Metal Ion Binding Sites Research Articles

Transition metal transporting P-type ATPases: terminal metal-binding domains serve as sensors for autoinhibitory tails.

Copper is an essential micronutrient and yet is highly toxic to cells at elevated concentrations. P1B-ATPase proteins are critical for this regulation, providing active extrusion across cellular membranes. One unique molecular adaptation of P1B-ATPases compared to other P-type ATPases is the presence of metal-binding domains (MBDs) at the cytosolic termini, which however are poorly characterized with an elusive mechanistic role. Here we present the MBD architecture in metal-free and metal-bound forms of the archetype Cu+-specific P1B-ATPase LpCopA, determined using NMR. The MBD is composed of a flexible tail and a structured core with a metal ion binding site defined by three sulfur atoms, one of which is pertinent to the so-called CXXC motif. Furthermore, we demonstrate that the MBD rather than being involved in ion delivery likely serves a regulatory role, which is dependent on the classical P-type ATPase E1-E2 transport mechanism. Specifically, the flexible tail appears responsible for autoinhibition while the metal-binding core is used for copper sensing. This model is validated by a conformation-sensitive and MBD-targeting nanobody that can structurally and functionally replace the flexible tail. We propose that autoinhibition of Cu+-ATPases occurs at low copper conditions via MBD-mediated interference with the soluble domains of the ATPase core and that metal transport is enabled when copper levels rise, through metal-induced dissociation of the MBD. This allows P1B-ATPase 'vacuum cleaners' to tune their own activity, balancing the levels of critical micronutrients in the cells.

Distinct association of HRAS and KRAS with Mn(II) ion illustrated by paramagnetic NMR

Rat sarcoma virus oncogene (RAS) proteins are among crucial oncogenic proteins and are involved in several essential intracellular processes. The RAS protein has an intrinsic metal binding site for Mg2+, which is important for the conformational stability of the active site. Recently, it was reported that a second metal ion binding site, located further from the active site in HRAS (Harvey RAS homolog), binds Ca2+ with millimolar affinity. As one of the most abundant metal ions in cells, Mn2+ is a potential candidate for the second metal ion binding site in RAS proteins. Here, we examined the interaction of Mn2+ with HRAS and KRAS (Kirsten RAS homolog) using high resolution NMR spectroscopy. The NMR data showed that both the second metal ion binding site and the switch I and II regions bind Mn2+ in the RAS proteins. Furthermore, our paramagnetic NMR results disclosed the conformational differences in helix α3 and the following loop between HRAS and KRAS, accompanied by the association with metal ion binding. These results provide new insights into the interaction of RAS proteins and Mn2+ in the respective biological processes in cells.

Chromogenic probes featuring hydroxyethyl acetate as metal ion binding site: Selective dual-mode response and quantitative analysis of Ag+ at micellar interface

This study presents the design and synthesis of Charge Transfer-based chromogenic probes utilizing hydroxyethyl acetate (HEA) as a metal ion chelating site, and anthraimidazoldione (1) and bisindolyl methane (2) as signalling moieties. Both compounds demonstrated pH-sensitive nanoaggregate formation in aqueous solutions, as confirmed by various spectroscopic studies, dynamic light scattering (DLS) analysis, and field emission scanning electron microscopy (FESEM) imaging. Despite containing the HEA unit, compound 1 displayed no interaction with metal ions either in water or acetonitrile medium. However, in Brij-58 micelles, compound 1 exhibited a selective color-changing response to Ag+ ions accompanied by fluorescence enhancement. Mechanistic investigations revealed that Ag+ ions bound to the HEA unit, altering the charge transfer state of the probe. Compound 2, with bisindolyl methane as signalling moiety, demonstrated a superior response to Ag+ ions, attributed to differences in the pKa values of coordinating tertiary nitrogen centers and aggregation behavior. The developed sensory system was applied for silver ion estimation in Silverex ionic gel and diluted human urine samples, demonstrating high recovery values (~100 %) with low standard deviation (<5 %). These results suggest suitability of the present method for quantitative analysis of real-life samples.

Alloxazine-Based Ligands and Their Ruthenium Complexes as NADH Oxidation Catalysts and G4 Binders.

Flavin-like ligands (L-1 and L-2) with extended π-conjugation were synthesized using microwave-assisted techniques. An N,N-chelating fragment was integrated into alloxazine units, providing binding sites for metal ions while retaining redox activity. The complexation capability of L-1 and L-2 with two prototypical Ru-scaffolds was examined to design Ru(II) complexes (M-1 and M-2), whose electronic properties were studied and compared with their corresponding ligands via absorption and emission spectroscopy, computational analysis (density functional theory (DFT) and time-dependent DFT (TD-DFT)), and cyclic voltammetry (CV). The ability of L-1 and M-1 to undergo alloxazine/isoalloxazine tautomerization was demonstrated to play a crucial role in the photocatalytic oxidation of NADH, including under green and red wavelengths. Moreover, the interaction of M-1 and M-2 with B-DNA and G-quadruplex structures was investigated. M-2 showed high stabilization of Kit1 and h-Telo oligonucleotides. Meanwhile, M-1 demonstrated switchable emissive properties with B-DNA and induced conformational changes in the h-Telo G-quadruplex structure.

CNRBind: Small Molecule-RNA Binding Sites Recognition via Site Significant from Nucleotide and Complex Network Information

Background: Small molecule-RNA binding sites play a significant role in developing drugs for disease treatment. However, it is a challenge to propose accurate computational tools for identifying these binding sites. Method: In this study, an accurate prediction model named CNRBind was constructed by extracting site significant information from nucleotide and complex networks. We designed complex networks and calculated three topological structural parameters according to RNA tertiary structure. Acknowledging nucleotide interdependence, a sliding window was selected to integrate the influence of adjacent sites. Finally, the model was constructed using a random forest classifier. Results: Compared to the other computational tools, CNRBind was competitive and had excellent discriminative ability for metal ion-binding site prediction. Furthermore, statistic analysis revealed significant differences between CNRBind and existing methods. Additionally, CNRBind is a promising predictor in cases where experimental tertiary structure is unavailable. Conclusion: These results show that CNRBind is effective because of the proposed site significant information encoding strategy. The approach provides a reasonable supplement for biology researches. The dataset and resource codes can be accessed at: https://github.com/Kangxiaoneuq/CNRBind.

Complex Formation and Hydrolytic Processes of Protected Peptides Containing the -SXH- Motif in the Presence of Nickel(II) Ion.

Interactions between metal ions and proteins are considered reversible, such as the coordination of a metal ion to a protein or enzyme, but irreversible processes like the oxidative reactions, aggregation or hydrolytic processes may occur. In the presence of Ni(II)-ions selective hydrolysis of the peptides containing the -SXH- or -TXH- motif was observed. Since the side chain of histidine serves as the metal ion binding site for many native proteins, and very often histidine is present in a -SXH- or -TXH- sequence, to study the complex formation and hydrolytic processes in presence of nickel(II) ion four peptides were synthesised: Ac-SKHM-NH2, A3SSH-NH2, A4SSH-NH2, AAAϵKSH-NH2. The Ni(II)-induced hydrolysis of Ac-SKHM-NH2 peptide occurs rapidly in alkaline medium already at room temperature. In two peptides containing -SSH- sequence on the C-termini, the N-terminal part is the major binding site for the nickel(II) ion, but the formation of dinuclear complexes was also observed. In the [Ni2LH-6]2- complex of hexapeptide, the coordination sphere of the metal ions is saturated with deprotonated Ser-O-, which does not result in hydrolysis of the peptide. For A4SSH-NH2, both Ni(II) ions fulfill the conditions for hydrolysis, which was confirmed by HPLC analyses at pH ≈8.2 and 25 °C.

Structural characteristics of alpha-fetoprotein, including N-glycosylation, metal ion and fatty acid binding sites

Alpha-fetoprotein (AFP), a serum glycoprotein, is expressed during embryonic development and the pathogenesis of liver cancer. It serves as a clinical tumor marker, function as a carcinogen, immune suppressor, and transport vehicle; but the detailed AFP structural information has not yet been reported. In this study, we used single-particle cryo-electron microscopy(cryo-EM) to analyze the structure of the recombinant AFP obtained a 3.31 Å cryo-EM structure and built an atomic model of AFP. We observed and identified certain structural features of AFP, including N-glycosylation at Asn251, four natural fatty acids bound to distinct domains, and the coordination of metal ions by residues His22, His264, His268, and Asp280. Furthermore, we compared the structural similarities and differences between AFP and human serum albumin. The elucidation of AFP’s structural characteristics not only contributes to a deeper understanding of its functional mechanisms, but also provides a structural basis for developing AFP-based drug vehicles.

Investigation of metal ion binding biomolecules one molecule at a time.

Metal ions can perform multiple roles ranging from regulatory to structural and are crucial for cell function. While some metal ions like Na+ are ubiquitously present at high concentrations, other ions, especially Ca2+ and transition metals, such as Zn2+ or Cu+/2+ are regulated. The concentrations above or below the physiological range cause severe changes in the behavior of biomolecules that bind them and subsequently affect the cell wellbeing. This has led to the development of specialized protocols to study metal ion binding biomolecules in bulk conditions that mimic the cell environment. Recently, there is growing evidence of influence of post-transcriptional and post-translational modifications on the affinity of the metal ion binding sites. However, such targets are difficult to obtain in amounts required for classical biophysical experiments. Single molecule techniques have revolutionized the field of biophysics, molecular and structural biology. Their biggest advantage is the ability to observe each molecule's interaction independently, without the need for synchronization. An additional benefit is its extremely low sample consumption. This feature allows characterization of designer biomolecules or targets obtained coming from natural sources. All types of biomolecules, including proteins, DNA and RNA were characterized using single molecule methods. However, one group is underrepresented in those studies. These are the metal ion binding biomolecules. Single molecule experiments often require separate optimization, due to extremely different concentrations used during the experiments. In this review we focus on single molecule methods, such as single molecule FRET, nanopores and optical tweezers that are used to study metal ion binding biomolecules. We summarize various examples of recently characterized targets and reported experimental conditions. Finally, we discuss the potential promises and pitfalls of single molecule characterization on metal ion binding biomolecules.

Bioinspired mp20 mimicking uricase in ZIF-8: Metal ion dependent for controllable activity

Mini protein mimicking uricase (mp20) has shown significant potential as a replacement for natural enzymes in the development of uric acid biosensors. However, the design of mp20 has resulted to an inactive form of peptide, causing of loss their catalytic activity. Herein, this paper delineates the impact of various metal cofactors on the catalytic activity of mp20. The metal ion-binding site prediction and docking (MIB) web server was employed to identify the metal ion binding sites and their affinities towards mp20 residues. Among the tested metal ions, Cu2+ displayed the highest docking score, indicating its preference for interaction with Thr16 and Asp17 residues of mp20. To assess the catalytic activity of mp20 in the presence of metal ions, uric acid assays was monitored using a colorimetric method. The presence of Cu2+ in the assays promotes the activation of mp20, resulting in a color change based on quinoid production. Furthermore, the encapsulation of the mp20 within zeolitic imidazolate framework-8 (ZIF-8) notably improved the stability of the biomolecule. In comparison to the naked mp20, the encapsulated ZIFs biocomposite (mp20@ZIF-8) demonstrates superior stability, selectivity and sensitivity. ZIF’s porous shells provides excellent protection, broad detection (3–100 μM) with a low limit (4.4 μM), and optimal function across pH (3.4–11.4) and temperature (20–100°C) ranges. Cost-effective and stable mp20@ZIF-8 surpasses native uricase, marking a significant biosensor technology breakthrough. This integration of metal cofactor optimization and robust encapsulation sets new standards for biosensing applications.

Chromo-Fluorogenic Rhodamine-Based Amphiphilic Probe as a Selective and Sensitive Sensor for Intracellular Cu(I) in Living Cells.

Fluorescent probes are widely studied for metal ion detection because of their multiple favorable properties such as high sensitivity and selectivity, quick response, naked eye detection, and in situ monitoring. However, optical probes that can effectively detect the Cu(I) level in cell interiors are rare due to the difficulty associated with selectively and sensitively detecting this metal ion in a cell environment. Therefore, we designed and synthesized three water-soluble probes (1-3) with a 1,3,5-triazine core decorated by three substituents: a hydrophobic alkyl chain, a hydrophilic maltose, and a rhodamine B hydrazine fluorophore. Among the probes, probe 1, which has an octyl chain and a branched maltose group, was the most effective at sensing Cu+ in aqueous solution. Upon addition of Cu+, this probe showed a dramatic color change from colorless to pink in daylight and displayed an intense yellow fluorescence emission under 365 nm light. The limit of detection and dissociation constant (Kd) of this probe were 20 nM and 1.1 × 10-12 M, respectively, which are the lowest values reported to date. The two metal ion-binding sites and the aggregation-induced emission enhancement effect, endowed by the branched maltose group and the octyl chain, respectively, are responsible for the high sensitivity and selectivity of this probe for Cu+ detection, as demonstrated by 1H NMR, dynamic light scattering, and transmission electron microscopy studies. Furthermore, the probe successfully differentiated the Cu(I) level of cancer cells from that of the normal cells. Thus, the probe holds potential for real-time monitoring of Cu(I) level in biological samples and bioimaging of cancer cells.

Olive industry liquid waste from trash to metal adsorbent for wastewater purification

The development of biobased polymeric materials for wastewater purification has become a demand due to the growing need for water free of hazardous metal ions for safe purposes. The organic components of the OLLW including carbohydrates, phenolics, aromatic acids and others are cost-effective and sustainable choices for this application. This work focuses on a method for turning the organic components of liquid waste from the olive industry (OILW) into a foam-based value-added polymer that has several metal ion binding sites. The process of making the target polymers involved reacting the components of the OILW with hexamethylene diisocyante and 1,4-phnyelene diisocynate to create the polymeric materials LHMIDIC and LPDIC that are in foam forms with urethane linkages, respectively. The adsorption competence of the polymeric foams toward Pb(II) was evaluated as a function of various parameters including adsorbent dose, pH, temperature, initial ion concentration and time. The optimum parameters values that led to a quantitative removal of Pb(II) were identified. The obtained thermodynamic parameters showed that the adsorption by the two foams was spontaneous at room temperature. The isothermal and kinetic values showed that the adsorption by synthesized foams follows a second order kinetic and obeys the Langmuir isothermal model. The foams showed a high tendency for removing multi metal ions present in a real sample of wastewater. The original nature of the starting material used in making the foam, cost and the obtained results showed the potential of using the foam in a large-scale plants of wastewater purification.Graphical

Metal ions in biomedically relevant macromolecular structures.

Understanding the functions of metal ions in biological systems is crucial for many aspects of research, including deciphering their roles in diseases and potential therapeutic use. Structural information about the molecular or atomic details of these interactions, generated by methods like X-ray crystallography, cryo-electron microscopy, or nucleic magnetic resonance, frequently provides details that no other method can. As with any experimental method, they have inherent limitations that sometimes lead to an erroneous interpretation. This manuscript highlights different aspects of structural data available for metal-protein complexes. We examine the quality of modeling metal ion binding sites across different structure determination methods, where different kinds of errors stem from, and how they can impact correct interpretations and conclusions.

Simultaneous Localization of Two High Affinity Divalent Metal Ion Binding Sites in the Tetracycline RNA Aptamer with Mn2+-Based Pulsed Dipolar EPR Spectroscopy.

Mg2+ ions play an essential part in stabilizing the tertiary structure of nucleic acids. While the importance of these ions is well documented, their localization and elucidation of their role in the structure and dynamics of nucleic acids are often challenging. In this work, pulsed electron-electron double resonance spectroscopy (PELDOR, also known as DEER) was used to localize two high affinity divalent metal ion binding sites in the tetracycline RNA aptamer with high accuracy. For this purpose, the aptamer was labeled at different positions with a semirigid nitroxide spin label and diamagnetic Mg2+ was replaced with paramagnetic Mn2+, which did not alter the folding process or ligand binding. Out of the several divalent metal ion binding sites that are known from the crystal structure, two binding sites with high affinity were detected: one that is located at the ligand binding center and another at the J1/2 junction of the RNA.

A novel highly thermostable and stress resistant ROS scavenging metalloprotein from Paenibacillus

Reactive oxygen species (ROS) are unstable metabolites produced during cellular respiration that can cause extensive damage to the body. Here we report a unique structural metalloprotein called RSAPp for the first time, which exhibits robust ROS-scavenging activity, high thermostability, and stress resistance. RSAPp is a previously uncharacterized DUF2935 (domain of unknown function, accession number: cl12705) family protein from Paenibacillus, containing a highly conserved four-helix bundle with binding sites for variable-valence metal ions (Mn2+/Fe2+/Zn2+). Enzymatic characterization results indicated that RSAPp displays the functionality of three different antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In particular, RSAPp exhibits a significant SOD-like activity that is remarkably effective in eliminating superoxide radicals (up to kcat/KM = 2.27 × 1011 mol−1 s−1), and maintains the catalytical active in a wide range of temperatures (25–100 °C) and pH (pH 2.0–9.0), as well as resistant to high temperature, alkali and acidic pH, and 55 different concentrations of detergent agents, chemical solvents, and inhibitors. These properties make RSAPp an attractive candidate for various industrial applications, including cosmetics, food, and pharmaceuticals.

Revisiting the hydrolysis of ampicillin catalyzed by Temoneira-1 β-lactamase, and the effect of Ni(II), Cd(II) and Hg(II).

β-Lactamases grant resistance to bacteria against β-lactam antibiotics. The active center of TEM-1 β-lactamase accommodates a Ser-Xaa-Xaa-Lys motif. TEM-1 β-lactamase is not a metalloenzyme but it possesses several putative metal ion binding sites. The sites composed of His residue pairs chelate borderline transition metal ions such as Ni(II). In addition, there are many sulfur-containing donor groups that can coordinate soft metal ions such as Hg(II). Cd(II) may bind to both types of the above listed donor groups. No significant change was observed in the circular dichroism spectra of TEM-1 β-lactamase on increasing the metal ion content of the samples, with the exception of Hg(II) inducing a small change in the secondary structure of the protein. A weak nonspecific binding of Hg(II) was proven by mass spectrometry and 119m Hg perturbed angular correlation spectroscopy. The hydrolytic process of ampicillin catalyzed by TEM-1 β-lactamase was described by the kinetic analysis of the set of full catalytic progress curves, where the slow, yet observable conversion of the primary reaction product into a second one, identified as ampilloic acid by mass spectrometry, needed also to be considered in the applied model. Ni(II) and Cd(II) slightly promoted the catalytic activity of the enzyme while Hg(II) exerted a noticeable inhibitory effect. Hg(II) and Ni(II), applied at 10 μM concentration, inhibited the growth of E. coli BL21(DE3) in M9 minimal medium in the absence of ampicillin, but addition of the antibiotic could neutralize this toxic effect by complexing the metal ions.

MMT and ZrO2 jointly regulate the pore size of graphene oxide-based composite aerogel materials to improve the selective removal ability of Cu(II)

In this study, based on the cross-linking effect of Ca(II) and Sodium Alginate (SA), the basic skeleton was established with the accumulation of nanosheets of Graphene oxide (GO) and Montmorillonite (MMT), and the Zirconia (ZrO2) nanoparticles were further loaded on it to successfully prepare GMZ. Selective removal of hydrated copper ions from complex wastewater systems was achieved by increasing the cross-linking density within the aerogel spheres as well as by providing binding sites for metal ions to functionalize the aerogel into a controlled slit pore structure. The system adsorption experiments showed that Cu(II) was selectively eliminated by GMZ, with a maximum removal rate of 97.35% and a distribution coefficient of 26.33 L g−1. Adsorption kinetics and isothermal adsorption tests demonstrated that it was a multi-molecular layer chemical adsorption process (155.712 mg g−1), which was stronger than the previous similar adsorption materials. SEM morphology analysis confirmed that the aerogel was endowed with controllable slit pores. FT-IR and XPS verified the synergistic effects of ion exchange, high electrostatic force, and complexation, which contributed to the remarkable adsorption performance of GMZ. In case of adsorbing Cu(II) on GO, the roles of MMT, ZrO2, and SA were also confirmed using Density Functional Theory (DFT). In summary, GMZ had infinitely feasibility that Cu(II) was selectively removed from complicated wastewater systems.

ABCE1 selectively promotes HIF-1α transactivation of angiogenic gene expression

BackgroundCopper (Cu), by inhibiting the factor inhibiting HIF-1 (FIH-1), promotes the transcriptional activity of hypoxia-inducible factor-1 (HIF-1). ObjectiveThe present study was undertaken to understand the molecular mechanism by which Cu inhibits FIH-1. MethodsHuman umbilical vein endothelial cells (HUVECs) were treated with dimethyloxalylglycine (DMOG) resulting in HIF-1α accumulation and the FIH-1 protein complexes were pulled down for candidate protein analysis. The metal binding sites were predicted by both MetalDetector V2.0 and Metal Ion-Binding Site Prediction Server, and then the actual ability to bind to Cu in vitro was tested by both Copper-Immobilized metal affinity chromatography (Cu-IMAC) and Isothermal Titration Calorimetry (ITC). Subsequently, subcellular localization was monitored by immunocytochemistry, GFP-fusion protein expression plasmid and Western blotting in the nuclear extract. The interaction of candidate protein with HIF-1α and FIH-1 was validated by Co-Immunoprecipitation (Co-IP). Finally, the effect of candidate protein on the FIH-1 structure and HIF-1α transcriptional activity was analyzed by the InterEvDock3 web server and real-time quantitative RT-PCR. ResultsATP-binding cassette E1 (ABCE1) was present in the FIH-1 complexes and identified as a leading Cu-binding protein as indicated by a number of possible Cu binding sites. The ability of ABCE1 to bind Cu was demonstrated in vitro. ABCE1 entered the nucleus along with FIH-1 under hypoxic conditions. Protein interaction analysis revealed that ABCE1 prevented FIH-1 to bind iron ions, inhibiting FIH-1 enzymatic activity. ABCE1 silencing suppressed the expression of Cu-dependent HIF-1 target gene BNIP3, not that of Cu-independent IGF-2. ConclusionThe results demonstrate that ABCE1, as a Cu-binding protein, enters the nucleus under hypoxic conditions and inhibits FIH-1degradation of HIF-1α, thus promoting HIF-1 transactivation of angiogenic gene expression.

A fully π-conjugated covalent organic framework with dual binding sites for ultrasensitive detection and removal of divalent heavy metal ions

Covalent organic frameworks (COFs) have become a promising candidate for the remediation of heavy metal pollution. However, researches on COF adsorbents still have challenges on maintaining good optical properties and adsorption performance under harsh conditions. Herein, a fully π-conjugated COF with dual binding sites (Bpy-sp2c-COF) is reported for rapid fluorescence recognition and enhanced adsorption towards divalent heavy metal ions. The vinylene-linkage lattice shows strong luminescence and excellent stability in both strong acidity and basicity. Bpy-sp2c-COF demonstrates not only nanomolar-scale detection of divalent heavy metal ions, but also good adsorption capacity (Hg2+ 718.48, Ni2+ 278.64, Cu2+ 260.11, and Co2+ 126.23 mg/g). Experimental and theoretical studies reveal the intramolecular charge transfer as the fluorescence quenching mechanism. Further simulation results demonstrate the cyano and bipyridine groups on the lattice can act as dual binding sites for divalent heavy metal ions. Experimental results confirmed the adsorption capacity of Bpy-sp2c-COF superior to that of COFs with either cyano groups (Hg2+ 415.34, Ni2+ 165.60, Cu2+ 160.55, and Co2+ 73.14 mg/g), or bipyridine groups (Hg2+ 369.25, Ni2+ 133.41, Cu2+ 133.32, and Co2+ 69.23 mg/g). Besides, robust regeneration of the adsorbent could be achieved over 10 cycles. The fully π-conjugated COF with dual binding sites provides a new approach for designing next-generation sensors and adsorbents with excellent performances.

Chemical reduction of indenocorannulene: A two-electron addition stop

Chemical reduction behavior of the indenyl-fused corannulene bowl, monoindenocorannulene (1), was investigated using two alkali metals with different binding abilities, namely Na and Rb. The sodium-induced reaction in THF in the presence of 18-crown-6 ether afforded a solvent-separated ion product, [Na+(18-crown-6)(THF)2]2[12−]·THF (2·THF), which enabled structural evaluation of the “naked” dianion. The controlled addition of the secondary ligand in rubidium-induced reduction reactions allowed modulation of metal coordination and solid-state packing of the doubly-reduced indenocorannulene. Two products with different topologies and metal ion binding, [Rb+(18-crown-6)]2[12−]·THF (3·THF) and [Rb+(18-crown-6)][Rb+(18-crown-6)0.5][12−]·4THF (4·4THF), were isolated and characterized crystallographically. A direct comparison of 1 and 12− using DFT calculation methods provided insights into consequences of two-fold reduction. The significant change in aromaticity was revealed by NICS calculations, while ACID plots showed a good agreement between the negative charge distribution patterns and the observed metal ion binding sites.

A butterfly-shaped ESIPT dye for pattern recognition of metal ions

Accurate monitoring of versatile metal ions in complicated environmental or biological samples is meaningful for avoiding heavy metal poisoning accidents. To reduce the production cost of a metal ion sensor array, we intended to develop solvent directed fluorescent sensor arrays on the basis of a single dye molecule. Herein, two fluorescent ESIPT dyes named SC1 and SC2 were designed by incorporating different numbers of benzothiazole units as the metal ion binding site. It was discovered that SC1 was highly selective toward Zn2+ in all tested solvents, while a solvent directed cross-responsive sensing behavior was observed for SC2. Therefore a three-component sensor array SC2SA was readily constructed by simply dissolving SC2 in common solvents including ethanol, DMF and DMSO. The sensor array was determined to be accurate for semi-quantitative discrimination and detection of Zn2+, Cd2+, Mg2+, Fe2+ and Fe3+ in diluted serum media. Moreover, sensor array SC2SA was also successfully applied for differentiating Zn2+/Cd2+ and Fe2+/Fe3+ in pure and mixed forms and reliable identification of unknown Zn2+, Cd2+ and Mg2+ in diluted serum samples.