Tripodal Receptors for Cation and Anion Sensors

A captivating approach to elevate the detection of Al3+ ions incorporates the utilization of a tripodal receptor intricately embellishing the surface of zinc oxide

The FDA (Food and Drug Administration, (USA)) lists ZnO as a material that is widely acknowledged to be safe. ZnO NPs with a range of tiny particle sizes were made using the precipitation process. ZnO nanoparticles' surface is embellished with a tripodal sensor containing naphthol units. The assembly with the same receptor decorated on ZnO NPs is contrasted with the cation detection capabilities of the purified tripodal receptor. The UV-visible spectrophotometric analysis was conducted to study the state transitions of the receptor and the decorated ZnO receptor. A positive selectivity to Al3+ cations is determined by the fluorescence study under ideal circumstances. The particle size and surface morphologies are determined by DLS and SEM analysis for the same receptor - TP1 and embellished with a tripodal receptor TP2. Using a fluorescence switch-on Photoinduced Electron Transfer (PET) mechanism, the receptor coated on ZnO detects the presence of Al3+ ions with specificity. The binding constant value was determined using the B-H plot equation. Binding stoichiometry for [TP1-Al3+, TP2-Al3+] showed a 1:1 ratio. The fluorescence switches ON-OFF process of the ZnO surface adorned - TP2 with Tripodal receptor- TP1 was used to create molecular logic gates, which can function as a module for sensors and molecular switches. The addition of Na2EDTA in the solution of the [TP1; TP2 - Al3+] complex resulted in a noticeable reduction in the emission of fluorescence. This finding offers compelling support for the reversibility of the chemosensor. To enable the practical application of this sensor, we have developed a cassette containing receptors TP1 and TP2. Successfully, it can detect Al3+ metal ions. We performed a comprehensive assessment of the dependability and appropriateness of our approach in measuring the concentration of Al3+ ions in wastewater produced by important industrial procedures.

Applying a Tripodal Hexaurea Receptor for Binding to an Antitumor Drug, Combretastatin-A4 Phosphate

Phosphates play a crucial role in drug design, but their negative charge and high polarity make the transmembrane transport of phosphate species challenging. This leads to poor bioavailability of phosphate drugs. Combretastatin-A4 phosphate (CA4P) is such an anticancer monoester phosphate compound, but its absorption and clinical applicability are greatly limited. Therefore, developing carrier systems to effectively deliver phosphate drugs like CA4P is essential. Anion receptors have been found to facilitate the transmembrane transport of anions through hydrogen bonding. In this study, we developed a tripodal hexaurea anion receptor (L1) capable of binding anionic CA4P through hydrogen bonding, with a binding constant larger than 104 M-1 in a DMSO/water mixed solvent. L1 demonstrated superior binding ability compared to other common anions, and exhibited negligible cell cytotoxicity, making it a promising candidate for future use as a carrier for drug delivery.

Biomass-Derived Core-Shell Carbon Dots with Embedded Tripodal Receptors for the Selective Recognition of Mefenamic Acid in Pharmaceutical Formulations and Urine

A tripodal amine (TPA) with -OH, N, and S donors is synthesized to functionalize a core-shell carbon dot composite (FCDs@SiO2-TPA) for sensing application. The TPA is characterized by spectroscopic and spectrometric techniques, and the composite is characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectra (EDS) techniques. The composite has the ability to recognize mefenamic acid (MFA) selectively even in the presence of other drugs like ibuprofen sodium, acetylsalicylic acid, naproxen sodium, diclofenac sodium, and ketoprofen. It can also be used for the quantification of MFA by recording the emission quenching response of the sample at λexc. = 350 nm and λems. = 460 nm (linear range = 1-8 μM and LOD = 197 nM). The density functional theory calculations and 1H NMR titration suggest quenching of the emission signal due to photoinduced electron transfer via hydrogen bonding between the probe and MFA. The composite FCDs@SiO2-TPA has been demonstrated as a reliable and cost-effective sensing probe for the detection of MFA in pharmaceutical formulations, water samples, and cow urine samples.

Rapid Access to Chiral and Tripodal Cavitands from β-Pinene

We report Pd-catalyzed cyclotrimerization of (+)-α-bromoenone, obtained from monoterpene β-pinene, into an enantiopure cyclotrimer. This C₃ symmetric compound has three bicyclo[3.1.1]heptane rings fused to its central benzene with each ring carrying a carbonyl group. The cyclotrimer undergoes diastereoselective threefold alkynylation with the lithium salts of five terminal alkynes (41-63 %, de=4-83 %). The addition enabled a rapid synthesis of a small library of novel chiral cavitands that, in shape, resemble a tripod stand. These molecular tripods include a tris-bicycloannelated benzene head attached to three alkyne legs twisted in one direction to form a nonpolar cavity with polar groups as feet. Tripods with methylpyridinium and methylisoquinolinium legs, respectively, form inclusion complexes with anti-inflammatory and chiral drugs (R)/(S)-ibuprofen and (R)/(S)-naproxen. The mode of binding shows drug molecules docked in the cavity of the host through ion-ion, cation-π, and C-H-π contacts that, in addition of desolvation, give rise to complexes having millimolar to micromolar stability in water. Our findings open the door to creating a myriad of enantiopure tripods with tunable functions that, in the future, might give novel chemosensors, catalysts or sequestering agents.

1,4,6,10-Tetraazaadamantanes (TAADs) with N-amino groups: synthesis and formation of boron chelates and host–guest complexes

A synthetic route to 1,4,6,10-tetraazaadamantanes (TAADs) bearing free and protected amino groups at the bridge N-atoms has been developed via intramolecular cyclotrimerization of C=N units in the corresponding tris(hydrazonoalkyl)amines. In a similar fashion, unsymmetrically substituted TAADs having both amino and hydroxy groups at the bridge N-atoms were prepared via a hitherto unknown co-trimerization of oxime and hydrazone groups. The use of N-TAAD derivatives as potential ligands and receptors was showcased through forming boron chelates and host–guest complexes with water and simple alcohols.

Co-crystals of tetrahaloauric acid and 1,3,5-(methylacetamide)benzene-based tectons: consistent trapping of high energy molecular conformation

Co-crystal engineering is a promising method to create new classes of advanced materials. Co-crystal structure prediction is more challenging when one or more of the lattice constituents (tectons) are flexible...

Development, Optimization, Characterization, and Application of Electrochemical Biosensors for Detecting Nickel Ions in Food

Nickel is naturally present in drinking water and many dietary items, which expose the general population to nickel ingestion. This heavy metal can have a variety of harmful health effects, causing allergies and skin disorders (i.e., dermatitis), lung, cardiovascular, and kidney diseases, and even certain cancers; therefore, nickel detection is important for public health. Recent innovations in the development of biosensors have demonstrated they offer a powerful new approach over conventional analytical techniques for the identification and quantification of user-defined compounds, including heavy metals such as nickel. We optimized five candidate nickel-biosensing receptors, and tested each for efficiency of binding to immobilization elements on screen-printed electrodes (SPEs). We characterized the application of nickel-detecting biosensors with four different cultivated vegetables. We analyzed the efficiency of each nickel-detecting biosensor by potentiostat and atomic absorption spectrometry and compared the results from the sample analytes. We then analyzed the performance characteristics and responses of assembled biosensors, and show they are very effective at measuring nickel ions in food, especially with the urease-alginate biosensor affixed to silver SPEs, measured by cyclic voltammetry (sensitivity-2.1921 µA Mm^-1 cm^-2 and LOD-0.005 mg/L). Given the many advantages of biosensors, we describe an optimization pipeline approach to the application of different nickel-binding biosensors for public health, nutrition, and consumer safety, which are very promising.

Halogen Bonding Ionophore for Potentiometric Iodide Sensing

Iodide (I^-) is an essential micronutrient for thyroid function. Hence, rapid and portable sensing is important for I^- quantification in food and biological samples. Herein, we report the first example of a halogen bonding (XB) tripodal ionophore (XB1) which is selective for the I^- anion. NMR binding studies of XB1 and its H-triazole analog HB2 with I^- demonstrated the dominant influence of XB interactions between the ionophore and the I^- analyte. The phase boundary model was applied to formulate iodide-selective electrodes with the ionophore XB1. The optimal electrode exhibited a near-Nernstian response of -51.9 mV per decade within a large dynamic range (10^-1 to 10^-6 M) and notably anti-Hofmeister selectivity for I^- over thiocyanate (SCN^-), enabling the in situ determination of I^- in complex samples. This work establishes XB as a viable supramolecular interaction in the potentiometric sensing of anions.

Alkylammonium Cation Affinities of Nitrogenated Organobases: The Roles of Hydrogen Bonding and Proton Transfer

Alkylammonium cation affinities of 64 nitrogen-containing organobases, as well as the respective proton transfer processes from the alkylammonium cations to the base, have been computed in the gas phase by using DFT methods. The guanidine bases show the highest proton transfer values (191.9-233 kJ mol^-1 ) whereas the cis-2,2'-biimidazole presents the largest affinity towards the alkylammonium cations (>200 kJ mol^-1 ) values. The resulting data have been compared with the experimentally reported proton affinities of the studied nitrogen-containing organobases revealing that the propensity of an organobase for the proton transfer process increases linearly with its proton affinity. This work can provide a tool for designing senors for bioactive compounds containing amino groups that are protonated at physiological pH.

Sulphonamidic Groups as Electron-Withdrawing Units in Ureido-Based Anion Receptors: Enhanced Anion Complexation versus Deprotonation

A sulphonamidic moiety was utilized as an electron-withdrawing group for enhancement of anion complexation features of urea-based receptors. A series of receptors varying in acidity of sulphonamidic and urea NH groups was synthesized and thoroughly tested. The individual complexation properties reflect deprotonation/complexation equilibrium in a given molecule as a function of the substitution. The receptors containing electron-donating groups in conjugation to the sulphonamidic moiety showed higher association constants towards H₂ PO₄ ^- and carboxylate anions, while those containing electron-withdrawing groups inclined to deprotonation of sulphonamidic NH. The deprotonation issue can be avoided by alkylation at the early step of receptor synthesis or it can be utilized for insertion of suitable groups that enable its anchoring on various substrates to form more elaborated receptor structures.

A new C-anionic tripodal ligand 2-{bis(benzothiazolyl)(methoxy)methyl}phenyl and its bismuth complexes

A new tripodal C-anionic ligand, 2-{bis(benzothiazolyl)(methoxy)methyl}phenyl (L), was stably generated by the reaction of the ligand precursor (L'), the corresponding bromide (2-BrC6H4)(MeO)C(C7H4NS)2 (C7H4NS = 2-benzothiazolyl), with nBuLi at -104 °C in the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine). The ligand lithium salt reacted with BiCl3 to give a 2 : 1 complex L2BiCl. A 1 : 1 complex LBiCl2 was obtained in good yield by the redistribution reaction between L2BiCl and BiCl3. X-ray diffraction analysis revealed that the ligand L coordinated in an expected κ3-C,N,N' coordination mode in LBiCl2, while it coordinated in κ3-C,N,O and κ2-C,O coordination modes in L2BiCl. The ligand precursor reacted with BiX3 (X = Cl, Br) to give 1 : 1 complexes L'BiX3 and was found to act as a neutral tripodal C(π),N,N-ligand.

Making Waxy Salts in Water: Synthetic Control of Hydrophobicity for Anion-Induced and Aggregation-Enhanced Light Emission

We show that multipodal polycationic receptors function as anion-responsive light-emitters in water. Prevailing paradigms utilize rigid holes and cavities for ion recognition. We instead built open amphiphilic scaffolds that trigger polar-to-nonpolar environment transitions around cationic fluorophores upon anion complexation. This ion-pairing and aggregation event produces a dramatic enhancement in the emission intensity, as demonstrated by perchlorate as a non-spherical hydrophobic anion model. A synergetic interplay of C-H⋅⋅⋅anion hydrogen bonding and tight anion-π⁺ contacts underpins this supramolecular phenomenon. By changing the aliphatic chain length, we demonstrate that the response profile and threshold of this signaling event can be controlled at the molecular level. With appropriate molecular design, inherently weak, ill-defined, and non-directional van der Waals interaction enables selective, sensitive, and tunable recognition in water.

Crystal structure of 2,2'-{[(2-nitro-benz-yl)aza-nedi-yl]bis-(propane-3,1-di-yl)}bis-[1H-iso-indole-1,3(2H)-dione]

The structure of the title compound, C29H26N4O6, exhibits a folded conformation with the three arms all on the same side of the tertiary N atom. The two phthalimide units make a dihedral angle of 12.18 (12)° and the dihedral angles between the benzyl plane and the phthalimide units are 68.08 (7) and 67.71 (7)°. The crystal packing features π-π inter-actions.

Highly Efficient, Tripodal Ion-Pair Receptors for Switching Selectivity between Acetates and Sulfates Using Solid-Liquid and Liquid-Liquid Extractions

A tripodal, squaramide-based ion-pair receptor 1 was synthesized in a modular fashion, and ¹H NMR and UV-vis studies revealed its ability to interact more efficiently with anions with the assistance of cations. The reference tripodal anion receptor 2, lacking a crown ether unit, was found to lose the enhancement in anion binding induced by presence of cations. Besides the ability to bind anions in enhanced manner by the “single armed” ion-pair receptor 3, the lack of multiple and prearranged binding sites resulted in its much lower affinity towards anions than in the case of tripodal receptors. Unlike with receptors 2 or 3, the high affinity of 1 towards salts opens up the possibility of extracting extremely hydrophilic sulfate anions from aqueous to organic phase. The disparity in receptor 1 binding modes towards monovalent anions and divalent sulfates assures its selectivity towards sulfates over other lipophilic salts upon liquid–liquid extraction (LLE) and enables the Hofmeister bias to be overcome. By changing the extraction conditions from LLE to SLE (solid–liquid extraction), a switch of selectivity from sulfates to acetates was achieved. X-ray measurements support the ability of anion binding by cooperation of the arms of receptor 1 together with simultaneous binding of cations.

Structural investigation of bromide complexation with bipodal, tripodal and tetrapodal cationic molecules

Various multipodal molecules comprising dicationic bipodal molecules, tricationic tripodal molecules and tetracationic tetrapodal molecules with adaptable functional groups have been synthesized and characterised.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4. ACS OMEGA 2019;4:10877-10890. [PMID: 31460185 PMCID: PMC6648501 DOI: 10.1021/acsomega.9b00377]

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10-8 M for Mo(VI), 1.2 × 10-10 M for AsO2 -, and 3.2 × 10-6 M for H2PO4 -, whereas the respective association constants are 4.21 × 105 M-1 for Mo(VI), 6.49 × 104 M-1 for AsO2 -, and 2.11 × 105 M-1 for H2PO4 -. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2 - from environmental samples by solid-phase extraction.

H-Bond donor parameters for cations

UV/Vis absorption and NMR spectroscopy titrations have been used to investigate the formation of complexes between cations and neutral H-bond acceptors in organic solvents. Complexes formed by two different H-bond acceptors with fifteen different cations were studied in acetone and in acetonitrile. The effects of water and ion pairing with the counter-anion were found to be negligible in the two polar solvents employed for this study. The data were used to determine self-consistent H-bond donor parameters (α) for a series of organic and inorganic cations; guanidinium, primary, tertiary and quaternary ammonium, imidazolium, methylpyridinium, lithium, sodium, potassium, rubidium and caesium. The results demonstrate the transferability of α parameters for cations between different solvents and different H-bond acceptor partners, allowing reliable prediction of cation recognition properties in different environments. Lithium and protonated nitrogen cations form the most stable complexes, but the α parameter is only 5.0, which is similar to the neutral H-bond donor 3-trifluoromethyl,4-nitrophenol (α = 5.1). Quaternary ammonium is the weakest H-bond donor investigated with an α value of 2.7, which is comparable to an alcohol. The α parameters for alkali metal cations decrease down the group from 5.0 (Li+) to 3.5 (Cs+).

Aggregation induced emission enhancement (AIEE) of tripodal pyrazole derivatives for sensing of nitroaromatics and vapor phase detection of picric acid

Organosoluble tris-pyrazole compounds aggregate in organic/aqueous solvent mixtures, showing aggregation-induced emission enhancement (AIEE), the latter being quenched by picric acid.

Tailoring the local environment around metal ions: a solution chemical and structural study of some multidentate tripodal ligands

Manganese(ii), copper(ii) and zinc(ii) complexes of four polydentate tripodal ligands (tachpyr (N,N',N''-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane), trenpyr (tris[2-(2-pyridylmethyl)aminoethyl]amine, tach3pyr (N,N',N''-tris(3-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane) and tren3pyr (tris[2-(2-pyridylmethyl)aminoethyl]amine)) were characterized in both solution and solid states. A combined evaluation of potentiometric, UV-VIS, NMR and EPR data allowed the conclusion of both thermodynamic and structural information about the complexes formed in solution. The four tailored polydentate tripodal ligands studied here exhibit a high thermodynamic stability, and a variety of coordination environments/geometries for the studied transition metal ions. Our data indicate that tachpyr is a more efficient zinc(ii) chelator and a similar copper(ii) chelator compared to trenpyr. Considering the higher number of N-donors and conformational flexibility of trenpyr, as well as the energy demanding switch to the triaxial conformation required for metal ion binding of tachpyr, the above observation is surprising and is very likely due to the encapsulating effect of the more rigid tachpyr skeleton. This relative binding preference of tachpyr for zinc(ii) may be related to the observation that zinc(ii) is one of the principal metals targeted by tachpyr in cells. In contrast, trenpyr is a considerably more efficient manganese(ii) chelator, since it acts as a heptadentate ligand in the aqueous Mn(trenpyr) complex. The crystal structures of copper(ii) and zinc(ii) complexes of tachpyr indicated important differences in the ligand conformation, induced by the position of counter ions, as compared to earlier reports. The closely related new ligands, tach3pyr and tren3pyr, have been designed to form oligonuclear complexes. Indeed, we obtained a three dimensional polymer with a copper(ii)/tren3pyr ratio of 11/6. Within this metal-organic framework, three distinctly different copper geometries can be identified: square pyramidal, trigonal bipyramidal and tetrahedral. Two square pyramidal and four trigonal bipyramidal copper centres create a hexanuclear subunit with a large inside cavity. These moieties are linked by tetrahedral copper(ii) centres, constructing the three-dimensional polymer structure. The formation of such polynuclear complexes was not detected in solution. Both tach3pyr and tren3pyr form only mononuclear complexes with square pyramidal and trigonal bipyramidal geometries, respectively.

Remarkably selective NH4+ binding and fluorescence sensing by tripodal tris(pyrazolyl) receptors derived from 1,3,5-triethylbenzene: structural and theoretical insights on the role of ion pairing

Differences in pyrazole substitution result in dramatic changes in NH₄⁺ binding and fluorescence sensing, due to ion pairing and solvation effects.

Efficient and selective separation of aqueous sulfate through recognition and precipitation

Sulfate anions are selectively separated from aqueous solution in the form of precipitates by a mono-protonated organic receptor, constructed in situ through anion-templated chemical synthesis.

Control of structure, stability and catechol oxidase activity of copper(ii) complexes by the denticity of tripodal platforms

The speciation and catecholase-like activity of trinuclear complexes can be fine tuned by the denticity of tripodal platforms.

Design, synthesis and ¹H NMR study of C3v-symmetric anion receptors with urethane-NH as recognition group

C3v-Symmetric anion receptors 3 and 4 with urethane groups were synthesized by using trindane triol as tripodal molecular framework. In (1)H NMR titration study, the receptors showed noticeable downfield shift/disappearance of the urethane-NH peak in presence of H2PO4(-) and F(-) due to the host-guest complexation occurred through multiple hydrogen bonding and/or the deprotonation of urethane-NH groups. Other tested anions such as Cl(-), Br(-), HSO4(-), and NO3(-) showed either no or negligible chemical shift of the urethane groups. The deprotonation event in 4 allowed selective detection of F(-) by perceptible color change from colorless to yellowish-red with the appearance of a new charge transfer absorption band at 450 nm.

Anion coordinated capsules and pseudocapsules of tripodal amide, urea and thiourea scaffolds

This review provides a detailed and comparative account of the solid- and solution-states anion (halides and oxyanions) binding affinities of hydrogen bonding tripodal scaffolds.

A reversible fluorescent-colorimetric chemosensor based on a novel Schiff base for visual detection of CO32− in aqueous solution

A novel Schiff base receptor L has been fabricated for fluorescent-colorimetric detection of CO₃²⁻ in aqueous media. L shows an excellent selectivity, rapid response and reversibility and its sensitivity for CO₃²⁻ is the lowest ever found (96 nM).