry of the species been extracted can also be determined from the experimental conditions. It has been demonstrated that with the GSEM, PZDE can be constructed for systems of one and two components. In this work, we intend to demonstrate that the algorithm is valid for the elaboration of PZDE in systems of three and four components. Examples of analytical interest are presented such as lead (II) extraction with diphenyltiocarbazone (dithizone) and that for cadmium (II) with 8-hydroxyquinolein (oxine) in chloroform. The influence of a masking agent, the etilendiaminotetraacetic acid (EDTA) over the extraction of both metals was also assessed.     

The role of hydroxy aluminium sulfate minerals in controlling Al<Superscript>3+</Superscript> concentration and speciation in acidic soils

A thermodynamic approach for the complex chemical equilibria investigation of two-phase systems containing hydroxy aluminium sulfate (HAS) minerals in soils has been developed. This approach utilizes thermodynamic relationships combined with original mass balance constraints, where the HAS mineral phases are explicitly expressed. The factors influencing the distribution and concentrations of various soluble aluminium species have been taken into account. The new type of diagrams, based on thermodynamic, graphical and computerized methods, which quantitatively describe the distribution of soluble and insoluble inorganic, and organic, monomeric and polymeric aluminium species in acidic soil solutions in a large range of pH values has been used. The thermodynamics of equilibria of different natural HAS in soils, the conditions under which solids involving common ions can coexist at equilibrium, the acid-base and mineral equilibria and complex formation have been examined. It has been proved that the presence of sulfate ion dramatically alters the HAS mineral solubility under acidic conditions. The obtained data regarding the factors influencing Al speciation, based on the constructed diagrams of heterogeneous chemical equilibria, are in good agreement with the current experimental and theoretical evidence. The proposed approach is intended to determine the dominant processes that are responsible for the Al³⁺ concentration levels and its speciation in acidic soils.

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Models of phase diagrams of one-and two-component systems with heterophase equilibria in the critical and supercritical regions of the coexistence of liquid and vapor

Formal model phase diagrams of one-and two-component systems with heterophase equilibria in the region of critical vapor-liquid states are constructed. The diagrams take into account the existence of the fluid phase.     

Model melting diagrams of ternary systems with a lower critical liquid stratification point

Model melting diagrams of ternary systems with lower critical liquid stratification points in the initial binary systems are considered. Phase equilibria are analyzed, and polythermal and isothermal sections in various interinvariant intervals are presented.     

Design of a hybrid biosensor for enhanced phosphopeptide recognition based on a phosphoprotein binding domain coupled with a fluorescent chemosensor

Protein-based fluorescent biosensors with sufficient sensing specificity are useful analytical tools for detection of biologically important substances in complicated biological systems. Here, we present the design of a hybrid biosensor, specific for a bis-phosphorylated peptide, based on a natural phosphoprotein binding domain coupled with an artificial fluorescent chemosensor. The hybrid biosensor consists of a phosphoprotein binding domain, the WW domain, into which has been introduced a fluorescent stilbazole having Zn(II)-dipicolylamine (Dpa) as a phosphate binding motif. It showed strong binding affinity and high sensing selectivity toward a specific bis-phosphorylated peptide in the presence of various phosphate species such as the monophosphorylated peptide, ATP, and others. Detailed fluorescence titration experiments clearly indicate that the binding-induced fluorescence enhancement and the sensing selectivity were achieved by the cooperative action of both binding sites of the hybrid biosensor, i.e., the WW domain and the Zn(II)-Dpa chemosensor unit. Thus, it is clear that the tethered Zn(II)-Dpa-stilbazole unit operated not only as a fluorescence signal transducer, but also as a sub-binding site in the hybrid biosensor. Taking advantage of its selective sensing property, the hybrid biosensor was successfully applied to real-time and label-free fluorescence monitoring of a protein kinase-catalyzed phosphorylation.     

Phase Equilibria and Critical Curves of Binary Ammonia–Hydrocarbon Mixtures

Liquid or dense supercritical ammonia has been suggested as an extraction fluid. It is indeed good solvent for very different classes of compounds, as can be seen from phase diagrams. Such diagrams for binary systems of ammonia and hydrocarbons are presented and discussed on the basis of their critical curves. Apparatus and methods for the measurement of phase equilibria and equation of state data of fluid mixtures at high pressure are described.     

电子活度和pH对二氧化氯制备和稳定性的影响

建立了氯体系电子活度（pε）和pH优势区域图（pε-pH）图,从酸化、氧化和还原的角度,探讨了标准状态下pε和pH对二氧化氯制备和稳定性的影响。实际生产不可能制备绝对纯净的二氧化氯。对于不同的水体,由于其pε和pH值不同,因而可能使二氧化氯表现出不同的稳定性特征。如果水溶液中二氧化氯不歧化为氯酸根,二氧化氯相对稳定,并与亚氯酸根、氯分子或氯离子稳定共存。当氯体系实现最终平衡时,二氧化氯仅在强酸介质中优势存在,随着酸度降低,二氧化氯歧化为氯酸根和氯气,水溶性和二氧化氯在常规pH条件下不稳定。     

Graphical representation of polynuclear acid-base and complex equilibria

A calculation procedure for diagrams of log C(M) = f(pL) at various values of the ratio of analytical concentrations, C(L)/C(M), in polynuclear binary systems is described. The diagrams are useful in the resolution of analytical problems of practical interest involving acid-base equilibria (such as the preparation of buffer solutions) and complex equilibria. The presence of a solid phase is also considered.     

Solution phase enantioselective recognition and discrimination by electrospray ionization--mass spectrometry: state-of-the-art, methods, and an eye towards increased throughput measurements

A review is given from the stand-point of applying methods utilizing electrospray ionization - mass spectrometry (ESI-MS) for quantitative binding (affinity and selectivity) determinations in small molecule host-guest (receptor-ligand, selector-selectand, etc.) systems. Advantages over more commonly utilized and traditional solution phase approaches, both in the context of developing new chiral selector molecules for separation and purification of enantiomers and in drug discovery applications, are presented. Although the majority of studies employing methods such as host-guest screening, competitive binding, and titrations have focused on large protein-ligand, DNA-ligand, and RNA-ligand systems, the use of ESI-MS for studying small molecule and chiral recognition systems is growing. For the latter case, greater care must be given to considering the effects of the ESI process on the ionization of the species involved in equilibria of interest. Some basic mechanistic and practical concerns for performing solution-phase-targeting quantitative measurements by ESI-MS are given in this light. Finally, an account of the application of these methods in a high throughput format is given, highlighting the potential of traditional and novel screening and titration approaches which allow scientists to screen the performance of hundreds, if not thousands, of compounds in a single day.     

Phase equilibria in polymer–solvent systems: Progress in the field of fibers

The progress in phase equilibria of polymer-solvent systems is briefly reviewed. The features of phase diagrams intended for production of fibers with high strength, deformation, and thermal properties are considered. Some attention is given to the fundamental role of S.P. Papkov in the creation and development of scientific concepts on phase equilibria in fiber-forming polymers involving solvents.     

A systematic evaluation of molecular recognition phenomena. 2. Interaction between phosphates and nucleotides with hexaazamacrocyclic ligands containing diethylic ether spacers

The host-guest interactions between ortho- (Ph), pyro- (Pp), and tripolyphosphate (Tr) anions together with ATP (At), ADP (Ad), and AMP (Am) nucleotides and the two hexaazamacrocyclic ligands 1,15-dioxa-4,8,12,18,22,26-hexaazacyclooctacosane (Pn) and 1,13-dioxa-4,7,10,16,20,24-hexaazacyclohexacosane (Op) have been investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic attraction between the host and the guest. Formation constants for all the species obtained are reported. The selectivity of the Pn and Op ligands with regard to the different phosphate and nucleotide substrates is discussed and illustrated with total species distribution diagrams. A comparison is also carried out, with the results obtained in this work and those obtained previously with three other closely related hexaazamacrocyclic ligands. This comparison manifests the importance of ligand basicity, rigidity, and pi-stacking capability in order to understand their binding and selectivity.     

Besondere Selektivitätseffekte in der Flüssigkeits-Chromatographie

Proceeding from expressions for the resolution of two components in a chromatogram the role of the selectivity of the phase system in liquid chromatography is discussed. The special selectivity effects are pointed out, which result from the use of phase systems implying chemical equilibria.     

Application of the PC-SAFT equation of state to modeling of solid-liquid equilibria in systems with organic components forming chemical compounds

Equilibrium diagrams of liquid and solid phases were calculated by the equation of state, based on the perturbed-chain statistical associating fluid theory (PC-SAFT) for binary and ternary systems constituted by associating substances (water, alcohols, amines, phenol, bisphenol A, acetamide). Phase diagrams were considered for systems in which congruently and incongruently melting intermolecular compounds are formed and for a system with limited mutual solubility of the components in the liquid state. The results of prognostication of phase equilibria were illustrated by the example of a ternary system constituted by bisphenol A, phenol, and water, in which an adduct of bisphenol A and phenol is formed.     

Speciation in the aqueous H+/H2VO4-/H2O2/picolinate system relevant to diabetes research

A detailed study of the quaternary aqueous H+/H2VO4-/H2O2/picolinate (Pi-) system has been performed at 25 degrees C in 0.150 M Na(Cl) medium using quantitative 51 V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4-/Pi- system, six complexes have been found in the pH region 1-10. In the quaternary H+/H2VO4-/H2O2/Pi- system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 1)C NMR data and available crystal structures.     

Solid-solute phase equilibria in aqueous solution. IV. Calculation of Phase Diagrams

The thermodynamic principles of conventional (T-x, P-T) phase diagrams and solubility (log ΣK-x) diagrams depicting solid-solute phase equilibria in aqueous solution are derived from a unifying point of view. It is shown that thermodynamic quantities necessary for the construction of conventional phase diagrams can be obtained from solubility measurements. The unary system calcite-aragonite and the binary system aragonite-strontianite, where solubility data are available over the whole compositional range, have been selected as examples. In the latter case, the constraint of constant composition of the solid phase leading to a metastable equilibrium with the respective solute species is an essential point in the thermodynamic derivation and was observed experimentally as well.     

Structural Features of Solid Phases and Topology of Phase Diagrams

The paper considers model phase diagrams of binary and ternary systems involving transformations (transitions) of phase equilibria. The relationship between the type of structural solidstate transformation and the type of phase diagram is shown. Topological series of phase diagrams of systems with continuous and limited types of solid solutions are considered, including phase diagrams with polymorphic transitions between intermediate solid phases of variable composition.     

Chemical equilibrium in a heterogeneous fluid phase system: thermodynamic regularities and topology of phase diagrams

Singularities of the systems with simultaneous phase and chemical equilibria were examined. The thermodynamic regularities were revealed and topology of phase diagrams was presented for multicomponent heterogeneous systems including two or several equilibrium liquid phases (solution layering). The thermodynamic conditions for displacement of phase and chemical equilibrium are considered.     

Development of the PhDi software package for the calculation of phase diagrams of binary systems using parameters of state equations and thermodynamic models for solutions

The PhDi software package developed earlier for calculations of phase equilibria by the convex hull method was modified by incorporating two additional modules: “State equations” and “Local composition thermodynamic models.” The possibility of the application of the convex hull method with cubic state equations to construct phase diagrams of binary systems was shown. A new database containing parameters of the corresponding thermodynamic models has been added to the initial version of the PhDi package. The efficiency of the performance of the package in solving the problem of choosing an appropriate state equation to predict conditions of phase equilibria in binary systems was demonstrated.