It is shown that data presented in a paper by Chao and co-workers do not support the formation of active “Carbon Radicals” as claimed according to the title. The assignments of observed ESR spectra and the mechanistic interpretation are severely flawed. Hence, other reactive intermediates must be responsible for the observed tumor-damaging effects.

References

1S. Kuang, L. Sun, X. Zhang, X. Liao, T. W. Rees, L. Zeng, Y. Chen, X. Zhang, L. Ji, H. Chao, Angew. Chem. 2020, 132, 20878–20884;
10.1002/ange.202009888
Web of Science® Google Scholar
Angew. Chem. Int. Ed. 2020, 59, 20697–20703.
10.1002/anie.202009888
CAS PubMed Web of Science® Google Scholar
2
2aA. R. Forrester, in Landolt-Börnstein, New Series, Vol. II/17d2, Magnetic Properties of Free Radicals (Ed.: H. Fischer), Springer, Berlin, 1989;
Google Scholar
2bA. Alberti in Landolt-Börnstein, New Series, Vol. II/26D, Magnetic Properties of Free Radicals (Ed.: H. Fischer), Springer, Berlin, 2005.
Google Scholar
3Spin Trap Data Base, NIH National Institutes of Environmental Health Services, Research Triangle Park, North Carolina USA 27709; https://tools.niehs.nih.gov/stdb/index.cfm.
Google Scholar
4The β-H splittings of C-radical adducts to DMPO are generally significantly larger than 15 G (mostly around 20 G), thus typically giving rise to 6-line ESR spectra.^[2,3] For example, DMPO-trapping of a carbon-centered radical generated by photolysis of a Ru-complex under similar conditions is reported in: N. Tian, W. Sun, X. Guo, J. Lu, C. Li, Y. Hou, X. Wang, Q. Zhou, Chem. Commun. 2019, 55, 2676–2679.
10.1039/C8CC09186B
CAS PubMed Web of Science® Google Scholar
5The authors exclude the formation of singlet oxygen, hydroxyl radical, and superoxide radical anion, respectively (p. 20700, first paragraph). However, the “hypoxic” conditions of 1 % O₂ (see legend to Figure 1 of ref. [1]) would still allow some contribution of oxygen-dependent reaction routes.
Google Scholar
6
6aK. Ranguelova, R. P. Mason, Magn. Reson. Chem. 2011, 49, 152–158;
10.1002/mrc.2709
CAS PubMed Web of Science® Google Scholar
6bL. Eberson, Acta Chem. Scand. 1999, 53, 584–593;
10.3891/acta.chem.scand.53-0584
CAS Web of Science® Google Scholar
6cP. Bilski, K. Reszka, M. Bilska, C. F. Chignell, J. Am. Chem. Soc. 1996, 118, 1330–1338;
10.1021/ja952140s
CAS Web of Science® Google Scholar
6dC. F. Chignell, A. G. Motten, R. H. Sik, C. E. Parker, K. Reszka, Photochem. Photobiol. 1994, 59, 5–11.
10.1111/j.1751-1097.1994.tb04994.x
CAS Web of Science® Google Scholar
7There is another puzzling feature with the reported ESR spectra: the “Ir4-red”-labelled spectrum is centered at about the same magnetic field (≈3511 G) as that of the “Ir4-red+ DMPO ”-labelled nitroxide radical spectrum. Reasonably assuming that both spectra were recorded using the same experimental setup and under similar recording conditions (see SI, p. 6), essentially identical microwave frequencies must be expected for both recordings. If so, the g-factor of the single-line “Ir4-red” spectrum would then in fact be very similar to that of the DMPO-OH nitroxide radical (g ≈2.006) rather than 2.0027. However, a g-factor of ≈2.006 would not be in agreement with a carbon-centered radical. Unfortunately, no information was given how the g-factors were determined, nor are (sufficiently precise) microwave frequencies for both recordings provided to allow a re-estimation of the g-factors by the reader.
Google Scholar
8The Chemistry of Phenols, Z. Rappoport, Ed., Wiley: Chichester, 2003; specifically see Ch. 16: S. Steenken, P. Neta, Transient phenoxyl radicals: Formation and properties in aqueous solutions, pp 1107–1152.
Google Scholar
9Y. Wan, G. Lu, J. Zhang, Z. Wang, X. Li, R. Chen, X. Cui, Z. Huang, Y. Xiao, J. Chelora, W. Zhang, Y. Liu, M. Li, H. Y. Xie, C. S. Lee, Adv. Funct. Mater. 2019, 29, 1903436.
10.1002/adfm.201903436
Web of Science® Google Scholar
10Q. Guo, S. Y. Qian, R. P. Mason, J. Am. Soc. Mass Spectrom. 2003, 14, 862–871.
10.1016/S1044-0305(03)00336-2
CAS PubMed Web of Science® Google Scholar

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A Mitochondrion-Localized Two-Photon Photosensitizer Generating Carbon Radicals Against Hypoxic Tumors

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