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Radical anions and radical cations of parent tetraphenylethene (1) and its cyclophane derivatives 2−8 were generated by chemical methods. These paramagnetic species were characterized by their ESR and simultaneously recorded optical spectra. The hyperfine coupling constants were substantiated by ENDOR and their signs by general TRIPLE spectroscopy. The structures of the radical ions were established with the help of quantum chemical calculations. The electron distribution in the phane radical ions is closely related to that found for 1^•-/1^•+. In the radical anions no specific complexation of alkali-metal counterions, K⁺ and Li⁺, by the crown-ether moieties could be observed. When the radical cations were generated by oxidation with Tl^III trifluoroacetate in 1,1,1,3,3,3-hexafluoropropanol, distinctly different ESR spectra were recorded as with the use of other oxidants. This observation is rationalized by the characteristic solvation properties of 1,1,1,3,3,3-hexafluoropropanol

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In an attempt to develop an efficient chemotherapeutic agent targeted at malignant cells that express receptors to gonadotropin releasing hormone (GnRH) we coupled [D-Lys 6 ]GnRH covalently to an emodin derivative, i.e. emodic acid (Emo) to yield [D-Lys 6 (Emo)]GnRH. Emodin is a naturally occurring anthraquinone which is widely used as a laxative and has other versatile biological activities. Physico-chemical studies employing electron paramagnetic resonance and electrochemistry of the conjugate as well as the (Emo) moiety showed that these compounds could be easily reduced either chemically, photochemically or enzymatically to their corresponding semiquinones. In the presence of oxygen the semiquinones generated reactive oxygen species (ROS), mainly superoxide and hydroxyl radicals, which were detected by the spin trapping method. Moreover, upon irradiation with visible light these compounds produced ROS and a highly reactive excited triplet state of Emo, which by itself may cause the oxidation of certain electron acceptors such as amino acids and bases of nucleic acids. Thus, [D-Lys 6 ]GnRH-photosensitizer conjugates may be potentially used for targeted photodynamic chemotherapy aimed at treating cancer cells that carry GnRH receptors. These conjugates may also induce cytotoxicity in the dark similar to common conventional chemotherapeutic agents. The peptidic moiety, [D-Lys 6 ]GnRH, was found to be stable toward highly reactive ROS generated either from enzymatic reduction or upon photoirradiation. The physico-chemical properties of Emo were only marginally influenced by the peptidic [D-Lys 6 ]GnRH carrier. ¶Posted on the website on