Navegando por Autor "Romani, Ana Paula"
Agora exibindo 1 - 3 de 3
Resultados por página
Opções de Ordenação
Item Fluorescence spectroscopy of small peptides interacting with microheterogeneous micelles.(2010) Romani, Ana Paula; Marquenzin, Cassia Alessandra; Ito, Amando SiuitiMany peptides containing tryptophan have therapeutic uses and can be studied by their fluorescent properties. The biological activity of these peptides involves interactions with many cellular components and micelles can function as carriers inside organisms. We report results from the interaction of small peptides containing tryptophan with several microheterogeneous systems: sodium dodecyl sulphate (SDS) micelles; sodium dodecyl sulphate–poly(ethylene oxide) (SDS–PEO) aggregates; and neutral polymeric micelles. We observed that specific parameters, such as wavelength of maximum emission and fluorescence anisotropy, could be used to ascertain the occurrence of interactions. Affinity constants were determined from changes in the intensity of emission while structural modifications in rotameric conformations were verified from time-resolved measurements. Information about the location and diffusion of peptides in the microheterogeneous systems were obtained from tryptophan emission quenching experiments using N-alkylpyridinium ions. The results show the importance of electrostatic and hydrophobic effects, and of the ionization state of charged residues, in the presence of anionic and amphiphilic SDS in the microheterogeneous systems. Conformational stability of peptides is best preserved in the interaction with the neutral polymeric micelles.Item Interaction of adrenocorticotropin peptides with microheterogeneous systems : a fluorescence study.(2009) Romani, Ana Paula; Ito, Amando SiuitiAdrenocorticotropin (ACTH) and α-melanocyte stimulating hormone (α-MSH) are peptides which present many physiological effects related to pigmentation, motor and sexual behavior, learning and memory, analgesia, anti-inflammatory and antipyretic processes. The 13 amino acid residues of α-MSH are the same initial sequence of ACTH and due to the presence of a tryptophan residue in position 9 of the peptide chain, fluorescence techniques could be used to investigate the conformational properties of the hormones in different environments and the mechanisms of interaction with biomimetic systems like sodium dodecyl sulphate (SDS) micelles, sodium dodecyl sulphate-poly(ethylene oxide) (SDS-PEO) aggregates and neutral polymeric micelles. In buffer solution, fluorescence parameters were typical of peptides containing tryptophan exposed to the aqueous medium and upon addition of surfactant and polymer molecules, the gradual change of those parameters demonstrated the interaction of the peptides with the microheterogeneous systems. From time-resolved experiments it was shown that the interaction proceeded with conformational changes in both peptides, and further information was obtained from quenching of Trp fluorescence by a family of N-alkylpyridinium ions, which possess affinity to the microheterogeneous systems dependent on the length of the alkyl chain. The quenching of Trp fluorescence was enhanced in the presence of charged micelles, compared to the buffer solution and the accessibility of the fluorophore to the quencher was dependent on the peptide and the alkylpyridinium: in ACTH(1–21) highest collisional constants were obtained using ethylpyridinium as quencher, indicating a location of the residue in the surface of the micelle, while in α-MSH the best quencher was hexylpyridinium, indicating insertion of the residue into the non-polar region of the micelles. The results had shown that the interaction between the peptides and the biomimetic systems where driven by combined electrostatic and hydrophobic effects: in ACTH(1–24) the electrostatic interaction between highly positively charged C-terminal and negatively charged surface of micelles and aggregates predominates over hydrophobic interactions involving residues in the central region of the peptide; in α-MSH, which presents one residual positive charge, the hydrophobic interactions are relevant to position the Trp residue in the non-polar region of the microheterogeneous systems.Item Spectrofluorimetric determination of second critical micellar concentration of SDS and SDS/Brij 30 systems.(2009) Romani, Ana Paula; Machado, Antonio Eduardo da Hora; Hioka, Noboru; Severino, Divinomar; Baptista, Mauricio da Silva; Codognoto, Lúcia; Magini, Maira Regina Rodrigues; Oliveira, Hueder Paulo Moisés dePotentially useful stead-state fluorimetric technique was used to determine the critical micellar concentrations (CMC1 and CMC2) for two micellar media, one formed by SDS and the other by SDS/Brij 30. A comparative study based on conductimetric and surfacial tension measurements suggests that the CMC1 estimated by the fluorimetric method is lower than the value estimated by these other techniques. Equivalent values were observed for SDS micelles without Brij 30 neutral co-surfactant. The use of acridine orange as fluorescent probe permitted to determine both CMC1 and CMC2. Based on it an explanation on aspects of micelle formation mechanism is presented, particularly based on a spherical and a rod like structures.