Luminescent transition metal complex biotin conjugates

Research Progress of Metal Anticancer Drugs

Cancer treatments, including traditional chemotherapy, have failed to cure human malignancies. The main reasons for the failure of these treatments are the inevitable drug resistance and serious side effects. In clinical treatment, only 5 percent of the 50 percent of cancer patients who are able to receive conventional chemotherapy survive. Because of these factors, being able to develop a drug and treatment that can target only cancer cells without affecting normal cells remains a big challenge. Since the special properties of cisplatin in the treatment of malignant tumors were accidentally discovered in the last century, metal anticancer drugs have become a research hotspot. Metal anticancer drugs have unique pharmaceutical properties, such as ruthenium metal drugs with their high selectivity, low toxicity, easy absorption by tumor tissue, excretion, and so on. In recent years, efficient and low-toxicity metal antitumor complexes have been synthesized. In this paper, the scientific literature on platinum (Pt), ruthenium (Ru), iridium (Ir), gold (Au), and other anticancer complexes was reviewed by referring to a large amount of relevant literature at home and abroad.

Physico-chemical characterization studies of collagen labelled with Ru(II) polypyridyl complex

The rich luminescence behaviour exerted by transition metal complexes has found significant role in the development of biomolecular and cellular probes. The conjugation of fluorophore to a protein has its own advantage over the label-free system due to its high sensitivity. While numerous proteins have been labelled with either organic or inorganic fluorophores, the conjugation of luminescent transition metal complexes with collagen has not yet been attempted. Here, in this study, the conjugation of a Ru(II) polypyridyl complex with collagen was carried out and its physico-chemical characterization was studied. The conjugation of Ru(II) to collagen was characterized by UV-Visible, fluorescence and ATR-FT-IR spectroscopy. The conjugation of Ru(II) did not alter the triple helical structure of the collagen as evidenced from CD spectral data. The luminescence behaviour of the Ru-tagged collagen was found to be similar to that of the commercially available fluorescein isothiocyanate (FITC) tagged collagen with increase in luminescence upon addition of collagenase. Gel-based collagenase assay showed that the digestion of collagen can be vizualized using UV light due to intrinsic fluorophore tag without carrying out the staining-destaining processes. Energy dispersive X-Ray analysis (EDAX) confirms the presence of Ru in Ru-collagen fibrils. To the best of our knowledge, this is the first report on the conjugation of a Ru(II) complex with the fibrous protein collagen that exhibits similar property as of FITC-collagen and can be used as an alternative.

Luminescent cis-Bis(bipyridyl)ruthenium(II) Complexes with 1,2-Azolylamidino Ligands: Photophysical, Electrochemical Studies, and Photocatalytic Oxidation of Thioethers

New 1,2-azolylamidino complexes cis-[Ru(bipy)₂(NH═C(R)az*-κ²N,N)](OTf)₂ (R = Me, Ph; az* = pz, indz, dmpz) are synthesized via chloride abstraction after a subsequent base-catalyzed coupling of a nitrile with the previously coordinated 1,2-azole. The synthetic procedure allows the easy obtainment of complexes having different electronic and steric 1,2-azoylamidino ligands. All of the compounds have been characterized by ¹H, ¹³C, and ¹⁵N NMR and IR spectroscopy and by monocrystal X-ray diffraction. Photophysical studies support their phosphorescence, whereas their electrochemistry reveals reversible Ru^II/Ru^III oxidations between +1.13 and +1.25 V (vs SCE). The complexes have been successfully used as catalysts in the photooxidation of different thioethers, the complex cis-[Ru(bipy)₂(NH═C(Me)dmpz-κ²N,N)]²⁺ showing better catalytic performance in comparison to that of [Ru(bipy)₃]²⁺. Moreover, the significant catalytic performance of the dimethylpyrazolylamidino complex is applied to the preparation of the drug modafinil, which is obtained using ambient oxygen as an oxidant. Finally, mechanistic assays suggest that the oxidation reaction follows a photoredox route via oxygen radical anion formation.

Dinuclear Rhenium Complexes with a Bridging Helicene-bis-bipyridine Ligand: Synthesis, Structure, and Photophysical and Chiroptical Properties

By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO)3 Cl}2 (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10-3 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

Metalloproteomics for molecular target identification of protein-binding anticancer metallodrugs

Proteomics has played an important role in elucidating the fundamental processes occuring in living cells. Translating these methods to metallodrug research ('metalloproteomics') has provided a means for molecular target identification of metal-based anticancer agents which should signifcantly advance the research field. In combination with biological assays, these techniques have enabled the mechanisms of action of metallodrugs to be linked to their interactions with molecular targets and aid understanding of their biological properties. Such investigations have profoundly increased our knowledge of the complex and dynamic nature of metallodrug-biomolecule interactions and have provided, at least for some compound types, a more detailed picture on their specific protein-binding patterns. This perspective highlights the progression of metallodrug proteomics research for the identification of non-DNA targets from standard analytical techniques to powerful metallodrug pull-down methods.

Luminescent Rhenium(I)tricarbonyl Complexes Containing Different Pyrazoles and Their Successive Deprotonation Products: CO2 Reduction Electrocatalysts

Cationic fac-[Re(CO)₃(pz*H)(pypzH)]OTf (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH; 3-(2-pyridyl)pyrazole, pypzH) were obtained from fac-[ReBr(CO)₃(pypzH)] by halide abstraction with AgOTf and subsequent addition of the corresponding pyrazole. Successive deprotonation with Na₂CO₃ and NaOH gave neutral fac-[Re(CO)₃(pz*H)(pypz)] and anionic Na{fac-[Re(CO)₃(pz*)(pypz)]} complexes, respectively. Cationic fac-[Re(CO)₃(pz*H)(pypzH)]OTf, neutral complexes fac-[Re(CO)₃(pz*H)(pypz)], and fac-[Re(CO)₃(pypz)₂Na] were subjected to photophysical and electrochemical studies. They exhibit phosphorescent decays from a prevalently ³MLCT excited state with quantum yields (Φ) in the range between 0.03 and 0.58 and long lifetimes (τ from 220 to 869 ns). The electrochemical behavior in Ar atmosphere of cationic and neutral complexes indicates that the oxidation processes assigned to Re^I → Re^II occurs at lower potentials for the neutral complex compared to cationic complex. The reduction processes occur at the ligands and do not depend on the charge of the complexes. The electrochemical behavior in CO₂ saturated media is consistent with CO₂ electrocatalyzed reduction, where the values of the catalytic activity [i_cat(CO₂)/i_cat(Ar)] ranged from 2.7 to 11.5 (compared to 8.1 for fac-[Re(CO)₃Cl(bipy)] studied as a reference). Controlled potential electrolysis for the pyrazole cationic (3a) and neutral (4a) complexes after 1 h affords CO in faraday yields of 61 and 89%, respectively. These values are higher for indazole complexes and may be related to the acidity of the coordinated pyrazole.

Tuning the Luminescent Properties of Ruthenium(II) Amino-1,10-Phenanthroline Complexes by Varying the Position of the Amino Group on the Heterocycle

Eight 1,10-phenanthrolines bearing one or two 2-(1-adamantyloxy)ethylamino substituents attached to different positions of the heterocyclic core were prepared according to S_N Ar or palladium-catalyzed amination reactions. Their reaction with cis-Ru(bpy)₂ Cl₂ (bpy=2,2'-bipyridine) was investigated and Ru(bpy)₂ (L)(PF₆ )₂ (phen=1,10-phenanthroline) (L=amino-substituted 1,10-phenanthroline) complexes were obtained in good yields. The electronic structure and emissive properties of these complexes are strongly dependent on the position of the amino substituent in the heterocycle. Emission bands of the complexes bearing 2- and 4-substituted 1,10-phenanthroline ligands are red-shifted (up to 56 nm) and less intense compared to that of the parent [Ru(phen)(bpy)₂ ](PF₆ )₂ . In contrast, the introduction of the substituent in 3- or 5-position of 1,10-phenanthroline ring induces only small decrease of luminescence and the brightness of the complex with the 3-substituted ligand is comparable to that of the parent complex.

Light-driven electron injection from a biotinylated triarylamine donor to [Ru(diimine)3](2+)-labeled streptavidin

Electron transfer from a biotinylated electron donor to photochemically generated Ru(iii) complexes covalently anchored to streptavidin is demonstrated by means of time-resolved laser spectroscopy. Through site-selective mutagenesis, a single cysteine residue was engineered at four different positions on streptavidin, and a Ru(ii) tris-diimine complex was then bioconjugated to the exposed cysteines. A biotinylated triarylamine electron donor was added to the Ru(ii)-modified streptavidins to afford dyads localized within a streptavidin host. The resulting systems were subjected to electron transfer studies. In some of the explored mutants, the phototriggered electron transfer between triarylamine and Ru(iii) is complete within 10 ns, thus highlighting the potential of such artificial metalloenzymes to perform photoredox catalysis.

Multimodal Probes: Superresolution and Transmission Electron Microscopy Imaging of Mitochondria, and Oxygen Mapping of Cells, Using Small-Molecule Ir(III) Luminescent Complexes

We describe an Ir(III)-based small-molecule, multimodal probe for use in both light and electron microscopy. The direct correlation of data between light- and electron-microscopy-based imaging to investigate cellular processes at the ultrastructure level is a current challenge, requiring both dyes that must be brightly emissive for luminescence imaging and scatter electrons to give contrast for electron microscopy, at a single working concentration suitable for both methods. Here we describe the use of Ir(III) complexes as probes that provide excellent image contrast and quality for both luminescence and electron microscopy imaging, at the same working concentration. Significant contrast enhancement of cellular mitochondria was observed in transmission electron microscopy imaging, with and without the use of typical contrast agents. The specificity for cellular mitochondria was also confirmed with MitoTracker using confocal and 3D-structured illumination microscopy. These phosphorescent dyes are part of a very exclusive group of transition-metal complexes that enable imaging beyond the diffraction limit. Triplet excited-state phosphorescence was also utilized to probe the O₂ concentration at the mitochondria in vitro, using lifetime mapping techniques.

Streptavidin as a Scaffold for Light-Induced Long-Lived Charge Separation

Long-lived photo-driven charge separation is demonstrated by assembling a triad on a protein scaffold. For this purpose, a biotinylated triarylamine was added to a Ru^II -streptavidin conjugate bearing a methyl viologen electron acceptor covalently linked to the N-terminus of streptavidin. To improve the rate and lifetime of the electron transfer, a negative patch consisting of up to three additional negatively charged amino acids was engineered through mutagenesis close to the biotin-binding pocket of streptavidin. Time-resolved laser spectroscopy revealed that the covalent attachment and the negative patch were beneficial for charge separation within the streptavidin hosted triad; the charge separated state was generated within the duration of the excitation laser pulse, and lifetimes up to 3120 ns could be achieved with the optimized supramolecular triad.

Methylation of Ir(iii)-tetrazolato complexes: an effective route to modulate the emission outputs and to switch to antimicrobial properties

Two neutral cyclometalated Ir(iii)-tetrazolato complexes that differ by variations of the substituents on either the phenylpyridine or the tetrazolate ligand have been converted into the corresponding methylated and cationic analogues. NMR (¹H and ¹³C) characterization of the Ir(iii) complexes provided the results in agreement with the chemo- and regioselective character of methylation at the N-3 position of the Ir(iii)-coordinated tetrazolato ring. This evidence was further corroborated by the analysis of the molecular structures of the cationic complexes obtained by X-ray diffraction. In view of the photophysical properties, the addition of a methyl moiety to neutral Ir(iii) tetrazolates, which behave as sky-blue or orange phosphors, caused a systematic red shift of their phosphorescence output. The transformation of neutral Ir(iii) tetrazolates into cationic Ir(iii)-tetrazole complexes was screened for any eventual antimicrobial activity in vitro against Gram negative (E. coli) and Gram positive (D. radiodurans) microorganisms. While both kinds of complexes were not active against E. coli, the conversion of the neutral Ir(iii) tetrazolates into the corresponding methylated and cationic Ir(iii)tetrazole derivatives determined the turn-on of a good to excellent antimicrobial activity toward Gram positive Deinococcus radiodurans, a non-pathogenic bacterium that is listed as one of the toughest microorganisms in light of its outstanding resistance to radiation and oxidative stress.

Pentafluorobenzene end-group as a versatile handle for para fluoro "click" functionalization of polythiophenes

A convenient method of introducing pentafluorobenzene (PFB) as a single end-group in polythiophene derivatives is reported via in situ quenching of the polymerization. We demonstrate that the PFB-group is a particularly useful end-group due to its ability to undergo fast nucleophilic aromatic substitutions. Using this molecular handle, we are able to quantitatively tether a variety of common nucleophiles to the polythiophene backbone. The mild conditions required for the reaction allows sensitive functional moieties, such as biotin or a cross-linkable trimethoxysilane, to be introduced as end-groups. The high yield enabled the formation of a diblock rod-coil polymer from equimolar reactants under transition metal-free conditions at room temperature. We further demonstrate that water soluble polythiophenes end-capped with PFB can be prepared via the hydrolysis of an ester precursor, and that such polymers are amenable to functionalization under aqueous conditions.

Highly Fluorinated Ir(III)-2,2':6',2″-Terpyridine-Phenylpyridine-X Complexes via Selective C-F Activation: Robust Photocatalysts for Solar Fuel Generation and Photoredox Catalysis

A series of fluorinated Ir(III)-terpyridine-phenylpyridine-X (X = anionic monodentate ligand) complexes were synthesized by selective C-F activation, whereby perfluorinated phenylpyridines were readily complexed. The combination of fluorinated phenylpyridine ligands with an electron-rich tri-tert-butyl terpyridine ligand generates a "push-pull" force on the electrons upon excitation, imparting significant enhancements to the stability, electrochemical, and photophysical properties of the complexes. Application of the complexes as photosensitizers for photocatalytic generation of hydrogen from water and as redox photocatalysts for decarboxylative fluorination of several carboxylic acids showcases the performance of the complexes in highly coordinating solvents, in some cases exceeding that of the leading photosensitizers. Changes in the photophysical properties and the nature of the excited states are observed as the compounds increase in fluorination as well as upon exchange of the ancillary chloride ligand to a cyanide. These changes in the excited states have been corroborated using density functional theory modeling.

SPIO@SiO2–Re@PEG nanoparticles as magneto-optical dual probes and sensitizers for photodynamic therapy

A superparamagnetic iron oxide core and a photoluminescent rhenium complex embedded in a silica shell are the active components of a dual magneto-optical nanoprobe, also able to generate singlet oxygen upon irradiation.

Theoretical study of the cis–trans isomerization mechanism of a pendant metal-bound azobenzene

Theoretical study of the cis–trans isomerization mechanism of azobenzene substituents in rhenium complexes.

Luminescent rhenium(I) tricarbonyl complexes with pyrazolylamidino ligands: photophysical, electrochemical, and computational studies

New pyrazolylamidino complexes fac-[ReCl(CO)3(NH[double bond, length as m-dash]C(Me)pz*-κ(2)N,N)] (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH) and fac-[ReBr(CO)3(NH[double bond, length as m-dash]C(Ph)pz*-κ(2)N,N)] are synthesized via base-catalyzed coupling of the appropriate nitrile with pyrazole, or via metathesis by halide abstraction with AgBF4 from a bromido pyrazolylamidino complex and the subsequent addition of LiCl. In order to study both the influence of the substituents present at the pyrazolylamidino ligand, and that of the "sixth" ligand in the complex, photophysical, electrochemical, and computational studies have been carried out on this series and other complexes previously described by us, of the general formula fac-[ReL(CO)3(NH[double bond, length as m-dash]C(R')pz*-κ(2)N,N)](n+) (L = Cl, Br; R' = Me, Ph, n = 0; or L = NCMe, dmpzH, indzH, R' = Me, n = 1). All complexes exhibit phosphorescent decays from a prevalently (3)MLCT excited state with quantum yields (Φ) in the range between 0.007 and 0.039, and long lifetimes (τ∼ 8-1900 ns). The electrochemical study reveals irreversible reduction for all complexes. The oxidation of the neutral complexes was found to be irreversible due to halido-dissociation, whereas the cationic species display a reversible process implying the ReI/ReII couple. Density functional and time-dependent density functional theory (TD-DFT) calculations provide a reasonable trend for the values of emission energies in line with the experimental photophysical data, supporting the (3)MLCT based character of the emissions.

Synthesis and characterization of N-2-aryl-1,2,3-triazole based iridium complexes as photocatalysts with tunable photoredox potential

N-2-Aryl chelated 1,2,3-triazole-Ir(iii) complexes with various substituents were prepared for the first time.

A ruthenium(II) complex supported by trithiacyclononane and aromatic diimine ligand as luminescent switch-on probe for biomolecule detection and protein staining

A new ruthenium(II) complex has been developed for detection of biomolecules. This complex is highly selective for histidine over other amino acids and has been applied to protein staining in an SDS-PAGE gel.

Phosphorescent sensor for phosphorylated peptides based on an iridium complex

A bis[(4,6-difluorophenyl)pyridinato-N,C(2')]iridium(III) picolinate (FIrpic) derivative coupled with bis(Zn(2+)-dipicolylamine) (ZnDPA) was developed as a sensor (1) for phosphorylated peptides, which are related to many cellular mechanisms. As a control, a fluorescent sensor (2) based on anthracene coupled to ZnDPA was also prepared. When the total negative charge on the phosphorylated peptides was changed to -2, -4, and -6, the emission intensity of sensor 1 gradually increased by factors of up to 7, 11, and 16, respectively. In contrast, there was little change in the emission intensity of sensor 1 upon the addition of a neutral phosphorylated peptide, non-phosphorylated peptides, or various anions such as CO3(2-), NO3(-), SO4(2-), phosphate, azide, and pyrophosphate. Furthermore, sensor 1 could be used to visually discriminate between phosphorylated peptides and adenosine triphosphate in aqueous solution under a UV-vis lamp, unlike fluorescent sensor 2. This enhanced luminance of phosphorescent sensor 1 upon binding to a phosphorylated peptide is attributed to a reduction in the repulsion between the Zn(2+) ions due to the phenoxy anion, its strong metal-to-ligand charge transfer character, and a reduction in self-quenching.

Polarization and symmetry of electronic transitions in long fluorescence lifetime triangulenium dyes

To fully exploit the capabilities of fluorescence probes in modern experiments, where advanced instrumentation is used to probe complex environments, other photophysical properties than emission color and emission intensity are monitored. Each dye property can be addressed individually as well as collectively to provide in-depth information unavailable from the standard intensity measurements. Dyes with long emission lifetimes and strongly polarized transitions enable the monitoring of lifetime changes as well as emission polarization (anisotropy). Thus experiments can be designed to follow slow dynamics. The UV and visible electronic transitions of a series of red-emitting dyes based on the triangulenium motif are investigated. We resolve overlapping features in the spectra and assign the orientation of the transition moments to the molecular axes. The result is the complete Jablonski diagram for the UV and visible spectral region. The symmetries of the studied dyes are shown to have a large influence on the optical response, and they are clearly separated into two groups of symmetry by their photophysical properties. The C(2v) symmetric dyes, azadioxatriangulenium (ADOTA(+)) and diazaoxatriangulenium (DAOTA(+)), have high emission anisotropies, fluorescence lifetimes around 20 ns, and fluorescence quantum yields of ∼50%. The trioxatriangulenium (TOTA(+)) and triazatriangulenium (TATA(+)) dyes-nominally of D(3h) symmetry-have fluorescence lifetimes around 10 ns lifetimes and fluorescence quantum yields of 10-15%. However, the D(3h) symmetry is shown to be lowered to a point group, where the axes transform uniquely such that the degeneracy of the E' states is lifted.

Phosphorescent imaging of living cells using a cyclometalated iridium (III) complex

A cell permeable cyclometalated iridium(III) complex has been developed as a phosphorescent probe for cell imaging. The iridium(III) solvato complex [Ir(phq)₂(H₂O]₂)] preferentially stains the cytoplasm of both live and dead cells with a bright luminescence.

A fluorescent "allosteric scorpionand" complex visualizes a biological recognition event

We describe a new class of fluorescent reporter and its employment to visualize the biotin/avidin binding interaction. Derivatives of the azamacrocycle cyclam that contain a pendant naphthalimide dye are inherently fluorescent when zinc(II) is coordinated. Introducing a second pendant group--biotin--affords an unsymmetrical bis-triazole-scorpionand ligand that interacts specifically with avidin. This ligand has been assembled by using a one-pot "double-click" strategy and complexed with copper(II) and zinc(II). The zinc(II) complex is fluorescent, and its fluorescence output changes in the presence of avidin. Upon avidin binding, the fluorescence output is diminished by interaction with the protein, at [complex]/[avidin] ratios of up to 4:1. The observed change might arise from a specific quenching effect in the biotin binding pocket or from a binding-induced change in the coordination geometry of the complex.