Design and Synthesis of a Fluorescent Probe for Zn2+, 5,7-Bis(N,N-dimethylaminosulfonyl)-8-hydroxyquinoline-Pendant 1,4,7,10-Tetraazacyclododecane and Zn2+-Dependent Hydrolytic and Zn2+-Independent Photochemical Reactivation of Its Benzenesulfonyl-Caged Derivative

Selective binding and fluorescence sensing of Zn(II)/Cd(II) using macrocyclic tetra-amines with different fluorophores: insights into the design of selective chemosensors for transition metals

Selective binding and optical sensing of Zn(II) and Cd(II) by L1, HL2, L3, H2L4 and H2L5 receptors were analysed in aqueous solutions by coupling potentiometric, UV-vis absorption and fluorescence emission measurements, with the aim to determine the effect of complex stability on selective signalling of metals with similar electronic configurations. All receptors share the same cyclic tetra-amine binding unit attached to a single quinoline (Q) or 8-hydroxyquinoline (8-OHQ) unit (L1 and HL2, respectively), two Q or 8-OHQ moieties (L3 and H2L4, respectively), and, finally, two Q and two acetate groups (H2L5). The crystal structures of the Cd(II) and Zn(II) complexes show that L3 and H2L4 feature a cavity in which the larger Cd(II) complex is better fitted than the Zn(II) complex, leading to the formation of more stable Cd(II) complexes. In turn, Zn(II) forms more stable complexes with L1 and HL2, owing to its high tendency to give 5-coordinated complexes. Considering optical selectivity, Zn(II) gives the most emissive complex with L3, while the corresponding Cd(II) complex is basically quenched. The gathered structure of the Zn(II) complex, in which the two Q units are associated with one another-a structural motif not observed in the [CdL3]2+ complex-leads to poor solvation of the Q units, favouring complex emission. Among 8-OHQ-containing receptors, the most emissive complex is formed by Cd(II) with HL2, containing a single 8-OHQ moiety. H2L4 forms non-emissive complexes: the presence of two coordinating 8-OHQ moieties weakens metal interactions with the tetra-amine unit, favouring PET to the excited fluorophore that quench the emission.

An innovative near-infrared fluorescent probe with FRET effect for the continuous detection of Zn2+ and PPi with high sensitivity and selectivity, and its application in bioimaging

As the second most abundant transition metal element in the human body, zinc ions play an important role in the normal growth and development of the human body. We have successfully synthesized a near-infrared fluorescent probe with FRET effect for the detection of Zn2+. Probe DR6G has good selectivity and anti-interference ability for Zn2+. When Zn2+ is added to the probe DR6G solution, it responds completely within seconds, releasing red fluorescence with a detection limit of 2.02 × 10-8 M. As the main product of ATP hydrolysis, PPi is indispensable in various metabolic activities in cells and the human body. Due to the strong binding ability of Zn2+ and PPi, it is easy to form ZnPPi precipitation, so we added PPi to the solution to complete the Zn2+ detection, and realized the continuous detection of PPi, and the detection limit was 2.06 × 10-8 M. Since Zn2+ and PPi play an important role in vivo, it is of great practical significance to design and synthesize a fluorescent probe that can continuously detect Zn2+ and PPi. Biological experiments have shown that the probe DR6G has low cytotoxicity and can complete the detection of exogenous Zn2+ and PPi in cells and living mice in vitro. Bacterial experiments have shown that the DR6G probe also has certain research value in the field of environmental monitoring and microbiology. Due to the constant variation of the fluorescence signals of Zn2+ and PPi during detection, we designed the logic gate program. In practical applications, the probe DR6G can quantitatively detect Zn2+ in zinc-containing oral liquids and qualitatively detect PPi in toothpaste.

Photocleavable Ortho-Nitrobenzyl-Protected DNA Architectures and Their Applications

This review article introduces mechanistic aspects and applications of photochemically deprotected ortho-nitrobenzyl (ONB)-functionalized nucleic acids and their impact on diverse research fields including DNA nanotechnology and materials chemistry, biological chemistry, and systems chemistry. Specific topics addressed include the synthesis of the ONB-modified nucleic acids, the mechanisms involved in the photochemical deprotection of the ONB units, and the photophysical and chemical means to tune the irradiation wavelength required for the photodeprotection process. Principles to activate ONB-caged nanostructures, ONB-protected DNAzymes and aptamer frameworks are introduced. Specifically, the use of ONB-protected nucleic acids for the phototriggered spatiotemporal amplified sensing and imaging of intracellular mRNAs at the single-cell level are addressed, and control over transcription machineries, protein translation and spatiotemporal silencing of gene expression by ONB-deprotected nucleic acids are demonstrated. In addition, photodeprotection of ONB-modified nucleic acids finds important applications in controlling material properties and functions. These are introduced by the phototriggered fusion of ONB nucleic acid functionalized liposomes as models for cell-cell fusion, the light-stimulated fusion of ONB nucleic acid functionalized drug-loaded liposomes with cells for therapeutic applications, and the photolithographic patterning of ONB nucleic acid-modified interfaces. Particularly, the photolithographic control of the stiffness of membrane-like interfaces for the guided patterned growth of cells is realized. Moreover, ONB-functionalized microcapsules act as light-responsive carriers for the controlled release of drugs, and ONB-modified DNA origami frameworks act as mechanical devices or stimuli-responsive containments for the operation of DNA machineries such as the CRISPR-Cas9 system. The future challenges and potential applications of photoprotected DNA structures are discussed.

A novel Near-Infrared fluorescent probe for Zn2+ and CN- double detection based on dicyanoisfluorone derivatives with highly sensitive and selective, and its application in Bioimaging

We have successfully synthesized NIRF as a near-infrared fluorescence probe for relay recognition of zinc and cyanide ions. The probe possesses well selectivity and anti-interference ability over common ions towards Zn²⁺ and CN^-. The results showed that Zn²⁺ and the probe formed [NIRF-Zn²⁺] complex after added Zn²⁺ into the probe NIRF solution, which emited red fluorescence. The probe can be used for quantitative detection of Zn²⁺ with a detection limit of 4.61 × 10^-8 M. It was determined that the binding stoichiometry between the NIRF and Zn²⁺ was 1:1 according to the job^,s curve. Subsequently, CN^- was added to the NIRF-Zn²⁺ solution, CN^- combined with Zn²⁺ to generate [Zn(CN^-)_x]^1-x due to the stronger binding ability between zinc ion and cyanogen, which lead to the red fluorescence disappeared. The quantitative detection of CN^- was realized with a detection limit of 7.9 × 10^*7 M. In addition, the probe has excellent specificity and selectivity for Zn²⁺ and CN^-. And the probe can be stable in a wide range of pH. Through biological experiments, we found that it can complete cell imaging in macrophages and imaging of living mice, which has application prospects in Bioimaging. In addition, the probe NIRF has good applicability for Zn²⁺ and CN^- detection in actual samples.

Design, Synthesis, and Biological Evaluation of Boron-Containing Macrocyclic Polyamines and Their Zinc(II) Complexes for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a binary therapeutic method for cancer treatment based on the use of a combination of a cancer-specific drug containing boron-10 (¹⁰B) and thermal neutron irradiation. For successful BNCT, ¹⁰B-containing molecules need to accumulate specifically in cancer cells, because destructive effect of the generated heavy particles is limited basically to boron-containing cells. Herein, we report on the design and synthesis of boron compounds that are functionalized with 9-, 12-, and 15-membered macrocyclic polyamines and their Zn²⁺ complexes. Their cytotoxicity, intracellular uptake activity into cancer cells and normal cells, and BNCT effect are also reported. The experimental data suggest that mono- and/or diprotonated forms of metal-free [12]aneN₄- and [15]aneN₅-type ligands are uptaken into cancer cells, and their complexes with intracellular metals such as Zn²⁺ would induce cell death upon thermal neutron irradiation, possibly via interactions with DNA.

A highly selective sequential recognition probe for Zn2+ and HSO4-/H2PO4- based on a diarylethene chemosensor

A novel diarylethene derivative chemosensor DTP-o connected to Schiff base unit for fluorescent detection of Zn²⁺ and relay-detection of HSO₄^-/H₂PO₄^- was designed and synthesized successfully. DTP-o displayed excellent photochromism and fluorometric sensing toward Zn²⁺ to form DTP-o-Zn²⁺ complex in acetonitrile with the detection limit of 5.62 × 10^-7 M. And the form of DTP-o combined with Zn²⁺ could further be verified by Job's plot titrations and mass spectrometry analysis. Furthermore, the complex of DTP-o-Zn²⁺ showed an excellent characteristic of fluorescent relay-response toward HSO₄^- and H₂PO₄^- with high sensitivity and selectivity. The detection limits for HSO₄^- and H₂PO₄^- were as low as 3.04 × 10^-8 M and 3.41 × 10^-8 M, respectively. Moreover, the sensor DTP-o could also be applied to detect Zn²⁺ on practical samples and test strips with high accuracy.

Inclusion of alkyl nitriles by tetra-armed cyclens with styrylmethyl groups

A new technique for the assignment of the absolute configurations of low [α]_D alkyl-nitriles using a Ag⁺ complex with a tetra-armed cyclen is reported.

A cost-effective chitosan–oxine based thin film for a volatile acid vapour sensing application

A polymer film based chemosensor was developed through the immobilization of chitosan and oxine, for the detection of TFA vapors.

Zinc complexes as fluorescent chemosensors for nucleic acids: new perspectives for a "boring" element

Zinc(II) complexes are effective and selective nucleic acid-binders and strongly fluorescent molecules in the low energy range, from the visible to the near infrared. These two properties have often been exploited to quantitatively detect nucleic acids in biological samples, in both in vitro and in vivo models. In particular, the fluorescent emission of several zinc(II) complexes is drastically enhanced or quenched by the binding to nucleic acids and/or upon visible light exposure, in a different fashion in bulk solution and when bound to DNA. The twofold objective of this perspective is (1) to review recent utilisations of zinc(II) complexes as selective fluorescent probes for nucleic acids and (2) to highlight their novel potential applications as diagnostic tools based on their photophysical properties.

Quinoline-attached triazacyclononane (TACN) derivatives as fluorescent zinc sensors

TACN (1,4,7-triazacyclononane) derivatives with three 6-methoxy-2-quinolylmethyl or 1-isoquinolylmethyl moieties were examined as fluorescent zinc sensors. Upon the addition of zinc, 6-MeOTQTACN (5) exhibited a 9-fold fluorescence increase at 420 nm (λex = 341 nm, ϕZn = 0.070). Fluorescence enhancement is specific for zinc and cadmium, although cadmium induces smaller increases (ICd/I0 = 3.6 and ICd/IZn = 40%). The isoquinoline analog 1-isoTQTACN (6) exhibits minimal fluorescence enhancement upon zinc binding. TPEN (N,N,N',N'-tetrakis(2-pyridylmethyl)ethylene-diamine) does not extract zinc from the 6-MeOTQTACN-Zn complex (5-Zn). The quantum yield, metal ion selectivity and metal binding affinity differences between TACN and ethylenediamine (EN) skeletons in quinoline-based ligands are discussed based on the X-ray crystallographic analysis of zinc and cadmium complexes, demonstrating the superiority of quinoline-TACN conjugates.

AS-2, a novel inhibitor of p53-dependent apoptosis, prevents apoptotic mitochondrial dysfunction in a transcription-independent manner and protects mice from a lethal dose of ionizing radiation

In a previous study, we reported that some tetradentate zinc(II) chelators inhibit p53 through the denaturation of its zinc-requiring structure but a chelator, Bispicen, a potent inhibitor of in vitro apoptosis, failed to show any efficient radioprotective effect against irradiated mice because the toxicity of the chelator to mice. The unsuitability of using tetradentate chelators as radioprotectors prompted us to undertake a more extensive search for p53-inhibiting agents that are weaker zinc(II) chelators and therefore less toxic. Here, we show that an 8-hydroxyquinoline (8HQ) derivative, AS-2, suppresses p53-dependent apoptosis through a transcription-independent mechanism. A mechanistic study using cells with different p53 characteristics revealed that the suppressive effect of AS-2 on apoptosis is specifically mediated through p53. In addition, AS-2 was less effective in preventing p53-mediated transcription-dependent events than pifithrin-μ (PFTμ), an inhibitor of transcription-independent apoptosis by p53. Fluorescence visualization of the extranuclear distribution of AS-2 also supports that it is ineffective on the transcription-dependent pathway. Further investigations revealed that AS-2 suppressed mitochondrial apoptotic events, such as the mitochondrial release of intermembrane proteins and the loss of mitochondrial membrane potential, although AS-2 resulted in an increase in the mitochondrial translocation of p53 as opposed to the decrease of cytosolic p53, and did not affect the apoptotic interaction of p53 with Bcl-2. AS-2 also protected mice that had been exposed to a lethal dose of ionizing radiation. Our findings indicate that some types of bidentate 8HQ chelators could serve as radioprotectors with no substantial toxicity in vivo.

Dynamic cyclen-metal complexes for molecular sensing and chirality signaling

Structural dynamism plays important roles in artificial and biological systems, because it controls structures and functions of various molecules and assemblies. In this review, molecular recognition and self-assembling behavior of dynamic armed cyclen-metal complexes are discussed at the molecular and supramolecular levels. These metal complexes provide useful platforms for molecular receptors, supramolecules, and molecular assemblies that can respond rapidly to guest molecules and environments. Since armed cyclens have many structural and geometrical variations, they form a wide variety of metal complexes having specific sensing and signaling functions. The Lewis acidity of the metal cations plays an essential role in anion binding and in hydrolytic catalysis of phosphate esters. Characteristic luminescence and magnetic properties of lanthanides also enable techniques for effective bio-imaging. They also serve as chiral building blocks for self-assembled architectures, which offer chirality integration effective for chirality sensing and signaling at the supramolecular level.

Structural basis for bifunctional zinc(II) macrocyclic complex recognition of thymine bulges in DNA

The zinc(II) complex of 1-(4-quinoylyl)methyl-1,4,7,10-tetraazacyclododecane (cy4q) binds selectively to thymine bulges in DNA and to a uracil bulge in RNA. Binding constants are in the low-micromolar range for thymine bulges in the stems of hairpins, for a thymine bulge in a DNA duplex, and for a uracil bulge in an RNA hairpin. Binding studies of Zn(cy4q) to a series of hairpins containing thymine bulges with different flanking bases showed that the complex had a moderate selectivity for thymine bulges with neighboring purines. The dissociation constants of the most strongly bound Zn(cy4q)-DNA thymine bulge adducts were 100-fold tighter than similar sequences with fully complementary stems or than bulges containing cytosine, guanine, or adenine. In order to probe the role of the pendent group, three additional zinc(II) complexes containing 1,4,7,10-tetraazacyclododecane (cyclen) with aromatic pendent groups were studied for binding to DNA including 1-(2-quinolyl)methyl-1,4,7,10-tetraazacyclododecane (cy2q), 1-(4-biphenyl)methyl-1,4,7,10-tetraazacyclododecane (cybp), and 5-(1,4,7,10-tetraazacyclododecan-1-ylsulfonyl)-N,N-dimethylnaphthalen-1-amine (dsc). The Zn(cybp) complex binds with moderate affinity but little selectivity to DNA hairpins with thymine bulges and to DNA lacking bulges. Similarly, Zn(dsc) binds weakly both to thymine bulges and hairpins with fully complementary stems. The zinc(II) complex of cy2q has the 2-quinolyl moiety bound to the Zn(II) center, as shown by (1)H NMR spectroscopy and pH-potentiometric titrations. As a consequence, only weak (500 μM) binding is observed to DNA with no appreciable selectivity. An NMR structure of a thymine-bulge-containing hairpin shows that the thymine is extrahelical but rotated toward the major groove. NMR data for Zn(cy4q) bound to DNA containing a thymine bulge is consistent with binding of the zinc(II) complex to the thymine N3(-) and stacking of the quinoline on top of the thymine. The thymine-bulge bound zinc(II) complex is pointed into the major groove, and there are interactions with the guanine positioned 5' to the thymine bulge.

11B NMR sensing of d-block metal ions in vitro and in cells based on the carbon-boron bond cleavage of phenylboronic acid-pendant cyclen (cyclen = 1,4,7,10-tetraazacyclododecane)

Noninvasive magnetic resonance imaging (MRI) including the "chemical shift imaging (CSI)" technique based on (1)H NMR signals is a powerful method for the in vivo imaging of intracellular molecules and for monitoring various biological events. However, it has the drawback of low resolution because of background signals from intrinsic water protons. On the other hand, it is assumed that the (11)B NMR signals which can be applied to a CSI technique have certain advantages, since boron is an ultratrace element in animal cells and tissues. In this manuscript, we report on the sensing of biologically indispensable d-block metal cations such as zinc, copper, iron, cobalt, manganese, and nickel based on (11)B NMR signals of simple phenylboronic acid-pendant cyclen (cyclen = 1,4,7,10-tetraazacyclododecane), L(6) and L(7), in aqueous solution at physiological pH. The results indicate that the carbon-boron bond of L(6) is cleaved upon the addition of Zn(2+) and the broad (11)B NMR signal of L(6) at 31 ppm is shifted upfield to 19 ppm, which corresponds to the signal of B(OH)(3). (1)H NMR, X-ray single crystal structure analysis, and UV absorption spectra also provide support for the carbon-boron bond cleavage of ZnL(6). Because the cellular uptake of L(6) was very small, a more cell-membrane permeable ligand containing the boronic acid ester L(7) was synthesized and investigated for the sensing of d-block metal ions using (11)B NMR. Data on (11)B NMR sensing of Zn(2+) in Jurkat T cells using L(7) is also presented.