Synthesis and photophysical properties of a fluorescent TREN-type ligand incorporating the coumarin chromophore and its zinc complex

A New Biphenol-bis(polyazacyclophane) Receptor with Unusual Photophysical Properties Towards Zn2

The new ligand 3,3'-bis(((2-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)amino)methyl)-[1,1'-biphenyl]-2,2'-diol (L) has been synthesized and characterized. It contains two pyridinacyclophane macrocycles spaced by a 2,2'-biphenol moiety. The acid-base behaviour of L as well as its binding properties towards Zn2+ ion have been investigated. This work is inserted in the field of fluorescent ditopic receptors, formed by two polyamines spaced by a aromatic fragments. This ligand represents a new example of a peculiar case of polyamine fluorescent receptor in which the interaction with Zn2+ is translated into a deactivation of the emission. Enough data to describe and explain this unusual behaviour was obtained through potentiometric, UV-Vis, fluorescence and NMR titrations as well as theoretical calculations. This studies have shown that the metal cation is indirectly affecting the emission favouring a conformation in which the fluorophore is at stacking distance from the electron poor pyridine moieties. This gives rise to an oxidative photoinduced electron transfer from the excited state of the fluorophore to the electron-poor Zn2+ coordined pyridine.

Fluorescent Chemosensors Based on Polyamine Ligands: A Review

Polyamine ligands are water-soluble receptors that are able to coordinate, depending on their protonation degree, either metal ions, anionic, or neutral species. Furthermore, the presence of fluorescent signaling units allows an immediate visual response/signal. For these reasons, they can find applications in a wide variety of fields, mainly those where aqueous media is necessary, such as biological studies, wastewater analysis, soil contamination, etc. This review provides an overview of the recent developments in the research of chemosensors based on polyamine ligands functionalized with fluorescent signaling units. The discussion focuses on the design, synthesis, and physicochemical properties of this type of fluorescent chemosensors in order to analyze the applications associated to the sensing of metal ions, anions, and neutral molecules of environmental and/or biological interest. To facilitate a quick access and overview of all the chemosensors covered in this review, a summary table of the chemosensor structures and analytes, with all the corresponding references, is also presented.

Sulfonamides Are an Overlooked Class of Electron Donors in Luminogenic Luciferins and Fluorescent Dyes

Many fluorophores, and all bright light-emitting substrates for firefly luciferase, contain hydroxyl or amine electron donors. Sulfonamides were found to be capable of serving as replacements for these canonical groups. Unlike "caged" carboxamides, sulfonamide donors enable bioluminescence, and sulfonamidyl luciferins, coumarins, rhodols, and rhodamines are fluorescent in water.

Efficient two-step synthesis of water soluble BODIPY–TREN chemosensors for copper(ii) ions

Two promising, highly selective, water soluble, Cu(ii) sensors were synthesized in two reaction steps, using C–H functionalization reactions.

Zn(II)-coordination modulated ligand photophysical processes - the development of fluorescent indicators for imaging biological Zn(II) ions

Molecular photophysics and metal coordination chemistry are the two fundamental pillars that support the development of fluorescent cation indicators. In this article, we describe how Zn(II)-coordination alters various ligand-centered photophysical processes that are pertinent to developing Zn(II) indicators. The main aim is to show how small organic Zn(II) indicators work under the constraints of specific requirements, including Zn(II) detection range, photophysical requirements such as excitation energy and emission color, temporal and spatial resolutions in a heterogeneous intracellular environment, and fluorescence response selectivity between similar cations such as Zn(II) and Cd(II). In the last section, the biological questions that fluorescent Zn(II) indicators help to answer are described, which have been motivating and challenging this field of research.

Theoretical studies on the structural and spectroscopic properties of an iminocoumarin-based probe and its metal complexation: an implication for a fluorescence probe

To understand the sensing behaviors of molecular fluorescent probes, an N,N-di(picolyl)aminoethyl-iminocoumarin probe (L) and its complexation with metal(II) ions (ML, M = Mg, Ca, Zn, Cd and Hg) were examined by relativistic density functional theory (DFT). Four stable conformational isomers (labeled as g1, g2, a1 and a2) for each of them have been optimized, except for CaL having only three without the g2 isomer. All of these structures have been confirmed by frequency calculations. In the aqueous solution, the a2 isomer of the L probe was calculated to be the most stable, while the g1 isomer turns out to be energetically favorable upon binding with metal ions. At these isomeric geometries, the experimentally obtained absorption was well reproduced by calculations of time-dependent DFT (TD-DFT) and a conductor-like polarized continuum model (CPCM). A slight red-shifting from L (508 nm) to ML (516-528 nm) was found. This is due to the metal affinity that stabilizes the LUMOs of ML greater than the HOMOs. Singlet excited-state structures of L and ML (M = Zn, Cd and Hg) were fully optimized using the TD-DFT approach, giving more relaxed geometries than their respective ground-state ones. Their fluorescent emissions in the aqueous solution were calculated to be 543 and 551-560 nm, respectively, agreeing with experimental values of 543 nm for L and 558 nm for ZnL. The present study also presents theoretical support for a sensing mechanism of photo-induced charge transfer of the L probe that was proposed in the previous experiment.

Anti-inflammatory and antioxidant activity of coumarins designed as potential fluorescent zinc sensors

A series of coumarin analogs, designed and synthesised as potential fluorescent zinc probes were evaluated for their biological activity as anti-inflammatory and antioxidant agents. The effect of the synthesised compounds on inflammation, using the carrageenin-induced rat paw oedema model, was studied. In general, the compounds were found to be potent anti-inflammatory agents (26.5-64%). Compound 5 was found to interact significantly with 1,1-diphenyl-2-picryl-hydrazyl stable free radical (DPPH) whereas the remainder were inactive in this assay. The compounds inhibit in general the soybean lipoxygenase and scavenge superoxide anion radicals. The anti-inflammatory activity seems to be connected with their reducing activity. Their RM values were determined as an expression of their lipophilicity. Theoretical calculations of their lipophilicity as clog P were performed indicating that only a poor relationship exists between their lipophilicity and anti-inflammatory activity.