Platinum Diimine Complexes Research Articles

Enhanced photocytotoxicity induced by a triphenylphosphonium-appended platinum diimine complex

Photodynamic therapy (PDT) agents induce photodamage only where photosensitizers localize in tumor cells. Since apoptosis is a major pathway of PDT-mediated cell death in vivo, the therapeutic efficacy of PDT drugs against tumor cells may be improved by regulating intrinsic apoptosis. Mitochondria are the major intracellular organelles that regulate apoptosis, thus triphenylphosphonium, a well-known mitochondria-targeting molecule, was appended to a photoactive platinum diimine complex. The ability of the triphenylphosphonium-appended complex to generate singlet oxygen was assessed by fluorescence spectroscopy using 1,3-diphenylisobenzofuran as a probe. The photocytotoxicity towards HeLa cells (human cervical cancer cell line) or HL-7702 cells (human liver cell line) was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assays. The platinum complex has moderate capability to generate singlet oxygen and it has more potent photocytotoxicity than its analogue Pt-CA. Both platinum diimine complexes studied are largely nontoxic to human liver cells either in the dark or after irradiation.

Platinum(II) diimine complexes containing phenylpyridine ligands decorated with anionic closo-monocarborane clusters [CB11H12

We report three Pt(II) diimine complexes containing ancillary ligands of phenylpyridine furnished with anionic closo-monocarborane clusters [CB11H12]-. Three neutral complexes exhibit intensive phosphorescence in the solid state and complex 1 was used to detect acetonitrile vapor in a quartz plate.

Photoactive silicon surfaces functionalized with high-quality and redox-active platinum diimine complex monolayers

Platinum diimine complexes can covalently be grafted onto oxide-free, hydrogen-terminated silicon(111) surfaces into clean and high-quality monolayers. The so modified surfaces offer great prospects as photocathodes for solar-driven electrocatalysis.

Luminescent Platinum(II) Complexes with Bidentate Diacetylide Ligands: Structures, Photophysical Properties and Application Studies

A series of platinum(II) complexes supported by terphenyl diacetylide as well as diimine or bis-N-heterocyclic carbene (NHC) ligands have been prepared. The diacetylide ligands adopt a cis coordination mode featuring non-planar terphenyl moieties as revealed by X-ray crystallographic analyses. The electrochemical, photophysical and photochemical properties of these platinum(II) complexes have been investigated. These platinum(II) diimine complexes show broad emission with peak maxima from 566 nm to 706 nm, with two of them having emission quantum yields >60% and lifetimes <2 μs in solutions at room temperature, whereas the platinum(II) diacetylide complexes having bis-N-heterocyclic carbene instead of diimine ligand display photoluminescence with quantum yields of up to 28% in solutions and excited state lifetimes of up to 62 μs at room temperature. Application studies revealed that one of the complexes can catalyze photoinduced aerobic dehydrogenation of alcohols and alkenes, and a relatively non-toxic water-soluble Pt(II) complex displays anti-angiogenic activity.

A valproic acid-modified platinum diimine complex as potential photosensitizer for photodynamic therapy

Histone deacetylase inhibitors have often been used in combination treatment of various types of cancers due to their non-genotoxic epigenetic potential. Valproic acid (VPA) is a well-known histone deacetylase inhibitor. Conjugate of VPA with a phtoactive platinum diimine complex through an ester bond has been fabricated to potentiate the photocytotoxicity of the photosensitizer. Its capability to generate singlet oxygen, behavior in the presence of esterase, and photocytotoxicity in tumor cells have also been studied. The results revealed that the novel VPA-modified platinum diimine complex could produce singlet oxygen efficiently and release VPA in the presence of porcine liver esterase. The results also suggested that incorporation of VPA moiety into the platinum diimine complex might significantly enhance the cytotoxicity of the complex.

Triphenylphosphonium-functionalized nanocomposites as carriers of a platinum diimine complex for photodynamic therapy

The photodamage induced by PDT drugs usually occurs at the site where the photosensitizers accumulate in the tumor cells, thus the modulation of intrinsic apoptosis by mitochondria-targeting PDT drugs might be a promising way to enhance the therapeutic efficacy of PDT drugs against tumor cells. Novel triphenylphosphonium-functionalized nanocomposites employed as carriers of a photoactive platinum diimine complex have been fabricated and characterized. Upon irradiation, the IC50 value of photosensitizer-loaded triphenylphosphonium-functionalized nanocomposites was found to be 17.4 or 14.4 times lower than that of the photosensitizer studied alone against HCT116 cells or A549 cells, respectively. The results suggested that the triphenylphosphonium- functionalized nanocomposites as drug delivery vehicles could significantly enhance the photodynamic therapy efficacy of the photosensitizer.

Role of Axial Ligation in Gating the Reactivity of Dimethylplatinum(III) Diimine Radical Cations

Electrochemical methods are coupled with chemical oxidant-based analytical strategies to evaluate the oxidative reactivity of the platinum(II) diimine complex (bpy)PtII(CH3)2 (bpy = 2,2′-bipyridine...

Ground State Nuclear Magnetic Resonance Chemical Shifts Predict Charge-Separated Excited State Lifetimes.

Dichalcogenolene platinum(II) diimine complexes, (LE,E')Pt(bpy), are characterized by charge-separated dichalcogenolene donor (LE,E') → diimine acceptor (bpy) ligand-to-ligand charge transfer (LL'CT) excited states that lead to their interesting photophysics and potential use in solar energy conversion applications. Despite the intense interest in these complexes, the chalcogen dependence on the lifetime of the triplet LL'CT excited state remains unexplained. Three new (LE,E')Pt(bpy) complexes with mixed chalcogen donors exhibit decay rates that are dominated by a spin-orbit mediated nonradiative pathway, the magnitude of which is proportional to the anisotropic covalency provided by the mixed-chalcogen donor ligand environment. This anisotropic covalency is dramatically revealed in the 13C NMR chemical shifts of the donor carbons that bear the chalcogens and is further probed by S K-edge XAS. Remarkably, the NMR chemical shift differences also correlate with the spin-orbit matrix element that connects the triplet excited state with the ground state. Consequently, triplet LL'CT excited state lifetimes are proportional to both functions, demonstrating that specific ground state NMR chemical shifts can be used to evaluate spin-orbit coupling contributions to excited state lifetimes.

Enhanced photocytotoxicity induced by a platinum diimine complex employing amine-functionalized magnetite-silica nanocomposites as delivery vehicles.

Core-shell magnetite-silica nanocomposites modified with 3-aminopropyltriethoxy silane (APTES) were prepared by silanization reaction, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Then the nanocomposites were employed as carriers of a photoactive platinum diimine complex. Photoinduced cytotoxicity by the photosensitizer-loaded nanocomposites in different human carcinoma cells has been studied by cell viability assay. The cellular uptake of the photosensitizer-loaded nanocomposites has also been studied by ICP-MS. The results suggest that the cytotoxicity induced by the platinum diimine complex in red light can be greatly enhanced when the photosensitizer is loaded with the magnetic nanocomposites, and the surface charge of the nanocomposites may also have effect on the photocytotoxicity of the photosensitizer.

Two-dimensional (2D) self-assembly of oligo(phenylene-ethynylene) molecules and their triangular platinum(ii) diimine complexes studied using STM.

In this investigation, the two-dimensional (2D) self-assembly nanostructures of a series of cyclic oligo(phenylene-ethynylene) (OPE) molecules (L1, L2-6 and L2-12) at the 1-phenyloctane/highly oriented pyrolytic graphite (HOPG) interface were thoroughly studied using scanning tunneling microscopy (STM). Comparative STM studies with their triangular Pt(ii) diimine complexes (C1, C2-6 and C2-12) were also carried out. Based on careful measurements on single molecule level STM images and density functional theory (DFT) calculations, the formation mechanisms of the nanoarrays formed were revealed.

Photoactive platinum diimine complexes showing induced cancer cell death by apoptosis.

Photoinduced cytotoxicity mediated by a triphenylenamine-modified platinum diimine complex in human breast adenocarcinoma cells has been studied by cell viability assay. The triphenylenamine-modified platinum diimine complex showed more potent cytotoxicity in light than its carboxylate-modified analogue. To gain insights into the mechanism of photodynamic activity of this class of platinum diimine complexes, flow cytometric analyses were performed. The results suggest that upon irradiation the two platinum diimine complexes studied could induce cell cycle arrest in G2/M or S phase, and both of them could induce cancer cell death by apoptosis.

Photoinduced cytotoxicity by a platinum diimine complex employing magnetite-silica nanocomposites as delivery vehicles.

Tartaric acid-modified core-shell magnetite-silica nanocomposites were prepared by a sol-gel method, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Then the nanocomposites were employed as carriers of a photoactive platinum diimine complex. Photoinduced cytotoxicity by the photosensitizer-loaded nanocomposites in different human carcinoma cells has been studied by cell viability assay. The results suggest that the as-synthesized nanocomposites have good stability in water, and the cytotoxicity induced by the platinum diimine complex in red light can be significantly enhanced when the photosensitizer is loaded with the magnetic nanocomposites.

Photoinduced DNA damage and cytotoxicity by a triphenylamine-modified platinum-diimine complex

Many planar photosensitizers tend to self-aggregate via van der Waals interactions between π-conjugated systems. The self-aggregation of the photosensitizer may reduce the efficiency of the photosensitizer to generate singlet oxygen, thereby diminishing its photodynamic activity. Efforts have been made to improve the photodynamic activity of bis-(o-diiminobenzosemiquinonato)platinum(II) which has planar geometry by the introduction of the sterically hindered triphenylamine moiety into the ligand. Herein we report the photoinduced DNA damage and cytotoxicity by a triphenylamine-modified platinum-diimine complex in red light studied by fluorescence spectra, agarose gel assay and cell viability assay. The results suggest that the triphenylamine-modified platinum-diimine complex has better capability to generate singlet oxygen than bis-(o-diiminobenzosemiquinonato)platinum(II), and it can induce DNA damage in red light, causing high photocytotoxicity in HepG-2 cells in vitro.

Trans-[PtCl2(NH2C6H4CO2H)2]: a platinum complex forming a two-dimensional hydrogen-bonded network

The compound trans-[PtCl2(NH2C6H4CO2H)2] has been prepared from the hydrolysis of a platinum diimine complex, and has been characterised by X-ray crystallography. The crystal structure revealed that the compound forms a two-dimensional hydrogen-bonded network in the solid state, with pairs of O–H···O hydrogen bonds between carboxylic acid groups linking the molecules into zigzag tapes, which are cross-linked into sheets by pairs of N–H···Cl hydrogen bonds. Key words: Metal-organic frameworks, metalloligands, two-dimensional hydrogen-bonded network.

Long-Lived π-Shape Platinum(II) Diimine Complexes Bearing 7-Benzothiazolylfluoren-2-yl Motif on the Bipyridine and Acetylide Ligands: Admixing π,π* and Charge-Transfer Configurations

Two π-shape platinum(II) diimine complexes (1 and 2) bearing 7-benzothiazolylfluoren-2-yl motif on the bipyridine and acetylide ligands were synthesized, and their photophysics and reverse saturable absorption were investigated systematically. Both complexes exhibit low-energy, broad, and weak 1MLCT (metal-to-ligand charge transfer)/1LLCT (ligand-to-ligand charge transfer) transitions and intense high-energy bipyridine ligand or acetylide ligand localized 1π,π* transitions mixed with some 1MLCT/1LLCT/1ILCT (intraligand charge transfer) characters in their UV–vis absorption spectra. The emission of 1 and 2 includes a weak fluorescence band and a broad, structureless phosphorescence band emanating from the 3MLCT/3LLCT/3π,π* states for 1 and predominantly from 3π,π* state for 2. Insertion of C≡C bond between the bipyridine and fluorene components induces pronounced red-shifts of the absorption and emission bands because of the extended π-conjugation in the bipyridine ligand. Because of the admixture of the 3π,π* excited state with the charge-transfer excited states, both complexes possess extremely long-lived, broadband (visible to the near-IR region) triplet excited-state absorption, resulting in remarkably strong reverse saturable absorption at 532 nm for nanosecond laser pulses. Therefore, complexes 1 and 2 are excellent candidates for devices that require strong reverse saturable absorption.

Core-shell magnetite-silica composite nanoparticles enhancing DNA damage induced by a photoactive platinum-diimine complex in red light

Lack of solubility under physiological conditions poses an additional risk for toxicity and side effects for intravenous delivery of the photodynamic therapeutic agent in vivo. Employing magnetite-silica composite nanoparticles as carriers of the photodynamic therapeutic agents may be a promising way to solve the problem. In this study, core-shell magnetite-silica composite nanoparticles were prepared by a sol–gel method, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering, then they were used as carriers of a photoactive platinum diimine complex. The interactions of the photosensitizer-loaded magnetic composite nanoparticles with DNA in red light were monitored by agarose-gel electrophoresis. The results suggest that high doses of magnetite-silica composite nanoparticles might facilitate the transformation of covalently closed circular (ccc)-DNA band to open circular (oc)-DNA band though they are harmless to DNA at their low concentrations, therefore enhancing the extent of DNA damage caused by the metal complex in red light.

Nonlinear Absorbing Platinum(II) Diimine Complexes: Synthesis, Photophysics, and Reverse Saturable Absorption

A series of platinum(II) diimine complexes with different substituents on fluorenyl acetylide ligands (1a-1e) were synthesized and characterized. The influence of the auxiliary substituent on the photophysics of these complexes has been systematically investigated spectroscopically and theoretically (using density functional theory (DFT) methods). All complexes exhibit ligand-centered (1)π,π* transitions in the UV and blue spectral region, and broad, structureless (1)MLCT/(1)LLCT (1a, 1b, 1d and 1e) or (1)MLCT/(1)LLCT/(1)π,π* (1c) absorption bands in the visible region. All complexes are emissive in solution at room temperature, with the emitting state is tentatively assigned to mixed (3)MLCT/(3)π,π* states. The degree of (3)π,π* and (3)MLCT mixing varies with different substituents and solvent polarities. Complexes 1a-1e exhibit relatively strong singlet and triplet transient absorption from 450 to 800 nm, at which point reverse saturable absorption (RSA) could occur. Nonlinear transmission experiments at 532 nm by using nanosecond laser pulses demonstrate that 1a-1e are strong reverse saturable absorbers and could potentially be used as broadband nonlinear absorbing materials.

Platinum(II) Diimine Complexes with Halide/Pseudohalide Ligands and Dangling Trialkylamine or Ammonium Groups

A series of platinum(II) complexes with the formulas Pt(diimine)(pip(2)NCNH(2))(L)(2+) [pip(2)NCNH(2)(+) = 2,6-bis(piperidiniummethyl)phenyl cation; L = Cl, Br, I, NCS, OCN, and NO(2); diimine = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO(2)phen), and 5,5'-ditrifluoromethyl-2,2'-bipyridine (dtfmbpy)] were prepared by the treatment of Pt(pip(2)NCN)Cl with a silver(I) salt followed by the addition of the diimine and halide/pseudohalide under acidic conditions. Crystallographic data as well as (1)H NMR spectra establish that the metal center is bonded to a bidentate phenanthroline and a monodentate halide/pseudohalide. The pip(2)NCNH(2)(+) ligand with protonated piperidyl groups is monodentate and bonded to the platinum through the phenyl ring. Structural and spectroscopic data indicate that the halide/pseudohalide group (L(-)) and the metal center in Pt(phen)(pip(2)NCNH(2))(L)(2+) behave as Brønsted bases, forming intramolecular NH···L/NH···Pt interactions involving the piperidinium groups. A close examination of the 10 structures reported here reveals linear correlations between N-H···Pt/L angles and H···Pt/L distances. In most cases, the N-H bond is directed toward the Pt-L bond, thereby giving the appearance that the proton bridges the Pt and L groups. In contrast to observations for Pt(tpy)(pip(2)NCN)(+) (tpy = 2,2';6',2"-terpyridine), the electrochemical oxidation of deprotonated adducts, Pt(diimine)(L)(pip(2)NCN), is chemically and electrochemically irreversible.

Luminescence Rigidochromism and Redox Chemistry of Pyrazolate-Bridged Binuclear Platinum(II) Diimine Complex Intercalated into Zirconium Phosphate Layers

The direct intercalation of a pyrazolate-bridged platinum(II) bipyridyl dimer ([{Pt(dmbpy)(μ-pz)}(2)](2+); dmbpy = 4,4'-dimethyl-2,2'-bipyridine, pz(-) = pyrazolate) within a zirconium phosphate (ZrP) framework has been accomplished. The physical and spectroscopic properties of [{Pt(dmbpy)(μ-pz)}(2)](2+) intercalated in ZrP were investigated by X-ray powder diffraction and X-ray photoelectron, infrared, absorption, and luminescence spectroscopies. Zirconium phosphate layers have a special microenvironment that is capable of supporting a variety of platinum oxidation states. Diffuse reflectance spectra from powders of the blue-gray intercalated materials show the formation of a low-energy band at 600 nm that is not present in the platinum dimer salt. The nonintercalated complex is nonemissive in room-temperature fluid solution, but gives rise to intense blue-green emission in a 4:1 ethanol/methanol 77 K frozen glassy solution. Powders and colloidal suspensions of [{Pt(dmbpy)(μ-pz)}(2)](2+)-exchanged ZrP materials exhibit intense emissions at room-temperature.

Cyclometalated platinum(ii) diimine complexes: synthetically tuning the photophysical and electrochemical properties

Presented is the synthesis of an array of 16 heteroleptic phosphorescent diimine complexes of platinum(II) with electronically diverse ligand spheres and their full spectroscopic, photophysical, and electrochemical characterization. The complexes were found to exhibit luminescence (480-500 nm) in deaerated solutions at room temperature from a long-lived (3)LC state (τ = 2-3 μs) that exhibits significant metal character perturbed by a low-lying (1)MLCT state. Interestingly, emission from a (3)MLCT state was not observed as is the case with many other polypyridine-based d-block complexes. Electrochemical intermediates proved stable as multiple reversible reductions between -1 and -2 V vs. SCE were noted during cyclic voltammetry experiments unveiling the potential of these luminophores for use in a variety of optoelectronic and solar energy conversion applications.