Adsorção de proteínas do soro do leite e do glicomacropeptídeo (GMP) na interface hidrofóbica de nanotubos de carbono de paredes múltiplas

• Autor(a) principal: Mageste, Aparecida Barbosa
• 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/123456789/219
• topic: Alfa-lactoalbumina; Beta-Lactoglobulina; Microcalorimetria; Adsorção; Termodinâmica; Alpha-lactalbumin; Beta-Lactoglobulin; Microcalorimetry; Adsorption; Thermodynamics; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::FISICO-QUIMICA

In this work we studied the adsorption behavior of the proteins &#945;-lactalbumin (&#945;-La), &#946;-Lactoglobulin (&#946;-Lg) and of the glicomacropeptídeo (GMP) in multiple-walled carbon nanotubes (MWCNT) in the presence and absence of electrolytes of Hofmeister series at different pH values, aimed in the understanding of the mechanism of protein adsorption on carbon nanotubes (NCTS). We investigated the effect of pH of the reaction medium, nature of electrolyte and protein structure on the amount adsorbed (&#915;) of different proteins and of the GMP. A variation in net charge of protein and of the electrolyte nature changes the process of nanotube-protein interaction. The &#915; of &#945;-La is greater when its net charge is positive (pH 3) and &#946;-Lg when the net charge is negative (pH 9). The high values of &#915; demonstrated the big potential of NCTs in the protein adsorption. At pH 9 there is an increase in &#915; of &#945;-La due to the presence of 100,0 mM electrolyte, for [&#945;-La] &#8776; 0,7000 mg mL-1 in the presence of only buffer pH 9 are: &#915; Buffer/&#945;-La = 197,0 mg g-1, going to &#915; NaSCN/&#945;-La = 233,0 mg g-1, &#915; Na2SO4/&#945;-La = 281,0 mg g-1, &#915; NaHPO4/&#945;-La = 256,0 mg g-1, opposite behavior was observed for &#946;-Lg. At pH 9 the highest values of &#915; were observed for the GMP and the process was little influenced by electrolytes. The results show that the mechanism of adsorption depend on the nature of the polyelectrolyte, and the isotherms of &#946;-Lg and &#945;-La features of monolayer adsorption while the adsorption isotherms GMP did not fit well to Langmuir model featuring two characterizing the regions of saturation adsorption bilayer. In addition, that is the first time that thermodynamic parameters were determined for adsorption of proteins in NCTs using two models: the Langmuir model and the thermodynamic model of infinite dilution. The thermodynamic analysis based on calorimetric titrations showed that the adsorption of proteins in all conditions evaluated occurs spontaneously (&#916;adsG° <0). The process is exothermic and enthalpy driven, for all thermodynamic states evaluated. Based on experimental results a mechanism was proposed for the process of adsorption of polyelectrolytes studied in the interface of MWCNTs consisting of conformational change of the protein molecule due to its interaction with the surface of the nanotube so that hydrophobic amino acid residues are directed to interface of MWCNT loaded and hydrophilic residues and form an adsorbed protein solution interface, meanwhile ions from the electrolyte that forms the buffer adsorb at the protein adsorbed at the interface / solution and it was proposed that the presence of electrolytes of the Hofmeister series - a competitive adsorption between the ions the salt of the Hofmeister series of ions and the ions that form the buffer by changing the enthalpy and entropy contributions to the adsorptive process. Electrocinetic potential measurements reinforced the proposed mechanism.