Macrocyclic chemosensors with anthraquinone signaling unit built into ionophore. Experimental and computational studies (part I) - synthesis and effect of proton binding on spectrophotometric and electrochemical properties

Two macrocyclic chemosensors with anthraquinone signaling unit incorporated into ionophore system (via positions 1 and 8) have been synthesized and subsequently their physicochemical properties became the subject of our extensive research. First ligand, labeled in the paper as AQ-Ncrown is characterized by a cyclic structure of a crown ether, while second one AQ-Ncrypt includes an additional ethoxy bridge, which ensures the bicyclic character of a cryptand. The studied macrocycles possess both oxygen and nitrogen heteroatoms in the ionophore cavity. Dualistic (chromophore and electrophore) signaling nature of described compounds, makes them potentially attractive molecular recognition systems. The aim of our research was to synthesize and analyze the spectroscopic, acid-base and redox properties of aforesaid macrocycles. Furthermore, we have combined experimental approach together with theoretical investigations. The equilibrium structures of AQ-Ncrown and AQ-Ncrypt were determined with the use of DFT calculations. The sensitivity of studied macrocycles towards interactions with protons was scrutinized. The complete pH-spectrophotometric characteristic of studied ligands together with their protolytic forms and corresponding pK_a values were determined. The influence of medium (aprotic and protic solvent) on spectral effects was described. Furthermore, the molecular electrostatic potential maps for ligands and differential electron densities for their mono and dianions were calculated. The redox reactions was investigated at different pHs by cyclic voltammetry. Electrochemical results have presented intriguing phenomenon: the specific stabilization of the reduced form of the protonated molecules. The calculations have revealed that this is a consequence of barrierless intramolecular proton transfer (from the macrocycle cavity onto the anthraquinone moiety) that might occur during the reduction process in acidic medium.

Anthraquinone-1,8-Derived (Pseudo-) Crown and Lariat Ethers: Design and Applications as Fluorescent and Chromogenic Ion (Pair) Sensors

Cyclic polyamine/ethers embedded with anthraquinone moieties and functional pendants, are structural analogues of crown ethers and (oxo-) cyclams, and could be utilized as sensitive and selective chemosensors towards metal cations. Those pseudo- (similar but geometrically distinct) crown and lariat ethers show various cation-binding patterns and stoichiometry, being modulated by donor type, cavity size and pendants' chelating ability. The luminescent and chromogenic properties also differ a lot along with the derivation of the parental macrocycle. Methodological designing including synthesis and post-functionalization through nucleophilic substitution, Mannich condensation etc., as well as the sensing performance of those pseudo- crown and lariat ethers are summarized in this review, basing on the spectroscopic, voltammetric and X-ray crystallographic determinations. Anion effect in sensing cations is evaluated according to the ion-pair recognition theory. Those results shed some light on exemplifying the anions' role in bioinorganic systems including metalloenzymes.

Structures and Chromogenic Ion-Pair Recognition of a Catechol-Functionalized 1,8-Anthraquinone Macrocycle in Dimethyl Sulfoxide

A lariat anthraquinone macrocycle functionalized with catechol (H₂L) was synthesized via the Mannich reaction. The Mannich base H₂L can be partially decomposed into L1·3H₂O and HL1·NO₃·2H₂O in the presence of tetrabutylammonium hydroxide/Al(NO₃)₃·9H₂O in dimethyl sulfoxide (DMSO). Free L1·3H₂O is essentially coplanar, while protonated HL1·NO₃·2H₂O is highly distorted. Dark-green FeCl₃·H₂L·2H₂O powder and Fe₂(HL)₂Cl₄ crystal can be isolated from ethanol (C₂H₅OH) in high/low H₂L concentration. Anthraquinone in H₂L is essentially coplanar but distorted in Fe₂(HL)₂Cl₄. The Fe(III) ion in Fe₂(HL)₂Cl₄ adopts a less common five-coordination with three catecholate O and two Cl atoms in the dimer. The distortion of inbound C═O is much higher than that of outbound C═O in anthraquinone in all of these compounds. H₂L responds to chlorides of Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe³⁺, Cu²⁺, Zn²⁺, and Al³⁺ in a DMSO solution, which can be observed by differential pulse voltammetry, UV-vis, and ¹H NMR. All of these metal ions shift E_p of anthraquinone to positive, especially the second reduction peak of anthraquinone. Fe³⁺, Zn²⁺, and Al³⁺ change the reduction of catechol fundamentally. H₂L (0.50 mM) shows a chromogenic response to FeCl₃ and Fe(NO₃)₃ to form uncommon 2:1 and 3:2 (H₂L/Fe) complexes, both peaking at 748 nm in DMSO. In the presence of 2 equiv of sodium hydroxide (NaOH), the 748 nm absorbance shifts to 777 nm, identical with Fe₂(HL)₂Cl₄ in DMSO. Different from the fast reaction between H₂L and FeCl₃, Fe(NO₃)₃ reacts with H₂L rather slowly in DMSO. Catechol can coordinate to FeCl₃ without any deprotonation in C₂H₅OH and DMSO. H₂L also shows a chromogenic response to fluorides and hydroxides, which peak at 670 and 684 nm, respectively, in DMSO. The binding ratio between H₂L and F^-/OH^- is 1:2. In a higher concentration of hydroxides, a 684 nm greenish-blue 1:2 complex forms immediately, which gradually transforms to a red complex and peaks at ∼530 nm in minutes at room temperature. No color change can be observed in an C₂H₅OH solution in the presence of OH^-.

Facile One-Pot Synthesis of Tellurium Nanorods as Antioxidant and Anticancer Agents

Nanorods have been utilized in targeted therapy, controlled release, molecular diagnosis, and molecule imaging owing to their large surface area and optical, magnetic, electronic, and structural properties. However, low stability and complex synthetic methods have substantially limited the application of tellurium nanorods for use as antioxidant and anticancer agents. Herein, a facile one-pot synthesis of functionalized tellurium nanorods (PTNRs) by using a hydrothermal synthetic system with a polysaccharide-protein complex (PTR), which was extracted from Pleurotus tuber-regium, as a capping agent is described. PTNRs remained stable in water and in phosphate-buffered saline and exhibited high hemocompatibility. Interestingly, these nanorods possessed strong antioxidant activity for scavenging 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS(.+) ) and 2,2-diphenyl-1-picrylhydrazylhydrate (DPPH) free radicals and demonstrated novel anticancer activities. However, these nanorods exhibited low cytotoxicity toward normal human cells. In addition, the PTNRs effectively induced a decrease in the mitochondrial membrane potential in a dose-dependent manner, which indicated that mitochondrial dysfunction might play an important role in PTNR-induced apoptosis. Therefore, this study provides a one-pot strategy for the facile synthesis of tellurium nanorods with novel antioxidant and anticancer application potentials.

Cyclodextrin-Based Metal-Organic Nanotube as Fluorescent Probe for Selective Turn-On Detection of Hydrogen Sulfide in Living Cells Based on H2S-Involved Coordination Mechanism

Hydrogen sulfide (H₂S) has been considered as the third biologically gaseous messenger (gasotransmitter) after nitric oxide (NO) and carbon monoxide (CO). Fluorescent detection of H₂S in living cells is very important to human health because it has been found that the abnormal levels of H₂S in human body can cause Alzheimer’s disease, cancers and diabetes. Herein, we develop a cyclodextrin-based metal-organic nanotube, CD-MONT-2, possessing a {Pb₁₄} metallamacrocycle for efficient detection of H₂S. CD-MONT-2′ (the guest-free form of CD-MONT-2) exhibits turn-on detection of H₂S with high selectivity and moderate sensitivity when the material was dissolved in DMSO solution. Significantly, CD-MONT-2′ can act as a fluorescent turn-on probe for highly selective detection of H₂S in living cells. The sensing mechanism in the present work is based on the coordination of H₂S as the auxochromic group to the central Pb(II) ion to enhance the fluorescence intensity, which is studied for the first time.

Near-IR luminescent lanthanide complexes with 1,8-diaminoanthraquinone-based chromophoric ligands

1,8-Anthraquinone derivatives can act as low energy, visible light sensitizers for near-IR emitting lanthanides.

Polyether complexes of groups 13 and 14

Notable aspects of the chemistry of polyether complexes of group 13 and 14 elements are reviewed.