Gabriel Max Dias Ferreira

Binding thermodynamics of synthetic dye Allura Red with bovine serum albumin.

The interaction between Allura Red and bovine serum albumin (BSA) was studied in vitro at pH 7.4. The fluorescence quenching was classified as static quenching due to the formation of AR-BSA complex, with binding constant (K) ranging from 3.26±0.09 to 8.08±0.0610(4)L.mol(-1), at the warfarin binding site of BSA. This complex formation was driven by increasing entropy. Isothermal titration calorimetric measurements also showed an enthalpic contribution. The Allura Red diffusion coefficient determined by the Taylor-Aris technique corroborated these results because it reduced with increasing BSA concentration. Interfacial tension measurements showed that the AR-BSA complex presented surface activity, since interfacial tension of the water-air interface decreased as the colorant concentration increased. This technique also provided a complexation stoichiometry similar to those obtained by fluorimetric experiments. This work contributes to the knowledge of interactions between BSA and azo colorants under physiological conditions.

Trimellitated sugarcane bagasse : a versatile adsorbent for removal of cationic dyes from aqueous solution. Part I : batch adsorption in a monocomponent system.

Trimellitated-sugarcane bagasse (STA) was used as an environmentally friendly adsorbent for removal of the basic dyes auramine-O (AO) and safranin-T (ST) from aqueous solutions at pH 4.5 and 7.0. Dye adsorption was evaluated as a function of STA dosage, agitation speed, solution pH, contact time, and initial dye concentration. Pseudo-first- and pseudo-second-order, Elovich, intraparticle diffusion, and Boyd models were used to model adsorption kinetics. Langmuir, Dubinin-Radushkevich, Redlich-Peterson, Sips, Hill-de Boer, and Fowler-Guggenheim models were used to model adsorption isotherms, while a Scatchard plot was used to evaluate the existence of different adsorption sites. Maximum adsorption capacities for removal of AO and ST were 1.005 and 0.638 mmol g-1 at pH 4.5, and 1.734 and 1.230 mmol g-1 at pH 7.0, respectively. Adsorption enthalpy changes obtained by isothermal titration calorimetry (ITC) ranged from -21.07 ± 0.25 to -7.19 ± 0.05 kJ mol-1, indicating that both dyes interacted with STA by physisorption. Dye desorption efficiencies ranged from 41 to 51%, and re-adsorption efficiencies ranged from 66 to 87%, showing that STA can be reused in new adsorption cycles. ITC data combined with isotherm studies allowed clarification of adsorption interactions.

Modeling adsorption of copper(II), cobalt(II) and nickel(II) metal ions from aqueous solution onto a new carboxylated sugarcane bagasse. Part II: Optimization of monocomponent fixed-bed column adsorption

In the second part of this series of studies, the monocomponent adsorption of Cu2+, Co2+ and Ni2+ onto STA adsorbent in a fixed-bed column was investigated and optimized using a 22 central composite design. The process variables studied were: initial metal ion concentration and spatial time, and the optimized responses were: adsorption capacity of the bed (Qmax), efficiency of the adsorption process (EAP), and effective use of the bed (H). The higher Qmax for Cu2+, Co2+ and Ni2+ were 1.060, 0.800 and 1.029 mmol/g, respectively. The breakthrough curves were modeled by the original Thomas and Bohart-Adams models. The changes in enthalpy (ΔadsH°) of adsorption of the metal ions onto STA were determined by isothermal titration calorimetry (ITC). The values of ΔadsH° were in the range of 3.0-6.8 kJ/mol, suggesting that the adsorption process involved physisorption. Desorption (Edes) and re-adsorption (Ere-ads) of metal ions from the STA adsorbent were also investigated in batch mode, and the optimum conditions were applied for three cycles of adsorption/desorption in a fixed bed column. For these cycles, the lowest values of Edes and Ere-ads were 95 and 92.3%, respectively, showing that STA is a promising candidate for real applications on a large scale.

Lactoferrin denaturation induced by anionic surfactants: The role of the ferric ion in the protein stabilization

Here, investigation was made of the interaction between lactoferrin (Lf) and the anionic surfactants sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and sodium decyl sulfate (DSS), using isothermal titration calorimetry, Nano differential scanning calorimetry (NanoDSC), and fluorescence spectroscopy. The Lf-surfactant interaction was enthalpically favorable (the integral enthalpy change ranged from -5.99 kJ mol-1, for SDS at pH 3.0, to -0.61 kJ mol-1, for DSS at pH 12.0) and promoted denaturation of the protein. The Lf denaturation efficiency followed the order DSS < SDS < SDBS. The adsorption capacity of the protein with respect to surfactant strongly depended on pH and the surfactant structure, reaching a maximum value of 505 SDBS molecules per gram of Lf at pH 3.0. The different efficiencies of the surfactants in denaturing Lf were attributed to the balance of hydrophobic and electrostatic interactions, which also depended on pH and the surfactant structure, highlighting the SDBS-tryptophan residue specific interaction, where SDBS acted as a quencher of fluorescence. Interestingly, the NanoDSC and fluorescence measurements showed that the ferric ion bound to Lf increased its stability against denaturation induced by the surfactants. The results have important implications for understanding the influence of surfactants on structural changes in metalloproteins.

A simple and inexpensive thermal optic nanosensor formed by triblock copolymer and polydiacetylene mixture

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<P123, indicating the importance of the hydrophobic environment for the colorimetric transition of nanoblends. The results here demonstrated that the balance of intermolecular interaction between TC-TC, TC-DA, and DA-DA enables the construction of strategic sensor for detecting temperature changes in different applications.

Effect of 1-Butyl-3-methylimidazolium Halide on the Relative Stability between Sodium Dodecyl Sulfate Micelles and Sodium Dodecyl Sulfate-Poly(ethylene oxide) Nanoaggregates.

It is well-known that ionic liquids (ILs) alter the properties of aqueous systems containing only surfactants. However, the effect of ILs on polymer-surfactant systems is still unknown. Here, the effect of 1-butyl-3-methylimidazolium bromide (bmimBr) and chloride (bmimCl) on the micellization of sodium dodecyl sulfate (SDS) and its interaction with poly(ethylene oxide) (PEO) was evaluated using conductimetry, fluorimetry, and isothermal titration calorimetry. The ILs decreased the critical micellar concentration (cmc) of the surfactant, stabilizing the SDS micelles. A second critical concentration (c2thc) was verified at high SDS concentrations, due to the micelle size decrease. The stability of PEO/SDS aggregates was also affected by ILs, and the critical aggregation concentration (cac) of SDS increased. Integral aggregation enthalpy changed from -0.72 in water to 2.16 kJ mol(-1) in 4.00 mM bmimBr. IL anions did not affect the SDS micellization or the beginning of PEO/SDS aggregation. Nevertheless, when chloride was replaced with bromide, the amount of SDS bound to the polymer increased. At 100.0 mM IL, the PEO-SDS interaction vanished. We suggest that the effect of ILs comes from participating in the structure of the formed aggregates, interacting with the SDS monomers at the core/interface of the micelles, and promoting preferential solvation of the polymer.

Synthesis and application of sugarcane bagasse cellulose mixed esters. Part I: Removal of Co2+ and Ni2+ from single spiked aqueous solutions in batch mode using sugarcane bagasse cellulose succinate phthalate

Sugarcane bagasse cellulose mixed ester succinate phthalate (SBSPh) was synthesized by a novel one-pot reaction method. The effects of temperature, time and mole fraction of succinic anhydride (χSA) on the responses weight gain (wg), number of carboxylic acid groups (nT,COOH), and adsorption capacity (q) of Co2+ and Ni2+ were evaluated by a 23 experimental design. The chemical structure of the material was elucidated by Fourier transform infrared, 13C Multiple Cross-Polarization solid-state NMR spectroscopy and 1H NMR relaxometry. The best SBSPh synthesis condition (100 °C, 11 h, χSA of 0.2) yielded a wg of 59.1%, nT,COOH of 3.41 mmol g-1, and values of qCo2+ and qNi2+ of 0.348 and 0.346 mmol g-1, respectively. The Sips model fitted better the equilibrium data, and the maximum adsorption capacities (pH 5.75 and 25 °C) estimated by this model were 0.62 and 0.53 mmol g-1 for Co2+ and Ni2+, respectively. The ΔadsH° values estimated by isothermal titration calorimetry were 8.43 and 7.79 kJ mol-1 for Co2+ and Ni2+, respectively. Desorption and re-adsorption efficiencies were evaluated by a 22 experimental design, which showed that SBSPh adsorbent can be recovered and reused without significant loss of adsorption capacity.

Thermodynamic and kinetic analyses of curcumin and bovine serum albumin binding

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 105L·mol-1 by fluorescence and microcalorimetric, and 103 and 104L·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=-8.67kJ·mol-1), while microcalorimetry showed an entropic driven binding process (ΔH○cal=29.11kJ·mol-1). For the unfolded BSA/curcumin complex, it was found thatp ΔH○F=-16.12kJ·mol-1 and ΔH○cal=-42.63kJ·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.

Effect of Acetonitrile and N,N-Dimethylformamide on the Formation of Poly(ethylene oxide)-Sodium Alkyl Sulfate Aggregates

The effects of low contents of acetonitrile (AN) or N,N-dimethylformamide (DMF) on the aggregation of sodium alkyl sulfate surfactants, in the absence and presence of poly(ethylene oxide) (PEO), were investigated using conductivity and isothermal titration calorimetry. The cosolvents slightly changed the critical micellar concentrations and did not alter the critical aggregation concentrations of the surfactants sodium decyl sulfate (DSS) and sodium dodecyl sulfate (SDS) with PEO. However, AN and DMF turned the micellization of the surfactants and their binding to the polymer enthalpically more favorable. For instance, for SDS, the micellization enthalpy, , decreased from close to 0 kJ mol–1 in water to −14.3 kJ mol–1 in the presence of 2.50 mol% AN, and the integral enthalpy change for aggregate formation with the polymer, ΔHagg(int), decreased from −1.1 kJ mol–1 in water to −15.5 kJ mol–1 in the same AN concentration. This was attributed to the modification of the solvation shells of both SDS and PEO by the cosolvent molecules, which reduced the entropic contribution to formation of the aggregates. Consequently, when SDS was replaced with DSS, the AN affected to a lesser extent, with a decrease of 9.1 kJ mol–1, while the ΔHagg(int) values were not altered, highlighting the influence of hydrophobic interactions in the surfactant aggregation process.

Kinetics and thermodynamics of bovine serum albumin interactions with Congo red dye

To optimize the therapeutic applications of Congo red (CR), a potential inhibitor of protein aggregation, the kinetics and thermodynamics of the interactions between CR and a model protein need to be understood. We used surface plasmon resonance (SPR) and fluorescence techniques to determine the dynamics and thermodynamic parameters for the formation of complexes between CR and bovine serum albumin (BSA). CR interacts with BSA through a transition complex; the activation energy for association (Eact(a)) was determined to be 35.88kJmol-1, while the activation enthalpy (ΔH‡), entropy (ΔS‡), and Gibbs free energy (ΔG‡) are 33.41kJmol-1, 0.18Jmol-1K-1, and 33.35kJmol-1, respectively. When this intermediate transforms into the final CR-BSA complex, the entropy of the system increases and part of the absorbed energy is released; this process is associated with a reverse activation energy (Eact(d)) of 20.17kJmol-1, and values of ΔH‡, ΔS‡, and ΔG‡ of 17.69kJmol-1, -162.86Jmol-1K-1, and 66.25kJmol-1, respectively. A comparison of the SPR and fluorescence results suggests that there is more than one site where BSA interacts with CR.