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The synthesis, photophysical and photodynamic properties of two water-soluble hybrid structures based on the polycationic or polyanionic fullerene [60] derivative covalently linked to fluorescein are described. The significant influence of electrostatic charges on the conformation of the studied fullerene–fluorescein structures in aqueous solution and on their photophysical properties and photochemical activity was demonstrated. A polycationic fullerene derivative–fluorescein conjugate exhibits a pronounced quenching of fluorescence (more than 25 times) due to the energy and/or electron transfer from dye to fullerene. Such activation of fullerene generates reactive oxygen species greater than 15 times more effectively than an individual dye or fullerene does. In contrast, for the polyanionic fullerene derivative–fluorescein conjugate such effects are practically absent. The demonstrated effects open up wide opportunities for a directional design of highly efficient water-soluble photosensitizers by combining the singlet-excited dyes and fullerene [60] for applications in photodynamic therapy.

Chlorin e6 derivative and water-soluble dyad resulting from covalent bonding of polyanionic fullerene С60 derivative to chlorin e6 derivative were synthesized and studied for spectral properties and photochemical activity. A considerable change in the absorption spectra and pronounced fluorescence quenching for the chlorin moiety included in the dyad were identified. The singlet excited state of chlorin is quenched via electron transfer from the excited chlorin to the fullerene core. A comparison of the photochemical activities of the test compounds in aqueous solutions showed a tenfold increase in the photochemical activity of the chlorin–fullerene dyad compared with free chlorin per absorbed light quantum.

By the use of absorption spectroscopy, steady-state and time resolved fluorimetry xanthene dyes fluorescein, eosin Y and erythrosin B were shown to form complexes with polycationic fullerene derivative due to electrostatic interactions in aqueous solution and in the structure of the liposomes. It was found that the singlet excited states of dyes are effectively quenched either due to excitation energy transfer or electron transfer from singlet excited state of the dye to the fullerene core. Photodynamic activity of the complex is much higher than the activity of the dye or the fullerene derivative as the individual compounds. Photostability of the dyes increases in the complex structure as well. These effects allow predicting the development of a new generation hybrid photosensitizers. Noteworthy, one can use a dye excited only in a singlet state in combination with fullerene, which greatly enhances the directional design of such hybrid structures.

The synthesis of water-soluble dyads PFD-Chl(1), PFD-Chl(Zn) and PFD-Chl(2) based on a polyanionic fullerene[60] derivative PFD covalently linked to chlorin e6 was described. Photophysical properties, generation of superoxide and singlet oxygen in water and liposomes, and photodynamic activity on HeLa cancer cells of obtained dyads were analyzed. The significant influence of linker length between fullerene[60] core and dye, presence of metal (Zn) atom in chlorin moiety on photophysical properties, and photodynamic activity of the dyads was demonstrated. All dyads exhibit quenching of chlorin fluorescence by 7–120 times due to the electron transfer from the dye to fullerene and they formed nanoassociates in aqueous solutions with an effective radius in the range of 30–500 nm due to their pronounced amphiphilic properties. Such nanoassociates were able to effectively interact with membranes of liposomes, which led to a sharp increase of fluorescence signal. This effect could be applied for the design of various fullerene-based nanoscale switch-off systems. The dyad PFD-Chl(1) – with the shortest linker and metal-free dye – had the superoxide generation efficiency 5.6 and 3.4 times higher compared to free chlorin Се6 in water and liposomes, respectively, while its singlet oxygen generation was reduced. The phototoxicity of this dyad in HeLa cells was almost equal to that of the native chlorin, despite the reduction of singlet oxygen generation efficiency. Upon the incorporation of zinc atom into a chlorin moiety of this dyad, photodynamic activity and phototoxicity of PFD-Chl(Zn) dyad became negligible. The PFD-Chl(2) dyad – with the longest linker and metal-free chlorin – had about two times lower photodynamic activity and phototoxicity compared to Ce6 due to weak interaction between fullerene core and the dye. A significant increase of the type I pathway efficiency, demonstrated in the PFD-Chl(1) dyad, could be applied for the creation of photosensitizers, highly effective against hypoxic tumors. The demonstrated approach opens up vast opportunities for a directional design of highly efficient fullerene-based water-soluble photosensitizers for photodynamic therapy.

229 As known, fullerenes are photoexcited to a triplet state in 100% quantum yield, which then is deacti vated to generate, depending on the polarity of a medium, either singlet oxygen О2 or superoxide radi cal anions and other active radicals [1]. Numerous studies have addressed the photodynamic effect of fullerene and their derivatives: the generation of active radicals upon photoexcitation is responsible for dam age of DNA, proteins, and membranes, as well as for the suppression of the reproduction of tumor cells, viruses, and bacteria [2]. However, the efficiency of the photodynamic action of fullerenes and the pros pects for their application in medicine are essentially limited by the weak absorption by fullerenes of visible light, especially in the range 650–800 nm, which is most suitable for photodynamic therapy. The photodynamic effect of fullerenes can be con siderably enhanced by creating hybrid nanostructures − О2 . (HNSs) via the formation of a fullerene complex with a dye that efficiently absorbs visible light [3]. In such a complex, the dye can efficiently absorb light and transfer excitation energy or electron to the fullerene. Further excitation transfer or electron transfer from the fullerene to molecular oxygen will generate active oxygen species. The creation of such an HNS based on fullerene and a dye can thereby significantly enhance the efficiency of photodynamic therapy.

It has been shown by the use of steady-state and time-resolved fluorimetry and kinetic phosphorescent spectroscopy that a polycationic fullerene derivative forms complexes with eosine Y in solution due to electrostatic interactions. It has been found that singlet excited states of eosine Y are effectively quenched due to either the excitation energy transfer or electron transfer from the dye to the fullerene core. This leads to a substantial increase in the photodynamic activity of the fullerene derivative and the dye in the structure of the complex when it is excited by light in the absorption band of the dye.

The review briefly outlines theoretical models developed in 1990s to describe electron transfer reactions (ETR) in proteins, as well as different variants of improvements in these models proposed by the present authors to describe ETR in reaction centers (RC) of photosynthetic bacteria with consideration of their molecular dynamics in a wide temperature range. Experimental data on electron transfer from reduced proximal heme c-559 of cytochrome to bacteriochlorophyll dimer radical cation P+ in RC from two types of bacteria, viz., native and mutant RC from Rps. viridis and native RC from Rps. sulfoviridis were analyzed within the framework of the models which take into account the quantum and classical (including diffusive) degrees of freedom responsible for reorganization of the protein globule.

Kinetic curves of reduction of the oxidized bacteriochlorophyll dimer by the proximal heme of cytochrome in seven mutated reaction centers from Rps. viridis was measured in the temperature range of 295-10 K under an ambient potential when two high-potential hemes were reduced. The data are analyzed in frames of a model which accounts for slow medium dynamics (the diffusion-reaction equation) and the quantum effect in the modes responsible for reorganization of the cofactors and the medium. The model reproduces the observed nonexponential kinetics down to the lowest temperature where the fast kinetic component still survives. The modeling results in determination of an average characteristic time for re-orientation of dipoles of the protein matrix as a function of temperature. At temperatures above the glass-transition temperature, this function shows Arrhenius behavior with the activation energy varying between the values of 0.5 eV for wild type Rps. viridis and 0 eV for Rps. sulfoviridis found previously. Possible reasons for disappearance of the fast kinetic component in some reaction centers under study at low temperatures are discussed.

Electron transfer (ET) in the reaction center from Rhodopseudomonas viridis has been studied experimentally by our group in the range of temperatures of 153–295 K. The kinetics of ET reaction from the proximal heme of cytochrome to the special pair was found to be non-exponential. The degree of non-exponentiality strongly depends on temperature, with increasing non-exponentiality at lower temperatures. Here, the experimental kinetic data for ET are analyzed in the frames of a theoretical Sumi–Marcus-type model, which allows establishing a connection between the observed kinetics and local structural dynamics of the protein in a close vicinity of the donor and acceptor sites. The phenomenological model subdivides the multi-time-scale dynamics of the protein into two groups: fast and slow. The division is determined by the rate of ET, which is dynamically controlled by the slow modes of the protein medium. The slow modes are described by a phenomenological collective coordinate , for which a diffusion type ...

Structural data on the nitrogenase complex of Azotobacter vinelandii, Av1·(Av2)2, stabilized by MgADP·AlF4− and, in particular, the structure and properties of a P-cluster involved in the nitrogenase ATPase reaction, were analyzed. The ATP-binding site and all nitrogenase metal clusters are arranged in one plane, the distances between the closest partners being 14–15 A. The ATP-binding site in the Fe-protein, which decreases the half-reduction potential (Em) of the [4Fe-4S]-cluster in Av2 to −0.43 V, does not affect the potentials of the P-cluster and Fe-Mo cofactor (FeMoco). Amino acids 74–95 in the β-subunit of Av1 “envelop” the P-cluster in Av1; therefore, the phosphate intermediate of the ATPase reaction of nitrogenase occurs apparently in the direct contact with the P-cluster. By increasing the acceptor properties of the P-cluster, this intermediate may favor the electron transfer from the Fe-protein to the P-cluster, thus bringing it into the super-reduced state.