Selected Metal Ions Research Articles

A novel COP adsorbent built up by thiophene group: Rapid and selective adsorption toward trace hazardous Hg(II)

Mercury is one of the most toxic heavy metals to humans. Developing highly efficient adsorbent for removing mercury is of great significance. Herein, two thiophene-based COPs were synthesized through Schiff base reaction by rationally selecting thiophene group as COP building block and functional component simultaneously, avoiding the drawbacks of functionalization strategy such as sacrificing the porous structure and blocking the active sites. The high S/N content in the COPs structure enables robust adsorption towards Hg(II), with maximum adsorption capacity up to 468.8 mg g−1. Notably, even in the presence of 12 interfering ions, the resulting COP-BTTS effectively reduced trace Hg(II) at 1000 μg L−1 to 33 μg L−1 within 30 s, achieving a removal rate up to 97 %, and below the regulatory discharge limit of 10 μg L−1 for wastewater in 15 min. Moreover, the temperature of COP-BTTS can rise to 140 °C-150 °C under xenon light due to its exceptional photothermal property, which can facilitate the efficient desorption of Hg2+. And the COP-BTTS maintains its exceptional recoverability after the successive repeated 5 cycles. This work sheds light on the feasible strategy for designing and synthesizing COP adsorbent with high adsorption capacity, selectivity, and irradiation-assisted desorption of metal ions.

Role of cation nature in crown ether appended 25-Oxasmaragdyrins with second-order NLO responses: As potential and selective metal ions detector

Crown ethers, known for their efficacy as metal ion traps, have garnered significant interest in optoelectronic applications due to their unique cavity structure and special binding ability with metals. Herein, we systematically designed and investigated the second-order nonlinear optical (NLO) properties of an intriguing compound, 18-crown-6 derivative appended with 25-oxasmaragdyrins (Cr-Prs), achieved through the incorporation of diverse metal ions into the crown ether ring. Significantly, the βtot values of compounds with alkaline earth metal ions (Mg2+, Ca2+) are greater than those compounds with alkali metal ions (Na+, K+). Interestingly, the Hg2+@Cr-Prs compound exhibits a tremendous second-order NLO property with the βtot value of 5.34 × 105 au. Further insights into substantial βtot values across all compounds were provided through a comprehensive analysis of the transition energies, the molecular orbitals, and the absorption spectra of the main excited states. The calculation results conclude that the second-order NLO properties of Cr-Prs can be modulated by incorporating metal ions into the crown ether ring. Crown ether emerges as a facilitator in detecting and identifying Hg2+ ions, serving as an effective NLO-based ion detector. These findings not only broaden the scope of cation detection and efficiency but also present innovative applications in analytical and optoelectronic research, encapsulating the essence of our study within a concise framework.

Explanation based on thermodynamic parameters regarding effect of sensing film thickness and amount of graphene oxide on sensor performance in aniline, N-phenylglycine and graphene oxide based electrochemical heavy metal ion sensor

Background: To construct a heavy metal ion sensor, selectivity and sensitivity are the key important parameters to be taken care of. In our earlier work, film thickness and amount of graphene oxide (GO) content in a novel composite ANGO, synthesized from aniline, N-phenylglycine and GO was varied and sensing parameters including sensitivity, limit of detection (LOD), thermodynamic parameter which includes -∆Gad and charge transport parameter including barrier width (BW), d, of charge transfer based on Simmon’s model were evaluated and compared and an LOD of 800 ppt for Cd2+ was achieved using square wave voltammetry (SWV) withstanding interference from several ions. Methods: In this work, thermodynamic factors such as -∆Gad, ∆H, reorganization energy, partition coefficient and solvated ionic radius were used to explain the sensor performance with respect to film thickness and amount of GO. All the parameters were analyzed for different film thicknesses and amount of GO and a correlation was achieved. Finally, effect of electrochemical surface area of different polyaniline-based material on thermodynamic properties of detection process of Cd2+ was studied. Results: The variation of the thermodynamic properties for Cd2+ sensing with respect to film thickness and amount of GO were examined. Similarly, variation of thermodynamic properties for polyaniline based different sensing materials were examined. Correlation coefficients were developed from the thermodynamic parameters and the d values to explain the underlying mechanism behind improved sensor performance. Conclusions: This study can provide information on the thermodynamic properties which can be predicted from BW technique. The correlation coefficients would help in designing polyaniline based novel sensing film material with the need of lesser number of experiments.

A dual-responsive RhB-doped MOF probe for simultaneous recognition of Cu2+ and Fe3+

Based on the dual response of RhB@UiO-67 (1:6) to Cu2+ and Fe3+, a proportional fluorescent probe with (I392/I581) as the output signal was developed to recognize Cu2+ and Fe3+. Developing highly sensitive and selective trace metal ions probes is crucial to human health and ecological sustainability. In this work, a series of ratio fluorescent probes (RhB@UiO-67) were successfully synthesized using a one-pot method to enable fluorescence sensing of Cu2+ and Fe3+ at low concentrations. The proportional fluorescent probe RhB@UiO-67 (1:6) exhibited simultaneous quenching of Cu2+ and Fe3+, which was found to be of interest. Furthermore, the limits of detection (LODs) for Cu2+ and Fe3+ were determined to be 2.76 μM and 0.76 μM, respectively, for RhB@UiO-67 (1:6). These values were significantly superior to those reported for previous sensors, indicating the probe’s effectiveness in detecting Cu2+ and Fe3+ in an ethanol medium. Additionally, RhB@UiO-67 (1:6) demonstrated exceptional immunity and reproducibility towards Cu2+ and Fe3+. The observed fluorescence quenching of Cu2+ and Fe3+ was primarily attributed to the mechanisms of fluorescence resonance energy transfer (FRET), photoinduced electron transfer (PET), and competitive absorption (CA). This work establishes a valuable foundation for the future study and utilization of Cu2+ and Fe3+ sensing technologies.

A review of direct recycling methods for spent lithium-ion batteries

The increasing demand for lithium-ion batteries (LIBs) in new energy storage systems and electric vehicles implies a surge in both the shipment and scrapping of LIBs. LIBs contain a lot of harmful substances, and improper disposal can cause severe environment damage. Developing efficient recycling technology has become the key to the sustainable growth of the LIBs industry. At present, the extraction of high-value materials from spent LIBs using pyrometallurgical and hydrometallurgical processes is most usual. However, they consume a lot of energy and lead to secondary environmental pollution, which is not consistent with the idea of creating a green circular economy. Direct recycling has been suggested as a possible alternative method of dealing with the spent LIBs under non-destructive conditions in the further. Compared with traditional metallurgical technologies, direct regeneration significantly reduces the consumption of energy and chemical reagents, and has a high selectivity for certain metal ions, which is environmentally friendly. However, direct cycling is still in its infancy with many scientific and technological barriers. In this review, we first consider the necessity of recycling spent LIBs, and then summarize the failure mechanisms of degraded cathode materials in order to choose a corresponding regeneration method. The direct cycling technologies, including hydrothermal, solid-state, eutectic medium and electrochemical regeneration are introduced separately from the perspective of the experimental process, operating parameters, regeneration principles, advantages, and effects. Furthermore, the current problems and potential future research on the direct cycling of spent LIBs are also discussed.

Enhanced luminescent properties of poly(sodium acrylate)-based composite and its selective interaction towards copper ions

This study investigates the luminescent properties and metal ion interactions of europium when combined with a polymer chain of poly (sodium acrylate) (PSA) and a phenanthroline (Phen) molecule, which acts as an efficient antenna. The study of interactions between lanthanide ions and various compounds in different matrices is crucial, providing valuable insights into the molecular environment, and enabling a deeper understanding of processes affecting their luminescence. In this study, we investigated the luminescent properties of the Eu(PSA)Phen complex and its remarkable capacity for selective interaction with Cu2+ ions in an aqueous solution. From this selective interaction, we conducted a series of detailed studies that provided valuable insights into the mechanisms of luminescence suppression, information about the europium chemical environment, and other related aspects. The luminescence of Eu(PSA)Phen is significantly quenched by Cu2+ ions, driven by both static and dynamic mechanisms. The presence of the PSA polymer chain and Phen molecules within the composite exerts a profound influence on energy transfer processes, enabling selective responses to Cu2+ ions, even in the presence of competing cations. Additionally, we observed a preferential interaction of the PSA molecule in the Eu(PSA)Phen composite with Cu2+ ions over the N groups of phenanthroline. These findings underscore the compound potential as a versatile tool in various fields, ranging from material science to biosensing, where rapid and selective metal ion detection is of paramount importance.

Unlocking Direct Lithium Extraction in Harsh Conditions through Thiol-Functionalized Metal-Organic Framework Subnanofluidic Membranes.

Metal-organic framework (MOF) membranes with high ion selectivity are highly desirable for direct lithium-ion (Li+) separation from industrial brines. However, very few MOF membranes can efficiently separate Li+ from brines of high Mg2+/Li+ concentration ratios and keep stable in ultrahigh Mg2+-concentrated brines. This work reports a type of MOF-channel membranes (MOFCMs) by growing UiO-66-(SH)2 into the nanochannels of polymer substrates to improve the efficiency of MOF membranes for challenging Li+ extraction. The resulting membranes demonstrate excellent monovalent metal ion selectivity over divalent metal ions, with Li+/Mg2+ selectivity up to 103 since Mg2+ should overcome a higher energy barrier than Li+ when transported through the MOF pores, as confirmed by molecular dynamics simulations. Under dual-ion diffusion, as the Mg2+/Li+ mole ratio of the feed solution increases from 0.2 to 30, the membrane Li+/Mg2+ selectivity decreases from 1516 to 19, corresponding to the purity of lithium products between 99.9 and 95.0%. Further research on multi-ion diffusion that involves Mg2+ and three monovalent metal ions (K+, Na+, and Li+, referred to as M+) in the feed solutions shows a significant improvement in Li+/Mg2+ separation efficiency. The Li+/Mg2+ selectivity can go up to 1114 when the Mg2+/M+ molar concentration ratio is 1:1, and it remains at 19 when the ratio is 30:1. The membrane selectivity is also stable for 30 days in a highly concentrated solution with a high Mg2+/Li+ concentration ratio. These results indicate the feasibility of the MOFCMs for direct lithium extraction from brines with Mg2+ concentrations up to 3.5 M. This study provides an alternative strategy for designing efficient MOF membranes in extracting valuable minerals in the future.

Green Synthesis of Highly Fluorescent NCQDs: A Comprehensive Study on Synthesis, Characterization, Photophysical Properties, pH Sensing, Heavy Metal Detection, and Solvatochromic Behavior through Hydrothermal Method.

Solvatochromic studies in conjunction with NCQDs and analysis of material at different pH levels provide valuable insights about the process of metal ion sensing. Metal ion sensing holds significant importance in various fields like environment monitoring, biomedical diagnostics and various industrial purpose. The detection of metal ions by mixing the nitrogen-doped quantum dots (NCQDs) in the solvent at different pH levels for the analysis of the photoluminescence spectra is the unique property to achieve selective metal ion detection.In present study, the synthesis of NCQDs was performed by the use of flowers of Tecoma stans. The synthesis of NCQDs to best of our knowledge using flowers of Tecoma stans as natural carbon source via hydrothermal process has been done for the first time. The NCQDs exhibit absorption bands ranging from 190 to 450nm, with the energy band gap varying from 3.55 to 5.42eV when mixed with different solvent such as, 1-4 dioxane, acetone, acetonitrile, ethyl- acetate, ethanol, methanol and toluene. The fluorescence spectra exhibited highly intense range from approximately 390 to 680nm across various solvents. XRD analysis further confirmed the crystalline nature of the particles with an average size of 6.96nm. Different peak positions of the FTIR spectra support functional groups having C-H stretching, C = O (carbonyl) stretching, and C = C stretching vibrations.In the study a notable solvatochromic shift was observed, indicating sensitivity to change in solvent polarity. Additionally, the investigation of the ratio of ground to excited state dipole moment based on solvatochromic shift yielded a value of 3.30. This provide valuable information about optical and electronic properties of NCQDs. Overall, our study sheds light on the unique properties of NCQDs synthesized from Tecoma stans flowers and their potential applications in metal ion sensing, pH probing, and solvent polarity studies.

Dual-responsive solvatochromic sensor for simultaneous detection and mechanism of Cr(III) and Co(II) cations by a new N2O4-donor tetrabenzodiaza-crown ether Macrocyclic ligand anchored to dipyridine moieties

The present study describes the chemosensing capability of an N2O4-donor tetrabenzodiaza-crown ether macrocyclic ligand derivatized by two pyridine side arms to afford the flexible macrocyclic ligand, 5,20-bis(pyridin-4-ylmethyl)-5,6,12,13,19,20,26,27octahydrotetrabenzo [e,i,o,s][1,4,11,14]tetraoxa[7,18]diazacycloicosine (PMHBOA). A selective colorimetric behavior of PMHBOA for the prompt detection of Cr(ΙΙΙ) and Co(ΙΙ) can be observed with naked eyes. The 1H, 13C{H} NMR, and infrared spectroscopy disclosed the ligand binding capability for selective metal ions, ascribed to a 1:1 complex formation with Cr(III) and Co(II) cations in isopropanol. The limit of detection (LOD) values were calculated as 580 and 850 nM for Cr(ΙΙΙ) and Co(ΙΙ), respectively, accompanied with suitable LOQs as 1.95 µM for Cr(III) and 2.85 µM for Co(II), respectively. The reusability was confirmed in the presence of ethylenediaminetetraacetic acid (EDTA). Moreover, a TLC-based fabricated paper strip successfully applied PMHBOA as a chemosensor for synchronous visible detection of Cr(III) and Co(II) in their alcoholic solution. Meanwhile, the observed color change along with the turn-off fluorescent of PMHBOA guaranteed a felicitous choice of candidate for Cr(III) in the presence of other library metal ions in isopropanol:H2O (9/1 v/v) solution. A fast separation test on the filter paper, impregnated with PMHBOA, was also employed to separate Cr(III) and Co(II) cations from aqueous solutions by recording UV–vis spectra. The 1H NMR spectroscopy supported the macrocycle ring and side arms as the parallel coordination site of PMHBOA with Cr(III) and Co(II).

Borophene Quantum Dots with Strong Photoluminescence for Selective Metal Ion Sensing

Borophene Quantum Dots with Strong Photoluminescence for Selective Metal Ion Sensing

Understanding adsorption mechanisms and metal ion selectivity of superparamagnetic beads with mesoporous CMK-3 carbon and commercial activated carbon

This study investigates, the adsorption capacities of synthesized magnetic hybrid beads containing ordered mesoporous carbon (CMK-3) and commercial activated carbon (commercial AC) for Cd (II), Ni (II), and Hg (II) ions adsorption in single and ternary systems. The order of maximum adsorption capacity was Cd (II) > Ni (II) > Hg (II) in both beads and systems. L13 beads containing CMK-3 exhibit superior adsorption efficiency compared to L3 beads with commercial AC, attributed to the large surface area, enhanced accessibility to adsorption sites, and the presence of O=C bonds, as well as other elements such as F−. Adsorption of all metal ions was described by Freundlich isotherm in L3 beads in both systems, meanwhile in L13 beads, Langmuir and Freundlich models described adsorption differently in both systems and among metal ions, indicating a more complex process. According to the reported maximum adsorption capacity values, L3 beads exhibit a greater affinity for Hg (II) ions, while L13 beads show a higher affinity for Cd (II) and Ni (II) ions. Adsorption in both beads occurred through several mechanisms involving surface complexation, ion-exchange, precipitation, physical and chemical processes. These findings highlight the importance of material design in optimizing adsorption performance for environmental applications, with potential for further enhancement of adsorption capacities and selectivities through future research.

Symmetrical Ligand's Fabricated Porous Silicon Surface Based Photoluminescence Sensor for Metal Detection and Entrapment.

This study was based on the development of surface-based photoluminescence sensor for metal detection, quantification, and sample purification employing the solid sensory chip having the capability of metal entrapment. The Co(II), Cu(II) and Hg(II) sensitive fluorescence sensor (TP) was first synthesized and characterized its sensing abilities towards tested metal ions by using fluorescence spectral investigation while the synthesis and complexation of the receptor was confirmed by the chromogenic, optical, spectroscopic and spectrometric analysis. Under optical investigation, the ligand solution exhibited substantial chromogenic changes as well as spectral variations upon reacting with copper, cobalt, and mercuric ions, while these behaviors were not seen for the rest of tested metallic ions i.e., Na+, Ag+, Ni2+, Mn2+, Pd2+, Pb2+, Cd2+, Zn2+, Sn2+, Fe2+, Fe3+, Cr3+, and Al3+. These colorimetric alterations and spectral shifting could potentially be employed to detect and quantify these specific metal ions. After the establishment of the ligand's selective complexation ability towards selected metals, it was fabricated over the substituted porous silicon surface (FPS) keeping in view of the development of surface-based photoluminescence sensor (TP-FPS) for the selected metal sensation and entrapment to purify the sample just be putting off the metal entrapped sensory solid chip. Surface characterization and ligand fabrication was inspected by plan and cross sectional electron microscopic investigations, vibrational and electronic spectral analysis. The sensitivity of the ligand (TP) in the solution phase metal discrimination was determined by employing the fluorescence titration analysis of the ligand solution after progressive induction of Co2+, Cu2+, and Hg2+, which afford the detection limit values of 2.14 × 10- 8, 3.47 × 10- 8 and 3.13 × 10- 3, respectively. Concurrently, photoluminescence titration of the surface fabricated sensor (TP-FPS) revealed detection limit values of 3.14 × 10- 9, 7.43 × 10- 9, and 8.21 × 10- 4, respectively, for the selected metal ions.

The treatment of petrochemical wastewater via ozone-persulfate coupled catalytic oxidation: mechanism of removal of soluble organic matter.

Petrochemical wastewater contains a variety of organic pollutants. Advanced oxidation processes (AOPs) are used for deep petrochemical wastewater treatment with distinct advantages, including the complete mineralization of organic substances, minimal residual byproducts, and compatibility with biological treatment systems. This work evaluates the effectiveness of three methods, namely, ozone, persulfate, and O3-PMS (ozone-persulfate) processes, which were compared to remove soluble organic matter. The O3-PMS process offered significant advantages in terms of organic matter removal efficiency. This process involves ozone dissolution in an aqueous persulfate solution, producing a more significant amount of hydroxyl radicals in comparison to single AOPs. The production of hydroxyl radicals and the synergistic effect of hydroxyl radicals and persulfate radicals were investigated. In the O3-PMS process, transition metal ions were added to understand the mechanism of the O3-PMS coupled catalytic oxidation system. The results showed that when the ozone concentration was in the range of 5 ~ 25mg/L, the dosage of persulfate was in the range of 0.01 ~ 0.05mol/L, the dosage of metal compounds was in the range of 0:0 ~ 2:1, and the reaction time was in the range of 0 ~ 2h; the optimum chemical oxygen demand (CODCr) and total organic content (TOC) removal effect was achieved under the coupled system with an ozone concentration of 10mg/L, a persulfate dosage of 0.02mol/L, a 1:2 dosage ratio of between Fe2+ and Cu2+ compounds, and a reaction time of 2h. Under optimal reaction conditions, the rates of CODCr and TOC removal reached 70% and 79.3%, respectively. Furthermore, the removal kinetics of the O3-PMS coupled catalytic oxidation system was analyzed to optimize the removal conditions of COD and TOC, and the mechanism regulating the degradation of dissolved organic matter was explored by three-dimensional fluorescence and GC-MS technology. Thus, O3-PMS coupled catalytic oxidation is an effective process for the deep treatment of wastewater. The careful selection of transition metal ions serves as a theoretical foundation for the subsequent preparation of catalysts for the ozone persulfate oxidation system, and this study provides a suitable reference for removing organic matter from petrochemical wastewater.

Reversible pH-Gated MXene Membranes with Ultrahigh Mono-/Divalent-Ion Selectivity.

Artificial ion channel membranes hold high promise in water treatment, nanofluidics, and energy conversion, but it remains a great challenge to construct such smart membranes with both reversible ion-gating capability and desirable ion selectivity. Herein, we constructed a smart MXene-based membrane via p-phenylenediamine functionalization (MLM-PPD) with highly stable and aligned two-dimensional subnanochannels, which exhibits reversible ion-gating capability and ultrahigh metal ion selectivity similar to biological ion channels. The pH-sensitive groups within the MLM-PPD channel confers excellent reversible Mg2+-gating capability with a pH-switching ratio of up to 100. The mono/divalent metal-ion selectivity up to 1243.8 and 400.9 for K+/Mg2+ and Li+/Mg2+, respectively, outperforms other reported membranes. Theoretical calculations combined with experimental results reveal that the steric hindrance and stronger PPD-ion interactions substantially enhance the energy barrier for divalent metal ions passing through the MLM-PPD, and thus leading to ultrahigh mono/divalent metal-ion selectivity. This work provides a new strategy for developing artificial-ion channel membranes with both reversible ion-gating functionality and high-ion selectivity for various applications.

Interaction of Tapentadol with Selected Metal Ions Studied by UV-Vis and FTIR Spectroscopy

Understanding the interaction between drug-metal complexes is important to find out the pharmacological characteristics of a drug. In this work, one of the μ-opioid analgesic type of drug, tapentadol has been used to study the interaction of tapentadol with several metal ions such as Ca (II), K (I) Cr (III), Cu (II), Fe (III), Co (II), and Ni (II) using UV-Vis and FTIR spectroscopy. It was found that tapentadol forms drug-metal complexes with transition metals like Fe (III) and Ni (II) only in acidic conditions. Whereas Cu (II) can interact with tapentadol both in acidic and basic conditions. This study may help to understand the interactions of μ-opioid drugs with the metal ions which ultimately help to develop new drugs of this class with more efficacy.

Computational, spectroscopic, sensor and biological studies of Cu(II) complex of Fluoro substituted Schiff base

Schiff base ligand (FHPB - 2-[N-(fluorophenyl)-4‑hydroxy-4-phenyl] 3-butene), and its copper complex Cu[FHPB]2 were prepared and the structural framework of prepared compounds were characterized by analytical, spectroscopic and DFT calculation techniques. The result suggests that, prepared Cu[FPB]2 complex possesses square planar geometry. Electrochemical studies reveal that Cu[FPB]2 complex is quasi reversible in nature. Sensing ability of prepared ligand with various cations were analyzed by absorption and emission spectral techniques and infer that the ligand FHPB is highly sensitive and selective sensor for the Cu2+ ion as compared to other selected metal ions. Antimicrobial activities of FHPB and Cu[FPB]2 against selected bacterial and fungal strains were checked by Disc Diffusion method. DNA interaction of prepared compounds were analyzed by spectrophotometric and spectrofluorometric techniques. The analysis illustrates that the synthesized compounds interact with calf thymus DNA by the way of an intercalation mode. Moreover, the binding ability of FHPB and Cu[FPB]2 were demonstrated by molecular docking and it evidences the strong binding with CT-DNA double helix.

Conformational investigations on three large dinuclear triple helicates by single crystal X-ray diffraction

Three new dinuclear triple helicates were synthesised using a ditopic semi-rigid pyridylylimine ligand L, separated by a diphenoxy-biphenol spacer providing considerable length to the backbone. L and the new large dinuclear triple helicate complexes [Fe2L3](BF4)4 (1), [Ni2L3](BF4)4 (2) and [Zn2L3](BF4)4 (3) have been characterised in solution and solid state. Single crystal X-ray diffraction was used to investigate overall complex ion shape as the coordination sphere was modulated by metal ion selection. Small differences in complex shape were seen to arise due to subtle distortions in coordination sphere environments. This study sheds light on how the length and twist of dinuclear triple helicates can be tuned by selection of coordinating metal ion.

Multifunctional Logic Operations Based Upon Congruent Ion Sensing Appended with a Strategic Molecular Device: Spectroscopic Approach

AbstractA multi‐responsive smart molecular system is constructed using a newly synthesized Salen molecule, 1,3‐bis((E)‐2,3,4‐trimethoxy benzylideneamino) propan‐2‐ol (TMBP), to selectively recognize the presence and absence of Cu2+ ions aided by another selective metal ion, Zn2+. The emission efficiency of the non‐emissive probe is selectively and significantly enhanced in presence of Zn2+, while the improved emission of probe‐Zn2+ complex is completely quenched upon interaction with Cu2+. Thus, the probe acts as a reporter molecule for the selective detection of Cu2+ in the co‐presence of Zn2+. Comprehensive spectroscopic studies indicate that Zn2+ ion‐coordination significantly reduces the flexibility of the Schiff base unit and the extent of photoinduced electron transfer which in turn enhance the fluorescence intensity. While Cu2+, a d9 system, induces paramagnetic quenching over the enhanced emission through stable ground‐state complexation and metal‐ligand charge transfer. The spectroscopic results are translated into the designing of a multifunctional smart‐molecular system that could function as YES, NOT, INHIBIT, PASS 0, TRANSFER and NOT TRANSFER logic gates. Finally, a blueprint of a smart molecular device is proposed to present the relay sensing of Zn2+ and Cu2+ through logical outputs that would work in‐sync with the spectroscopic results.

A Molecular Hybrid of the GFP Chromophore and 2,2'-Bipyridine: An Accessible Sensor for Zn2+ Detection with Fluorescence Microscopy.

The few commercially available chemosensors and published probes for in vitro Zn2+ detection in two-photon microscopy are compromised by their flawed spectroscopic properties, causing issues in selectivity or challenging multistep syntheses. Herein, we present the development of an effective small molecular GFP chromophore-based fluorescent chemosensor with a 2,2'-bipyridine chelator moiety (GFZnP BIPY) for Zn2+ detection that has straightforward synthesis and uncompromised properties. Detailed experimental characterizations of the free and the zinc-bound compounds within the physiologically relevant pH range are presented. Excellent photophysical characteristics are reported, including a 53-fold fluorescence enhancement with excitation and emission maxima at 422 nm and 492 nm, respectively. A high two-photon cross section of 3.0 GM at 840 nm as well as excellent metal ion selectivity are reported. In vitro experiments on HEK 293 cell culture were carried out using two-photon microscopy to demonstrate the applicability of the novel sensor for zinc bioimaging.

Flexibility of Binding Site is Essential to the Ca2+ Selectivity in EF-Hand Calcium-Binding Proteins.

High binding affinity and selectivity of metal ions are essential to the function of metalloproteins. Thus, understanding the factors that determine these binding characteristics is of major interest for both fundamental mechanistic investigations and guiding of the design of novel metalloproteins. In this work, we perform QM cluster model calculations and quantum mechanics/molecular mechanics (QM/MM) free energy simulations to understand the binding selectivity of Ca2+ and Mg2+ in the wild-type carp parvalbumin and its mutant. While a nonpolarizable MM model (CHARMM36) does not lead to the correct experimental trend, treatment of the metal binding site with the DFTB3 model in a QM/MM framework leads to relative binding free energies (ΔΔGbind) comparable with experimental data. For the wild-type (WT) protein, the calculated ΔΔGbind is ∼6.6 kcal/mol in comparison with the experimental value of 5.6 kcal/mol. The good agreement highlights the value of a QM description of the metal binding site and supports the role of electronic polarization and charge transfer to metal binding selectivity. For the D51A/E101D/F102W mutant, different binding site models lead to considerable variations in computed binding affinities. With a coordination number of seven for Ca2+, which is shown by QM/MM metadynamics simulations to be the dominant coordination number for the mutant, the calculated relative binding affinity is ∼4.8 kcal/mol, in fair agreement with the experimental value of 1.6 kcal/mol. The WT protein is observed to feature a flexible binding site that accommodates a range of coordination numbers for Ca2+, which is essential to the high binding selectivity for Ca2+ over Mg2+. In the mutant, the E101D mutation reduces the flexibility of the binding site and limits the dominant coordination number of Ca2+ to be seven, thereby leading to reduced binding selectivity against Mg2+. Our results highlight that the binding selectivity of metal ions depends on both the structural and dynamical properties of the protein binding site.