Selective Detection of Fe3+, F-, and Cysteine by a Novel Triazole-Linked Decaamine Derivative of Pillar[5]arene and Its Metal Ion Complex in Water

Development of the Colorimetric and/or Fluorescent Probes for Detecting Fluoride ions in Aqueous Solution

Fluoride ion is a strong Lewis base and one of the essential trace elements in human body. It plays a very important role in human health and ecological balance. The deficiency or excessive intake of fluoride ions will cause serious health problems, so the development of a sensitive and accurate detection method for fluoride ions is very important. The colorimetric and/or fluorescence sensing method has been a long standing attractive technique with high sensitivity and fast response. To date, most reported probes for fluoride ion are applicable only in organic solvents or organic-containing aqueous solutions. However, the probes for fluoride ion used in aqueous solution are more practically needed in view of environment protection and human health. In this paper, the materials and designing ideas of the colorimetric and/or fluorescent probes for fluoride ion based on different detection mechanisms in recent years were reviewed. Two main categories including formation of hydrogen bonds and formation of coordination covalent bonds were discussed. The latter one is further subdivided into three types, formation of B-F bond, formation of Si-F bond and formation of Mn+-F bond.

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

Aggregation-caused dual-signal response of gold nanoclusters for ratiometric optical detection of cysteine

Designing ratiometric sensors for cysteine (Cys) monitoring with high accuracy is of great significance for disease diagnosis and biomedical studies. The current ratiometric methods mainly rely on multiplex probes, which not only complicates the operation but also increases the cost, making it difficult for quantitative Cys detection in resource-limited areas. Herein, one-pot prepared gold nanoclusters (Au NCs) that glow red fluorescent were synthesized by employing glutathione as the stabilizer and reducing agent. When Fe3+ is present with Au NCs, the fluorescence is quenched and the scattering is strong because of the aggregation of Au NCs. With introduction of Cys, Cys can efficiently compete with glutathione-modified Au NCs for Fe3+, which leads to increase of fluorescence and decrease of scattering. The ratiometric determination of Cys can be thereby realized by collecting the fluorescence and SRS spectrum simultaneously. The linear range for Cys was 5-30 µM with a detection limit of 1.5 µM. In addition, the sensing system exhibits good selectivity for Cys and shows potential application in biological samples.

Selective Fluorescent Sensing for Iron in Aqueous Solution by A Novel Functionalized Pillar[5]arene

Iron ion is one of the most physiologically important elements in metabolic processes, indispensable for all living systems. Since its excess can lead to severe diseases, new approaches for its monitoring in water samples are urgently needed to meet requirements. Here, we firstly report a novel and universal route for the synthesis of a series of pillar[n]arene derivates containing one benzoquinone unit by photocatalysis. With this in hand, an anthracene - appended water - soluble pillar[5]arene (H) with excellent fluorescence sensing potency was prepared. H enabled the ultrasensitive detection of iron ions in aqueous solution with limits of detection of 10-8  M. Over a wide range of metal ions, H exhibited specific selectivity toward Fe3+ . More importantly, H could still properly operate in a simulated sewage sample, coexisting with multiple interference ions.

Chain length effect of spiro-ring N-alkylation on photophysical signalling parameters in Fe(III) selective rhodamine probes

Manifestation of photophysical signalling parameters in rhodamine derivatives exhibiting complexation induced spiro-ring opening is crucial for the realization of selective metal ion detection at trace levels. Substitution of various functional groups, such as alkylation to the core architecture, modulates the physico-chemical properties of such molecular probes. Despite a few studies, relationships between the extent of photophysical signal modulations and the chain lengths of n-alkyl substituents are still elusive. In this investigation, a few molecular probes based on the rhodamine B (1-5) and rhodamine 6G (6-10) platform were synthesized by their derivatization with n-alkyl substituents of varying chain lengths at the amino-donor of their spiro-ring end, which exhibited Fe(III)-selective absorption and fluorescence 'off-on' signal transduction along with colorization of solution. The Fe(III)-selectivity in these probes remained the same despite their structural distinctions through varied n-alkyl chain lengths of the substituents; however, the quantifiable signalling parameters such as spectroscopic enhancement factors, sensitivity, the kinetics of spiro-ring opening and effectiveness of probe-Fe(III) interactions were analyzed. These parameters were also correlated in terms of the influence of different chain lengths of n-alkyl substituents that efficiently contributed to their inter-componential interactive stereo-electronic environment.