Singlet Oxygen: Discovery, Chemistry, C60 -Sensitization†

Characterization and efficacy of C60 nano-photosensitive drugs in colorectal cancer treatment

BACKGROUND

Fullerenes C60 shows great potential for drug transport. C60 generates large amounts of singlet oxygen upon photoexcitation, which has a significant inhibitory effect on tumor cells, so the photosensitive properties of C60 were exploited for photodynamic therapy of tumors by laser irradiation.

METHODS

In this study, C60-NH2 was functionalized by introducing amino acids on the surface of C60, coupled with 5-FU to obtain C60 amino acid-derived drugs (C60AF, C60GF, C60LF), and activated photosensitive drugs (C60AFL, C60GFL, C60LFL) were obtained by laser irradiation. The C60 nano-photosensitive drugs were characterized in various ways, and the efficacy and safety of C60 nano-photosensitive drugs were verified by cellular experiments and animal experiments. Bioinformatics methods and cellular experiments were used to confirm the photosensitive drug targets and verify the therapeutic targets with C60AF.

RESULTS

Photosensitised tumor-targeted drug delivery effectively crosses cell membranes, leads to more apoptotic cell death, and provides higher anti-tumor efficacy and safety in vitro and in vivo colorectal cancer pharmacodynamic assays compared to free 5-FU.C60 photosensitized drug promotes tumor killing by inhibiting the colorectal cancer FLOR1 tumor protein target, with no significant toxic effects on normal organs.

CONCLUSION

C60 photosensitized drug delivery systems are expected to improve efficacy and reduce side effects in the future treatment of colorectal cancer. Further and better development and design of drugs and vectors for colorectal cancer therapy.

Singlet oxygen generation on a superhydrophobic surface: Effect of photosensitizer coating and incident wavelength on 1O2 yields

Photochemical generation of singlet oxygen (1O2) often relies on homogenous systems; however, a dissolved photosensitizer (PS) may be unsuitable for some applications because it is difficult to recover, expensive to replenish, and hazardous to the environment. Isolation of the PS onto a solid support can overcome these limitations, but implementation faces other challenges, including agglomeration of the solid PS, physical quenching of 1O2 by the support, photooxidation of the PS, and hypoxic environments. Here, we explore a superhydrophobic polydimethylsiloxane (SH-PDMS) support coated with the photosensitizer 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin (TFPP). This approach seeks to address the challenges of a heterogeneous system by using a support that exhibits low 1O2 physical quenching rates, a fluorinated PS that is chemically resistant to photooxidation, and a superhydrophobic surface that entraps a layer of air, thus preventing hypoxia. Absorbance and fluorescence spectroscopy reveal the monomeric arrangement of TFPP on SH-PDMS surfaces, a surprising but favorable characteristic for a solid-phase PS on 1O2 yields. We also investigated the effect of incident wavelength on 1O2 yields for TFPP in aqueous solution and immobilized on SH-PDMS and found overall yields to be dependent on the absorption coefficient, while the yield per absorbed photon exhibited wavelength independence, in accordance with Kasha-Vavilov's rule.

Oxidative cage opening in the C70 fullerene facilitated by preceding trifluoromethylation

Two novel derivatives of the C70 fullerene with 9- and 10-membered cage openings were obtained by means of oxidation and decarbonylation of C70(CF3)8. The major product, C70(O)(CF3)8O2, features a cleaved C-C bond transformed into two carbonyl functions plus an ether bridge. The second product, C69O(CF3)8O, has one of the carbonyls replaced with another ether bridge. We provide a DFT analysis of the possible formation pathways to give the oxidized compounds under the action of pyridine N-oxide.

C60-CN: A bifunctional interface modification material for perovskite solar cells

Titanium dioxide (TiO2) is regularly used as an electron transport material in n-i-p perovskite solar cells (PSCs). However, massive defects exist on the TiO2 surface, which will lead to serious hysteresis and interface charge recombination of the device, thus affecting the device's efficiency. In this study, a cyano fullerene pyrrolidine derivative (C60-CN) was synthesized and applied to PSCs for the first time to modify the TiO2 electron transport layer. Systematic studies have shown that the addition of the C60-CN modification layer on the TiO2 surface will enlargement the perovskite grain size, improve the perovskite film quality, enhance electron transport, and reduce charge recombination. The C60-CN layer can significantly reduce the density of trap states in the perovskite solar cells. As a result, the PSCs based on C60-CN/TiO2 obtained a power conversion efficiency (PCE) of 18.60%, suppressing the hysteresis and improving the stability, whereas the PCE of the control device using the original TiO2 ETL was lower, 17.19%.

Luminescence enhancement by deuterium

Created literally at the dawn of time, deuterium has been extremely valuable in so many chemistry roles. The subject of this review focuses on one deuterium application in particular: its enhancement of luminescence in many substances. After providing general overviews of both deuterium and luminescence, the early exploration of deuterium's effect on luminescence is described, followed by a number of specific topics. These sections include a discussion of deuterium-influenced luminescence for dyes, proteins, singlet oxygen, and the lanthanide elements, as well as anomalous inverse deuterium luminescence effects. Future directions for this important research topic are also proposed, as well as a summary conclusion.

Use of Singlet Oxygen in the Generation of a Mononuclear Nonheme Iron(IV)-Oxo Complex

Nonheme iron(III)-superoxo intermediates are generated in the activation of dioxygen (O₂) by nonheme iron(II) complexes and then converted to iron(IV)-oxo species by reacting with hydrogen donor substrates with relatively weak C-H bonds. If singlet oxygen (¹O₂) with ca. 1 eV higher energy than the ground state triplet oxygen (³O₂) is employed, iron(IV)-oxo complexes can be synthesized using hydrogen donor substrates with much stronger C-H bonds. However, ¹O₂ has never been used in generating iron(IV)-oxo complexes. Herein, we report that a nonheme iron(IV)-oxo species, [Fe^IV(O)(TMC)]²⁺ (TMC = tetramethylcyclam), is generated using ¹O₂, which is produced with boron subphthalocyanine chloride (SubPc) as a photosensitizer, and hydrogen donor substrates with relatively strong C-H bonds, such as toluene (BDE = 89.5 kcal mol^-1), via electron transfer from [Fe^II(TMC)]²⁺ to ¹O₂, which is energetically more favorable by 0.98 eV, as compared with electron transfer from [Fe^II(TMC)]²⁺ to ³O₂. Electron transfer from [Fe^II(TMC)]²⁺ to ¹O₂ produces an iron(III)-superoxo complex, [Fe^III(O₂)(TMC)]²⁺, followed by abstracting a hydrogen atom from toluene by [Fe^III(O₂)(TMC)]²⁺ to form an iron(III)-hydroperoxo complex, [Fe^III(OOH)(TMC)]²⁺, that is further converted to the [Fe^IV(O)(TMC)]²⁺ species. Thus, the present study reports the first example of generating a mononuclear nonheme iron(IV)-oxo complex with the use of singlet oxygen, instead of triplet oxygen, and a hydrogen atom donor with relatively strong C-H bonds. Detailed mechanistic aspects, such as the detection of ¹O₂ emission, the quenching by [Fe^II(TMC)]²⁺, and the quantum yields, have also been discussed to provide valuable mechanistic insights into understanding nonheme iron-oxo chemistry.

Mo2C as Pre-Catalyst for the C-H Allylic Oxygenation of Alkenes and Terpenoids in the Presence of H2O2

In this study, commercially available molybdenum carbide (Mo2C) was used, in the presence of H2O2, as an efficient pre-catalyst for the selective C-H allylic oxygenation of several unsaturated molecules into the corresponding allylic alcohols. Under these basic conditions, an air-stable, molybdenum-based polyoxometalate cluster (Mo-POM) was formed in situ, leading to the generation of singlet oxygen (1O2), which is responsible for the oxygenation reactions. X-ray diffraction, SEM/EDX and HRMS analyses support the formation mainly of the Mo6O192− cluster. Following the proposed procedure, a series of cycloalkenes, styrenes, terpenoids and methyl oleate were successfully transformed into hydroperoxides. After subsequent reduction, the corresponding allylic alcohols were produced with good yields and in lab-scale quantities. A mechanistic study excluded a hydrogen atom transfer pathway and supported the twix-selective oxygenation of cycloalkenes on the more sterically hindered side via the 1O2 generation.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (¹O₂) is the excited state of ground, triplet state, molecular oxygen (O₂). Photosensitized ¹O₂ has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of ¹O_2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of ¹O₂, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring ¹O₂ generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor ¹O₂ generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.