Hexaphyrin(1.0.1.0.0.0). A new colorimetric actinide sensor

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

DNAzyme recognition triggered cascade signal amplification for rapid and highly sensitive visual detection of uranyl ions

A 40 min rapid and highly sensitive assay for visualized detection of UO22+ in water samples is reported. A dynamic range 1~50 nM and a LOD of 0.48 nM were obtained. Concentrations as low as 5 nM UO22+ could be distinguished by the naked eye.

Comparing coordination uranyl(vi) complexes with 2-(1H-imidazo[4,5-b]phenazin-2-yl)phenol and derivatives

Four derivatives of 2-(1H-imidazo[4,5-b]phenazin-2-yl)phenol have been synthesized and characterized structurally using X-ray crystallography. Coordination complexes with uranyl (UO₂²⁺) and copper (Cu²⁺) were prepared and absorption/emission spectra detailed. We observed increased fluorescence upon uranyl binding, in stark contrast to rapid quenching observed with the addition of copper. These phenomena have been further examined by DFT computational methods.

Pyrrophens: Pyrrole-Based Hexadentate Ligands Tailor-Made for Uranyl (UO22+) Coordination and Molecular Recognition

Derivatives of a novel pyrrole-containing Schiff base ligand system (called "pyrrophen") are presented which feature substituted phenylene linkers (R¹ = R² = H (H₂L¹); R¹ = R² = CH₃ (H₂L²)) and a binding pocket modeled after macrocyclic species. These ligands bind neutral CH₃OH in the solid state through pyrrolic hydrogen-bonding. The interaction of the uranyl cation (UO₂²⁺) and H₂L^1-2 yields planar hexagonal bipyramdial uranyl complexes, while the Cu²⁺ and Zn²⁺ complexes were found to self-assemble as dinuclear helicate complexes (M₂L₂) with H₂L¹ under identical conditions. The favorable binding of UO₂²⁺ over Zn²⁺ provides insight into the molecular recognition of uranyl over other metal species. Structural features of these complexes are examined with special attention to features of the UO₂²⁺ coordination environment which distinguish them from other related salophen and porphyrinoid complexes.

Structure and magnetism of a tetrahedral uranium(iii) β-diketiminate complex

We describe the functionalisation of the previously reported uranium(iii) β-diketiminate complex (BDI)UI₂(THF)₂ (1) with one and two equivalents of a sterically demanding 2,6-diisopropylphenolate ligand (ODipp) leading to the formation of two heteroleptic complexes: [(BDI)UI(ODipp)]₂ (2) and (BDI)U(ODipp)₂ (3). The latter is a rare example of a tetrahedral uranium(iii) complex, and it shows single-molecule magnet behaviour.

Prediction of Binding Stability of Pu(IV) and PuO2(VI) by Nitrogen Tridentate Ligands in Aqueous Solution

Plutonium has potential applications in energy production in well-controlled nuclear reactors. Since nuclear power plants have great merit as environmentally friendly energy sources with a recyclable system, a recycling system for extracting Pu from spent fuels using suitable extractants has been proposed. Pu leakage is a potential environmental hazard, hence the need for chemical sensor development. Both extractants and chemical sensors involve metal–ligand interactions and to develop efficient extractants and chemical sensors, structural information about Pu ligands must be obtained by quantum calculations. Herein, six representative nitrogen tridentate ligands were introduced, and their binding stabilities were evaluated. The tridentate L6, which contains tri-pyridine chelate with benzene connectors, showed the highest binding energies for Pu(IV) and PuO₂(VI) in water. Analysis based on the quantum theory of atoms in molecular analysis, including natural population analysis and electron density studies, provided insight into the bonding characteristics for each structure. We propose that differences in ionic bonding characteristics account for the Pu-ligand stability differences. These results form a basis for designing novel extractants and organic Pu sensors.

A light activated CMP conjugated 8-aminoquinoline turn-on fluorescent optode for selective determination of Th4+ in an aqueous environment

A new dibutyl(2-oxo-2-(quinolin-8-ylamino)ethyl)phosphinate (L) was designed, synthesised and developed as a light activated optode for Th⁴⁺ determination.

New supporting ligands in actinide chemistry: tetramethyltetraazaannulene complexes with thorium and uranium

We report the synthesis, characterization, and preliminary reactivity of new heteroleptic thorium and uranium complexes supported by the macrocyclic TMTAA ligand (TMTAA = Tetramethyl-tetra-aza-annulene). The dihalide complexes Th(TMTAA)Cl₂(THF)₂ (1), [UCl₂(TMTAA)]₂ (2) and U(TMTAA)I₂ (3) are further functionalized to the Cp* derivatives ThCp*(TMTAA)Cl (4), UCp*(TMTAA)Cl (5) and UCp*(TMTAA)I (6) (Cp* = pentamethylcyclopentadienide). Compounds 4-6 are also obtained through a one-pot reaction from standard thorium(iv) and uranium(iv) starting materials, Li2TMTAA and KCp*. Complexes 1-6 function as valuable starting materials for salt metathesis chemistry. Treatment of precursors 4 or 5 with trimethylsilylmethyllithium (LiCH₂TMS) results in the new actinide TMTAA alkyl complexes ThCp*(TMTAA)(CH₂TMS) (7) and UCp*(TMTAA)(CH₂TMTS) (8), respectively. The TMTAA-derived alkyl complexes (7 and 8) show unexpected stability and are stable for several weeks at room temperature in solution and in the solid-state. Additionally, double substitution of the halide ligands in 1-3 shows a strong dependence on the nucleophile used. While weaker nucleophiles, such as amides, and more sterically demanding nucleophiles, such as Cp (Cp = cyclopenadienide), favour the formation of bis-TMTAA "sandwich" complexes [An(TMTAA)₂] (An = Th (9) and An = U (10)), the use of oxygen-functionalized ligands like the ODipp anion (Dipp = diisopropylphenyl) results in the formation of the doubly substituted species Th(ODipp)₂TMTAA (11) and U(ODipp)₂TMTAA (12). We also describe the divergent reactivity of the TMTAA ligand towards uranium(iii). Unlike the syntheses of actinide(iv) TMTAA complexes, the synthesis of a uranium(iii) TMTAA was not successful and only uranium(iv) species could be obtained.

Porphyrins in troubled times: a spotlight on porphyrins and their metal complexes for explosives testing and CBRN defense

A critical perspective on (metallo)porphyrins in security-related applications: the past, present and future of explosives detection, CBRN defense, and beyond.

Ligand size dependence of U–N and U–O bond character in a series of uranyl hexaphyrin complexes: quantum chemical simulation and density based analysis

A quantum chemical and density based analysis of bonding in uranyl hexaphyrin complexes, looking for trends in stability and covalency.

Membrane optode for uranium(vi) preconcentration and colorimetric determination in real samples

A membrane optode formed by physical inclusion of a chromophore 2-(2-benzothiazolylazo)phenol (BTAP) and uranium(vi) anions into a plasticized cellulose triacetate (CTA) matrix was illustrated for preconcentration and colorimetric determination of U(vi) from aqueous samples.

Synthesis and characterization of a dipyriamethyrin–uranyl complex

A bench stable uranyl complex of a hexaazadipyriamethryin macrocyclic ligand has been prepared and characterized.

A new synthesis of isoamethyrins: A 4+2 route

A concise and versatile strategy for the preparation of isoamethyrins is presented. The novel procedure is predicated on the acid catalyzed condensation of a quaterpyrrole and a bipyrrole dialdehyde. As application of this procedure an aryl substituted isoamethyrin has been synthetized and characterized.

Development of Ion Chemosensors Based on Porphyrin Analogues

Sensing of metal ions and anions is of great importance because of their widespread distribution in environmental systems and biological processes. Colorimetric and fluorescent chemosensors based on organic molecular species have been demonstrated to be effective for the detection of various ions and possess the significant advantages of low cost, high sensitivity, and convenient implementation. Of the available classes of organic molecules, porphyrin analogues possess inherently many advantageous features, making them suitable for the design of ion chemosensors, with the targeted sensing behavior achieved and easily modulated based on their following characteristics: (1) NH moieties properly disposed for binding of anions through cooperative hydrogen-bonding interactions; (2) multiple pyrrolic N atoms or other heteroatoms for selectively chelating metal ions; (3) variability of macrocycle size and peripheral substitution for modulation of ion selectivity and sensitivity; and (4) tunable near-infrared emission and good biocompatibility. In this Review, design strategies, sensing mechanisms, and sensing performance of ion chemosensors based on porphyrin analogues are described by use of extensive examples. Ion chemosensors based on normal porphyrins and linear oligopyrroles are also briefly described. This Review provides valuable information for researchers of related areas and thus may inspire the development of more practical and effective approaches for designing high-performance ion chemosensors based on porphyrin analogues and other relevant compounds.

Assessing covalency in equatorial U–N bonds: density based measures of bonding in BTP and isoamethyrin complexes of uranyl

N-donor complexes of uranyl have been investigated with density-based analytical methods in order to quantify equatorial bond covalency and its effect on axial U–O_yl bonding.

Solid state π–π stacking and higher order dimensional crystal packing, reactivity, and electrochemical behaviour of salphenazine actinide and transition metal complexes

Here, we describe and compare the synthesis, solution characterization, and solid-state behaviour of the salphenazine ligand and metal complexes.

A turn-off fluorescent biosensor for the rapid and sensitive detection of uranyl ion based on molybdenum disulfide nanosheets and specific DNAzyme

A novel fluorescent biosensor for detecting uranyl ion (UO2(2+)) in aqueous environment has been developed based on the specific recognition of DNAzyme and the fluorescence quenching ability of molybdenum disulfide (MoS2) nanosheets. The DNAzyme contains a DNA enzyme strand and a 6-carboxylfluorescein (FAM)-labeled DNA substrate strand. We demonstrated that MoS2 nanosheets have low affinity to the substrate-enzyme complex DNAzyme. Whereas, in the presence of UO2(2+), UO2(2+) can specifically cleave DNAzyme to release FAM-labeled single-strand DNA and the released FAM-labeled single-strand DNA can be firmly adsorbed on the surface of MoS2 nanosheets, which resulted in an obvious decrease of fluorescence intensity. This provided a sensing platform for the rapid, simple and sensitive fluorescent detection of UO2(2+). By using the sensing platform, a sensitive and selective fluorescent method for the rapid detection of UO2(2+) has been developed. In comparison with previous biosensor, the proposed method has obvious analytical advantage such as relatively high sensitivity and good stability, short analytical time and low cost. It can be used to detect as low as 2.14 nM of UO2(2+) in aqueous environment with a recovery of 96-102% and a RSD<5% (n=6). The success of this study provides a promising alternative for the rapid and on-site detection of UO2(2+) in environmental monitoring.

Synthesis, structural characterization, electronic spectroscopy, and microfluidic detection of Cu(+2) and UO2(+2) [di-tert-butyl-salphenazine] complexes

Metal templation by condensation of 2,3-diaminophenazine with 3,5-di-tert-butyl-2-hydroxybenzaldehyde around the metal centers [M = Cu(II), and UO2(VI)] affords a new class of M[di-tert-butyl salphenazine] metal complexes. Reported here is the synthesis, single crystal X-ray structural characterization, electronic spectroscopy, and microfluidic detection of the formation of these M[di-tert-butyl sal-phenazine] complexes.

Fluorescent and colorimetric ion probes based on conjugated oligopyrroles

In this tutorial review, the design strategies, syntheses, and ion sensing properties of conjugated oligopyrroles are described.

Synthesis and characterization of a hexaphyrin(1.0.1.0.0.0) bearing both meso- and β-substituents

The synthesis of an isoamethyrin-type expanded porphyrin bearing both meso- and β-substituents is presented. The diprotonated form of this macrocycle was characterized by conventional spectroscopic means and via a single crystal X-ray diffraction analysis. This species is observed to adopt a planar conformation in the solid state. Nonetheless, the inner ring current, as inferred from 1 H NMR spectroscopic studies, is found to be severely diminished as compared to isoamethyrin, by the presence of the two meso-phenyl moieties. A second crystal structure, in which a molecule of water is hydrogen-bound to a pyrrole NH , was also solved.

Spectroelectrochemical behavior of N-confused dioxohexaphyrins

Doubly N -confused dioxohexaphyrins were characterized by cyclic voltammetry and spectroelectrochemistry in the -2.5 to +2.0 V vs Ag | Ag + (0.10 M, in CH3CN) range. Six reversible monoelectronic processes were found suggesting that the rich electrochemistry of porphyrin systems was preserved in that expanded macrocycle. However, the electronic and electrochemical properties of the free-base, Cu(II) and Ni(II) species were shown to be sensitive to the coordinated transition metal ions and solvent revealing a quite complex behavior, probably reflecting the higher flexibility and strong conformational effects on the energy levels and stability of those complexes.

Functionalized gold nanoparticle supported sensory mechanisms applied in detection of chemical and biological threat agents: a review

There is a great necessity for development of novel sensory concepts supportive of smart sensing capabilities in defense and homeland security applications for detection of chemical and biological threat agents. A smart sensor is a detection device that can exhibit important features such as speed, sensitivity, selectivity, portability, and more importantly, simplicity in identifying a target analyte. Emerging nanomaterial based sensors, particularly those developed by utilizing functionalized gold nanoparticles (GNPs) as a sensing component potentially offer many desirable features needed for threat agent detection. The sensitiveness of physical properties expressed by GNPs, e.g. color, surface plasmon resonance, electrical conductivity and binding affinity are significantly enhanced when they are subjected to functionalization with an appropriate metal, organic or biomolecular functional groups. This sensitive nature of functionalized GNPs can be potentially exploited in the design of threat agent detection devices with smart sensing capabilities. In the presence of a target analyte (i.e., a chemical or biological threat agent) a change proportional to concentration of the analyte is observed, which can be measured either by colorimetric, fluorimetric, electrochemical or spectroscopic means. This article provides a review of how functionally modified gold colloids are applied in the detection of a broad range of threat agents, including radioactive substances, explosive compounds, chemical warfare agents, biotoxins, and biothreat pathogens through any of the four sensory means mentioned previously.

Oligopyrrole macrocycles: receptors and chemosensors for potentially hazardous materials

Oligopyrroles represent a diverse class of molecular receptors that have been utilized in a growing number of applications. Recently, these systems have attracted interest as receptors and chemosensors for hazardous materials, including harmful anionic species, high-valent actinide cations, and nitroaromatic explosives. These versatile molecular receptors have been used to develop rudimentary colorimetric and fluorimetric assays for hazardous materials.

Synthesis of bimetallic uranium and neptunium complexes of a binucleating macrocycle and determination of the solid-state structure by magnetic analysis

Syntheses of the bimetallic uranium(III) and neptunium(III) complexes [(UI)(2)(L)], [(NpI)(2)(L)], and [{U(BH(4))}(2)(L)] of the Schiff-base pyrrole macrocycles L are described. In the absence of single-crystal structural data, fitting of the variable-temperature solid-state magnetic data allows the prediction of polymeric structures for these compounds in the solid state.

Highly sensitive and selective colorimetric sensors for uranyl (UO2(2+)): development and comparison of labeled and label-free DNAzyme-gold nanoparticle systems

Colorimetric uranium sensors based on uranyl (UO2(2+)) specific DNAzyme and gold nanoparticles (AuNP) have been developed and demonstrated using both labeled and label-free methods. In the labeled method, a uranyl-specific DNAzyme was attached to AuNP, forming purple aggregates. The presence of uranyl induced disassembly of the DNAzyme functionalized AuNP aggregates, resulting in red individual AuNPs. Once assembled, such a "turn-on" sensor is highly stable, works in a single step at room temperature, and has a detection limit of 50 nM after 30 min of reaction time. The label-free method, on the other hand, utilizes the different adsorption properties of single-stranded and double-stranded DNA on AuNPs, which affects the stability of AuNPs in the presence of NaCl. The presence of uranyl resulted in cleavage of substrate by DNAzyme, releasing a single stranded DNA that can be adsorbed on AuNPs and protect them from aggregation. Taking advantage of this phenomenon, a "turn-off" sensor was developed, which is easy to control through reaction quenching and has 1 nM detection limit after 6 min of reaction at room temperature. Both sensors have excellent selectivity over other metal ions and have detection limits below the maximum contamination level of 130 nM for UO2(2+) in drinking water defined by the U.S. Environmental Protection Agency (EPA). This study represents the first direct systematic comparison of these two types of sensor methods using the same DNAzyme and AuNPs, making it possible to reveal advantages, disadvantages, versatility, limitations, and potential applications of each method. The results obtained not only allow practical sensing application for uranyl but also serve as a guide for choosing different methods for designing colorimetric sensors for other targets.