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The effects of iron and manganese (hydr)oxide formation processes on the trace metal adsorption properties of these metal (hydr)oxides and their mixtures was investigated by measuring lead adsorption by iron and manganese (hydr)oxides prepared by a variety of methods. Amorphous iron (hydr)oxide formed by fast precipitation at pH 7.5 exhibited greater Pb adsorption (gamma(max) = 50 mmol of Pb/mol of Fe at pH 6.0) than iron (hydr)oxide formed by slow, diffusion-controlled oxidation of Fe(II) at pH 4.5-7.0 or goethite. Biogenic manganese(III/IV) (hydr)oxide prepared by enzymatic oxidation of Mn(II) by the bacterium Leptothrix discophora SS-1 adsorbed five times more Pb (per mole of Mn) than an abiotic manganese (hydr)oxide prepared by oxidation of Mn(II) with permanganate, and 500-5000 times more Pb than pyrolusite oxides (betaMnO2). X-ray crystallography indicated that biogenic manganese (hydr)oxide and iron (hydr)oxide were predominantly amorphous or poorly crystalline and their X-ray diffraction patterns were not significantly affected by the presence of the other (hydr)oxide during formation. When iron and manganese (hydr)oxides were mixed after formation, or for Mn biologically oxidized with iron(III) (hydr)oxide present, observed Pb adsorption was similar to that expected for the mixture based on Langmuir parameters for the individual (hydr)oxides. These results indicate that interactions in iron/manganese (hydr)oxide mixtures related to the formation process and sequence of formation such as site masking, alterations in specific surface area, or changes in crystalline structure either did not occur or had a negligible effect on Pb adsorption by the mixtures.
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PMID:Effect of oxide formation mechanisms on lead adsorption by biogenic manganese (hydr)oxides, iron (hydr)oxides, and their mixtures. 1187 57

Hydroxamic acids are widespread in the tissues of plants, in metabolites of bacteria and fungi, including complex compounds with metal ions. These acids have wide spectrum of biological activity and therefore are perspective reagents for analysis of chemical elements. Fourteen aliphatic and aromatic derivatives of hydroxamic acids have been synthesized from esters of carboxylic acids. Photometric reactions of hydroxamic acids with iron (II) and (III) were investigated. Complex formation of iron (II) and (III) depending on pH was studied with series of synthesized hydroxamic acids: octanohydroxamic, maleic hydroxamic, 2-hydroxybenzoxydroxamic, benzoxydroxamic, phthalmonoxydroxamic and 3-metoxybenzohydroxamic acids. Composition of iron (III) complexes with 2-hydroxybenzohydroxamic, octanoxydroxamic, 3-metoxybenzohydroxamic acids and iron (II) with 2-hydroxybenzohydroxamic acid was studied by methods of mole ratio and isomolar solutions. Sensitivity of reagents was evaluated by values of absorption coefficients (epsilon). Stability of complexes in water and organic solvents was investigated. Interaction between iron (III) and hydroxamic acids (octanoxydroxamic, 2-hydroxybenzohydroxamic, 3-metoxybenzohydroxamic) have been applied for quantitative photometric analysis of iron (III) salts. Color reaction of iron (II) with 2-hydroxybenzohydroxamic acid was applied for quantitative photometric determination of iron (II) salts. 3-Metoxybenzohydroxamic acid was proposed as a new indicator for complexonometric analysis of iron (III). Chelatometric titration of iron (III) using this indicator is not influenced by copper, cobalt, zinc, manganese, so this methods is recommended for iron quantity detection in antianemic drugs, which are composed of latter microelements. Synthesis procedure of 2-benzoylamino-3-arylacrylhydroxamic acids from saturated azlactones was created. Color and precipitate reactions of iron (II) and (III), copper (II), nickel (II) and cobalt (II) ions with four newly synthesized acids (with and without substitutes in aromatic ring) were studied. Sensitivities of reactions between 2-benzoylamino-3-arylacrylhydroxamic acids and iron (II) and (III) were evaluated and compared with 2-hydroxybenzohydroxamic acid.
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PMID:[Synthesis of hydroxamic acids and study of their complexes with iron (II) and (III) ions]. 1247 60

Recombinant phospholipase D (PLD) from Streptomyces chromofuscus (scPLD) has been characterized using colorimetric assays, spectroscopic investigations, and site-directed mutagenesis. scPLD, which shows phosphodiesterase activity toward a wide variety of phospholipids and phosphatase activity toward p-nitrophenyl phosphate, exhibits a visible absorption band with lambda(max) at 570 nm. Metal ion analysis performed by inductively coupled plasma mass spectroscopy shows the presence of approximately 1 equivalent of iron, 0.27 equivalent of manganese, and 0.1 equivalent of zinc per mole of protein as isolated. The metal ion content coupled with the visible absorption feature is compatible with the presence of Fe(3+)-tyrosinate coordination. When scPLD was dialyzed against solutions containing Mn(2+), Zn(2+) or EDTA, the Fe(3+) content was reduced to variable extents, and the residual specific activity correlated well with the residual iron content. Sequence homology with metal ion binding motifs in known alkaline phosphatases and purple acid phosphatase from red kidney bean shows that most of the residues involved in metal ion coordination are conserved among all the sequences considered. Mutation of some of these conserved residues (C123A, D151A, Y154F, and H391A) produced enzymes lacking iron with dramatically reduced PLD activity but little change in secondary structure or ability to bind to small unilamellar vesicles of phosphatidylcholine (with Ba(2+)) or phosphatidic acid. We suggest that scPLD is a member of a family of phosphodiesterase/phosphatases with structural and mechanistic similarity to iron-dependent purple acid phosphatases.
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PMID:An iron-dependent bacterial phospholipase D reminiscent of purple acid phosphatases. 1251 26

Proton-ligand dissociation and metal-ligand formation constants of 2-amino-4-chloro-6-[alpha-(phenyl)ethylidenehydrazino]pyrimidine; (AHP) and its p-chloro (ClAHP) and p-methoxy (OMeAHP) derivatives (Str.I&II) with Mn2+, Co2+ Ni2+, Cu2+, Zn2+, Cd2+, UO2(2+), Th4+, Ce3+ and Pr3+ ions have been evaluated potentiometrically in 75% (v/v) dioxane-water and 0.1 mol dm(-3) KNO3. The thermodynamic functions (deltaG, deltaH and deltaS) for the complexation of OMeAHP were evaluated and discussed. The effect of the temperature, dielectric constant of the solvents, mole fraction of dioxane and ionic strength of the medium on the stability of Pr3+-complexes show that the stability of the chelates increases by increasing both the electron repelling property of the substituents and the organic solvent content, and by decreasing the temperature, the ionic strength and the dielectric constant of the medium.
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PMID:Stability constants and thermodynamic parameters of Mn2+, Co2+, Ni2+ Cu2+, Zn2+, Cd2+, UO2(2+), Th4+, Ce3+ and Pr3+-complexes with some Schiff base hydrazones containing the pyrimidine moiety. 1273 93

A series of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)](2) (M(II) = Zn (1), Cu (2), Ni (3), Co (4), Fe(5), and Mn (6)) have been synthesized by the assembly reaction of K[CuL] and [M(II)(hfac)(2)(H(2)O)(2)] with a 1:1 mole ratio in methanol, where H(3)L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane and Hhfac = hexafluoroacetylacetone. The crystal structures of 2, 4, and [Cu(II)LMn(II)(acac)](2) (6a) (Hacac = acetylacetone) were determined by single-crystal X-ray analyses. Each complex has a cyclic tetranuclear Cu(II)(2)M(II)(2) structure, in which the Cu(II) complex functions as a "bridging ligand complex", and the Cu(II) and M(II) ions are alternately arrayed. One side of the planar Cu(II) complex coordinates to one M(II) ion at the two phenoxo and the methoxy oxygen atoms, and the opposite side of the Cu(II) complex coordinates to another M(II) ion at the amido oxygen atom. The temperature-dependent magnetic susceptibilities revealed spin states of S(M) = 0, 1/2, 1, 3/2, 2, and 5/2 for the Zn(II), Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) ions, respectively. Satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a rectangular arrangement with two different g-factors for the Cu(II) and M(II) ions, two different isotropic magnetic exchange interactions, J(1) and J(2), between the Cu(II) and M(II) ions, and a zero-field splitting term for the M(II) ion. In all cases, the antiferromagnetic coupling constants were found for both exchange interactions suggesting nonzero spin ground states with S(T) = 2/S(M) - S(Cu)/, which were confirmed by the analysis of the field-dependent magnetization measurements.
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PMID:Synthesis and magnetic properties of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)]2 (M(II) = Zn, Cu, Ni, Co, Fe, Mn; H3L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane; Hhfac = hexafluoroacetylacetone). 1295 Jan 97

We conducted batch-reactor experiments to measure the reductive dissolution of pyrolusite-coated (beta-MnO2) quartz by Fe(II) under conditions representative of an acid mine-drainage subsurface plume. The results reveal that reductive dissolution rates were initially rapid but declined considerably as Fe(III)(aq), a product of the reductive-dissolution reaction, was removed from solution by heterogeneous precipitation. The inhibition of reductive-dissolution was attributed to blocking of the beta-MnO2 surface sites by the Fe(III)(s) precipitate. Calculations of a simple model that accounts for the effects of Fe(III)(s) precipitate formation on reductive dissolution rates closely match temporal changes in Mn(II), Fe(II), and Fe(II) concentrations measured in 10 experiments, distinguished on the basis of the initial Fe(II)-to-Mn(IV) mole ratio and the initial Fe(III)(aq) concentration. The model-data comparisons reveal that the initial reaction rate on a clean beta-MnO2 surface exceeds the long-term reaction rate by 3 orders of magnitude, highlighting the importance of linking Fe(III) precipitation with the reductive dissolution of beta-MnO2 by Fe(II).
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PMID:The effects of reaction-product formation on the reductive dissolution of MnO2 by Fe(II). 1471 68

Topotecan can be encapsulated in liposomes, however little is known about the role encapsulated counter ions play in drug loading efficiency and drug release. Using 1,2-distearoyl-sn-glycero-3 phosphatidylcholine and cholesterol liposomes (55:45 mole ratio), encapsulation was achieved using manganese ion gradients (MnSO(4) or MnCl(2)), with the addition of A23187, a divalent cation/proton exchanger, to maintain a pH gradient. This methodology was compared to procedures where the pH gradient was generated by use of encapsulated (NH(4))(2)SO(4) or citrate (300 mM, pH 3.5). All methods facilitated topotecan encapsulation. Liposomes prepared in the presence of the citrate and MnCl(2) (+A23187) exhibited reduced loading capacities. Liposomes prepared in the presence of (NH(4))(2)SO(4) and MnSO(4) (+A23187) could be used to generate liposomes exhibiting a drug-to-lipid ratio of 0.3 (wt/wt) with an encapsulation efficiency of >90%. In vitro drug release data suggested that the (NH(4))(2)SO(4) and MnSO(4) (+A23187) formulations released drug at a reduced rate. For these formulations, the drug release rates decreased as the drug-to-lipid ratio (wt/wt) increased from 0.1 to 0.2. Cryo-electron micrographs indicated that encapsulated topotecan precipitated as linear particles within liposomes. The stability of topotecan loaded liposomes appeared to be dependent on the presence of both a pH gradient and encapsulated sulfate.
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PMID:An evaluation of transmembrane ion gradient-mediated encapsulation of topotecan within liposomes. 1512 Sep 1

In the present study, doxorubicin was encapsulated into two thermosensitive liposome formulations which were composed of DPPC/MSPC/DSPE-PEG(2000) (90/10/4 mole ratio) or DPPC/DSPE-PEG(2000) (95/5 mole ratio). Doxorubicin loading was achieved through the use of a pH gradient or a novel procedure that involved doxorubicin complexation with manganese. Regardless of the initial drug-to-lipid ratios (D:L), the final D:L reached a maximum of 0.05 (w/w) when doxorubicin was encapsulated via a pH gradient for both thermosensitive liposome formulations. In contrast, the final maximum D:L achieved through manganese complexation was 0.2 (w/w), and this loading method did not affect temperature-induced drug release, with 85% of drug released from MSPC-containing liposomes within 10 min at 42 degrees C but <5% released over 60 min at 37 degrees C. When the thermosensitive liposomes prepared via the two different loading methods were injected into mice, similar plasma elimination profiles were observed. Cryo-transmission electron microscopy analysis indicated the presence of doxorubicin fiber bundles in liposomes loaded via pH gradient, compared to a stippled and diffuse morphology in those loaded via manganese complexation. To investigate the effect of intraliposomal pH on drug precipitate morphology, the A23187 ionophore (mediates Mn(2+)/H(+) exchange) was added to liposomes loaded with doxorubicin-manganese complex, and the stippled and diffuse appearance could be converted to one exhibiting fiber bundles after acidification of the liposome core. This suggests that the formation of doxorubicin-manganese complex is favored when the intraliposomal pH is >6.5. During the conversion to the fiber bundle morphology, no doxorubicin release was observed when A23187 was added to liposomes exhibiting a 0.05 (w/w), whereas a significant release was noted when the initial D:L was 0.2 (w/w). Following acidification of the liposomal interior and establishment of an apparent new D:L equilibrium, the measured D:L ratio was 0.05 (w/w). In conclusion, the manganese complexation loading method increased the encapsulation efficiency of doxorubicin in thermosensitive liposomes with no major impact on temperature-triggered drug release or pharmacokinetics.
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PMID:Encapsulation of doxorubicin into thermosensitive liposomes via complexation with the transition metal manganese. 1590 79

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.
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PMID:Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides. 1592 78

The open reading frames (ORFs) encoding two potential protein-serine/threonine phosphatases from the cyanobacterium Synechocystis sp. strain PCC 6803 were cloned and their protein products expressed in Escherichia coli cells. The product of ORF sll1033, SynPPM3, is a homologue of the PPM family of protein-serine/threonine phosphatases found in all eukaryotes as well as many members of the Bacteria. Surprisingly, the recombinant protein phosphatase dephosphorylated phosphotyrosine- as well as phosphoserine-containing proteins in vitro. While kinetic analyses indicate that the enzyme was more efficient at dephosphorylating the latter, replacement of Asp608 by asparagine enhanced activity toward a phosphotyrosine-containing protein fourfold. The product of ORF sll1387, SynPPP1, is the sole homolog of the PPP family of protein phosphatases encoded by the genome of Synechocystis sp. strain PCC 6803. Like many other bacterial PPPs, the enzyme dephosphorylated phosphoserine- and phosphotyrosine-containing proteins with comparable efficiencies. However, while previously described PPPs from prokaryotic organisms required the addition of exogenous metal ion cofactors, such as Mg2+ or Mn2+, for activity, recombinantly produced SynPPP1 displayed near-maximal activity in the absence of added metals. Inductively coupled plasma mass spectrometry indicated that recombinant SynPPP1 contained significant quantities, 0.32 to 0.44 mol/mole total, of Mg and Mn. In this respect, the cyanobacterial enzyme resembled eukaryotic members of the PPP family, which are metalloproteins. mRNA encoding SynPPP1 or SynPPM3 could be detected in cells grown under many, but not all, environmental conditions.
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PMID:The protein phosphatases of Synechocystis sp. strain PCC 6803: open reading frames sll1033 and sll1387 encode enzymes that exhibit both protein-serine and protein-tyrosine phosphatase activity in vitro. 1610 28

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