František Šeršeň

Cut-off Effect in Antimicrobial Activity and in Membrane Perturbation Efficiency of the Homologous Series of N,N-Dimethylalkylamine Oxides†

Abstract— The antimicrobial activity of the homologous series of N,N‐dimethylalkylamine oxides (DMAO) was found to be quasi parabolically dependent on alkyl chain length with a maximum at n ∼ 15 and n ∼ 12 for Staphylococcus aureus and Escherichia coli, respectively. The physicochemical properties of DMAOs as characterized by critical micelle concentrations, retention times of 1‐alkenes generated from DMAOs by gas‐liquid chromatography, Rm values in reversed phase chromatography, and bacterial lipid/aqueous phase partition coefficients were found to correlate with the alkyl chain length. The effect of DMAOs on the structure of the model membrane prepared from isolated lipids from Escherichia coli as detected by a spin probe method was maximal for the alkyl chain length n ∼ 10–12 coinciding with the maximum in the antimicrobial activity observed with Escherichia coli. It is suggested that the cut‐off in the DMAO antimicrobial activity is caused by the cut‐off in the DMAO perturbing effect on the membrane structure.

Study of fungicidal and antibacterial effect of the Cu(II)-complexes of thiophene oligomers synthesized in ZSM-5 zeolite channels.

The influence of the Cu(II)-complexes of thiophene oligomers synthesized by oxidative polymerization of thiophene with Cu2+ ions in ZSM-5 zeolite channels on fungicidal and antimicrobial properties was studied. It has been found that the heterogeneous system culture medium-modified zeolite increases sporulation of the tested fungus (Aspergillus niger) and concurrently kills yeast (Candida albicans). These effects are attributed to a slow release of Cu2+ ions and thiophene oligomers into the culture medium. As for the tested bacteria (G+ Staphylococcus aureus, G- Escherichia coli), the percentage of the killed cells increases due to light activation of the system. The light effect is assigned to photogeneration of the reactive oxygen species (ROS), mainly *OH radicals, which were registered in the water solution by EPR spectroscopy. It has been confirmed that the thiophene oligomers present in the Cu-ZSM-5 microstructure slow down the release of copper into the medium.

Antimutagenic activity and radical scavenging activity of water infusions and phenolics from Ligustrum plants leaves.

Water infusions of Ligustrum delavayanum and Ligustrum vulgare leaves and eight phenolics isolated therefrom have been assayed in vitro on ofloxacin-induced genotoxicity in the unicellular flagellate Euglena gracilis. The tested compounds luteolin, quercetin, luteolin-7-glucoside, luteolin-7-rutinoside, quercetin-3-rutinoside, apigenin-7-rutinoside, tyrosol and esculetin inhibited the mutagenic activity of ofloxacin (43 µM) in E. gracilis. Water infusions from leaves of L. delavayanum and L. vulgare showed higher antimutagenic effect (pt < 0.001). The activity of these samples against ofloxacin (86 µM)-induced genotoxicity was lower, but statistically significant (pt < 0.05), excluding the water infusion of L. delavayanum leaves (pt < 0.01). Efficacy of quercetin, luteolin-7-rutinoside, apigenin-7-rutinoside was insignificant. The antimutagenic effect of most phenolics we studied could be clearly ascribed to their DPPH scavenging activity, substitution patterns and lipophilicity.

Action of Mercury on the Photosynthetic Apparatus of Spinach Chloroplasts

In chloroplasts of Spinacea oleracea L., Hg2+ ions interact with some sites in the photosynthetic electron transport chain: (l) with the intermediates Z+/D+ situated in the D1 and D2 proteins and with the manganese cluster in the oxygen evolving complex which are located on the donor side of photosystem (PS) 2, (2) with the chlorophyll a dimer in the core of PS1 (P700). P700 is oxidized in the dark by HgCl2. The Hg2+ ions form organometallic complexes with amino acids contained in chloroplast proteins.

Anomaly in magnetic properties of poly(3-alkylthiophene)s depending on alkyl chain length

Abstract The influence of the alkyl side-chain length exerted on the magnetic properties of poly(3-alkylthiophene)s, i.e. poly(3-dodecylthiophene) (PDDT) and poly(3-hexadecylthiophene) (PHDT), has been studied. The temperature dependences of the magnetic susceptibility and EPR signal have shown that PDDT displays some antiferromagnetic properties at the Neel temperature of 237 K. However, these properties were unnoticed for PHDT. The anomaly in the magnetic properties of PDDT and PHDT is discussed within the scope of differences in the crystalline phase of polymer derivatives brought about by a different alkyl side-chain length.

The effect of Cu(II) ions bound with tridentate Schiff base ligands upon the photosynthetic apparatus

Summary The effect of diaqua-(N-pyruvidene-β-alaninato) copper (II) monohydrate (Cu(pyr-β-ala)) on the photosynthetic apparatus of spinach chloroplasts was investigated. It was found that Cu(pyr-β-ala) inhibits the photosynthetic electron transport in chloroplasts due to its interaction with the photosynthetic centers. Its sites of action have been determined to be not only the intermediate Tyr Z (reported by Schroder et al., 1994), but also the intermediate Tyr D , which are situated in D 1 and D 2 proteins on the donor side of PS 2. The interaction of Cu(pyr-β-ala) with these intermediates was manifested by a decrease of the intensity of EPR signals II slow and II very fast , respectively, in chloroplasts treated with Cu(pyr-β-ala). The appearance of lines corresponding to Mn 2+ ions in EPR spectrum of Cu(pyr-β-ala)-treated chloroplasts and simultaneous disappearance of the manganese band in spectra of band radionuclide X-ray fluorescence analysis (RFA) confirm that a further site of Cu(pyr-β-ala) action is the manganese cluster in the oxygen evolving complex (OEC) on the donor side of PS 2. One of the suggested mechanisms of action of Cu(pyr-β-ala), namely chelatation of its copper(II) ions with tryptophan and tyrosine constituents of proteins situated in photosynthetic centres, has been confirmed by the results of fluorescence studies (quenching of the emission bands of the above mentioned aromatic amino acids in the presence of Cu(pyr-β-ala)) and EPR spectroscopy (differences in the form of spectra of Cu 2+ ions corresponding to the dissolved Cu(pyr-β-ala) and to chloroplast-trapped Cu 2+ ions of this compound). The second suggested mechanism of action of Cu(pyr-β-ala) is the substitution of manganese and calcium ions present in OEC by copper, which was confirmed by the intensity decrease of their bands (channel numbers: 91, 106 for Mn and 39 for Ca) in RFA spectra of Cu(pyr-β-ala)-treated chloroplasts and simultaneous increase of the intensity of corresponding bands belonging to Cu (channel numbers: 146, 168).

Photosynthesis-inhibiting Effects of Cationic Biodegradable Gemini Surfactants

Abstract Cationic biodegradable gemini surfactants 3,8-diaza-4,7-dioxodecane-1,10-diylbis(alkyldimethylammonium bromide) (I) with R = C9H19–C18H37 inhibited photosynthetic electron transport (PET) in spinach chloroplasts and reduced chlorophyll (Chl) content in Chlorella vulgaris. The inhibitory effects of I intensively depended on the length of alkyl chain showing quasi-parabolic (Chlorella vulgaris) or bilinear (PET) course. IC50 value related to reduction of Chl content in C. vulgaris for dodecyl derivative was 0.6 × 10−6 mol dm−3 indicating its strong anti-algal effect. Using EPR spectroscopy as the site of inhibitory action of I in the photosynthetic apparatus the intermediates Z∗ and D∗ or their close surroundings were determined. As a further target of I inhibitory action the manganese cluster occurring on the donor side of photosystem II was estimated.

5-Bromo- and 3,5-dibromo-2-hydroxy-N-phenylbenzamides — inhibitors of photosynthesis

Abstract5-Bromo-(Br-PBA) and 3,5-dibromo-2-hydroxy-N-phenylbenzamides (Br2-PBA) inhibited photosynthetic electron transport (PET) and their inhibitory efficiency depended on the compound lipophilicity as well as on the electronic properties of the R substituent in the N-phenyl moiety. Br-PBA showed higher PET inhibiting activity than Br2-PBA with the same R substituent. The most effective inhibitors in the tested series were the derivatives with R = 3-F (Br-PBA; IC50 = 4.3 μmol dm−3) and R = 3-Cl (Br2-PBA; IC50 = 8.6 μmol dm−3). Bilinear dependence of the PET inhibiting activity on the lipophilicity of the compounds as well as on the Hammett constant, σ, of the R substituent was observed for both investigated series. Using EPR spectroscopy it was found that the site of action of the tested compounds in the photosynthetic apparatus is situated on the donor side of PS 2, in D· or in the Z·/D· intermediates. Interaction of the studied compounds with chlorophyll a and aromatic amino acids present in the pigment-protein complexes mainly in photosystem 2 was documented by fluorescence spectroscopy.

Characterization and properties of the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine with 3-dodecylthiophene

Abstract The method of chemical oxidative polymerization with FeCl 3 was used to synthesize the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine (DPTA) and 3-dodecylthiophene (DDT). The copolymer was characterized by UV–VIS, Raman, 1 H and 13 C NMR and EPR spectroscopy. It has been found that the DPTA/DDT copolymer exhibits properties of the low-band-gap polymer ( E g

Role of polarons in the antiferromagnetic behaviour of poly (3-dodecylthiophene)

Abstract A mathematical model was suggested and tested to elucidate the antiferromagnetic behaviour of temperature dependence of the magnetic susceptibility of poly (3-dodecylthiophene) (PDDT) which takes advantage of the physical properties of polarons and bipolarons. It has been found that the responsibility for the antiferromagnetic behaviour of temperature dependence of the magnetic susceptibility of PDDT is the conversion of polarons to bipolarons, rather than the presence of several crystalline sublattices of the polymer with different orientations of magnetic moments. The antiferromagnetic character is caused by paramagnetic polarons, the number of which decreases with lowering temperature. The proposed model was verified, with good results also for other conductive polymers exhibiting antiferromagnetic properties known from the literature.