Nina V. Kozhemyakina

Universitätsklinikum Erlangen, Erlangen, Bavaria, Germany

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Publications (6)23.66 Total impact

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    ABSTRACT: Twenty-two different graphite grades of the families natural, synthetic, intercalated, expanded, amorphous, and turbostratic graphite, as well as platelets and activated carbon, were analyzed on their dispersibility in N-methylpyrrolidone, cyclohexylpyrrolidone and water-sodium cholate solution. They were characterized for their properties (grain size, density, purity, surface area, pH in water) and morphology. Thermogravimetric analysis, Raman spectroscopy studies, and electrical conductivity measurements were also used. XRPD followed by a Rietveld refinement provided information on the amounts of the rhombohedral (3R) and hexagonal (2H) phases for the crystalline part of the material and the interlayer distances. The properties of graphites favoring better dispersibility are: small grain size and bulk density, neutral pH in water. The electrical conductivity in inversely proportional to the Raman D-band intensity and is highest for the graphites with shortest interlayer spacing. The D-, G- and 2D-bands in the Raman spectra of graphites are in an exponential relation.
    Fullerenes Nanotubes and Carbon Nanostructures 10/2013; 21(9):10.1080/1536383X.2012.702162. DOI:10.1080/1536383x.2012.702162 · 0.64 Impact Factor
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    ABSTRACT: A new fulleride, (K[DB18C6])(4)(C(60))(5)·12THF, was prepared in solution using the "break-and-seal" approach by reacting potassium, fullerene, and dibenzo[18]crown-6 in tetrahydrofuran. Single crystals were grown from solution by the modified "temperature difference method". X-ray analysis was performed revealing a reversible phase transition occurring on cooling. Three different crystal structures of the title compound at different temperatures of data acquisition are addressed in detail: the "high-temperature phase" at 225 K (C2, Z=2, a=49.055(1), b=15.075(3), c=18.312(4) Å, β=97.89(3)°), the "transitional phase" at 175 K (C2 m, Z=2, a=48.436(5), b=15.128(1), c=18.280(2) Å, β=97.90(1)°), and the "low-temperature phase" at 125 K (Cc, Z=4, a=56.239(1), b=15.112(3), c=36.425(7) Å, β=121.99(1)°). On cooling, partial radical recombination of C(60)(·-) into the (C(60))(2)(2-) dimeric dianion occurs; this is first time that the fully ordered dimer has been observed. Further cooling leads to formation of a superstructure with doubled cell volume in a different space group. Below 125 K, C(60) exists in the structure in three different bonding states: in the form of C(60)(·-) radical ions, (C(60))(2)(2-) dianions, and neutral C(60), this being without precedent in the fullerene chemistry, as well. Experimental observations of one conformation exclusively of the fullerene dimer in the crystal structure are further explained on the basis of DFT calculations considering charge distribution patterns. Temperature-dependent measurements of magnetic susceptibility at different magnetic fields confirm the phase transition occurring at about 220 K as observed crystallographically, and enable for unambiguous charge assignment to the different C(60) species in the title fulleride.
    Chemistry - A European Journal 02/2011; 17(6):1798-805. DOI:10.1002/chem.201002731 · 5.70 Impact Factor
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    ABSTRACT: Mutual attraction: pi-pi bonding promotes electronic interactions between graphene and a pi-conjugated perylene in a liquid dispersion.
    Advanced Materials 12/2010; 22(48):5483-7. DOI:10.1002/adma.201003206 · 15.41 Impact Factor
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    ABSTRACT: A study is made on a strain of higher basydiomycete Flammulia velutipes (Fr.) P. Karst. The conditions of maximum biomass production by Flammulia velutipes were studied. Soluble and insoluble fractions were isolated from mycelium. The composition of cultured mycelium and aqueous extracts from mycelium were investigated. These objects mainly contained carbohydrates (65.3 and 84.0% in insoluble and soluble fractions, respectively, and 56% mycelium), proteins (7.5–10.0% in fractions and 17.5% in mycelium), as well as an insignificant amount of mineral substances. The main carbohydrate component of fractions was glucose (53.6–78.8%); galactose and mannose were also present, as well as fucose and xylose in insignificant amounts. The aqueous extracts from mycelium demonstrated immunomodulating activity. They rendered a stimulating effect on the functional activity of macrophages—central cells of the reticluoendothelial system. The soluble fraction had a more pronounced effect than the insoluble fraction.
    Applied Biochemistry and Microbiology 09/2010; 46(5):536-539. DOI:10.1134/S0003683810050121 · 0.66 Impact Factor
  • Nina V. Kozhemyakina, Jürgen Nuss, Martin Jansen
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    ABSTRACT: The “break-and-seal” approach was applied to synthesize the new fulleride [K(DB24C8)(DME)]2C60·DME by reacting fullerene C60 with potassium and dibenzo-24-crown-8 (DB24C8) in dimethoxyethane (DME). Single crystals were grown from solution by the modified “temperature difference method”, single-crystal X-ray analysis was performed revealing the structure [C2/c, Z = 4, a = 31.133(4), b = 15.127(2), c = 21.433(3) Å, β = 117.506(3)°, R1 = 0.056, wR(all) = 0.171, 8459 independent reflections]. Due to crystal symmetry, the C602– anion is disordered between two well distinguishable orientations. The distribution of the bond lengths within the fullerene is discussed and attributed to a Jahn–Teller distortion.
    Berichte der deutschen chemischen Gesellschaft 08/2009; 2009(26):3900 - 3903. DOI:10.1002/ejic.200900542
  • Nina V. Kozhemyakina, Jürgen Nuss, Martin Jansen Prof. Dr
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    ABSTRACT: The “break-and-seal” method known to be used for synthesis of sensitive compounds (alkalides, electrides and for living anionic polymerization) was applied for the first time for fulleride synthesis providing highest purity of the reaction conditions. A new fulleride KC60(THF)5·2THF was prepared in solution by reacting fullerene C60 with potassium and dibenzo-24-crown-8 in tetrahydrofurane. Single crystals were grown from solution by the modified “temperature difference method”, single- crystal X-ray analysis was performed revealing the structure [P21212, Z = 4, a = 17.802(5), b = 30.085(9), c = 9.863(3) Å, R1 = 0.069, wR(all) = 0.191, 5563 independent reflections]. In this compound, the charge of fulleride is –1, the C60– radical-anion being fully ordered. A constitutive structural feature is octahedrally coordinated potassium atoms with five THF and one fullerideas ligands. C60– is functioning as a η3-ligand: [K(η3-C60)(η1-THF)5]·2THF.
    Zeitschrift für anorganische und allgemeine Chemie 07/2009; 635(9‐10):1355 - 1361. DOI:10.1002/zaac.200900283 · 1.25 Impact Factor
  • Nina V. Kozhemyakina
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    ABSTRACT: The present dissertation deals with the synthesis and characterization of fullerides. For the first time the "break-and-seal" technique was applied for fulleride synthesis. The reaction was performed in a completely all-glass apparatus under vacuum, avoiding the use of glass connections and use of grease. Starting from crown-ethers, potassium metal and C60 fullerene, six new fullerides have been synthesized. The modified "temperature difference method" was successfully used for growing single crystals from solution within a few days. In [K(DB24C8)(DME)]2C60*(DME) the fullerene unit has a charge of 2-. The (C60)2- units are arranged in hexagonal layers parallel to the ab plane, forming distorted trigonal prisms. The fullerene anions and potassium cations develop a pseudobinary topology which is reminiscent of the CdI2 structure type. Bond lengths' distribution in (C60)2- was examined. One orientation of the dianion was found to match perfectly the one predicted by calculations. KC60(THF)5*(THF)2 crystallizes in a structure with fully ordered C60 units. C60- anion-radicals and K+ form ion pairs. The ion pairs form corrugated layers in the ac crystallographic plane, the given compound being an example for a low-dimensional fulleride partial structure. For the compound [K(DB24C8)(THF)]2C60*THF the structure solution was complicated by the disorder of crown-ether and solvent molecules which could not be overcome, although the (C60)2- unit was ordered. In [K(DB24C8)(DME)]C60 the fullerene unit exists as a monomeric anion-radical and in [K(DB24C8)(DME)]2[C60]2 - as a dimer-dianion. The latter compound is an example of rather not many fulleride structures, where C60 exists in the form of dimers. The interfullerene C-C bond length is 1.57(3) Å. In [4{K(DB18C6)(C60-)}(THF)6]*[C60]*(THF)6 at temperatures above 220 K each of the four C60- units exists in form of anion-radicals, and at lower temperatures - as a dimer-dianion, the interfullerene bond being 1.63(0) Å. The dimers are fully ordered. In addition, uncharged disordered C60 molecules are found, what follows from the charge balance. The low-temperature phase is a first example of a fulleride structure where fullerene exists in three different bonding states: anion-radical monomer, dianion-dimer, and a neutral C60. In the dimer, the pentagons adjacent to sp3-hybridized carbon atoms, are in trans-conformation. DFT calculations were performed, and it is now for the first time that a localization of the negative charge on a small fragment of the C60 cage was found out. Knowing this, it becomes conclusive, considering the Coulombic repulsion, that the preferred orientation of two bound C60- units is trans-conformation. Magnetic measurements were performed. The method for fulleride synthesis used in the present work has a big potential for broadening by using different metals (e.g. alkali, alkali-earth), varying the complexing agents (crown-ethers, cryptands), as well as the organic solvent (or solvent mixtures).
    01/2009, Degree: Doctoral, Supervisor: Martin Jansen