Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformati...Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.展开更多
To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in ...To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in water solutions have been carried out. The pH-rate profile (log kobs = f(pH)), shows that the hydrolysis reaction of the LAS, is conducted by a catalysis acid-base mechanism, with multiple reaction pathways. The rate constants, kH, kOH and k0 to the reaction pathways catalyzed by H3O+, HO– ions and to the spontaneous reaction, for the hydrolysis reaction of the reagent LAS, were determined. The results show that the studied compound LAS is unstable in basic medium and the hydrolysis reaction catalyzed by HO– ions is predominant.For a known acidity (pH ≈ 10), studies conducted for different temperatures of the medium, clearly indicate, that the experimental rate constant kobs,depends on the temperature according to the Arrhenius equation. The activation parameters: activation energy (Ea), enthalpy (ΔH≠) and entropy (ΔS≠), for the transition state were determined, The very negative value obtained for the activation parameter ΔS*, first indicates that in the transition state there is gain in order, then this late state, resembles the products and that probably for the mechanism of the LAS hydrolysis reaction catalyzed by HO– ions, the rate-determining step is a bimolecular reaction. Finally from all these results, the mechanism for the reaction pathway catalyzed by HO– ions has been elucidated.展开更多
The physical properties of water, particularly the nature of interfacial water and pH shifts associated with dynamics of the hydronium ion near any surface, may be a primary source of the complex electromagnetic patte...The physical properties of water, particularly the nature of interfacial water and pH shifts associated with dynamics of the hydronium ion near any surface, may be a primary source of the complex electromagnetic patterns frequently correlated with consciousness. Effectively all of the major correlates of consciousness, including the 40 Hz and 8 Hz coupling between the cerebral cortices and hippocampal formation, can be accommodated by the properties of water within a specific-shaped volume exposed to a magnetic field. In the present study, quantitative electroencephalographic activity was measured from an experimental simulation of the human head constructed using conductive dough whose pH could be changed systematically. Spectral analyses of electrical potentials generated over the regions equivalent to the left and right temporal lobes in humans exhibited patterns characteristic of Schumann Resonance. This fundamental and its harmonics are generated within the earth-ionospheric cavity with intensities similar to the volumetric intracerebral magnetic (~2 pT) and electric field (~6 × 10-1 V·m-1) strengths. The power densities for specific pH values were moderately correlated with those obtained from normal human brains for the fundamental (first) and second harmonic for the level simulating the cerebral cortices. Calculations indicated that the effective pH would be similar to that encountered within a single layer of protons near the plasma membrane surface. These results reiterate recent measurements in a large population of human brains showing the superimposition of Schumann power densities in QEEG data and indicate that intrinsic features of proton densities within cerebral water may be a fundamental basis to consciousness that can be simulated experimentally.展开更多
Six new solvated proton salts of highly halogenated carborane anions, [H(solvent),] [carborane] (carborane = 1-R-CB11-Y5X6-(R=H, Me; X, Y=CI, Br, I), 1-H-CB9Br9?) were prepared from the salt metathesis reaction of Ag(...Six new solvated proton salts of highly halogenated carborane anions, [H(solvent),] [carborane] (carborane = 1-R-CB11-Y5X6-(R=H, Me; X, Y=CI, Br, I), 1-H-CB9Br9?) were prepared from the salt metathesis reaction of Ag(carborane) and HO in high yields. Single-crystal X-ray analyses show that they are all discrete molecules in the solid-state. The number of the solvated molecules surrounding H+ ion can not be determined with the knowledge of the size and substituents of the carborane anions. These salts provide convenient weighable sources of Br?nsted acid reagents having a wide range of acidities and good thermal stabilities. TGA results indicate that the solvated molecules (water or organic molecules) in the cations [H(solvent)n]+ can be removed under high temperature and high vacuum conditions to give superacidic materials H(carborane) which can protonate olefin.展开更多
文摘Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.
文摘To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in water solutions have been carried out. The pH-rate profile (log kobs = f(pH)), shows that the hydrolysis reaction of the LAS, is conducted by a catalysis acid-base mechanism, with multiple reaction pathways. The rate constants, kH, kOH and k0 to the reaction pathways catalyzed by H3O+, HO– ions and to the spontaneous reaction, for the hydrolysis reaction of the reagent LAS, were determined. The results show that the studied compound LAS is unstable in basic medium and the hydrolysis reaction catalyzed by HO– ions is predominant.For a known acidity (pH ≈ 10), studies conducted for different temperatures of the medium, clearly indicate, that the experimental rate constant kobs,depends on the temperature according to the Arrhenius equation. The activation parameters: activation energy (Ea), enthalpy (ΔH≠) and entropy (ΔS≠), for the transition state were determined, The very negative value obtained for the activation parameter ΔS*, first indicates that in the transition state there is gain in order, then this late state, resembles the products and that probably for the mechanism of the LAS hydrolysis reaction catalyzed by HO– ions, the rate-determining step is a bimolecular reaction. Finally from all these results, the mechanism for the reaction pathway catalyzed by HO– ions has been elucidated.
文摘The physical properties of water, particularly the nature of interfacial water and pH shifts associated with dynamics of the hydronium ion near any surface, may be a primary source of the complex electromagnetic patterns frequently correlated with consciousness. Effectively all of the major correlates of consciousness, including the 40 Hz and 8 Hz coupling between the cerebral cortices and hippocampal formation, can be accommodated by the properties of water within a specific-shaped volume exposed to a magnetic field. In the present study, quantitative electroencephalographic activity was measured from an experimental simulation of the human head constructed using conductive dough whose pH could be changed systematically. Spectral analyses of electrical potentials generated over the regions equivalent to the left and right temporal lobes in humans exhibited patterns characteristic of Schumann Resonance. This fundamental and its harmonics are generated within the earth-ionospheric cavity with intensities similar to the volumetric intracerebral magnetic (~2 pT) and electric field (~6 × 10-1 V·m-1) strengths. The power densities for specific pH values were moderately correlated with those obtained from normal human brains for the fundamental (first) and second harmonic for the level simulating the cerebral cortices. Calculations indicated that the effective pH would be similar to that encountered within a single layer of protons near the plasma membrane surface. These results reiterate recent measurements in a large population of human brains showing the superimposition of Schumann power densities in QEEG data and indicate that intrinsic features of proton densities within cerebral water may be a fundamental basis to consciousness that can be simulated experimentally.
基金thefoundationfromtheResearchGrantsCounciloftheHongKongSpecialAdministrationRegion (No .CUHK42 6 7/ 0 0P)
文摘Six new solvated proton salts of highly halogenated carborane anions, [H(solvent),] [carborane] (carborane = 1-R-CB11-Y5X6-(R=H, Me; X, Y=CI, Br, I), 1-H-CB9Br9?) were prepared from the salt metathesis reaction of Ag(carborane) and HO in high yields. Single-crystal X-ray analyses show that they are all discrete molecules in the solid-state. The number of the solvated molecules surrounding H+ ion can not be determined with the knowledge of the size and substituents of the carborane anions. These salts provide convenient weighable sources of Br?nsted acid reagents having a wide range of acidities and good thermal stabilities. TGA results indicate that the solvated molecules (water or organic molecules) in the cations [H(solvent)n]+ can be removed under high temperature and high vacuum conditions to give superacidic materials H(carborane) which can protonate olefin.
