Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(II)-terpyridine complexes bearing boronic acids

Selective recognition of fructosyl amino acids in water by arylboronic acid-based receptors is a central field of modern supramolecular chemistry that impacts biological and medicinal chemistry. Fructosyl valine (FV) and fructosyl glycyl histidine (FGH) occur as N-terminal moieties of human glycated hemoglobin; therefore, the molecular design of biomimetic receptors is an attractive, but very challenging goal. Herein, we report three novel cationic Zn-terpyridine complexes bearing a fluorescent N-quinolinium nucleus covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2Zn; meta-, 3Zn and para-, 4Zn) for the optical recognition of FV, FGH and comparative analytes (D-fructose, Gly, Val and His) in pure water at physiological pH. The complexes were designed to act as fluorescent receptors using a cooperative action of boric acid and a metal chelate. Complex 3Zn was found to display the most acidic -B(OH)2 group (pKa = 6.98) and exceptionally tight affinity for FV (K = 1.43 × 105 M-1) with a strong quenching analytical response in the micromolar concentration range. The addition of fructose and the other amino acids only induced moderate optical changes. On the basis of several spectroscopic tools (1H, 11B NMR, UV-Vis, and fluorescence titrations), ESI mass spectrometry, X-ray crystal structure, and DFT calculations, the interaction mode between 3Zn and FV is proposed in a 1 : 1 model through a cooperative two-point recognition involving a sp3 boronate-diol esterification with simultaneous coordination bonding of the carboxylate group of Val to the Zn atom. Fluorescence quenching is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments. The addition of FGH to 3Zn notably enhanced its emission intensity with micromolar affinity, but with a lower apparent binding constant than that observed for FV. FGH interacts with 3Zn through boronate-diol complexation and coordination of the imidazole ring of His. DFT-optimized structures of complexes 3Zn-FV and 3Zn-FGH show a picture of binding which shows that the Zn-complex has a suitable (B⋯Zn) distance to the two-point recognition with these analytes. Molecular recognition of fructosyl amino acids by transition-metal-based receptors has not been explored until now.

Synthesis and anticancer mechanisms of four novel platinum(II) 4'-substituted-2,2':6',2''-terpyridine complexes

Mitophagy, a selective autophagic process, has emerged as a pathway involved in degrading dysfunctional mitochondria. Herein, new platinum(II)-based chemotherapeutics with mitophagy-targeting properties are proposed. Four novel binuclear anticancer Pt(II) complexes with 4'-substituted-2,2':6',2''-terpyridine derivatives (tpy1-tpy4), i.e., [Pt2(tpy1)(DMSO)2Cl4]·CH3OH (tpy1Pt), [Pt(tpy2)Cl][Pt(DMSO)Cl3]·CH3COCH3 (tpy2Pt), [Pt(tpy3)Cl][Pt(DMSO)Cl3] (tpy3Pt), and [Pt(tpy4)Cl]Cl·CH3OH (tpy4Pt), were designed and prepared. Moreover, their potential antitumor mechanism was studied. Tpy1Pt-tpy4Pt exhibited more selective cytotoxicity against cisplatin-resistant SK-OV-3/DDP (SKO3cisR) cancer cells compared with those against ovarian SK-OV-3 (SKO3) cancer cells and normal HL-7702 liver (H702) cells. This selective cytotoxicity of Tpy1Pt-tpy4Pt was better than that of its ligands (i.e., tpy1-tpy4), the clinical drug cisplatin, and cis-Pt(DMSO)2Cl2. The results of various experiments indicated that tpy1Pt and tpy2Pt kill SKO3cisR cancer cells via a mitophagy pathway, which involves the disruption of the mitophagy-related protein expression, dissipation of the mitochondrial membrane potential, elevation of the [Ca2+] and reactive oxygen species levels, promotion of mitochondrial DNA damage, and reduction in the adenosine triphosphate and mitochondrial respiratory chain levels. Furthermore, in vivo experiments indicated that the dinuclear anticancer Pt(II) coordination compound (tpy1Pt) has remarkable therapeutic efficiency (ca. 52.4%) and almost no toxicity. Therefore, the new 4'-substituted-2,2':6',2''-terpyridine Pt(II) coordination compound (tpy1Pt) is a potential candidate for next-generation mitophagy-targeting dinuclear Pt(II)-based anticancer drugs.

Optical properties, bioimaging and theoretical calculation of a Zn(II) complex based on triphenylamine derivative

A luminescent material with various optical properties based on a triphenylamine Zn(II) complex is described. The ultraviolet-visible absorption, one-photon excited fluorescence (OPEF) and two-photon excited fluorescence (TPEF) of the complex indicate that the material has good OPEF and TPEF properties. And the results of one- and two-photon HepG2 cells imaging experiments show the potential of the complex in fluorescence microscopy bioimaging. The experimental Stokes shift and the FWHM (full-width at half-maximum) in different solvents were correlated with the rMPI polarity of the solvent, and the perfect Boltzmann curves were obtained, where the Boltzmann correlation between Stokes shift and solvent polarity is reported for the second time. But the Boltzmann correlation between FWHM and solvent polarity is reported for the first time. In addition, the computational results indicate that, the covalent bond within the salt ZnBr₂ is strengthened by the coordination, and the newly formed coordination bond Zn-N is stronger than the original covalent bond Zn-Br.

Dichlorido-{2,6-bis(4,5-dihydro-1H-pyrazol-3-yl)pyridine-κ3 N,N′,N″}zinc(II), C11H9C12N5Zn

C11H9C12N5Zn, monoclinic, C2/c (no. 15), a = 10.256(3) Å, b = 17.110(5) Å, c = 7.967(3) Å, β = 104.361(4)°, V = 1354.36 Å3, Z = 4, R gt (F) = 0.0270, wR ref(F 2) = 0.0659, T = 293 K.

Low-cost photo-switches based on stilbene-appended Zn(II)-terpyridine complexes

We report herein the synthesis, characterization, photophysics, and photo-isomerization behaviors of three Zn(II)-terpyridine complexes of the type [Zn(tpy-pvp-X)₂]²⁺ (X = H, Me, and NO₂) covalently tethered with stilbene moiety. The complexes exhibit absorption bands stretching up to the edge of the visible domain due to ligand → ligand charge transfer (LLCT) transitions and strong emission at room temperature in the visible due to radiative deactivation of ³LLCT state having lifetime within 1.0-3.0 ns. The stilbene motifs in the complexes undergo trans to cis isomerization upon irradiating with UV and visible light accompanied by significant alteration of their absorption, emission, and ¹H NMR spectral profiles. Apart from the variation of electron donating and electron withdrawing substituent (X), the isomerization studies were also carried out in three different solvents (DCM, MeCN, and DMSO) to further tune their kinetic and thermodynamic parameters. The rate, rate constant and quantum yield of isomerization were estimated in all the solvents. The reverse process (cis to trans) also occurs very slowly on keeping but could be accelerated upon heating. Trans to cis photoisomerization leads to quenching of emission in case of 1 and 2, whereas backward thermal cis to trans conversion leads to restoration of emission. By contrast, for the nitro-derivative (3) forward process induces emission enhancement, while backward process gives rise to emission quenching. In essence, "on-off" and "off-on" emission switching is feasible for 1 and 2, whereas "off-on" and "on-off" emission switching occurs in case of 3. Emission spectral responses upon successive action of photonic and thermal input lead to the fabrication of INHIBIT and IMPLICATION logic gates. DFT and TD-DFT computational investigations were also undertaken to visualize their electronic structures, correct assignment of the spectral bands, and mode of isomerization process.

Ultra-trace level detection of Cu2+ in an aqueous medium by novel Zn(ii)-dicarboxylato–pyridyl coordination polymers and cell imaging with HepG2 cells

Fluorescent 1D Zn(ii) coordination polymers are aggregated via noncovalent interactions. The emission of the CPs is exclusively quenched by Cu²⁺ and the LOD is at μM range. In aqueous medium internalization CPs within HepG2 cells is detected by microscopic cell image using Cu²⁺.

A chitosan-based fluorescent hydrogel for selective detection of Fe2+ ions in gel-to-sol mode and turn-off fluorescence mode

A novel chitosan-based fluorescent hydrogel has been synthesized by chemically bonding terpyridine-bearing aldehydes onto chitosan via an acid condensation reaction.

A series of two-photon absorption organotin (IV) cyano carboxylate derivatives for targeting nuclear and visualization of anticancer activities

Compared to organotin (IV) compounds with biochemical activity, two-photon absorption (2PA) organotin (IV) complexes for targeting nuclear with anticancer activities are rarely reported. Here, two novel 2PA organotin (IV) cyano carboxylate complexes (C1Sn-1, C1Sn-2) are synthesized and characterized. The two-photon absorption cross section values (δ) in the near-infrared region are significantly enhanced for C1Sn-2 compared to C1Sn-1_, thus developing for targeting nuclear by two-photon fluorescence microscopy (2PFM). C1Sn-2 could specifically target nuclear DNA in vitro. The mechanism demonstrated that there are abundant hydrogen bond interactions between hydroxy group of C1Sn-2 and DNA. The animal mode studies are first proposed that C1Sn-2 displayed a certain anti-cancer efficiency with non-significant toxicity.

Nitroxide–nitroxide and nitroxide–metal distance measurements in transition metal complexes with two or three paramagnetic centres give access to thermodynamic and kinetic stabilities

Broadband and highly resolved EPR distance measurements reveal multimers and their kinetic stabilities.

Lighting the Way to See Inside Two-Photon Absorption Materials: Structure-Property Relationship and Biological Imaging

The application of two-photon absorption (2PA) materials is a classical research field and has recently attracted increasing interest. It has generated a demand for new dyes with high 2PA cross-sections. In this short review, we briefly cover the structure-2PA property relationships of organic fluorophores, organic-inorganic nanohybrids and metal complexes explored by our group. (1) The two-photon absorption cross-section (δ) of organic fluorophores increases with the extent of charge transfer, which is important to optimize the core, donor-acceptor pair, and conjugation-bridge to obtain a large δ value. Among the various cores, triphenylamine appears to be an efficient core. Lengthening of the conjugation with styryl groups in the D-π-D quadrupoles and D-π-A dipoles increased δ over a long wavelength range than when vinylene groups were used. Large values of δ were observed for extended conjugation length and moderate donor-acceptors in the near-IR wavelengths. The δ value of the three-arm octupole is larger than that of the individual arm, if the core has electron accepting groups that allow significant electronic coupling between the arms; (2) Optical functional organic/inorganic hybrid materials usually show high thermal stability and excellent optical activity; therefore the design of functional organic molecules to build functional organic-inorganic hybrids and optimize the 2PA properties are significant. Advances have been made in the design of organic-inorganic nanohybrid materials of different sizes and shapes for 2PA property, which provide useful examples to illustrate the new features of the 2PA response in comparison to the more thoroughly investigated donor-acceptor based organic compounds and inorganic components; (3) Metal complexes are of particular interest for the design of new materials with large 2PA ability. They offer a wide range of metals with different ligands, which can give rise to tunable electronic and 2PA properties. The metal ions, including transition metals and lanthanides, can serve as an important part of the structure to control the intramolecular charge-transfer process that drives the 2PA process. As templates, transition metal ions can assemble simple to more sophisticated ligands in a variety of multipolar arrangements resulting in interesting and tailorable electronic and optical properties, depending on the nature of the metal center and the energetics of the metal-ligand interactions, such as intraligand charge-transfer (ILCT) and metal-ligand charge-transfer (MLCT) processes. Lanthanide complexes are attractive for a number of reasons: (i) their visible emissions are quite long-lived; (ii) their absorption and emission can be tuned with the aid of appropriate photoactive ligands; (iii) the accessible energy-transfer path between the photo-active ligands and the lanthanide ion can facilitate efficient lanthanide-based 2PA properties. Thus, the above materials with excellent 2PA properties should be applied in two-photon applications, especially two-photon fluorescence microscopy (TPFM) and related emission-based applications. Furthermore, the progress of research into the use of those new 2PA materials with moderate 2PA cross section in the near-infrared region, good Materials 2017, 10, 223 2 of 37 biocompatibility, and enhanced two-photon excited fluorescence for two-photon bio-imaging is summarized. In addition, several possible future directions in this field are also discussed (146 references).

A series of terpyridine-based zinc(ii) complexes assembled for third-order nonlinear optical responses in the near-infrared region and recognizing lipid membranes

Two-photon (TP) microscopy has advantages for biological imaging in that it allows deeper tissue-penetration and excellent resolution compared with one-photon (OP) microscopy.

Nanomolar pyrophosphate detection and nucleus staining in living cells with simple terpyridine-Zn(II) complexes

Great efforts have been made to develop fluorescent probes for pyrophosphate (PPi) detection. Nucleus staining with fluorescence microscopy has been also widely investigated. But fluorescent probes for PPi detection with high sensitivity in water medium and nucleus staining with low-cost non-precious metal complexes in living cells are still challenging. Herein, we report simple terpyridine-Zn(II) complexes for selective nanomolar PPi detection over ATP and ADP in water based on aggregation induced emission (AIE) and intramolecular charge transfer (ICT). In addition, these terpyridine-Zn(II) complexes were successfully employed for nucleus staining in living cells. These results demonstrated simply obtained terpyridine-Zn(II) complexes are powerful tool for PPi detection and the development of PPi-related studies.

A two-photon fluorescent RNA probe screened from a series of oxime-functionalized 2,2′:6′,2′′-terpyridine ZnX2(X = Cl, Br, I) complexes

An oxime-functionalized terpyridine ZnCl₂complex is a RNA two-photon fluorescent probe exhibiting RNA binding, fluorescence intensity enhancement and compatibility with Hoechst 33342.

A water-soluble two-photon fluorescence chemosensor for ratiometric imaging of mitochondrial viscosity in living cells

We report a novel water-soluble ratiometric TPEF chemosensor EIN that is specifically responsive and singularly sensitive to mitochondria viscosity in living cells.