Browsing by Author "Hespanhol, Maria do Carmo"

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    Partitioning of cocaine and its adulterants in aqueous two-phase systems : an alternative drug identification method.
    (2020) Ferreira, Gabriel Max Dias; Ferreira, Guilherme Max Dias; Maldaner, Adriano Otávio; Silva, Luis Henrique Mendes da; Hespanhol, Maria do Carmo
    The partitioning behaviors of cocaine freebase (CoF), cocaine hydrochloride (CoH), and a range of adulterants (procaine (PRO), phenacetin (PHE), caffeine (CAF), benzocaine (BEN), and lidocaine (LID)) in aqueous two-phase systems (ATPS) were evaluated, with the aim of developing a selective and efficient alternative technique for the identification of cocaine in samples confiscated by the police. The partition coefficients (KS) of all the solutes were obtained in ATPS formed using a macromolecule (PEO1500 or L35 copolymer), a salt (Na2SO4 or Li2SO4), and water. The KS values were consistently higher than 1 and increased with increase of the tie-line length. For the PEO1500 + Li2SO4 + water ATPS at pH 6.0, the KS values increased in the order: KLID < KPRO < KCAF < KCoF < KCoH < KPHE < KBEN. The greatest effect on the partitioning was shown by the polymer hydrophobicity, followed by the nature of the electrolyte and the pH of the ATPS. The ratio between two KS values for two different ATPS types was used as a strategic parameter for distinguishing between the two forms of cocaine, as well as between cocaine and the adulterants. The K12/K6 ratio, where K6 and K12 are the KS values for the PEO1500 + Li2SO4 + water ATPS at pH 6.0 and 12.0, respectively, enabled CoH to be distinguished from all the other solutes studied. In addition, the effect of the hydrophobicity of the polymer on the KS values was fundamental for distinguishing CoF from the other solutes.
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    A simple and inexpensive thermal optic nanosensor formed by triblock copolymer and polydiacetylene mixture.
    (2018) Ferreira, Gabriel Max Dias; Ferreira, Guilherme Max Dias; Hespanhol, Maria do Carmo; Rezende, Jaqueline de Paula; Pires, Ana Clarissa dos Santos; Ortega, Paulo Fernando Ribeiro; Silva, Luis Henrique Mendes da
    Polydiacetylene (PDA) vesicles have been applied as optical sensors in different areas, although there are difficulties in controlling their responses. In this study, we prepared nanoblends of PDA with triblock copolymers (TC) as a better sensor system for detecting temperature change. The influences of diacetylene (DA) monomer, and the TC chemical structure and concentration on the colorimetric response (CR) were examined. The TC/PDA nanoblend was remarkably more sensitive to temperature change, than classical vesicles. A higher L64 concentration of 12.0% (w/w) reduced the chromatic transition temperature (Ttr) to as low as 24 °C. When using different TCs, the Ttr values can be ordered as L35 < F68< L64 < F127
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    Thermodynamic and kinetic analyses of curcumin and bovine serum albumin binding.
    (2018) Hudson, Eliara Acipreste; Paula, Hauster Maximiler Campos de; Ferreira, Guilherme Max Dias; Ferreira, Gabriel Max Dias; Hespanhol, Maria do Carmo; Silva, Luis Henrique Mendes da; Pires, Ana Clarissa dos Santos
    Bovine serum albumin (BSA)/curcumin binding and dye photodegradation stability were evaluated. BSA/curcumin complex showed 1:1 stoichiometry, but the thermodynamic binding parameters depended on the technique used and BSA conformation. The binding constant was of the order of 105 L·mol−1 by fluorescence and microcalorimetric, and 103 and 104 L·mol−1 by surface plasmon resonance (steady-state equilibrium and kinetic experiments, respectively). For native BSA/curcumin, fluorescence indicated an enthalpic and entropic driven process based on the standard enthalpy change (ΔH○F = −8.67 kJ·mol−1), while microcalorimetry showed an entropic driven binding process (ΔH○cal = 29.11 kJ·mol−1). For the unfolded BSA/curcumin complex, it was found thatp ΔH○F = −16.12 kJ·mol−1 and ΔH○cal = −42.63 kJ·mol−1. BSA (mainly native) increased the curcumin photodegradation stability. This work proved the importance of using different techniques to characterize the protein-ligand binding.