Synergistic Effects of Metals in a Promising Ru(II) -Pt(II) Assembly for a Combined Anticancer Approach: Theoretical Exploration of the Photophysical Properties

Chalcogen atom effect on the intersystem crossing kinetic constant of oxygen- and sulfur disubstituted heteroporphyrins

The modulation of the photophysical properties of di-substituted porphyrin rings upon the oxygen and sulfur-for-nitrogen replacement has been investigated at density functional theory (DFT) and its time-dependent formulation (TDDFT). The considered properties range from structural behaviors and excitation energies to spin-orbit coupling (SOC) and nonradiative intersystem kinetic constants. Results show that the SOC strongly increase upon chalcogen substitution and, accordingly, the computed nonradiative kinetic constant also indicate an efficient singlet-triplet intersystem crossing in the sulfur containing macrocycle. The presented results indicate an alternative way to properly modulate the porphyrin's crucial properties for their use in photodynamic therapy, without resorting to the use of heavy atoms.

On the antibacterial photodynamic inactivation mechanism of Emodin and Dermocybin natural photosensitizers: A theoretical investigation

A DFT and TDDFT study has been carried out on monomeric anthraquinones Emodin and Dermocybin (Em, Derm) recently proposed as natural antibacterial photosensitizers able to act also against gram-negative microbes. The computational study has been performed considering the relative amount of neutral and ionic forms of each compound in water, with the variation of pH. The occurrence of both Type I and Type II photoreactions has been explored computing the absorption properties of each species, the spin-orbit coupling constants (SOC), the vertical ionization potentials and the vertical electron affinities. The most plausible deactivation channels leading to the population of excited triplet states have been proposed. Our data indicate Emodin as more active than Dermocybin in antimicrobial photodynamic therapy throughout the Type II mechanism. Our data support a dual TypeI/II activity of the monomeric anthraquinones Emodin and Dermccybin in water, in all the considered protonation states.

Ru(II) Oligothienyl Complexes with Fluorinated Ligands: Photophysical, Electrochemical, and Photobiological Properties

A series of Ru(II) complexes incorporating two 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (4,4'-btfmb) coligands and thienyl-appended imidazo[4,5-f][1,10]phenanthroline (IP-nT) ligands was characterized and assessed for phototherapy effects toward cancer cells. The [Ru(4,4'-btfmb)2(IP-nT)]2+ scaffold has greater overall redox activity compared to Ru(II) polypyridyl complexes such as [Ru(bpy)3]2+. Ru-1T-Ru-4T have additional oxidations due to the nT group and additional reductions due to the 4,4'-btfmb ligands. Ru-2T-Ru-4T also exhibit nT-based reductions. Ru-4T exhibits two oxidations and eight reductions within the potential window of -3 to +1.5 V. The lowest-lying triplets (T1) for Ru-0T-2T are metal-to-ligand charge-transfer (3MLCT) excited states with lifetimes around 1 μs, whereas T1 for Ru-3T-4T is longer-lived (∼20-24 μs) and of significant intraligand charge-transfer (3ILCT) character. Phototoxicity toward melanoma cells (SK-MEL-28) increases with n, with Ru-4T having a visible EC50 value as low as 9 nM and PI as large as 12,000. Ru-3T and Ru-4T retain some of this activity in hypoxia, where Ru-4T has a visible EC50 as low as 35 nM and PI as high as 2900. Activity over six biological replicates is consistent and within an order of magnitude. These results demonstrate the importance of lowest-lying 3ILCT states for phototoxicity and maintaining activity in hypoxia.

Ru(II) Phenanthroline-Based Oligothienyl Complexes as Phototherapy Agents

Ru(II) polypyridyl complexes have gained widespread attention as photosensitizers for photodynamic therapy (PDT). Herein, we systematically investigate a series of the type [Ru(phen)2(IP-nT)]2+, featuring 1,10-phenanthroline (phen) coligands and imidazo[4,5-f][1,10]phenanthroline ligands tethered to n = 0-4 thiophene rings (IP-nT). The complexes were characterized and investigated for their electrochemical, spectroscopic, and (photo)biological properties. The electrochemical oxidation of the nT unit shifted by -350 mV as n = 1 → 4 (+920 mV for Ru-1T, +570 mV for Ru-4T); nT reductions were observed in complexes Ru-3T (-2530 mV) and Ru-4T (-2300 mV). Singlet oxygen quantum yields ranged from 0.53 to 0.88, with Ru-3T and Ru-4T being equally efficient (∼0.88). Time-resolved absorption spectra of Ru-0T-1T were dominated by metal-to-ligand charge-transfer (3MLCT) states (τTA = 0.40-0.85 μs), but long-lived intraligand charge-transfer (3ILCT) states were observed in Ru-2T-4T (τTA = 25-148 μs). The 3ILCT energies of Ru-3T and Ru-4T were computed to be 1.6 and 1.4 eV, respectively. The phototherapeutic efficacy against melanoma cells (SK-MEL-28) under broad-band visible light (400-700 nm) increases as n = 0 → 4: Ru-0T was inactive up to 300 μM, Ru-1T-2T were moderately active (EC50 ∼ 600 nM, PI = 200), and Ru-3T (EC50 = 57 nM, PI > 1100) and Ru-4T (EC50 = 740 pM, PI = 114,000) were the most phototoxic. The activity diminishes with longer wavelengths of light and is completely suppressed for all complexes except Ru-3T and Ru-4T in hypoxia. Ru-4T is the more potent and robust PS in 1% O2 over seven biological replicates (avg EC50 = 1.3 μM, avg PI = 985). Ru-3T exhibited hypoxic activity in five of seven replicates, underscoring the need for biological replicates in compound evaluation. Singlet oxygen sensitization is likely responsible for phototoxic effects of the compounds in normoxia, but the presence of redox-active excited states may facilitate additional photoactive pathways for complexes with three or more thienyl groups. The 3ILCT state with its extended lifetime (30-40× longer than the 3MLCT state for Ru-3T and Ru-4T) implicates its predominant role in photocytotoxicity.

Watching the Interplay between Photoinduced Ultrafast Charge Dynamics and Nuclear Vibrations

Here is presented the ultrafast hole-electron dynamics of photoinduced metal to ligand charge-transfer (MLCT) states in a Ru(II) complex, [Ru(dcbpy)2(NCS)2]4- (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine), a photoactive molecule employed in dye sensitized solar cells. Via cutting-edge computational techniques, a tailored computational protocol is here presented and developed to provide a detailed analysis of the electronic manifold coupled with nuclear vibrations to better understand the nonradiative pathways and the resulting overall dye performances in light-harvesting processes (electron injection). Thus, the effects of different vibrational modes were investigated on both the electronic levels and charge transfer dynamics through a theoretical-computational approach. First, the linear response time-dependent density functional (LR-TDDFT) formalism was employed to characterize excitation energies and spacing among electronic levels (the electronic layouts). Then, to understand the ultrafast (femtosecond) charge dynamics on the molecular scale, we relied on the nonperturbative mean-field quantum electronic dynamics via real-time (RT-) TDDFT. Three vibrational modes were selected, representative for collective nuclear movements that can have a significant influence on the electronic structure: two involving NCS- ligands and one involving dcbpy ligands. As main results, we observed that such MLCT states, under vibrational distortions, are strongly affected and a faster interligand electron transfer mechanism is observed along with an increasing MLCT character of the adiabatic electronic states approaching closer in energy due to the vibrations. Such findings can help both in providing a molecular picture of multidimensional vibro-electronic spectroscopic techniques, used to characterize ultrafast coherent and noncoherent dynamics of complex systems, and to improve dye performances with particular attention to the study of energy or charge transport processes and vibronic couplings.

Tuning the Photophysical Properties of Ru(II) Photosensitizers for PDT by Protonation and Metallation: A DFT Study

Due to their activity, photosensitizers with the Ru(II)-polypyridyl complex structure represent an intriguing class of photodynamic therapy agents used to treat neoplasms. However, their solubility is poor, intensifying experimental research into improving this property. One recently proposed solution is to attach a polyamine macrocycle ring. In this paper, the density functional theory (DFT) and time-dependent DFT (TD-DFT) studies on such derivative were performed to assess the impact of the protonation-capable macrocycle and its ability to chelate transition state metals, as illustrated by the Cu(II) ion, on the expected photophysical activity. These properties were determined by examining ultraviolet-visible (UV-vis) spectra, intersystem conversion, and type I and II photoreactions of all species possibly present in a tumor cell. For comparison purposes the structure devoid of the macrocycle was also examined. The results show that the subsequent protonation of amine groups improves the reactivity, with [H₂L]⁴⁺/[H₃L]⁵⁺ being borderline, whereas complexation appears to weaken the desired photoactivity.

On the origin of photodynamic activity of hypericin and its iodine-containing derivatives

The main photophysical properties, useful for establishing whether hypericin in anionic form and some of its derivatives containing heavy atoms such as iodine, can be proposed for their use in photodynamic therapy, were determined using density functional based computations. The results showed that in the anionic form and in the iodinated derivatives, the absorption wavelength undergoes a bathochromic shift, the singlet-triplet energy gap assumes values ​that allow to excite the oxygen molecule from its ground to the excited singlet state, and that the spin-orbit couplings between singlet and triplet states significantly increase.

Chalcogen Effects in the Photophysical Properties of Dimethylamino-1,8-naphthalimide Dyes Revealed by DFT Investigation

Thionation of carbonyl groups of known dyes is a rapidly emerging strategy to propose an advance toward heavy-atom-free photosensitizers to be used in photodynamic therapy (PDT). The sulfur-for-oxygen replacement has recently proved to enhance the singlet oxygen quantum yield of some existing fluorophores and to shift the absorption band at longer wavelengths. Drawing inspiration from this challenging evidence, the effect of both sulfur- and selenium-for-oxygen replacement in the skeleton of the oxo-4-dimethylamino-1,8-naphthalimide molecule (DMN) has been analyzed by means of a DFT study. The thio- and seleno-derivatives (SDMN and SeDMN, respectively) have been shown to offer the possibility to access a multitude of ISC (intersystem crossing) pathways involved in the triplet deactivation mechanisms with a consequent enhancement of the singlet oxygen production, also arising from the change of orbital type involved in the radiationless ¹nπ* → ³ππ* transitions. Moreover, the change in nature from a ¹ππ* to a ¹nπ* observed in the SeDMN has been revealed to be crucial to reach more clinically useful regions of the spectrum suggesting that the selenium-for-oxygen replacement can be proposed as a strategy to achieve more suitable PDT agents while proposing an advance toward heavy-atom-free PSs.

Synthesis, Characterization, Thermal Analysis, DFT, and Cytotoxicity of Palladium Complexes with Nitrogen-Donor Ligands

Three new palladium complexes ([Pd(DABA)Cl₂], [Pd(CPDA)Cl₂], and [Pd(HZPY)Cl₂]) bearing dinitrogen ligands (DABA: 3,4-diaminobenzoic acid; CPDA: 4-chloro-o-phenylenediamine; HZPY: 2-hydraziniopyridine) were synthesized, characterized, and tested against breast cancer (MCF-7), prostate carcinoma cell line (PC3) and liver carcinoma cell line (HEPG2). [Pd(DABA)Cl₂] complex exhibited the highest inhibition percentage, lying between 68-71%. The hydrolysis mechanism of each palladium complex, the key step preceding the binding to the biological target, as well as their photophysical properties were explored by means of DFT and TDDFT computations. Results indicate a faster hydrolysis process for the Pd(DABA)Cl₂ complex. The computed activation energies for the first and second hydrolysis processes suggest that all the compounds could reach DNA in their monohydrated form.

A Multiscale Free Energy Method Reveals an Unprecedented Photoactivation of a Bimetallic Os(II)-Pt(II) Dual Anticancer Agent

The photoreactivity of relatively large transition metal complexes is often limited to the description of the static potential energy surfaces of the involved electronic states. While useful to grasp some...

Photophysical properties of heavy atom containing tetrasulfonyl phthalocyanines as possible photosensitizers in photodynamic therapy

The excitation energies, singlet-triplet energy gap and spin-orbit coupling constants for Zn-, GaCl-, Pd-, and Pt- tetrasulfonyl phthalocyanines complexes (ZnPc, GaClPc, PdPc, and PtPc) have been computed by using the density functional theory and employing the M06 exchange-correlation functional. Results show that these systems possess interesting photophysical properties, which make them possible photosensitizers to be proposed in photodynamic therapy (PDT). Absorption energies of all the complexes examined have been found falling inside the so-called therapeutic window (550-800 nm). Singlet-triplet energy gap values are higher than those required for the production of cytotoxic molecular oxygen and the spin-orbit coupling constants are such as to ensure an efficient spin orbit intersystem crossing. The obtained data are consistent with the experimental oxygen singlet quantum yields. The platinum complex appears to be the most effective candidate to propose for PDT.

Theoretical insights on type I/II photoreactions of potential Zn(II) polypyridyl photosensitizers for two-photon photodynamic therapy

Large two-photon absorption cross-sections are vital to photosensitizers (PSs) in TP-PDT, which can be used to develop in-depth treatment for diseased cells and minimize the harm to surrounding cells. Here, we conduct a study about photophysical properties of one Ru(II) polypyridyl complex and two designed Zn(II) polypyridyl complexes by means of DFT and TD-DFT methods. The main results are as follows: firstly, the two-photon absorption spectrum of two designed complexes Zn-OMe and Zn-OCOOCH₃ are all within the phototherapeutic window (550-900 nm). Secondly, large SOC values and small energy gaps ΔE_S-T of these complexes guarantee the efficiency of ISC process. Thirdly, their T₁ energy is greater than that required for generating ¹O₂ (0.98 eV) via Type II photoreaction. In addition, the calculated results of vertical electron affinities (VEA) and vertical ionization potentials (VIP) show that these complexes are able to form superoxide ions O₂^(-) via Type I photoreaction. Specifically, both of two designed Zn-centric complexes have larger TPA cross-sections than that of Ru-centric complex. In a word, we are pleased to report two potential photosensitizers with excellent performance and reasonable price for Type I/II photoreactions. We expect our study will offer some theoretical guidance and help in TP-PDT.

Os(II) Oligothienyl Complexes as a Hypoxia-Active Photosensitizer Class for Photodynamic Therapy

Hypoxia presents a challenge to anticancer therapy, reducing the efficacy of many available treatments. Photodynamic therapy is particularly susceptible to hypoxia, given that its mechanism relies on oxygen. Herein, we introduce two new osmium-based polypyridyl photosensitizers that are active in hypoxia. The lead compounds emerged from a systematic study of two Os(II) polypyridyl families derived from 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb) as coligands combined with imidazo[4,5-f][1,10]phenanthroline ligands tethered to n = 0-4 thiophenes (IP-nT). The compounds were characterized and investigated for their spectroscopic and (photo)biological activities. The two hypoxia-active Os(II) photosensitizers had n = 4 thiophenes, with the bpy analogue 1-4T being the most potent. In normoxia, 1-4T had low nanomolar activity (half-maximal effective concentration (EC50) = 1-13 nM) with phototherapeutic indices (PI) ranging from 5500 to 55 000 with red and visible light, respectively. A sub-micromolar potency was maintained even in hypoxia (1% O2), with light EC50 and PI values of 732-812 nM and 68-76, respectively -currently among the largest PIs for hypoxic photoactivity. This high degree of activity coincided with a low-energy, long-lived (0.98-3.6 μs) mixed-character intraligand charge-transfer (3ILCT)/ligand-to-ligand charge-transfer (3LLCT) state only accessible in quaterthiophene complexes 1-4T and 2-4T. The coligand identity strongly influenced the photophysical and photobiological results in this study, whereby the bpy coligand led to longer lifetimes (3.6 μs) and more potent photo-cytotoxicity relative to those of dmb. The unactivated compounds were relatively nontoxic both in vitro and in vivo. The maximum tolerated dose for 1-4T and 2-4T in mice was greater than or equal to 200 mg kg-1, an excellent starting point for future in vivo validation.

Breaking the barrier: an osmium photosensitizer with unprecedented hypoxic phototoxicity for real world photodynamic therapy

Hypoxia presents a two-fold challenge in the treatment of cancer, as low oxygen conditions induce biological changes that make malignant tissues simultaneously more aggressive and less susceptible to standard chemotherapy. This paper reports the first metal-based photosensitizer that approaches the ideal properties for a phototherapy agent. The Os(phen)2-based scaffold was combined with a series of IP-nT ligands, where phen = 1,10-phenanthroline and IP-nT = imidazo[4,5-f][1,10]phenanthroline tethered to n = 0-4 thiophene rings. Os-4T (n = 4) emerged as the most promising complex in the series, with picomolar activity and a phototherapeutic index (PI) exceeding 106 in normoxia. The photosensitizer exhibited an unprecedented PI > 90 (EC50 = 0.651 μM) in hypoxia (1% O2) with visible and green light, and a PI > 70 with red light. Os-4T was also active with 733 nm near-infrared light (EC50 = 0.803 μM, PI = 77) under normoxia. Both computation and spectroscopic studies confirmed a switch in the nature of the lowest-lying triplet excited state from triplet metal-to-ligand charge transfer (3MLCT) to intraligand charge transfer (3ILCT) at n = 3, with a lower energy and longer lifetime for n = 4. All compounds in the series were relatively nontoxic in the dark but became increasingly phototoxic with additional thiophenes. These normoxic and hypoxic activities are the largest reported to date, demonstrating the utility of osmium for phototherapy applications. Moreover, Os-4T had a maximum tolerated dose (MTD) in mice that was >200 mg kg-1, which positions this photosensitizer as an excellent candidate for in vivo applications.

Theoretical exploration of the photophysical properties of two-component RuII-porphyrin dyes as promising assemblies for a combined antitumor effect

Due to the extraordinary success of porphyrins in photodynamic therapy (PDT) and Ru compounds as chemotherapeutics, a series of RuII-porphyrin complexes have recently been synthesized and proposed as promising dual-action therapeutic agents. The results of a careful DFT and TDDFT investigation on four mononuclear pyridyl triphenylporphyrin RuII-arene complexes are herein reported and compared with those obtained for the metal-free derivatives. The investigation aims at shedding light on the modulation of the photophysical properties of the light absorber upon metalation and exploring the hydrolysis process of the RuII-moiety in the presence of the bulky porphyrin unit. Type I and Type II photoreactions were analyzed computing absorption spectra, singlet-triplet energy gaps, spin orbit coupling constants and vertical electron affinity (VEA) along with ionization potentials (VIP) for all the investigated compounds, while the chloride/water exchange reaction kinetics were determined by exploring the first and second aquation reactions of the Ru-moiety. Despite the highly similar photophysical properties displayed by the members of this class of compounds, an analysis of the hydrolysis processes in the dark allows to point out an interesting difference related to the type of pyridylporphyrin isomer and could be a preliminary explanation of the greater phototoxicity experimentally found for 3'-pyridyl substituted compounds.

Hypoxia-Selective Dissociation Mechanism of a Nitroimidazole Nucleoside in a DNA Environment

Photodynamic therapy is a promising approach to treat a variety of superficial tumors and other diseases. One of its major limitations arises from its dependence on molecular oxygen, which decreases the efficiency of the therapy in hypoxia conditions commonly developed by solid tumors. The present contribution reveals the molecular mechanism of a modified thymine bearing a nitroimidazole substituent, a photosensitizer able to produce highly harmful interstrand cross-links in the DNA double strand after irradiation selectively in absence of oxygen. The mechanism is resolved at a fully atomistic and electronic level relying on quantum mechanics (CASPT2, coupled-cluster, DFT, and TD-DFT methods), classical molecular dynamics, and advanced biased QM/MM simulations, revealing an energy penalty of ∼8 kcal/mol for the anionic nitromidazole release. Our findings indicate that the global interstrand cross-link production is driven by a combination of multiple factors, namely, the reverse energy penalty, the diffusion of the nitroimidazole anion, and the further reactivity of the formed thymine radical. On the basis of these results, we also suggest some possible strategies to improve the efficiency of interstrand cross-link production.

Tuning the Optical Properties of Novel Antitumoral Drugs Based on Cyclometalated Iridium(III) Complexes

Most of the current efforts in drug discovery are devoted to the design of molecules able to mitigate side effects by concentrating the biological action in the targeted tissue. One promising strategy is photodynamic therapy, which is based on the in situ generation of reactive singlet oxygen upon radiation exposure. However, such an approach requires the use of an efficient photosensitizer. This contribution deals with the optical properties of an Ir(III) complex, [Ir(pbz)₂(N^N)] (pbz = 2-phenylbenzimidazole; N^N = methyl 1-butyl-2-pyridyl-benzimidazole-5-carboxylate), which has recently been shown to exhort a strong photoactivity, but still needs further improvements to reach clinical applications. We performed density functional theory calculations at the M06, PBE0, ωB97xD, and CAM-B3LYP levels to predict the impact of introducing electron donor-acceptor groups into the nature of the lowest excited states. The simulations performed demonstrate that the presence of a NH₂ at the pbz ligand and a NO₂ group at the N^N ligand yield a bathochromic shift of absorption spectrum. We report the most sensitive positions to tune the optical signatures of this family of complexes.

Theoretical insight into the photophysical properties of long-lifetime Ir(iii) and Rh(iii) complexes for two-photon photodynamic therapy

Two-photon photodynamic therapy (TP-PDT) plays crucial roles in curing tumors because it involves deep penetration of drugs into the tissue and has minimal damage to the surrounding cells.

Theoretical insight into joint photodynamic action of a gold(i) complex and a BODIPY chromophore for singlet oxygen generation

Inclusion of a heavy gold atom in a peripheral position of BODIPY is enough to promote ISC.

Synthesis and Computational Study of a Pyridylcarbene Fe(II) Complex: Unexpected Effects of fac/ mer Isomerism in Metal-to-Ligand Triplet Potential Energy Surfaces

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial ( fac) and meridional ( mer) isomers' potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding ³MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet ³MC region is excluded, we identify the enlargement of iron-nitrogen bonds as the main normal modes driving the excited-state decay.

BODIPY for photodynamic therapy applications: computational study of the effect of bromine substitution on 1O2 photosensitization

Density functional theory and its time-dependent extension (DFT, TDDFT) were employed to establish the feasibility of using a series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) in photodynamic therapy. Their absorption electronic spectra, singlet-triplet energy gaps, and spin-orbit matrix elements were computed and are discussed here. The effects of bromine substitution on the photophysical properties of BODIPY were elucidated. The investigated compounds were found to possess different excited triplet states that lie below the energy of the bright excited singlet state (S₁ or S₂), depending on the positions occupied by the bromine atoms. The computed spin-orbit matrix elements for the radiationless intersystem crossing S_n →  T_m and the relative singlet-triplet energy gaps allowed the prediction of plausible nonradiative decay pathways for the production of singlet excited molecular oxygen, the key cytotoxic agent in photodynamic therapy. Graphical Abstract The photophysical properties affected by the presence of bromine atoms in different positions of a BODIPY core have been here elucidated. In particular it has been found that SOC values strongly depend on the position of heavy atoms into the BODIPY core, suggesting positions 1 and 7 as the best ones to enhance the ISC kinetics.

Theoretical Insights into the Switching Off/On of 1 O2 Photosensitization in Chemicontrolled Photodynamic Therapy

Density Functional Theory and time-dependent (TD) DFT calculations were carried out for recently reported 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based photosensitizers (PSs) that could be activated by reactive oxygen species (ROS) to generate ¹ O₂ specifically in target tissues. To assess the applicability of the compounds as activatable PSs (a-PSs) in photodynamic therapy, absorption wavelengths; singlet-triplet energy gaps; and spin-orbit matrix elements for the radiationless transition, S_n →T_m , were investigated. A TD-DFT qualitative analysis indicated that only a Br-substituted BODIPY derivative with the chromanol ring of α-tocopherol linked by methylene functioned as an a-PS. The chromanol ring promotes photoinduced electron transfer to the BODIPY unit that reduces the probability of intersystem crossing and triplet-state population, and can turn off ¹ O₂ photosensitization. Therefore, ¹ O₂ photosensitization can be switched on only in target cells in which the chromanol ring is oxidized by ROS. The oxidation reaction pathways of the most promising derivative, by either ¹ O₂ or cumyloxyl radical as typical ROS, have been examined to reveal that oxidation by the cumyloxyl radical is more effective than that by ¹ O₂ .

Synergistic Effects in PtII -Porphyrinoid Dyes as Candidates for a Dual-Action Anticancer Therapy: A Theoretical Exploration

The combination of a photosensitizer (PS) with a cisplatin-like unit represents a challenging strategy to increase the effectiveness of photodynamic therapy and to afford a dual-action anticancer treatment. Recently, new tetra-Pt^II -porphyrin conjugates have been proposed as promising multitarget agents. To reveal the effect of the Pt^II center on the chemical and physical properties of the PS and to explore the effect of the PS on the activation mechanism of Pt^II ligand before reaching its biological target, we carried out a first-principle investigation on these tetra-Pt^II -porphyrin conjugates. To propose a further advance in this novel field and to gain useful insights for the design of new, more efficient Pt^II -PS conjugates, we introduced structural modifications into the porphyrin dye, which involved the synthesis of the tetra-Pt^II -chlorin and tetra-Pt^II -bacteriochlorin derivatives. Results showed that the designed dyes better met the criteria to be successful in a dual-action therapy, as they displayed improved optical properties and reduced the hydrolysis rate of the Pt^II moiety, the latter being a desirable feature to avoid many side reactions of the conjugate during their transport to the biological target.

Exploring the activity of a polyazine bridged Ru(ii)–Pt(ii) supramolecule in F98 rat malignant glioma cells

[(Ph₂phen)₂Ru(dpp)PtCl₂]Cl₂exhibits multiple light-dependent cytotoxicity pathways that preferentially target DNA, offering promise for the development of novel photodynamic therapy agents.