Azulene-based fluorescent chemosensor for adenosine diphosphate

A GFP Inspired 8-Methoxyquinoline-Derived Fluorescent Molecular Sensor for the Detection of Zn2+ by Two-Photon Microscopy

An effective, GFP-inspired fluorescent Zn2+ sensor is developed for two-photon microscopy and related biological application that features an 8-methoxyquinoline moiety. Excellent photophysical characteristics including a 37-fold fluorescence enhancement with excitation and emission maxima at 440 nm and 505 nm, respectively, as well as a high two-photon cross-section of 73 GM at 880 nm are reported. Based on the experimental data, the relationship between the structure and properties was elucidated and explained backed up by DFT calculations, particularly the observed PeT phenomenon for the turn-on process. Biological validation and detailed experimental and theoretical characterization of the free and the zinc-bound compounds are presented.

Macrocyclic Conformational Switch Coupled with Pyridinium-Induced PET for Fluorescence Detection of Adenosine Triphosphate

The binding of nucleotides is crucial for signal transduction as it induces conformational protein changes, leading to downstream cellular responses. Synthetic receptors that bind nucleotides and transduce the binding event into global conformational rearrangements are highly challenging to design, especially those that operate in an aqueous solution. Much work is focused on evaluating functionalized dyes to detect nucleotides, whereas coupling of a nucleotide-induced conformational switching to a sensing event has not been reported to date. We disclose synthetic receptors that undergo a global conformational rearrangement upon nucleotide binding. Integrating naphthalimide and the pyridinium ion into the structure enables stabilization of the folded conformation and efficient fluorescence quenching. The binding of a nucleotide rearranges the receptor conformation and alters the strong fluorescence enhancement. The methylpyridinium-containing receptor demonstrated high sensing selectivity for adenosine 5'-triphosphate (ATP) and a record 160-fold fluorescence enhancement. It can detect fluctuations of ATP in HeLa cells and possesses low cytotoxicity. The developed systems present an attractive approach for designing ATP-responsive artificial molecular switches that operate in water and integrate a strong fluorescence response.

Selective turn-on sensing of adenosine diphosphate and phosphate anions by ruthenium (II) polypyridine anchored p-tert-butylcalix[4]arene platform

BACKGROUND

Nucleoside polyphosphate (NPP) anions are important for enzymatic activity and should be monitored by scientists in industry and medicine. By elucidating enzyme kinetics and processes, it aids in the discovery of effective inhibitors and activators. Nucleoside polyphosphate (NPP) anions are used by kinases, GTPases, and glycosyltransferases (GTs). Phosphorylation of certain amino acid residues (Ser, Thr, and Tyr) on proteins requires the breakdown of ATP by protein kinases, which produces ADP. Protein kinases, breakdown of ATP, and NPP are the focus of oncology drug development because the aberrant control of kinase activity is a common cause of cancer.

RESULTS

However, a discriminative turn-on fluorescent property is exhibited by non-fluorescent p-tertbutylcalix[4]arene modified 1,2,3-triazole containing bis-ruthenium polypyridyl complex (RL) upon the addition of phosphate anions such as (dihydrogen pyrophosphate (H2P2O72-) and dihydrogen phosphate (H2PO4-)) in CH3CN solvent and Adenosine Diphosphate (ADP) in CH3CN/HEPES (pH = 7.4) buffer (9/1, v/v). The probe RL shows a better-recognizing ability with pyrophosphate anion (H2P2O72-) than dihydrogen phosphate anion (H2PO4-). With H2P2O72- and H2PO4- anions, the RL detection limit was calculated to be as low as 83 nM and 198 nM, respectively.

SIGNIFICANCE

The calix[4]arene macrocycle's excellent size and binding cone conformation make it a good host-guest interface for the pyrophosphate anion and ADP. The bis-ruthenium polypyridyl complex's connection to the p-tertbutyl calix[4]arene moiety creates the ADP selectivity turn-on sensor. When moving from mono-nuclear to bi-nuclear ruthenium complex anchored on p-tertbutyl calix[4]arene, the probe can differentiate ADP, ATP, and AMP. Furthermore, this platform is a great resource for creating devices to simultaneously assess phosphate anions in environmental samples.

Persistent azulene α-carbocations: synthesis from aldehydes, spectroscopic and crystallographic properties

The non-benzenoid aromatic system azulene is sufficiently nucleophilic at C1 that it can react with a protonated aldehyde to form an α-azulenyl alcohol. This in turn may be protonated and undergo loss of water to give an azulene α-carbocation. We report the isolation of such azulenyl cations as salts with non-coordinating anions. The salts have been characterised by NMR, UV/Vis absorption and (in certain cases) X-ray crystallography. Reduction of representative salts to afford azulenyl(aryl) methylenes has been demonstrated.

Synthesis of donor-acceptor compounds based on azulene

At present, non-benzenoid aromatic hydrocarbons are widely used as precursors for the synthesis of new materials with useful electronic properties. In particular, the non-alternative aromatic hydrocarbon azulen with a unique dipole structure and a tendency to form stabilized radical ions should be predetermined as a building block for obtaining new π-conjugated systems with interesting optoelectronic properties. This article discusses the directed synthesis and study of optical properties of new donor-acceptor compounds based on azulene. It was shown that for the synthesis of donor-acceptor phenylketone azulenes, the reaction of directed (to positions С1 and С3) acylation with benzoyl chloride in the presence of Li2MnCl4 in tetrahydrofuran was used for the first time as a key step. It was found that push-pull phenyldicyanovinyl azulenes obtained by Knoevenagel condensation of azulenylketones with malononitrile flow easily (with an increase in the yield of end products) in the presence of pyridine in dimethyl sulfoxide. Electron UV-visible spectra of phenyldicyanovinyl azulene compounds showed strong absorption bands in the visible region (λmax = 452 and 434 nm) caused by intense intramolecular charge transfer between the donor azulene ring and the acceptor phenyldicyanovinyl group.

2,6-Azulene-based Homopolymers: Design, Synthesis, and Application in Proton Exchange Membrane Fuel Cells

Azulene-based homopolymers are of great interest from the point view of chemistry and material science. Herein, by means of Friedel-Crafts acylation to introduce solubilizing chains on the 1-position of azulene, we designed and synthesized two examples of 2,6-azulene-based homopolymers RP(Az-AC16) and P(Az-AC16). The arrangement of 2,6-azulene units is irregular for RP(Az-AC16), while P(Az-AC16) has head-to-head/tail-to-tail arranged 2,6-azulene units. Proton-responsive studies demonstrate that RP(Az-AC16) and P(Az-AC16) show reversible proton responsiveness in both solution and thin film. To utilize the dynamically reversible proton-responsive property of these polymers in thin films, RP(Az-AC16) and P(Az-AC16) were incorporated into a Nafion matrix as proton exchange membranes, wherein the Nafion/P(Az-AC16) composite membrane exhibits significant increases in proton conductivity relative to the Nafion membrane at different temperatures of each relative humidity (RH), which further results in a 64% improvement in hydrogen fuel cell output power under 30% RH at 80 °C. Our studies have realized the first solution synthesis of 2,6-azulene-based homopolymers and the first application of azulene-based π-systems in hydrogen fuel cells.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.