Interaction of amphiphilic derivatives of chitosan with DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine)

The interaction of chitosan and its N-dodecyl and poly(ethylene glycol) derivatives with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles was studied to evaluate the influence of molecular architecture of the polymers on the liposomes. The study was carried out in aqueous solution using differential scanning microcalorimetry (DSC) and dynamic light scattering. The interaction of these polymers with DPPC vesicles altered the gel-liquid crystalline phase transition temperature and decreased both the enthalpy (Delta H) and cooperativity of the phase transition. The results obtained indicate that perturbations in the vesicles surface and the incorporation of chitosan and its derivatives into the lipid bilayer upon polysaccharides interaction are responsible for the formation of large vesicles.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Effect of Sonication on the Thermotropic Behavior of DODAB Vesicles Studied by Fluorescence Probe Solubilization

The effect of sonication on fluorescence probe solubilization in cationic vesicles of dioctadecyldimethylammonium bromide (DODAB) was investigated by steady-state fluorescence of pyrene (Py), trans-diphenylpolyenes-diphenylbutadiene (DPB), diphenylhexatriene (DPH), and their corresponding 4,4'-dialkyl derivatives 4B4A and 4H4A fluorescence probes. The data indicate that sonication affects the bilayer polarity, the melting temperature (T (m)), and the cooperativity of the melting process due to changes in vesicle morphology. The effect of temperature on the fluorescence intensity and yielding I broken vertical bar(f) and anisotropy shows that the ionizable probes 4B4A and 4H4A are solubilized close to the vesicle interfaces, whereas the non-ionizable DPH and DPB are deeper in the bilayers. Py solubilization indicates that sonicated vesicles exhibit less densely packed bilayers

Effect of surfactants and polyethylene glycol on the activity and stability of a lipase from oilseeds of Pachira aquatica

Lipases from oilseeds have a great potential for commercial exploration as industrial enzymes. Lipases are used mixed with surfactants in cleaning and other formulated products, and accordingly, both components must be compatible with each other. This work presents the results of the effects of anionic, cationic and nonionic surfactants, polyethylene glycol and urea on the activity and stability of a lipase extracted of oilseeds from Pachira aquatica. The enzyme was purified and the spectrophotometric assays were done using p-nitrophenyl acetate (p-NPA) as substrate pH 7.5 and 25 degrees C. The activity was significantly enhanced by the cationic surfactant CTAB. Bile salts increased the lipase activity in the tested concentration range, whereas anionic and nonionic surfactants showed an inhibitory effect. Aqueous solutions of PEG activated the lipase and maximum activation (161%) occurred in PEG 12,000. This effect on lipase that can be due to exposition of some hydrophobic residues located in the vicinity of the active site or aggregation

The Interaction Between N-Isopropylacrylamide-Acrylic Acid-Ethyl Methacrylate Thermosensitive Polymers and Cationic Surfactants

The interaction between cationic surfactants and isopropylacrylamide-acrylic acid-ethyl methacrylate (IPA:AA:EMA) terpolymers has been investigated using steady-state fluorescence and spectrophotometric measurements to assess the effect of the polymer composition on the aggregation process and terpolymers' thermosensitivities. Micropolarity studies using pyrene show that the interaction of cationic surfactants with IPA:AA:EMA terpolymers occurs at surfactant concentrations much smaller than that observed for the pure surfactant in aqueous solution. The critical aggregation concentration (CAC) values decrease with both the hydrocarbon length of the surfactant and the content of ethyl methacrylate. These results were interpreted as a manifestation of the increasing contribution of attractive hydrophobic and electrostatic forces between negatively charged polymer chains and positively charged surfactant molecules. The increase of ethyl methacrylate in the copolymers lowers the CAC due to the larger hydrophobic character of the polymer backbone. The cloud point determination reveals that the lower critical solution temperatures (LCST) depend strongly on the copolymer composition and surfactant nature. The binding of surfactants molecules to the polymer chain screens the electrostatic repulsion between the carboxylic groups inducing a conformational transition and the dehydration of the polymer chain

Chitosan derivatives targeting lipid bilayers: Synthesis, biological activity and interaction with model membranes

The antimicrobial activity of chitosan and derivatives to human and plant pathogens represents a high-valued prospective market. Presently, two low molecular weight derivatives, endowed with hydrophobic and cationic character at different ratios were synthesized and characterized. They exhibit antimicrobial activity and increased performance in relation to the intermediate and starting compounds. However, just the derivative with higher cationic character showed cytotoxicity towards human cervical carcinoma cells. Considering cell membranes as targets, the mode of action was investigated through the interaction with model lipid vesicles mimicking bacterial, tumoral and erythrocyte membranes. Intense lytic activity and binding are demonstrated for both derivatives in anionic bilayers. The less charged compound exhibits slightly improved selectivity towards bacterial model membranes, suggesting that balancing its hydrophobic/hydrophilic character may improve efficiency. Observing the aggregation of vesicles, we hypothesize that the "charge cluster mechanism", ascribed to some antimicrobial peptides, could be applied to these chitosan derivatives.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), BrasilUniv Estadual Paulista Unesp, Dept Quim & Ciencias Ambientais, Inst Biociencias Letras & Ciencias Exatas Ibilce, Campus Sao Jose do Rio Preto, BR-15054000 Sao Jose Do Rio Preto, SP, BrazilUniv Estadual Paulista Unesp, Dept Fis, Inst Biociencias Letras & Ciencias Exatas Ibilce, Campus Sao Jose do Rio Preto, BR-15054000 Sao Jose Do Rio Preto, SP, BrazilUniv Fed Sao Paulo, Lab Neurobiol Estrutural & Func LaNEF, Dept Biofis, R Botucatu 862, BR-04023062 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Lab Neurobiol Estrutural & Func LaNEF, Dept Biofis, R Botucatu 862, BR-04023062 Sao Paulo, SP, BrazilFAPESP: 2009/11707-2, 2012/03619-9, 2012/02065-0, 2010/11823-0, 2012/24259-0, 2014/08372-7Web of Scienc

The finance-growth nexus in the age of financialisation: an empirical reassessment for the European Union countries

This paper draws an empirical reassessment of the finance-growth nexus by performing a panel data econometric analysis for all 28 European Union countries over 27 years from 1990 to 2016. Since the mid-1980s, the financial system has experienced a strong liberalisation and deregulation by preventing its beneficial effects on the real economy. This phenomenon, typically called financialisation, points to a negative view of finance and contradicts the well-entrenched hypothesis on the finance-growth nexus. We estimate both linear and non-linear growth models by incorporating seven proxies of finance (money supply, domestic credit, financial value added, short-term interest rate, long-term interest rate, stock market volume traded and stock market capitalisation) and five control variables (the lagged growth rate of the real per capita gross domestic product, the inflation rate, the general government consumption, the degree of trade openness and the education level of the population). Our results show that finance has impaired economic growth in the EU countries, both in the pre-crisis period and in the crisis and post-crisis periods. The enormous growth of domestic credit and of the financial value added have been restraining the economic growth of the EU countries since 1990 and particularly up until the Great Recession. This implies the need to reduce the prominence of finance, i.e. so-called de-financialisation, in the coming years in order to avoid the potential new ‘secular stagnation’ in the current age of financialisation.info:eu-repo/semantics/publishedVersio