Absence Of Zn Research Articles

Trace metal limitations (Co, Zn) increase PIC/POC ratio in coccolithophore Emiliania huxleyi

Abstract The effect of cobalt (Co), zinc (Zn) or cadmium (Cd) availability on the growth and particulate inorganic (PIC) to organic (POC) carbon ratio of the cosmopolitan coccolithophore Emiliania huxleyi was examined using batch cultures. Growth co-limitation by Co and Zn occurred at low free metal ion concentrations below 10–12 pM. The two metals could replace one another in biochemical functions: full replacement of Zn by Co was possible, but the 20% higher growth rate observed with high Co levels in the absence of Zn than observed in the presence of high Zn but no added Co suggested that there was an absolute growth requirement of Co that could only partly be met by Zn. In contrast, Cd had no effect on growth in the absence of Co and Zn, indicating that this strain cannot use Cd under these conditions. The co-limitation by inorganic Co and Zn led to highly calcified cells containing a large quota of nitrogen, but diminished organic carbon content, likely due to a lower photosynthetic production rate. Deficiency of Zn and Co cofactors could have dramatically decreased the activity of carbonic anhydrase, lowering CO2 availability for photosynthesis. In contrast to the large decreases in carbon fixation rates at low Zn and Co ion concentrations, calcification rates were unaffected at low Zn levels and were only minimally decreased by low Co. As a result the PIC:POC ratios in E. huxleyi increased by up to 8-fold under Zn limitation and 3–5-fold under Co limitation to values where coccolithophores act as a source of atmospheric CO2. As a result, low Co and Zn availability in seawater could affect the efficiency of the biological carbon pump, and atmospheric CO2 levels. Thus, the impact of Co and Zn limitation may need to be considered to improve assessments of the impact of E. huxleyi and other biogenic calcifiers on oceanic sequestration of CO2.

Graphitization reaction via zinc reduction: How low can you go?

In a previous work, isotopic fractionation in the graphitization reaction for Radiocarbon Accelerator Mass Spectrometry (14C-AMS) was evaluated for amounts of Zn ranging from 20 to 50mg. The results have shown that a slightly lower variation in δ3C during graphitization was achieved with less Zn. In the present paper, assuming that low amounts of Zn would provide the best results, we go further and test isotopic fractionation for 0, 10 and 20mg of Zn in the graphitization reaction. The results show that the use of 10mg of Zn yields similar fractionation to that using 20mg, while using only TiH2 and no Zn produces the same scattering for amounts from 30 to 50mg. The absence of Zn, on the other hand, plays a major role on the reaction yield for the tested conditions, limiting it to 50%.

Reversible Insulin Hexamer Assembly Promoted by Ethyl Violet: pH-Controlled Uptake and Release.

Therapeutically improved long-acting insulin preparations require in-depth understanding of the hexamer assembly, structural selectivity, and its stability in solution. This Letter demonstrates, for the first time, an efficient method for the hexamerization of human insulin by a structure-specific triphenylmethane (TPM) dye, Ethyl Violet (EV), particularly, in the absence of Zn2+. Upon detailed spectroscopic evaluation and comparison with other TPM homologues, we establish that the diethylamino phenyl arms of EV are specific and effective in clipping the three dimer helices in a hexameric assembly. We establish that at physiological pH 7.4 and in the presence of the EV, insulin exists predominantly in its hexameric form, a condition appropriate for storage and preparation of long-acting insulin formulations. On the other hand, the disassembly of the hexamer into the monomeric form is accomplished at pH 5, highlighting its potential as a delivery vehicle for such custom-modified dyes/drugs.

Cis→Trans Isomerization of Pro(7) in Oxytocin Regulates Zn(2+) Binding.

Ion mobility/mass spectrometry techniques are employed to investigate the binding of Zn(2+) to the nine-residue peptide hormone oxytocin (OT, Cys(1)-Tyr(2)-Ile(3)-Gln(4)-Asn(5)-Cys(6)-Pro(7)-Leu(8)-Gly(9)-NH2, having a disulfide bond between Cys(1) and Cys(6) residues). Zn(2+) binding to OT is known to increase the affinity of OT for its receptor [Pearlmutter, A. F., Soloff, M. S.: Characterization of the metal ion requirement for oxytocin-receptor interaction in rat mammary gland membranes. J. Biol. Chem. 254, 3899-3906 (1979)]. In the absence of Zn(2+), we find evidence for two primary OT conformations, which arise because the Cys(6)-Pro(7) peptide bond exists in both the trans- and cis-configurations. Upon addition of Zn(2+), we determine binding constants in water of KA = 1.43 ± 0.24 and 0.42 ± 0.12 μM(-1), for the trans- and cis-configured populations, respectively. The Zn(2+) bound form of OT, having a cross section of Ω = 235 Å(2), has Pro(7) in the trans-configuration, which agrees with a prior report [Wyttenbach, T., Liu, D., Bowers, M. T.: Interactions of the hormone oxytocin with divalent metal ions. J. Am. Chem. Soc. 130, 5993-6000 (2008)], in which it was proposed that Zn(2+) binds to the peptide ring and is further coordinated by interaction of the C-terminal, Pro(7)-Leu(8)-Gly(9)-NH2, tail. The present work shows that the cis-configuration of OT isomerizes to the trans-configuration upon binding Zn(2+). In this way, the proline residue regulates Zn(2+) binding to OT and, hence, is important in receptor binding. Graphical Abstract ᅟ.

Self-Assembled Pyridine-Dipyrrolate Cages.

An inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bis(3,4-diethyl-5-carboxy-1H-pyrrol-2yl)pyridine (compound 1), is able to distinguish between different zinc(II) cation sources, namely Zn(acac)2 and Zn(OAc)2, respectively. This differentiation is manifest both in terms of the observed fluorescent behavior in mixed organic media and the reaction chemistry. Treatment of 1 with Zn(acac)2 gives rise to a cage dimer, cage-1, wherein two molecules of compound 1 act as double bridging units to connect two individual cage subunits. As inferred from X-ray crystallographic studies, this cage system consists of discrete zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. When a different zinc source, Zn(OAc)2, is used to carry out an ostensibly similar complexation reaction with compound 1, an acetate-bridged 1D abacus-like cage polymer is obtained as inferred from X-ray diffraction analysis. This extended solid state structure, cage-2, contains individual zinc dimer cage submits and appears stabilized by solvent molecules (DMF) and the counteranion (acetate). Rod-like assemblies are also observed by DLS and SEM. This construct, in contrast to cage-1, proved fluorescent in mixed organic media. The structure of the ligand itself (i.e., in the absence of Zn(II)) was confirmed by X-ray crystallographic analysis and was found to assemble into a supramolecular polymer. Conversion to a dimer form was seen upon the addition of TBAOAc. On the basis of the metric parameters, the structures seen in the solid state are stabilized via hydrogen bonding interactions involving solvent molecules.

A ratiometric fluorescent chemosensor for Zn2+ in aqueous solution through an ESIPT coupled AIE process

In this study, an efficient chemosensor (HL) has been designed and synthesized based on bis–Schiff base. The sensor could detect Zn2+ ions in a ratiometric way, which might be mainly due to an ESIPT coupled AIE process. In the absence of Zn2+, the sensor displays fluorescence emission at 500nm, on addition of Zn2+ to an aqueous solution of HL, the sensor shows significant fluorescence enhancement at 457nm. More importantly, the detection limit for Zn2+ can reach at 10−7M level.

Label-free Detection of Zn(2+) Based on G-quadruplex.

Herein, we developed a sensing strategy for the label-free detection of Zn(2+) based on G-quadruplex. In the absence of Zn(2+), there was a fluorescence enhancement of thioflavin T by interaction with human telomere sequence. On the addition of Zn(2+), Zn(2+) induced a more compact G-quadruplex structure to release thioflavin T, resulting in a fluorescence decrease. This simple "mix-then-detect" method gave the detection limit of 0.91 μM with linear dynamic ranges from 0 to 10 μM. Because it does not require the use of expensive and unstable DNAzyme systems, or need synthesis and modification of nanomaterials, this label-free biosensor is simple, fast, cost-effective and applicable for real samples taken from lake water.

Zinc affects miR-548n, SMAD4, SMAD5 expression in HepG2 hepatocyte and HEp-2 lung cell lines.

MicroRNAs affect disease progression and nutrient status. miR-548n increased 57 % in Zn supplemented plasma from adolescent females (ages 9 to 13 years). The purpose of this study was to determine the effects of Zn concentration in cell culture on the expression of miR-548n, SMAD4 and SMAD5 in hepatocyte (HepG2) and lung epithelium (HEp-2) cell lines. Cells were incubated for 48 h in media containing 10 % Chelex 100-treated FBS (0 μM Zn), or with 15 or 50 μM Zn, before isolation of total RNA and cDNA. Expression of miR-548n, SMAD4 and SMAD5 was measured by qPCR. The ΔΔCT method was used to calculate the fold-change, and 15 µM expression levels were used as reference values. HepG2 miR-548n expression decreased 5-fold, and SMAD4 expression increased 4-fold in the absence of Zn, while HEp-2 miR-548n expression increased 10.5-fold, and SMAD5 expression increased 20-fold in the absence of Zn. HEp-2 miR-548n expression increased 23-fold, while SMAD4 expression decreased twofold, in 50 μM Zn-treated cells. However, SMAD4 and SMAD5 expression was not correlated. These data indicate that miR-548n expression is in part regulated by Zn in a cell-specific manner. SMAD4 and SMAD5 are genes in the TGF-β/BMP signaling pathway, and SMAD5 is a putative target for miR-548n; Zn participates in regulating this pathway through controlling SMAD4 and SMAD5 expression. However, SMAD5 expression may be more sensitive to Zn than to miR-548n since SMAD5 expression was not inversely correlated with miR-548n expression.

Effect of a Procaspase-Activating Compound on the Catalytic Activity of Mature Caspase-3

Abstract Caspase-3, an apoptosis-executing enzyme with a dimeric structure, and its zymogen (procaspase-3) are target proteins in cancer chemotherapy using synthetic compounds. Previous work has shown that PAC-1 (1st procaspase-activating compound) affects the activation of procaspase-3 in cancerous cells through the Zn2+-chelation mechanism. However, we found that the compound also enhances the mature caspase-3 activity in the absence of Zn2+. The enhancement of the mature caspase-3 activity by PAC-1 followed a Michaelis–Menten-type saturation dependency with respect to the concentration of the compound. PAC-1 induced the change in the UV–vis spectrum of the mature caspase-3. From these findings, we propose a direct structural interaction of PAC-1 with the protein core. According to a molecular dynamics calculation for the complex of PAC-1 and mature caspase-3, PAC-1 is likely to bind to the interface between the dimeric structure in mature caspase-3. The interactions between PAC-1 and amino acid residues that affect the catalytic activity of mature caspase-3 are suggested. Throughout this work, diverse functions of the apoptosis-inducing compound are disclosed.

Assessment of salinity tolerance threshold for two wheat genotypes in response to zinc

Plants’ tolerance to salt stress is different among species, nevertheless, mineral nutrition might also affect it. A greenhouse experiment was conducted to evaluate the effect of Zinc (Zn) on salinity tolerance using a sigmoid response model in two wheat (Triticum aestivum L.) genotypes ‘Falat’ and ‘Bam’ with different salinity tolerances. The treatments consisted of three Zn rates (0, 5 and 10 mg Zn kg−1) and five levels of soil salinity (1.1, 6.5, 12.3, 18.7 and 25.1 dS m−1). The results showed that dry weight of straw and grain decreased, as salinity increased in both genotypes although this decrease in ‘Falat’ genotype was higher than that of ‘Bam’ genotype. Application of 10 mg kg−1 Zn increased the dry weight by 25% (straw) and 32% (grain) in ‘Falat’ but 67% (straw) and 60% (grain) in ‘Bam’ as compared with the absence of added Zn. According to the fitted function, in the absence of Zn, grain production began to decline at ECe-values of 4.7 dS m−1 in ‘Falat’ genotype, and 7.5 dS m−1 in ‘Bam’ genotype. Application of Zn led to a decrease of salinity tolerance in ‘Falat’ genotype, but an increase in ‘Bam’ genotype. The study found that Zn application under saline conditions, depending on genetic differences of wheat genotypes, would have different effects on their tolerance to salinity.

Zinc significantly changes the aggregation pathway and the conformation of aggregates of human prion protein

Prion diseases are caused by the conformational change of cellular prion protein PrPC into pathological prion protein PrPSc. Here we study the effect of zinc on the aggregation and conformational change of human prion protein (PrP). As revealed by thioflavin T binding assays, Sarkosyl-soluble SDS-PAGE, and transmission electron microscopy, aggregation of wild-type PrP in the absence of Zn2+ undergoes four steps: amorphous aggregates, profibrils, mature fibrils, and fragmented fibrils. When the molar ratio of Zn2+ to PrP was 9:1, however, aggregation of wild-type PrP undergoes another pathway in which wild-type PrP forms oligomers quickly and then forms short-rod aggregates. Unlike wild-type PrP, the octarepeats deletion mutant PrPΔocta forms typical mature fibrils either with or without zinc. As evidenced by isothermal titration calorimetry, Fourier transform infrared spectroscopy, and proteinase K digestion assays, Zn2+ strongly binds to wild-type PrP monomers with the first binding constant exceeding 107M−1 under denaturing conditions, and changes the conformation of wild-type PrP aggregates remarkably, but weakly binds to PrPΔocta with binding affinity around 104M−1 and has no obvious effects on the conformation of PrPΔocta aggregates. Our data demonstrate that zinc significantly changes the aggregation pathway and the conformation of wild-type PrP aggregates mainly via interaction with its octarepeat region. Our findings could explain how zinc modifies pathological PrP conformation associated with prion diseases.

The Interplay between Zinc, Vitamin D and, IL-17 in Patients with Chronic Hepatitis C Liver Disease.

Objectives. To assess zinc (Zn) and vitamin D (Vit. D) status in chronic Hepatitis C virus- (HCV) infected patients and their relationship to interleukin- (IL-) 17 and disease severity and then investigate whether Zn and Vit. D3 modulate IL-17 expression in chronic HCV patients. Methods. Seventy patients and fifty healthy subjects were investigated. Serum levels of Zn, Vit. D, and IL-17 were assessed in the patients group and subgroups. Patients lymphocytes were activated in vitro in the presence or absence of Zn or Vit. D3 and then intracellular IL-17 production was assessed using flow cytometry. Results. Zn and Vit. D were significantly decreased in HCV patients. Increasing disease severity leads to more reduction in Zn level opposed by increasing IL-17 level. Zn potently reduced IL-17 production in a dose-related fashion; however it did not exert any toxic effects. Although Vit. D apparently increases IL17 expression, it is unclear whether it is due to its toxic effect on cell count or lack of definite association between Vit. D and both IL-17 and disease severity. Conclusions. This study demonstrates that Zn modulates IL-17 expression and provides a rationale for evaluating this compound as a supplementary agent in the treatment of chronic HCV.

Mechanisms behind bacteria induced plant growth promotion and Zn accumulation in Brassica juncea

The growth and metal-extraction efficiency of plants exposed to toxic metals has been reported to be enhanced by inoculating plants with certain bacteria but the mechanisms behind this process remain unclear. We report results from glasshouse experiments on Brassica juncea plants exposed to 400mgZnkg−1 that investigated the abilities of Pseudomonas brassicacearum and Rhizobium leguminosarum to promote growth, coupled with synchrotron based μXANES analysis to probe Zn speciation in the plant roots. P. brassicacearum exhibited the poorest plant growth promoting ability, while R. leguminosarum alone and in combination with P. brassicacearum enhanced plant growth and Zn phytoextraction. Reduced growth in un-inoculated plants was attributed to accumulation of Zn oxalate and Zn sulfate in roots. In plants inoculated with P. brassicacearum the high concentration of Zn polygalacturonic acid in the root may be responsible for the stunted growth and reduced Zn phytoextraction. The improved growth and increased metal accumulation observed in plants inoculated with R. leguminosarum and in combination with P. brassicacearum was attributed to the storage of Zn in the form of Zn phytate and Zn cysteine in the root. When combined with the observation that both bacteria do not statistically improve B. juncea growth in the absence of Zn, this work suggests that bacteria-induced metal chelation is the key mechanism of plant growth promoting bacteria in toxicity attenuation and microbial-assisted phytoremediation.

Effect of Fe and Zn promoters on Mo/HZSM-5 catalyst for methane dehydroaromatization

The promotional effect of Fe in the presence and absence of Zn was studied over Mo/HZSM-5 catalysts for the methane dehydroaromatization reaction. The reaction was conducted at 700°C, 3000scc/g/h and atmospheric pressure. Adding Fe as the only promoter increased the benzene formation rate by 35% compared to unpromoted Mo after 12h of reaction time. With Zn as the only promoter the benzene formation rate was initially slightly higher (up to 10%); however, after 3h it performed similarly to the unpromoted Mo catalyst. When Mo/HZSM-5 was promoted with both Fe and Zn a significant drop (31%) in benzene formation was observed. Temperature programmed oxidation of the spent catalysts suggested that unhydrogenated, high-temperature carbon plays a role in catalyst deactivation of Fe–Zn promoted Mo/HZSM-5 catalyst. Further, Zn-loaded catalysts had a higher formation rate of ethylene, with and without Fe, compared to MoFe catalyst, possibly due to coke formation associated with Zn. Characterization of the catalysts suggested the presence of two types of Zn species. The first type is likely a loosely bound, unstable ZnO, which was reduced and vaporized during the reaction. This was supported by elemental microanalysis of spent catalysts, which showed that more than 50% of Zn was lost during the reaction testing. The second type of Zn is more strongly bound to HZSM-5. This is consistent with the NH3-TPD results, where significantly fewer Bronsted acid sites were observed after Zn addition to Mo catalyst. The catalysts were also characterized by XRD, SEM, surface area and micropore analysis, and the correlation between performance and catalyst properties is discussed.

Biophysical characterization of 21.5-kDa myelin basic protein (MBP) and the effects of zinc on its structure

Myelin Basic Protein (MBP) is a highly abundant protein in central nervous system (CNS) myelin that has a critical role in its proper formation and functioning. The 21.5-kDa isoform of MBP has been shown to be selectively imported into the nucleus of myelin-producing cells, oligodendrocytes, and may be involved in signaling pathways that affect the formation and recovery of CNS myelin. The first step in understanding potential nuclear binding partners of 21.5-kDa MBP is to characterize the structure of the protein. In this study, circular dichroism and fluorescence spectroscopy were used to analyze the structure of 21.5-kDa rmMBP (recombinant murine MBP) in vitro in the presence and absence of Zn2+, an abundant trace metal in CNS myelin that has been suggested to affect MBP structure. Fluorescence spectroscopy with a probe for hydrophobic protein regions showed that Zn2+ may affect the conformation of 21.5-kDa MBP in aqueous solution.
 
 Keywords: myelin basic protein (MBP); intrinsically-disordered protein; circular dichroism; fluoresence spectroscopy

Zn(II) sequestration by fungal biogenic manganese oxide through enzymatic and abiotic processes

Here, we examined the ability of biogenic manganese oxide (BMO), formed in the cultures of a Mn(II) oxidizing fungus Acremonium strictum strain KR21-2, to sequester Zn(II) in the presence and absence of extra Mn(II) and found that BMOs sequester Zn(II) through various paths involving enzymatic and abiotic processes. Newly formed BMOs were observed to effectively sequester Zn(II), with virtually no release of Mn(II), when treated with Zn(II) in 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES) buffer (pH7.0) under aerobic conditions. Under anaerobic conditions, smaller amounts of Zn(II) were sequestered, whereas a significant amount of Mn(II) was released. Similar trends were observed when the BMOs were heated at 85°C for 1h to inactivate the Mn(II) oxidase associated with the BMOs. Combined with a two-step extraction of the resulting solid phase, these results demonstrated that the Mn(II) oxidase associated with BMOs can oxidize Mn(II) which is released through an ion exchange at the BMO surface and can subsequently reduce the competition for sorption with released Mn(II). Assays using the concentrated Mn(II) oxidase crude solution indicated that coexisting Zn(II) had a decreased inhibitory effect on enzymatic Mn(II) oxidation if the preformed Mn oxide phase was present. XRD revealed that no alteration of the bulk structure occurred after Zn(II) treatment under either aerobic or anaerobic conditions. When the newly formed BMOs were repeatedly treated with mixed solutions of Zn(II) and Mn(II), the Mn(II) was effectively oxidized to an oxide phase, thereby sequestering Zn(II). The XRD of the resulting solid phases indicated the formation of woodruffite (ZnMn3IVO7·2H2O) in addition to the original vernadite (birnessite) structure, which suggested that ongoing Mn(II) oxidation by the associated Mn(II) oxidase in the presence of Zn(II) may participate in the formation of mixed Zn–Mn oxide phases. Following repeated treatment of the heated BMOs in the mixed Zn(II)/Mn(II) solution at a Mn(II)/Zn(II) ratio of ~4.0, the resulting solid phase possessed well-defined XRD peaks consistent with hetaerolite (ZnMn2IIIO4) formation through an abiotic comproportionation reaction between added Mn(II) and structural Mn(IV). With a decrease in the Mn(II)/Zn(II) ratio in the bathing solution, the XRD peaks weakened and shifted toward a pattern that was identified as hydrohetaerolite rather than hetaerolite. Thus, the higher concentration of Zn(II) relative to Mn(II) in the bathing solution may have inhibited the proper formation of crystalline hetaerolite. No comproportionation reaction occurred in the absence of Zn(II) under the evaluated experimental conditions (pH7.0, ~1mM added Mn(II)), indicating that Zn(II) triggered the comproportionation reaction at the BMO surface. The results presented here increase our understanding of the role of BMO in Zn(II) sequestration through microbial (enzymatic) and abiotic processes in natural environments and provide new insights into the application of enzymatically active BMOs for Zn(II) removal processes.

A novel dual-emission ratiometric fluorescent nanoprobe for sensing and intracellular imaging of Zn2+

The integration of unique characteristics of nanomaterials with highly specific recognition elements, such as biomolecules and organic molecules, are the foundation of many novel nanoprobes for bio/chemical sensing and imaging. In the present report, branched polyethylenimine (PEI) was grafted with 8-chloroacetyl-aminoquinoline to synthesize a water-soluble and biocompatible quinoline-based Zn2+ probe PEIQ. Then the PEIQ was covalently conjugated to [Ru(bpy)3]2+-encapsulated SiNPs to obtain the ratiometric fluorescence nanoprobe which exhibits a strong fluorescence emission at 600nm and a negligible fluorescence emission at 500nm in the absence of Zn2+ upon a single wavelength excitation. After the addition of different amounts of Zn2+, the fluorescence intensity at 500nm increased continuously while the fluorescence intensity at 600nm remained stable, thus changing the dual emission intensity ratios and displaying continuous color changes from red to green which can be clearly observed by the naked eye. The nanoprobe exhibits good water dispersivity, biocompatibility and cell permeability, high selectivity over competing metal ions, and high sensitivity with a detection limit as low as 0.5μM. Real-time imaging of Zn2+ in A549 cells has also been realized using this novel nanoprobe.

Responsive polymer-based multicolor fluorescent probes for temperature and Zn2+ ions in aqueous media

We report on the fabrication of fluorescent and multicolor probes for Zn2+ ions and temperature from a mixture of three types of fluorophore-labeled responsive block copolymers in aqueous media. Quinoline-based Zn2+-recognizing fluorescent monomer ZQMA, red-emitting rhodamine B-based monomer RhBEA, and blue-emitting coumarin derivative Coum-OH, were synthesized first. A ZQMA-labeled well-defined double hydrophilic block copolymer (DHBC), PEG-b-P(MEO2MA-co-ZQMA), was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and ZQMA by utilizing a PEG-based macroRAFT agent. Following similar procedures, PEG-b-P(St-co-RhBEA) amphiphilic diblock copolymer and PEG-b-P(MEO2MA-co-Coum) DHBC were also synthesized, where P(St-co-RhBEA) was a RhBEA-labeled polystyrene (PS) block. At room temperature in aqueous solution, almost nonfluorescent PEG-b-P(MEO2MA-co-ZQMA) can effectively bind Zn2+ ions, leading to prominent green fluorescence enhancement due to the coordination of ZQMA with Zn2+ ions. However, by mixing red-emitting PEG-b-P(St-co-RhBEA) and blue-emitting PEG-b-P(MEO2MA-co-Coum) with PEG-b-P(MEO2MA-co-ZQMA) at an appropriate ratio, three color transitions could be observed. In the absence of Zn2+ ions, a mixed pink fluorescent originating from Coum and RhBEA was observed; upon the addition of a certain amount of Zn2+ ions, the green fluorescence enhanced dramatically, leading to a white fluorescence readout. By further increasing the amount of Zn2+ ions, the green fluorescence further enhanced and overwhelmed the blue and red emissions, leading to a green-dominant mixed-fluorescence emission. In addition, upon increasing the temperature, the fluorescence of Coum decreased considerably due to the fluorescence-resonance energy transfer (FRET) between Coum and ZQMA moieties. In this way, a ratiometric fluorescent thermometer can be constructed.

Nanopore Analysis of the Effect of Metal Ions on the Folding of Peptides and Proteins

In this minireview, the nanopore analysis of peptides and proteins in the presence of divalent metal ions will be surveyed. In all cases the binding of the metal ions causes the peptide or protein to adopt a more compact conformation which can no longer enter the α-hemolysin pore. In the absence of Zn(II) the 30-amino acid Zn-finger peptide can readily translocate the pore; but upon addition of Zn(II) the peptide folds and only bumping events are observed. Similarly, the octapeptide repeat from the N-terminus of the prion protein binds Cu(II), which prevents it from translocating. The full-length prion protein also undergoes conformational changes upon binding Cu(II), which results in an increase in the proportion of bumping events. Myelin basic protein of 170 residues is intrinsically disordered and, perhaps surprisingly, for a basic protein of this size, can translocate against the electric field based on the observation that the event time increases with increasing voltage. It, too, folds into a more compact conformation upon binding Cu(II) and Zn(II), which prevents translocation. Finally even proteins such as maltose binding protein which does not contain a formal binding site for metal ions undergoes conformational changes in the presence of the metal chelator, EDTA. Thus, contamination of proteins with trace metal ions should be considered when studying proteins and peptides by nanopore analysis.

Lanthanide Complexes with Heteroditopic Ligands as Fluorescent Zinc Sensors

AbstractWe report the synthesis of two ligands containing a DO3A unit (H3DO3A = 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) linked to a triazacyclononane (TACN) moiety by a 2,6‐dimethylpyridine spacer designed to form stable Ln3+ complexes in solution that respond to the presence of Zn2+ ions. The Eu3+ and Gd3+ complexes have been characterized by using a combination of experimental and theoretical techniques that include absorption and emission electronic spectroscopy, NMR spectroscopy, 1H relaxometry, and DFT calculations. The Ln3+ ions are eight‐coordinated by the ligand, which binds to the metal ion through the seven donor atoms of the DO3A unit and the nitrogen atom of the pyridyl linker. Luminescence lifetime measurements recorded from solutions of the Eu3+ complexes in H2O and D2O and relaxometric measurements point to the absence of inner‐sphere water molecules. The addition of Zn2+ causes important changes in the absorption spectra of the complexes that evidence the formation of both 1:1 and 2:1 (Ln3+/Zn2+) complex species. However, the emission lifetimes of the Eu3+ complexes and relaxivity experience weak changes, thus indicating that Zn2+ addition does not significantly affect the number of coordinated water molecules. The Gd3+ complexes show a weak emission band at 325 nm, the intensity of which dramatically increases in the presence of Zn2+. However, the “turn‐on” behaviour induced by Zn2+ is not observed for other metal cations such as Ca2+, Mg2+ or Cu2+. DFT calculations indicate that a photoinduced electron‐transfer (PET) process is responsible for the quenching of the luminescence in the absence of Zn2+.