Aminoxy-linked rhodamine hydroxamate as fluorescent chemosensor for Fe in aqueous media

A novel feric ion-selective rhodamine-based fluorescent chemosensor, which contains a bis-aminoxy chain moiety, has been developed. The multi-dentate binding site of rhodamine fluorophore shows selective detection of ferric iron over other biologically important metal ions in aqueous media and also shows 1:1 binding stoichiometry.     

Rhodamine-hydroxamate-based fluorescent chemosensor for Fe

A hydroxamate-based chemosensor, which responds fluorescently and colorimetrically to Fe^III in micromolar ranges, has been developed. The rhodamine hydroxamate probe is prepared in two steps from rhodamine B base. The biomimetic hydroxamate binding site is attached to the rhodamine fluorophore to recognize Fe^III selectively over other biologically important metal ions.     

Bile Acids-Selective Chemosensors Based on NBD-amine-Modified Cyclodextrins

A new type of fluorescent chemosensor, based on modified cyclodextrins bearing the fluorophore unit NBD-amine, was prepared. One of these new chemosensors, NC0γCD is very sensitive to bile acids, but is not sensitive to other guests (e.g. adamantane and borneol derivatives). The response of the new type of chemosensor to a guest was an increase in the fluorescence intensity and the sensitivity parameter (ΔI/I ₀ ) dose not correlate to the binding affinity of NC0γCD.     

Fluorescent sensing of anions with acridinedione based neutral PET chemosensor

Newly synthesised fluorescent chemosensor ADDTU contains the thiourea receptor connected to the acridinedione (ADD) fluorophore via a covalent bond, giving rise to a fluorophore-receptor motif. In this fluorescent chemosensor, the anion recognition takes place at the receptor site which result in the concomitant changes in the photophysical properties of a ADD fluorophore by modulation of photoinduced electron transfer (PET) process. The binding ability of these sensor with the anions F(-), Cl(-), Br(-), I(-), HSO(4)(-), ClO(4)(-), AcO(-), H(2)PO(4)(-) and BF(4)(-) (as their tetrabutylammounium salts) in acetonitrile were investigated using UV-vis, steady state and time-resolved emission techniques. ADDTU system allows for the selective fluorescent sensing of AcO(-), H(2)PO(4)(-) and F(-) over other anions in acetonitrile.     

Highly selective and sensitive fluorescent turn-on chemosensor for Al3+ based on a novel photoinduced electron transfer approach

A photoinduced electron transfer (PET)-based chemosensor possessing dual PET processes by simultaneously introducing both nitrogen and sulfur donors was achieved. The fluorescence signal of the free chemosensor is in a normal-off state due to the sulfur donor being insensitive to environmental pH stimuli. As a result, the device can be used over a wide pH span of 3-11. Upon binding Al(3+), a significant fluorescence enhancement with a turn-on ratio over 110-fold was triggered by the inhibition of PET processes from both the sulfur and the nitrogen donors to the fluorophore.     

Action of a Fluorescent Chemosensor for Cu2+ Encapsulated in Silica Xerogel

The fluorescent chemosensor of the type Ant-NH-O-O-NH-Ant for Cu²⁺ ions has been designed by means of a supramolecular approach, as follows: two anthracene (Ant) fragments as fluorophore subunits have been linked by a noncyclic NH-O-O-NH quadridentate ligand as a receptor. The interaction of Cu²⁺ - receptor is signalled through the enhancement of the anthracene fluorescence when the receptor, i.e., the dioxodiamine chain subunit of the sensor is able to stop a photoinduced electron-transfer mechanism. The experiments with the chemosensor encapsulated in silica xerogel by the sol-gel processing are described.     

Selective sensing of Zn(II) ion by a simple anthracene-based tripodal chemosensor

A new and an easy-to-make simple tripodal shaped chemosensor 1, comprising an anthracene moiety as a fluorophore and amide, alcohol functionalities as ligating groups has been designed and synthesized for Zn(II). In CH₃CN containing 0.1% DMSO, upon excitation at 370 nm, the chemosensor 1 exhibited an emission at 412 nm, which increased to a large extent upon complexation of Zn(II). Among the other metal ions examined in the study, Cd²⁺ moderately perturbed the emission of 1 under similar conditions.     

Calix[4]arene based selective fluorescent chemosensor for organic acid recognition

A novel calix[4]arene-based fluorescent chemosensor bearing a 2-aminopyridine moiety and a naphthalenic fluorophore was synthesized The chemical structure of the product was elucidated by FT-IR, MS-FAB, NMR and elemental analyses. Then, the properties and identification mechanism of the synthesized chemosensor were investigated. The results show that the chemosensor exhibits selective fluorescent quenching in the presence of aromatic organic acid in acetonitrile solution, and that the binding ability of the chemosensor with organic acid is in the order of p-cyanic-benzyl acid > p-chloric-benzyl acid > p-methoxyl-benzyl acid > benzyl acid. __________ Translated from Journal of South China University of Technology (Natural Science Edition), 2007, 35(4): 20–24 [译自: 华南理工大学学报(自然科学版)]     

An efficient thiourea-based colorimetric chemosensor for naked-eye recognition of fluoride and acetate anions: UV-vis and HNMR studies

An efficient colorimetric chemosensor with a thiourea binding site and 2-amino-6-nitrobenothiazole as a signaling unit has been synthesized by dithiocarbamate approach. The chemosensor has been utilized for selective recognition of fluoride and acetate anions in dry DMSO solution by UV-vis and ¹H NMR titration experiments. The chemosensor has shown naked-eye sensitivity for both the anions in solution.     

A fluorescence chemosensor based on peptidase for detecting nickel(II) with high selectivity and high sensitivity

We report herein a new class of metal ion chemosensors and give the first example of a metal-dependent peptidase chemosensor for metal ions. The chemosensor contains the basic specific Ni(II)-dependent peptide bond hydrolysis sequence (Gly-Ala-Ser-Arg-His-Trp-Lys-Phe-Lys). The substrate was labeled with a fluorophore at the N-terminal and a quencher at the C-terminal Lys side chain. Initially, the MOCAc ((7-methoxycoumarin-4-yl)acetyl-) emission was quenched by the nearby quencher. In the presence of Ni(II), the substrate was irreversibly cleaved at the cleavage site, leading to a 20-fold increase in fluorescence intensity. The chemosensor combines the high selectivity of a peptidase (at least greater than tenfold for Ni(II) over other metal ions) with the high sensitivity of fluorescence detection limit of 50 nM and can be applied for the quantitative detection of Ni(II) over a concentration range of three orders of magnitude. Given this degree of selectivity and sensitivity, our molecular engineering design may prove useful in the future development of other peptidase-based probes for different metal ions in toxicological and environmental monitoring.     

Synthesis of dipicolylamino substituted quinazoline as chemosensor for cobalt(II) recognition based on excited-state intramolecular proton transfer

A new fluorescent chemosensor for sensing Co(II) using di(2-picolyl)amino (DPA) as a recognition group and quinazoline as a reporting group has been synthesized and characterized. The quinazoline derivative contains an intramolecular hydrogen bond, which would undergo excited-state intramolecular proton transfer (ESIPT) at illumination. The fluorescence quenching is attributed to cation-induced inhibition of ESIPT, which constitutes the basis for the determination of Co(II) with the prepared chemosensor. The fluorophore forms 1:1 cobalt(II) complex with the logarithm of apparent dissociation constant log K(a)=6.8. The analytical performance characteristics of the proposed Co(II)-sensitive sensor were investigated. The chemosensor exhibits a linear response toward Co(II) in the concentration range 3.2 x 10(-8) to 1.4 x 10(-6) M, with a working pH range from 7.0 to 9.5 and high selectivity.     

Highly sensitive detection of mercury (II) in aqueous media by tetraphenylporphyrin with a metal ion receptor

We provide a highly sensitive and selective assay to detect Hg²⁺ in aqueous solutions using a novel β-functionalised porphyrin-based chemosensor 5 at room temperature. The binding properties of the chemosensor 5 for cations were examined by UV–vis spectroscopy and ¹H NMR. The results indicate that a 1:1 stoichiometric complex is formed between chemosensor 5 and mercury (II) ion. The recognition mechanism between chemosensor 5 and metal ion was discussed based on their absorbance changes and the chemical shift changes when they interact with each other. Control experiments revealed that chemosensor 5 has a selective response to mercury (II) ion compared with other metal ions.     

Ion Interactions with a New Ditopic Naphthalimide‐Based Receptor: A Photophysical,NMR and Theoretical (DFT) Study

A new multi‐component chemosensor system comprising a naphthalimide moiety as fluorophore is designed and developed to investigate receptor–analyte binding interactions in the presence of metal and non‐metal ions. A dimethylamino moiety is utilized as receptor for metal ions and a thiourea receptor, having acidic protons, for binding anions. The system is characterized by conventional analytical methods. The absorption and fluorescence spectra of the system consist of a broad band typical for an intramolecular charge transfer (ICT). The effects of various metal‐ion additives on the spectral behavior of the present sensor system are examined in acetonitrile. It is found that among the metal ions studied, alkali/alkaline earth‐metal ions and transition‐metal ions modulate the absorption and fluorescence spectra of the system. As an additional feature, the anion signaling behavior of the system in acetonitrile is studied. A decrease in fluorescence efficiency of the system is observed upon addition of fluoride and acetate anions. Fluorescence quenching is most effective in the case of fluoride ions. This is attributed to the enhancement of the photoinduced electron transfer from the anion receptor to the fluorophore moiety. Hydrogen‐bond interactions between the acidic NH protons of the thiourea moiety and the F^? anions are primarily attributed to the fluoride‐selective signaling behavior. Interestingly, a negative cooperativity for the binding event is observed when the interactions of the system are studied in the presence of both Zn²⁺ and F^? ions. NMR spectroscopy and theoretical calculations are also carried out to better understand the receptor–analyte binding.     

3-[2-(8-Quinolinyl)benzoxazol-5-yl]alanine derivative—a specific fluorophore for transition and rare-earth metal ion detection

A novel aromatic amino acid, 3-[2-(8-quinolinyl)benzoxazol-5-yl]alanine derivative was synthesized as a potential Zn(II) and rare-earth metal, Eu(III) and Tb(III), ion chemosensor. The fluorophore was obtained using lead tetraacetate in DMSO to oxidize the Schiff base obtained from N-Boc-3-amino-tyrosine methyl ester and quinoline-8-carboxaldehyde. Preliminary photophysical properties of this ligand show that it possesses the properties necessary to be an effective chemosensor for Zn²⁺, Tb³⁺ and Eu³⁺ ions.     

Naphthalimide as Highly Selective Fluorescent Sensor for Ag^＋ Ions

The naphthalimide derivative. NA1 was synthesized, which consists of a bis（2-（ethylthio）ethyl）amine group binding cations and naphthalimide unit as chromogenic and fluorogenic signaling subunit. Absorption and emission spectra and the effect of polarity of solvents and pH values were studied. The photo-induced electron transfer （PET） occurred from the donor of bis（2-（ethylthio）ethyl）amine group to the naphthalimide fluorophore. The present study demonstrates that NA1 is a viable candidate as a fluorescent receptor for a new Ag^＋ ion sensor. This silver ion chemosensor can discriminate Ag^＋ ion well among heavy metal ions by an enhancement of the fluorescence intensity in ethanol-water （1 ： 9, V ： V）. And NA1 is also a pH-sensor because the fluorescence of the compound varies with the pH values.     

A novel intramolecular charge transfer fluorescent chemosensor highly selective for Cu<Superscript>2+</Superscript> in neutral aqueous solutions

A selective and sensitive intramolecular charge transfer (ICT) fluorescent chemosensor was designed for Cu²⁺ in neutral aqueous solutions of pH 7.0. The design of this totally water-soluble fluorescent chemosensor was based on the binding motif of Cu²⁺ to aminoacid, which is coupled to an ICT fluorophore bearing a 1,3,4-thiodiazole moiety in the electron acceptor. The formation of a 1:1 complex of Cu²⁺ to 2 was suggested to lead to fluorescence quenching. The quenching obeyed Stern-Volmer theory in neutral aqueous solution of pH 7.0 for Cu²⁺ over 5.0 × 10⁻⁷ to 3.0 × 10⁻⁵ mol·L⁻¹, with a quenching constant of 1.8 × 10⁵ L·mol⁻¹ and a detection limit of 2.0 × 10⁻⁷ mol·L⁻¹. The binding of Cu²⁺ to 2 can be fully reversed by addition of chelator EDTA, affording a reversible sensing performance.     

Amplified fluorescence response of chemosensors grafted onto silica nanoparticles

In conventional fluorescent chemosensors, the recognition of the target by the receptor unit affects the fluorescence properties of a single covalently coupled fluorescent moiety. Here we show for the first time that when a suitable TSQ derivative is densely grafted onto the surface of preformed silica nanoparticles electronic interactions between the individual chemosensor units enable the free units to recognize the state of the surrounding complexed ones. As a result, the fluorescence transduction is not limited to the local site where binding occurs, but it involves a wider region of the fluorophore network that is able to transfer its excitation energy to the complexed units. Such behavior leads to an amplification of the fluorescence signal. What we report here is the first example of amplification in the case an off-on chemosensor due to its organization onto the surface of silica nanoparticles. We also describe a simple general model to approach amplification in multifluorophoric systems based on the localization of the excited states, which is valid for assemblies such as the supramolecular ones where molecular interactions are weak and do not significantly perturb the individual electronic states. The introduction of an amplification factor f in particular allows for a simple quantitative estimation of the amplification effects.     

Highly Effective Fluorescent Sensor for Hg2+ in Aqueous Solution

A new anthracene fluorophore senses Hg²⁺ selectively in aqueous solution. Among the metal ions examined, fluorescent chemosensor 1 shows selective large CHEQ effects with Hg²⁺ and Ag⁺ at pH 7.     

A new window towards multidimensional sensing of transition metal cations through dual mode sensing ability of N-benzyl-(3-hydoxy-2-naphthalene): emission enhancement coupled remarkable spectral shift

A structurally simple Schiff base N-benzyl-(3-hydroxy-2-naphthalene) (NBHN32) has been synthesized and characterized by (1)H NMR, (13)C NMR, and DEPT spectroscopy. The photophysical behaviour of NBHN32 in response to the presence of various transition metal cations has been explored by means of steady-state absorption, emission and time-resolved emission spectroscopy techniques. Efficient through space intramolecular photoinduced electron transfer (PET) between the naphthalene fluorophore and the imine group has been argued for extremely low fluorescence yield of NBHN32 compared to the parent molecule 3-hydroxy-2-naphthaldehyde (HN32) containing the same fluorophore but lacking the receptor moiety. Transition metal ion-induced emission enhancement is thus addressed on the lexicon of perturbation of the PET by the metal ions. Apart from fluorescence enhancement, transition metal ion imparts remarkable shift of the emission maxima of NBHN32, which is another unique aspect on the proposed ability of NBHN32 to function as a fluorescence chemosensor.     

Appending zinc tetraphenylporphyrin with an amine receptor at β-pyrrolic carbon for designing a selective histamine chemosensor

Adopting the rarely used β-functionalisation strategy in porphyrin-based sensor design, an amine receptive site is appended onto the zinc(II) porphyrin molecular framework affording a ditopic chemosensor 4. The assembled chemosensor interacts selectively with histamine in toluene via a ‘two-site’ binding mode. Association constant of the complex evaluated from the respective UV–vis spectra is found to be (2.32 ± 0.57) × 10⁶, which is approximately 4-fold greater than those complexes derived from 4 and nicotine/histidine. On the basis of a combined spectroscopic method and molecular modelling, the binding model of the porphyrin host and biogenic guest molecules is established. Our results clearly demonstrate the viability of the design and development of the porphyrin-based chemosensor by appending a receptor at the β-pyrrolic carbon of the porphyrin scaffold.