The sorption of divalent metal ions on AlPO4

The sorption of Cu(2+), Pb(2+), Ni(2+), and Cd(2+) ions on the aluminum(III) phosphate was observed to increase with increases in the concentration, temperature, and pH of the system. The apparent dissociation (pK(a)), binding (pK(b)) and exchange (pK(ex)) constants of aluminum(III) phosphate were evaluated and found to be dependent upon the temperature and nature of the metal cations. The values of the dissociation constants (pK(a)) followed the order Pb(2+)相似文献   

Interactions of the hormone oxytocin with divalent metal ions

The interaction of the cyclic nonapeptide oxytocin (OT) with a number of alkaline earth and divalent transition metal ions (X(2+)) was examined employing mass spectrometry (MS) and ion mobility spectrometry (IMS) techniques in combination with molecular dynamics (MD) and density functional theory (DFT) calculations. Under acidic conditions it was found that OT exhibits an exceptionally strong affinity for all divalent metal ions resulting in strong [OT + X](2+) peaks in the mass spectrum. Under basic conditions only Cu(2+) and Ni(2+)-OT complexes were detected and these were singly, doubly, triply, or quadruply deprotonated. Collision-induced dissociation of the [OT - 3H + Cu](-) complex yielded exclusively C-terminal Cu(2+)-containing fragments (Cu(2+)fragment(3-)), suggesting that the Cu(2+) ligation site includes deprotonated C-terminal backbone amide nitrogen atoms and the N-terminal amino nitrogen atom in [OT - 3H + Cu](-). MD and DFT calculations indicate a square-planar complex is consistent with these observations and with experimental collision cross sections. MD and DFT calculations also indicate either an octahedral or trigonal-bipyramidal complex between Zn(2+) and OT is lowest in energy with carbonyl oxygens being the primary ligation sites. Both complexes yield cross sections in agreement with experiment. The biological impact of the structural changes induced in OT by divalent metal ion coodination is discussed.     

Effect of divalent metal ions on DNA studied by capillary electrophoresis

Divalent metal ions, such as Zn(2+), Co(2+), and Ni(2+), are capable of incorporating into DNA under certain conditions to form complexes termed M-DNA. To better understand the effects of these cations on DNA we used capillary electrophoresis (CE). The presence of these metal ions in a typical genotyping buffer led to broad peaks with low fluorescence intensities. In addition, some of the metal-complexed DNA molecules had different electrophoretic mobilities than their normal DNA counterparts. It is likely that the mobility shifts observed in the electropherograms of these affected fragments are due to the divalent cations causing structural changes in the single-stranded DNA. However, as can be seen from the resulting peak shapes, the structure, charge, and/or mass changes due to metal binding are not conserved among all of the DNA fragments. The extent of both peak-broadening and mobility shifts were found to be dependent on the metal cation and its concentration, the length of time that the DNA sample existed in formamide prior to injection into the capillary, and also the fragment size and sequence. These results suggest that the presence of metal ions might be responsible for the poor CE performance that occurs when genotyping certain kinds of DNA samples.     

Sorption of heavy metal ions by silica gel-immobilized, proton-ionizable calix[4]arenes

Silica gel-immobilized, di-ionizable calix[4]arenes are employed as stationary phases in ion-exchange chromatography for selected heavy metal ions. Sorption efficiencies for Pb²⁺ are dependent on the structure of the calix[4]arene ligand and the linker that joins the ligand to the silica gel, as well as the acidity of the sample solution. Although the resins exhibit only poor sorption of Cd²⁺, they are found to be scavengers for Hg²⁺. Competitive sorption studies are conducted with selected resins.     

Interactions between divalent metal ions and an octacoordinate macrocyclic ligand

A dinucleating hexaazadiphenol macrocyclic ligand, 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo[27.3.1.1.(5,9)1.(13,17)1. (21,25)]hexatriaconta-5,7,9(33),13,15,17(34),21,23,25(35),29,31,1(36)- dodecaene-34,36-diol (H2L), forms a number of protonated, neutral, and/or hydroxo mononuclear, homodinuclear, and heterodinuclear complexes with the divalent metal ions Cu2+, Cd2+, Mn2+, and Zn2+, controlled by the stoichiometry of the metal ion and ligand as well as the pH values of the solution. Their stability constants and species distribution as a function of p[H] are determined. The pH potentiometric studies show that the dinuclear complexes are formed via the mononuclear chelates in which two kinds of coordination patterns are observed. One is that the metal ions are complexed by exactly half of coordination sites of the dinucleating macrocycle (N3O-), and the other is that the metal ions occupy salen-like sites of the macrocycle (N3O(2)2-). In the 2:1 systems (2:1 molar ratio of metal ion to ligand), the mononuclear species predominate in acidic solutions while the dinuclear species predominate in basic solutions, except for the case of copper. The protonated mononuclear complex [H2LZn](NO3)(2).5H2O forms triclinic crystals, of space group P1, with a = 10.7797(12) A, b = 10.9047(12) A, c = 17.0176(15) A, alpha = 106.857(9) degrees, beta = 95.822(8) degrees, gamma = 100.191(9) degrees, and Z = 2; the neutral heterodinuclear complex [LZnCdCl2].6H2O forms monoclinic crystals, of space group C2/c, with a = 16.234(5) A, b = 15.976(9) A, c = 29.829(11) A, alpha = 90 degrees, beta = 90.28(2) degrees, gamma = 90 degrees, and Z = 8.     

Sorption of metal ions by technical lignins and their derivatives

Atomic absorption analysis has been used to study the sorption of lead, zinc, and iron ions by technical lignins and their derivatives. The capacity of technical lignins and some of their derivatives for forming complexes can be used for nature-protecting purposes and for the enterosorption of heavy-metal ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 362–363, May–June, 1998.     

o-hydroxyaroyl-isonicotinoyl hydrazones as chelating agents with divalent transition metal ions

Summary Two series of bivalent metal complexes of the type M(Sal)· xH₂O and M(Naph) have been synthesized; where M = Co, Ni, Cu, Zn, Pd and Cd, and H₂-Sal and H₂-Naph are salicylaldehyde and o-hydroxynaphthaldehyde isonicotinoyl hydrazones which acted as dibasic terdentate ligands. The polymeric nature and coordination sites of the complexes have been characterized by elemental, d.t.a. and t.g.a analyses, molar conductance, pH, room temperature magnetic susceptibility and spectral (i.r., ¹H n.m.r, u.v.) measurements. The protonation constants of the ligands have been determined potentiometrically at different temperatures, ionic strengths and at different EtOH-H₂O compositions.     

Solvent extraction of divalent metal ions with azacrown ether substituted acylpyrazolones

Novel 4-acyl-5-pyrazolones having aza-15-crown-5 (HPMP-A15C5) and aza-18-crown-6 (HPMP-A18C6) moieties as an intramolecular synergist have been synthesized by simple coupling reactions between 1-phenyl-3-methyl-4-chloroacetyl-5-pyrazolone and the corresponding azacrown ethers. The solvent extraction of the divalent metal ions (Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+)) were examined. Synergistic extractions with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) and benzocrown ethers were also examined for a comparison. Extractions with the novel acylpyrazolones were unique and quite different from those with HPMBP and benzocrown ethers. The synergistic effect with benzocrown ethers was low, and an obvious difference brought by the ring size was not observed. The extractions of the divalent metal ions with HPMP-A18C6 were generally enhanced, as compared to those alone with HPMBP; on the contrary, the extractions with HPMP-A15C5 were relatively poor.     

Sorption of metal ions to untreated,alkali-treated and peroxide-bleached TMP

Knowledge about how different metal ions are bound to pulp fibers is very important for optimal metal management in pulping processes. A column chromatographic method was used to assess the differences in affinity of 14 metal ions to untreated, alkali-treated and peroxide-bleached thermomechanical pulp (TMP). A method of competition between cations in the column chromatographic experiments was used in the sorption experiments, with an excess of each metal ion compared to the total capacity of the pulp studied. The method is very sensitive and even small differences in affinities can be detected. By combining the results from sorption experiments with four different metal ion mixtures the following order of affinity was obtained: Pb²⁺ ≫ Cu²⁺ ≫ Cd²⁺ > Zn²⁺ > Ni²⁺ > Ba²⁺ > Ca²⁺ > Mn²⁺ > Sr²⁺ > Mg²⁺ ≫ Rb⁺ ≈ K⁺ > Na⁺ > Li⁺. All three types of pulps showed the same affinity order. Lead and copper ions were clearly most strongly bound to the pulp fibers. Within the alkali and alkaline earth metal groups the differences in affinity were quite small. The sorption of metal ions to pulp fibers takes place mainly by complexation, where the divalent metal ions are coordinated to functional groups (acid groups) in the fiber phase. Protonation constants and concentrations of acid groups were determined by potentiometric titration. A model with two carboxyl groups and two phenolic hydroxyl groups satisfied best the experimental data. By treatment with alkali and peroxide new acid groups were created and the total binding capacity of hydrogen ions increased from 137 μeq/g for untreated pulp to 187 and 228 μeq/g for alkali-treated and peroxide-treated pulp, respectively.     

Sorption recovery of metal ions using silica gel modified with salicylaldoxime

Trace metals in water were preconcentrated with silica gel modified with salicylaldoxime and determined by AAS. Optimum conditions for the maximum recovery of metal ions, viz. Cu(II), Ni(II), Co(II), Zn(II) and Fe(III), for both batch and column methods were developed. The efficiency of the adsorbent with respect to different experimental conditions was established.     

Thermal properties of some complexes of quinolinic acid with divalent metal ions

Studies of the complexes of pyridinecarboxylic acids with divalent metal ions as a function of the position of the carboxyl groups were extended. The thermal properties of the complexes of quinoline acid (pyridine-2,3-dicarboxylic acid) with several divalent metal ions were determined by thermogravimetry (TG) and differential thermal analysis (DTA). A correlation between these compounds and others obtained by reaction between the studied metal ions with similar acids (lutidinic acid (pyridine-2,4-dicarboxylic acid) and isocinchomeronic acid (pyridine-2,5-di-carboxylic acid) is discussed in terms of the position of the carboxyl group far from the aza group. The thermal stability of the metal complexes is in the order Mn(II) > Fe(II) > Zn(II) ? Co(II) > Ni(II) > Cu(II).     

Interaction of dinucleotides with divalent metal ions: A circular dichroism study

The interactions between NAD⁺ and NADP⁺ and the divalent ions Mg²⁺, Mn²⁺ and Co²⁺ have been studied by circular dichroism in the UV range. A visible C.D. study has been carried on the Co²⁺ complexes.The observed changes of the UV and C.D. as a function of temperature clearly show that the metal ion does not bridge the purine base and the nicotinamide.The observed changes of the UV C.D. as a function of temperature clearly show that the metal ion does not bridge the purine base and the nicotinamide.The strong modification of the UV C.D. and the appearance of visible C.D. in 0.1 M NAD⁺ or NADP⁺ solutions in presence of Co²⁺ which occurs when the N(1) adenine atom is deprotonated, has been ascribed to the formation of a 1:2 Co²⁺-dinucleotide complex where the two adenine bases are stacked.     

Complexes of divalent metal ions with cinchomeronic and dinicotinic acid thermal properties

The thermal properties of the complexes of cinchomeronic and dinicotinic acid with several divalent metal ions were determined by thermogravimetry (TG) and differential thermal analysis (DTA).For the thermal stability of the anhydrous compounds a sequence may be observed for the metal ions with cinchomeronic (3,4-H₂PC) and dinicotinic acid (3,5-H₂PC):

The thermal stability of the pyridine carboxylic acid for each metal of the series is: dinicotinic > cinchomeronicThe activation energy values for each thermal reaction were also calculated, using the Coats and Redfern algorism, by the Univac 1108 computer, by a program properly implemented for the statistical analysis of the data to obtain the reaction order and the activation parameters with the relative confidence limits.     

Coordination numbers of hydrated divalent transition metal ions investigated with IRPD spectroscopy

Hydration of the divalent transition metal ions, Mn, Fe, Co, Ni, Cu, and Zn, with 5-8 water molecules attached was investigated using infrared photodissociation spectroscopy and photodissociation kinetics. At 215 K, spectral intensities in both the bonded-OH and free-OH stretch regions indicate that the average coordination number (CN) of Mn(2+), Fe(2+), Co(2+), and Ni(2+) is ~6, and these CN values are greater than those of Cu(2+) and Zn(2+). Ni has the highest CN, with no evidence for any population of structures with a water molecule in a second solvation shell for the hexa-hydrate at temperatures up to 331 K. Mn(2+), Fe(2+), and Co(2+) have similar CN at low temperature, but spectra of Mn(2+)(H(2)O)(6) indicate a second population of structures with a water molecule in a second solvent shell, i.e., a CN < 6, that increases in abundance at higher temperature (305 K). The propensity for these ions to undergo charge separation reactions at small cluster size roughly correlates with the ordering of the hydrolysis constants of these ions in aqueous solution and is consistent with the ordering of average CN values established from the infrared spectra of these ions.     

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.     

Artificial G-wire switch with 2,2'-bipyridine units responsive to divalent metal ions

Development of a guanine nanowire (G-wire) that is controllable and can be switched by external signals is important for the creation of molecular electronic technologies. Here, we constructed a G-wire in which the thymines of the main chain of d(G4T4G4) were replaced with 2,2'-bipyridine units, which have two aromatic rings that rotate arbitrarily upon coordination with metal ions. Circular dichroism of the DNA oligonucleotides with or without the 2,2'-bipyridine unit showed that divalent metal ions induce the bipyridine-containing oligonucleotide to switch from an antiparallel to a parallel G-quadruplex. Native polyacrylamide gel electrophoresis showed that the parallel-stranded G-quadruplex DNA had a high-order structure. Circular dichroism and native gel electrophoresis analyses suggested that adding Na2EDTA causes a reverse structural transition from a parallel-stranded high-order structure to an antiparallel G-quadruplex. Moreover, atomic force microscopy showed a long nanowire ( approximately 200 nm) in the presence of Ni2+ but no significant image in the absence of Ni2+ or in the presence of both Ni2+ and Na2EDTA. These observations revealed that the parallel-stranded high-order structure is a G-wire containing numerous DNA oligonucleotide strands bound together via divalent metal ion-2,2'-bipyridine complexes. Finally, we found that alternating addition of Ni2+ and Na2EDTA can cycle the G-wire between the high-order and disorganized structures, with an average cycling efficiency of 0.95 (i.e., 5% loss per cycle). These results demonstrate that a DNA oligonucleotide incorporating the 2,2'-bipyridine unit acts as a G-wire switch that can be controlled by chemical input signals, namely, divalent metal ions.     

A spectroscopic investigation of complexes of divalent metal ions with maleic acid copolymers

The absorption spectra of complexes of copper(II), nickel(II), and barium(II) with three partially neutralized maleic acid copolymers in aqueous solution have been investigated in the range 195–720 nm. Copper ions are always very strongly bound, giving electron transfer complexes. Relevant spectral features are found to depend on the number of methyl groups in the polymer backbone, and in particular, for each given polymer, on the amount of available ligand negative charge per divalent counterion. The spectra of the complexes of nickel(II) and barium(II) suggest that they interact with the polycarboxylates much more weakly than copper(II).     

Tetracyanomanganate(II) and its salts of divalent first-row transition metal ions

The first known paramagnetic, tetrahedral cyanide complex, [Mn(II)(CN)(4)](2)(-), is formed by the photoinduced decomposition of [Mn(IV)(CN)(6)](2)(-) in nonaqueous solutions or by thermal decomposition in the solid state. In acetonitrile or dichloromethane, photoexcitation into the ligand-to-metal charge transfer band (lambda(max) = 25 700 cm(-1), epsilon = 3700 cm(-1) M(-1)) causes the homolytic cleavage of cyanide radicals and reduction of Mn(IV). Free cyanide in dichloromethane leads to the isolation of polycyanide oligomers such as [C(12)N(12)](2)(-) and [C(4)N(4)](-), which was crystallographically characterized as the PPN(+) salt C(40)H(30)N(5)P(2): monoclinic space group = I2/a, a = 18.6314(2) A, b = 9.1926(1) A, c = 20.8006(1), beta =106.176(2) degrees, Z = 4]. In the solid state Mn(IV)-CN bond homolysis is thermally activated above 122 degrees C, according to differential scanning calorimetry measurements, leading to the reductive elimination of cyanogen. The [Mn(II)(CN)(4)](2-) ion has a dynamic solution behavior, as evidenced by its concentration-dependent electronic and electron paramagnetic spectra, that can be attributed to aggregation of the coordinatively and electronically unsaturated (four-coordinate, 13-electron) metal center. Due to dynamics and lability of [Mn(II)(CN)(4)](2-) in solution, its reaction with divalent first-row transition metal cations leads to the formation of lattice compounds with both tetrahedral and square planar local coordination geometries of the metal ions and multiple structural and cyano-linkage isomers. alpha-Mn(II)[Mn(II)(CN)(4)] has an interpenetrating sphalerite- or diamond-like network structure with a unit cell parameter of a = 6.123 A (P43m space group) while a beta-phase of this material has a noninterpenetrating disordered lattice containing tetrahedral [Mn(II)(CN)(4)](2-). Linkage isomerization or cyanide abstraction during formation results in alpha-Mn(II)[Co(II)(CN)(4)] and Mn(II)[Ni(II)(CN)(4)] lattice compounds, both containing square planar tetracyanometalate centers. alpha-Mn(II)[Co(II)(CN)(4)] is irreversibly transformed to its beta-phase in the solid state by heating to 135 degrees C, which causes a geometric isomerization of [Co(II)(CN)(4)](2)(-) from square planar (nu(CN) = 2114 cm(-1), S = (1)/(2)) to tetrahedral (nu(CN) = 2158 cm(-1), S = (3)/(2)) as evidenced by infrared and magnetic susceptibility measurements. Mn(II)[Ni(II)(CN)(4)] is the only phase formed with Ni(II) due to the high thermodynamic stability of square planar [Ni(II)(CN)(4)](2)(-).     

Fragmentation and charge transfer in gas-phase complexes of divalent metal ions with acetonitrile

The development of electrospray has enabled generation of gas-phase multiply charged metal ion complexes with various solvent molecules. These species exhibit rich fragmentation chemistry, involving competition among neutral ligand loss, ligand cleavage, and dissociative electron and proton transfer. Acetonitrile is a common aprotic solvent. Here we present a comprehensive MS/MS study on acetonitrile complexes of divalent metal cations. We measured the critical sizes below which dissociation channels other than the trivial neutral evaporation become operative and minimum sizes at which dications remain stable against charge reduction. For all sizes between the two, low-energy fragmentation patterns have been elucidated in detail.     

Sorption of selenite ions on hematite

The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2-12), ionic strength (0.01-0.1 M), and concentration of selenium (10(-7)-10(-2) M). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [Se] = 4 x 10(-4) M (surface coverage>ca. 2 at nm(-2)). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeOSe(O)O- or >FeOSe(O)OH and bidentate (>FeO)2SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area (K(D) in L m(-2)), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid-base properties which depend on the nature of the oxide and its level of purity.