The effect of metal ions on the decomposition of N-nitrosamides: A reexamination

The kinetic data of R. Preussman, R. Deutsch-Wenzel, and G. Eisenbrand (Z. Krebsforsch., 84, 75(1975)) showing the effect of metal ions on the decomposition of N-nitrosamides have been reexamined, a rate equation determined, and a mechanism proposed for the decomposition     

基于银离子和镧离子掺杂效应的氧敏感材料研究

在固定敏感物质为钌的络合物的基础上,Sol—gel方法是一种广泛应用的将敏感物质固定于含硅支持体系中制作氧传感器的方法。Choi等人发现将敏感物质固定在硅胶上再用硅胶成膜的方法可以极大地提高其对气态氧及溶解氧的检测灵敏度。本文探讨了将Ag^＋和La^3＋掺杂到硅胶上再在其上固定敏感物质[Ru（bpy）3]Cl2的支持体系对氧的响应特性,并对其响应机理做了分析。     

Chemical and thermal stability of isotypic metal-organic frameworks: effect of metal ions

Chemical and thermal stabilities of isotypic metal-organic frameworks (MOFs) like Al-BDC (Al-benzenedicarboxylate called MIL-53-Al), Cr-BDC (MIL-53-Cr) and V-BDC (MIL-47-V), after purification to remove uncoordinated organic linkers, have been compared to understand the effect of the central metal ions on the stabilities of the porous MOF-type materials. Chemical stability to acids, bases, and water decreases in the order of Cr-BDC>Al-BDC>V-BDC, suggesting stability increases with increasing inertness of the central metal ions. However, thermal stability decreases in the order of Al-BDC>Cr-BDC> V-BDC, and this tendency may be explained by the strength of the metal-oxygen bond in common oxides like Al(2)O(3), Cr(2)O(3), and V(2)O(5). In order to evaluate precisely the stability of a MOF, it is necessary to remove uncoordinated organic linkers that are located in the pores of the MOF, because a filled MOF may be more stable than the same MOF after purification.     

The effect of temperature on single-column ion-chromatography of metal ions

Temperature is shown to be a valuable parameter for optimizing single-column ion-chromatographic separations of metal ions. With a perchloric acid eluent, retention times of bivalent metal ions decrease with an increase in system temperature, but with doubly protonated amines as eluents the retention times increase with an increase in temperature. Consequently, increasing the system temperature improves separations of bivalent metal ions when p-phenylenediamine dilhydrochloride is used as the eluent. Both conductivity detection and post-column reaction followed by spectrophotometric detection are suitable detection methods at above-ambient temperatures.     

Adaptation of the ORAC assay to the common laboratory equipment and subsequent application to antioxidant plastic films

The oxygen radical absorbance capacity (ORAC) method has been adapted to the instrumental laboratory and optimized for the determination of the antioxidant capacity of a novel active packaging. As the ORAC assay requires the monitorization of a reaction at controlled temperature by means of the fluorescence signal decrease over time, specific instrumental is usually necessary. In this work, a common liquid chromatographic device has been adapted to perform the ORAC assay, leaving it accessible to any laboratory. Using this adaptation, five different essential oils have been determined resulting in the following antioxidant order: clove (2.66 g Trolox per gram of essential oil), oregano (2.25), cinnamon (1.93), rosemary (1.66), and ginger (1.47). After incorporating the essential oils to the film, its antioxidant capacity has also been checked and related to the concentration of essential oil as well as the thickness of the active film. The results point out that for the same amount of essential oil incorporated measured as grams per square meter, thicker films have more antioxidant capacity than the thinner and more concentrated ones. Furthermore, the antioxidant capacity found in the films was always higher than expected taking into account the amount of essential oil incorporated. Some likely explanations have been proposed, leading to the improvement of the antioxidant film under development.     

Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

The effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR₁, CR₂, and CR₃. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1?M MgCl₂, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.     

Electrocatalytic effect of metal ions on lead and lead dioxide electrode reactions

The electrochemical reactions which take place on lead and lead dioxide electrodes of a lead-acid battery are highly influenced by the presence in the electrolytic solution of ions Cd(II), Ni(II), Zn(II) and Co(II). Current density-potential curves were obtained in this work by using a Pb/Ca alloy. It was observed that Co(II) and Ni(II) ions catalyzed both hydrogen and oxygen evolution reactions. On the other hand, Cd(II) and Zn(II) ions decreased the hydrogen evolution rate.

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, - , Cd(II), Ni(II), Zn(II) Co(II). - , Pb/Ca. , Co(II) Ni(II) , . , Cd(II) Zn(II) .

     

The effect of paramagnetic metal ions on proton-decoupled C-13 NMR intensities

The C-13 nuclear overhauser enhancement (NOE) in proton decoupled NMR spectra is reduced by paramagnetic metal ions. The similarity of the limiting intensities for various ions suggests the NOE is quantitatively eliminated, with the “three spin effect” relatively unimportant.     

Fluoride complexes of the alkali metal ions

Measurements by fluoride ion-selective electrode potentiometry on the very weak monofluoride complexes of the alkali metal ions in aqueous solution at 25°C and an ionic strength of 1M indicate their stability constants lie in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ ? Cs⁺. Data at varying ionic strengths and temperatures were used to calculate infinite dilution stability constants and enthalpies and entropies of complexation for LiF and NaF.     

Fragmentation of electrospray-produced oligodeoxynucleotide ions adducted to metal ions

In this article, we describe the unique fragmentations of oligodeoxynucleotides (ODNs) whose phosphate groups are completely depleted of protons and replaced with metal ions. The production of the ubiquitous [a(n) - base] ions still occurs, but no longer by transfer of an acidic phosphate proton to an adjoining 3' base. Nor is the extent of the reaction determined by the proton affinity of that base. Rather, the reaction now occurs via a cleavage 3' to both pyrimidines and purines; cleavage 3' to pyrimidine is more favorable than that 3' to purine. We also demonstrate that an ODN is more stable in the gas phase when its phosphate groups are bound to metal ions than when its phosphate groups are attached to hydrogens. This study also provides further evidence for the ODN fragmentation mechanism that involves H transfer to a nucleobase. To establish the structural utility of this new fragmentation, we applied it to distinguishing small ODNs containing a photomodified cis,syn-cyclobutane pyrimidine dimer from the parent ODNs, a system that cannot be distinguished by collisional activation of precursor species that do not contain metal ions.     

Torands: Planar polyazamacrocyclic ligands for metal ions

A series of macrocyclic ligands related to hexaaza[18]-annulene form stable complexes with alkali metal and alkaline earth ions. A planar, substituent-solubilized torand, consisting of multiply fused pyridine rings, has been synthesized and has been found to sequester calcium from a dilute source.     

金属离子对4-氨基安替比林与牛血清白蛋白相互作用的影响

采用荧光法研究了金属离子Ca~(2+)、Zn~(2+)和Mg~(2+)存在下4-氨基安替比林(4-AAP)与牛血清白蛋白(BSA)的相互作用.结果表明,金属离子存在时,4-AAP对BSA的猝灭常数减小,但猝灭机制仍旧为静态猝灭,4-AAP与BSA之间的结合常数(KA)及结合位点数(n)均增大,分析认为,金属离子在二者的结合作用中起了"离子架桥"的作用.     

A fast assay of water hardness ions based on alkaline earth metal induced coacervation (HALC)

In this work, a rapid assay of water hardness is presented based on the formation of a coacervate phase made up of multilamellar vesicles and close bilayers produced upon the reaction of alkaline earth metals with a carboxylate anionic surfactant in the presence of a co-surfactant (methanol). The procedure exploits the light scattering abilities of the coacervate phase which can be logarithmically linked to total hardness as CaCO₃ equivalents via spectrophotometric detection at 350 nm. The method, abbreviated as HALC, stemming from hardness by alkaline earth metal coacervation, is straightforwardly applicable overcoming the requirement for regulation of the experimental parameters involved in the determination procedure. In total, 28 water samples with various matrix compositions and hardness contents were analyzed with satisfactory accuracy as evidenced by comparison of the results with EDTA complexometric titration. The method is free from interferences from environmentally significant metal cations and inorganic anions affording detection limits as low as 13.5 mg L⁻¹ CaCO₃ with the aid of a correction factor, which is determined by the non-linear absorbance properties of the solution mixture, and satisfactory reproducibility (RSD = 4.21-8.08%).     

On-line dialysis of some metal ions and metal complexes

The effect of ionic strength, pH and complexing ligands on the dialysis of metal ions, particularly zinc(II), through cellulose acetate membranes, was studied under flow conditions. The dialysis factor, which depends on both the mass transfer and the membrane permeability, was found to be independence of ionic strength in the interaval 0.05–0.3 M and to increase only slightly with pH 4.6 and 7.0. Some common buffer constituents had no effect, but chloride and calcium ions affected the transfer rates. The rate of transfer of the ligands histidine, NTA and EDTA was of the same order of magnitude as that of the metal ions. The transfer rate of the Ni(II)-EDTA complex was the same as that of a mixture of Ni(II) and EDTA. Generally, addition of the chelating agents decreased the metal-ion transfer rates. Partition coefficients between the membrane polymer and the buffers were evaluated and compared with the dialysis factors and there were significant differences with regard to the range of variation, effect of concentration and pH-dependence. The time scale of uptake or release of metal ions by the polymer is much longer than that of a steady-state transfer in dialysis. Partition and dialysis may not be directly related to each other.     

Calixarene complexes with metal ions

Selected complexes of metal ions are presented showing their syntheses and possible applications, an attention was paid to their usefulness in chemosensors design and in the environmental protection.     

Role of metal ions in the destruction of TATP: theoretical considerations

The safe decomposition of solid TATP (triacetone triperoxide) explosive is examined theoretically. The route to destruction starts with formation of metal complexes between a metal ion and the TATP molecule. The second step is decomposition of the molecules into stable final products. We examined the structure and stability of both metal ion (including Na(+), Cu(+), Cu(2+), Co(2+), and Zn(2+)) and proton complexes with TATP using quantum chemical calculations at the DFT-PBE0 level of theory. In addition, for each ion complex, we determined the initial steps in the pathway to decomposition together with the associated transition states. We find that the products of decomposition, in particular, acetone, are also stabilized by ion metal complexes. In agreement with experiment, we find the best candidates for metal ion induced decomposition are Cu(2+) and Zn(2+).