Cation Recognition Research Articles

Visual‐Detection of Cu2+ in DMSO aAqueous Solution Based on Benzimidazole Azo‐dye as a Colorimetric Chemosensor

AbstractIn this work, a novel colorimetric chemosensor (BIAD) containing azo chromophore, 1,5dihydroxynaphthalene, and benzimidazole was synthesized and characterized by using IR, 1H,13C NMR, and mass spectral data, and elemental analysis. The cation recognition studies (including fourteen metal cations) exhibited that the synthesized azo dye can act as a rapid, sensitive, and selective colorimetric chemosensor for detecting Cu2+ ions. The addition of Cu2+ ions to the BIAD solution, changed immediately the solution color from purple to blue‐green, which could be observed by the naked eye. Comparison of the UV/Visible spectra of BIAD and (BIAD+Cu2+) revealed a red shift from 543 nm to 616 nm, which confirms the formation of a complex between Cu2+ cations and BIAD molecules. The result of Job's plot indicated that the stoichiometry binding ratio of BIAD to Cu2+ is 1 : 1. The limit of detection (LOD) was found for BIAD toward Cu2+ ion to be 0.10 μM. Furthermore, the BIAD‐based test paper strips were successfully used for the rapid detection of Cu2+ ions (<1 sec) in the aqueous solution (H2O‐DMSO, 9 : 1).

Expanding the library of sumanene molecular receptors for caesium-selective potentiometric sensors.

This paper reports the synthesis and characterization of eight sumanene molecular receptors for the selective recognition of caesium cations (Cs+). The sumanene derivatives differed in the number (from one to nine), type (electron donating or electron withdrawing) and method of the attachment (functionalization of sumanene at the benzylic or aromatic carbons) of substituents in the sumanene skeleton. The ultimate goal of this work was to investigate the prospective use of various sumanene derivatives in the design of Cs+-selective potentiometric sensors, thus, expanding the library of sumanene receptors for such applications. Spectroscopic fluorescence titration with caesium hexafluorophosphate revealed that the formation of sandwich complexes is highly favourable, but the steric hindrance of bulky substituents can disrupt this preference. In the case of triaryl-substituted sumanene derivatives, theoretical calculations show that, indeed, sandwich complexes are energetically more advantageous by 2.3 times than 1 : 1 complexes. Furthermore, such functionalization significantly increases receptor solubility in the polymeric membrane of the potentiometric sensors, which was quantitatively evaluated with the COSMO model.

Metal cations recognition by bowl-shaped N-pyrrolic polycyclic aromatic hydrocarbons.

Bowl-shaped, nitrogen-doped polycyclic aromatic hydrocarbons were examined for the first time as molecular receptors for the recognition of metal cations. Potentiometric and spectrofluorimetric assays, supported with density functional theory computations, revealed that the title compounds recognise metal cations with a special focus on caesium (Cs+) cations.

A pyridine-N-oxide catenane for cation recognition.

The rapid preparation of a pyridine-N-oxide containing [2]catenane is described. The [2]catenane was characterized by NMR spectroscopy, mass spectrometry and X-ray single crystal structure determination. 1H NMR titration experiments reveal the [2]catenane may be reversibly protonated, as well as an ability to bind lithium cations more strongly than sodium cations.

Cation Recognition by Dibenzoarsacrowns

AbstractWe recently reported dibenzoarsacrowns as a novel class of host molecules, and in this work, prepared four dibenzoarsacrowns:12‐dibenzoarsacrown‐4, 15‐dibenzoarsacrown‐5, 18‐dibenzoarsacrown‐6, and 21‐dibenzoarsacrown‐7, and investigated their guest recognition behaviors for alkali metal and ammonium cations (Li+, Na+, K+, and NH4+). It was found that the triphenylarsine moiety of the dibenzoarsacrowns could be electrochemically oxidized and that their oxidation potentials shifted in response to perturbation because of the weak interaction between the arsenic atom and guest cations. Thus, dibenzoarsacrowns could electrochemically detect cations with sizes that fit the host cavity. Electron spin resonance measurements revealed the generation of cation radical species of arsenic under the application of voltage and supported the idea that the interaction between the arsenic atom and guest cations played a crucial role in the detection of cations. In addition, ion chromatography studies showed that size‐selective cation recognition by dibenzoarsacrowns was achievable even in aqueous solutions.

Novel fluorescent sensors based on coumarin-hydrazide-hydrazone hybrid for the detection of CN−, Co2+ and Ni2+ ions: DFT and bioimaging in living cells

Novel coumarin-hydrazide-hydrazone hybrids, (E)-7-(diethylamino)-N′-(2-hydroxy-3-methoxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (1) and (E)-7-(diethylamino)-N′-(4-(diethylamino)-2-hydroxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (2), were synthesized and investigated their chemosensor properties. The sensors showed recognition properties of CN−, Co2+, and Ni2+ ions. After interaction with the cyanide anion, the coumarin-hydrazide-hydrazone sensors exhibited a color change visible to the naked eye, from yellow to colorless under daylight and from blue to green under UV light. The sensors exhibited a significant fluorescent enhancement response to the cyanide anion by the intramolecular charge transfer (ICT) mechanism. Furthermore, the recognition of cations was observed by the redshift of the emission band based on the complexation mechanism of Co2+ and Ni2+ ions with the sensors. Sensor 1 showed that CN− and Ni2+ ions could be detected at a limit of detection (LOD) of 0.187 μM and 0.169 μM, respectively, while sensor 2 showed that Co2+ anion could be detected at a LOD of 0.177 μM. Anion and cation recognition mechanisms were also investigated by Density Functional Theory (DFT) analysis for the sensors. Cell viability and proliferation-based cytotoxicity (MTT) and live cell imaging assays of sensor 2 were performed to elucidate whether it could be used as cell bioimaging. It was determined that sensor 2 was not cytotoxic against the A549 cell line at the concentrations where it could act as a chemosensor for the detection of CN−, Co2+, and Ni2+ ions, and it penetrated into the cell and accumulated around the nucleus. These properties of sensor 2 indicate that it can be used as a potential sensor in cell imaging systems. In addition, the photophysical properties of the sensors in various solvents with different polarities were investigated using spectroscopic techniques for absorption and emission maximum wavelengths. The thermal stability of the sensors was determined by Thermal Gravimetric Analysis (TGA), and it can be said that the theoretical and experimental studies are in perfect harmony.

Two-dimensional MXene membranes with biomimetic sub-nanochannels for enhanced cation sieving

Membranes with high ion permeability and selectivity are of considerable interest for sustainable water treatment, resource extraction and energy storage. Herein, inspired by K+ channel of streptomyces A (KcsA K+), we have constructed cation sieving membranes using MXene nanosheets and Ethylenediaminetetraacetic acid (EDTA) molecules as building blocks. Numerous negatively charged oxygen atoms of EDTA molecules and 6.0 Å two-dimensional (2D) sub-nanochannel of MXene nanosheets enable biomimetic channel size, chemical groups and tunable charge density for the resulting membranes. The membranes show the capability to recognize monovalent/divalent cations, achieving excellent K+/Mg2+ selectivity of 121.2 using mixed salt solution as the feed, which outperforms other reported membranes under similar testing conditions and transcends the current upper limit. Characterization and simulations indicate that the cation recognition effect of EDTA and partial dehydration effects play critical roles in cations selective sieving and increasing the local charge density within the sub-nanochannel significantly improves cation selectivity. Our findings provide a theoretical basis for ions transport in sub-nanochannels and an alternative strategy for design ions separation membranes.

Molecular basis of polyspecific drug and xenobiotic recognition by OCT1 and OCT2.

A wide range of endogenous and xenobiotic organic ions require facilitated transport systems to cross the plasma membrane for their disposition. In mammals, organic cation transporter (OCT) subtypes 1 and 2 (OCT1 and OCT2, also known as SLC22A1 and SLC22A2, respectively) are polyspecific transporters responsible for the uptake and clearance of structurally diverse cationic compounds in the liver and kidneys, respectively. Notably, it is well established that human OCT1 and OCT2 play central roles in the pharmacokinetics and drug-drug interactions of many prescription medications, including metformin. Despite their importance, the basis of polyspecific cationic drug recognition and the alternating access mechanism for OCTs have remained a mystery. Here we present four cryo-electron microscopy structures of apo, substrate-bound and drug-bound OCT1 and OCT2 consensus variants, in outward-facing and outward-occluded states. Together with functional experiments, in silico docking and molecular dynamics simulations, these structures uncover general principles of organic cation recognition by OCTs and provide insights into extracellular gate occlusion. Our findings set the stage for a comprehensive structure-based understanding of OCT-mediated drug-drug interactions, which will prove critical in the preclinical evaluation of emerging therapeutics.

Alkali Metal Ion Recognition by 18-Crown-6 in Aqueous Solutions: Evidence from Local Structures

The underlying recognition mechanisms of alkali metal ions by crown ethers in aqueous solutions are yet to be fully understood at the molecular level. We report direct experimental and theoretical evidence for the structure and recognition sequence of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) by 18-crown-6 in aqueous solutions by wide-angle X-ray scattering combined with an empirical potential structure refinement modeling and ab initio molecular dynamics simulation. Li+, Na+, and K+ are located in the negative potential cavity of 18-crown-6, with Li+ and Na+ deviating from the centroid of 18-crown-6 by 0.95 and 0.35 Å, respectively. Rb+ and Cs+ lie outside the 18-crown-6 ring and deviate from the centroid of 18-crown-6 by 0.05 and 1.35 Å, respectively. The formation of the 18-crown-6/alkali metal ion complexes is dominated by electrostatic attraction between the cations and the oxygen atoms (Oc) of 18-crown-6. Li+, Na+, K+, and Rb+ form the H2O···18-crown-6/cation···H2O "sandwich" hydrates, while water molecules only hydrate with Cs+ of the 18-crown-6/Cs+ complex on the same side of Cs+. Based on the local structure, the recognition sequence of 18-crown-6 for alkali metal ions in an aqueous solution follows K+ > Rb+ >Na+ >Li+, which is completely different from that (Li+ > Na+ > K+ > Rb+ > Cs+) in the gas phase, confirming that the solvation medium seriously affects the cation recognition of crown ethers. This work provides atomic insights into understanding the host-guest recognition and solvation behavior of crown ether/cation complexes.

A Neural Network to Decipher Organic Electrochemical Transistors’ Multivariate Responses for Cation Recognition

Extracting relevant data from real-world experiments is often challenging with intrinsic materials and device property dispersion, such as in organic electronics. However, multivariate data analysis can often be a mean to circumvent this and to extract more information when larger datasets are used with learning algorithms instead of physical models. Here, we report on identifying relevant information descriptors for organic electrochemical transistors (OECTs) to classify aqueous electrolytes by ionic composition. Applying periodical gate pulses at different voltage magnitudes, we extracted a reduced number of nonredundant descriptors from the rich drain-current dynamics, which provide enough information to cluster electrochemical data by principal component analysis between Ca2+-, K+-, and Na+-rich electrolytes. With six current values obtained at the appropriate time domain of the device charge/discharge transient, one can identify the cationic identity of a locally probed transient current with only a single micrometric device. Applied to OECT-based neural sensors, this analysis demonstrates the capability for a single nonselective device to retrieve the rich ionic identity of neural activity at the scale of each neuron individually when learning algorithms are applied to the device physics.

Oriented Zinc Metal Anode Based on Directional Recognition and Assembly.

The practical application of aqueous zinc batteries are highly limited by unsatisfied Zn anodes for the unavoidable dendrite growth and side reactions. Crystal orientation engineering is an effective way to overcome these inherent drawbacks. However, how to achieve Zn plating with manipulated crystallographic orientation is still a great challenge. Herein, a uniform (002)-oriented Zn metal anode is reported based on a directional cation recognition and crystal assembly strategy. The activated layered double hydroxide (Act-LDH) exhibits favorable adsorption energy with Zn2+ and high lattice matching with Zn (002) plane, which can be served as directional recognition layer to anchor Zn2+ and regulate crystallographic orientation of Zn as well. As demonstration, Zn crystals with ultrahigh ratio of (002)/(100) plane of 15.7 are assembled parallelly on horizontal Act-LDH, in which high CE of 99.85% maintains over 18000 cycles. The symmetric battery with (002)-oriented Zn shows stable plating/stripping process over 1650 and 420h at 1mAcm-2 /0.5mAhcm-2 and 10mAcm-2 /5mAhcm-2 , respectively, which is 9 and 12 times higher than unoriented polycrystalline Zn. Moreover, as-assembled full battery displays high specific capacity of 120mAhg-1 at 2Ag-1 over 1800 cycles.

Reduced P-glycoprotein recognition of a radioiodine-labeled phosphonium cation by stilbenylation for mitochondrial membrane potential based-imaging

The accumulation of radiolabeled phosphonium cations in cells is dependent on the mitochondrial membrane potential (MMP). However, the efflux of these cations from tumor cells via P-glycoprotein (P-gp) limits their clinical application as MMP-based imaging tracers. In the present study, we designed (E)-diethyl-4-[125I]iodobenzyl-4-stilbenylphosphonium ([125I]IDESP), which contains a stilbenyl substituent, as a P-gp inhibitor to reduce P-gp recognition, and evaluated its biological properties in comparison with 4-[125I]iodobenzyl dipropylphenylphosphonium ([125I]IDPP). The in vitro cellular uptake ratio of [125I]IDESP in P-gp expressing K562/Vin cells to the parent (P-gp negative) K562 cells was significantly higher than that of [125I]IDPP. The efflux rate of [125I]IDESP was not significantly different between K562 and K562/Vin, while [125I]IDPP was rapidly effluxed from K562/Vin compared with K562, and the efflux of [125I]IDPP from K562/Vin was inhibited by the P-gp inhibitor, cyclosporine A. The cellular uptake of [125I]IDESP was well correlated with the MMP levels. These results suggested that [125I]IDESP was accumulated in cells depending on the MMP levels, without being effluxed via P-gp, while [125I]IDPP was rapidly effluxed from the cells via P-gp. Despite having suitable in vitro properties for MMP-based imaging, [125I]IDESP showed rapid blood clearance and lower tumor accumulation than [125I]IDPP. Improvement in the normal tissue distribution of [125I]IDESP is required to develop an agent for use in in vivo MMP-based tumor imaging.

Effect of Alkali Metal Cations on the Unilamellar Vesicle of a Squalene Bearing 18-Crown-6.

Squalene bearing 18-crown-6 was synthesized and formed unilamellar vesicles with a membrane thickness of about 6 nm and a diameter of about 0.32 μm. In the wake of the recognition of alkali metal cations, squalene unilamellar vesicles become larger as multilamellar vesicles or smaller while maintaining unilamellar vesicles depending on cations.

Synthesis and Optoelectronic Features of Rhodamine-Triazole Dyads as Metallochromic Probes for Copper-Selective Chemosensing.

Rhodamine-based chromic materials have attracted significant interest owing to their cation recognition ability with high sensitivity. However, rhodamine chromophores with controllable sensing selectivity towards transition metal species are only at the advent. Herein, three triazole-conjugated rhodamine dyads with different peripheral substituents were synthesized. The key triazole precursors required for the desired chemistry were prepared by adopting our recently developed CTAB catalyzed mechano-click chemistry. Molecular properties derived from photophysics, electrochemistry and surface morphology of the synthesized dyads were analyzed. Furthermore, frontier molecular orbitals, electronic structure and secondary quantum chemical parameters of dyads were also compared. Screening of dyads for their sensing ability towards an array of alkali, alkaline and transition metal ions exhibited a noticeable naked-eye detection of Cu2+ ions and was confirmed by spectrophotometric titration. The specific binding mode of dyads as probable with Cu2+ over other metal ions attributes to the chemoselectivity.

Determination of trace amount of iron cations using electrochemical methods at N, S doped GQD modified electrode

In this work, nitrogen and sulfur co-doped graphene quantum dot-modified glassy carbon electrodes (N, S-GQD/GCE) were used for the recognition of iron cations in aqueous solutions. The dissolved cations are detected based on the faradaic reduction or oxidation current of Fe(III) and Fe(II) obtained at the N, S-GQD/GCE surface. Cyclic voltammetry (CV), square wave voltammetry (SWV), and hydrodynamic amperometry are used as suitable electrochemical techniques for studying electrochemical behavior and determination of Fe cations. Based on the obtained results, it is concluded that the presence of free electrons in the structure of N, S-GQD could facilitate electron transfer reaction between Fe(III) and electrode surface which with increased surface area results in increased sensitivity and lower limit of detection. By performing suitable experiments, the best condition for preparing the modified electrode and determining Fe(III) was selected. Under optimized conditions, the amperometric response is linear from 1 to 100 nM of Fe(III) with a detection limit of 0.23 nM. The validity of the method and applicability of the sensor is successfully tested by the determination of Fe(III) in drug and water real samples. This sensor opened a new platform based on doped nanoparticles for highly sensitive and selective detection of analytes.

Cation recognition controlled by protonation or chemical reduction: a computational study.

To control biochemical processes, non-covalent interactions involving cations are activated by protons or electrons. In the present study, the bonding situation between: (i) carboxylic acid or (ii) ferrocene-functionalized crown ether derivatives and cations (Li+, Na+ or K+) has been elucidated and, mainly, tuned by the substitution of hydrogen atoms by electron donor (-NH2) or acceptor (-NO2) groups. The deprotonation of the carboxyl groups improves the interaction with the cations through more favorable electrostatic O⋯cation interactions. Reducing the ferrocene structures favors cationic recognition supported by a less unfavorable iron⋯cation binding. The receptors preferably interact with smaller cations because of more attractive electrostatic and orbital (σ or π) O⋯cation interactions. The presence of electron donor or acceptor groups in the carboxylic acid-functionalized crown ethers promotes less attractive interactions with the cations, mainly due to the less favorable electrostatic O⋯Na+ interactions. The -H → -NH2 substitution in the ferrocene framework favors the cationic recognition. It is based on the strengthening of the electrostatic and σ O⋯Na+ and H2N⋯Na+ bonds. The (i) absence of repulsive electrostatic iron⋯cation interactions, or (ii) the presence of oxygen atoms with large electron density, ensures carboxylic acid-functionalized crown ethers have more favorable interactions with cations than ferrocene compounds. Therefore, this work has demonstrated how cation recognition can be improved by structural changes in carboxylic acid- or ferrocene-functionalized crown ethers and has shown that the carboxylic acid molecules appear to be better candidates for cation recognition than ferrocene derivatives.

Semicarbazone and thiosemicarbazone appended 4-diethylamino-2‑hydroxybenzyl compounds as highly selective bifunctional chemosensors: An experimental and computational approach

Three bifunctional chemosensors, 2-(4-(diethylamino)-2-hydroxybenzylidene)hydrazinecarboxamide (S1), 2-(4-(diethylamino)-2-hydroxybenzylidene)hydrazinecarbothioamide (S2) and 2-(4-(diethylamino)-2-hydroxybenzylidene)-N-methylhydrazinecarbothioamide (S3) have been designed and synthesized for recognition of inorganic cations and anions in solution at room temperature. The structure of the receptor S2 was confirmed by single crystal X-ray diffraction technique, which crystallizes in the monoclinic P21/n space group. The selectivity and sensitivity of cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ and Pb2+) and anions (F−, Cl−, Br−, I−, HSO4− and H2PO4−) were investigated using colorimetric, UV–vis absorption, emission and 1H NMR studies. The receptors (S1–S3) with ONO/ONS donors allow bare-face recognition of Co2+, Ni2+ and Cu2+ cations, and F− anion in a mixture of solvent, CH3CN:CH3OH (8:2, v/v). The receptor S3 possesses high sensitivity and selectivity in comparison with the receptors S1 and S2. The binding constant and limit of detection of the receptors with sensed cations and anion showed high sensitivity and selectivity towards Co2+ cation with order of magnitude 6, greater than the other sensed cations. In addition, the receptors S3 also shows 6 order of magnitude for Cu2+ cation and F− anion. The optimized geometry determined by DFT studies shows that the receptors in its conjugated state provide binding sites for cations and F− anion. The HOMO-LUMO energy gap between the receptors and the Co2+ cation was found to be the least among the studied receptors-cations binding interaction, possibly due to charge transfer effect.

Bifunctional Receptor Based on Calix[4]arene with Chromone Groups as An Efficient Colorimetric Sensor for Co2+, Cu2+, CN− and F−

AbstractNew calix[4]arene derivatives based on chromone linked through a thiosemicarbazone bridge have been designed and synthesized. It has been determined by UV‐visible absorption and IR‐spectroscopic study that molecular receptors are efficient for recognition of cations (Co2+, Cu2+, Ni2+ and Zn2+) and anions (F− and CN−), because calixarene plays a role as a molecular platform and the interaction is explained by the presence of the thiosemicarbazone bridge bound to chromone. The sensors showed selective colorimetric changes with cobalt (II), copper (II), cyanide and fluoride ions. The detection limits of 0.19 to 0.70 mg L−1 and the association constants ranging between 1.28×104 and 9.87×104 mol−1L can be estimated for these three sensors.

A new lipophilic cationic rhodamine-based chemosensor for detection of Al(III)/Cu(II) and intracellular pH change and its application as a smartphone-assisted sensor in water sample analysis

A new probe, RTPP was prepared by condensation of rhodamine B hydrazide with (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride. The structure of sensor RTPP was elucidated using spectroscopic methods and single crystal X-ray diffraction. Colourless and non-fluorescence sensor RTPP solution turns pink in the presence of Cu2+ and showed orange fluorescence enhancement in the presence of Al3+. Cation recognition performance and binding mechanisms of the probe were studied through UV, fluorescence, IR, MS, and NMR spectroscopic studies; where the results revealed that sensor RTPP has a high affinity towards Al3+/Cu2+ with the limit of detection down to at least 10-7 M. The developed system was applicable for tracing Cu2+ through colorimetric method in two selected water samples with satisfactory results. More significantly, “naked-eye” detection of Cu2+ using RTPP has been effectively incorporated with a smartphone RGBColorDetector application to make it suitable for on-site qualitative and quantitative colorimetric investigation. In addition, RTPP can act as a sensor for detecting acidic pH change in HCT 116 human colorectal carcinoma cell line through fluorescence response.

Rational Design of a Fluorescent Chromophore as a Calcium Receptor via DFT and Multivariate Approaches.

Computational and experimental approaches were adopted to utilize a chromophore diglycolic functionalized fluorescein derivative as a Ca2+ receptor. Fluorescein diglycolic acid (Fl-DGA, 1) was synthesized and used in multivariate determination of Ca2+ and K+. Full-structure computation shows that the complexes of 1 and Ca2+ have comparable energies regardless of additional interaction with lactone moiety. The initial formation of diglycolic-Ca2+ complex followed by macrocyclization is thermodynamically disfavored. A U-shaped pre-organized 1 allows Ca2+ to interact simultaneously with diglycolic and lactone motifs. Both motifs actively participate in Ca2+ recognition and the eleven methylene units in the undecyl arm provides excellent flexibility for reorganization and optimum interaction. Principal component analysis (PCA) of computational molecular properties reveals a simple method in evaluating motifs for cation recognition. Fragment models support full-structure results that negative charge causes significant structural changes, but do not reproduce the full extent of C-O bond breaking observed in the latter. Experimental optical responses show that 1 is selective towards Ca2+ and discriminates against K+ and Mg2+. PCA of emission intensities affords distinct clusters of 0.01, 0.1 and 1 mM Ca2+ and K+, and suggests applicability of this technique for simultaneous determination of cationic plant macronutrients in precision agriculture and a wide variety of other applications.