Navegando por Palavras-chave "Monolayers"

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    Adsorption and enzyme activity of asparaginase at lipid Langmuir and Langmuir-Blodgett films
    (Elsevier Science Bv, 2017) da Rocha Junior, Carlos [UNIFESP]; Caseli, Luciano [UNIFESP]
    In this present work, the surface activity of the enzyme asparaginase was investigated at the air-water interface, presenting surface activity in high ionic strengths. Asparaginase was incorporated in Langmuir monolayers of the phospholipid dipaltnitoylphosphatidylcholine (DPPC), forming a mixed film, which was characterized with surface pressure-area isotherms, surface potential-area isotherms, polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The adsorption of the enzyme at the air-water interface condensed the lipid monolayer and increased the film compressibility at high surface pressures. Amide bands in the PM-IRRAS spectra were identified, with the C - N and C = 0 dipole moments lying parallel to monolayer plane, revealing the structuring of the enzyme into alpha-helices and beta-sheets. The floating monolayers were transferred to solid supports as Langmuir-Blodgett (LB) films and characterized with fluorescence spectroscopy and atomic force microscopy. Catalytic activities of the films were measured and compared to the homogenous medium. The enzyme accommodated in the LB films preserved more than 78% of the enzyme activity after 30 days, in contrast for the homogeneous medium, which preserved less than 13%. The method presented in this work not only allows for an enhanced catalytic activity, but also can help explain why certain film architectures exhibit better performance. (C) 2016 Elsevier B.V. All rights reserved.
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    Avaliação da interação molecular de 1,4 naftoquinona em modelos de membrana celular utilizando filmes de Langmuir
    (Universidade Federal de São Paulo, 2014-01-31) Hussein, Nadia [UNIFESP]; Caseli, Luciano [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Cancer is a disease characterized by the uncontrolled multiplication and spread of abnormal forms of cells. In order to treat cancer, anticancer drugs were used, which are natural or organosynthetic compounds that act against the development of cancer cells and tumor growth. In this group, we can include 1,4- naphthoquinone, which is present in various chemotherapeutics. It is a derivative of vitamin K, and a potent inhibitor of cell growth and tumor angiogenesis. Thus, this study aims to understand at the molecular level the interaction between this drug and cell membrane by means of simplified models of cell membrane (Langmuir monolayers formed by lipids). For this purpose, we performed measurements of surface tensiometry, curved surface pressure - area and infrared spectroscopy. For that, we employed the phospholipid DPPC (dipalmitoylphosphatidylcholine) for the formation of lipid monolayers (Langmuir films) which mimicked a healthy cell membrane, and DPPS (dipalmitoylphosphatidyl serine), representing cancerous membranes. Rabbit aorta endothelialcell cultures for healthy and tumorigenic cells were also employed. Phospholipids were spread on aqueous solutions, and surface pressure – area isotherms and infrared spectra were obtained. After that, different amounts of 1,4- naphthoquinone were added to the lipid monolayer and new isotherms and spectra were obtained . Similar procedures were performed with cell cultures. Three phenomena were observed due to the interaction between the monolayer and the drug: 1 ) the isotherms were shifted to smaller molecular areas, 2) 1,4- naphthoquinone increased the compressibility of the monolayer , causing a disruption in the organization of the film, which was confirmed later by infrared spectroscopy, and 3) the phase transitions has not been well defined in the surface pressure-area isotherms, suggesting a non-ideal mixture, due to interactions between the drug and the monolayer. For cell cultures, whereas minor changes were observed for cultures representing non-tumorigenic cells after the incorporation of the drug, significant changes were observed for cultures representing tumorigenic cells. Therefore, we conclude that 1,4-naphthoquinone interacts with cell membrane models represented by monolayers of DPPC, DPPS and cell cultures studied with a more expressive interaction with models of tumorigenic cells.
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    Implications of the structure for the luminescence properties of NBR-PF blend devices nanostructured as Langmuir-Blodgett films
    (Elsevier B.V., 2014-01-20) Barbosa, Camila G. [UNIFESP]; Faez, Roselena [UNIFESP]; Caseli, Luciano [UNIFESP]; Peres, Laura O. [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar)
    Properties of polymers in blends can be enhanced if molecular control is achieved. in this paper, we spread nitrile rubber (NBR) and polyfluorene (PF) on the air-water interface to form stable monolayers, as observed with surface pressure-area isotherms and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Mixed monolayers showed that the isotherms were shifted to lower areas in relation to the areas predicted for an ideal mixture, which indicates attractive interactions between the polymeric constituents. Also, the transfer of the polymeric films to solid supports was possible using the Langmuir-Blodgett (LB) technique and the optical properties of the films were evaluated with infrared, UV-vis and fluorescence spectroscopies. Molecular-level interactions between the components lead to marked changes in the properties of the films, which exhibited optical (photoluminescence) properties that could be controlled at the molecular level. (C) 2013 Elsevier B.V. All rights reserved.
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    Langmuir and Langmuir-Blodgett films of a quinoline-fluorene based copolymer
    (Elsevier B.V., 2012-01-20) Correia, Fabio Conte; Wang, Shu H.; Peres, Laura O. [UNIFESP]; Caseli, Luciano [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP)
    The fabrication of Langmuir-Blodgett (LB) films of synthetic polymers allows the control of molecular architecture in order to optimize physical properties. in this paper, the surface chemistry of a quinoline-fluorene based copolymer spread on the air-water interface is investigated. Surface pressure-area isotherms as well as Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) were employed to characterize the films, which could be transferred to solid supports by the LB technique. Atomic force microscopy as well as UV-Vis and fluorescence spectroscopies have shown a regular deposition of the polymers, and the luminescence properties could be controlled with the number of layers deposited on the solid support. As a result, the photoluminescence of the LB films was considerably higher than that observed for the spin coated film, and the maximum emission peak was shifted to higher energies, which is attributed to the molecular-level interactions within the layer-ordered structure of the LB film. the luminescence response would possibly be tuned to approach the highest level, which allows the films to be employed in future applications in efficient optical devices such as organic light-emitting diodes (OLEDs). (C) 2011 Elsevier B.V. All rights reserved.
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    Lipopolysaccharides and peptidoglycans modulating the interaction of Au naparticles with cell membranes models at the air-water interface
    (Elsevier Science Bv, 2018) Silva, Rafael Leonardo Cruz Gomes da [UNIFESP]; Silva, Heloiza Fernanda Oliveira da; Gasparotto, Luiz Henrique da Silva; Caseli, Luciano [UNIFESP]
    Understanding the interactions between nanoparticles and biological surfaces is of great importance for many areas of nanomedicine and calls for detailed studies at the molecular level using simplified models of cellular membranes. In this paper, water-dispersed polyvinylpyrrolidonestabilized gold nanoparticles (AuNPs) were incorporated in floating monolayers of selected lipids at the air-water interface as cell membrane models. Surface pressure-area isotherms showed the condensation of glycoside-free lipid monolayers, suggesting their adsorption on the nanoparticle surface through the hydrophilic head groups. On the other hand, monolayers containing glycoside derivatives expanded upon AuNPs incorporation, pointing that the supramolecular structure formed should facilitate the incorporation of these nanoparticles in cellular membranes. These findings can be therefore correlated with the possible toxicity, microbicide and antitumorigenic effects of these nanoparticles in lipidic surfaces of erythrocyte and microbial membranes.
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    Molecular features of nonionic detergents involved in the binding kinetics and solubilization efficiency, as studied in model (Langmuir films) and biological (Erythrocytes) membranes
    (Elsevier Science Bv, 2018) Casadei, Bruna Renata [UNIFESP]; Domingues, Cleyton Crepaldi; Clop, Eduardo M.; Couto, Veronica Muniz; Perillo, Maria Angelica; Paula, Eneida de
    The effect of the nonionic detergents Brij-98 and Brij-58 over human erythrocytes was studied through quantitative hemolysis and in Langmuir films. Hemolytic tests revealed that Brijs are stronger membrane solubilizers than Triton X-100 (TX-100), with effective detergent/lipid ratios of 0.18 and 0.37 for Brij-98 and Brij-58, respectively. Experiments with Langmuir films provided significant information on the kinetics and thermodynamics of detergent-membrane interaction. The adsorption (k(a)) and desorption (k(d)) rate constants of Brijs were lower than those of TX-100. In the case of k(a), that is probably due to their larger hydrophilic head (with twice (20) the oxyethylene units of TX-100). As for the thermodynamic binding constant, the linear and longer hydrophobic acyl chains of Brijs favor their stabilization in-between the lipids, through London van der Waals forces. Consequently, K-b,K-m values of Brij-98 (12,500 M-1) and Brij-58 (19,300 M-1) resulted higher than TX-100 (7500 M-1), in agreement with results from the hemolytic tests. Furthermore, Brij-58 binds with higher affinity than Brij-98 to bilayers and monolayers, despite its shorter (palmitic) hydrocarbon chain, showing that unsaturation restrains the detergent insertion into these environments. Our results provide significant information about the mechanism of interaction between Brijs and membranes, supporting their distinct solubilization effect. (C) 2018 Elsevier B.V. All rights reserved.
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    Organization of polythiophenes at ultrathin films mixed with stearic acid investigated with polarization-modulation infrared reflection-absorption spectroscopy
    (Elsevier Science Bv, 2017) da Silva, Edilene Assuncao; Caseli, Luciano [UNIFESP]; Olivati, Clarissa de Almeida
    In this present work, the polymers poly(3-alkylthiophene)s, regioregular poly(3-butylthiophene), poly(3-hexylthiophene) and poly(3-octylthiophene) were spread at the air-water interface to form Langmuir monolayers. They formed stable films by mixing them with Stearic Acid (SA), as confirmed with surface pressure-area isotherms and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The floating monolayers were transferred from the liquid interface to solid supports by using the Langmuir-Blodgett (LB) and Langmuir-Schaeffer (LS) techniques, and characterized with PM-IRRAS. Surface pressure-area isotherms showed that SA monolayers are expanded upon polymer incorporation altering the rheological properties of the monolayer since the monolayer became less elastic at higher pressures and presented first-order transitions at lower pressures. PM-IRRAS showed that the organization of the films is affected at the molecular level depending on the chemical structure of the polymer chosen. Among the polymers analysed, the poly(3-butylthiophene) shows a more irregular conformational behaviour depending on the amount of stearic acid. The conformation of the films when transferred to solid support changes and is dependent on the type of deposition (LB or LS). The importance of this paper relies on the fact that SA can be employed to help the formation of stable floating monolayers of these polythiophenes at the air-water interface, and the successful transfer to solid supports may provide nanostructured films with a high control of their molecular properties, which may enable a molecular architecture to be applied as electronic devices of interest.