Singlet Oxygen Pathway Research Articles

Improving the non-free radical activated peroxymonosulfate capability of sludge biochar through sacrificial template method: Efficacy and mechanism evaluation

Improving the non-free radical activation ability of persulfate has great significance for the degradation of persistent contaminant in complex water environments. Here, special nitrogen-doped sludge-based catalysts for peroxymonosulfate (PMS) activation were developed through sacrificial template method by employing polymer surfactant (PS) as template agent. The PS usage and acid etching significantly improved the catalyst’s non-radical activation performance for PMS, the contribution of singlet oxygen (1O2) and electron transfer pathway (ETP) to bisphenol A (BPA) removal could be well matched to 72.31 % and 27.69 % in NCF-1/PMS system, respectively. Such non-radical activation characteristic ensures that NCF-1/PMS systems exhibit super oxidation ability of BPA (Kobs = 0.3714 min−1) and strong anti-interference ability to environmental matrixes via simultaneously enhancing both 1O2 and ETP. The critical roles of graphitic N and as-formed Si-O-C sites in activating PMS were revealed through electrochemical analysis, in-situ characterization technology and theoretical calculations. Density functional theory calculations confirmed that the PS addition and desilication process reduced the adsorption energy of the NCF-1 for PMS, and achieved lower energy barrier to cleave the O–H bond of NCF-1/PMS complex, significantly achieving the surge in the major active species of 1O2. This study provides novel regulatory strategies to modulate the non-radical path for persistent pollutant treatment.

In situ N-doping engineered biochar catalysts for oxidation degradation of sulfadiazine via nonradical pathways: Singlet oxygen and electron transfer

Understanding the structure of non-metallic heteroatom-doped carbon catalysts and the subsequent degradation of new pollutants is crucial for designing more efficient carbon catalysts. Environmentally friendly in situ N-doped biochar catalysts were prepared for peroxymonosulfate (PMS) activation and sulfadiazine (SDZ) degradation. The acid washing process and calcination temperature of catalyst increased π-π* shake up, graphitic N percentage, specific surface area and defects, promoting the transformation of pollutant degradation mechanism from radical pathway to non-radical pathway. 100 % of the SDZ with the initial concentration of 10 mg/L was quickly degraded within 60 min using 0.2 g/L catalysts and 0.5 mM PMS. Excellent catalytic performance was attributed to singlet oxygen and electron transfer-dominated non-radical pathways. The four potential degradation pathways of SDZ were proposed, and toxicity predication indicated that overall biotoxicity of the intermediates during SDZ degradation was decreased. This research deepens our understanding of the mechanisms of non-radical pathways and guides the synthesis of carbon-based catalysts.

Efficient degradation of acetaminophen by activated peroxymonosulfate using Mn/C composites: Performance and mechanism

The synthesis of manganese oxide (MnOx) composites often leads to particle aggregation and the formation of larger metal nanoparticles, which greatly reduces the efficient use of manganese (Mn) as catalyst. Additionally, the structurally unstable Mn matrix composites increase the risk of metal precipitation during the reaction process. To address these issues, a series of Mn-carbon (Mn/C) co-doped composites (Mn@CA400, Mn@CA500, and Mn@CA600) were synthesized using potassium permanganate (KMnO4) and citric acid (CA) as precursors. The Mn@CA400 exhibited exceptional catalytic activity towards peroxymonosulfate (PMS) resulting in complete removal of 10 mg/L acetaminophen (ACT) within 10 min. Furthermore, Mn@CA400 demonstrated significant selectivity and resistance in complex matrices to interference for pollutant degradation. The results showed that Mn@CA400 exhibited higher catalytic activity and better stability compared with the reported Mn-based composites. Quenching experiments, electron paramagnetic resonance (EPR), solvent exchange experiments, and electrochemical analysis confirmed that singlet oxygen (1O2) and electron transfer pathways were responsible for ACT degradation. The mechanism analysis revealed that ACT could be degraded under three pathways. The current study not only presents an effective method to solve the problem of metal agglomeration and precipitation in the synthesis of MnOx composites but also establishes an efficient and selective oxidation system. In addition, it greatly improves the understanding of PMS activation and ACT degradation mechanisms.

Peroxymonosulfate activation by cobalt-doped ferromanganese magnetic oxides through singlet oxygen and radical pathways for efficient sulfadiazine degradation.

In this paper, cobalt-doped MnFe2O4 (CMFO-0.4) with oxygen vacancies was successfully synthesised by the sol-gel method and applied as a high-performance catalyst for the activation of peroxomonosulfate (PMS). The catalyst showed an excellent catalytic effect for the degradation of sulfadiazine (SDZ) by activated PMS, and the degradation rate can reach 100% in 10 minutes. The effects of different conditions on the degradation of SDZ were investigated, and it was determined that the optimal concentrations of catalyst and PMS were 0.2 g L-1 and 1 mM, respectively, and had good degradation effects in the pH 5-11 range. Free radical quenching experiments, XPS, and electron paramagnetic resonance (EPR) analyses revealed the presence of hydroxyl radicals (˙OH), sulphate radicals (SO4˙-), singlet oxygen (1O2), and superoxide radicals (˙O2 -) in the CMFO-0.4/PMS system, with 1O2 being the main reactive oxygen species (ROS). In addition, CMFO-0.4 has good reusability and adaptability to the presence of other substances.

Length-independent and selective sensing of CCG trinucleotide repeat foldings by a monovalency-binding fluorogenic probe

Tandem CNG (N = C, T, A, G) DNA trinucleotide repeats (TNRs) are the main expansion to cause severe neurodegenerative diseases. Small molecule ligands with a capacity to sense the CNG TNRs foldings have received considerable attention because of therapeutic and diagnostic perspectives. This requires development of effectual ligands that have a preference to a particular CNG TNRs foldings. However, the previously developed ligands using hydrogen-bonding interaction as the dominantly driving force usually exhibit a multimolecular binding behavior with TNRs. This multivalency interaction usually compromises the sensing selectivity towards CNG TNRs. Herein, we reported a monovalency probe of pseudohypericin (PHP) to selectively sense only the CCG TNRs foldings by a signal-on fluorescence, while total signal-off responses were otherwise observed for CTG, CAG, and CGG TNRs. In addition, the monovalency association of PHP to CCG TNRs is independent of the repeat length. This selective sensing occurs in the loop region, in which a triad is formed between the terminal Watson-Crick CG base pair and the mismatched cytosine adopting an extrahelical conformation. We believe that the specific interaction of PHP with the triad is in charge of the selective association of CCG TNRs over other counterparts. Furthermore, the sensitivity to CCG TNRs can be strengthened by the repeat-activated photocatalysis activity of the TNRs-based DNAzymes via a singlet oxygen (1O2) pathway. Our work offers an alternative way to sense CNG TNRs with a high selectivity and promising applications in developing TNRs-based sensors.

Synergizing electron transfer with singlet oxygen to expedite refractory contaminant mineralization in peroxymonosulfate based heterogeneous oxidation system

This work explored the feasibility of synergizing singlet oxygen (1O2) and electron transfer pathway (ETP) during catalytic decomposition of peroxymonosulfate to advance the refractory pollutant mineralization. N doping strategy was employed to synthesize Mn-C-N catalyst with two independent catalytic sites. The results showed that the contribution of 1O2 and ETP to diclofenac removal could be well matched to 56% and 44% in Mn-C-N/PMS oxidation system, respectively. Mechanism studies revealed that 1O2 would generate intermediate products with low ELUMO, which were rapidly transformed via ETP and finally resulted in improved mineralization performance. Under 0.2 g/L Mn-C-N, 50 mg/L diclofenac, 0.4 g/L peroxymonosulfate, and actual water quality conditions, about 100% removal (15 min) and 70% mineralization efficiency (1 h) was achieved. The above non-radical oxidation system was effective for treating livestock wastewater and secondary effluent. This work prospects the synergy of non-radicals for remediating refractory contaminants-laden wastewater.

Atomically dispersed vanadium on g-C3N4 for effective ciprofloxacin degradation via peroxymonosulfate activation: Insights on the nonradical pathway and V redox cycles

This work describes the preparation and characterization of atomically-dispersed V on graphitic carbon nitride (g-C3N4, CN) via a facile calcination method. The V atoms were found to coordinate with the –N and –O in the triazine units of g-C3N4. The catalytic activity of the as-prepared materials was evaluated in ciprofloxacin (CIP) degradation via peroxymonosulfate (PMS) activation. It was found that the presence of V (0.10 at%) noticeably enhanced the catalytic activity of CN, and the V-CN catalyst showed substantial tolerance towards pH changes, interfering species, various water sources, and different antibiotics. Chemical scavenging and electrochemical methods illustrated that the V-CN/PMS/CIP system encompassed of a nonradical electron-transfer pathway (50.0%), singlet oxygen (1O2) pathway (30.8%), sulfate radical (SO4•-) generation (11.5%), and other reactive species (7.7%), and the activation process was due to the V-redox cycles. Peculiarly, V(IV)/V(III) redox cycles were responsible for the nonradical electron-transfer pathway while V(V)/V(IV) redox cycles were behind the SO4•- and 1O2 generation. Additionally, comprehensive investigation on the catalytic affinity of V-CN towards different antibiotics elucidated that the electrochemical properties of the organic pollutant play a major role in the electron-transfer direction during nonradical activation. Lastly, the CIP degradation pathway was proposed, and the toxicity of its degradation intermediates was estimated. Overall, this work deepens the understanding on the potential of V-based materials in catalytic PMS activation.

Enhanced degradation of cefalexin using Co2SnO4@rGO as an effective peroxymonosulfate activator in hybrid ozonation system

This study successfully developed a nanocomposite catalyst (Co2SnO4 @rGO) at optimal composite ratio of 2:1 between Co2SnO4 and GO for effectively activation of peroxymonosulfate (PMS) to degrade cefalexin (CFX) from water by hybrid ozonation system (O3/Co2SnO4 @rGO/PMS). The CFX removal efficiency was compared in three oxidation systems, including O3, Co2SnO4 @rGO/PMS and O3/Co2SnO4 @rGO/PMS under various operational conditions. The effect of co-existing anions and scavengers was studied to determine the CFX removal mechanisms. The characteristics of catalyst were analyzed using SBET, SEM, EDS and mapping, XRD, FTIR and pHPZC. The results illustrated that supplementation of O3 into Co2SnO4 @rGO/PMS system exhibited the highest degradation and mineralization efficiencies of CFX, reaching 99.93% and 67.03%, respectively under optimal operational conditions. At this condition, the CFX degradation and mineralization rates in O3/ Co2SnO4 @rGO/PMS system were higher than those in Co2SnO4 @rGO/PMS system by 2.8 and 1.32 times, respectively, thanks to synergistic effect of O3 and Co2SnO4 @rGO/PMS in the same reactor. The CFX removal mechanisms were proposed through both pathways: non-radical and radical pathway. The non-radical mechanism was through singlet oxygen (1O2) and radical pathway was via the free radicals of *OH, *SO4- and *O2. The scavenging experiments further confirmed CFX removal mechanism was through both non-radical and radical pathways. Among them, the 1O2 was predominately species in removal of CFX. Besides, the Co2SnO4 @rGO catalyst exhibited a high reusability over four consecutive catalytic cycles. These findings demonstrated the occurrence of O3 and Co2SnO4 @rGO in hybrid ozonation system effectively activated PMS to enhance CFX removal from wastewater.

Enhancement of peroxymonosulfate activation by humic acid-modified sludge biochar: Role of singlet oxygen and electron transfer pathway

Sludge biochar (SBC) modified by humic acid (HA) was used to activate peroxymonosulfate (PMS) for degrading naproxen (NPX). HA-modified biochar (SBC-50HA) boosted the catalytic performance of SBC for PMS activation. The SBC-50HA/PMS system had good reusability and structural stability, and was unaffected by complex water bodies. The results of Fourier transform infrared (FTIR) and X-ray diffraction spectroscopy (XPS) indicated that graphitic carbon (CC), graphitic N, and C–O on SBC-50HA played a vital part on the removal of NPX. The key role of non-radical pathways such as singlet oxygen (1O2) and electron transfer in the SBC-50HA/PMS/NPX system was verified by inhibition experiments, electron paramagnetic resonance (EPR), electrochemistry, and PMS consumption. The possible degradation pathway of NPX was proposed by density functional theory (DFT) calculations, and the toxicity of NPX and its degradation intermediates were evaluated.

Nanocarbon shells with self-inherent N, P derived from chlorella pyrenoidosa for aqueous catalytic ozonation: nonradical-dominated mechanisms

Nanocarbon shells with self-inherent N, P derived from waste chlorella pyrenoidosa (CP) as N/P/C precursors were prepared for the first time using a one-step pyrolysis method to remove ibuprofen (IBU) for catalytic ozonation. The CP at 1000 °C (NPC1000) had superior catalytic ozonation performance over MnO2, Al2O3, and g-C3N4. The catalytic ozonation process follows a nonradical oxidation mechanism via surface adsorbed atomic oxygen (*Oad), singlet oxygen (1O2) and electron transfer pathway. The result indicated that graphitic N, pyridinic N and C3PO functional groups were the major active sites based on the correlation between material structure and catalytic performance. Furthermore, the catalytic activity has little impact on the removal of IBU wastewater containing inorganic anions and humic acid (HA). This study opens new applications for microalgae-derived biocarbon materials and provides a new insight into the mechanism of metal-free heterogeneous ozone catalyst.

Photoacclimation of photosystem II photochemistry induced by rose Bengal and methyl viologen in Nannochloropsis oceanica.

The photosynthetic apparatus is a major reactive oxygen species (ROS) proliferator, especially in high-light environments. The role of ROS in photoinhibition and photoacclimation mechanisms has been extensively explored, primarily in model plant species. However, little work has been performed on the topic in non-Archaeplastida organisms, such as the model heterokont species Nannochloropsis oceanica. To investigate the photoacclimation and damaging impact of singlet oxygen and superoxide anions on the photosynthetic apparatus of N. oceanica, we subjected cells to two doses of methyl viologen and rose bengal. Significant findings: Rose bengal (a singlet-oxygen photosensitizer) induced changes to the photosynthetic apparatus and PSII photochemistry mirroring high-light-acclimated cells, suggesting that singlet-oxygen signaling plays a role in the high-light acclimation of PSII. We further suggest that this singlet-oxygen pathway is mediated outside the plastid, given that rose bengal caused no detectable damage to the photosynthetic apparatus. Methyl viologen (a superoxide-anion sensitizer) induced an enhanced non-photochemical quenching response, similar to what occurs in high-light-acclimated cells. We propose that superoxide anions produced inside the plastid help regulate the high-light acclimation of photoprotective pathways.

Electron transfer mechanism of peroxydisulfate activation by sewage sludge-derived biochar for enhanced degradation of sulfamethoxazole

The electron-transfer process is the main pathway occurring in the BC800/PDS system and the singlet oxygen pathway is determined to have little contribution to the oxidation of SMX.

Photoswitchable Solubility of Fullerene-Doped Polymer Thin Films

Controlling polymer film solubility is of fundamental and practical interest and is typically achieved by synthetically modifying the polymer structure to insert reactive groups. Here, we demonstrate that the addition of fullerenes or its derivatives (C60 or phenyl-C61-butyric acid methyl ester, PCBM) to polymers, followed by ultraviolet (UV) illumination can change the film solubility. Contrary to most synthetic polymers which dissolve in organic solvents but not in water, the fullerene-doped polymer films (such as polystyrene) can dissolve in water, yet remain stable in organic solvents. This photoswitchable solubility effect is not observed in either film constituents individually and derives from a synergy of photochemistries. Firstly, polymer photooxidation generates macroradicals which crosslink with radical-scavenging PCBM, thereby contributing to the films' insolubility in organic solvents. Secondly, light exposure enhances polymer photooxidation in the presence of PCBM via the singlet oxygen pathway. This results in polymer backbone scission and formation of photooxidised products which can form hydrogen bonds with water, both contributing to water solubility. Nevertheless, the illuminated doped polymer thin films are mechanically robust, exhibiting significantly increased modulus and density compared to their pristine counterpart, such that they can remain intact, even upon sonication in conventional organic solvents. We further demonstrate the application of this solubility-switching effect in dual tone photolithography, via a facile, economical and environmentally benign solution-processing route made possible by the photoactive nature of polymer-PCBM thin films.

Mechanisms of Photosensitized Lipid Oxidation and Membrane Permeabilization

Lipid oxidation encompasses chemical transformations affecting animals and plants in many ways, and light is one of the most common triggers of lipid oxidation in our habitat. Still, the molecular mechanisms and biological consequences of photoinduced lipid oxidation were only recently understood at the molecular level. In this review, we focus on the main mechanisms of photosensitized lipid oxidation and membrane permeabilization, dissecting the consequences of both singlet oxygen and contact-dependent pathways and discussing how these reactions contribute to chemical and biophysical changes in lipid membranes. We aim to enable scientists to develop novel and more efficient photosensitizers in photomedicine, as well as better strategies for sun protection.

A Novel Theranostic Nanoprobe for In Vivo Singlet Oxygen Detection and Real-Time Dose-Effect Relationship Monitoring in Photodynamic Therapy.

Singlet oxygen, as the main member of reactive oxygen species, plays a significant role in cancer photodynamic therapy. However, the in vivo real-time detection of singlet oxygen remains challenging. In this work, a Förster resonance energy transfer (FRET)-based upconversion nanoplatform for monitoring the singlet oxygen in living systems is developed, with the ability to evaluate the in vivo dose-effect relationship between singlet oxygen and photodynamic therapy (PDT) efficacy. In details, this nanoplatform is composed of core-shell upconversion nanoparticles (UCNPs), photosensitizer MC540, NIR dye IR-820, and poly(acryl amine) PAA-octylamine, where the UCNPs serve as an energy donor while IR-820 serves as an energy acceptor. The nanoparticles are found to sensitively reflect the singlet oxygen levels generated in the tumor tissues during PDT, by luminescence intensity changes of UNCPs at 800 nm emission. Furthermore, it could also enable tumor treatment with satisfactory biocompatibility. To the best knowledge, this is the first report of a theranostic nanoplatform with the ability to formulate the in vivo dose-effect relationship between singlet oxygen and PDT efficacy and to achieve tumor treatment at the same time. This work might also provide an executable strategy to evaluate photodynamic therapeutic efficacy based on singlet oxygen pathway.

Enhancing Rose Bengal-Photosensitized Protein Crosslinking in the Cornea.

Rose bengal (RB)-photosensitized protein crosslinking has been proposed for several applications in the eye. This study identifies oxygen-dependent and oxygen-independent mechanistic pathways in cornea for RB-photosensitized crosslinking to enhance its efficiency for ocular treatments. Rabbit corneas ex vivo were stained with 1 mM RB and irradiated at 532 nm. RB photobleaching, measured by spectrophotometry and linear tensile strength testing, were performed with and without oxygen present. The effects of sodium azide, D2O, arginine, and ascorbate were used to discriminate between mechanisms involving energy transfer (forming singlet oxygen) and electron transfer (forming radical ions). The influence of corneal depth on RB photobleaching was determined using inclined corneal incisions. RB photobleaching was greater in the presence than the absence of oxygen, enhanced by D2O and partially inhibited by azide, indicating a singlet oxygen pathway. Photobleaching without oxygen was enhanced by arginine and ascorbate and accompanied by a shift in the absorption to shorter wavelengths, suggesting that electron transfer initiates RB photodecomposition. The RB-photosensitized tensile strength increase in air was enhanced by D2O and inhibited by azide. In an O2-free environment, arginine was required for an increase in tensile strength, which matched that attained by irradiation in air without arginine, suggesting an efficient electron transfer pathway. Rapid photobleaching was observed below 80 to 120 μm only when arginine was present. These results indicate that RB photosensitizes crosslinking in cornea by both singlet oxygen and electron transfer mechanisms and that adding enhancers may increase the efficiency of this treatment.

Depicting the DNA binding and photo-nuclease ability of anti-mycobacterial drug rifampicin: A biophysical and molecular docking perspective

Rifampicin, an important member of ansamycin family, exhibits various biological activities. It is frequently used for the treatment of tuberculosis and leprosy. Recently, its interaction with protein is evidenced. But, its interaction with DNA is still unknown. Whether, exhibition of anti-cancer activity of rifampicin is associated with DNA-cleavage activity is also unknown. In this study, an attempt has been taken to understand these two unknown aspects. Spectroscopic studies indicated that rifampicin binds to CT-DNA with a binding constant of ~5.22 × 105 M−1. Several independent experiments like CD analysis, competitive displacement experiments and viscosity measurements revealed that rifampicin intercalates into the CT-DNA. Molecular docking studies corroborate this fact and depicted that this drug binds to the GC-rich region of DNA through multiple hydrogen bonding having the relative binding energy of −9.21 kcal mol−1. Besides, DNA binding ability, rifampicin causes the photo-cleavage of pUC19 DNA via singlet oxygen pathway. To the best of our knowledge, we report for the first time the DNA binding and DNA cleavage ability of rifampicin. This study provides a clue behind the execution of the anti-cancer activity of rifampicin. Overall, all these information can be used for further understanding the pharmacological effects of rifampicin.

Catalytic Removal of Aqueous Contaminants on N-Doped Graphitic Biochars: Inherent Roles of Adsorption and Nonradical Mechanisms.

Environmentally friendly and low-cost catalysts are important for the rapid mineralization of organic contaminants in powerful advanced oxidation processes (AOPs). In this study, we reported N-doped graphitic biochars (N-BCs) as low-cost and efficient catalysts for peroxydisulfate (PDS) activation and the degradation of diverse organic pollutants in water treatment, including Orange G, phenol, sulfamethoxazole, and bisphenol A. The biochars at high annealing temperatures (>700 °C) presented highly graphitic nanosheets, large specific surface areas (SSAs), and rich doped nitrogen. In particular, N-BC derived at 900 °C (N-BC900) exhibited the highest degradation rate, which was 39-fold and 6.5-fold of that on N-BC400 and pristine biochar, respectively, and the N-BC900 surpassed most popular metal or nanocarbon catalysts. Different from the radical-based oxidation in N-BC400/PDS via the persistent free radicals (PFRs), singlet oxygen and nonradical pathways (surface-confined activated persulfate-carbon complexes) were discovered to dominate the oxidation processes in N-BC900/PDS. Moreover, the adsorption of organics was determined to be the key step determining reaction rate, revealing that the pre-adsorption of reactants significantly accelerated the nonradical oxidation pathway. This study not only provides robust and cheap carbonaceous materials for environmental remediation but also enables the first insight into the graphitic biochar-based nonradical catalysis.

Synthesis, DNA/BSA binding and DNA photocleavage properties of water soluble BODIPY dyes

In this study, new BODIPY dyes (2, 3) and their water soluble derivatives (2a, 3a) were synthesized for the first time. The identity of BODIPY dyes 2-3a were confirmed by 1H NMR, 13C NMR, FT-IR, UV–Vis and mass spectrometry. The binding properties of 2a and 3a with CT-DNA have been investigated absorption titration, competitive ethidium bromide, viscosity and electrophoresis experiments. These binding studies claimed that 2a and 3a intercalate with CT-DNA. The Kb values of 2a and 3a calculated as 3.58 ± (0.08) × 105 M−1 and 1.27 ± (0.10) × 105 M−1, indicating that the compounds have strong binding affinities to CT-DNA. The DNA-photocleavage activities of 2a and 3a were investigated using supercoiled pBR322 plasmid DNA on agarose gel electrophoresis. 2a and 3a have remarkable photocleavage activities in the presence of irradiation at 650 ± 20 nm via hydroxyl radical and singlet oxygen pathways. To determine to quenching mechanism of BSA with compounds were performed using UV–Vis absorption spectroscopy. The results demonstrated that the compounds might bind to BSA via static quenching mechanism. The results suggested that synthesized new water soluble BODIPY compounds have strong affinity to CT-DNA and BSA and can effectively cleavage activities by irradiation.

Anticancer activity of heterodinuclear ruthenium(II)–platinum(II) complexes as photochemotherapeutic agents

The purpose of the present study was to investigate the DNA-binding properties of mononuclear ruthenium(II) complex [Ru(tBu2bpy)2(dpp)]2+ and heterodinuclear ruthenium(II)–platinum(II) complexes [Ru(tBu2bpy)2(μ-dpp)PtX2]2+ (X=Cl (1), Br (2), I (3)) and [Ru(bpy)2(μ-dpp)PtCl2]2+ (4). We presented the interaction study of the complexes with CT-DNA and the DNA photocleavage properties using pBR322 supercoiled plasmid DNA when irradiated with visible light and their cytotoxicity against HeLa cervical cancer cell line. All the complexes were cleavage inactive in the dark, while the photoinduced DNA cleavages were observed for these complexes. It appeared that the DNA photocleavage for [Ru(tBu2bpy)2(dpp)]2+ proceeded via a singlet oxygen pathway, whereas complexes 1–3 proceeded via a photoredox pathway. [Ru(tBu2bpy)2(dpp)]2+, 2, and 3 in the light displayed favorable cytotoxicity, which were in all cases similar to cisplatin. 2 (IC50=9.1μM) which was less toxic than [Ru(tBu2bpy)2(dpp)]2+ (IC50=5.6μM) produced the largest PI (>22), indicating a highly effective photocytotoxic agent. The order of cytotoxicity of 1–4 in the light may be due to the lipophilicity (2>3>1≫4).