The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions.

Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:-[6,6]-phenyl-C61-butyric acid methyl ester (PCDTBT:PC61BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

[Laser hyperthermia of tumors with the use of golden nanoparticles under the control of optical coherent tomography and acoustothermometry].

The local laser hyperthermia of an experimental tumor RShM-5 of mice with the use of golden plasmin resonance nanoparticles has been carried out. The accumulation of particles in the tumor was controlled by the in vivo noninvasive method of optical coherent tomography. Using this method, the time of the maximum content of nanoparticles in the tumor was determined to be 5 h after the intravenous administration during which the laser hyperthermia was performed. The control of the tumor temperature during the hyperthermia seance showed that the application of nanoparticles provides an effective temperature elevation inside the node and a more targeted heating. The local laser hyperthermia with nanoparticles induced the inhibition of the tumor growth from day 5 to day 7 after the seance with a maximum value of 56%.

Light-induced EPR study of charge transfer in poly(3-hexylthiophene)/fullerene bulk heterojunction.

The first results of the light-induced EPR study of magnetic, relaxation, and dynamic parameters of charge carriers background photoinduced by optical photons (1.7-3.4 eV) in poly(3-hexylthiophene)/fullerene bulk heterojunctions are described. All magnetic resonance parameters for positively charged polaron and negatively charged fullerene ion-radical in radical pairs photoinduced in the composite were determined separately by the steady-state microwave saturation method. Paramagnetic susceptibility of charge carriers reflects their activation dynamics and exchange interaction. A decay of long-living radical pairs depends on the spatial distance between photoinduced charge carriers. The one-dimensional polaron diffusion along the polymer chain and fullerene rotation near the main molecular axis was shown to follow activation Elliot hopping model and to be governed by photon energy. The difference in activation energies of the charge carriers' dynamics and in their dependence on the exciting photon energy proves their noninteracting character in the polymer/fullerene composite. Main magnetic, relaxation and dynamics parameters of charge carriers are governed by the photon energy band due to inhomogeneity of distribution of polymer and fullerene domains in the composite.

The effect of fullerene derivative on polaronic charge transfer in poly(3-hexylthiophene)/fullerene compound.

The effect of a structure of a fullerene derivative on electronic properties of poly(3-hexylthiophene)/fullerene composite was studied at 3 cm wave band EPR in wide (77-320 K) temperature region. All the systems with different fullerene derivatives demonstrate sum spectrum of small polarons with different mobilities and contributions depending on the structure of the fullerene derivative. Both the spin-lattice and spin-spin relaxation times were determined separately by using the steady-state saturation method. The treatment of polymer matrix by fullerene derivative changes its dimensionality and conformation. This leads to the change in the spin relaxation and susceptibility as well as in the rate of polaron diffusion along polymer chain.

Covalent attachment of proteins to calcite surface for the single molecule experiments.

Two protocols of covalent attachment of proteins onto the calcite surface, viz. one using the metallochelat and second using the aminohexil, are elaborated. Single molecule force spectroscopy method has been used to test their efficiency and practical applicability. Experiments were performed measuring the specific interaction force between bovine serum albumin (BSA) fixed onto the freshly cleaved calcite single crystal surface (procedure under the study here) and its polyclonal antibody (Ab-BSA) immobilized onto an AFM tip using standard and well studied procedure. We found the conditions, when up to 3-3.5% of tip-sample approaches lead to the formation of a single specific bond.

Kinetics of elementary steps of electron transfer in nitrogenase in the presence of a photodonor.

The kinetics of transfer of two electrons from a photodonor (a system containing eosin and NADH or 4;,5;-dibromofluorescein and NADH) to Fe-protein (Av2) and the kinetics of transfer of the first and second electrons from Av2 to Mo-Fe-protein (Av1) were studied by kinetic laser spectroscopy of nitrogenase from Azotobacter vinelandii. The effects of the substrates of nitrogenase (nitrogen, acetylene, and protons) on the intramolecular electron transfer in nitrogenase were studied. Analysis of the effect of photodonor excitation radiation intensity on the rate of electron transfer was used to determine the transfer rate constants for the first (k1) and second (k2) electrons from Av2 to Av1. In the presence of MgATP, two electrons are sequentially transferred from Av2 to Av1, and no delay between these reactions was detected. The first electron transferred from Av2 to Av1 is not targeted to the substrate; k1 = 154 +/- 15 sec-1 at 23 degrees C for the system 4;,5;-dibromofluorescein-NADH; k2 = 53 +/- 5 sec-1, 95 +/- 9 sec-1, and 24 +/- 2 sec-1 at 23 degrees C in the presence of nitrogen, acetylene, and argon, respectively. An unidentified slow step (k3 = 18 +/- 2 sec-1 at 23 degrees C) may be associated with electron transfer within Av1.

Xanthene dyes as photochemical donors for the nitrogenase reaction.

The ability of xanthene dyes to mediate photoinduced reduction of nitrogenase was tested. In addition to eosin, which was studied in the preceding work (Biochemistry (Moscow), 1996, 61, 2165-2172), 4', 5'-dibromofluorescein (DBF), cyanosine, and erythrosin are effective photodonors of an electron in the presence of NADH. Fluorescein, rhodamine B, rhodamine 6G, and porphyrins are unable to mediate photoinduced reduction of nitrogenase. The mechanism underlying different efficiency of xanthene dyes in this reaction was studied. At high concentrations, all xanthene dyes tested were shown to inhibit the intramolecular electron transfer in nitrogenase. The inhibiting concentration of DBF is 1.5.10-4 M, whereas for other dyes, the inhibiting concentrations are less than 1.5.10-4 M. Under otherwise identical conditions, the ATPase activity was inhibited by xanthene dyes to a lesser extent than the nitrogenase activity. DBF, the most effective photodonor, was also studied by differential kinetic pulse laser spectroscopy. Photoinduced reduction of nitrogenase, (Fe-proteinox.Mo-Fe-protein).MgATP or (Av2ox.Av1).MgATP, was studied within the time range from 0 to 100 msec. Two initial stages of the nitrogenase turnover were detected: photoinduced reduction of Av2 and electron transfer from Av2red to Av1. The kinetics of the photoinduced reduction of Av2.MgADP was studied in the presence of DBF (up to 1.3.10-4 M) both in solution and the complex with Av1. The apparent second-order rate constants of the photoinduced reduction of Av2.MgADP in solution and the complex with Av1 were determined as 9.7.107 +/- 106 and 1.2.108 +/- 1.2.107 M-1. sec-1, respectively. The rate constant of the second reaction in the presence of another donor (dithionite) is 2500 times less. In complexes with Av1, the photochemical donor system DBF--NADH reduces Av2 more effectively than in free state in solution. In the presence of the photochemical donor system, neither photoreduction of Av2 in complexes with Av1 nor electron transfer from Av2red to Av1 are the rate-limiting stages of nitrogenase turnover.

[Possibility of destroying gallstones by pulse YAG-Nd laser radiation using an endoscope]. / O vozmozhnosti razrusheniia zhelchnykh kamnei izlucheniem impul'snogo YAG-Nd-lazera s primeneniem éndoskopa.

Four sets of in vitro experiments have been performed to study the effect of pulse YAG-Nd laser inserted into a quartz lightguide on gall-stones and walls of gall ducts. The consistent destruction of stones has been demonstrated no matter what their dimensions and chemical compositions. The method is believed to be safe for clinical usage.