Good linear relationship between logarithms of Eigen’s water exchange constants for several divalent metal ions and activation energies of corresponding metal-catalyzed alkoxysilane hydrolysis in ethylene-propylene copolymer system

Catalytic efficiencies of seven divalent metal acetylacetonate complexes [M(acac)₂; M = Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II)] with respect to the water-crosslinking kinetics of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-VTMS) were investigated to examine the effects of progressive changes in metal ion using ATR-FTIR spectroscopy. The hydrolysis activation energies of EPR-g-VTMS follows the order: No catalyst ≈ Ni(acac)₂ > Co(acac)₂ > Fe(acac)₂ ≈ Zn(acac)₂ > Cd(acac)₂ ≈ Cu(acac)₂ > Pb(acac)₂. Interestingly, the kinetics results revealed that the plots of hydrolysis activation energies of EPR-g-VTMS containing M(acac)₂ complexes and Eigen’s water exchange constants for corresponding metal ions showed a excellent linear relationship, suggesting that the reaction pathway for the silane water-crosslinking with hydrous M(acac)₂ complex in EPR-g-VTMS system may be similar to that for water exchange of the metal ion in an aqueous system. Based on the knowledge of traditional kinetics studies by Eigen and Wilkins and hybrid sol-gel chemistry, the plausible catalytic mechanism for M(acac)₂ complexes in EPR-g-VTMS system was proposed.     

Influence of ionic composition in aqueous solution on wettability of rock surface-experiment and economics evaluation

In this study, the influence of different ionic composition in aqueous solution on the minerals surface wettability was studied. The differences effect of monovalent ion and divalent ions onto the wettability alteration were studied. The anions were Cl^- and SO₄^2-. The SO₄^2- could make the minerals surface more hydrophilic. Besides, the influence of NaCl, MgCl₂, CaCl₂, Na₂SO₄, K₂SO₄ and MgSO₄ on the mineral wettability alteration were studied. The results indicated that divalent ions showed significant impact on the minerals wettability alteration, compared with monovalent ion. The reasons were due to the fact that divalent ions showed higher ions adsorption than monovalent ion, and divalent ions have higher effect on compressing the electric double layer. The static contact angle and dynamic contact angle were measured. Different heavy oils were studied, including heavy oil with 100 ppm, heavy oil, heavy oil without resins, heavy oil without asphaltenes. The results showed that the asphaltenes would make it difficult for the heavy oils to liberate from minerals, thus decreasing the oil drops contact angle. Then the resins would decrease the heavy oil contact angles. CaCl₂/MgCl₂ and K₂SO₄ have synergistic effect on the change of the minerals surface wettability. Atomic force microscope (AFM) measurement indicated that the ions would effectively decrease the interaction force on the surface of heavy oil-minerals, which was beneficial to the heavy oil liberation. The roughness measurement indicated that the different ions would effectively increase the minerals surface wettability.     

Separation of multiply charged anions by capillary electrophoresis using alkyl phosphonium pairing agents

Two newly developed UV transparent phosphonium-based cationic reagents were evaluated as background electrolyte additives for capillary electrophoresis for the separation of multiply charged anions, including several complex anions. These cationic reagents showed moderate suppression of the electroosmotic flow, interacted with the analytes to improve their separation and often improved the peak shape. The effects of the additives and their concentration on the separation were studied, as well as the buffer type, pH, and voltage. The dicationic reagent effectively separated eight divalent anions within 17 min and the tetracationic reagent best separated nine trivalent anions, as well as a mixture of all the anions.     

Geometrical and vibrational features of phosphate, phosphorothioate and phosphorodithioate linkages interacting with hydrated cations: A DFT study

The effect of hexahydrated monovalent and divalent cations on the geometrical and vibrational features of dimethyl phosphate, dimethyl phosphorothioate and dimethyl phosphorodithioate anions (simple suitable model compounds representing the anionic moieties of natural and some modified nucleic acids) was studied. For this purpose, density functional theory (DFT) calculations were carried out at the B3LYP/6-31++G* level.Our results indicate that only K⁺ and Mg²⁺ prefer to be located in the bisector plane of the PO₂⁻ angle, whereas Li⁺ and Na⁺ deviate from this plane. Monovalent and divalent cations are slightly deviated from the OPS⁻ bisector plane and are found closer to the free oxygen atom. Moreover, the present calculations have shown that in contrast to the general belief, the g⁻g⁻ conformer (with respect to the torsion angles defined around the P–O ester bonds) is not always the energetically most favorable. For instance, the g⁻t conformer presents the lowest energy in the case of dimethyl phosphorothioate. The calculated vibrational wavenumbers obtained for dimethyl phosphate and dimethyl phosphorothioate interacting with hydrated sodium counterion, were compared with those previously recorded by Raman scattering and infrared absorption (IR) in aqueous solutions. It has been evidenced that the use of explicit solvent versus dielectric continuum, considerably improves the agreement between the theoretical and observed characteristic wavenumbers.