Fullerene C60-silver nanoparticles hybrid structures: optical and photoelectric characterization.

A detailed optical and photoelectric characterization of pristine fullerene C60 films deposited onto n-silicon substrates (C60/Si), C60 films crosslinked by means of the solvent-free chemical functionalization with 1,8-diaminooctane (C60-DA/Si), and the pristine and crosslinked films decorated with silver nanoparticles (C60-Ag/Si and C60-DA-Ag/Si), was carried out. The reflectance spectra obtained allowed to calculate the absorption coefficient (alpha = 4pik/lamda) spectral dependencies and the spectra of light transmittance in layered barrier structures metal(Au)/fullerene/Si. Photoelectric properties of the films were investigated as well. The experimentally measured values of band gap were in a good agreement with mobility gap values (2.3 +/- 0.1 eV). The decoration of fullerene films (both pristine and chemically crosslinked) with silver nanoparticles did not change the photocurrent spectra as compared to those for undecorated fullerene films, but lowered the values of internal quantum efficiency Qint. The photocurrent generated in fullerene/Si heterostructure, showed a maximum value at lamda to appromimately 450 nm (Qint max approximately = 0.25 for decorated and undecorated C60-DA/Si films), and it was higher for the samples based on pristine C60 films, in accordance with their higher absorption coefficient. Diminishing of Qint for C60-DA/Si and C60-DA-Ag/Si films was observed for the spectral range of photocurrent generated in Si layer. The analysis of dark current-voltage characteristics showed that the barrier properties differ insignificantly, though a certain increase of series resistance was observed for the C60-DA/Si samples.

Phototransformation of C60 thin films by UV pulsed laser irradiation: comparative photoacoustic, AFM, and Raman studies.

Fullerene C60 films deposited by sublimation were irradiated with Kr-F laser in a wide fluence interval from 15 to 40 mJ/cm2. In situ photoacoustic analysis was applied to study the phase transformation during the irradiation. The results obtained were discussed in conjunction with atomic force microscopy (AFM) and Raman spectroscopy data. It was found that for a irradiation fluence interval from 22 to 30 mJ/cm2, 80% of C60 undergoes photopolymerization (presumably through 2 + 2 cycloaddition). For a laser energy higher than 30 mJ/cm2, a new amorphous carbon phase forms, having a large content of diamond-like, tetra-amorphous carbon (ta-C).

Cross-linking of C60 films with 1,8-diaminooctane and further decoration with silver nanoparticles.

We applied the direct solvent-free functionalization of fullerene C60 with aliphatic bifunctional amine, 1,8-diaminooctane, to prepare chemically cross-linked C60 thin films capable of binding silver nanoparticles. The gas-phase diamine treatment of C60 reduced dramatically the fullerene solubility in toluene, indicating the transformation of pristine C60 into a different solid phase with cross-linked fullerene molecules. Compared to the spectra of pristine C60 film and powder samples, Fourier-transform infrared, UV-Visible, Raman, and 13C nucleic magnetic resonance spectra of the functionalization products exhibited new features, which point to a breaking of C60 ideal structure during the formation of new covalent bonds and to the appearance of sp3 hibridization. The covalent functionalization with 1,8-diaminooctane allowed for a stable and homogeneous deposition of silver nanoparticles of ca. 5-nm diameter onto the functionalized films through the coordination bonding between metal atoms and nitrogen donor atoms of the fullerene derivatives. The proposed mechanism of Ag nanoparticle binding was supported by density functional theory calculations using the hybrid BLYP functional in conjunction with the double numerical basis set DND.

(C-rac-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane-kappa4N)(nicotinato-O,O')nickel(II) perchlorate.

In the title compound, [Ni(C(6)H(4)NO(2))(C(16)H(36)N(4))]ClO(4), the macrocyclic unit adopts a folded conformation, allowing the two carboxyl O atoms to occupy two neighbouring coordination sites and thus form an additional four-membered chelate ring. The less crowded side of the macrocycle (that with the two asymmetric C-H groups) is directed towards the nicotinate anion and the asymmetric C-CH(3) groups are directed away from it. The macrocyclic NH groups neighbouring the C-CH(3) groups are also directed away from the nicotinate anion, while those NH groups which are near to the geminal methyl groups are directed towards the nicotinate anion. Although the complex does not include water molecules, three types of hydrogen bond were found, involving NH groups of the macrocyclic ligand, pyridine N atoms and O atoms of the perchlorate anions.

Behavior of amino acids when volatilized in the presence of silica gel and pulverized basaltic lava.

To evaluate the types of amino acid thermal transformations caused by silicate materials, we studied the volatilization products of Aib, L-Ala, L-Val and L-Leu under temperatures of up to 270 degrees C in the presence of silica gel as a model catalyst and pulverized basaltic lava samples. It was found that silica gel catalyzes nearly quantitative condensation of amino acids, where piperazinediones are the major products, whereas lava samples have much lower catalytic efficiency. In addition bicyclic and tricyclic amidines and several products of their subsequent thermal decomposition have been identified using the coupled technique of GC-FTIR-MS and HPLC-PB-MS, with auxiliary computer simulation of IR spectra and NMR spectroscopy. The decomposition is due to dehydrogenation, elimination of the alkyl substituents and dehydration as well as cleavage of the bicyclic ring system. The imidazole ring appears to be more resistant to thermal decomposition as compared to the pyperazine moiety, giving rise to the formation of different substituted imidazolones. The amidines were found to hydrolyze under treatment with concentrated HCl, releasing the starting amino acids and thus behaving as amino acid anhydrides. The thermal transformations cause significant racemization of amino acid residues. Based on our observations, the formation of amidine-type products is suggested to be rather common in the high-temperature experiments on amino acid condensation.

Corona chemistry in Titan.

The atmosphere of Titan is constantly bombarded by galactic cosmic rays and Saturnian magnetospheric electrons causing the formation of free electrons and primary ions, which are then stabilized by ion cluster formation and charging of aerosols. These charged particles accumulate in drops in cloud regions of the troposphere. Their abundance can substantially increase by friction, fragmentation or collisions during convective activity. Charge separation occurs with help of convection and gravitational settling leading to development of electric fields within the cloud and between the cloud and the ground. Neutralization of these charged particles leads to corona discharges which are characterized by low current densities. We have therefore, experimentally studied the corona discharge of a simulated Titan's atmosphere (10% methane and 2% argon in nitrogen) at 500 Torr and 298 K by GC-FTIR-MS techniques. The main products have been identified as hydrocarbons (ethane, ethyne, ethene, propane, propene+propyne, cyclopropane, butane, 2-methylpropane, 2-methylpropene, n-butane, 2-butene, 2,2-dimethylpropane, 2-methylbutane, 2-methylbutene, n-pentane, 2,2-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, 2,2-dimethylhexane, 2,2-dimethylpentane, 2,2,3-trimethylbutane, 2,3-dimethylpentane and n-heptane), nitriles (hydrogen cyanide, cyanogen, ethanenitrile, propanenitrile, 2-methylpropanenitrile and butanenitrile) and a highly branched hydrocarbon deposit. We present the trends of hydrocarbons and nitriles formation as a function of discharge time in an ample interval and have derived their initial yields of formation. The results clearly demonstrate that a complex organic chemistry can be initiated by corona processes in the lower atmosphere. Although photochemistry and charged particle chemistry occurring in the stratosphere can account for many of the observed hydrocarbon species in Titan, the predicted abundance of ethene is too low by a factor of 10 to 40. While some ethene will be produced by charged-particle chemistry, the production of ethene by corona processes and its subsequent diffusion into the stratosphere appears to be an adequate source. Because little UV penetrates to the lower atmosphere to destroy the molecules formed there, the corona-produced species may be long-lived and contribute significantly to the composition of the lower atmosphere and surface.

[Identification and expression of plasmid genes participating in the synthesis of microcin C51]. / Identifikatsiia i ékspressiia plazmidnykh genov, uchastvuiushchikh v sinteze mikrotsina C51.

A structural gene of heptapeptide, which is a component of the microcin C51 molecule, was identified by hybridization of plasmid DNA fragments and a mixture of synthesized oligonucleotides with the sequence corresponding to that of amino acids in the peptide. Sequence analysis of the structural gene of microcin peptide and its promoter region was performed. The data obtained indicate that the peptide of microcin C51 is synthesized on ribosomes. Four polypeptides of 67, 39, 16, and 14 kDa were identified using the system of minicells. These polypeptides are specified by a DNA fragment responsible for microcin synthesis and immunity in a producer cell. Apparently, three of these polypeptides with molecular masses of 67, 39, and 16 kDa are responsible for microcin production and immunity. The 67 kDa polypeptide is involved in the expression of immunity to microcin and, probably, in microcin production.

[Cloning and analysis of genetic determinants determining the production of microcin B2 and B27]. / Klonirovanie i analiz geneticheskikh determinantov, opredeliaiushchikh produktsiiu mikrotsinov B2 i B27.

Cloning of plasmid genes for the synthesis of two peptide broad-spectrum antibiotics-microcins B2 and B27- and for host cell immunity to their action was performed. Recombinant plasmids containing these genes were designated pBE108 and pVB27, respectively. Deletional derivatives of plasmid pBE108 and mutant plasmids were obtained via transposon Tn5 insertions, which did not determine production of microcin B2 and immunity to it. Phenotypic study and physical mapping of these plasmids demonstrated that a 4.2-kb DNA fragment is responsible for B2 microcin production; immunity is provided by a 1.4-kb DNA fragment. A 5-kb DNA fragment is necessary for microcin B27 synthesis and expression of immunity to its action. Homology between these fragments and with plasmid DNA for the synthesis of microcin B17 and immunity to it was found. Homology between plasmid genes determining synthesis of type B and C microcins and host cell immunity to them was not observed. The production of B27 microcin is controlled by the product of the ompR gene; B2 microcin synthesis does not depend on this product. The mutations recA and lexA increase the susceptibility of Escherichia coli cells to the action of microcins B2 and B27 but not microcin C51.

[Plasmid genes participating in the synthesis of microcin C51]. / Plazmidnye geny, uchastvuiushchie v sinteze mikrotsina C51.

Microcin C51 is an antibiotic with a wide application range produced by Escherichia coli cells. Using insertions of transposon Tn5 a set of mutations was induced in the recombinant plasmid pAST, which determines synthesis of microcin C51. The mutations were physically mapped. Complementation analysis was performed for insertions and deletions in the Mic+ plasmids pAST and pUHAB that lead to the absence of microcin or immunity to it. The analysis showed that at least three plasmid genes take part in microcin production and two genes determine immunity of producer cells to microcin. Functioning of the ompR gene product was necessary for synthesis of microcin C51.

[Characterization of enterobacteria producing the broad-spectrum antibiotics microcins]. / Kharakteristika énterobakterii, produtsiruiushchikh antibiotiki shirokogo spektra deistviia mikrotsiny.

As a result of screening among 11956 enterobacteria strains isolated from feces of normal children, grown-ups and lambs, seven active microcin-producing strains were obtained. The microcins were shown to be peptides or their derivatives with a low molecular weight (less than 10,000) and a broad spectrum of activity, mainly against gram-negative bacteria. According to cross immunity criteria the microcins studied belonged to two different types. Those of type I could be further classified into two subtypes on the account of difference in the spectrum of antibacterial activity. In 5 cases out of 7 the microcin-producing ability and immunity to microcins have been attributed to plasmids that the strains harboured. The effect of microcins on sensitive cells depended on ompR and ompF gene products.

[The role of peritoneal macrophages in realizing the growth inhibiting effect of glucocorticoids on reinoculated murine hepatoma 22 cells: the effect of hydrocortisone on the cytotoxic activity and metabolism of phospholipids by macrophages]. / Rol' peritoneal'nykh makrofagov v realizatsii rost-ingibiruiushchego deistviia gliukokortikoidov na kletki perevivaemoi myshinoi gepatoma 22: vliianie gidrokortizona na tsitotoksicheskuiu aktivnost' i obmen fosfolipidov makrofagov.

A single injection of hydrocortisone to rats with ascite hepatoma 22 had practically no effect on tumour growth. Inhibition of tumour growth was observed only after reinoculation of ascite hepatoma to mice that had received no less than 8 daily injections of the hormone. A single injection of hydrocortisone induced inhibition of the cytotoxic activity and decreased phospholipid metabolism in peritoneal macrophages. Contrariwise, long-term administration of the hormone caused marked activation of macrophage cytotoxicity. In this case incorporation of 32P into macrophage phospholipids was restored up to the control level. It is concluded that one of mechanisms underlying the inhibitory effect of glucocorticoids on macrophages is inhibition of phospholipid turnover. Presumably, long-term administration of the hormone promotes the formation of a new population of macrophages insensitive to the inhibitory effect of glucocorticoids and possessing a high cytostatic activity. The appearance of such activated macrophages may account for the enhancement of hydrocortisone effect on tumour cells upon prolonged administration of the hormone.