A convenient synthesis of 2,5-diaroyl-4-hydroxy cyclopent-2-enones incorporating aromatic and heteroaromatic moieties

Abstract

The base-catalyzed reaction of 1,5-diphenyl-pentane-1,3,5-trione with aromatic/heteroaromatic 1,2-diones leading to the synthesis of 2,5-diaroyl-4-hydroxycyclopent-2-enones and its conversion to 2,5-diaroylcyclopentadienones is reported here. 2,5-Dibenzoyl-4-hydroxycyclopent-2-enone and 2,5-dithenoyl-4-hydroxycyclopent-2-enone are valuable compounds which act as chemosensors for selective detection of Fe³⁺ and Cu²⁺, respectively.     

Squaraine-based colorimetric and fluorescent sensors for Cu-specific detection and fluorescence imaging in living cells

New squaraine-based chemosensors SQ1 and SQ2 functionalized with 2-picolyl units were first synthesized and used as highly selective and sensitive colorimetric and fluorometric dual-channel sensors for Cu²⁺-specific recognition in aqueous systems. Among a series of individual metal ions, only Cu²⁺ could result in dramatic color changes. We also evaluated their capability of biological applications and found that SQ2 could be successfully employed as a Cu²⁺-selective probe in the fluorescence imaging of living cells.     

Sulfonamide and Morpholine‐Based Dual Chemosensor for Cu2+ and Ag+ in Different Solvent Media

The detection of cations has attracted considerable interest because of their importance in various physiological processes. In this study, compound 1 bearing sulfonamide and morpholine functionalities was synthesized. Its structure was well characterized by NMR spectroscopy and mass spectrometry. UV/vis absorption spectra and fluorescence spectra indicated that it displayed high sensitivity and selectivity for Cu²⁺ and Ag⁺ by switching solvent media. It means that: (1) it showed selective response to Cu²⁺ in acetonitrile, (2) whereas it exhibited high selectivity for Ag⁺ in water. The density functional theory calculations were used to clearly explain the different recognition behaviors in different solvent media. This research suggests that compound 1 bearing sulfonamide and morpholine functionalities could act as a multifunctional chemosensor for monitoring multiple cations by changing solvent media and provides an alternative approach to design novel dual cations chemosensors.     

Near-IR region absorbing 1,4-diaminoanthracene-9,10-dione motif based ratiometric chemosensors for Cu

1,4-Bis[2-aminoethylamino]anthracene-9,10-diones selectively bind with Cu²⁺ to form complexes with unusual selectivity under basic conditions. The deprotonation of the aryl amine NH in the case of these chemosensors causes a bathochromic shift in the absorption band from 585 nm and 635 nm to 725 nm and enables ratiometric estimation of Cu²⁺ between pH 8 and 12.     

Ferrocene containing N-tosyl hydrazones as optical and electrochemical sensors for Hg2+, Cu2+ and F− ions

Ferrocene containing N-tosyl hydrazones as selective and sensitive optical and electrochemical chemosensors were synthesized and characterized by ¹H NMR, ¹³C NMR, ESI-MS and X-ray analysis. The cation and anion binding studies were carried out using various techniques including electrochemistry, UV–vis and ¹H NMR spectroscopy. Chemosensors 2a and 2b have shown excellent selective recognition toward Hg²⁺, Cu²⁺ and F^? through optical and electrochemical signals. The color of 2a and 2b in solution changed visibly from pale yellow to red upon addition of Hg²⁺ion, while the color of solution changed from pale yellow to yellow green upon addition of Cu²⁺, which can be easily detected by the naked eye.     

Selective colorimetric sensing of Cu using triazolyl monoazo derivative

Although the high sensitivity, high selectivity and fast response make emission (fluorescence) based technique as one of the most promising tool for developing the chemosensors for metal ions, the past few years have witnessed a demand for the absorption based chemosensors for paramagnetic heavy metal ions, especially Cu²⁺. Being paramagnetic, Cu²⁺ leads to the low signal outputs (“turn-off”) caused by decreased emission which may sometimes give false positive response, rendering the emission based technique less reliable for analytical purposes. Herein, we report synthesis and characterization of a hetarylazo derivative, characterized by a strong charge-transfer band which gets attenuated convincingly in the presence of Cu²⁺ leading to distinct naked-eye color change (yellow to purple), and to a lesser extent in the presence of Cd²⁺, Zn²⁺, Co²⁺, Pb²⁺, Fe²⁺, Ni²⁺, Fe³⁺ and Hg²⁺ for which the naked eye sensitivity was comparatively (w.r.t. Cu²⁺) much less. No response was observed for the other metal ions including Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Mn²⁺, Ag⁺, Zn²⁺, Cd²⁺, Pb²⁺, and lanthanides Ce³⁺, La³⁺, Pr³⁺, Eu³⁺, Nd³⁺, Lu³⁺, Yb³⁺, Tb³⁺, Sm³⁺, Gd³⁺. The proposed sensing mechanism has been ascribed to the stabilization of LUMO after complexation with Cu²⁺ and a 1:1 stoichiometry has been deduced.     

Open-chain polyazaalkanes functionalised with pyrene groups as sensing fluorogenic receptors for metal ions

The new open-chain polyazaalkanes ligands L¹, L², L³ and L⁴ functionalised with one or two pyrene groups were synthesised and characterised and their potential use as selective cation and anion sensing chemosensors studied. Solution studies by potentiometric methods were carried out in the presence of the metal cations Cu²⁺ and Zn²⁺ in acetonitrile–water (70:30 v/v, 0.1 mol dm⁻³ tetrabutylammonium perchlorate, 25 °C) The results are compared with those reported for the analogous non-functionalised ligand triethylentetraamine (tta). The fluorescence behaviour of the ligands L¹–L⁴ has been studied as a function of the pH in the presence of the metal cations Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ in acetonitrile–water 70:30 v/v mixtures. The Zn²⁺ and Cd²⁺ cations enhance the fluorescence emission of the L¹–L⁴ chemosensors at basic pH, whereas Cu²⁺ induce quenching of the fluorescence emission at acid pH. The fluorescence behaviour of L¹–L⁴ receptors was also studied as a function of the pH in acetonitrile–water 70:30 v/v in the presence of anions.     

Novel highly selective fluorescent chemosensors for Zn(II)

Two novel fluorescent Zn²⁺ chemosensors were synthesized in four steps from inexpensive starting materials. They exhibited very strong fluorescence responses to Zn²⁺ and had remarkably high selectivity to Zn²⁺ than other metal ions including Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺, and Cd²⁺. These two new molecules could be used as low-priced yet high-quality Zn²⁺ chemosensors.     

A ‘turn-on’ fluorescent sensor for the selective detection of cobalt and nickel ions in aqueous media

Two newly designed turn-on fluorescein-based chemosensors are highly sensitive and selective for Co²⁺ and Ni²⁺ in both absorption and emission modes, normally difficult to achieve with these paramagnetic ions. Binding to both ions is reversible, as indicated by the bleaching of the color when the metal is extracted with EDTA. Given the difficulty of designing enhanced fluorescent sensors for paramagnetic Co²⁺ and Ni²⁺ ions, the fluorescein compounds may inspire the further development of more sophisticated sensing constructs for the detection of these ions.     

Fluorescent and colourimetric 1, 8-naphthalimide-appended chemosensors for the tracking of metal ions: selected examples from the year 2010 to 2017

The global sensing science in the past couple of years has seen brilliant successes in the designs and syntheses of diverse fluorescent and colourimetric chemosensors of ultra-high selectivities and sensitivities for the tracking of metal ions in environmental and biological systems. Amongst the most widely employed fluorophores for the development of fluorescent and colourimetric chemosensors is the 1, 8-naphthalimide fluorophore, which is distinctive due to its possession of outstanding photophysical properties unequalled by other fluorophores. Many reported literatures are replete with employment of 1, 8-naphthalimide as a unique fluorophore for the construction of chemosensors for the monitoring of metal ions (such as Cu²⁺, Hg²⁺, Cr³⁺, Fe³⁺, Zn²⁺, Ag⁺, Pd²⁺, Al³⁺, Ba²⁺, Au³⁺, and Bi²⁺, and/or a combination of any of them) with remarkable results documented from various labs. This review summarises recent advances in the development of representative fluorescent and colourimetric 1, 8-naphthalimide-based chemosensors reported within the past 7 years. It is believed that gaining insights into the various highlighted examples would help to refine our knowledge of the field and pave the way for further advancement in the constructions of fluorescent and colourimetric 1, 8-naphthalimide-based chemosensors of improved sensing parameters and practical application values.     

Rhodamine-based chemosensing monolayers on glass as a facile fluorescent “turn-on” sensing film for selective detection of Pb

Rhodamine-based chemosensors 1 and 2 were synthesized and self-assembled onto glass surfaces for the selective fluorescent sensing of Pb²⁺. The immobilized chemosensors showed fluorescent responses that were turned-on with Pb²⁺ in CH₃CN, selectively over various metal ions. The Pb²⁺-selective fluorescent switch of the immobilized chemosensors was also reversible, allowing for repeated use for Pb²⁺ detection.     

Dansylated Polyamines as Fluorescent Sensors for Metal Ions: Photophysical Properties and Stability of Copper(II) Complexes in Solution

Protonation and the Cu^II complexation constants of the dansylated polyamines N‐dansylethylenediamine ( 1 ), N‐dansyldiethylenetriamine ( 2 ), N‐dansyltriethylenetetramine ( 3 ), N′‐[2‐(dansylamino)ethyl]diethylenetriamine ( 4 ), and tris(2‐dansylaminoethyl)amine ( 5 ) were determined by glass‐electrode potentiometry in MeOH/H₂O 9 : 1 (v/v) solution. For ligands 3 and 4 , the determinations were also performed in aqueous solution. The complexes formed by these ligands in neutral form correspond to those observed for the analogous unsubstituted monoprotonated amines, whereas, when the ligands are deprotonated at the sulfonamide moiety, the species parallel those of the corresponding amines. The molecular structures of the complexes were deduced from the VIS absorption spectra. The crystal structure of the [CuL₂H₋₂] complex 6 of ligand 1 (L) was determined by X‐ray diffraction. The study of the photophysical properties of the ligands 3 – 5 showed that they are good fluorescent sensors for copper(II), which induced fluorescence quenching. Time‐resolved fluorescence measurements allowed us to clarify the sensing mechanism. The pH dependence of the quenching effect demonstrated that it occurs for all Cu²⁺ complexes, even for species in which the sulfonamide moiety is not deprotonated. Sensing of Cu²⁺ was compared with that of other metal ions (Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Hg²⁺), and selectivity was studied as a function of pH. Ligands 3 and 4 were found to be selective chemosensors for Cu²⁺ in weakly acidic solution (pH ca. 4 – 5).     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

Ratiometric fluorescence chemosensors for copper(II) and mercury(II) based on FRET systems

A system based on FRET mechanism, comprising a coumarin donor and a rhodamine acceptor, was developed for the selective and quantitative detection of metal ions. Fluorescent chemosensors RCs, linked by 1,2-diethylamine, exhibit significant fluorescence enhancement and excellent selectivity toward Cu²⁺. Fluorescent probes CRB and CR6G, linked by hydrazide, function as ratiometric receptors for Cu²⁺ chromogentically and fluorogentically in organic-aqueous media. Furthermore, the characteristic rhodamine-based fluorescence response of CRB (excitation at 550 nm) exhibits high selectivity for Hg(II). The construction of this kind of universal FRET system opens a broader prospect for future design of ratiometric fluorescent probes.     

A Highly Selective Chemosensor for Cu2+ Based on a Diarylethene Linking an Aminoquinoline Unit

A new diarylethene derivative containing an aminoquinoline unit was synthesized and its structure was determined by single crystal X‐ray diffraction analysis. Its properties such as photochromism, fluorescent switches and detection for metal ions were measured. The results indicated that the closed‐ring of the diarylethene was highly selective toward Cu²⁺ with an obvious absorption decrease and color changes from blue to colorless, even in the presence of other metal ions. The binding constant for the closed isomer of this new diarylethene and Cu²⁺ was 2.0×10⁴ L·mol^?1 and the limit of detection for Cu²⁺ was calculated to be lower than that in drink water. Finally, a logic circuit was constructed by using the absorption intensity as the output signal with the inputs of the combinational stimuli of light and Cu²⁺.     

Synthesis and evaluation of benzothiazolyl and benzimidazolyl asparagines as amino acid based selective fluorimetric chemosensors for Cu

A series of emissive N-tert-butyloxycarbonyl benzyl ester asparagines bearing benzothiazole and benzimidazole units at the side chain, functionalised with electron donor or acceptor groups, were evaluated as novel amino acid based fluorimetric chemosensors for transition metal cations, such as Cu²⁺, Zn²⁺, Co²⁺ and Ni²⁺. Selective removal of the protecting groups at the N- and C-terminals was carried out in order to assess the influence of the presence of blocking groups on the overall coordination ability. The results indicate that there is a strong interaction through the donor N, O and S atoms at the side chain of the various asparagines, with high selectivity towards Cu²⁺ in a 1:1 complex stoichiometry. Association constants and detection limits for Cu²⁺ were calculated. The photophysical and metal ion sensing properties of these asparagines suggest that they can be suitable for incorporation into peptidic chemosensor frameworks.     

A highly selective chemosensor for the detection of Cu through the formation of coordination polymer

A highly selective chemosensor (1) bearing three salphen pockets fulfilled the recognition of Cu²⁺ via obvious color change and significant absorption enhancement upon the introduction of Cu²⁺. Additionally, the coordination of 1 and Cu²⁺ led to the formation of coordination polymer which further generated nanospheres, as evidenced by SEM, TEM, AFM, PXRD, and EDX investigations.     

Fluorescence switch-on sensor for Cu by an amide linked lower rim 1,3-bis(2-picolyl)amine derivative of calix[4]arene in aqueous methanol

A highly selective fluorescence switch on sensor, L for detecting Cu²⁺ has been synthesized by introducing a bis-(2-picolyl)amine moiety at the lower rim of a calix[4]arene platform via amide linkage. Binding properties of L toward ten different biologically relevant Mⁿ⁺ ions have been studied by fluorescence and absorption spectroscopy in methanol and aqueous methanol. L was found to detect Cu²⁺ selectively down to a concentration of 196 and 341 ppb, respectively, in methanol and 1:1 aqueous methanol even in the presence of other metal ions. The composition of the complex has been found to be 1:1 based on the Job plot and is further confirmed by ESI MS. The role of calix[4]arene platform as well as the pre-organized binding core in the selective recognition of Cu²⁺ has been demonstrated by studying appropriate reference molecules. The possible modes of binding of L with Cu²⁺ have been modeled by computational calculations. L and its Cu²⁺ complex could very well be differentiated based on the nano-structural features observed in SEM and AFM.     

Synthesis, coordination properties, and analytical applications of mixed donor macrocycles containing the 1,10-phenanthroline sub-unit

The coordination properties towards different metal ions of a new class of mixed N/S-, and N/S/O-donor macrocycles containing the 1,10-phenanthroline sub-unit in the cyclic framework are reviewed. The conformational constraints imposed by the heteroaromatic fragment onto the aliphatic portion of the ring determine the coordination mode of these ligands which can stabilise low-valent Ni⁺, Pd⁺, Pt⁺, and Rh⁺ metal complexes. Structural and thermodynamic aspects of the coordination chemistry of these ligands are considered together with possible applications as building blocks in the synthesis of multi-centred systems, and as template in the construction of extended polyiodide networks. However, solution studies demonstrate the inability of these ligands to work as selective and specific fluorescent chemosensors for heavy transition and post-transition metal ions and the formation constants evaluated for the formation of 1:1 complexes with Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, and Ag⁺ in acetonitrile are of the same order of magnitude. Nevertheless, some of these macrocyles are extremely effective to recognise Cu²⁺ or Ag⁺ over the other metal ions in transport processes, and have been successfully used as neutral ionophore in the construction of PVC-based ionselective electrodes and supported liquid membranes for analytical detection and separation, respectively, of these metal ions.     

Unique blue shift due to the formation of static pyrene excimer: highly selective fluorescent chemosensor for Cu

New binaphthyl derivatives bearing pyrene groups have been synthesized and studied as fluorescent chemosensors for Cu²⁺ ions. A unique blue shift along with fluorescent enhancement in pyrene excimer emission was observed, which were induced by the formation of a static pyrene excimer.