Dendrimers with a Photoactive and Redox-Active [Ru(bpy)3]2+-Type Core: Photophysical Properties, Electrochemical Behavior, and Excited-State Electron-Transfer Reactions

Anticancer Potential of Dendritic Poly(aryl ether)-Substituted Polypyridyl Ligand-Based Ruthenium(II) Coordination Entities

This paper studies the anticancer potency of dendritic poly(aryl ether)-substituted polypyridyl ligand-based ruthenium(II) coordination entities. The dendritic coordination entities were successfully designed, synthesized, and characterized by different spectral methods such as Fourier transform infrared (FTIR), 1H and 13C- NMR, and mass spectrometry. Further, to understand the structure and solvation behavior of the coordination entities, we performed all-atom molecular dynamics (MD) simulations. The behavior, configuration, and size of the coordination entities in DMSO and water were studied by calculating the radius of gyration (Rg) and solvent-accessible surface area (SASA). The MTT assay was used to assess the in vitro cytotoxicity of all of the coordination entities against cancerous A549 (lung cancer cells), MDA MB 231 (breast cancer cells), and HepG2 (liver cancer cells) and was found to be good with comparable IC50 values with respect to the standard drug cisplatin. The coordination entities exhibited dose dependence, and the highest activity was shown against HepG2 cell lines in comparison to the other cancer cell lines. In addition, fluorescence staining studies, such as AO/EB, DAPI, and cell death analysis by PI staining, were performed on the coordination entities to understand the apoptosis mechanism. Furthermore, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) assays confirmed apoptosis in cancer cells via the mitochondrial pathway. The DNA fragmentation assay was done followed by molecular docking analysis with DNA executed to strengthen and support the experimental observations.

Ratiometric oxygen sensors of cyclometalated iridium(III) with enhanced quantum yields and variable dynamic ranges

Four luminescent ratiometric oxygen sensors, pairing phosphorescent cyclometalated iridium with coumarin or BODIPY fluorophores, are presented here. These compounds realize three key improvements over our previous designs, namely higher phosphorescence quantum yields, the ability to access intermediate dynamic ranges better suited for typical atmospheric O₂ levels, and the possibility of using visible excitation instead of UV. These ratiometric sensors are accessed via very simple, 1-step syntheses involving direct reaction of the chloro-bridged cyclometalated iridium dimer with the pyridyl-substituted fluorophore. They have phosphorescent quantum yields up to 29% with short to intermediate phosphoresence lifetimes ranging from 1.7 to 5.3 μs in three of the sensors, with the fourth having a long lifetime of 440 μs that is very responsive to oxygen. In one case, visible excitation of 430 nm is used to provide dual emission instead of UV excitation.

Interaction with a Biomolecule Facilitates the Formation of the Function-Determining Long-Lived Triplet State in a Ruthenium Complex for Photodynamic Therapy

TLD1433 is the first ruthenium (Ru)-based photodynamic therapy (PDT) agent to advance to clinical trials and is currently in a phase II study for treating nonmuscle bladder cancer with PDT. Herein, we present a photophysical study of TLD1433 and its derivative TLD1633 using complex, biologically relevant solvents to elucidate the excited-state properties that are key for biological activity. The complexes incorporate an imidazo [4,5-f][1,10]phenanthroline (IP) ligand appended to α-ter- or quaterthiophene, respectively, where TLD1433 = [Ru(4,4'-dmb)₂(IP-3T)]Cl₂ and TLD1633 = [Ru(4,4'-dmb)₂(IP-4T)]Cl₂ (4,4'-dmb = 4,4'-dimethyl-2,2'-bipyridine; 3T = α-terthiophene; 4T = α-quaterthiophene). Time-resolved transient absorption experiments demonstrate that the excited-state dynamics of the complexes change upon interaction with biological macromolecules (e.g., DNA). In this case, the accessibility of the lowest-energy triplet intraligand charge-transfer (³ILCT) state (T₁) is increased at the expense of a higher-lying ³ILCT state. We attribute this behavior to the increased rigidity of the ligand framework upon binding to DNA, which prolongs the lifetime of the T₁ state. This lowest-lying state is primarily responsible for O₂ sensitization and hence photoinduced cytotoxicity. Therefore, to gain a realistic picture of the excited-state kinetics that underlie the photoinduced function of the complexes, it is necessary to interrogate their photophysical dynamics in the presence of biological targets once they are known.

Excited-State Dynamics of [Ru(bpy)3 ]2+ Thin Films on Sensitized TiO2 and ZrO2

The excited state dynamics of Tris(2,2'-bipyridine)ruthenium(II) hexafluorophosphate, [Ru(bpy)3 (PF6 )2 ], was investigated on the surface of bare and sensitized TiO2 and ZrO2 films. The organic dyes LEG4 and MKA253 were selected as sensitizers. A Stern-Volmer plot of LEG4-sensitized TiO2 substrates with a spin-coated [Ru(bpy)3 (PF6 )2 ] layer on top shows considerable quenching of the emission of the latter. Interestingly, time-resolved emission spectroscopy reveals the presence of a fast-decay time component (25±5 ns), which is absent when the anatase TiO2 semiconductor is replaced by ZrO2 . It should be specified that the positive redox potential of the ruthenium complex prevents electron transfer from the [Ru(bpy)3 (PF6 )2 ] ground state into the oxidized sensitizer. Therefore, we speculate that the fast-decay time component observed stems from excited-state electron transfer from [Ru(bpy)3 (PF6 )2 ] to the oxidized sensitizer. Solid-state dye sensitized solar cells (ssDSSCs) employing MKA253 and LEG4 dyes, with [Ru(bpy)3 (PF6 )2 ] as a hole-transporting material (HTM), exhibit 1.2 % and 1.1 % power conversion efficiency, respectively. This result illustrates the possibility of the hypothesized excited-state electron transfer.

Transition Metal Complexes and Photodynamic Therapy from a Tumor-Centered Approach: Challenges, Opportunities, and Highlights from the Development of TLD1433

Transition metal complexes are of increasing interest as photosensitizers in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT). In recent years, Ru(II) polypyridyl complexes have emerged as promising systems for both PDT and PCT. Their rich photochemical and photophysical properties derive from a variety of excited-state electronic configurations accessible with visible and near-infrared light, and these properties can be exploited for both energy- and electron-transfer processes that can yield highly potent oxygen-dependent and/or oxygen-independent photobiological activity. Selected examples highlight the use of rational design in coordination chemistry to control the lowest-energy triplet excited-state configurations for eliciting a particular type of photoreactivity for PDT and/or PCT effects. These principles are also discussed in the context of the development of TLD1433, the first Ru(II)-based photosensitizer for PDT to enter a human clinical trial. The design of TLD1433 arose from a tumor-centered approach, as part of a complete PDT package that includes the light component and the protocol for treating non-muscle invasive bladder cancer. Briefly, this review summarizes the challenges to bringing PDT into mainstream cancer therapy. It considers the chemical and photophysical solutions that transition metal complexes offer, and it puts into context the multidisciplinary effort needed to bring a new drug to clinical trial.

Phosphorus dendrimers functionalised with nitrogen ligands, for catalysis and biology

Phosphorus dendrimers (dendrimers having one phosphorus atom at each branching point) possess versatile properties, depending on the type of their terminal functions.

Energy Transfer in Dendritic Systems Having Pyrene Peripheral Groups as Donors and Different Acceptor Groups

In this feature article, a specific overview of resonance energy transfer (FRET) in dendritic molecules was performed. We focused mainly on constructs bearing peripheral pyrene groups as donor moieties using different acceptor groups, such as porphyrin, fullerene C60, ruthenium-bipyridine complexes, and cyclen-core. We have studied the effect of all the different donor-acceptor pairs in the energy transfer efficiency (FRET). In all cases, high FRET efficiency values were observed.

Orange Fluorescent Ru(III) Complexes Based on 4'-Aryl Substituted 2,2':6',2″-Terpyridine for OLEDs Application

A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy)₂]Cl₃(1) [Ru(L ₁ )], [Ru(3,4,5-tmphtpy)₂]Cl₃(2) [Ru(L ₂ )], and [Ru(4-thptpy)₂]Cl₃(3) [Ru(L ₃ )], (where L = terpy = 2.2':6'2″ terpyridine ligands) are synthesized. The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. The density functional theory (DFT) outlines the geometric optimisation and electronic charge transition of these complexes. Photophysical studies describe that the luminescence of Ru(III) complexes is due to electronic transition between the energy levels of singly unoccupied molecular orbitals (SUMO) and singly occupied molecular orbitals (SOMO). It also exhibits the potential charge transfer to π-π* and n-π* states due to MLCT and ILCT processes of the complexes. The observed bands centered at 591 and 620 nm demonstrate that these emissions originated from the transition of SUMO to SOMO energy levels, that is, from the radiative decay from the doublet exciton. Due to the heavy metal effect of Ru(III) ions the photophysical behaviour depends on the MLCT process. In conclusion, that the all three Ru(L ₁ -L ₃ ) complexes are fallen orange emission.

Protection of densely populated excited triplet state ensembles against deactivation by molecular oxygen

Different approaches towards protection of triplet excited states against deactivation by molecular oxygen are summarized and reviewed.

Aggregation enhanced excimer emission (AEEE) with efficient blue emission based on pyrene dendrimers

A series of fluorescent dendrimers with pyrene moieties exhibited aggregation enhanced excimer emission (AEEE). Increases in the dendrimer generation caused emission at 480 nm with a high excimer/monomer emission intensity ratio.

Functional supramolecular polymers for biomedical applications

As a novel class of dynamic and non-covalent polymers, supramolecular polymers not only display specific structural and physicochemical properties, but also have the ability to undergo reversible changes of structure, shape, and function in response to diverse external stimuli, making them promising candidates for widespread applications ranging from academic research to industrial fields. By an elegant combination of dynamic/reversible structures with exceptional functions, functional supramolecular polymers are attracting increasing attention in various fields. In particular, functional supramolecular polymers offer several unique advantages, including inherent degradable polymer backbones, smart responsiveness to various biological stimuli, and the ease for the incorporation of multiple biofunctionalities (e.g., targeting and bioactivity), thereby showing great potential for a wide range of applications in the biomedical field. In this Review, the trends and representative achievements in the design and synthesis of supramolecular polymers with specific functions are summarized, as well as their wide-ranging biomedical applications such as drug delivery, gene transfection, protein delivery, bio-imaging and diagnosis, tissue engineering, and biomimetic chemistry. These achievements further inspire persistent efforts in an emerging interdisciplin-ary research area of supramolecular chemistry, polymer science, material science, biomedical engineering, and nanotechnology.

The polar side of polyphenylene dendrimers

The site-specific functionalization of poly(phenylene) dendrimers can produce macromolecules with a range of different polarities.

A detailed investigation of light-harvesting efficiency of blue color emitting divergent iridium dendrimers with peripheral phenylcarbazole units

The increase in phosphorescence efficiency was estimated by the energy transfer mechanism for divergent iridium dendrimers with peripheral phenylcarbazole units. A series of Ir-core/phenylcarbazole-end dendrons of the type, Ir(dfppy)2(pic-Czn) (Gn, n = 0, 1, 2, and 3), was synthesized, where dfppy, pic, and Czn (n = 2, 4, and 8) are 2-(4,6-difluorophenyl)pyridine, picolinate substituted with Czn at the 3-position, and 4-(9-carbazolyl)phenyldendrons connected with 3,5-di(methyleneoxy)benzyloxy branches, respectively. Selective excitation of the Czn units of G1–G3 resulted in >90% quenching of the Cz fluorescence accompanied by the growth of phosphorescence from the Ir(dfppy)2(pic) core as a consequence of energy transfer from the excited-singlet Czn chromophore to the core. The rate constants of energy transfer were determined by steady-state and transient spectroscopic measurements to be 4.32 × 10(9) s(−1) (G1), 2.37 × 10(9) s(−1) (G2), and 1.46 × 10(9) s(−1) (G3), which were in good agreement with those calculated using the Förster model. The phosphorescence enhancements were 157 (G1), 213 (G2), and 264% (G3) when compared to the phosphorescence of the core Ir(dfppy)2(pic-Ph2) (G0), in which pic-Ph2 is 3-(3,5-dibenzyloxybenzyl)picolinate.

Supramolecular dendritic polymers: from synthesis to applications

CONSPECTUS: Supramolecular dendritic polymers (SDPs), which perfectly combine the advantages of dendritic polymers with those of supramolecular polymers, are a novel class of non-covalently bonded, highly branched macromolecules with three-dimensional globular topology. Because of their dynamic/reversible nature, unique topological structure, and exceptional physical/chemical properties (e.g., low viscosity, high solubility, and a large number of functional terminal groups), SDPs have attracted increasing attention in recent years in both academic and industrial fields. In particular, the reversibility of non-covalent interactions endows SDPs with the ability to undergo dynamic switching of structure, morphology, and function in response to various external stimuli, such as pH, temperature, light, stress, and redox agents, which further provides a flexible and robust platform for designing and developing smart supramolecular polymeric materials and functional supramolecular devices. The existing SDPs can be systematically classified into the following six major types according to their topological features: supramolecular dendrimers, supramolecular dendronized polymers, supramolecular hyperbranched polymers, supramolecular linear-dendritic block copolymers, supramolecular dendritic-dendritic block copolymers, and supramolecular dendritic multiarm copolymers. These different types of SDPs possess distinct morphologies, unique architectures, and specific functions. Benefiting from their versatile topological structures as well as stimuli-responsive properties, SDPs have displayed not only unique characteristics or advantages in supramolecular self-assembly behaviors (e.g., controllable morphologies, specific performance, and facile functionalization) but also great potential to be promising candidates in various fields. In this Account, we summarize the recent progress in the synthesis, functionalization, and self-assembly of SDPs as well as their potential applications in a wide range of fields. A variety of synthetic methods using non-covalent interactions have been established to prepare different types of SDPs based on varied mono- or multifunctionalized building blocks (e.g., monomer, dendron, dendrimer, and hyperbranched polymer) with homo- or heterocomplementary units. In addition, SDPs can be further endowed with excellent functionalities by employing different modification approaches involving terminal, focal-point, and backbone modification. Similar to conventional dendritic polymers, SDPs can self-assemble into diverse supramolecular structures such as micelles, vesicles, fibers, nanorings, tubes, and many hierarchical structures. Finally, we highlight some typical examples of recent applications of SDP-based systems in biomedical fields (e.g., controlled drug/gene/protein delivery, bioimaging, and biomimetic chemistry), nanotechnology (e.g., nanoreactors, catalysis, and molecular imprinting), and functional materials. The current research on SDPs is still at the very early stage, and much more work needs to be done. We anticipate that future studies of SDPs will focus on developing multifunctional, hierarchical supramolecular materials toward their practical applications by utilization of cooperative non-covalent interactions.

Photoexpulsion of surface-grafted ruthenium complexes and subsequent release of cytotoxic cargos to cancer cells from mesoporous silica nanoparticles

Ruthenium(II) polypyridyl complexes have emerged both as promising probes of DNA structure and as anticancer agents because of their unique photophysical and cytotoxic properties. A key consideration in the administration of those therapeutic agents is the optimization of their chemical reactivities to allow facile attack on the target sites, yet avoid unwanted side effects. Here, we present a drug delivery platform technology, obtained by grafting the surface of mesoporous silica nanoparticles (MSNPs) with ruthenium(II) dipyridophenazine (dppz) complexes. This hybrid nanomaterial displays enhanced luminescent properties relative to that of the ruthenium(II) dppz complex in a homogeneous phase. Since the coordination between the ruthenium(II) complex and a monodentate ligand linked covalently to the nanoparticles can be cleaved under irradiation with visible light, the ruthenium complex can be released from the surface of the nanoparticles by selective substitution of this ligand with a water molecule. Indeed, the modified MSNPs undergo rapid cellular uptake, and after activation with light, the release of an aqua ruthenium(II) complex is observed. We have delivered, in combination, the ruthenium(II) complex and paclitaxel, loaded in the mesoporous structure, to breast cancer cells. This hybrid material represents a promising candidate as one of the so-called theranostic agents that possess both diagnostic and therapeutic functions.

Nitric oxide releasing-dendrimers: an overview

Platforms able to storage, release or scavenge NO in a controlled and specific manner is interesting for biological applications. Among the possible matrices for these purposes, dendrimers are excellent candidates for that. These molecules have been used as drug delivery systems and exhibit interesting properties, like the possibility to perform chemical modifications on dendrimers surface, the capacity of storage high concentrations of compounds of interest in the same molecule and the ability to improve the solubility and the biocompatibility of the compounds bonded to it. This review emphasizes the recent progress in the development and in the biological applications of different NO-releasing dendrimers and the nitric oxide release pathways in these compounds.

Evaluation of phototoxicity of dendritic porphyrin-based phosphorescent oxygen probes: an in vitro study

Biological oxygen measurements by phosphorescence quenching make use of exogenous phosphorescent probes, which are introduced directly into the medium of interest (e.g. blood or interstitial fluid) where they serve as molecular sensors for oxygen. The byproduct of the quenching reaction is singlet oxygen, a highly reactive species capable of damaging biological tissue. Consequently, potential probe phototoxicity is a concern for biological applications. Herein, we compared the ability of polyethyleneglycol (PEG)-coated Pd tetrabenzoporphyrin (PdTBP)-based dendritic nanoprobes of three successive generations to sensitize singlet oxygen. It was found that the size of the dendrimer has practically no effect on the singlet oxygen sensitization efficiency in spite of the strong attenuation of the triplet quenching rate with an increase in the dendrimer generation. This unexpected result is due to the fact that the lifetime of the PdTBP triplet state in the absence of oxygen increases with dendritic generation, thus compensating for the concomitant decrease in the rate of quenching. Nevertheless, in spite of their ability to sensitize singlet oxygen, the phosphorescent probes were found to be non-phototoxic when compared with the commonly used photodynamic drug Photofrin in a standard cell-survival assay. The lack of phototoxicity is presumably due to the inability of PEGylated probes to associate with cell surfaces and/or penetrate cellular membranes. In contrast, conventional photosensitizers bind to cell components and act by generating singlet oxygen inside or in the immediate vicinity of cellular organelles. Therefore, PEGylated dendritic probes are safe to use for tissue oxygen measurements as long as the light doses are less than or equal to those commonly employed in photodynamic therapy.

Ru(II) glycodendrimers as probes to study lectin-carbohydrate interactions and electrochemically measure monosaccharide and oligosaccharide concentrations

We describe a novel platform on which to study carbohydrate-protein interactions based on ruthenium(II) glycodendrimers as optical and electrochemical probes. Using the prototypical concanavalin A (ConA)-mannose lectin-carbohydrate interaction as an example, oligosaccharide concentrations were electrochemically monitored. The displacement of the Ru(II) complex from lectin-functionalized gold surfaces was repeatedly regenerated. This new platform presents a method to monitor many different complex sugars in parallel.

Remote control of bipyridine-metal coordination within a peptide dendrimer

The metal coordinating ability of a bipyridine ligand at the core of a peptide dendrimer was found to be controlled by the nature of amino acids placed at the dendrimer periphery, with coordination being promoted by anionic residues and inhibited by cationic residues; heterotrimers with mixed charges were preferentially formed.

Dendritic phosphorescent probes for oxygen imaging in biological systems

Oxygen levels in biological systems can be measured by the phosphorescence quenching method using probes with controllable quenching parameters and defined biodistributions. We describe a general approach to the construction of phosphorescent nanosensors with tunable spectral characteristics, variable degrees of quenching, and a high selectivity for oxygen. The probes are based on bright phosphorescent Pt and Pd complexes of porphyrins and symmetrically pi-extended porphyrins (tetrabenzoporphyrins and tetranaphthoporphyrins). pi-Extension of the core macrocycle allows tuning of the spectral parameters of the probes in order to meet the requirements of a particular imaging application (e.g., oxygen tomography versus planar microscopic imaging). Metalloporphyrins are encapsulated into poly(arylglycine) dendrimers, which fold in aqueous environments and create diffusion barriers for oxygen, making it possible to regulate the sensitivity and the dynamic range of the method. The periphery of the dendrimers is modified with poly(ethylene glycol) residues, which enhance the probe's solubility, diminish toxicity, and help prevent interactions of the probes with the biological environment. The probe's parameters were measured under physiological conditions and shown to be unaffected by the presence of biomacromolecules. The performance of the probes was demonstrated in applications, including in vivo microscopy of vascular pO(2) in the rat brain.