Jiří Ludvík

Electrochemical oxidation of substituted 1,4-dihydropyridines in non-aqueous acetonitrile

Abstract A series of 29 substituted 1,4-dihydropyridines has been studied in acetonitrile by means of voltammetric methods at a platinum electrode. The formation of radical intermediates has been investigated with the help of ESR spectroscopy. A cell for in situ electrochemical generation of radical ions in ESR measurements has been described. In the detection of radicals a comparison has been made between fast cyclic voltammetry (up to 50 V s −1 ) at low temperatures (down to −40°C) and ESR spectroscopy. The influence of substituents on oxidation potentials and on oxidation mechanisms has been studied.

Electrochemical oxidation mechanisms of different type 1,4-dihydropyridine derivatives in acetonitrile

Abstract A series of 32 substituted dihydropyridines of essentially two types (PyH and PyR) was electrochemically oxidized at a platinum electrode in acetonitrile. Based upon voltammetric experiments in anhydrous, acid, basic and neutral, partially aqueous media, on cp. coulometric results and on preparative electrolyses, side reactions were detected within the framework of the investigated electro-oxidation mechanism; these reactions elucidate some as yet non-investigated aspects in the behaviour of these compounds. With the PyH type a one-electron EC mechanism was also discovered in addition to the dominating ECE mechanism; moreover a pronounced protonation of the reactant was observed. With the PyR type compounds relatively stable radical cations homogeneously catalyse the oxidation of acetonitrile giving rise to proton splitting off on account of the oxidation proper. On the basis of the above results, overall mechanisms of the electro-oxidation of both 1,4-dihydropyridine types in acetonitrile were suggested or supplemented.

Physiological activity of immobilized cells of Claviceps fusiformis during long-term semicontinuous cultivation

SummaryThe 550-day semicontinuous cultivation of Claviceps fusiformis immobilized in calcium alginate is documented. The vegetative mycelium from seed or from early-production submerged culture is the best choice for immobilization. No extracellular glucans are produced by immobilized cells. Immobilized spores give low yields of clavine alkaloids. Alginate concentrations in a range of 2%–4% do not influence yield and spectrum of alkaloids. The cytoplasm of the immobilized cells becomes condensed (after 3 days), polysaccharides disappear, and centres of lipid synthesis are formed in the cytoplasm. After 60 days the cells harbour a great number of lipid particles, mitochondria are diminishing and their cristae partly disappear, indicating a decreased respiration capacity. After 350–500 days the volume of most cells is increased many times and the cells are filled with large oval bodies of electrondense material. Chloramphenicol protects immobilized cultures against bacterial contamination.

Determination of water in acetonitrile, propionitrile, dimethylformamide and tetrahydrofuran by infrared and near-infrared spectrometry

For determining small amounts of water in non-aqueous solvents (acetonitrile, propionitrile, dimethylformamide and tetrahydrofuran) IR and near-IR spectrometry were applied. In order to prevent overlapping of the observed water band with that of the solvent, either one of the fundamental vibrations (v1 or v3 at about 3500 cm–1) was selected or combination vibrations (v1+v2) at 5200 cm–1. This method is rapid and convenient, especially in laboratories that are not equipped with a single-purpose analytical titrator according to Karl Fischer, or where water is not often determined. The detection limit is about 20 p.p.m. of water, i.e., 10–3 mol l–1. Further uses of the method were verified experimentally and are discussed.

New bacteriophage-like particles in Corynebacterium glutamicum.

Three new phage-like particles (CG1, CG2, and CGK1) were isolated from Corynebacterium glutamicum CBII. Particles CG1 and CG2 are DNA phages with long, noncontractile tails, CGK1 is a killer particle according to electron microscopy. A heat-stable low-molecular-weight bacteriocidal substance affecting various coryneform bacteria was observed to be joined to the killer particle CGK1.

Ultrastructure of Bacillus licheniformis bacteriophage BLE and its DNA.

Abstract A new bacteriophage has been isolated and its form has been described. As far as we know, it is active on Bacillus licheniformis only and is called BLE. The phage particles were negatively stained with phosphotungstic acid. The head of phage BLE is bacilliform and is about 50 nm wide and 130 nm in length. The noncontractile tail is 240 nm in length and 6.3 nm thick and has a cross-striated sheath. The base plate of the tail exhibits the shape of a six-pointed star. From the phage BLE, phenol-extracted DNA molecules were prepared for electron microscopy by the cytochrome c film technique of A. Kleinschmidt and R. K. Zahn (Z. Naturforsch. B, 14, 770–779). Some DNA molecules probably of circular form were observed. Measurement of contour lengths of DNA molecules gave a value 21 ± 0.8 gm, which corresponds to a molecular weight of (41.1 ± 1.5) × 103.

Netropsin suppresses the rise of activity of an intracellular proteolytic system in sporulatingBacillus megaterium

Intracellular catabolism of proteins labeled at the end of the exponential growth proceeded in two phases during sporulation. The first phase was induced by starvation and took place also in cells whose sporulation was inhibited by netropsin. The second phase of degradation, which was triggered at the onset of the irreversible sporulation phase, was inhibited by netropsin. Intracellular proteolytic activity determined in disintegrated cells, i.e., primarily the activity of the cytoplasmic Ca2+-dependent serine proteinase(s) at the first place, was increasing throughout the sporulation process and reached its maximum during the irreversible sporulation phase. Its increase was suppressed by netropsin. Fractionation of the cell sap by HPLC revealed a similar distribution of proteolytic activities in the extract from control and netropsin-inhibited cells. The antibiotic thus probably affected the activation, not the formation of the cytoplasmic serine proteinase(s). Netropsin also inhibited an increase of proteolytic activity in the membrane fraction, probably owing to the presence of two different proteolytic enzymes.

Non-uniform current density distribution at a rde. Observation by means of photographing electrochemiluminescence

Abstract Equations for the current at a rde have been derived with the presumption that equal accessibility for any place on the electrode surface. An example of non-homogeneous current density distribution at the Pt- rde was observed in photographs of electrogenerated chemiluminescence (ECL) where the intensity of emission changes with the distance from the centre and depends on the type of the process and on the rotation velocity.

Cell structure and reproduction process in the Blue-Green algaChamaesiphon

Ultrathin sections were studied in 2 strains and 2 samples from the nature of the genusChamaesiphon, representing 4 different species. Thylakoids are distributed mainly on the periphery of the cells, the cell-wall is probably 2-layered, and variable multilayered mucilaginous envelopes are developed around the cells. The cell division starts, as well as in otherCyanophyceae, by the invagination of the cytoplasmic membrane and of cell-wall layers into the protoplast; the mucilaginous envelopes—pseudovaginae—do not participate in this process but they form only the firm sheaths around the cells. The way of reproduction is, therefore, essentially the same as that described in other chroococcal Blue-Green algae (e.g.,Synechococcus), and the main difference is the polarized growth of theChamaesiphon cells. The taxonomical position of chamaesiphonoid algae is not as isolated as it was earlier supposed, the similarity withEntophysalidaceae is evident.

Laser photosensitized oxidation of tetrafluoroethene by molecular oxygen

Abstract Surface-less conditions of CO 2 laser photosensitized (SF 6 ) oxidation of tetrafluoroethene with molecular O 2 ( 3 Σ) oxygen reveal that the true gas-phase reaction is accompanied with chemiluminiscence and proceeds via intermediary dioxetane to yield solely carbonyl fluoride.