Kinetic and thermodynamic studies on [Omim]Cl/ZnCl2 catalyzed synthesis of polyoxymethylene dimethyl ethers

Polyoxymethylene dimethyl ethers (OMEs) emerging as green additives for soot emission suppression receive significant attention due to their similar physical properties to diesel. Herein, the transformative pathways of dimethoxymethane (DMM) and trioxane reactions for OMEs production catalyzed by [Omim]Cl/ZnCl₂ having different ZnCl₂ content were demonstrated in combination with the clarification of active species, kinetic and thermodynamic properties, and chemical nature for trioxane decomposition and subsequential formaldehyde insertion steps. The role of [Omim]Cl, which could transform to [Omim]ZnCl₃ or [Omim]Zn₂Cl₅ under different ZnCl₂ content, laid in the formation of active zinc species and promotion of their homogeneity with reactants. The DMM chain growth, which followed the same mechanism and kinetic law, showed kinetic and thermodynamic regimes and had identical equilibrium distribution of OMEs. Only Zn₂Cl₅⁻ species were active for trioxane decomposition, which was the kinetic-relevant step, while both ZnCl₃⁻ and Zn₂Cl₅⁻ were effective for DMM chain elongation.     

Lewis acidity dependency of the electrochemical window of zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquids

Negative ion fast atom bombardment mass spectra (FAB-MS) recorded for ZnCl₂-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquids with various compositions indicate that various Lewis acidic chlorozincate clusters (ZnCl₃⁻, Zn₂Cl₅⁻ and Zn₃Cl₇⁻) are present in ZnCl₂-EMIC ionic liquids depending on the percentage of ZnCl₂ used in preparing the ionic liquids; higher ZnCl₂ percentage favors the larger clusters. Cyclic voltammetry reveals that the potential limits for a basic 1:3 ZnCl₂-EMIC melt correspond to the cathodic reduction of EMI⁺ and anodic oxidation of Cl⁻, giving an electrochemical window of approximately 3.0 V which is the same as that observed for basic AlCl₃-EMIC ionic liquids. For acidic ionic liquids that have a ZnCl₂/EMIC molar ratio higher than 0.5:1, the negative potential limit is due to the deposition of metallic zinc, and the positive potential limit is due to the oxidation of the chlorozincate complexes. All the acidic ionic liquids exhibit an electrochemical window of approximately 2 V, although the potential limits shifted in the positive direction with increasing ZnCl₂ mole ratio. Underpotential deposition of zinc was observed on Pt and Ni electrodes in the acidic ionic liquids. At proper temperatures and potentials, crystalline zinc electrodeposits were obtained from the acidic ionic liquids.     

Complexes of 1‐vinylazoles with transition metals in radical polymerization

Radical polymerization of the complexes of 1‐vinylimidazole, 1‐vinylbenzimidazole, and 1‐vinylbenztriazole with MnCl₂, NiCl₂, and ZnCl₂ was investigated. It was found that the polymerization is accompanied by spontaneous polymerization in the case of MnCl₂ and ZnCl₂, inhibition by coordination of macroradicals with Ni²⁺ ions, and a gel effect by crosslinking of the formed polymer during the complexing with Zn²⁺. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 101–108, 2000     

Influence of ZnCl2 on the structure and mechanical properties of polyacrylonitrile fibers

The structure and mechanical properties of polyacrylonitrile fibers containing small amounts of Zn²⁺ were investigated. It is possible to interpret the influence of ZnCl₂ on the fibers by diffusion. Fibers spun from spinning dope containing ZnCl₂ may have a denser and finer structure because ZnCl₂ in the spinning dope retards the coagulation rate. The tensile strength and modulus of the fibers are much improved because of the retardation of coagulation. It is probable that the complexation between Zn²⁺ and CN groups does not contribute to the improvement of the mechanical properties because the amount of ZnCl₂ added in a spinning dope is extremely small.     

Enhancement of the Water Affinity of Histidine by Zinc and Copper Ions

Histidine (His) is widely involved in the structure and function of biomolecules. Transition-metal ions, such as Zn²⁺ and Cu²⁺, widely exist in biological environments, and they are crucial to many life-sustaining physiological processes. Herein, by employing density function calculations, we theoretically show that the water affinity of His can be enhanced by the strong cation–π interaction between His and Zn²⁺ and Cu²⁺. Further, the solubility of His is experimentally demonstrated to be greatly enhanced in ZnCl₂ and CuCl₂ solutions. The existence of cation–π interaction is demonstrated by fluorescence, ultraviolet (UV) spectroscopy and nuclear magnetic resonance (NMR) experiments. These findings are of great importance for the bioavailability of aromatic drugs and provide new insight for understanding the physiological functions of transition metal ions.     

Improving the efficiency of dye-sensitized Zn2SnO4 solar cells: The role of Al ions

The dye-sensitized Zn₂SnO₄ solar cells were treated with Al³⁺ ions to enhance the power conversion efficiency for the first time. Usually, the surface treatment on photoanodes with Al³⁺ ions generated an overlayer of Al₂O₃. For Zn₂SnO₄ photoanode, another reaction pathway was found. The treatment with Al³⁺ ions led to decreasing open circuit voltage, and a 22.6% enhancement of efficiency. Mott–Schottky measurements revealed that the flat band of Zn₂SnO₄ had a positive shift owing to the introduction of Al³⁺ ions. XPS confirmed that Al³⁺ ions were introduced into the lattice of Zn₂SnO₄ and occupied the position of Sn⁴⁺, resulting in decreased conduction band edge. TEM demonstrated the size of Zn₂SnO₄ nanoparticles became larger due to the reaction of Al³⁺ with Zn₂SnO₄. Although the adsorption amounts of dyes lowered by 21%, the driving force for electron injection was greatly enhanced as a result of decreased conduction band edge, resulting in significantly enhanced cell efficiency.     

Adsorption characteristics of metal ions by CO2-fixing Chlorella sp. HA-1

Single and binary metal systems were employed to investigate the removal characteristics of Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ by Chlorella sp. HA-1 that were isolated from a CO₂ fixation process. Adsorption test of single metal systems showed that the maximum metal uptakes were 0.767 mmol Pb²⁺, 0.450 mmol Cd²⁺, 0.334 mmol Cu²⁺ and 0.389 mmol Zn²⁺ per gram of dry cell. In the binary metal systems, the metal ions on Chlorella sp. HA-1 were adsorbed selectively according to their adsorption characteristics. Pb²⁺ ions significantly inhibited the adsorption of Cu²⁺, Zn²⁺, and Cd²⁺ ions, while Cu²⁺ ions decreased remarkably the metal uptake of Cd²⁺ and Zn²⁺ ions. The relative adsorption between Cd²⁺ and Zn²⁺ ions was reduced similarly by the presence of the other metal ions.     

Influence de l'antimoine et du cuivre sur la cementation du cobalt par le zinc

Zinc sulphate solution (160g/l Zn²⁺) used for zinc electrowinning is purified for cobalt by cementation with metallic zinc powder. Industrial practice shows that considerable acceleration of this operation is achieved by the presence of trace impurities in solution. Eventually, CuSO₄ and Sb₂O₃ are deliberately added to the solution. The aim of this work is to elucidate the mechanism of action of those impurities.Zn²⁺ ions present in the solution are responsible for the slow speed of cobalt deposition (160g/l Zn²⁺; 10 mg/l Co²⁺).The cathodic part of the cementation reaction was simulated on a flat electrode through potentiostatic deposits at ?730 mV/ENH (potential at zero current of metallic zinc in the solution). The deposits were studied by anodic dissolution, radioactive tracers, X-ray diffraction and fluorescence, atomic absorption spectrophotometry, optical and electronic microscopy (transmission and scanning). The results were compared with cementation on zinc plate and zinc powder.Antimony and copper are deposited together with cobalt and form alloys with reduced cobalt activity. Total voltage available to overcome the inhibitor effect of zinc ions is thus increased and the reduction of cobalt ions accelerated. Antimony, copper and cobalt triple alloys resist particularly well to corrosion with hydrogen evolution. Copper has a higher accelerating effect on cobalt cementation than antimony, but the latter stabilizes the deposit very effectively.The electrochemical methods used and the knowledge of the mechanism of action of the impurities open new trends for industrial practice.     

KLPAAM复合高吸水树脂吸附

采用自制高岭土/木质素磺酸钠接枝丙烯酸-丙烯酰胺复合高吸水树脂(KLPAAM),测定了其在CuCl²、ZnCl²溶液中的吸附性能;通过FTIR、TG、SEM及吸附动力学方程模拟,对其吸附机理进行了探讨。KLPAAM对Cu²⁺的吸附量随Cu²⁺相似文献   

Synaptic Zinc: An Emerging Player in Parkinson’s Disease

Alterations of zinc homeostasis have long been implicated in Parkinson’s disease (PD). Zinc plays a complex role as both deficiency and excess of intracellular zinc levels have been incriminated in the pathophysiology of the disease. Besides its role in multiple cellular functions, Zn²⁺ also acts as a synaptic transmitter in the brain. In the forebrain, subset of glutamatergic neurons, namely cortical neurons projecting to the striatum, use Zn²⁺ as a messenger alongside glutamate. Overactivation of the cortico-striatal glutamatergic system is a key feature contributing to the development of PD symptoms and dopaminergic neurotoxicity. Here, we will cover recent evidence implicating synaptic Zn²⁺ in the pathophysiology of PD and discuss its potential mechanisms of actions. Emphasis will be placed on the functional interaction between Zn²⁺ and glutamatergic NMDA receptors, the most extensively studied synaptic target of Zn²⁺.     

Vulcanization of chlorobutyl rubber. II. A revised cationic mechanism of ZnO/ZnCl2 initiated crosslinking

Data relating to the ZnO/ZnCl₂‐accelerated vulcanization of chlorinated poly(isoprene‐coisobutylene) (CIIR or chloro‐butyl) is examined. ZnCl₂ and conjugated diene butyl units on the polymer chain are both precursors to crosslinking, and a revised cationic mechanism is proposed to account for crosslinking, taking into account the involvement of conjugated diene butyl in the process. It is demonstrated that Zn₂OCl₂ will catalyze dehydrohalogenation, and the formation of catalytic amounts of Zn₂OCl₂ by the reaction of ZnCl with ZnO, followed by H⁺ abstraction to give Zn₂OCl₂ and HCl, is essential in the overall crosslinking reaction sequence. The HCl is trapped by ZnO as ZnCl₂. It is proposed that the abstraction by Zn₂OCl₂ of HCl in a concerted reaction leads to Zn(OH)Cl and ZnCl₂. Zn(OH)Cl remains in the polymer as an unextractable salt, while 50% of the chlorine in the rubber is extracted as ZnCl₂ when compounds reach their equilibrium crosslink density. ZnCl₂ initiates crosslinking by the abstraction of chlorine from the chain, but a crosslink will only result when a carbocation on a dechlorinated isoprenoid unit is close to a conjugated diene butyl on an adjacent chain; if not, dehydrohalogenation will result in the formation of a further conjugated diene butyl unit at that point in the chain. The maximum crosslink density achieved is only 1/4 that theoretically possible, as crosslinking restricts chain movement and limits the number of chance meetings between carbocations on the polymer and conjugated diene butyl units. Zinc stearate promotes dehydrohalogenation, ZnCl₂ being the only chloro‐zinc salt formed. Reversion occurs in compounds where there is insufficient ZnO to trap all of the chlorine present in the rubber. HCl per se does not attack the polymer, but promotes reversion only in the presence of carbocations on the chain, i.e., during the crosslinking process. Trapping of HCl by ZnO prevents reversion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2302–2310, 2000     

Zn2+-Dependent DNAzymes: From Solution Chemistry to Analytical,Materials and Therapeutic Applications

Since 1994, deoxyribozymes or DNAzymes have been in vitro selected to catalyze various types of reactions. Metal ions play a critical role in DNAzyme catalysis, and Zn²⁺ is a very important one among them. Zn²⁺ has good biocompatibility and can be used for intracellular applications. Chemically, Zn²⁺ is a Lewis acid and it can bind to both the phosphate backbone and the nucleobases of DNA. Zn²⁺ undergoes hydrolysis even at neutral pH, and the partially hydrolyzed polynuclear complexes can affect the interactions with DNA. These features have made Zn²⁺ a unique cofactor for DNAzyme reactions. This review summarizes Zn²⁺-dependent DNAzymes with an emphasis on RNA-/DNA-cleaving reactions. A key feature is the sharp Zn²⁺ concentration and pH-dependent activity for many of the DNAzymes. The applications of these DNAzymes as biosensors for Zn²⁺, as therapeutic agents to cleave intracellular RNA, and as chemical biology tools to manipulate DNA are discussed. Future studies can focus on the selection of new DNAzymes with improved performance and detailed biochemical characterizations to understand the role of Zn²⁺, which can facilitate practical applications of Zn²⁺-dependent DNAzymes.     

Effect of magnesium carbonate on the uptake of aqueous zinc and lead ions by natural kaolinite and clinoptilolite

Adsorption behavior of Zn²⁺ and Pb²⁺ ions on kaolinite and clinoptilolite, originating from natural resources, was studied as a function of contact time and concentration. Zn²⁺ and Pb²⁺ ions are quickly adsorbed on both minerals and the uptake of the latter is more favored. The uptake of both ions was then examined on kaolinite–MgCO₃ and clinoptilolite–MgCO₃ mixtures over a metal ions range from 1 to 10 000 mg/L. The sorption behavior of Zn²⁺ and Pb²⁺ on pure MgCO₃ was also studied. MgCO₃ is much more effective in the retention of Zn²⁺ and Pb²⁺ ions, in particular at higher concentrations. The large increase in the retarded amounts of both ions was associated with formation of the hydroxy-carbonate phases; namely hydrozincite for Zn²⁺, and cerussite and hydrocerussite in the case of Pb²⁺.     

The spatial distribution of Zn during galvanic corrosion of a Zn/steel couple

The spatial distribution of Zn²⁺ during galvanic corrosion of a model Zn/steel couple in 0.01 M NaCl was investigated using a scanning zinc disk electrode. The couple had a coplanar arrangement of a steel substrate with an electroplated zinc layer at the center. During galvanic corrosion, the marked changes in the Zn²⁺ concentration were confined to a thin solution layer ca. 1.0 mm thick above the couple surface. In this thin solution layer above the zinc layer, a higher concentration region of Zn²⁺ in the range of 5-18 mM extended around the zinc layer in the solution during galvanic corrosion. Conversely, above the steel surface distant from the zinc layer, the surface concentration of Zn²⁺ was almost zero during galvanic corrosion. On this surface, the precipitation of zinc corrosion products due to the hydrolysis reaction of Zn²⁺ was observed. The distribution of the Zn²⁺ concentration supported that Zn²⁺ acted as a buffer that suppressed the increased pH due to the cathodic reaction on the steel surface near the zinc layer and almost no corrosion products formed there. The spatial distribution of Zn²⁺ is discussed in relation to the distributions of potential and pH and the surface morphology of the galvanic couple.     

Optimization of Opto-Electrical and Photocatalytic Properties of SnO<Subscript>2</Subscript> Thin Films Using Zn<Superscript>2+</Superscript> and W<Superscript>6+</Superscript> Dopant Ions

Abstract  

A series of Zn²⁺ and W⁶⁺ doped tin oxide (SnO₂) thin films with various dopant concentrations were prepared by spray pyrolysis deposition, and were characterized by X-ray diffraction, atomic force microscopy, contact angle, absorbance, current density–voltage (J–V) and photocurrent measurements. The results showed that W⁶⁺ doping can prevent the growth of nanosized SnO₂ crystallites. When Zn²⁺ ions were used, the crystallite sizes were proved to be similar with the undoped sample due to the similar ionic radius between Zn²⁺ and Sn⁴⁺. Regardless of the dopant ions’ type or concentration, the surface energy has a predominant dispersive component. By using Zn²⁺ dopant ions it is possible to decrease the band gap value (3.35 eV) and to increase the electrical conductivity. Photocatalytic experiments with methylene blue demonstrated that with zinc doped SnO₂ films photodegradation efficiencies close to 30% can be reached.     

Ion migration law in flotation pulp and its influence on the separation of smithsonite and quartz

This study investigated the migration law of ion release and adsorption in the flotation pulp of oxide zinc ore, and found that numerous different ions existed in the pulp. The total concentrations and major sources of various ions (Pb²⁺, Zn²⁺, Fe³⁺, Ca²⁺, Mg²⁺, SO₄^2-, etc.), released from the minerals after grinding, were determined. The zeta potential tests indicated that a mixed-ion solution strongly influences the surface charge of the minerals. The flotation tests show that the migration law of ions is detrimental to the separation and concentration of minerals.     

Interplay between Zn2+ Homeostasis and Mitochondrial Functions in Cardiovascular Diseases and Heart Ageing

Zinc plays an important role in cardiomyocytes, where it exists in bound and histochemically reactive labile Zn²⁺ forms. Although Zn²⁺ concentration is under tight control through several Zn²⁺-transporters, its concentration and intracellular distribution may vary during normal cardiac function and pathological conditions, when the protein levels and efficacy of Zn²⁺ transporters can lead to zinc re-distribution among organelles in cardiomyocytes. Such dysregulation of cellular Zn²⁺ homeostasis leads to mitochondrial and ER stresses, and interrupts normal ER/mitochondria cross-talk and mitophagy, which subsequently, result in increased ROS production and dysregulated metabolic function. Besides cardiac structural and functional defects, insufficient Zn²⁺ supply was associated with heart development abnormalities, induction and progression of cardiovascular diseases, resulting in accelerated cardiac ageing. In the present review, we summarize the recently identified connections between cellular and mitochondrial Zn²⁺ homeostasis, ER stress and mitophagy in heart development, excitation–contraction coupling, heart failure and ischemia/reperfusion injury. Additionally, we discuss the role of Zn²⁺ in accelerated heart ageing and ageing-associated rise of mitochondrial ROS and cardiomyocyte dysfunction.     

A new Zn2+ chemosensor based on functionalized 8-hydroxylquinoline

A new fluorescent Zn²⁺ chemosensor (3) based on functionalized 8-hydroxylquinoline has been synthesized and characterized. Compound 3 shows weak fluorescence in CH₃CN–HEPES buffer solution (50 mM, pH 7.2 v/v = 1:9), but the fluorescence is significantly enhanced upon binding to Zn²⁺ through a zinc(II)-catalyzed ester hydrolysis reaction to form a highly emissive zinc(II) complex. This suggests that 3 can be served as a typical “switch–on” chemosensor with high selectivity for Zn²⁺ over other metal ions.     

Effects of electrolytes upon potential-pH relation of synthetic beta manganese dioxide

The pH-response of electrode potential of a synthetic beta manganese dioxide was obtained as ?0.060 V.pH^?1 in concentrated ZnCl₂ solutions. The pH-response of ?0.060 V.pH^?1 was also obtained in (C₂H₅)₄NClO₄ solutions in the pH range 4–7 where the pH-response in 1 M NH₄Cl was ?0.100 V.pH^?1. Such pH-response seemed to be resulted from inhibiting completely disproportionation reaction of trivalent manganese being present in the MnO₂ sample. Accordingly, Mn²⁺ ions which would cause a high responsibility of potential on pH were not formed. The effect of ZnCl₂ seemed to be based on ion-exchange adsorption of Zn²⁺ ion onto the oxide surface to inhibit the disproportionation reaction. On the other hand, the effect of (C₂H₅)₄NClO₄ was based on both univalency and large radius of cation and anion which were not adsorptive on MnO₂ surface and not a proton donor for the disproportionation reaction.The pH-response in the presence of Mn²⁺ was close to the theoretical value of ?0.118 V.pH^?1 at 25°C as expected. Effects of ZnCl₂ upon such pH-response were also examined.