Cyclometalated Platinum(II) Complexes Bearing Bidentate O,O′-Di(alkyl)dithiophosphate Ligands: Photoluminescence and Cytotoxic Properties

Synthesis of a light-responsive platinum curcumin complex, chemical and biological investigations and delivery to tumor cells by means of polymeric nanoparticles

Platinum-based anticancer drugs are common in chemotherapy, but problems such as systemic toxicity and acquired resistance of some tumors hamper their clinical applications and therapeutic efficacy. It is necessary to synthesize Pt-based drugs and explore strategies to reduce side effects and improve pharmacokinetic profiles. Photo-responsive chemotherapeutics have emerged as an alternative strategy against several cancers, as photoactivation offers spatial selectivity and fewer side effects. Here, we combine chemical synthesis and nanotechnology to create a multifunctional platinum drug delivery system based on the novel metal complex [Pt(ppy)(curc)] (ppy = deprotonated 2-phenylpyridine, curc = deprotonated curcumin)] embodying the naturally occurring bioactive molecule, curcumin. The ultrasonication method coupled with the layer-by-layer technology was employed to produce nanocolloids, which demonstrated a good biocompatibility, higher solubility in aqueous solution, stability, large drug loading, and good biological activity in comparison with the free drug. In vitro release experiments revealed that the polymeric nanoformulation is relatively stable under physiological conditions (pH = 7.4 and 37 °C) but sensitive to acidic environments (pH = 5.6 and 37 °C) which would trigger the release of the loaded drug. Our approach modifies the bioavailability of this Pt-based drug increasing its therapeutic action in terms of both cytotoxic and anti-metastasis effects.

Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties

We present the synthesis and characterization of two series of mononuclear heteroleptic anionic cycloplatinated(II) complexes featuring terminal cyanide ligand Q⁺[Pt(C^N)(p-MeC₆H₄)(CN)]^- [C^N = benzoquinolate (bzq), Q⁺ = K⁺ 1 and NBu₄⁺ 4; 2-phenylpyridinate (ppy), Q⁺ = K⁺ 2 and NBu₄⁺ 5 and 2-(2,4- difluorophenyl)pyridinate (dfppy), Q⁺ = K⁺ 3 and NBu₄⁺ 6] and a series of symmetrical binuclear complexes (NBu₄)[Pt₂(C^N)₂(p-MeC₆H₄)₂(μ-CN)] (C^N = bzq 7, ppy 8, dfppy 9). Compounds 5, 6, and 7-9 were further determined by single-crystal X-ray diffraction. There are no apparent intermolecular Pt···Pt interactions owing to the presence of bulky NBu₄⁺ counterion. Slow crystallization of K[Pt(ppy)(p-MeC₆H₄)(CN)] 2 in acetone/hexane evolves with formation of yellow crystals, which were identified by single-crystal X-ray diffraction methods as the salt complex {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}[Pt(ppy)(p-MeC₆H₄)(μ-CN)Pt(ppy)(p-MeC₆H₄)]·2acetone (10), featuring the binuclear anionic unit 8^- neutralized by an hybrid inorganic-organometallic coordination polymer {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}⁺. The photophysical properties of all compounds were recorded in powder, polystyrene film, and solution states with a quantum yield up to 21% for 9 in the solid state. All complexes displayed bright emission in rigid media, and for the interpretation of their absorption and emission properties, density functional theory (DFT) and time-dependent DFT calculations were applied.

Design, synthesis and evaluation of novel 1,2,4-triazole derivatives as promising anticancer agents

Herein, we reported the synthesis of nineteen novel 1,2,4-triazole derivatives including 1,3-diphenyl-2-(1H-1,2,4-triazol-1-yl) propan-1-ones (7a-e), 1-(1,3-diphenylpropan-2-yl)-1H-1,2,4-triazole (8a-c) and 1,4-diphenyl-2-(1H-1,2,4-triazol-1-yl) butane-1,4-diones (10a-k). The structures of these derivatives were confirmed by spectroscopic techniques like IR, 1H-NMR, Mass spectroscopy and Elemental analysis. The cytotoxic activities of the synthesized compounds were evaluated against three human cancer cell lines including MCF-7, Hela and A549 using MTT assay. Compounds 7d, 7e, 10a and 10d showed a promising cytotoxic activity lower than 12 μM against Hela cell line. The safety of these compounds was also, evaluated on MRC-5 as a normal cell line and relieved that most of the synthesized compounds have proper selectivity against normal and cytotoxic cancerous cell lines. Finally, molecular docking studies were also, done to understand the mechanism and binding modes of these derivatives in the binding pocket of aromatase enzyme as a possible target.

Antiproliferative activity and DNA binding studies of cyclometalated complexes of platinum(II) containing 2-vinylpyridine

The cytotoxic activity of four cyclometalated platinum(II) complexes [PtMe(vpy)(L)], containing 2-vinylpyridine (vpy) and the phosphine ligands (L) PMe₂Ph (1a), PPh₃ (1b), PMePh₂ (1c), and P(c-Hex)₃ (1d), were evaluated against human breast cancer (MDA-MB-231), human lung cancer (A549), human colon cancer (SW1116), and non-tumor epithelial breast (MCF-10 A) cell lines. The highest activity was found for 1c with IC₅₀ values of 21.10 µM, 23.36 µM, and 12.96 µM, compared to cisplatin, which was 10.12 µM, 47.57 µM, and 19.50 µM against the A549, SW1116, and MDA-MB-231 cell lines, respectively. 1a-d showed a higher selectivity index (SI) than cisplatin. Docking studies confirmed interaction to the DNA minor groove for all complexes. Genotoxicity studies on 1c showed interactions with the genomic content of malignant cells. Compared with cisplatin as a positive control, a slight shift was found in the electrophoresis mobility, which was utilized further to study the direct interaction of 1c with DNA.

An insight into triel bonds in O,O′-diarylphosphorodithioates of thallium(i): experimental and theoretical investigations

Two new thallium(i) compounds have been synthesized and structurally characterized. The existence of triel bonds in these compounds has been confirmed by HSA and DFT calculations using QTAIM and NCI plot index methods.

Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR₃)], Vpy = 2-vinylpyridine and PR₃ = PPh₃ (1a); PPh₂Me (1b); PPhMe₂ (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow–orange region’s structured bands. The PPhMe₂ derivative was the strongest emissive among the complexes, and the complex with PPh₃ was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an S_N2 mechanism. The complex with PPhMe₂ ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh₃ derivative showed the slowest one. Interestingly, for the PPhMe₂ analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization.

The impact of cyclometalated and phosphine ligands on the luminescence properties of cycloplatinated(ii) complexes: photophysical and theoretical investigations

The effects of various C^N cyclometalated and phosphine ligands on the photophysical properties of cycloplatinated(ii) complexes were investigated experimentally and theoretically.

Fluorinated Cycloplatinated(II) Complexes Bearing Bisphosphine Ligands as Potent Anticancer Agents

A family of cationic cycloplatinated(II) complexes [Pt(dfppy)(P^P)]Cl, dfppy = 2-(2,4-difluorophenyl)pyridine, incorporating bisphosphine ligands, P^P = bis(diphenylphosphino)methane (1, dppm), 1,2-bis(diphenylphosphino)ethane (2, dppe) and 1,2-bis(diphenylphosphino)benzene (3, dppbz), was prepared. The complexes were characterized by means of several analytical and spectroscopic methods. These complexes displayed acceptable stability in the biological environments which was confirmed by NMR, HR ESI-MS and UV-vis techniques. The antiproliferative properties of these complexes were evaluated by National Cancer Institute (NCI) at National Institutes of Health (NIH) against 60 different human tumor cell lines such as leukemia, melanoma, lung, colon, brain, ovary, breast, prostate and kidney. These complexes showed higher cytotoxicity than cisplatin against a wide variety of cancer cell lines such as K-562 (leukemia), HOP-92 (lung), HCT-116 (colon), OVCAR-8 (ovarian), PC-3 (prostate), MDA-MB-468 (breast), and melanoma cancer cell lines. Complex 3 as the most potent compound in this study furnished an excellent anti-proliferative activity compared to the cisplatin against Hela, SKOV3, and MCF-7 cancer cell lines. The main mode of the interaction of 1-3 with DNA was also determined using molecular docking studies.

Ligand-Mediated C-Br Oxidative Addition to Cycloplatinated(II) Complexes and Benzyl-Me C-C Bond Reductive Elimination from a Cycloplatinated(IV) Complex

Reaction of the Pt(II) complexes [PtMe₂(pbt)], 1a, (pbt = 2-(2-pyridyl)benzothiazole) and [PtMe(C^N)(PPh₂Me)] [C^N = deprotonated 2-phenylpyridine (ppy), 1b, or deprotonated benzo[h]quinoline (bhq), 1c] with benzyl bromide, PhCH₂Br, is studied. The reaction of 1a with PhCH₂Br gave the Pt(IV) product complex [PtBr(CH₂Ph)Me₂(pbt)]. The major trans isomer is formed in a trans oxidative addition (2a), while the minor cis products (2a' and 2a″) resulted from an isomerization process. A solution of Pt(II) complex 1a in the presence of benzyl bromide in toluene at 70 °C after 7 days gradually gave the dibromo Pt(IV) complex [Pt(Br)₂Me₂(pbt)], 4a, as determined by NMR spectroscopy and single-crystal XRD. The reaction of complexes 1b and 1c with PhCH₂Br gave the Pt(IV) complexes [PtMeBr(CH₂Ph)(C^N)(PPh₂Me)] (C^N = ppy; 2b; C^N = bhq, 2c), in which the phosphine and benzyl ligands are trans. Multinuclear NMR spectroscopy ruled out other isomers. Attempts to grow crystals of the cycloplatinated(IV) complex 2b yielded a previously reported Pt(II) complex [PtBr(ppy)(PPh₂Me)], 3b, presumably from reductive elimination of ethylbenzene. UV-vis spectroscopy was used to study the kinetics of reaction of Pt(II) complexes 1a-1c with benzyl bromide. The data are consistent with a second-order S_N2 mechanism and the first order in both the Pt complex and PhCH₂Br. The rate of reaction decreases along the series 1a ≫ 1c > 1b. Density functional theory calculations were carried out to support experimental findings and understand the formation of isomers.

A C^N Cycloplatinated(II) Fluoride Complex: Photophysical Studies and Csp3-F Bond Formation

This work reports the synthesis and characterization of a new C^N-based cycloplatinated(II) fluoride complex, [Pt(ppy)(PPh₃)F] (2; ppy = 2-phenylpyridinate), involving a Pt-F bond. The new complex is highly luminescent in the green area with a high quantum yield of 94.6% at 77 K. A comparison study of the heavier halogen derivatives reveals a descending emission quantum yield order of F > Cl > Br > I. Time-dependent density functional theory calculations ascribe the decreased emission efficiency to the decreasing trend of an intraligand (IL) transition from F to I, which accounts for the major radiative pathway. In addition, 2 is capable of the fluorinating alkyl halides, leading to C_sp³-F bond formation at room temperature.

Chelating and Bridging Roles of 2-(2-Pyridyl)benzimidazole and Bis(diphenylphosphino)acetylene in Stabilizing a Cyclic Tetranuclear Platinum(II) Complex

The reaction of complex [Pt(Me)(DMSO)(pbz)], 1, (pbz = 2-(2-pyridyl)benzimidazolate) with [PtMe(Cl)(DMSO)₂], B, followed by addition of bis(diphenylphosphino)acetylene (dppac), gave the novel tetranuclear platinum complex [Pt₄Me₄(μ-dppac)₂(pbz)₂Cl₂], 2, bearing both the pbz and dppac ligands. In this structure, the pbz ligands are both chelating and bridging to stabilize the tetraplatinum framework. The tetranuclear Pt(II) complex was fully characterized by NMR spectroscopy, X-ray crystallography, and mass spectrometry, and its electronic structure was investigated and supported by DFT calculations.

Synthesis and biological evaluation of thiolate gold(i) complexes as thioredoxin reductase (TrxR) and glutathione reductase (GR) inhibitors

Au(i) complexes with PPh₂py and thiolate ligands are prepared. The complexes are shown considerable cytotoxic activities and those efficiently inhibit the TrxRs and GR.

A double rollover cycloplatinated(ii) skeleton: a versatile platform for tuning emission by chelating and non-chelating ancillary ligand systems

Described here is the synthesis and characterization of heteroleptic binuclear platinum(ii) complexes of the type [Pt2(μ-bpy-2H)(S^S)2] and [Pt2(μ-bpy-2H)(L)2(X)2], containing a 2,2'-bipyridine-based double rollover cycloplatinated core (Pt(μ-bpy-2H)Pt), in combination with the anionic S^S- chelate ligands di(ethyl)dithiocarbamate (dedtc) and O,O'-di(cyclohexyl)dithiophosphate (dcdtp) or non-chelating L/X ancillary ligands (PPh3/Me, t-BuNC/Me, PPh3/SCN and PPh3/N3). The new complexes were characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and some of them additionally using single crystal X-ray diffraction. The absorption and photoluminescence of the complexes show a strong dependence on the ancillary ligands. Upon excitation at 365 nm, in a CH2Cl2 rigid matrix (77 K), the complexes exhibit structured emission bands with λmax between 488 nm and 525 nm and vibrational spacing around 1350 cm-1, indicating the excited states centered on the cyclometalated ligand (3ILCT) with some mixing 3MLCT characteristics. In the case of the PPh3/N3 complex, a dual emission band (orange color) is observed in the solid state at 298 K for which the low energy band arises from an aggregation-induced emission (AIE). Upon lowering the temperature (77 K), thermochromism is observed (orange to yellow) which is accompanied by the intensification of the high energy band (ligand-centered structured band). Finally, in order to rationalize the obtained photophysical data, complete DFT (density functional theory) and TD-DFT (time-dependent DFT) calculations were performed on the selected complexes.

The influence of thiolate ligands on the luminescence properties of cycloplatinated(ii) complexes

Complexes [Pt(C^{^}N)(PPh₃)Cl] (C^{^}N = bzq (7,8-benzoquinolinyl, A) and ppy (2-phenylpyridinyl, B)) were reacted with various thiolate ligands to afford complexes [Pt(C^{^}N)(PPh₃)(κ¹-S-SR)], C^{^}N = bzq, R = SPh (thiophenolate, 1a); C^{^}N = ppy, R = SPh (1b); C^{^}N = bzq, R = Spy (pyridine-2-thiolate, 2a); C^{^}N = ppy, R = Spy (2b); C^{^}N = bzq, R = SpyN (pyrimidine-2-thiolate, 3a); C^{^}N = ppy, R = SpyN (3b). Complexes 1-3 were characterized by NMR spectroscopy, and the solid-state structures of 1a and 2a were determined by X-ray diffraction methods. Replacing a chloride ligand with electron-rich thiolates changes the lowest energy singlet and triplet excited states to the ones that feature charge transfer from the thiolate (mixed with some metal character) to the C^{^}N ligand, which was supported by TD-DFT calculations. All complexes are emissive at 298 K in the solid state except 2b and 3b, which are emissive only at 77 K having a less rigid structure compared to others. The emission of 1a and 1b originates from a low-energy excited state of d_Pt/π_SR → π*_C^N while 3a exhibits a ³LC/³MLCT transition. For 1a and 1b, the radiative rate and the quantum efficiency are higher in a rigid environment such as a solid compared to a polymer and solution. Decreasing the rigidity of the environment leads to a flexibility of rotation of the -SR around the axis of the Pt-S bond. So the geometry can be easily changed after radiation and the lowest lying triplet excited state would have the effective contribution of the dd* transition, which opens a nonradiative pathway at room temperature.

Cycloplatinated(ii) complexes bearing 1,1′-bis(diphenylphosphino)ferrocene ligand: biological evaluation and molecular docking studies

Cycloplatinated(ii) complexes containing dppf ligand were prepared. These complexes exhibited high cytotoxicity and apoptosis-inducing activities to human cancer cell lines.

Cycloplatinated(ii) complexes bearing an O,S-heterocyclic ligand: search for anticancer drugs

Cycloplatinated(ii) complexes containing the 2-mercaptopyridine N-oxide ligand were synthesized and characterized spectroscopically. The biological activities of these complexes were also investigated.

A new approach to the effects of isocyanide (CN-R) ligands on the luminescence properties of cycloplatinated(ii) complexes

Cycloplatinated complexes bearing isocyanides were prepared and characterized. The complexes exhibited strong luminescence while the nature of R substituents in isocyanides affected the luminescence characteristics.