Termodinâmica de interação entre lactato e vesículas nanoestruturadas de polidiacetileno

• Autor(a) principal: Camilloto, Geany Peruch
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/476
• topic: Biossensores; Polidiacetileno; Enterotoxinas; Biosensors; Polydiacetylene; Enterotoxins; CNPQ::CIENCIAS AGRARIAS::CIENCIA E TECNOLOGIA DE ALIMENTOS::TECNOLOGIA DE ALIMENTOS

Polydiacetylenes are conjugated polymers that exhibit chromatic properties in the presence of different molecules. This work aimed: I) to develop vesicles of 10,12-pentacosadiynoic acid (PCDA) and different lipids (1,2-dimyristoyl-snglycero- 3-phosphatidylcholine (DMPC), 1,2-dimyristoyl-sn-glycero-3- phosphatidylglycerol (DMPG), sphingomyelin (ES) and cholesterol (CO)); II) to evaluate the colorimetric responses of the vesicles as a function of calcium lactate and sodium lactate concentrations; III) to evaluate the effect of the addition of calcium lactate and sodium lactate on the pH of the vesicles; IV) to evaluate the effect of the addition of different lipids, calcium lactate, and sodium lactate on the size of the vesicles; V) to quantify Gibbs free energy and enthalpy changes related to the interaction between the different vesicles and sodium and calcium lactates; VI) to evaluate the effect of the addition of calcium lactate and sodium lactate on the colorimetric responses, pH, and size of vesicles prepared in different pHs. The incorporation of lipids into the nanostructures did not prevent the polymerization of the polydiacetylene monomers since all vesicles showed an intense blue color after polymerization. The vesicles of PCDA, PCDA/DMPC, PCDA/DMPG and PCDA/ES/CO showed hydrodynamic diameters of 106.12 ± 0.06, 176.94 ± 14.06, 213.36 ± 5.82 and 361.51 ± 51. 41 nm, as well as pHs of 6.42 ± 0.22, 6.13 ± 0.15, 5.57 ± 0.17 and 4.61 ± 0.22, respectively. The presence of lipids in the polydiacetylene nanostructures led to increased hydrodynamic diameters and changes in the balance of carboxyl groups on vesicle surfaces. In pHs of synthesis and 7.0, all vesicles showed colorimetric transitions in the presence of calcium lactate and sodium lactate, but in pH 2.0 such molecules did not induce colorimetric transitions. The calcium lactate caused higher colorimetric responses in the vesicles of PCDA/DMPC and PCDA/ES/CO when compared to sodium lactate. The addition of calcium lactate induced higher colorimetric transition in the vesicles of PCDA/DMPC then in those of PCDA/ES/CO, whereas the addition of sodium lactate caused higher colorimetric responses in the vesicles of pure PCDA. The Gibbs free intG) between the vesicles and lactate was negative in the pHs of synthesis and 7.0, demonstrating that the interaction between these species was thermodynamically favorable. Contrastingly, this interaction in pH intG values. From microcalorimetric measurements, it was observed that the changes in enthalpy of interaction intH) between the vesicles and lactate was positive and constant, and that the interaction between the species and the colorimetric transition are endothermic phenomena entropically governed. The addition of lactate increased the size of the polydiacetylene nanostructures, though the growth of the vesicles was associated to the colorimetric changes due to conformational changes in polydiacetylene molecules. The outcomes of this work demonstrate that the presence of lactate induced colorimetric changes in polydiacetylene vesicles, and that the interaction between the species was dependent upon the composition of the vesicle nanostructures, the thermodynamic condition of the medium (pH), and the counterion of the lactate molecule.