Influence of metal ions on antioxidant behaviour in polypropylene

The effect of Cr(III), Fe(III) and Cu(II) ions, at trace levels, on the effectiveness of four commercial antioxidant systems, viz. Topanol, Santowhite, Hostanox 03 and Irganox 1425, in polypropylene (PP) films is examined using infra-red and second-order derivative uv spectroscopy. The results show that at these levels the metal ions have a minor effect on the unstabilised polymer. However, the ions can have a beneficial or adverse effect on antioxidant activity, particularly under oven ageing conditions. The observed effect depends on the metal/antioxidant system, and is attributed to an indirect interaction between the components which can delay or accelerate antioxidant decomposition in the polymer. An exception to this behaviour is the metal complex Irganox 1425, which interacts strongly with copper ions in the polymer matrix. The antioxidant is partially transformed by copper ions during the compression moulding stage. The beneficial effect present in some cases is in direct contrast with what has generally been observed in studies using unstabilised polymers.     

Influence of transition metal ions on the textural properties of alumina and aluminasilicates

Accelerated phase transformations and chemical reactions of metastable aluminas and kaolinite, doped with Cu^{2 +}, Mn^{3 +}/Mn^{2 +} and Fe^{3 +}/Fe^{2 +} ions, are accompanied with accelerated decrease of surface area and pore volume values. The phenomena in metal ion doped samples are explained by a catalytic mechanism, in terms of the Jahn-Teller effect. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of metal ions on the alkali-swelling behavior of carboxylated acrylic polymer latexes

The alkalization of carboxylated acrylic polymer latexes by sodium hydroxide gives rise to swelling of the particles. For a poly(n-butyl acrylate) latex copolymerized with 15 wt % methacrylic acid (MAA) and 7 wt % acrylonitrile the particle volume increases by a factor of 30. The alkali-swelling does not depend on the type of monovalent cation used in the base (LiOH, NaOH, KOH, NH₄OH). In contrast, when bivalent cation bases such as Ca(OH)₂ are employed no latex swelling is observed during neutralization because of ionic crosslinking of the copolymer chains. Crosslinking also takes place when the bivalent cations (Ca²⁺, Zn²⁺, Mg²⁺) are added as chlorides to dispersions with latexes previously swollen by sodium hydroxide. In these experiments the original size of the latexes is reached again at a molar ratio MAA: bivalent metal ion of 2:1, i.e. at charge compensation of the carboxyl groups. The shrinking behavior is almost independent of the type of bivalent metal ion used. On the other hand, it is more pronounced when trivalent cations such as Fe³⁺ are added. In general, the experiments demonstrate that the alkali swelling of acrylic latexes is dominated by electrostatic forces. Received: 18 August 1998 Accepted in revised form: 26 October 1998     

Influence of d orbital occupation on the binding of metal ions to adenine

Threshold collision-induced dissociation of M(+)(adenine) with xenon is studied using guided ion beam mass spectrometry. M(+) includes all 10 first-row transition metal ions: Sc(+), Ti(+), V(+), Cr(+), Mn(+), Fe(+), Co(+), Ni(+), Cu(+), and Zn(+). For the systems involving the late metal ions, Cr(+) through Cu(+), the primary product corresponds to endothermic loss of the intact adenine molecule, whereas for Zn(+), this process occurs but to form Zn + adenine(+). For the complexes to the early metal ions, Sc(+), Ti(+), and V(+), intact ligand loss competes with endothermic elimination of purine and of HCN to form MNH(+) and M(+)(C(4)H(4)N(4)), respectively, as the primary ionic products. For Sc(+), loss of ammonia is also a prominent process at low energies. Several minor channels corresponding to formation of M(+)(C(x)H(x)N(x)), x = 1-3, are also observed for these three systems at elevated energies. The energy-dependent collision-induced dissociation cross sections for M(+)(adenine), where M(+) = V(+) through Zn(+), are modeled to yield thresholds that are directly related to 0 and 298 K bond dissociation energies for M(+)-adenine after accounting for the effects of multiple ion-molecule collisions, kinetic and internal energy distributions of the reactants, and dissociation lifetimes. The measured bond energies are compared to those previously studied for simple nitrogen donor ligands, NH(3) and pyrimidine, and to results for alkali metal cations bound to adenine. Trends in these results and theoretical calculations on Cu(+)(adenine) suggest distinct differences in the binding site propensities of adenine to the alkali vs transition metal ions, a consequence of s-dsigma hybridization on the latter.     

Influence of metal ions on the interaction between gatifloxacin and calf thymus DNA

To study the interaction between gatifloxacin (GT), metal ions (Cu²⁺, Cd²⁺, Co²⁺, Mg²⁺) and calf thymus DNA under condition of physiology pH, UV absorption and fluorescence methods were adopted. Result shows that metal ions and DNA are able to react with GT in ground state. In further research, by studying the influence of metal ions on binding of GT with DNA in metal ions–GT–DNA ternary system, we found that influential mechanism of Mg²⁺ on the binding of GT with DNA may be different from the other three. Mg²⁺ can act as a bridge in the binding of GT's carboxyl/carbonyl with DNA phosphate in certain concentration range; while Cu²⁺, Cd²⁺, Co²⁺ can combine directly with GT by reaction between GT carboxyl/carbonyl and DNA base, and enhance the binding ability of GT with DNA. The influence extent and type depend not only on the binding site of DNA with metal ions (phosphate or base), but also the binding ability of which. The stronger the binding ability of metal ions with DNA base is, the larger their promotion to binding of GT with DNA is. The order of metal ions’ influential ability on the binding of GT–DNA is identical to the binding ability order of metal ions with DNA base, that is: Cu²⁺ > Cd²⁺ > Co²⁺ > Mg²⁺.     

Influence of the matrix on the complexation of metal ions by chelating ion exchangers

Summary Chelating ion exchangers show distribution coefficients that are considerably lower than those expected from complexation equilibria with the corresponding free ligands in solution. Furthermore, dependence of distribution coefficients on the concentration of exchanging ions in solution is observed. Both effects are due to the influence of the surrounding matrix on the anchor groups. The distribution coefficients of Fe³⁺, Ni²⁺, Cu²⁺, Pb²⁺ and UO ₂₊ ² on two cellulose exchangers carrying different anchor groups are investigated as function of the concentration in solution. In case of the anchor group of high flexibility a strong increase of the distribution coefficients with decreasing concentration in solution is measured. This is explained by the fact that the anchor groups located at the surface are less affected by interactions with the matrix, with the result of higher distribution coefficients. The explanation is in agreement with the sorption isotherm.

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Einfluß der Matrix auf die Komplexierung von Metallionen durch chelatbildende Ionenaustauscher

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Dedicated to Prof. Dr. G. Tölg on the occasion of this 60th birthday     

Influence of metal ions on the acquisition and quality of 252Cf plasma-desorption mass spectra

The presence of a few mol per cent of Ca2+ ions considerably modified the 252Cf plasma-desorption mass spectrum of a phosphorylated glycolipid. In the negative-ion mode, increasing amounts of Ca2+ caused gradual disappearance of the spectrum; it was quenched at the molar ratio 3 Ca2+/4 glycolipid. Clusters as big as 5500 were observed at certain ratios of Ca2+/glycolipid. Similar, but less pronounced effects were seen in the positive-ion mode.     

Influence of different divalent metal ions on the properties of alginate microcapsules and microencapsulated cells

Different divalent metal ions (Ba²⁺, Sr²⁺, Ca²⁺, Zn²⁺) were selected as crosslinkers. The mechanical properties, cytocompatibility, histocompatibility, cell proliferation and long-term cultivation were investigated. The resulting microcapsules had good sphericity, smooth surface and particle size distribution of 300–400 μm. Sr²⁺ microcapsules exhibited a better mechanical strength. The molecular weights cut-off of all membranes were between 24 and 67 kDa. All microcapsules had no cytotoxicity. After intraperitoneal transplantation, the recovered microcapsules still maintained good mechanical strength and morphology with no fibrosis or macrophage aggregation phenomena. The microencapsulated PC12 cells showed no significant variation after recultivation following microcapsule breaking. The cell activity sequence of different microcapsules after 72 h was as follows: bare control cell >Sr²⁺ > Ca²⁺ > Ba²⁺ > Zn²⁺. After 9 weeks’ in vitro culture, the cell survival rate was higher than 80 %. This paper will be of scientific interests for the basic research and clinical application of alginate/chitosan microcapsules embedded with drugs or cells.     

Influence of anion-induced adsorption on D.C. polarography of metal ions

Some adsorption isotherms for anion-induced adsorption of metal ions are proposed. The influences of adsorption on d.c polarograms are examined theoretically. The consequences for the determination of stability constants from polarographic data are discussed.     

Influence of transition metal ions on the photo-behaviour of BHT in polypropylene: A uv-study

The photo-behaviour of 2,6-di-tert-butyl-4-methylphenol, commercially known as BHT, has been examined in diluent phase and experimental gas phase polypropylene films by uv-derivative spectroscopy.Whilst the lower photolytic stability of BHT in the latter type polymer is associated with the catalytic effect of higher levels of residual titanium and aluminium, an additional reaction due to loss of one or both ortho-tert-butyl groups is more associated with trace levels of iron. The commercial implications of the experimental findings are discussed.     

Influence of metal ions on the activity and stability of the glucose isomerase from Streptomyces atratus

The influence of a number of bivalent metals on the activity ofStreptomyces atratus glucose isomerase has been studied. Mg²⁺ ions are activators and Co²⁺ ions are stabilizers of the glucose isomerase activity. The effective kinetic parameters for the action of the enzyme have been determined.     

Influence of metal ions on the activity and stability of the glucose isomerase from Streptomyces atratus

The influence of a number of bivalent metals on the activity ofStreptomyces atratus glucose isomerase has been studied. Mg²⁺ ions are activators and Co²⁺ ions are stabilizers of the glucose isomerase activity. The effective kinetic parameters for the action of the enzyme have been determined.Institute of Microbiology, Uzbek Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 838–842, November–December, 1991.     

Influence of metal ions on oscillatory behavior of zinc anode in nitric acid-potassium dichromate media

A zinc anode in acidic media is a new oscillatory electrochemical system which manifests interesting behaviors, from steady states to simple oscillations and chaos. This paper presents an experimental study of the influence of metal ions on the shape, amplitude and duration of the cell potential oscillations, and gives a qualitative explanation of the system’s behavior. A small quantity of Cu²⁺, Zn²⁺ or Fe³⁺ ions added to the system change dramatically the potential oscillations from chaotic behavior to simple oscillations. The method may be used for chaos attenuation.     

Effect of metal ions on monolayer collapses

A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed.     

Adsorbability of halide ions on metal electrodes

Klopman's scheme was used to estimate the relative changes in ionic energy (E_t) in the transition state: aquo complex-metal electrode surface, from the electronic constitutions of the aquo systems [NaHal·10H₂O] (where Hal = F^–, Cl^–, I^–) calculated by the LCAO MO method in the MVG form, and made self-consistent with respect to the charges on the atoms and configurations. It was shown that the experimental data for halide ion adsorption on electrodes are explained, in the model adopted, not by the Coulomb but by the exchange contribution to E_t. The adsorbability of the fluoride ions is small owing to the very small contribution made to E_t by the interaction between the aquo system [NaF·10H₂O] and the metal surface through the fluorine atom.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 732–737, November–December, 1990.The authors thank I. B. Bersuker and I. Ya. Ogurtsov for their interest in the work and participation in the discussion.     

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.     

Cancer therapeutic strategies based on metal ions

As a necessary substance to maintain the body''s normal life activities, metal ions are ubiquitous in organisms and play a major role in various complex physiological and biochemical processes, such as material transportation, energy conversion, information transmission, metabolic regulation, etc. Their abnormal distribution/accumulation in cells can interfere with these processes, causing irreversible physical damage to cells or activating biochemical reactions to induce cell death. Therefore, metal ions can be exploited against a wide spectrum of cancers with high efficiency and without drug resistance, which can effectively inhibit the growth of cancer cells by triggering biocatalysis, breaking the osmotic balance, affecting metabolism, interfering with signal transduction, damaging DNA, etc. This perspective systematically summarizes the latest research progress of metal ion-based anti-tumor therapy, and emphasizes the challenges and development directions of this type of therapeutic strategy, hoping to provide a general implication for future research.

This perspective systematically summarizes the latest research progress of metal ion-based anti-tumor therapy, and emphasizes the challenges and development directions of this type of therapeutic strategy.