75 research outputs found

    Sequential Proton Loss Electron Transfer in Deactivation of Iron(IV) Binding Protein by Tyrosine Based Food Components

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    The iron­(IV) binding protein ferrylmyoglobin, MbFe­(IV)O, was found to be reduced by tyrosine based food components in aqueous solution through a sequential proton loss electron transfer reaction mechanism without binding to the protein as confirmed by isothermal titration calorimetry. Dopamine and epinephrine are the most efficient food components reducing ferrylmyoglobin to oxymyoglobin, MbFe­(II)­O<sub>2</sub>, and metmyoglobin, MbFe­(III), as revealed by multivariate curve resolution alternating least-squares with second order rate constants of 33.6 ± 2.3 L/mol/s (Δ<i>H</i><sup>⧧</sup> of 19 ± 5 kJ/mol, Δ<i>S</i><sup>⧧</sup> of −136 ± 18 J/mol K) and 228.9 ± 13.3 L/mol/s (Δ<i>H</i><sup>⧧</sup> of 110 ± 7 kJ/mol, Δ<i>S</i><sup>⧧</sup> of 131 ± 25 J/mol K), respectively, at pH 7.4 and 25 °C. The other tyrosine based food components were found to reduce ferrylmyoglobin to metmyoglobin with similar reduction rates at pH 7.4 and 25 °C. These reduction reactions were enhanced by protonation of ferrylmyoglobin and facilitated proton transfer at acidic conditions. Enthalpy–entropy compensation effects were observed for the activation parameters (Δ<i>H</i><sup>⧧</sup> and Δ<i>S</i><sup>⧧</sup>), indicating the common reaction mechanism. Moreover, principal component analysis combined with heat map were performed to understand the relationship between density functional theory calculated molecular descriptors and kinetic data, which was further modeled by partial least squares for quantitative structure–activity relationship analysis. In addition, a three tyrosine residue containing protein, lysozyme, was also found to be able to reduce ferrylmyoglobin with a second order rate constant of 66 ± 28 L/mol/s as determined by a competitive kinetic method

    Solubilities of Naringin Dihydrochalcone in Pure Solvents and Mixed Solvents at Different Temperatures

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    Naringin dihydrochalcone (naringin DC) is an intense sweetener and a strong antioxidant with potential applications in many food and pharmaceutical products. However, the poor solubility and stability of naringin DC in aqueous systems at room temperature severely limits its applications in these areas. The solubility of naringin dihydochalone was quantified in water, ethyl acetate, binary solvent mixtures of methanol + water and ethanol + water by a synthetic method at different temperatures. The solubility of naringin DC in a given solvent increases with the rising temperature. The experimental data were well correlated with an Apelblat equation and Universal Quasichemical model. Moreover, the physical properties and crystal habit of naringin DC were discussed through a thermogravimetric analyzer, a differential scanning colorimeter, and a scanning electron microscope

    Zinc Bioavailability from Phytate-Rich Foods and Zinc Supplements. Modeling the Effects of Food Components with Oxygen, Nitrogen, and Sulfur Donor Ligands

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    Aqueous solubility of zinc phytate (<i>K</i><sub>sp</sub> = (2.6 ± 0.2) × 10<sup>–47</sup> mol<sup>7</sup>/L<sup>7</sup>), essential for zinc bioavailability from plant foods, was found to decrease with increasing temperature corresponding to Δ<i>H</i><sub>dis</sub> of −301 ± 22 kJ/mol and Δ<i>S</i><sub>dis</sub> of −1901 ± 72 J/(mol K). Binding of zinc to phytate was found to be exothermic for the stronger binding site and endothermic for the weaker binding site. The solubility of the slightly soluble zinc citrate and insoluble zinc phytate was found to be considerably enhanced by the food components with oxygen donor, nitrogen donor, and sulfur donor ligands. The driving force for the enhanced solubility is mainly due to the complex formation between zinc and the investigated food components rather than ligand exchange and ternary complex formation as revealed by quantum mechanical calculations and isothermal titration calorimetry. Histidine and citrate are promising ligands for improving zinc absorption from phytate-rich foods

    Modified Method for Measuring the Solubility of Pharmaceutical Compounds in Organic Solvents by Visual Camera

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    A modified synthetic method with a high definition visual camera technique for measuring the solubility of solutes in solvents or mixed solvents was proposed. To verify the reliability of the experimental apparatus, the solubility of NH<sub>4</sub>Cl in water was determined at different temperatures. The relative standard errors were less than 1%, compared to the literature data. The solubilities of betulonic acid in six organic solvents from (278.15 to 313.15) K were measured and correlated with the Apelblat equation and universal quasichemical equation, respectively. The modified method was quite concise and user-friendly, and made the process of dissolution to become visualized and automatic

    Solubilities of Three Flavonoids in Different Natural Deep Eutectic Solvents at <i>T</i> = (288.15 to 328.15) K

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    The solubilities of phloretin, phlorizin, and naringin dihydrochacone (naringin DC) respectively were determined in a ternary system made of natural deep eutectic solvents (NADES) at the temperature range from 288.15 to 328.15 K with an analytical method. Compared with the solubility of phloretin in water, there was a dramatic improvement in the solubility of phloretin in the selected NADES, especially in CCiH and CSH. The density and viscosity of four kinds of NADES choline chloride + glucose + H<sub>2</sub>O, choline chloride + citric acid + H<sub>2</sub>O, citric acid + glucose + H<sub>2</sub>O, and choline chloride + sucrose + H<sub>2</sub>O were studied in this work. The solubility data were correlated with Apelblat equation and <i>λh</i> equation. The fitted results showed that the models are capable of representing the data with high accuracy

    Measurement and Correlation of Solubility of Theobromine, Theophylline, and Caffeine in Water and Organic Solvents at Various Temperatures

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    The solubility of theobromine, theophylline, and caffeine in water and five organic solvents including methanol, ethanol, 1-propanol, ethyl acetate, and acetone was determined by a high performance liquid chromatography method at <i>T</i> = (288.15 to 328.15) K and atmospheric pressure. It was found that the solubility of theobromine, theophylline, and caffeine in these solvents increased with increasing temperature. The empirical Apelblat equation and universal quasichemical model were used to correlate the experimental solubility. The results showed that both models can satisfactorily correlate the solubility data. The crystal forms of the solutes in equilibrium with the saturated solution were analyzed using scanning electron microscopy and powder X-ray diffraction

    Expression of genes associated with auxin and GA signaling in ovaries after pollination and 2,4-D/GA<sub>3</sub> treatments.

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    <p>Expression of genes associated with auxin and GA signaling in ovaries after pollination and 2,4-D/GA<sub>3</sub> treatments.</p

    Three trinuclear Ru(II) complexes containing 4,5-diazafluorene and 2,2′-bipyridine: synthesis, absorption spectrum, luminescence, and redox behavior

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    <div><p>Three heterotopic ligands L<sup>1</sup>, L<sup>2</sup>, and L<sup>3</sup> have been prepared by the reaction of 4,4′-bis(bromomethyl)-2,2′-bipyridine with 4,5-diazafluoren-9-oxime, 9-(2-hydroxy)phenylimino-4,5-diazafluorene, and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively, in DMF. The three ligands consist of two 4,5-diazafluorene units and one 2,2′-bipyridine unit. Ru(II) complexes [{Ru(bpy)<sub>2</sub>}<sub>3</sub>(μ<sub>3</sub>-L<sup>1−3</sup>)](PF<sub>6</sub>)<sub>6</sub> (bpy = 2,2′-bipyridine) were prepared by refluxing Ru(bpy)<sub>2</sub>Cl<sub>2</sub>·2H<sub>2</sub>O and the ligands in 2-methoxyethanol. The three Ru(II) complexes display metal-to-ligand charge-transfer absorption at 445–450 nm and one Ru(II)-centered oxidation at 1.32 V in CH<sub>3</sub>CN solution at room temperature. Upon excitation into the metal-to-ligand charge-transfer band, the emission intensities of [{Ru(bpy)<sub>2</sub>}<sub>3</sub>(μ<sub>3</sub>-L<sup>2</sup>)]<sup>6+</sup> and [{Ru(bpy)<sub>2</sub>}<sub>3</sub>(μ<sub>3</sub>-L<sup>3</sup>)]<sup>6+</sup> are almost equal to that of [{Ru(bpy)<sub>2</sub>}<sub>3</sub>(μ<sub>3</sub>-L<sup>1</sup>)]<sup>6+</sup> in CH<sub>3</sub>CN solution at room temperature, but weaker than that of [{Ru(bpy)<sub>2</sub>}<sub>3</sub>(μ<sub>3</sub>-L<sup>1</sup>)]<sup>6+</sup> in EtOH–MeOH (4 : 1, v/v) glassy matrix at 77 K.</p></div

    Highly Iso-Selective and Active Catalysts of Sodium and Potassium Monophenoxides Capped by a Crown Ether for the Ring-Opening Polymerization of <i>rac</i>-Lactide

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    Sodium and potassium complexes supported by a bulky monophenoxy with one xanthenyl group at the ortho-position and 18-crown-6 or 15-crown-5 as an auxiliary ligand were synthesized and characterized. These complexes are highly iso-selective and active catalysts for the controlled ring-opening polymerization of <i>rac</i>-lactide. The best isotacticity (<i>P</i><sub>m</sub>) achieved was 0.86, which is the highest iso-selectivity reported to date for an alkali-metal complex. In addition, the corresponding polymer exhibited a high <i>T</i><sub>m</sub> of 182 °C. Furthermore, the polymerization looks like an anti-Arrhenius reaction, which is slower at high temperatures than at low temperatures

    Summary of the RNA-Seq data in ovaries during fruit set.

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    <p>Summary of the RNA-Seq data in ovaries during fruit set.</p
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