Photodynamic Applications of New Imidazo[4,5‐f][1,10]phenanthroline Oxidovanadium(IV) Complexes: Synthesis, Photochemical, and Cytotoxic Evaluation

Pyrenyl-Substituted Imidazo[4,5-f][1,10]phenanthroline Rhenium(I) Complexes with Record-High Triplet Excited-State Lifetimes at Room Temperature: Steric Control of Photoinduced Processes in Bichromophoric Systems

Photochemical applications based on intermolecular photoinduced energy triplet state transfer require photosensitizers with strong visible absorptivity and extended triplet excited-state lifetimes. Using a bichromophore approach, two Re(I) tricarbonyl complexes with 2-(1-pyrenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (pyr-imphen) and 1-(4-(methyl)phenyl)-2-(1-pyrenyl)-imidazo[4,5-f][1,10]phenanthroline (pyr-tol-imphen) showing extraordinary long triplet excited states at room temperature (>1000 μs) were obtained, and their ground- and excited-state properties were thoroughly investigated by a wide range of spectroscopic methods, including femtosecond transient absorption (fs-TA). It is worth noting that the designed [ReCl(CO)3(pyr-imphen)] (1) and [ReCl(CO)3(pyr-tol-imphen)] (2) complexes form a unique pair differing in the mutual chromophore arrangement due to introduction of a 4-(methyl)phenyl substituent into the imidazole ring at the H1-position, imposing an increase in the dihedral angle between the pyrene and {ReCl(CO)3(imphen)} chromophores. The magnitude of the electronic coupling between the pyrene and {ReCl(CO)3(imphen)} chromophores was found to be an efficient tool to tune the photophysical properties of 1 and 2. The usefulness of designed Re(I) compounds as triplet photosensitizers was successfully verified by examination of their abilities for 1O2 generation and triplet-triplet annihilation upconversion. The phosphorescence lifetimes, ∼1800 μs for 1 and ∼1500 μs for 2, are the longest lifetimes reported for Re(I) diimine carbonyl complexes in solution at room temperature.

In Vitro and In Vivo Biological Activities of Dipicolinate Oxovanadium(IV) Complexes

The work is focused on anticancer properties of dipicolinate (dipic)-based vanadium(IV) complexes [VO(dipic)(N^∩N)] bearing different diimines (2-(1H-imidazol-2-yl)pyridine, 2-(2-pyridyl)benzimidazole, 1,10-phenanthroline-5,6-dione, 1,10-phenanthroline, and 2,2'-bipyridine), as well as differently 4,7-substituted 1,10-phenanthrolines. The antiproliferative effect of V(IV) systems was analyzed in different tumors (A2780, HCT116, and HCT116-DoxR) and normal (primary human dermal fibroblasts) cell lines, revealing a high cytotoxic effect of [VO(dipic)(N^∩N)] with 4,7-dimethoxy-phen (5), 4,7-diphenyl-phen (6), and 1,10-phenanthroline (8) against HCT116-DoxR cells. The cytotoxicity differences between these complexes can be correlated with their different internalization by HCT116-DoxR cells. Worthy of note, these three complexes were found to (i) induce cell death through apoptosis and autophagy pathways, namely, through ROS production; (ii) not to be cytostatic; (iii) to interact with the BSA protein; (iv) do not promote tumor cell migration or a pro-angiogenic capability; (v) show a slight in vivo anti-angiogenic capability, and (vi) do not show in vivo toxicity in a chicken embryo.

Red light-activable biotinylated copper(II) complex-functionalized gold nanocomposite (Biotin-Cu@AuNP) towards targeted photodynamic therapy

We report the synthesis and characterization of red-light activable gold nanoparticle functionalized with biotinylated copper(II) complex of general molecular formula, [Cu(L³)(L⁶)]-AuNPs (Biotin-Cu@AuNP), where L³ = N-(3-((E)-3,5-di-tert-butyl-2-hydroxybenzylideneamino)-4-hydroxyphenyl)-5-((3aS,4S,6aR)-2-oxo-hexahydro-1H-thieno[3,4-d]imidazol-4-yl)pentanamide, L⁶ = 5-(1,2-dithiolan-3-yl)-N-(1,10-phenanthrolin-5-yl)pentanamide, which was explored for their photophysical, theoretical and photo-cytotoxic potentials. The nanoconjugate exhibits differential uptake in biotin positive and biotin negative cancer cells as well as normal cells. The nanoconjugate also shows remarkable photodynamic activity against biotin positive A549 (IC₅₀: 13 μg/mL in red light; >150 μg/mL in dark) and HaCaT (IC₅₀: 23 μg/mL in red light; >150 μg/mL in dark) cells under red light (600-720 nm, 30 Jcm^-2) irradiation, with significantly high photo-indices (PI>15). The nanoconjugate is less toxic to HEK293T (biotin negative) and HPL1D (normal) cells. Confocal microscopy confirms preferential mitochondrial and partly cytoplasmic localization of Biotin-Cu@AuNP in A549 cells. Several photo-physical and theoretical studies reveal the red light-assisted generation of singlet oxygen (¹O₂) (Ф (¹O₂) =0.68) as a reactive oxygen species (ROS) which results in remarkable oxidative stress and mitochondrial membrane damage, leading to caspase 3/7-dependent apoptosis of A549 cells. Overall, the nanocomposite (Biotin-Cu@AuNP) exhibiting red light-assisted targeted photodynamic activity has emerged as the ideal next generation PDT agents.

Impact of the Anthryl Linking Mode on the Photophysics and Excited-State Dynamics of Re(I) Complexes [ReCl(CO)3(4′-An-terpy-κ2N)]

Rhenium(I) complexes with 2,2′:6′,2″-terpyridines (terpy) substituted with 9-anthryl (1) and 2-anthryl (2) were synthesized, and the impact of the anthryl linking mode on the ground- and excited-state properties of resulting complexes [ReCl(CO)₃(4′-An-terpy-κ²N)] (An—anthryl) was investigated using a combination of steady-state and time-resolved optical techniques accompanied by theoretical calculations. Different attachment positions of anthracene modify the overlap between the molecular orbitals and thus the electronic coupling of the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores. Following the femtosecond transient absorption, the lowest triplet excited state of both complexes was found to be localized on the anthracene chromophore. The striking difference between 1 and 2 concerns the triplet-state formation dynamics. A more planar geometry of 2-anthryl-terpy (2), and thus better electronic communication between the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores, facilitates the formation of the ³An triplet state. In steady-state photoluminescence spectra, the population ratio of ³MLCT and ³An was found to be dependent not only on the anthryl linking mode but also on solvent polarity and excitation wavelengths. In dimethyl sulfoxide (DMSO), compounds 1 and 2 excited with λ_exc > 410 nm show both ³MLCT and ³An emissions, which are rarely observed. Additionally, the abilities of the designed complexes for ¹O₂ generation and light emission under the external voltage were preliminary examined.

The impact of the anthryl linking mode on the ground- and excited-state properties of [ReCl(CO)₃(4′-An-terpy-κ²N)] with 2,2′:6′,2″-terpyridines (terpy) substituted with 9-anthryl (1) and 2-anthryl (2) was thoroughly investigated. Different attachment positions of anthracene were evidenced to modify the overlap between the molecular orbitals and electronic coupling of the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores and thus the optical properties of the resulting complexes. The striking difference between 1 and 2 was demonstrated in the triplet-state formation dynamics.

La(iii)–curcumin-functionalized gold nanocomposite as a red light-activatable mitochondria-targeting PDT agent

Functionalization of La(iii)–curcumin to gold nanoparticles resulted in remarkable red-shifted UV-visible absorption and exhibited remarkable differential photodynamic ability towards cancer cells upon red-light activation.

Iron(III) Complex-Functionalized Gold Nanocomposite as a Strategic Tool for Targeted Photochemotherapy in Red Light

Iron(III)-phenolate/carboxylate complexes exhibiting photoredox chemistry and photoactivated reactive oxygen species (ROS) generation at their ligand-to-metal charge-transfer (LMCT) bands have emerged as potential strategic tools for photoactivated chemotherapy. Herein, the synthesis, in-depth characterization, photochemical assays, and remarkable red light-induced photocytotoxicities in adenocarcinomic human immortalized human keratinocytes (HaCaT) and alveolar basal epithelial (A549) cells of iron(III)-phenolate/carboxylate complex of molecular formula, [Fe(L¹)(L²)] (1), where L¹ is bis(3,5 di-tert-butyl-2-hydroxybenzyl)glycine and L² is 5-(1,2-dithiolan-3-yl)-N-(1,10-phenanthroline-5-yl)pentanamide, and the gold nanocomposite functionalized with complex 1 (1-AuNPs) are reported. There was a significant red shift in the UV-visible absorption band on functionalization of complex 1 to the gold nanoparticles (λ_max: 573 nm, 1; λ_max: 660 nm, 1-AuNPs), rendering the nanocomposite an ideal candidate for photochemotherapeutic applications. The notable findings in our present studies are (i) the remarkable cytotoxicity of the nanocomposite (1-AuNPs) to A549 (IC₅₀: 0.006 μM) and HaCaT (IC₅₀: 0.0075 μM) cells in red light (600-720 nm, 30 J/cm²) while almost nontoxic (IC₅₀ > 500 μg/mL, 0.053 μM) in the dark, (ii) the nontoxicity of 1-AuNPs to normal human diploid fibroblasts (WI-38) or human peripheral lung epithelial (HPL1D) cells (IC₅₀ > 500 μg/mL, 0.053 μM) both in the dark and red light signifying the target-specific anticancer activity of the nanocomposite, (iii) localization of 1-AuNPs in mitochondria and partly nucleus, (iv) remarkable red light-induced generation of reactive oxygen species (ROS: ¹O₂, ^•OH) in vitro, (v) disruption of the mitochondrial membrane due to enhanced oxidative stress, and (vi) caspase 3/7-dependent apoptosis. A similar cytotoxic profile of complex 1 was another key finding of our studies. Overall, our current investigations show a new red light-absorbing iron(III)-phenolate/carboxylate complex-functionalized gold nanocomposite (1-AuNPs) as the emerging next-generation iron-based photochemotherapeutic agent for targeted cancer treatment modality.