Metal Ion Recognition Research Articles

Intramolecularly Hydrogen-Bonded Aromatic Pentamers as Modularly Tunable Macrocyclic Receptors for Selective Recognition of Metal Ions.

Despite the tremendous progress that has been made in macrocyclic chemistry since the discovery of corands, cryptands, and spherands more than four decades ago, macrocyclic systems possessing a high level of controllability in structural configuration concurrent with a systematic tunability in function are still very rare. Employing an inner design strategy to orient H-bonding forces toward a macrocyclic cavity interior while convergently aligning exchangeable ion-binding building blocks that dictate a near-identical backbone curvature, we demonstrate here a novel pentagonal framework that not only enables its variable interior cavity to be maintained at near-planarity but also allows its ion-binding potential to be highly tunable. The H-bonded macrocyclic pentamers thus produced have allowed a systematic and combinatorial evolution of ion-selective pentamers for preferential recognition of Cs(+), K(+), or Ag(+) ions.

Selective interactions of trivalent cations Fe3 +, Al3 + and Cr3 + turn on fluorescence in a naphthalimide based single molecular probe

Synthesis and fluorescence turn-on behavior of a naphthalimide based probe is described. Selective interactions of trivalent cations Fe3+, Al3+ or Cr3+ with probe 1 inhibit the PET operating in the probe, and thereby, permit the detection of these trivalent cations present in aqueous samples and live cells. Failure of other trivalent cations (Eu3+, Gd3+ and Nb3+) to inhibit the PET process in 1 demonstrates the role of chelating ring size vis-à-vis ionic radius in the selective recognition of specific metal ions.

Design and synthesis of chalcone-based macrocyclic polyethers

AbstractA series of chalcone-based macrocyclic ethers have been synthesized. These macrocyclic ethers contain polyether as well as extended conjugation to the benzene ring to function as fluorescent sensor for cations. The modeling studies show that the chalcone part of the receptors remains partially out of plane from the polyether part and the keto moiety of the receptors always directed outwardly in the receptor itself. This may be changed during the recognition of metal ions. The tendency of the fluorophore, to be out of plane, increases with increasing the ring size.

A naphthopyran-rhodamine based fluorescent and colorimetric chemosensor for recognition of common trivalent metal ions and Cu2+ ions

A well-designed naphthopyran derivative bearing a rhodamine 6G unit as a chemosensor has been synthesized successfully and characterized by single crystal X-ray diffraction, nuclear magnetic resonance and mass spectrometry. The naphthopyran-rhodamine 6G dyad (R6GNP) exhibits excellent photochromism with reversible color change upon alternating ultraviolet irradiation and thermal bleaching. The as-prepared R6GNP as fluorescent sensor is sensitive to common trivalent metal ions, such as Fe3+, Cr3+, Ga3+, In3+ and Al3+. Furthermore, the optical and colorimetric sensing properties of R6GNP for Cu2+ ions were investigated by the naked eye and UV–vis absorption spectra. Upon the addition of Cu2+, there was no obvious color change of the solution. Interestingly, upon UV irradiation with light of 360nm, changes can be observed by the naked eye. The colorless solution gradually turned pink as induced by photoirradiation at room temperature. Compared to other fluorophore-photochrome dyes, R6GNP possesses distinctive multi-selective ability for metal ions and shows potential applications in fluorescent molecular probe, photoprinting and UV strength measurement.

Quinoline-functionalized norbornene for fluorescence recognition of metal ions

Abstract A quinoline-functionalized norbornene (1) and its homopolymer (P1) for metal ions recognition have been synthesized and characterized. In CH3CN solution, 1 exhibited fluorescence enhancement response toward Hg2+, Zn2+ and Cu2+, with Hg2+ resulting in a green emission at 465 nm, and Zn2+/Cu2+ increasing 1’s original emission at 406 nm. NMR titrations and DFT calculations results indicated that 1 bound Hg2+ in an imidic acid tautomeric form of the amide quinoline receptor, while Zn2+ and Cu2+ were bound to 1 in an amide tautomeric form. In addition, owing to the strong imidic acid tautomeric binding mode of 1-Hg2+ complex, 1 can recognized Hg2+ from Zn2+/Cu2+ and other competitive metal ions. In contrast, the homopolymer P1, which was obtained by ring opening metathesis polymerization (ROMP) method, exhibited only fluorescence enhancement sensing to Hg2+ and Cu2+ in an amide tautomeric binding mode with increasing emission at 416 nm.

Highly stable ionic liquid-in-water emulsions as a new class of fluorescent sensors for metal ions: the case study of Fe3+ sensing

A stable fluorescent ionic liquid can act as a fluorescent sensor for metal ion recognition.

Solvent effect on the fluorescence response of hydroxycoumarin bearing a dipicolylamine binding site to metal ions.

The fluorescence behavior of a probe dpa-HC, which has a coumarin derivative that acts as a fluorophore and a dipicolylamine (DPA) unit that functions as a metal ion-recognition site, was investigated with various metal ions in aqueous and several non-aqueous solvents. In aqueous solution, the fluorescence of dpa-HC was enhanced by Zn(2+) and Cd(2+), but was quenched by other metal ions. On the other hand, in an acetonitrile solution, only Mg(2+) enhanced the fluorescence, and the addition of a small amount of water quenched this fluorescence. This dramatic selectivity change is explained by stabilization of a metal-dpa-HC complex due to acetonitrile coordination and ON-OFF switching of the intramolecular photoinduced electron transfer (PET) from the nitrogen lone pair of DPA to the coumarin derivative.

2-Aminotryptanthrin Derivative with Pyrene as a FRET-based Fluorescent Chemosensor for Metal Ions

1-(2-tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P) was synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of T2NH-P5P by separately adding Mg(2+), Ca(2+), Ba(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Zn(2+), Cd(2+), Hg(2+), Al(3+), and Pb(2+) in an acetonitrile solution. When using excitation at 325 nm, which corresponds to the absorption of the pyrene unit of T2NH-P5P, emission at 600 nm, from the 2-aminotryptanthrin unit, was observed, indicating that intramolecular fluorescence resonance energy transfer (FRET) occurs in T2NH-P5P (FRET-on). However, when Fe(2+), Fe(3+), Ni(2+), Cu(2+), Cd(2+), Hg(2+), and Al(3+) were added to an acetonitrile solution of T2NH-P5P, the behavior changed from FRET-on to FRET-off, which means that the fluorescence of 2-aminotryptanthrin was quenched, whereas that of the pyrene group was revived (FRET-off). Especially, this behavior was remarkable for Fe(2+), Fe(3+), Cu(2+), and Hg(2+). T2NH-P5P is suitable for use as a fluorescent chemosensor for Fe(2+), Fe(3+), Cu(2+), and Hg(2+).

Fluorogenic ratiometric dipodal optode containing imine-amide linkages: Exploiting subtle thorium (IV) ion sensing

The (13E,19E)-N1′,N3′-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been developed for the detection of Th4+ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L–Th4+ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L–Th4+. The detection limit of L for Th4+ recognition is to a concentration down to 0.1μM (0.023μgg−1). The present sensing system is also successfully applied for the detection of Th4+ ion present in soil near nuclear atomic plants.

ChemInform Abstract: Aromatic Amide and Hydrazide Foldamer‐Based Responsive Host‐Guest Systems

AbstractReview: 61 refs.

Development of chemosensor for Sr(2+) using organic nanoparticles: application of sensor in product analysis for oral care.

A new series of compounds has been developed for the recognition of metal ions and it was found that the position of substituent in the organic compound proved to be the deciding factor for the development of a chemosensor. Reprecipitation method was used to develop organic nanoparticles (ONPs) in aqueous medium and the suspension of ONP in aqueous medium remained stable for one month. These ONPs were studied for their recognition abilities using fluorescence spectroscopy and only ONPs of compound 1 resulted in a sensor for Sr(2+) and the sensor activities were found to be unaffected by the presence of any other cation. The sensor was successfully used to investigate the level of Sr(2+) in an oral gel, as well as toothpastes used to cure sensitive teeth.

Synthesis of 1,10-phenanthroline functionalized periodic mesoporous organosilicas as metal ion-responsive sensors

The periodic mesoporous organosilicas with 1,10-phenanthroline (Phen) integrated in the framework (Phen-PMOs) were synthesized by co-condensation of tetramethoxysilane (TMOS) and the phenanthroline bridged organosilicas (Phen-Si) using triblock copolymer P123 as a template in weak acidic medium. The FT-IR, 13C CP-MAS and 29Si MAS NMR characterizations confirmed the integration of phenanthroline ligand in material. The Phen-PMOs have ordered 2-D hexagonal mesostructure though the structural order decreases with the increment in Phen content based on XRD and TEM characterizations. The hybrid materials exhibited specific surface area of 328–106m2/g and total pore volume of 0.43–0.17cm3/g. These Phen-functionalized PMOs, with strong blue fluorescent emission originated from phenanthroline group in the framework, have potential application in recognition of different metal ions, with luminescence intensity sensed to the type and concentration of the metal ions.

Synthesis and reactivity of Ln- and LnNa-macrocyclic compartmental Schiff base and polyamino complexes

The [1+1] Schiff base macrocyclic ligands H2LA and H3LB, synthesized by condensation of 3,3′-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) (H2L′) with 1,5-diamino-3-azamethylpentane (A′) and N,N-bis(2-aminoethyl)-2-hydroxybenzylamine·3HCl (HB′·3HCl), respectively, and their related polyamines H2RA and H3RB, which exhibit enhanced stability toward hydrolysis and greater flexibility, give rise to a wide series of mono-Ln and heterodinuclear-LnNa complexes. The crystal structure of [LuNa(RB)(OH)]2, determined by single-crystal X-ray diffraction, indicates the preference of the lutetium(III) ion and of the sodium(I) ion for the Schiff base and the crown-ether like chambers, respectively. To test the flexibility of reduced ligands and the possibility to encapsulate different lanthanide(III) ions in the coordinating moiety, [LuNa(RB)(CH3COO)]·2iPrOH, [LuNa(LB)(Cl)], [LaNa(RB)(Cl)] and [LaNa(LB)(Cl)] are mixed with different lanthanide(III) salts to detect metalation, demetalation, transmetalation and/or site migration processes by ESI mass spectrometry and NMR spectroscopy. In particular the role of the metals and of the coordinating moiety in directing these processes is discussed.Furthermore, the possibility to use these complexes as probe for selective recognition of alkali and alkaline earth metal ions is tested by ESI mass spectrometry on [LuNa(RB)(CH3COO)]·2iPrOH and by the 23Na NMR shift on [YbNa(RB)(CH3COO)]. The partial or total transmetalation of the sodium(I) ion represents a relevant result capable to open interesting scientific opportunities.

Recognition of metal ions using ProMOL to improve protein function assignation (777.1)

ProMOL is a plugin for PyMOL that utilizes the 3D visualization and measurement capacities of PyMOL to predict enzyme function by aligning query structures with a collection of annotated active sites found in our motif template library. The focus of this initiative is a response to the >3000 structures in the Protein Data Bank that are labeled as having “unknown function”. ProMOL undergoes constant revision and development from the various team members from RIT and Dowling College. The motif capabilities of ProMOL have been expanded to include metal ions and prosthetic groups that are found in enzyme active sites, as nearly 40% of all the PDB structures contain at least one metal ion. This is biologically significant as metal ions such as Mn, Zn, Ca and Fe, play a vital role in both the structure and function of many different proteins. The addition of metal ion recognition to ProMOL/PyMOL promises to lead us to better function assignments to this collection of protein structures. There are current plans to launch a database with specific information pertaining to the metal ion binding sites and 3D visualization of motifs with metal ions. This work has been supported in part by National Institute of General Medical Sciences 2R15GM078077‐02, 3R15GM078077‐02S1.Grant Funding Source: Supported by NIGMS 2R15GM078077‐02, 3R15GM078077‐02S1

Aromatic Amide and Hydrazide Foldamer-Based Responsive Host–Guest Systems

CONSPECTUS: In host-guest chemistry, a larger host molecule selectively and noncovalently binds to a smaller guest molecule or ion. Early studies of host-guest chemistry focused on the recognition of spherical metal or ammonium ions by macrocyclic hosts, such as cyclic crown ethers. In these systems, preorganization enables their binding sites to cooperatively contact and attract a guest. Although some open-chain crown ether analogues possess similar, but generally lower, binding affinities, the design of acyclic molecular recognition hosts has remained challenging. One of the most successful examples was rigid molecular tweezers, acyclic covalently bonded preorganized host molecules with open cavities that bind tightly as they stiffen. Depending on the length of the atomic backbones, hydrogen bonding-driven aromatic amide foldamers can form open or closed cavities. Through rational design of the backbones and the introduction of added functional groups, researchers can regulate the shape and size of the cavity. The directionality of hydrogen bonding and the inherent rigidity of aromatic amide units allow researchers to predict both the shape and size of the cavity of an aromatic amide foldamer. Therefore, researchers can then design guest molecules with structure that matches the cavity shape, size, and binding sites of the foldamer host. In addition, because hydrogen bonds are dynamic, researchers can design structures that can adapt to outside stimuli to produce responsive supramolecular architectures. In this Account, we discuss how aromatic amide and hydrazide foldamers induced by hydrogen bonding can produce responsive host-guest systems, based on research by our group and others. First we highlight the helical chirality induced as binding occurs in solution, which includes the induction of helicity by chiral guests in oligomeric and polymeric foldamers, the formation of diastereomeric complexes between chiral foldamer hosts and guests, and the induction of helical chirality by chiral guests into inherently flexible backbones. In addition, molecular or ion-pair guests can produce supramolecular helical chirality in the organogel state. Such structures exhibit remarkable time-dependence and a "Sergeants and Soldiers" effect that are not observed for other two-component organogels that have been reported. We further illustrate that the reversible folding behavior of an aromatic amide foldamer segment can modulate the switching behavior of donor-acceptor interaction-based [2]rotaxanes. Finally we show that a folded oligomer can induce folding in one or two attached intrinsically flexible oligomers, an example of a solvent-responsive intramolecular host-guest system.

Multiaddressing Fluorescence Switch Based on a New Photochromic Diarylethene with a Triazole-Linked Rhodamine B Unit

A novel diarylethene with a triazole-linked rhodamine B unit has been synthesized by click chemistry. When triggered by light, proton, and metal ions, the diarylethene can be used as a fluorescence switch, leading to a multiaddressable system. The diarylethene shows sequence-dependent responses through efficient interaction of the specific triazole-linked rhodamine B unit with proton and metal ions. Furthermore, the diarylethene can serve as a naked-eye chemosensor for highly selective recognition of different metal ions in different solvent systems. The diarylethene was highly selective toward Al3+ with remarkable fluorescence change from dark to yellow in acetonitrile, while it selectively recognized Cu2+ with significant fluorescence change from dark to bright yellow in the mixture of acetonitrile and water (v/v = 4/6). Finally, a logic circuit was constructed with the unimolecular platform by using the combinational stimuli of light and chemical species as inputs and the fluorescence intensity at 595 ...

2-Pyridine-1H-benzo[d]imidazole based conjugated polymers: A selective fluorescent chemosensor for Ni2+ or Ag+ depending on the molecular linkage sites

Three conjugated polymers comprised of 9,9-didodecyl-2,7-diethynyl-9H-fluorene and 2-pyridine-1H-benzo[d]imidazole units, which are alternatively linked to 4,7-position (P1) and 5,5′-position (P2, P3), respectively, have been synthesized via Sonogashira reaction. P2 and P3 with the twisted conjugated backbones were proved to show selectivity for nickel ion. By contrast, P1 with the linear conjugated backbone exhibited highly selectivity for silver ion. The results suggest that the metal ion recognition feature of the chemosensors based on the conjugated polymers can be adjusted by fine-tuning the linkage pattern between the recognition group and the conjugated backbone. Thus, a selective chemosensor for detection of nickel ion was developed.

Synthesis of coumarin derivatives containing 2-aminothiazole moiety and their recognition of metal ions

Two new coumarin derivatives bearing 2-aminothiazole moiety were synthesized and the molecular structures were confirmed by NMR and HRMS. In acetonitrile, C1 exhibited a selective fluorescence enhancement effect to Mg2+ among the metal ions examined. C2 showed a selective fluorescence quenching effect to Co2+.

Size-dependent patterned recognition and extraction of metal ions by a macrocyclic aromatic pyridone pentamer.

A macrocyclic aromatic pyridine pentamer was found to exhibit patterned recognition of metal ions and efficiently extract larger ions, such as Cs(+), Ba(2+), Tl(+), Au(+), K(+) and Rb(+) preferentially over the other 18 smaller metal ions from the aqueous phase into the chloroform layer.

A surfactant-modulated fluorescent sensor with pattern recognition capability: sensing and discriminating multiple heavy metal ions in aqueous solution

Surfactant aggregates modulating the cross-reactive responses of bispyrene fluorophore containing hydrophilic spacer for the pattern recognition of multiple heavy metal ions.