Pillararene-based fluorescent sensors for the tracking of organic compounds

Fluorescent chemosensors based on pillararene complexes represent a new, promising branch in sensor technology. Because of CH-π interactions, aliphatic chains are well suited for the columnar cavities of pillararenes and bulky or sheet-like(sub)structures can be arranged on the portals. Thus, pillararenes form versatile receptors and an alteration of the fluorescence behavior upon complexation ensures the function of these chemosensors as the reporter. Although this field of research exists only since a few years, remarkable chemosensors were developed for substances as diverse as medical drugs,biochemicals, herbicides and explosives.     

Through bond energy transfer (TBET)-based fluorescent chemosensors

Excitation energy transfer is one of the crucial issues in photophysical and photochemical process of any muti-chromophoric molecular systems, such as energy harvester and fluorescent chemosensor. Through bond energy transfer (TBET)-based fluorescent chemosensors are composed of three main parts: energy donor, energy acceptor, and rigid linker. Comparing with the often used Förster resonance energy transfer (FRET) mechanism, TBET does not require spectral overlap, thus it may enable more possible combination of energy donors and acceptors to be employed and afford higher sensitivity toward targets through ratiometric fluorescence. In this review, we highlight the recent progress in the design and biological applications of the organic TBET-based fluorescent chemosensors during 2014–2019, which will provide profound guidance for designing powerful chemosensors as well as exploring further biological applications.     

基于喹啉和三唑环的开链冠醚对金属离子的选择传感

本文通过Click化学反应合成了一种含喹啉基和三唑基的开链冠醚, 考察和比较了主体化合物对镉等金属离子的荧光传感和选择性键合行为, 并通过荧光和核磁等手段研究了溶剂对其荧光传感的影响.     

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.     

识别过渡金属离子的1,8-萘二甲酰亚胺多胺衍生物荧光传感器的研究

A series of fluorescent chemosensors 1-3 were synthesized to detect transition metal ions. At the room temperature, fluorescence intensities of these chemosensors in acetonitrile without transition metal ions were found to be very weak, due to the process of the e±cient intramolecular photoinduced electron transfer (PET). However, after addition of the transition metal ions, the chemosensor 1-3 exhibits obvious fluorescence enhancement. Moreover, the intensity of the fluorescence emission of chemosensors increases significantly in the presence of Zn2+ and Cd2+. The fluorescent chemosensors with different polyamine as receptors show diverse a±nity abilities to the transition metal ions and signal the receptor-metal ion interaction by the intensity change of fluorescence emission.     

Novel Fluorescent Chemosensors Based on Tryptophan Unit for Cu2+ and Fe3+ in Aqueous Solution

We reported four fluorescent chemosensors containing tryptophan units. The fluorescence spectrum titration experiments suggest that chemosensors 1, 2, 3 and 4 are highly selective for Cu²⁺ and Fe³⁺ over Li⁺, Na⁺, K⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺ and Cr³⁺ via forming complexes with Cu²⁺ or Fe³⁺, which is confirmed by dramatical quench of fluoreseence in aqueous solution at pH 7.4, thus making all the chemosensors suitable for Cu²⁺ and Fe³⁺ fluorescent sensors.     

Dicarboxylated ethynylarenes as buffer-dependent chemosensors for Cd(II), Pb(II), and Zn(II)

Two dicarboxylated ethynylarenes were prepared efficiently from condensation of 1,3-bis(3-aminophenylethynyl)benzene with 2 equiv of either succinic anhydride or glutaric anhydride. These compounds behave as fluorescent chemosensors selective for Cd(II), Pb(II), and Zn(II) cations under buffered aqueous conditions, with analyte binding observed as bathochromically shifted, intensified fluorescence. It was noteworthy that the fluorescence responses varied significantly with buffer identity. A conformational restriction mechanism involving reversible interactions between the fluorophore, metal cation, and buffer itself is proposed.     

Fluorescent anion chemosensors using 2-aminobenzimidazole receptors

Simple and easy-to-make fluorescent anion chemosensors using 2-aminobenzimidazole moieties as binding subunits showed selective anion-induced fluorescent changes. The receptors effectively recognized fluoride, chloride, bromide, acetate, dihydrogen phosphate ions with a 1:1 stoichiometry.     

Novel chemosensor for alkaline earth metal ion based on 9-anthryl aromatic amide using a naphthalene as a TICT control site and intramolecular energy transfer donor

Novel fluorescent chemosensors 1 and 2 with two different fluorophores (naphthalene and anthracene) at the both ends of polyether was synthesized. These compounds based on 9-anthryl aromatic amide adopted a naphthalene as a TICT controller and an intramolecular energy transfer source. Compound 1 shows high fluorescence efficiency upon complexation with metal ion, and the fluorescence efficiency of 2 is regulated by metal ionic size.     

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.     

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.     

Zinc-supported azobenzene derivative-based colorimetric fluorescent ‘turn-on’ sensing of bovine serum albumin

Fluorescence sensing with small molecular chemosensors is a versatile technique for elucidation of function of various substances. Herein, a new zinc ion supported fluorescent turn-on system for bovine serum albumin (BSA) has been demonstrated. The fluorescence intensity increases 15.4-fold and visual color changes from light reddish orange to yellow can be detected after adding BSA.     

Synthesis and optical characterization of novel azacrown ethers containing an acridinone or an N-methylacridinone unit as potential fluorescent chemosensors

Four new achiral and four new chiral monoazacrown ethers containing an acridinone or an N-methylacridinone fluorescent signalling unit were prepared by reacting chloromethyl-substituted acridinone derivatives with achiral monoazacrown ethers with different cavity sizes and enantiopure monoaza-18-crown-6 ethers having two methyl and two isobutyl groups on their chiral centres, respectively. The operation of these chemosensors is based on the photoinduced electron transfer (PET) process, thus they show fluorescence enhancement in the presence of cationic guests. Their fluorescent behaviour as well as their complexation properties towards selected metal ions and the enantiomers of α-(1-naphthyl)ethylammonium perchlorate and potassium mandelate were examined.     

Highly sensitive detection of nitroaromatic explosives using an electrospun nanofibrous sensor based on a novel fluorescent conjugated polymer

An electrospun nanofibrous explosive sensor was first constructed based on a newly developed fluorescent conjugated polymer P containing heteroatom polycyclic units. Electrospinning by doping polymer P as a fluorescent probe in a polystyrene supporting matrix afforded a fluorescence nanofibrous film with unique porous structures, and effectively avoided the aggregation of polymer P. The novel explosive sensor exhibited stable fluorescence property, satisfactory reversibility with less than 5% loss of signal intensity after four quenching–regeneration cycles, and good reproducibility among three batches with a relative standard deviation of 2.8%. Such fabricated sensor also showed remarkable sensitivity toward a series of trace nitroaromatic explosive vapors, including picric acid (parts-per-trillion level) and 2,4,6-trinitrotoluene vapor (parts-per-billion level), as well as good selectivity with less than 10% response to typical interferents. Therefore, the present strategy extends the application of different kinds of conjugated polymers for the construction of optical chemosensors.     

2-(1,2,3-Triazol-4-yl)pyridine-containing ethynylarenes as selective ‘turn-on’ fluorescent chemosensors for Ni(II)

A series of ethynylarene compounds containing 2-(1,2,3-triazol-4-yl)pyridine chelating units were studied as fluorescent chemosensors for metal cations in aqueous solution. Analogs possessing two chelating units bridged by either 1,4-diethynylphenyl or 2,7-diethynylnaphthyl subunits displayed large hypsochromic shifts coupled with signal intensification when exposed to increasing concentrations of Ni(II), a unique response among 22 metal cation analytes. This response was shown to be reversible, and is proposed to derive from disruption of aggregate formation upon Ni(II) binding at the peripheral chelating units.     

Hybrid vesicles of pillar[5]arene/silica: Host-guest complexation and application in pH-triggered release

Integrating silica with organic nanoparticles can generate unique properties.Here pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes,as well as the catalytic hydrolysis of tetraethoxysilane.Such vesicles exhibited the high strength of silica and unique molecular recognition of pillararenes,both of which could tune the pH-trigge red release behavior.Furthermore,a rhodamine B derivative with hexyl group(RhB-C6) was synthesized,which can form a complex with the pillar[5]arene.Based on the host-guest interaction and high strength of silica,the hybrid vesicles could load more RhB-C6 and the rhodamine B was released more slowly compared with the organic vesicles.     

Fe-selective naked-eye ‘off–on’ fluorescent probe: its crystal structure and imaging in living cells

Four novel rhodamine-active probes L1–L4 have been proposed and characterized as fluorescent chemosensors for Fe³⁺. An ‘off-on’ type fluorescent enhancement was observed, which was induced by the interactions between Fe³⁺ and the probe, proven to adopt a 1:1 binding stoichiometry. The recognition properties of the target compounds with metal ions have been investigated in methanol–water (1:1, v/v) solution by the fluorescence and ultraviolet spectrum. In addition, a plausible application of probes in the imaging of HepG2 (liver cells) under the condition of reoxygenation (95% air, 5% CO₂) exposed to Fe³⁺ ions was also demonstrated.     

Evidence for a Bulky Unit of a Pillar[5]arene Flipping in the Solid State

It is well known that pillar[5]arenes have two most stable conformations (pS and pR) in their crystal structures. Because of the intramolecular H‐bonding interactions, substituents, temperature, solvent and so on, the rotational behaviors of the phenolic units on pillararenes are also common. This paper showed some other kinds of conformations in the functionalized pillar[5]arenes and gave evidence for a bulky unit (1,4‐methoxycarbonylmethoxybenzene unit) flipping in the solid state. The presence of hydrogen bonding facilitated the intermolecular self‐assembly in terms of energy‐minimized packing in the crystals. Thus, the main driving force for the flipping of this bulky unit might be both the intramolecular hydrogen bonding between the phenolic units on pillararenes and quadrupolar hydrogen bonding between the host and water. This paper helps us to have a better understanding on the conformations of pillar[5]arenes.     

Pillararene-based supramolecular systems for theranostics and bioapplications

As an emerging type of important macrocycles for supramolecular chemistry, pillararenes and their derivatives have been widely studied and applied in numerous fields, which intensively promotes the development of chemistry, materials science and biology.Pillararene-based theranostic systems are of special interest in the biological and medical areas as they have shown very promising results. Owing to easy preparation, reliable guest affinity, good biocompatibility and stability, pillararenes are frequently used to construct functional biomaterials. On one hand, pillararenes can either be used individually or form diversiform self-assemblies such as micelles, nanoparticles and vesicles to increase water solubility and biocompatibility of drugs.On the other hand, it is promising to modify solid materials like framework materials, silica nanoparticles and graphene oxides with pillararene derivatives to enhance their functions and controllability. In this review, we summarize recent endeavors of pillararene-based supramolecular systems with theranostics and other biological applications comprising drug delivery/chemotherapy, photodynamic/photothermal therapy, antimicrobials, bioimaging, etc. By introducing several typical examples, the design principles, preparation strategies, identifications and bio-applications of these pillararene-based supramolecular systems are described. Future challenges and directions of this field are also outlined.     

含芘荧光化学敏感器化合物同小牛胸腺DNA分子间的相互作用

研究了含芘荧光化学敏感器分子被ctDNA猝灭的荧光光谱.ctDNA分子对该化学敏感器中芘的激发单体,激基缔合物都有猝灭作用.对激发单体的猝灭速度顺序为;化合物(2)>化合物(1)>芘丁酸>化合物(3);对激基缔合物的猝灭速度顺序为;化合物(2)化合物(3).由得到的荧光猝灭数据,可按公式(2)求得荧光化学敏感器分子与ctDNA分子相互作用的稳定常数.发现化合物(2)与ctDNA分子间有着最强的相互作用能力.按ctDNA和含芘荧光化学敏感器的分子结构、构型以及分子内原子-原子的间距等提出了ctDNA分子与该荧光化学敏感器的作用模型,并对上述结果进行了初步解释.