Aminated cellulose as a versatile adsorbent for batch removal of As(V) and Cu(II) from mono- and multicomponent aqueous solutions.

A bioadsorbent (CEDA) capable of adsorbing As(V) and Cu(II) simultaneously was prepared by tosylation of microcrystalline cellulose (MC) and nucleophilic substitution of the tosyl group by ethylenediamine. MC, tosyl cellulose, and CEDA were characterized by elemental C, H, N, and S analysis, infrared spectroscopy, and 13C solid-state nuclear magnetic resonance spectroscopy. The adsorption of As(V) and Cu(II) on CEDA was evaluated as a function of solution pH, contact time, and initial solute concentration. The maximum adsorption capacities of CEDA for As(V) and Cu(II) were 1.62 and 1.09 mmol g-1, respectively. The interactions of As(V) and Cu(II) with CEDA were elucidated using thermodynamic parameters, molecular quantum mechanics calculations, and experiments with ion exchange of Cd(II) by Cu(II), and As(V) by SO42-. Adsorption enthalpies were determined as a function of surface coverage of the CEDA, using isothermal titration calorimetry, with ΔadsH° values of -32.24 ± 0.07 and -93 ± 2 kJ mol-1 obtained for As(V) and Cu(II), respectively. The potential to reuse CEDA was evaluated and the interference of other ions in the adsorption of As(V) and Cu(II) was investigated. Multi-component experiments showed that Cd(II), Co(II), Ni(II), and Pb(II) did not interfere in the adsorption of Cu(II), while SO42- inhibited As(V) adsorption.

Adsorption of organic and inorganic arsenic from aqueous solutions using MgAl-LDH with incorporated nitroprusside.

An evaluation was made of the use of MgAl-LDH with incorporated nitroprusside as an adsorbent to remove inorganic arsenic (As(III) and As(V)) and organic arsenic (DMA) from aqueous matrices. The material was synthesized by the co-precipitation method at constant pH and was characterized by Raman spectroscopy, infrared spectroscopy, thermogravimetry, X-ray diffraction, and high-resolution transmission electron microscopy, before and after use in the adsorption process. The effects on adsorption of contact time, initial metalloid concentration, and pH were investigated. For an initial concentration of 10 mg L-1 and pH 2.00, the MgAl-LDH with incorporated nitroprusside was only able to adsorb the DMA and As(V) species, with removal percentages of 25.10 and 103.8%, respectively. At pH 6.02 and 12.00, only the inorganic species were adsorbed, with removal percentages of 22.93% and 60.07%, respectively, for As(III), and 89.81% and 71.64%, respectively, for As(V). Application of the Langmuir and Freundlich isotherm models indicated that the features of the adsorption process depended on the pH of the medium and the arsenic species. The results showed that the use of MgAl-LDH with incorporated nitroprusside has potential for the development of techniques for the speciation of arsenic species.

Anthocyanin immobilization in carboxymethylcellulose/starch films: A sustainable sensor for the detection of Al(III) ions in aqueous matrices.

A robust and sustainable sensor for the detection of Al(III) ions in water was developed by immobilization of anthocyanin (AN) from black rice in a film formed by carboxymethylcellulose (CMC) and starch. Characterization of the films was performed using solubility, thickness, FTIR, and mechanical analysis. The film exhibited an irreversible color change from red to purple in response to the presence of Al(III). The best colorimetric response of the sensor was observed at pH 4.5 and a time of 60 min, achieving the detection of 3 mg L-1 of Al(III). For concentrations higher than 5 mg L-1, the sensor response time decreased to 20 min. The minimum Al(III) concentration detected with the naked eye was lower than the maximum permissible concentrations in aqueous effluents according to different legislations, indicating the potential of this study to develop sensors for the detection of Al(III).

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

Sugarcane bagasse cellulose succinate trimellitate (SBST) was prepared by a one-pot synthesis method. The synthesis of this novel mixed ester was investigated by a 23-factorial design. The parameters investigated were time, temperature, and succinic anhydride mole fraction (χSA). The responses evaluated were the adsorption capacity (qCo2+ and qNi2+), weight gain (wg), and number of carboxylic acid groups (nT,COOH). 13C Multiple Cross-Polarization solid-state NMR spectroscopy, 1H NMR relaxometry, and Fourier-transform infrared spectroscopy were used to elucidate the SBST structure. The best SBST reaction conditions were 100 °C, 660 min, and χSA of 0.2, which yielded SBST with a wg of 57.1%, nT,COOH of 4.48 mmol g-1, and qCo2+ and qNi2+ of 0.900 and 0.963 mmol g-1, respectively. The maximum adsorption capacities (Qmax) (pH 5.75, 25 °C) estimated by the Redlich-Peterson model for Co2+ and Ni2+ were 1.16 and 1.29 mmol g-1. The ΔadsH° values for Co2+ and Ni2+ adsorption obtained by isothermal titration calorimetry were 8.03 and 6.94 kJ mol-1. Regeneration and reuse of SBST were investigated and the best conditions applied for fixed-bed column adsorption in five consecutive cycles. SBST was fully desorbed and Qmax values for Co2+ (0.95 mmol g-1) and Ni2+ (1.02 mmol g-1) were estimated using the Bohart-Adams model.

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.

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.

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.

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 ±â€¯0.25 to -7.19 ±â€¯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.

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

Synthesis and application of a new carboxylated cellulose derivative. Part III: Removal of auramine-O and safranin-T from mono- and bi-component spiked aqueous solutions.

In the third part of this series of studies, the adsorption of the basic textile dyes auramine-O (AO) and safranin-T (ST) on a carboxylated cellulose derivative (CTA) were evaluated in mono- and bi-component spiked aqueous solutions. Adsorption studies were developed as a function of solution pH, contact time, and initial dye concentration. Adsorption kinetic data were modeled by monocomponent kinetic models of pseudo-first- (PFO), pseudo-second-order (PSO), intraparticle diffusion, and Boyd, while the competitive kinetic model of Corsel was used to model bicomponent kinetic data. Monocomponent adsorption equilibrium data were modeled by the Langmuir, Sips, Fowler-Guggenhein, Hill de-Boer, and Konda models, while the IAST and RAST models were used to model bicomponent equilibrium data. Monocomponent maximum adsorption capacities for AO and ST at pH 4.5 were 2.841 and 3.691 mmol g-1, and at pH 7.0 were 5.443 and 4.074 mmol g-1, respectively. Bicomponent maximum adsorption capacities for AO and ST at pH 7.0 were 1.230 and 3.728 mmol g-1. Adsorption enthalpy changes (ΔadsH) were obtained using isothermal titration calorimetry. The values of ΔadsH ranged from -18.83 to -5.60 kJ mol-1, suggesting that physisorption controlled the adsorption process. Desorption and re-adsorption of CTA was also evaluated.

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.

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.

Polydiacetylene/triblock copolymer nanosensor for the detection of native and free bovine serum albumin.

Bovine serum albumin (BSA) has been recognized as a marker of the cow's health, milk quality, an allergenic protein and as a carrier. Its detection is important in the food, pharmaceutical and medical industries. However, traditional techniques used to detect BSA are often time-consuming, expensive, and show limited sensitivity. This paper describes properties of polydiacetylene-triblock copolymer (L64) nanosensors, synthesized to easily detect BSA. Sensor efficiency was studied as a function of nanosensor composition, polydiacetylene chemical structures, BSA conformation and hydrophobic domain availability, using spectroscopic, calorimetric, light scattering, and electrokinetic analyses. Nanosensors were sensitive to detect the average BSA concentration of milk and dairy products and discriminated between native and denatured protein through naked-eye detectable blue-to-red transition. The standard Gibbs free energy (-10.44<ΔG°<-49.52kJM), stoichiometry complex (1<"n"<3), and binding constant (6.7×102

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.

Synthesis and application of a new carboxylated cellulose derivative. Part I: Removal of Co(2+), Cu(2+) and Ni(2+) from monocomponent spiked aqueous solution.

A new carboxylated cellulose derivative (CTA) was prepared from the esterification of cellulose with 1,2,4-Benzenetricarboxylic anhydride. CTA was characterized by percent weight gain (pwg), amount of carboxylic acid groups (nCOOH), elemental analysis, FTIR, TGA, solid-state (13)C NMR, X-ray diffraction (DRX), specific surface area, pore size distribution, SEM and EDX. The best CTA synthesis condition yielded a pwg and nCOOH of 94.5% and 6.81mmolg(-1), respectively. CTA was used as an adsorbent material to remove Co(2+), Cu(2+) and Ni(2+) from monocomponent spiked aqueous solution. Adsorption studies were developed as a function of the solution pH, contact time and initial adsorbate concentration. Langmuir model better fitted the experimental adsorption data and the maximum adsorption capacities estimated by this model were 0.749, 1.487 and 1.001mmolg(-1) for Co(2+), Cu(2+) and Ni(2+), respectively. The adsorption mechanism was investigated by using isothermal titration calorimetry. The values of ΔadsH° were in the range from 5.36 to 8.09kJmol(-1), suggesting that the mechanism controlling the phenomenon is physisorption. Desorption and re-adsorption studies were also performed. Desorption and re-adsorption efficiencies were closer to 100%, allowing the recovery of both metal ions and CTA adsorbent.