Mesoscale simulations of confined Nafion thin films.

The morphology and transport properties of thin films of the ionomer Nafion, with thicknesses on the order of the bulk cluster size, have been investigated as a model system to explain the anomalous behaviour of catalyst/electrode-polymer interfaces in membrane electrode assemblies. We have employed dissipative particle dynamics (DPD) to investigate the interaction of water and fluorocarbon chains, with carbon and quartz as confining materials, for a wide range of operational water contents and film thicknesses. We found confinement-induced clustering of water perpendicular to the thin film. Hydrophobic carbon forms a water depletion zone near the film interface, whereas hydrophilic quartz results in a zone with excess water. There are, on average, oscillating water-rich and fluorocarbon-rich regions, in agreement with experimental results from neutron reflectometry. Water diffusivity shows increasing directional anisotropy of up to 30% with decreasing film thickness, depending on the hydrophilicity of the confining material. A percolation analysis revealed significant differences in water clustering and connectivity with the confining material. These findings indicate the fundamentally different nature of ionomer thin films, compared to membranes, and suggest explanations for increased ionic resistances observed in the catalyst layer.

Characterization of metalloanticancer capacity of an agglutinin from wheat.

Many anticancer drugs cannot recognize selectively tumor tissues, and cause destruction to normal ones. Although it is very toxic, cisplatin is still one of the most applied chemotherapeutics used for treatment of sarcomas, carcinomas, etc. It causes severe side effects as a result of the lack of selectivity of the drug to tumor tissue and acquired or intrinsic resistance occurs. Wheat germ agglutinin (WGA) is a lectin that specifically recognizes transformed cells: prostate cancer cells, pancreatic cells etc., and is uptaken into the tumor cells for which it appears to be a suitable target for anticancer agents. A fluorescence spectroscopy method was used to study the interaction of WGA with four metal-based anticancer drugs: cisplatin, Pt porphyrin and two gold porphyrins. The affinity constant (k(D)) for binding of cisplatin with WGA was k(D) = 6.67 ± 2.5 µM. The hyperbolic curve indicated the presence of a single cisplatin binding site. The affinity of Au and Pt porphyrin to WGA (k(D) = 0.08-0.49 µM) is almost two orders of magnitude higher than that for cisplatin. We found that Pt porphyrin could displace fluorescent dye ANS showing an increase in the fluorescence intensity with a concomitant blue shift of the emission maximum suggesting that the compounds accommodate the same binding site. Current research characterizes the metalloanticancer binding capacity of WGA. Our results indicate that four metal-based anticancer agents have high affinity for WGA. Since WGA recognizes transformed cells, the obtained data show that this protein might have putative usage as a drug delivery molecule in cancer.

Allelopathic activity of micropropagated Hyssopus officinalis L., Lamiaceae, water infusions / Atividade alelopática de micropropagado Hyssopus officinalis L. infusãos aquosos

The natural habitats of Hyssopus officinalis L. (Lamiaceae) in Bulgaria are not sufficient to satisfy the needs of this herb. Micropropagation might be used for obtaining plants with desirable traits. Hyssopus is a medicinal aromatic plant that has not been studied very much. Recently aromatic plants were investigated as potent allelopathic plants. Determining the modes of action of allelochemicals is one of the challenging aspects in allelopathic studies. The objective of this study was to determine the allelopathic activity of micropropagated Hyssopus officinalis L. water infusions. We evaluated the influence of hot and cold infusions made from the aerial parts of hyssopus under laboratory conditions. For this purpose we tested the effects of infusions on germination and root elongation of Cucumis sativus L. and Triticum aestivum L. We determined also the effect on mitotic activity using Allium cepa L. chromosome aberration test. The results demonstrated the presence of water soluble allelopathic compounds in hyssopus tissue. Infusions exhibited growth depressive effect which was stronger at early stage of growth. The inhibitory effects on germination and root elongation were stronger in T. aestivum than in C. sativus. Hyssopus also exerted mitodepressive and genotoxic effect in Allium cepa root tip cells.

Os hábitats naturais de Hyssopus officinalis L. (Lamiaceae) na Bulgária não são suficientes para satisfazer as necessidades desta erva. A micropropagação poderia ser usada para obter plantas com características desejáveis. Hyssopus é uma planta aromática medicinal que não foi estudada muito. Recentemente plantas aromáticas foram investigadas como potentes plantas alelopáticas. A determinação dos modos da ação de aleloquímicos é um dos aspectos desafiantes em estudos alelopáticos. O objetivo deste estudo foi determinar a atividade alelopática de micropropagado Hyssopus officinalis L. infusãos aquosos. Foi avaliada a influência de infusões quentes e frias feito de partes aéreas de hyssopus sob condições de laboratório. Com este propósito nós testou os efeitos de infusões em germinação e alongamento de raiz de Cucumis sativus L. e Triticum aestivum L. Determinamos também o efeito na atividade mitótica usando os Allium cepa L. teste de aberração cromossômica. Os resultados demonstraram a presença de compostos alelopáticos solúveis de água em tecido de hyssopus. As infusões exibiram o efeito depressivo do crescimento que era mais forte na fase inicial de crescimento. Os efeitos inibitivos em germinação e alongamento de raiz foram mais fortes em T. aestivum que em C. sativus. Hyssopus também exerceu efeito genotóxico e mitodepressivo em células de ponta de raiz de Allium cepa.

Human galectin-3 interacts with two anticancer drugs.

Human galectin-3 (hGal-3) is a mammalian lectin involved in regulation of RNA splicing, apoptosis, cell differentiation, and proliferation. Multimerized extracellular hGal-3 is thought to crosslink cells by binding to glycoproteins and glycosylated cancer antigens on the cell surface or extracellular matrix. Fluorescence spectroscopy and circular dichroism were used to study the interaction of hGal-3 with two anticancer agents: bohemine and Zn porphyrin (ZnTPPS(4)). The dissociation constant (k(D)) for binding of bohemine with hGal-3 was k(D) 0.23+/-0.05 microM. The hyperbolic titration curve indicated the presence of a single bohemine binding site. The binding of ZnTPPS(4) to hGal-3 (with and without lactose) is of high affinity having k(D)=0.18-0.20 microM and is not inhibited by lactose, indicating that ZnTPPS(4) and carbohydrate bind different sites. Circular dichroism spectra of the hGal-3 complexes suggested that the binding of the hydrophobic compounds changed the hGal-3 secondary structure. In summary, we show that two compounds with anticancer activity, bohemine and ZnTPPS(4), have high affinity for hGal-3 at a site that is distinct from its carbohydrate site. Since hGal-3 binds to several carbohydrate cancer antigens, the results suggest that it may have utility in the targeted delivery of drugs for cancer.

Cytotoxic and genotoxic effects of Br-containing oxaphosphole on Allium cepa L. root tip cells and mouse bone marrow cells.

The continuous production and release of chemicals into the environment has led to the need to assess their genotoxicity. Numerous organophosphorus compounds with different structures have been synthesized in recent years, and several oxaphosphole derivatives are known to possess biological activity. Such chemical compounds may influence proliferating cells and cause disturbances of the genetic material. In this study, we examined the cytotoxicity and genotoxicity of 4-bromo-N,N-diethyl-5,5-dimethyl-2,5-dihydro-1,2-oxaphosphol-2-amine 2-oxide (Br-oxph). In A. cepa cells, Br-oxph (10(-9) M, 10 (-6) M and 10 (-3) M) reduced the mitotic index 48 h after treatment with the two highest concentrations, with no significant effect at earlier intervals. Mitotic cells showed abnormalities 24 h and 48 h after treatment with the two lowest concentrations but there were no consistent changes in interphase cells. Bone marrow cells from mice treated with Br-oxph (2.82 x 10 (-3) µg/kg) also showed a reduced mitotic index after 48 h and a greater percentage of cells with aberrations (principally chromatid and isochromatid breaks). These findings indicate the cytotoxicity and genotoxicity of Br-oxph in the two systems studied.

Cytotoxic and genotoxic effects of Br-containing oxaphosphole on Allium cepa L. root tip cells and mouse bone marrow cells

The continuous production and release of chemicals into the environment has led to the need to assess their genotoxicity. Numerous organophosphorus compounds with different structures have been synthesized in recent years, and several oxaphosphole derivatives are known to possess biological activity. Such chemical compounds may influence proliferating cells and cause disturbances of the genetic material. In this study, we examined the cytotoxicity and genotoxicity of 4-bromo-N,N-diethyl-5,5-dimethyl-2,5-dihydro-1,2-oxaphosphol-2-amine 2-oxide (Br-oxph). In A. cepa cells, Br-oxph (10-9 M, 10-6 M and 10-3 M) reduced the mitotic index 48 h after treatment with the two highest concentrations, with no significant effect at earlier intervals. Mitotic cells showed abnormalities 24 h and 48 h after treatment with the two lowest concentrations but there were no consistent changes in interphase cells. Bone marrow cells from mice treated with Br-oxph (2.82 x 10-3 µg/kg) also showed a reduced mitotic index after 48 h and a greater percentage of cells with aberrations (principally chromatid and isochromatid breaks). These findings indicate the cytotoxicity and genotoxicity of Br-oxph in the two systems studied.

Fluorescence study of steroid hormone binding activity of Helix pomatia agglutinin.

Helix pomatia agglutinin (HPA) is a N-acetylgalactosamine (GalNAc) binding lectin, found in the reproductive gland of a Roman snail. The present study has shown that HPA, in addition to its carbohydrate binding capacity possesses a hydrophobic binding activity. This protein binds with high affinity (k(D)=1.9-2.4 microM) steroid hormones: testosterone and progesterone, identified as putative ligands for the animal lectin HPA. Additionally, we have found that this lectin also interacts with adenine (k(D)=5.4+/-0.5 microM) and arylaminonaphthalene sulfonate TNS (k(D)=12+/-0.3 microM). Binding of HPA to hormones and adenine was accompanied by a significant increase of the intrinsic Trp fluorescence (up to 50%), characterizing the conformational changes in the lectin molecule. The hyperbolic shape of the binding curves indicated one high affinity site for the two steroid hormones and adenine, and more than one hydrophobic site for TNS, showed by the sigmoidal curve fit and Hill coefficient of (n(H)=1.5+/-0.2). Hormones and adenine compete for an identical binding site, suggested to occupy the central hydrophobic cavity of the HPA hexamer. Fluorescence resonance energy transfer (FRET) was applied to calculate the intramolecular distance between TNS and Trp chromophores.

PA-I lectin from Pseudomonas aeruginosa binds acyl homoserine lactones.

The study analyses the binding affinities of Pseudomonas aeruginosa PA-I lectin (PA-IL) to three N-acyl homoserine lactones (AHSL), quorum sensing signal molecules responsible for cell-cell communication in bacteria. It shows that like some plant lectins, PA-IL has a dual function and, besides its carbohydrate-binding capacity, can accommodate AHLS. Formation of complexes between PA-IL and AHSL with acyl side chains composed of 4, 6 or 12 methyl groups is characterized by changes in the emissions of two incorporated fluorescent markers, TNS and IAEDANS, both derivatives of naphthalene sulfonic acid. PA-IL shows increasing affinities to lactones with longer aliphatic side chains. The values of the apparent dissociation constants (K(d)), which are similar to the previously determined K(d) for the adenine high affinity binding, and the similar effects of lactones and adenine on the TNS emission indicate one identical binding site for these ligands, which is suggested to represent the central cavity of the oligomeric molecule formed after the association of the four identical subunits of PA-IL. Intramolecular distances between the fluorescent markers and protein Trp residues are determined by fluorescence resonance energy transfer (FRET).

Fluorescence analysis of hormone binding activities of wheat germ agglutinin.

Wheat germ agglutinin (WGA) from embryos of the monocotyledonous plant Triticum vulgaris (Graminaceae) is a carbohydrate binding protein characterized by high specificity to N-acetyl-d-glucosamine and N-acetyl-d-neuraminic acid. In this study we show that parallel to its carbohydrate binding activities, WGA binds with several orders of magnitude higher affinity adenine, adenine-related cytokinins: kinetin, zeatin and isopentenyl-adenine as well as abscisic and gibberellic acids (K(d) 0.43-0.65 microM). Its interactions with these ligands cause conformational rearrangements in the protein molecules and significant enhancement of the protein tryptophan fluorescence (up to 60%) allowing characterization of the protein-hormone complexes. Dimeric WGA molecules possess two different classes of binding sites for the fluorescent hydrophobic probe 2-(p-toluidinyl) naphthalene sulfonic acid (TNS) as suggested by the sigmoid shape of the fluorescence titration curve and the value of the Hill coefficient (n(H) 1.6+/-0.3). The plant hormones displace part of the bound TNS probe and share the higher affinity TNS binding sites. These results characterize WGA as a hormone-binding protein.