Navegando por Palavras-chave "Micelle"

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    Chemical equilibria of Eosin Y and its synthetic ester derivatives in non-ionic and ionic micellar environments
    (W. Schröer, 2021-04-01) Freitas, Camila Fabiano de; Estevão, Bianca Martins; Pellosi, Diogo Silva [UNIFESP]; Scarminio, Ieda Spacino; Caetano, Wilker; Hioka, Noboru; Batistela, Vagner Roberto; http://lattes.cnpq.br/4319283598735971
    Eosin (EOS) and its synthetic ester derivatives have adequate properties to be employed as histological markers for and as drugs for photodynamic therapy. However, they present a very complex protolytic and tautomeric equilibrium that reflects on their photophysical properties. Hence their biomedical applications are strongly affected by the medium's pH, charge and hydrophobicity. In this study, we evaluated the effects of two neutral (Pluronic® F-127 and P-123) and two ionic (anionic SDS and cationic CTAB) surfactant micelles as a simple membrane model on the protolytic/tautomeric equilibrium of EOS and its ester derivative dyes. Multivariate analysis based on Q-Imbrie's factor and the K-matrix method on the electronic absorption spectroscopy data in different pH conditions allowed for the understanding of the complex protolytic/tautomeric equilibrium, and the influence of medium microenvironment on the EOS dyes at each pH. Our results demonstrated that, when close to physiological pH (~7.4), and electrostatic attraction towards cationic surfaces favor dyes locating close to the micelle's (biomembrane model) interface, where their biomedical applications are favored. Therefore, the analysis in different environments shows that the interactions of EOS and its derivatives with biomembranes can be modulated based on the hydrophobicity of the xanthene derivative and the cell membrane charge.
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    Conformational Properties of Angiotensin II and Its Active and Inactive TOAC-Labeled Analogs in the Presence of Micelles. Electron Paramagnetic Resonance, Fluorescence, and Circular Dichroism Studies
    (Wiley-Blackwell, 2009-01-01) Vieira, Renata de Freitas Fischer [UNIFESP]; Casallanovo, Fabio; Marin, Nelida; Paiva, Antonio Cechelli de Mattos [UNIFESP]; Schreier, Shirley; Nakaie, Clovis Ryuichi [UNIFESP]; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
    The interaction between angiotensin II (AII, DRVYIHPF) and its analogs carrying 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) and detergents-negatively charged sodium dodecyl sulfate (SDS) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS)-was examined by means of EPR, CD, and fluorescence. EPR spectra of partially active TOAC(1)-AII and inactive TOAC(3)-AII in aqueous solution indicated fast tumbling, the freedom of motion being greater at the N-terminus. Line broadening occurred upon interaction with micelles. Below SDS critical micelle concentration, broader lines indicated complex formation with tighter molecular packing than in micelles. Small changes in hyperfine splittings evinced TOAC location at the micelle-water interface. the interaction with anionic micelles was more effective than with zwitterionic micelles. Peptide-micelle interaction caused fluorescence increase. the TOAC-promoted intramolecular fluorescence quenching was more, pronounced for TOAC(3)-AII because of the proximity between the nitroxide and Tyr(4). CD spectra showed that although both AII and TOAC(1)-AII presented flexible conformations in water, TOAC(3)-AII displayed conformational restriction because of the TOAC-imposed bend (Schreier et al., Biopolymers 2004, 74, 389). in HPS, conformational changes were observed for the labeled peptides at neutral and basic pH. in SDS, all peptides underwent pH-dependent conformational changes. Although the spectra suggested similar folds for All and TOAC(1)-AII, different conformations were acquired by TOAC(3)-AII. the membrane environment has been hypothesized to shift conformational equilibria so as to stabilize the receptor-bound conformation of ligands. the fact that TOAC(3)-AII is unable to acquire conformations similar to those of native AII and partially active TOAC(1)-AII is probably the explanation for its lack of biological activity. (C) 2009 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 92: 525-537, 2009.
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    Conformational studies of TOAC-labeled bradykinin analogues in model membranes
    (Kluwer Academic Publ, 2002-01-01) Vieira, Renata de Freitas Fischer [UNIFESP]; Casallanovo, Fabio; Cilli, Eduardo Maffud [UNIFESP]; Paiva, Antonio Cechelli de Mattos [UNIFESP]; Schreier, Shirley; Nakaie, Clovis Ryuichi [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP)
    Spin-labeled analogues of bradykinin (BK) were synthesized containing the amino acid TOAC ( 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) either before Arg(1) (TOAC(0)-BK) or replacing Pro(3) (TOAC(3)-BK). Whereas the latter is inactive, the former retains about 70% of BK's activity in isolated rat uterus. A combined electron paramagnetic resonance (EPR)-circular dichroism ( CD) approach was used to examine the conformational properties of the peptides in the presence of membrane-mimetic systems ( negatively charged sodium dodecyl sulfate, SDS, and zwitterionic N-hexadecyl-N, N-dimethyl-3-ammonio-1-propanesulfonate, HPS). While the peptides bind to both monomeric and micellar SDS, no interaction occurs with HPS, evincing the contribution of electrostatic interactions. TOAC(3)-BK's EPR spectral lineshapes are broader than those of TOAC(0)-BK, indicating a more restricted degree of motion at position 3. Moreover, the motional freedom of both peptides decreased upon binding to SDS. BK and TOAC(0)-BK solution CD spectra indicate highly flexible conformations ( possibly an equilibrium between rapidly interconverting forms), while TOAC(3)-BK's spectra correspond to a more ordered structure. SDS binding induces drastic changes in BK and TOAC(0)-BK spectra, indicating stabilization of similar folds. the micelle interface promotes a higher degree of secondary structure by favoring intramolecular hydrogen bonds. in contrast, TOAC(3)-BK spectra remain essentially unchanged. These results are interpreted as due to TOAC's ring imposing a more constrained conformation. This rigidity is very likely responsible for the inability of TOAC(3)-BK to acquire the correct receptor-bound conformation, leading to loss of biological activity. On the other hand, the greater flexibility of TOAC(0)-BK and the similarity between its conformational behavior and that of the native hormone are probably related to their similar biological activity.