ZnII Complexes for Bioimaging and Correlated Applications

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.

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy

Photodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination-driven self-assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn-porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo-supramolecular PSs (S1-S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Thermo-Induced Fluorochromism in Two AIE Zinc Complexes: A Deep Insight into the Structure-Property Relationship

Solid-state emitters exhibiting mechano-fluorochromic or thermo-fluorochromic responses represent the foundation of smart tools for novel technological applications. Among fluorochromic (FC) materials, solid-state emissive coordination complexes offer a variety of fluorescence responses related to the dynamic of noncovalent metal-ligand coordination bonds. Relevant FC behaviour can result from the targeted choice of metal cation and ligands. Herein, we report the synthesis and characterization of two different colour emitters consisting of zinc complexes obtained from N,O bidentate ligands with different electron-withdrawing substituents. The two complexes are blue and orange solid-state fluorophores, respectively, highly responsive to thermal and mechanical stress. These emitters show a very different photoluminescent (PL) pattern as recorded before and after the annealing treatment. Through X-ray structural analysis combined with thermal analysis, infrared (IR) spectroscopy, PL, and DFT simulation we provide a comprehensive analysis of the structural feature involved in the fluorochromic response. Notably, we were able to correlate the on-off thermo-fluorochromism of the complexes with the structural rearrangement at the zinc coordination core.

Synthesis, characterization, antimicrobial and cytotoxic activity and DNA-binding properties of d-metal complexes with hydrazones of Girard's T and P reagents

In this work synthesis, characterization and crystal structures of 1, Zn(II) complex ([ZnL¹(NCS)₂]), with (E)-1-(2-oxo-2-(2-(quinolin-2-ylmethylene)hydrazinyl)ethyl)pyridin-1-ium chloride (HL¹Cl) and 2, Bi(III) complex ([BiHL²Cl₄] × 1/2CH₃OH), with (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(thiazol-2-yl)ethylidene)hydrazinyl)ethan-1-aminium chloride (HL²Cl), have been reported. Zn(II) complex possesses a distorted trigonal bipyramidal geometry while surroundings around Bi(III) ion are extended pentagonal bipyramidal. Antimicrobial activity, brine shrimp assay and DPPH radical scavenging activity of both complexes, including previously synthesized complexes with HL²Cl ligand (Zn(II) and Ni(II)) and complexes with (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium chloride (HL³Cl) (Zn(II), Cu(II), Cd(II), Co(II), Fe(III), Ni(II)), were evaluated. For the most active complexes, cytotoxic activity against five malignant cancer cell lines (HeLa, A375, MCF7, PC-3 and A549) and normal cell line HaCaT, as well as generation of reactive oxygen species (ROS), was tested.

Functional Analysis of the Promoter Regions of Two Apoptosis-Related Genes (Bcl-2 and Cycs) and Their Regulation by Zn in Yellow Catfish

B-cell lymphoma 2 (Bcl-2) and cytochrome c (Cycs) are two important proteins relevant to cellular apoptosis. In this study, we characterized the functions of the promoter regions of two apoptosis-related genes, Bcl-2 and Cycs, in yellow catfish Pelteobagrus fulvidraco. We obtained a 1989 bp Bcl-2 promoter and an 1830 bp Cycs promoter and predicted several key transcription factor binding sites (TFBSs) on the promoters, such as Kruppel-like factor 4 (KLF4), signal transducer and activator of transcription factor 3 (STAT3), forkhead box O (FOXO), metal-responsive element (MRE) and hepatocyte nuclear factor 1α (HNF-1α). Zinc (Zn) increased the activities of the Bcl-2 promoter but decreased the activities of the Cycs promoter. Metal-responsive transcription factor 1 (MTF-1) and HNF-1α directly bound with Bcl-2 and Cycs promoters, and they positively regulated the activity of the Bcl-2 promoter but negatively regulated the activity of the Cycs promoter. Zn promoted the binding ability of HNF-1α to the Bcl-2 promoter but decreased its binding ability to the Cycs promoter. However, Zn had no significant effect on the binding capability of MTF-1 to the regions of Bcl-2 and Cycs promoters. Zn upregulated the mRNA and total protein expression of Bcl-2 but downregulated the mRNA and total protein expression of Cycs. At the same time, Annexin V-FITC/PI staining showed that Zn significantly reduced the apoptosis of primary hepatocytes. For the first time, our study provides evidence for the MRE and HNF-1α response elements on the Bcl-2 and Cycs promoters, offering new insight into the mechanism by which Zn affects apoptosis in vertebrates.

Fluorescent salen-type Zn(II) Complexes As Probes for Detecting Hydrogen Sulfide and Its Anion: Bioimaging Applications

In this work, we investigate the mode of interaction of a family of fluorescent zinc complexes with HS- and H2S. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS- binds the zinc center of all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS- over H2S of the systems under investigation. Striking color changes, visible to the naked eye, occur when treating the systems with HS- or by an H2S flow. Accordingly, also the fluorescence is modulated by the presence of HS-, with the possible formation of multiple adducts. The results highlight the potential of the devised systems to be implemented as HS-/H2S colorimetric and fluorescent sensors. Bioimaging experiments indicate the potential of using this class of compounds as probes for the detection of H2S in living cells.

A Cyclometalated Iridium (III) Complex as a Microtubule Probe for Correlative Super-Resolution Fluorescence and Electron Microscopy

The visualization of microtubules by combining optical and electron microscopy techniques provides valuable information to understand correlated intracellular activities. However, the lack of appropriate probes to bridge both microscopic resolutions restricts the areas and structures that can be comprehended within such highly assembled structures. Here, a versatile cyclometalated iridium (III) complex is designed that achieves synchronous fluorescence-electron microscopy correlation. The selective insertion of the probe into a microtubule triggers remarkable fluorescence enhancement and promising electron contrast. The long-life, highly photostable probe allows live-cell super-resolution imaging of tubulin localization and motion with a resolution of ≈30 nm. Furthermore, correlative light-electron microscopy and energy-filtered transmission electron microscopy reveal the well-associated optical and electron signal at a high specificity, with an interspace of ≈41 Å of microtubule monomer in cells.

Monitoring intracellular metal ion complexation with an acetylene-tagged ligand by Raman spectroscopy

We propose to monitor molecular vibrations to identify metal ion-ligand complexation by means of Raman spectroscopy, which has been applied to track vibrational modes of molecules and to obtain a structural fingerprint. We prepared ligand molecules for Zn²⁺ ion complexation with a dipycolylaminoethyl aniline (DPEA) skeleton and phenylacetylene unit as the Raman tag which showed a typical band around 2200 cm^-1. Among the labeled ligands synthesized in this study, A-DPEA showed a strong band attributed to the acetylene unit at 2212 cm^-1, while the addition of Zn²⁺ ion resulted in a band shift to 2220 cm^-1 due to complex formation. The addition of other metal ions and titration experiments showed that A-DPEA bound with Zn²⁺ selectively with a dissociation constant (K _d) that was estimated to be 0.22 μM. We also conducted cellular experiments and found that complexation between A-DPEA and Zn²⁺ also occurred in cells, with a shift in the Raman signal of the ligand from 2212 to 2215 cm^-1. Thus, complex formation of the metal ion was identified by monitoring the Raman band shift.

Construction of Zn(II) Linear Trinuclear Secondary Building Units from A Coordination Polymer Based on α-Acetamidocinnamic Acid and 4-Phenylpyridine

The synthesis and characterization of one coordination polymer and two trinuclear complexes are presented. The coordination polymer [Zn2(µ-O,O'-ACA)2(ACA)2(4-Phpy)2]n (1) has been obtained by the reaction between Zn(OAc)2·2H2O, α-acetamidocinnamic acid (HACA), and 4-phenylpyridine (4-Phpy) using EtOH as solvent. Its recrystallization in CH3CN or EtOH yields two trinuclear complexes, both having pinwheel arrays with formulas [Zn3(µ-ACA)6(4-Phpy)2]·4CH3CN (2·4CH3CN) and [Zn3(µ-ACA)6(EtOH)2]·4EtOH (3·4EtOH), respectively. These trinuclear species, unavoidably lose their solvent co-crystallized molecules at RT yielding the complexes [Zn3(µ-ACA)6(4-Phpy)2] (2) and [Zn3(µ-ACA)6(EtOH)2] (3). In addition, compound 2 has also been obtained reacting Zn(OAc)2·2H2O, HACA, and 4-Phpy in a 1:2:2 ratio using CH3CN as solvent. Compounds 1-3 have been characterized by analytical and spectroscopic techniques. Furthermore, single crystals suitable for X-ray diffraction method for compounds 1, 2·4CH3CN, and 3·4EtOH were obtained and their supramolecular interactions have been studied and discussed, showing 2D supramolecular planes for the trinuclear complexes and a 3D supramolecular network for the coordination polymer. Finally, the supramolecular interactions of 2·4CH3CN and 3·4EtOH have been compared using Hirshfeld surface analysis and electrostatic potential calculations.

Pancreatic human islets and insulin-producing cells derived from embryonic stem cells are rapidly identified by a newly developed Dithizone

We developed an optimized Dipheylthiocarbazone or Dithizone (DTZ) with improved physical and chemical properties to characterize human islets and insulin-producing cells differentiated from embryonic stem cells. Application of the newly formulated iDTZ (i stands for islet) over a range of temperatures, time intervals and cell and tissue types found it to be robust for identifying these cells. Through high transition zinc binding, the iDTZ compound concentrated in insulin-producing cells and proved effective at delineating zinc levels in vitro.