Abstract
The ready availability of [60] fullerene (C60) and its homologues has increasingly invited exploration of their outstanding new physical and chemical properties. Among them, one of the most important applications is the medicinal use : for example, they act as a singlet oxygen (1O2) photosensitizer to cleave DNA and as an inhibitor to suppress the HIV protease activity. In spite of their high potentials, however, the applications have been very limited because of their poor water-solubility. Several lines of effort have so far been devoted toward compensation for this drawback, for example, by introduction of water-soluble substituents, mixing with water-soluble polymers, solubilization in γ-cyclodextrin (γ-CD), and water-soluble calix [8] arenes. We considered that among these methods, the host-guest method should be superior to others because (i) one can directly use “unmodified C60” which can act as electron pool more efficiently than other C60 derivatives, (ii) one can suppress undesired photo-dimerization of C60 and (iii) dioxygen or substrates can collide with C60 more efficiently. With these objects in mind, we designed a new water-soluble cationic homooxacalix [3] arene with a cone conformation. The homooxacalix [3] arene solubilized C60 into water and the C60 · homooxacalix [3] arene complex acted as an efficient DNA photocleavage reagent. On the other hand, the homooxacalix [3] arene- [60] fullerene complex can be deposited on an anion-coated gold surface as a monolayer (or at least as a monolayer-liked ultra-thin film). This membrane efficiently shows a redox response in cyclic voltammometry and a photoelectrochemical response under visible light irradiation.
