Increase In Metal Ion Concentration Research Articles

Novel Molecular Building Blocks Based on the Boradiazaindacene Chromophore: Applications in Fluorescent Metallosupramolecular Coordination Polymers

We designed and synthesized novel boradiazaindacene (Bodipy) derivatives that are appropriately functionalized for metal-ion-mediated supramolecular polymerization. Thus, ligands for 2-terpyridyl-, 2,6-terpyridyl-, and bipyridyl-functionalized Bodipy dyes were synthesized through Sonogashira couplings. These fluorescent building blocks are responsive to metal ions in a stoichiometry-dependent manner. Octahedral coordinating metal ions such as Zn(II) result in polymerization at a stoichiometry corresponding to two terpyridyl ligands to one Zn(II) ion. However, at increased metal ion concentrations, the dynamic equilibria are re-established in such a way that the monomeric metal complex dominates. The position of equilibria can easily be monitored by (1)H NMR and fluorescence spectroscopies. As expected, although open-shell Fe(II) ions form similar complex structures, these cations quench the fluorescence emission of all four functionalized Bodipy ligands.

Potentials of 3, 31, 41, 5, 7-pentahydroxyflavylium of Hibiscus rosa-sinensis L. (Malvaceae) flowers as ligand in the quantitative determination of Pb, Cd and Cr.

3, 31,41,5,7-Pentahydroxyflavylium chloride (cyanidin chloride) was extracted from the flowers of Hibiscus rosa-sinensis L. and blackberry fruits and the purity confirmed by co-chromatography with authentic marker on thin layer chromatography (TLC) and paper chromatography (PC). UV-Visible spectrophotometric determinations of the sample and its Pb (II), Cr (III) and Cd (II) complexes at various pH were carried out. The cyanidin sample absorbs at 530 and 540 nm in methanol and ethanol respectively. A Cyanidin-Pb (II) complex was formed at pH 4.2 (λmax = 555 nm, in methanol). A Cyanidin-Cr (III) complex was formed at pH 1.0 (λmax = 682 nm, methanol and ethanol) while a Cyanidin-Cd (II) complex was formed at pH 3.0 [λmax = 706 nm (methanol) and 679 nm (ethanol)]. All the metal-ligand complexes occur in the ratio of 1:2 and the molar absorptivities are 9.66 x 102, 8.77 x 102 and 9.77 x 102 L.mol-1.cm-1 for Pb, Cr and Cd respectively. Under optimum conditions, the absorbance of the complexes was found to increase linearly with increase in metal-ion concentrations, which corroborated with the correlation coefficient values. The linear range of the calibration graph was 0.1 – 0.5 mM for all the complexes. The results show that cyanidin could be used as a reagent for the spectrophotometric determination of Cr (III), Pb (II) and Cd (II) and by varying the pH, these metals could be determined simultaneously in solution. Key words: Cyanidin chloride, Hibiscus rosa-sinensis, metal - ligand complex, Lead (II), chromium (III), Cadmium (II), spectrophotometric assay.

The Rheological Behavior of Salt Tolerant Polyacrylamide Solutions

The rheological behavior of viscoelastic fluids was investigated with regard to the specialty of tertiary oil recovery. Aqueous polyacrylamide solutions at different concentrations were selected to simulate viscoelastic polymer systems, and the Haake RS 150 type rheometer was used to measure the rheological behavior. The experimental results showed that the viscoelasticity was positively influenced by polyacrylamide solution concentrations and negatively affected by solution temperatures. The coefficient of first normal stress deference decreased with increasing shear rate. In addition, the relationship between viscosity and the coefficient of first normal stress with shear rate obeyed a power law model. The viscosity decreased with increasing metal ion concentration and time.

Copper and zinc dismetabolism in the mouse brain upon chronic cuprizone treatment

Recent reports describe successful treatment using copper chelation therapy in neurodegenerative animal models. However, the success claimed for chelation therapy in neurodegenerative diseases is still rather controversial. To acquire new information on copper metabolism/homeostasis, we utilized cuprizone, a very sensitive and selective copper-chelating agent with well-known neurotoxic properties, as a relevant chemical model in mice. Upon cuprizone treatment, mice developed a pronounced astrocytosis, with brain oedema and spongiosis characterised by vacuolisations of the neuropil predominantly in the white matter. In addition, cuprizone treatment severely altered copper and zinc homeostasis in the central nervous system (CNS) as well as in all other tissues examined, with increasing metal ion concentrations particularly in the CNS. Concomitant with this increase in the Cu and Zn concentration in the brain, metallothionein-I and -II were also highly immunoreactive in astrocyte, consistent with the astrocytosis and demyelination observed in our and other laboratories.

Investigation of adsorption of lead, mercury and nickel from aqueous solutions onto carbon aerogel

AbstractRecently a new form of activated carbon has appeared: carbon aerogel (CA). Its use for the removal of inorganic (and especially metal ions) has not been studied. In the present study, the adsorption of three metal ions, Hg(II), Pb(II) and Ni(II), onto carbon aerogel has been investigated. Batch experiments were carried out to assess adsorption equilibria and kinetic behaviour of heavy metal ions by varying parameters such as agitation time, metal ions' concentration, adsorbent dose and pH. They facilitated the computation of kinetic parameters and maximum metal ion adsorption capacities. Increasing the initial solution pH (2–10) and carbon concentration (50–500 mg per 50 cm3) increases the removal of all three metal ions. A decrease of equilibrium pH with an increase of metal ion concentration led us to propose an adsorption mechanism by ion exchange between metal cations and H+ at the carbon aerogel surface. Carboxylic groups are especially involved in this adsorption mechanism. Langmuir and Freundlich isotherm models were used to analyse the experimental data of carbon aerogel. The thermodynamics of the metal adsorption was also investigated for the practical implementation of the adsorbent. The sorption showed significant increase with increase of temperature. Kinetics models describing the adsorption of Hg(II), Pb(II) and Ni(II) ions onto carbon aerogel have been compared. Kinetics models evaluated include the pseudo‐first order and second order model. The parameters of the adsorption rate constants have been determined and the effectiveness of each model assessed. The result obtained showed that the pseudo‐second order kinetic model correlated well with the experimental data and better than the pseudo‐first order model examined in the study. Mass transfer coefficients obtained can be useful in designing wastewater treatment systems or in the development of environmental technologies. Copyright © 2005 Society of Chemical Industry

Effects of copper, cadmium, and zinc on the production and exudation of thiols by Emiliania huxleyi

Cultures of the ubiquitous coccolithophore Emiliania huxleyi grown at field-relevant fixed free ion concentrations of Cu, Cd, and Zn exude a broad array of thiols, some of which increase with increasing metal ion concentration. The primary thiols released are contingent on the particular metal or combination of metals added to the culture media. Exposure to Cu results in the release of arginine-cysteine, glutamine-cysteine, and cysteine; Cd causes these thiols and glutathione to be released; and high Zn results in the synthesis and exudation of predominantly γ-glutamate- cysteine (γ-Glu-Cys). Because the free ion concentrations of Cu and Cd used in these experiments are similar to those observed in the field, active exudation could be an important source of thiols to surface seawater and thus might affect trace metal speciation in the open ocean. Intracellular thiol concentrations were also clearly affected by metal concentrations, with γ-Glu-Cys being particularly dynamic. Additionally, the shift from exponential to stationary growth in batch cultures caused approximately two- to fourfold declines in the concentrations of nearly all intracellular thiols.

Effects of metal ions on photoinduced electron transfer in zinc porphyrin-naphthalenediimide linked systems.

Zinc porphyrin-naphthalenediimide (ZnP-NIm) dyads and zinc porphyrin-pyromellitdiimide-naphthalenediimide (ZnP-Im-NIm) triad have been employed to examine the effects of metal ions on photoinduced charge-separation (CS) and charge-recombination (CR) processes in the presence of metal ions (scandium triflate (Sc(OTf)(3)) or lutetium triflate (Lu(OTf)(3)), both of which can bind with the radical anion of NIm). Formation of the charge-separated states in the absence and in the presence of Sc(3+) was confirmed by the appearance of absorption bands due to ZnP(.) (+) and NIm(.) (-) in the absence of metal ions and of those due to ZnP(.) (+) and the NIm(.) (-)/Sc(3+) complex in the presence of Sc(3+) in the time-resolved transient absorption spectra of dyads and triad. The lifetimes of the charge-separated states in the presence of 1.0 x 10(-3) M Sc(3+) (14 micros for ZnP-NIm, 8.3 micros for ZnP-Im-NIm) are more than ten times longer than those in the absence of metal ions (1.3 micros for ZnP-NIm, 0.33 micros for ZnP-Im-NIm). In contrast, the rate constants of the CS step determined by the fluorescence lifetime measurements are the same, irrespective of the presence or absence of metal ions. This indicates that photoinduced electron transfer from (1)ZnP(*) to NIm in the presence of Sc(3+) occurs without involvement of the metal ion to produce ZnP(.) (+)-NIm(.) (-), followed by complexation with Sc(3+) to afford the ZnP(.) (+)-NIm(.) (-)/Sc(3+) complex. The one-electron reduction potential (E(red)) of the NIm moiety in the presence of a metal ion is shifted in a positive direction with increasing metal ion concentration, obeying the Nernst equation, whereas the one-electron oxidation potential of the ZnP moiety remains the same. The driving force dependence of the observed rate constants (k(ET)) of CS and CR processes in the absence and in the presence of metal ions is well evaluated in terms of the Marcus theory of electron transfer. In the presence of metal ions, the driving force of the CS process is the same as that in the absence of metal ions, whereas the driving force of the CR process decreases with increasing metal ion concentration. The reorganization energy of the CR process also decreases with increasing metal ion concentration, when the CR rate constant becomes independent of the metal ion concentration.

Treatment of humic acids with ferric, aluminum, and chromium ions in water

The interaction of ferric, aluminum, and chromium ions with humic acids at different pH of mixture has been investigated. The concentration of metal ions, bound with humic acid is proportional to the concentration of metal ion in water solution at pH 3 at low metal ion concentrations. The ratio of the number of ferric ions, bound with humic acid, to the number of acidic groups in humic acid is more than 1.5 at high ferric ion concentration in solution. That is bound with the formation of dimers of ferric ions and their treatment with acidic groups of humic acid. The radius of particles formed in the reaction of humic acid with ferric ion does not depend on the pH and decreases in the reaction with chromium and aluminum ions at pH higher than 4. An increase of metal ion concentration leads to the increase of the particle radius at low metal ion concentration reaching the constant value at high metal ion concentration and pH 6.1.

Bioremoval of zinc ions by Scenedesmus obliquus and Scenedesmus quadricauda and its effect on growth and metabolism

Zinc biosorption by two green algae, Scenedesmus obliquus and Scenedesmus quadricauda, was investigated. Data show that, at concentrates between 0.5 and 8 ppm , zinc adsorption by algae increased with increasing metal ion concentration. The maximum specific adsorptive capacity of zinc ions obtained from the Langmuir adsorption isotherms was higher for S. obliquus (6.67) and lower for S. quadricauda (5.03). These S. obliquus appears to be more efficient than S. quadricauda for removing zinc ions. However, the affinity constant of zinc on the biomass of both algae were 0.19 and 0.27 indicating that S. obliquus is more tolerant to zinc phytotoxicity than S. quadricauda. Algal growth, pigment fractions, total amino acids, and the activities of some phosphatases enzyme (acid phosphatase, alkaline phosphatase, and ATPase) in the algal cells were measured in the exponential growth phase after exposure to various concentrations of zinc. Lower concentrations of zinc increased dry weight, chlorophyll a, b, carotenoids, and total amino acid contents in both algae. On the other hand, higher concentrations of zinc were inhibitory for growth and the other metabolic activities.

The modification of ABS resin by introducing metal salts of unsaturated acids

Graft polymerization of methacrylic acid onto ABS resin was carried out using BPO as an initiator in THF solution. Degree of grafting increased with reaction time and reached 35% in 10 hrs. Carboxyl groups were converted to carboxylates (metal salts) by refluxing MAA-g-ABS and the metal acetate in THF. In the solid graft polymers in solid, the infrared absorption of the asymmetrical C= O vibration of the carboxylic acid shifted to lower wavenumbers with increasing metal ion concentration. The absorption peak for the carboxylate anion is shifted to higher wavenumbers with the increase of alkali metal ion concentration, however, for the Mg2+ salt, it is shifted to lower wavenumbers. The surface and volume resistivities of the K+ and Na+ salts of MAA-g-ABS were 9.0 × 109 Ω□ and 9.5 × 109 Ω at 80% neutralization, respectively, and decreased with alkali metal ion concentration. The electric resistance of Li+, Mg2+ and Zn2+ salts decreased only slightly. The modulus of the K+ salt of MAA-g-ABS decreased with neutralization, whereas in Li+, Mg2+ and Zn2+ salts, the modulus increased with increasing metal ion concentration.

Virgin olive oil: Free radical production studied with spin‐trapping electron paramagnetic resonance spectroscopy

AbstractSpin trapping using 5,5‐dimethyl‐1‐pyrroline N‐oxide (DMPO) has been used to detect and distinguish free radicals in samples of Greek extra virgin olive oils. A number of the samples examined immediately after the addition of the spin trap showed a spontaneous complex electron paramagnetic resonance (EPR) signal. The majority of DMPO‐radical adducts formed (80–90%) represented peroxyl and alkoxyl radical adducts. Similar spectra were recorded when DMPO was added in oxidized triolein and then treated with Fe2+, Fe3+, or Cu2+ or when EPR‐silent olive oil samples were treated with these metallic ions. Metal ion‐catalyzed decomposition of triolein hydroperoxides, as recorded by EPR signal intensity, increased with increasing metal ion concentration in the micromolar range. The relative concentration of alkoxyl‐DMPO adducts increased with increasing Fe2+ or Fe3+ concentration, whereas that of peroxyl‐DMPO species decreased. In contrast, the relative concentrations of alkoxyl and peroxyl species produced by Cu2+ were similar over the whole metal concentration range examined. Exposure of EPR‐silent virgin olive oil or oxidized triolein to ultraviolet light in the presence of DMPO resulted in the detection of a three‐line spectrum characterized by wide line widths.

Adsorption of Cesium, Strontium, and Cobalt Ions on Magnetite and a Magnetite−Silica Composite

Constant pH adsorption isotherms for nonradioactive Cs+, Sr2+, and Co2+ on pure magnetite and a 80% (w/w) magnetite−silica composite were measured at 25 °C over a wide range of metal ion concentrations. The adsorption studies were carried out at four different pH's: 6, 7, 8, and 9 for Cs+ and Sr2+ and 5, 6, 7, and 8 for Co2+. All of the constant pH isotherms exhibited type I behavior with a saturation capacity that was pH-dependent and increased with increasing pH. The corresponding distribution coefficients increased with increasing pH but decreased with increasing metal ion concentration; they were also 10−1000 times lower than those reported in the literature for more selective but more expensive adsorbents. These two magnetite-based adsorbents also exhibited moderate regeneration conditions, with nearly 90−100% regeneration achieved in most cases at pH values between 1 and 3. A Langmuir model with pH-dependent parameters was also fitted successfully to all of the constant pH adsorption isotherms. Thi...

The Cu(II)-2,2′-bipyridine system revisited

The system formed by Cu(II) and 2,2′-bipyridine (bpy) has been revisited by use of EPR and electronic absorption spectroscopies. The mono-chelated [Cu(bpy)] 2+, bis-chelated trans-[Cu(bpy) 2] 2+ with pseudo-tetrahedral geometry due to the steric hindrance of the 3,3′ hydrogen atoms and tris-chelated [Cu(bpy) 3] 2+ species exist in aqueous solution. In basic media hydrolysis yields [Cu(bpy)OH] + and [Cu(bpy)(OH) 2]. The dimer [Cu(bpy)(OH)] 2 2+ is favoured by increasing metal ion concentration in the pH range 8–10. The EPR spectrum of the dimeric species shows well-resolved Δ M=1 and 2 features, and is different from that observed in the solid state. The zero-field splitting is consistent with a distance of ∼3.4 Å between metallic centres. The behaviour of the complex system is in agreement with potentiometric data reported in the literature. In the EtOH–H 2O mixture the bis-chelated complex adopts a five-coordinate cis structure exhibiting a rhombic EPR spectrum and, in basic solution, the [Cu(bpy) 2(OH)] + species is formed. The attribution of the solution species has been confirmed by the analysis of solid compounds, [Cu(bpy)SO 4]·2H 2O, [Cu(bpy)(H 2O) 2](NO 3) 2, [Cu(bpy) 2OSO 3]·4H 2O and [Cu(bpy) 2ONO 2]NO 3·H 2O, after dissolution.

Effects of heavy metals on growth of species of Micrococcus and Pseudomonas in a crude oil/mineral salts medium

Bioassays were conducted to observe the responses of species of Micrococcus and Pseudomonas to the metals zinc, lead, copper and manganese, added singly or in combination to a crude oil/mineral salts medium. Bacterial density decreased with increasing metal ion concentration. A 50% reduction (LC 50) in the bacterial density of Micrococcus sp. occurred on the addition of either 0·46 μg zinc/ml, 1·41 μg lead/ml, 11·25 μg copper/ml or 28·2 μg managanese/ml. For Pseudomonas sp., the corresponding values were 0·43 μg zinc/ml, 2·80 μg lead/ml, 6·30 μg copper/ml or 317·0 μg manganese/ml. Of the metals tested, only zinc was found in higher concentrations in the oil contaminated site than the LC 50 value obtained.

Effects of alkaline earth metal ions on the growth ofCalothrixstrain RC3, a natural isolate from Rock Creek, British Columbia

Calothrix is a filamentous cyanobacterium that has a single terminal heterocyst and a tapering morphology. It exists in two forms: mature filaments as described and motile hormogonia, which have a distinct morphology and serve as a dispersal mechanism for the organism. These cyanobacteria are common inhabitants of freshwater environments, where they are subjected to a variety of fluctuating conditions, including levels of dissolved metal ions. The present study represented an initial investigation of the effects of increasing metal ion concentrations on Calothrix as assessed ultrastructurally by transmission electron microscopy and through alterations observable by light microscopy and growth studies. Exposure of filaments to various levels of the alkaline earth cations Ca2+, Mg2+, Sr2+, and Ba2+led to various changes in structure, indicating effects on the organism's physiology. These included perturbation of cell envelope layers, such that the formation of outer membrane vesicles was enhanced, alteration to the patterns and abundance of sheath material formed, alteration of thylakoid (photosynthetic) membrane structure, and inhibition of hormogonium formation and release. It was interesting to note that even cations that are not typically thought of as toxic (Ca2+and Mg2+) could have profound effects on the cells to the extent of inhibiting growth at the maximum levels used in this study (5 mM), which are below these often found in natural environments. These results give an indication that the presence of metal ions in natural environments can have an important influence on the structural and growth characteristics of commonly found cyanobacteria to the extent of making them appear, on a macroscopic basis, as different organisms entirely. This puts a note of caution on future field observations and interpretations of the effects of pollutants on natural microbial communities.Key words: cyanobacteria, metals, ultrastructure.

Interaction of Alkaline Earth Metal Ions with Acetic and Lactic Acid in Aqueous Solutions Studied by 13C NMR Spectroscopy

Abstract Interaction of alkaline earth metal (magnesium, calcium, strontium and barium) ions with acetic and lactic acid in aqueous media was investigated by 13C NMR spectroscopy. In the acetate systems, signals whose chemical shifts were the averages of those of the free and bound acetate ions were observed. Downfield shifts of the carboxylate carbon signals with increasing metal ion concentration indicated that the acetate ion acted as a monodentate ligand coordinating to the metal ion using the carboxylate group. The metal ion concentration dependence of the peak positions of the methine and carboxylate carbon signals of the lactate ion in the lactate systems suggested that the lactate ion coordinated to a metal ion using the carboxylate and hydroxyl groups. Unique upfield shifts upon complexation in the magnesium lactate systems suggested that the lactate ion coordinated to the magnesium ion from outside the primary hydration sphere. The present results were consistent with the isotope effects of the alkaline earth metals observed in cation exchange chromatography.

An investigation of P, P′-di(2-ethylhexyl) methanediphosphonic acid and some of its metal complexes

Copper(II), iron(III), europium(III), thorium(IV) and uranium(VI) complexes of P,P′-di(2-ethylhexyl) methanediphosphonic acid, H 2DEH[MDP], were prepared along with calcium and sodium salts. The compounds were characterized by elemental analysis, infrared spectroscopy, and vapor phase osmometry (VPO). Infrared spectra reveal that the asymmetric, ν asym(POO −), and symmetric, ν sym(POO −), phosphorus-oxygen stretching models of the ligand are sensitive to the nature of the metal ion metal present in the compound. The dramatic variation in ν asym(POO −) with metal ion indicates a wide range in strength of the metal-diphosphonate interaction. The shift of both ν asym(POO −) and ν asym(POO −1) to lower energies relative to their values in the sodium salt indicates symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The difference Δν between the POO − stretching frequencies, [ ν asym(POO −)− ν asym(POO −1)], becomes smaller as the ionic potential of the metal ion increases. H 2DEH[MDP] was found by VPO to be dimeric in toluene at 25°C in the 0.2–0.005 m concentration range. Dimerization is achieved through strong intermolecular hydrogen bonding between the phosphoryl and POH groups of two H 2DEH[MDP] molecules. Pre-equilibration with water or 1.0 M nitric acid does not effect the aggregation of the ligand in toluene. The apparent aggregation numbers measured for H 2DEH[MDP] solutions contacted with aqueous metal ions indicate that the ligand has a tendency to form polynuclear complexes. Aggregation increases with increasing metal ion concentration, deprotonation of the POH groups, and the ionic potential of the metal ion. The absence of nitrate ion in these solutions shows that, under high metal loading conditions, cations are extracted from aqueous nitric acid by H 2DEH[MDP] with displacement of hydrogen ions. Ligand band shifts indicate that when excess un-ionized H 2DEH[MDP] is present in solution, the phosphoryl oxygen atoms of the acid participate in the complexation process.

Effect of Metal Cations on the Viscosity of a Pectin-Like Capsular Polysaccharide from the Cyanobacterium Microcystis flos-aquae C3-40

The properties of purified capsular polysaccharide from the cyanobacterium Microcystis flos-aquae C3-40 were examined by capillary viscometry. Capsule suspensions exhibited similar viscosities between pH 6 and 10 but were more viscous at pH <=4 than at pH 6 to 11. At pH 7, a biphasic effect of metal ion concentration on capsule viscosity was observed: (i) capsule viscosity increased with increasing metal ion concentration until a maximal viscosity occurred at a specific concentration that was a reproducible characteristic of each metal ion, and (ii) the viscosity decreased with further addition of that ion. Because the latter part of the biphasic curve was complicated by additional factors (especially the precipitation or gelation of capsule by divalent metal ions), the effects of various metal chlorides were compared for the former phase in which capsule viscosity increased in the presence of metal ions. Equivalent increases in capsule viscosity were observed with micromolar concentrations of divalent metal ions but only with 10 to 20 times greater concentrations of Na(sup+). The relative abilities of various metal salts to increase capsule viscosity were as follows: CdCl(inf2), Pb(NO(inf3))(inf2), FeCl(inf2) > MnCl(inf2) > CuCl(inf2), CaCl(inf2) >> NaCl. This pattern of metal efficacy resembles known cation influences on the structural integrity of capsule in naturally occurring and cultured M. flos-aquae colonies. The data are the first direct demonstration of an interaction between metal ions and purified M. flos-aquae capsule, which has previously been proposed to play a role in the environmental cycling of certain multivalent metals, especially manganese. The M. flos-aquae capsule and the plant polysaccharide pectin have similar sugar compositions but differ in their relative responses to various metals, suggesting that capsular polysaccharide could be a preferable alternative to pectin for certain biotechnological applications.

Thermotropic behavior of phospholipid bilayers interacting with metal ions at subzero region

Thermotropic phase behaviors of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylglycerol (DPPG), and ox brain phosphatidylserine (PS) interacting with metal ions (Ca 2+, Mg 2+, and Ba 2+) have been investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. It was found that the endothermic change in the range −20 to −30°C revealed a characteristic binding between phospholipids and metal ions. In the subzero region, DPPC, DPPE and PS showed a similar pattern to buffer blank solution where the thermograms varied with metal ion concentrations. However, the DPPG system in the subzero region showed no significant change in thermogram with increasing metal ion concentrations. It may be suggested that DPPG exists in a bound state with metal ions due to the lack of a new peak of concentrated metal ions in the subzero region. The metal ion effect on DPPG took place at the main phase transition temperature of gel to liquid crystalline phase of acyl chains corresponding to a higher temperature shift. In particular, the negative phospholipids of DPPG and PS showed quite different phase behaviors in the subzero region: DPPG showed no temperature shift, while PS revealed a remarkable shift to a lower temperature with increasing metal ion concentrations. This may imply that metal ions, especially Ca 2+ and Mg 2+, have been captured by DPPG through binding to phospholipid and/or to the interior of a vesicle, but predominantly free from PS.

A comparative study of the biosorption of lead(II) ions to Z. ramigera and R. arrhizus

Parameters that affected adsorption rates of lead(II) ions on Z. ramigera and R. arrhizus were investigated. The adsorption rates and equilibrium metal removal were strongly affected by pH, temperature, and initial metal concentration. Both micro-organisms exhibited the highest lead-adsorptive rate at pH 4.5–5.0. Maximum adsorption rates of metal ions to Z. ramigera and R. arrhizus were obtained at temperatures ranging from 25 to 45°C. The initial adsorption rate of metal ion increased with increasing metal ion concentration for Z. ramigera and R. arrhizus up to 150–200 mg litre −1 and 200–300 mg litre −1, respectively. Isotherms for the adsorption of lead on Z. ramigera and R. arrhizus were developed and Freundlich constants determined from the Freundlich adsorption isotherms.