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Abstract: There is an urgent need for a biorelevant antioxidant capacity assay, which is crucial to quality-assured polyphenol dietary supplements. We hypothesize that the 'position', more than the 'number' of phenolic groups, is critical to the antioxidant capacity of polyphenols. Computational Antioxidant Capacity Simulation (CAOCS) assay was implemented to test the hypothesis, while refinement of existing assay protocol was aimed at reducing the cost of analysis. The antioxidant capacities of resorcinol, catechol and hydroquinone (3 diphenol positional isomers) were determined by CAOCS assay. Photometric titration experiments and associated informatics that constitute CAOCS assay were evaluated through the use of small increments (< 1 mL) of antioxidant solution. Antioxidant capacity ranking of the positional isomers was found to be; hydroquinone > catechol > resorcinol, (60/g, 46/g and 28/g respectively). The relative bond strength of the phenolic groups, which governs the ranking, was accounted for by structural theory. Optimal 250 µL increment of antioxidant solution afforded a 75% reduction of the amount of antioxidant required in the original assay protocol, where a 1 mL increment was used. CAOCS values vary widely for the positional isomers. The unique structure-antioxidant capacity-correlation (SACC) which confirmed our hypothesis is a signature of biorelevance. Significantly, microliter increments reduced the amount of active material required and hence, the cost of analysis. The methodology is thus attractive for profiling exotic and more expensive polyphenols. CAOCS assay holds a great promise of enabling quality-by-design (QbD) of polyphenol dietary supplements. Keywords: Diphenol positional isomers, antioxidant capacity, photometric titration, model fitting, hydroquinone, biorelevant assay.Download Full Article |
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Abstract: This study aims at providing a model for the internalmixing energy of two liquids. The concerned variables are the solute molar volume V (cm3/mol.), the cohesion parameters and the Drago's parameters. The model is based on the following fundamental novelties: The fragmentation of molar cohesive energy ΔEcoh (kJ/mol) into two distinct categories. Indeed, the dispersive and polar cohesion energies are magnetic and electrical in nature, and the cohesive energy of the chemical bonds (Hydrogen Bond) is due to charge transfer and orbital overlap. The origins of these two categories of energy are different, requiring two different treatments in use. For the first time, a relationship has been established between the cohesive energy from chemical bonds ΔEh (kJ/mol) and Drago's parameters Ea, Eb, Ca, and Cb (KJ1/ 2mol-1/2). A simple equation has been proposed for the salvation energy of a gaseous solute in a liquid solvent. This equation contains a term for the perturbation energy of the solvent in the presence of the solute, namely the cavity formation energy, and different types of interaction energies between the solvent and the solute at infinite dilution. Based on calorimetric data published, the proposed model is compared with the classic model in terms of the mixing energy. The result shows a clear advantage of the new model over the old or conventional one. Clearly, this new model should provide a new method to determine the interaction parameters or interaction capacities of complex pharmaceutical molecules using a series of simple and well-chosen solvents. Keywords: Internal energy, molecular interaction, Drago’s parameters, solubility parameters, solvent, magnetic field, electric field.Download Full Article |
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Abstract: The solid–liquid phase equilibria of the system H3PO4– Ca(OH)2–H2O were studied under air pressure using a synthetic method based on conductivity measurements. Two isotherms at 15 and 45 °C were completely defined. The stable solid phases which appear in this range of temperature are hydroxyapatite (Ca10(PO4)6(OH)2), calcium hydrogen phosphate dihydrate (CaHPO4.2H2O), calcium hydrogen phosphate anhydrous (CaHPO4) and calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2.H2O). These solid phases were characterized using X ray diffraction. Keywords: Solid-liquid phase equilibria, ternary system H3PO4– Ca(OH)2–H2O, calcium phosphate, isotherm.Download Full Article |
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Abstract: Ion-pair formation constants (KMA0) for MA+ = MPic+ and MCl+ in water were determined at 298 K and ionic strength → 0 by extraction experiments of picric acid (HPic) in the presence of M(II) in the water phase into benzene (Bz) and by potentiometry with a commercial Cl--selective electrode, respectively. Here, M denotes Ca(II), Sr(II), Ba(II), Cu(II), and Cd(II). In adding Pb(II) data, a relation between KMA0 values was KMCl0<KMPic0 for a given M(II).For CdPic+, the KMA0 value (= 136mol-1 dm3) determined by the HPic extraction was somewhat larger than that (= 108) potentiometrically-determined before with a Cd2+-selective electrode, while for CaPic+ the former value (= 89) equaled the latter one (= 88) determined before with a Ca2+-selective electrode. Keywords: Ion-pair formation constants, extraction, potentiometry, divalent metal ions, picrates, chlorides.Download Full Article |
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Abstract: A sol–gel method has been proposed for obtaining the sintering mixture used in the preparing of a photosensitive Au/Ag-containing glasses of the Li2O - SiO2 system. It has been established that the use of sol–gel method for the production of the batch for synthesizing photosensitive Au/Ag-containing glasses gives more homogeneous distribution of Au/Ag metals in the bulk of the glass. Crystal-nucleation main characteristics have been defined in a large area of compounds of photo-structured compositions of a lithium–silicate system (23.4–46.0 Li2O mol % by analysis) both for spontaneous and catalyzed nucleations. The spontaneous (homogeneous) nucleation happened in the samples without any photosensitive metals and with photosensitive gold–silver additives (0.05 wt % above 100%) without irradiation; the catalyzed (heterogeneous) nucleation happened in the samples with photosensitive silver ore gold additives under x-ray CuKα irradiation. The ranges of the compositions of the glasses in which the effect of catalyzing irradiation is reversed (suppressing nucleation in accordance with the autocatalytic mechanism) under certain conditions. The spontaneous and catalyzed nucleation of crystals in the glasses of Li2O – SiO2 system caused by the addition of photosensitive impurities and X-ray irradiation was analyzed in glasses with a very wide range of compositions in Li2O – SiO2 system. Composition ranges with positive (+) and negative (-) differences in the rates of catalyzed and spontaneous steady-state nucleation were established. This finding point is favorable for obtaining photostructured (photosensitive) materials. The concentration limit was determined to be 37.98 mol % Li2O. About this value, we observe a modification of the mechanism of nucleation of crystals. The behavior of crystal nucleation in photostructured glasses under X-ray irradiation changes to the reverse: autocatalytic nucleation is suppressed rather than induced by x-ray CuKα irradiation. These peculiarities of crystallization mechanism in glasses under study give one the possibility to choose the correct composition range depending on the problems facing researchers. Keywords: Photosensitive glasses, stages of preparation of crystallized photosensitive glass, sol–gel method for producing the batch, parameters of crystal nucleation in photosensitive glass, catalyzed nucleation on photosensitive Ag and Au impurities, effect of X-rays CuKα on crystal nucleation.Download Full Article |