Osmium(IV) complexes with 1H- and 2H-indazoles: tautomer identity versus spectroscopic properties and antiproliferative activity.
Bottom Line: A one-pot synthesis of osmium(IV) complexes with two different tautomers of indazole, 1H-indazole and 2H-indazole, namely (H(2)ind)[Os(IV)Cl(5)(2H-ind)] (1) and (H(2)ind)[Os(IV)Cl(5)(1H-ind)] (2) is reported.Both compounds have been comprehensively characterized by NMR spectroscopy, ESI (electrospray ionization) mass spectrometry, electronic absorption spectroscopy, IR spectroscopy, cyclic voltammetry and tested for antiproliferative activity in vitro in three human cancer cell lines, CH1 (ovarian carcinoma), A549 (non-small cell lung cancer) and SW480 (colon carcinoma), as well as in vivo in a Hep3B SCID mouse xeno-transplantation model. 2H-Indazole tautomer stabilization in 1 has been confirmed by X-ray diffraction.
Affiliation: University of Vienna, Institute of Inorganic Chemistry, Währinger Strasse 42, A-1090 Vienna, Austria.Show MeSH
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Mentions: The cyclic voltammograms (CV) of 1 and 2 in DMSO (0.2 M (n-Bu4N)[BF4]/DMSO) at a carbon disk working electrode, recorded with a scan rate of 0.2 V/s, display a reversible one-electron reduction wave attributed to the OsIV → OsIII process with a potential value of 0.03 and 0.13 V for 1 and 2 respectively. Irreversible single electron reduction wave (Ired) attributed to the OsIII → OsII process is observed at − 1.43 (Fig. 2) and − 1.33 V for 1 and 2, correspondingly. The redox waves OsIV/OsIII for 1 and 2 are characterized by a peak-to-peak separation (ΔEp) of 74 and 95 mV respectively, and an anodic peak current (ipa) that is almost equal to the cathodic peak current (ipc) in both cases, as expected for a reversible electron transfer process. The one-electron nature of the electron transfer process was verified by comparing the peak current height (ip) with that of the standard ferrocene/ferrocenium couple under the same experimental conditions. The application of Lever's equation  (Eq. (1)) [EL(Cl) = − 0.24 , SM(OsIII/OsII) = 1.01 , and IM(OsIII/OsII) = − 0.40 ](1)E=SM∑EL+IMfor OsIII → OsII process has allowed the estimate of the yet unknown EL ligand parameter for 2H-ind tautomer (1, EL = 0.18 V), whereas EL ligand parameter for 1H-ind tautomer in 2, according to Eq. (1), is 0.28 V. Reported EL value for 1H-ind tautomer is 0.26 V .
Affiliation: University of Vienna, Institute of Inorganic Chemistry, Währinger Strasse 42, A-1090 Vienna, Austria.