Competitive adsorption of Pb, Cd and Zn ions onto Eichhornia crassipes in binary and ternary systems

A batch sorption technique was used to study the biosorption of Pb²⁺, Cd²⁺ and Zn²⁺ ions onto the vastly abundant water hyacinth weed, Eichhornia crassipes biomass in binary and ternary systems at a temperature of 30 °C and pH 4.84. Mutual interference effects were probed using equilibrium adsorption capacity ratios, , where the prime indicates the presence of one or two other metal ions. The combined action of the metals was found to be antagonistic, and the metal sorption followed the order Pb²⁺  Cd²⁺  Zn²⁺. The behaviour of competitive biosorption for Pb–Cd and Pb–Zn combinations were successfully described by the Langmuir Competitive Model (CLM), whilst the model showed poor fitting to the Cd–Zn data. In conclusion, Pb²⁺ ions could still be effectively removed from aqueous solution in the presence of both Cd²⁺ and Zn²⁺ ions, but removal of the Cd²⁺ and Zn²⁺ ions would be suppressed in the presence of Pb²⁺.     

Cd, Cu, Ni, Mn and Zn resistance and bioaccumulation by thermophilic bacteria, Geobacillus toebii subsp. decanicus and Geobacillus thermoleovorans subsp. stromboliensis

Bioaccumulation and heavy metal resistance of Cd²⁺, Cu²⁺, Ni²⁺, Zn²⁺ and Mn²⁺ ions by thermophilic Geobacillus toebii subsp. decanicus and Geobacillus thermoleovorans subsp. stromboliensis were investigated. The metal resistance from the most resistant to the most sensitive was found as Mn > Ni > Cu > Zn > Cd for both Geobacillus thermoleovorans subsp. stromboliensis and Geobacillus toebii subsp. decanicus. It was determined that the highest metal bioaccumulation was performed by Geobacillus toebii subsp. decanicus for Zn (36,496 μg/g dry weight cell), and the lowest metal bioaccumulation was performed by Geobacillus toebii subsp. decanicus for Ni (660.3 μg/g dry weight cell). Moreover, the dead cells were found to biosorbe more metal in their membranes compared to the live cells. In the presence of 7.32 mg/l Cd concentration, the levels of Cd absorbed in live and dead cell membranes were found as 17.44 and 46.2 mg/g membrane, respectively.     

Alkaline phosphatase conductometric biosensor for heavy-metal ions determination

Alkaline phosphatase conductometric biosensors consisting of interdigitated gold electrodes and enzyme membranes have been used for assessment of heavy-metal ions in water. These analytes act as enzyme inhibitors. Enzyme residual activity has been measured in Tris-nitrate buffer without metal preincubation in the presence of Mg²⁺ ions as activator. The results indicate that the toxicity of the various metals tested toward immobilized phosphatase is ranged as follows: Cd²⁺ > Co²⁺ > Zn²⁺ > Ni²⁺ > Pb²⁺. Detection limits were about 0.5 ppm for Cd²⁺, 2 ppm for both Zn²⁺ and Co²⁺, 5 ppm for Ni²⁺ and 40 ppm for lead ions. In addition, the responses during 10 h were stable (RSD 4%) and a drift of about 7% per day was observed. The storage stability in buffer solution at 4 °C remained stable for more than one month.     

Biochemical Characterization of Allantoinase from <Emphasis Type="Italic">Escherichia coli</Emphasis> BL21

Bacterial allantoinase (ALLase; EC 3.5.2.5), which catalyzes the conversion of allantoin into allantoate, possesses a binuclear metal center in which two metal ions are bridged by a posttranslationally carboxylated lysine. Here, we characterized ALLase from Escherichia coli BL21. Purified recombinant ALLase exhibited no activity but could be activated when preincubating with some metal ions before analyzing its activity, and was in the order: Mn²⁺- ≫ Co²⁺- > Zn²⁺- > Ni²⁺- > Cd²⁺- ~Mg²⁺-activated enzyme; however, activity of ALLase (Mn²⁺-activated form) was also significantly inhibited with 5 mM Co²⁺, Zn²⁺, and Cd²⁺ ions. Activity of Mn²⁺-activated ALLase was increased by adding the reducing agent dithiothreitol (DTT), but was decreased by treating with the sulfhydryl modifying reagent N-ethylmaleimide (NEM). Inhibition of Mn²⁺-activated ALLase by chelator 8-hydroxy-5-quinolinesulfonic acid (8-HQSA), but not EDTA, was pH-dependent. Analysis of purified ALLase by gel filtration chromatography revealed a mixture of monomers, dimers, and tetramers. Substituting the putative metal binding residues His59, His61, Lys146, His186, His242, and Asp315 with Ala completely abolished the activity of ALLase, even preincubating with Mn²⁺ ions. On the basis of these results, as well as the pH-activity profile, the reaction mechanism of ALLase is discussed and compared with those of other cyclic amidohydrolases.     

Probing the coordination properties of glutathione with transition metal ions (Cr2+,Mn2+,Fe2+,Co2+, Ni2+,Cu2+,Zn2+,Cd2+,Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr²⁺, Mn²⁺,Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺,Hg²⁺) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu²⁺>Ni²⁺>Co²⁺>Fe²⁺>Cr²⁺>Zn²⁺>Mn²⁺; and for the same group of metal ions, the general trend of binding energies was Zn²⁺>Hg²⁺>Cd²⁺. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺ and Hg²⁺ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr²⁺ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu²⁺, Ni²⁺,Co²⁺ and Hg²⁺ had obvious tendencies to be reduced to Cu⁺,Ni⁺,Co⁺ and Hg⁺ during the coordination process.     

A micro-scale method for determining relative metal-binding affinities of proteins

This article describes a quick and easy method for determining relative binding affinities between proteins and metal ions. The method is based on separating unbound metal ions from metal ions bound to protein by ultrafiltration using microcentrifuge ultrafiltration units. Bovine serum albumin (BSA) was used as the test protein and the relative affinity towards divalent metal ions was found to be Cu²⁺>Zn²⁺>Cd²⁺>Pb²⁺>Ni²⁺>Co²⁺, which corresponds to the relative orders reported in the literature.     

Biosorption of Cd, Cu, Pb, and Zn from aqueous solutions by the fruiting bodies of jelly fungi (Tremella fuciformis and Auricularia polytricha)

In this study, dried and humid fruiting bodies of Tremella fuciformis and Auricularia polytricha were examined as cost-effective biosorbents in treatment of heavy metals (Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺) in aqueous solution. The humid T. fuciformis showed the highest capacity to adsorb the four metals in the multi-metal solutions. The Pb²⁺ adsorption rates were 85.5%, 97.8%, 84.8%, and 91.0% by dried T. fuciformis, humid T. fuciformis, dried A. polytricha, and humid A. polytricha, respectively. The adsorption amount of Pb²⁺ by dried and humid T. fuciformis in Cd²⁺ + Pb²⁺, Cu²⁺ + Pb²⁺, Pb²⁺ + Zn²⁺, Cd²⁺ + Cu²⁺ + Pb²⁺, and Cd²⁺ + Zn²⁺ + Pb²⁺ solutions were not lower than that in Pb²⁺ solutions. The results suggested that in humid T. fuciformis, Cd²⁺, Cu²⁺, and Zn²⁺ promoted the Pb²⁺ adsorption by the biomass. In the multi-metal solutions of Cd²⁺ + Cu²⁺ + Pb²⁺ + Zn²⁺, the adsorption amount and rates of the metals by all the test biosorbents were in the order of Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺. Compared with the pseudo first-order model, the pseudo second-order model described the adsorption kinetics much better, indicating a two-step biosorption process. The present study confirmed that fruiting bodies of the jelly fungi should be useful for the treatment of wastewater containing Cd²⁺, Cu²⁺, Pb²⁺, and Zn²⁺.     

Characterization of a metal resistant Pseudomonas sp. isolated from uranium mine for its potential in heavy metal (Ni2+, Co2+, Cu2+, and Cd2+) sequestration

Heavy metal sequestration by a multimetal resistant Pseudomonas strain isolated from a uranium mine was characterized for its potential application in metal bioremediation. 16S rRNA gene analysis revealed phylogenetic relatedness of this isolate to Pseudomonas fluorescens. Metal uptake by this bacterium was monophasic, fast saturating, concentration and pH dependent with maximum loading of 1048 nmol Ni²⁺ followed by 845 nmol Co²⁺, 828 nmol Cu²⁺ and 700 nmol Cd²⁺ mg^?1 dry wt. Preferential metal deposition in cell envelope was confirmed by TEM and cell fractionation. FTIR spectroscopy and EDX analysis revealed a major role of carboxyl and phosphoryl groups along with a possible ion exchange mechanism in cation binding. Binary system demonstrated selective metal binding affinity in the order of Cu²⁺ > Ni²⁺ > Co²⁺ > Cd²⁺. A comparison with similar metal uptake reports considering live bacteria strongly indicated the superiority of this strain in metal sequestration, which could be useful for developing efficient metal removal system.     

Heterologous Expression and Metal-Binding Characterization of a Type 1 Metallothionein Isoform (OsMTI-1b) from Rice (Oryza sativa)

Metallothioneins (MTs) are ubiquitous, low molecular mass and cysteine-rich proteins that play important roles in maintaining intracellular metal homeostasis, eliminating metal toxification and protecting the cells against oxidative damages. MTs are able to bind metal ions through the thiol groups of their cysteine residues. Plants have several MT isoforms which are classified into four types based on the arrangement of cysteine residues. In the present study, a rice (Oryza sativa) gene encoding type 1 MT isoform, OsMTI-1b, was inserted in vector pET41a and overexpressed in Escherichia coli as carboxy-terminal extensions of glutathione-S-transferase (GST). The recombinant protein GST-OsMTI-1b was purified using affinity chromatography and its ability to bind with Ni²⁺, Cd²⁺, Zn²⁺ and Cu²⁺ ions was analyzed. The results demonstrated that this isoform has ability to bind Ni²⁺, Cd²⁺ and Zn²⁺ ions in vitro, whereas it has no substantial ability to bind Cu²⁺ ions. From competitive reaction with 5,5′-dithiobis(2-nitrobenzoic acid), DTNB, the affinity of metal ions for recombinant form of GST-OsMTI-1b was as follows: Ni²⁺/Cd²⁺ > Zn²⁺ > Cu²⁺     

The interaction of zinc, nickel and cadmium with serum albumin and histidine-rich glycoprotein assessed by equilibrium dialysis and immunoadsorbent chromatography

Human serum albumin (HSA) has been shown to bind 2–3 mol of Zn²⁺, Ni²⁺, or Cd²⁺ per mole of protein with apparent dissociation constants (K_d) in the range of 10 μm. Rabbit histidine-rich glycoprotein (HRG) binds 13, 9, and 6 mol of Zn²⁺, Ni²⁺, and Cd²⁺ per mole of protein, respectively, with apparent K_ds also near 10 μm. However, the binding of metals by HRG exhibits positive cooperativity, so that the apparent K_ds may underestimate HRGs true affinity for metal ions. The relative affinities of HSA and HRG for metal ions were found to be Zn²⁺ > Ni²⁺ > Cd²⁺. In addition, histidine (a serum metal chelator) affected the binding of Ni²⁺ by both proteins but not that of Zn²⁺ or Cd²⁺. At physiological concentrations of HSA (250 μm), HRG (2.5 μm), and histidine (100 μm), HRG bound 36% of the Zn²⁺, 9% of the Ni²⁺, and 13% of the Cd²⁺ at a total metal concentration of 25 μm. Under the same conditions HSA held 37% of the Zn²⁺, 14% of the Ni²⁺, and 56% of the Cd²⁺. Thus, HSA appears to have a lower intrinsic affinity for the three metals than HRG but would be expected to bind a higher proportion of these metals in serum. A specific immunoadsorbent column was prepared and used to study the metal binding by HRG in serum directly. Both ⁶⁵Zn²⁺ and ⁶³Ni²⁺ were associated with HRG in aliquots of rabbit serum after incubation with the corresponding metal ion. This evidence indicates that HRG must be considered as a metal binding component of serum.     

Comparative studies of zinc metabolism in cultured chinese hamster cells with differing metallothionein-induction capacities

Previous work in our laboratory led to the isolation of a cadmium (Cd)-resistant variant (Cd^r2C10) of the line CHO Chinese Hamster cell having a 10-fold greater resistance to the cytotoxic action of Cd²⁺ compared with the CHO cell. This resistance was attributed to an increased capacity of the Cd²⁺-resistant Cd^r2C10 subline to induce synthesis of the Cd²⁺- and Zn²⁺-binding protein(s), metallothionein(s) (MT). Evidence that Cd²⁺ behaves as an analog of the essential trace metal, Zn²⁺, especially as an inducer of MT synthesis, suggested that the Cd^r and CHO cell types could be employed to investigate cellular Zn²⁺ metabolism. In the present study, measurements were made to compare CHO and Cd^r cell types for (a) growth as a function of the level of ZnCl₂ added to the culture medium, (b) uptake and subcellular distribution of Zn²⁺, and (c) capacity to induce MT synthesis. The results of these measurements indicated that (a) both CHO and Cd^r cell types grew normally (T _d≊16–18 h) during exposures to Zn²⁺ at levels up to 100 μM added to the growth medium, but displayed abrupt growth inhibition at higher Zn²⁺ levels, (b) Cd^r cells incorporate fourfold more Zn²⁺ during a 24-h exposure to the maximal subtoxic level of Zn²⁺ and (c) the CHO cell lacks the capacity to induce MT synethesis while the Cd^r cell is proficient in this response during exposure to the maximal subtoxic Zn²⁺ level. These findings suggest that (a) the CHO and Cd^r cell systems will be useful in further studies of cellular Zn²⁺ metabolism, especially in comparisons of Zn²⁺ metabolism in the presence and absence of induction of the Zn²⁺-sequestering MT and (b) a relationship exists between cellular capacity to induce MT synthesis and capacity for cellular Zn²⁺ uptake.     

Luminescent sensor for Cd2+, Hg2+ and Ag+ in water based on a sulphur‐containing receptor: quantitative binding–softness relationship

A water‐soluble, high‐output fluorescent sensor, based on a lumazine ligand with a thiophene substituent for Cd²⁺, Hg²⁺ and Ag⁺ metal ions, is reported. The sensor displays fluorescence enhancement upon Cd²⁺ binding (log  β = 2.79 ± 0.08) and fluorescence quenching by chelating with Ag⁺ and Hg²⁺ (log β = 4.31 ± 0.15 and 5.42 ± 0.1, respectively). The mechanism of quenching is static and occurs by formation of a ground‐state non‐fluorescent complex followed by rapid intersystem crossing. The value of the Stern–Volmer quenching rate constant (k_q) by Ag⁺ ions is close to 6.71 × 10¹² mol/L/s at 298 K. The thermodynamic parameters (ΔG, ΔH and ΔS) were also evaluated and indicated that the complexation process is spontaneous, exothermic and entropically favourable. The quantitative linear relationship between the softness values of Klopman (σ_K) or Ahrland (σ_A) and the experimental binding constants (β) being in the order of Hg²⁺ > Ag⁺ > Cd²⁺ suggests that soft–soft interactions are the key for the observed sensitivity and selectivity in the presence of other metal ions, such as: Pb²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Co²⁺, Zn²⁺ and Mg²⁺ ions. Copyright © 2008 John Wiley & Sons, Ltd.     

Modeling the Zn and Cd metalation mechanism in mammalian metallothionein 1a

Mammalian metallothioneins (MTs) are a family of small cysteine rich proteins believed to have a number of physiological functions, including both metal ion homeostasis and toxic metal detoxification. Mammalian MTs bind 7 Zn²⁺ or Cd²⁺ ions into two distinct domains: an N-terminal β-domain that binds 3 Zn²⁺ or Cd²⁺, and a C-terminal α-domain that binds 4 Zn²⁺ or Cd²⁺. Although stepwise metalation to the saturated M₇-MT (where M = Zn²⁺ or Cd²⁺) species would be expected to take place via a noncooperative mechanism involving the 20 cysteine thiolate ligands, literature reports suggest a cooperative mechanism involving cluster formation prior to saturation of the protein. Electrospray ionization mass spectrometry (ESI-MS) provides this sensitivity through delineation of all species (M_n-MT, n = 0-7) coexisting at each step in the metalation process. We report modeled ESI-mass spectral data for the stepwise metalation of human recombinant MT 1a (rhMT) and its two isolated fractions for three mechanistic conditions: cooperative (where the binding affinities are: K₁ < K₂ < K₃ < ··· < K₇), weakly cooperative (where K₁ = K₂ = K₃ = ··· = K₇), and noncooperative, (where K₁ > K₂ > K₃ > ··· > K₇). Detailed ESI-MS metalation data of human recombinant MT 1a by Zn²⁺ and Cd²⁺ are also reported. Comparison of the experimental data with the predicted mass spectral data provides conclusive evidence that metalation occurs in a noncooperative fashion for Zn²⁺ and Cd²⁺ binding to rhMT 1a.     

The role of antioxidants enzymes of E. coli ASU3, a tolerant strain to heavy metals toxicity, in combating oxidative stress of copper

The current study describes the isolation and characterization of E. coli from wastewater that collected from El-Malah canal in Assiut, Egypt. Twelve isolates were investigated for heavy metal resistance by which one of them showed multiple metal resistances. Furthermore, the bacterium was identified as E. coli ASU3 according to biochemical tests and then, preserved at Assuit University Mycological Centre with accession number AUMC B83. It exhibited high minimal inhibitory concentrations for metals and antibiotic resistance. The order of metals toxicity to the bacterium was Cr⁶⁺ > Cu²⁺ > Co²⁺ > Pb²⁺ > Ni²⁺ > Cr³⁺ > Cd²⁺ > Zn²⁺. Total protein content of E. coli ASU3 decreased with the increase of copper concentration. Under exposure of different concentrations of copper, the induction of antioxidant enzymes such as catalase, peroxidase and ascorbate peroxidase was increased and these antioxidant enzymes can contribute to combating oxidative stresses.     

Gating of aquaporins by heavy metals in <Emphasis Type="Italic">Allium cepa</Emphasis> L. epidermal cells

Changes in the water permeability, aquaporin (AQP) activity, of leaf cells were investigated in response to different heavy metals (Zn²⁺, Pb²⁺, Cd²⁺, Hg²⁺). The cell pressure probe experiments were performed on onion epidermal cells as a model system. Heavy metal solutions at different concentrations (0.05 μM–2 mM) were used in our experiments. We showed that the investigated metal ions can be arranged in order of decreasing toxicity (expressed as a decrease in water permeability) as follows: Hg>Cd>Pb>Zn. Our results showed that β-mercaptoethanol treatment (10 mM solution) partially reverses the effect of AQP gating. The magnitude of this reverse differed depending on the metal and its concentration. The time course studies of the process showed that the gating of AQPs occurred within the first 10 min after the application of a metal. We also showed that after 20–40 min from the onset of metal treatment, the water flow through AQPs stabilized and remained constant. We observed that irrespective of the metal applied, the effect of AQP gating can be recorded within the first 10 min after the administration of metal ions. More generally, our results indicate that the toxic effects of investigated metal ions on the cellular level may involve AQP gating.     

Inhibition of proton-transfer steps in transhydrogenase by transition metal ions

Transhydrogenase couples proton translocation across a bacterial or mitochondrial membrane to the redox reaction between NAD(H) and NADP(H). Purified intact transhydrogenase from Escherichia coli was prepared, and its His tag removed. The forward and reverse transhydrogenation reactions catalysed by the enzyme were inhibited by certain metal ions but a “cyclic reaction” was stimulated. Of metal ions tested they were effective in the order Pb²⁺ > Cu²⁺ > Zn²⁺ = Cd²⁺ > Ni²⁺ > Co²⁺. The results suggest that the metal ions affect transhydrogenase by binding to a site in the proton-transfer pathway. Attenuated total-reflectance Fourier-transform infrared difference spectroscopy indicated the involvement of His and Asp/Glu residues in the Zn²⁺-binding site(s). A mutant in which βHis91 in the membrane-spanning domain of transhydrogenase was replaced by Lys had enzyme activities resembling those of wild-type enzyme treated with Zn²⁺. Effects of the metal ion on the mutant were much diminished but still evident. Signals in Zn²⁺-induced FTIR difference spectra of the βHis91Lys mutant were also attributable to changes in His and Asp/Glu residues but were much smaller than those in wild-type spectra. The results support the view that βHis91 and nearby Asp or Glu residues participate in the proton-transfer pathway of transhydrogenase.     

重金属铜、锌、镉复合胁迫对麻疯树幼苗生理生化的影响

该研究以Cu~(2+)、Zn~(2+)、Cd~(2+)单一胁迫为对照,探讨不同浓度的Cu~(2+)、Zn~(2+)、Cd~(2+)复合胁迫对麻疯树幼苗生理生化指标的影响。结果表明:随着Cu~(2+)、Zn~(2+)、Cd~(2+)浓度的增加,麻疯树幼苗叶片中的蛋白质(Pro)、丙二醛(MDA)含量均逐渐增加,其叶片叶绿素含量随着Zn~(2+)胁迫浓度的增加呈现出先降后升的趋势,在中等浓度(100 mg·L-1)的Zn~(2+)胁迫时含量最低、随着Cu~(2+)胁迫浓度的增加叶绿素含量先升高后降低,在Cu~(2+)浓度为200 mg·L-1时含量最高,达到1 200 mg·g-1FW; Cd~(2+)胁迫对叶绿素含量和根系活力无明显影响。根系活力在Zn~(2+)浓度为100 mg·L~(-1)时最强,随着Cu~(2+)浓度的增加而减弱。低浓度的Cu~(2+)、Zn~(2+)、Cd~(2+)对过氧化物酶活性和可溶性糖含量都具有促进作用。Cu~(2+)、Zn~(2+)、Cd~(2+)复合胁迫时对可溶性蛋白、叶绿素和丙二醛含量均无明显影响,随着复合胁迫时浓度的增加,可溶性糖含量和根系活力先增后减。这表明麻疯树对三种重金属的胁迫具有一定的抗性,过高浓度的胁迫会影响麻疯树幼苗生理生化的一些指标,但是麻疯树可以通过自身的防御系统使伤害降到最小。此外,重金属复合胁迫可以在一定程度上减轻单一胁迫对麻疯树幼苗造成的毒害作用。     

Effects of heavy metals on the Ca2+-ATPase activity present in gill cell plasma-membrane of mussels (Mytilus galloprovincialis Lam.)

1. Heavy metals (Hg²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺) at micromolar concentrations strongly inhibit the Ca²⁺-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate.2. All the heavy metals tested inhibit the Ca²⁺-ATPase activity, the effect following the order: Hg²⁺ > Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺; the simultaneous addition of different heavy metals causes a summatory inhibition of the enzyme activity; addition to the reaction mixture of GSH at a final concentration of 0.5 mM, reverses inhibitory effects of heavy metals.3. The inhibitory effects of Cu²⁺ on Ca²⁺-ATPase are highly enhanced by addition of ascorbate to the reaction mixture. In the presence of ascorbate (100 μM), copper strongly stimulates the lipid peroxidation damage of the gill plasma-membranes, a result that may explain the high copper cytotoxicity.     

‘Turn‐on’ fluorescent chemosensors based on naphthaldehyde‐2‐pyridinehydrazone compounds for the detection of zinc ion in water at neutral pH

A series of naphthaldehyde‐2‐pyridinehydrazone derivatives were discovered to display interesting ‘turn‐on’ fluorescence response to Zn²⁺ in 99% water/DMSO (v/v) at pH 7.0. Mechanism study indicated that different substituent groups in the naphthaldehyde moiety exhibited significant influence on the detection of Zn²⁺. The electron rich group resulted in longer fluorescence wavelengths but smaller fluorescence enhancement for Zn²⁺. Among these compounds, 1 showed the highest fluorescence enhancement of 19‐fold with the lowest detection limit of 0.17 μmol/L toward Zn²⁺. The corresponding linear range was at least from 0.6 to 6.0 μmol/L. Significantly, 1 showed an excellent selectivity toward Zn²⁺ over other metal ions including Cd²⁺.     

Effects of Cd2+, Mn2+, and Al3+ on rat brain synaptosomal uptake of noradrenaline and serotonin

Cd²⁺, Mn²⁺, and Al³⁺ inhibited synaptosomal amine uptake in a concentration-dependent and time-dependent manner. In the absence of Ca²⁺, the rank order of inhibition of noradrenaline uptake was: Cd²⁺ (IC₅₀ = 250 μM) > Al³⁺ (IC₅₀ = 430 μM) > Mn²⁺ (IC₅₀ = 1.50 mM), the IC₅₀ being the concentration of metal ions that gave rise to 50% inhibition of uptake. In the presence of 1 mM Ca²⁺, the rank order of inhibition of uptake was: Al³⁺ (IC₅₀ = 330 μM) > Cd²⁺ (IC₅₀ = 540 μM) > (IC₅₀ = 1.5 mM). The rank order of inhibition of serotonin uptake without Ca²⁺ was: Al³⁺ (IC₅₀ = 370 μM) > Cd²⁺ (IC₅₀ = 610 μM) > Mn²⁺ (IC₅₀ = 3.4 mM) and the rank order in the presence of 1 mM Ca²⁺ was: Al³⁺ (IC₅₀ = 290 μM) > Cd²⁺ (IC₅₀ = 1.5 mM) > Mn²⁺ (IC₅₀ = 4.0 mM). Ca²⁺, at 1 mM, definitely antagonized the inhibitory actions of Cd²⁺ on noradrenaline and serotonin uptake. Al³⁺ stimulated noradrenaline uptake at concentrations around 20–250 μM but inhibited this uptake at concentrations exceeding 300 μM in a dose-related fashion. Ca²⁺, at 1 mM, enhanced both the stimulatory and inhibitory effects of Al³⁺. Ca²⁺ also enhanced the inhibitory actions of Al³⁺ on seotonin uptake. These results, in conjunction with those we have previously published, suggest that Cd²⁺, Mn²⁺, and Al³⁺ exert differential and selective effects on the structure and function of synaptosomal membranes.