Nikolay G. Vassilev

Production of organic acids by immobilized filamentous fungi

This article reviews current knowledge of the production of organic acids by immobilized filamentous fungi. The most widely used methods of immobilization are based on the adsorption and entrapment of the fungal cells. A variety of carriers have been employed but the open-porous materials and polymers with controlled characteristics are most suitable. Further elucidation of the mechanisms of interaction between cells and carriers may increase control of immobilization procedures. In general, immobilized systems show higher productivity than freely suspended cells and fluidized-bed reactors enable long-term operation of highly aerobic fermentations. The performance of the immobilized filamentous fungi is significantly affected by the nature and age of the cells, medium composition and process parameters, but published work merely describes such effects, with little information on underlying mechanisms.

Ab initio study of the barrier to internal rotation in simple amides: 1. N,N-dimethylformamide and N,N-dimethylcarbamic halogenides

Abstract Free energies of activation for rotation about the amide C–N bond in X–C(O)N(CH 3 ) 2 (X=H, F, Cl and Br) were calculated at the MP2(fc)/6-31+G*//6-31G* and MP2(fc)/6-311++G**//6-311++G** levels and compared with NMR gas-phase data. The results of calculations indicate that the repulsion between X and methyl group in ground state and the repulsion between X or oxygen and nitrogen lone pair in transition states (TS) are largely responsible for the difference in the free energies of the studied amides. For X=H (DMF), the anti TS is more stable; for the cases X=Cl, Br, the syn TS is more stable, while for the case X=F the two transition states are energetically almost equivalent.

Effect of gamma-ray irradiation on the fatty acid profile of irradiated beef meat

The effect of γ-ray irradiation on the fatty acid profile of beef meat was examined at doses of 2.5, 5.0, 7.5, 10.0 and 15.0kGy by means of (1)H NMR spectroscopy. NMR results revealed a clear trend toward an increase in the amount of saturated fatty acids and a decrease in the amount of polyunsaturated fatty acids in the triacylglycerol composition of the irradiated samples compared to the unirradiated sample with increasing the irradiation dose. The observed changes in the fatty acid profile were confirmed by gas chromatography analysis of the samples irradiated at doses of 7.5, 10.0 and 15.0kGy.

Ab initio study of the barrier to internal rotation in simple amides. Part 2. N,N-dimethylacetamide and N,N-dimethyl-2-(mono-, di- and tri-) halogenacetamides

Abstract The free energies of activation for rotation about the amide C–N bond in R–C(O)N(CH 3 ) 2 (R=CH 3 , CH 2 F, CHF 2 , CF 3 and CCl 3 ) were calculated at the MP2(fc)/6-31+G ∗ //6-31G ∗ level and compared with the NMR gas-phase data. The results of calculations indicate that the repulsion between the substituent R and methyl group in ground state and the conformation of R are largely responsible for the difference in the free energies of the studied amides. The anti transition state is the preferred one in all the studied compounds.

Antimycobacterial activity of novel hydrazide-hydrazone derivatives with 2H-chromene and coumarin scaffold.

This study reports the synthesis of new 2H-chromene or coumarin based acylhydrazones, which were evaluated for their in vitro antimycobacterial activity against reference strain Mycobacterium tuberculosis H37Rv and compared to the first-line antituberculosis drugs, isoniazid (INH) and ethambutol (EMB). The most active compounds 7m (MIC 0.13μM), 7o (MIC 0.15μM) and 7k (MIC 0.17μM) demonstrated antimycobacterial activity at submicromolar concentration level and remarkably minimal associated cytotoxicity in the human embryonic kidney cell line HEK-293T. Structure-activity relationship for this class of compounds has been established.

H-TETRAOXASPIROPHOSPHORANES AS POSSIBLE INTERMEDIATES IN THE PHOSPHONYLATION BY PHOSPHOROUS ACID/OXIRANES

Abstract The detailed 31P-NMR study of the mechanism of the ribozymomimetic phosphonylation with phosphorous acid / oxirane revealed consecutive formation of β-hydroxy H-phosphonate monoester, di-(β-hydroxyalkyl) H-phosphonate, alkylene H-phosphonate. β-hydroxyalkyl alkylene phosphite and the corresponding stereoelectronically stabilized pentacoordinated H-tetraoxaspirophosphorane. The equilibrium between the triphosphite and the spirophosphorane shifts towards the β-hydroxyalkyl alkylene phosphite at high temperatures. In the presence of alcohol and controlled amounts of water transesterification of the β-hydroxyalkyl alkylene phosphite to the corresponding alkyl alkylene phosphite, and hydrolysis to β-hydroxyalkyl alkyl H-phosphonate proceed at the elevated temperature. β-Hydroxyalkyl alkyl H-phosphonates are model compounds of the phosphodiester bond and undergo hydrolysis with a diol leaving in the presence of one equivalent of water.

REACTION OF THE LITHIUM DERIVATIVE OF DIETHYL 2-(OR 3-)METHYLPHENYLMETHANEPHOSPHONATE WITH KETONES. AN EXAMPLE OF HIGH SYN-STEREOSELECTIVITY

Abstract The reaction of the lithium derivative of diethyl ester of 2-(or 3-)methylphenylmethanephosphonic acid (1-Li) with a large number of symmetric and unsymmetric ketones 2a-r is studied at −70°C in THF, the corresponding adducts—diethyl esters of 1-(2- or 3-methylphenyl)-2,2-dialkyl(phenyl)-2-hydroxy-ethanephosphonic acid 3a-r being isolated. The results of stereospecific olefination of the β-hydroxyphosphonates 3j, 3k, 3o and 3p indicate the influence of combined steric effects in ketones 2 and ortho- and metha-methyl substituted benzylphosphonates 1. Spectral investigations and PM3-calculations prove high synstereoselectivity of the reaction of ortho-methyl substituted benzylphosphonates 1a with studied ketones.

trans-Dichloro(η 2-ethylene) (N-3-pyridinylmethanesulfonamide)platinum(II). Crystal structure, spectroscopic, and thermoanalytical characterization, and cytotoxicity assays

The organometallic complex, trans-[PtCl2(η 2-C2H4)(PMSA)] (1), where PMSA = N-3-pyridinylmethanesulfonamide, has been synthesized and characterized by elemental analysis, molar electric conductivity, IR, electronic, and NMR (1H, 13C, and 195Pt) spectroscopy, and thermal analysis. X-ray crystallography revealed that in 1 [monoclinic, P21 c, a = 5.1260(1), b = 19.1600(4), c = 12.7990(3) Å, β = 97.242(2)°, Z = 4] Pt(II) shows planar coordination geometry with PMSA coordinated via the pyridine. The ethylene is virtually perpendicular to the PtCl2N plane with the pyridine ring twisted relative to this plane by 47°. In in vitro assays, PMSA, K[PtCl3(η 2-C2H4)] · H2O, and 1 do not exhibit appreciable cytotoxic activity against human K562 and HepG2 tumor cell lines.

Coordination chemistry of a para-tert-octylcalix[4]arene fitted with phosphinoyl pendant arms towards 4f-elements: Extraction, synergism, separation

Abstract The solvent extraction of trivalent lanthanoids (Ln3+) by 5,11,17,23-tetra(para-tert-octyl)-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene (S), bearing four phosphine oxide donor groups at the lower rim as synergistic agent in combination with a 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) in CHCl3 from chloride medium at µ = 0.1 was quantitatively described in the form of LnP3·S complexes. The role of the synergistic agent on the extraction process was discussed. The values of the separation factors have been evaluated. On the basis of the IR and NMR spectra the stoichiometry and the structure of the solid mixed complex of Eu(III) with HP and S were proposed.

Synthesis of 4-Aminocoumarin Derivatives with N-Substitutents Containing Hydroxy or Amino Groups

Reactions of 4-hydroxycoumarin (1a) and 4-chlorocoumarin-3-carbaldehyde (1b) with amino alcohols or alkylene diamines led to the formation of the corresponding N-substituted 4-aminocoumarins 3, 5 and 6. However, 4-hydroxycoumarin-3-carbaldehyde (8) reacted with 2-aminoethanol and ethylenediamine to give N-substituted 3-(aminomethylene)-chromane-2,4-diones 9a, b. The structure and the E-configuration of compound 6 were proven by X-ray crystal structure analysis. Products 9a, b displayed signals of both E- and Z-isomers in their NMR spectra. All novel products have been characterized by means of spectral (IR, NMR, MS) data and elemental analyses Graphical Abstract Synthesis of 4-Aminocoumarin Derivatives with N-Substitutents Containing Hydroxy or Amino Groups