Response surface and DFT protocols for improvement of the adsorption process of lignocellulosic-based biomass for the removal of basic dyes.

Jatobá-do-cerrado fruit shells, archetypical of lignocellulosic-based biomass, were used as an adsorbent to remove crystal violet (CV) and methylene blue (MB) from water. The adsorbent was characterized using various techniques, and kinetic studies showed dye adsorption followed second-order kinetics. An experimental design investigated the effects of pH and temperature on removal efficiency, with a quadratic model fitting the data best. The results suggest pH influences MB's adsorption capacity more than temperature and at 25 °C and pH 8, MB had a desirability value of 0.89, with 95 % removal efficiency. For CV, temperature had a greater influence, with a desirability value of 0.874 at 25 °C and pH 10, and 95 % removal efficiency. Adsorption isotherm studies revealed maximum adsorption capacities of 123.0 mg·g-1 and 113.0 mg·g-1 for CV and MB, respectively. Experimental thermodynamic parameters indicated an endothermic and spontaneous process which it was supported by quantum chemistry calculations. The protocols developed confirmed the potential for adsorbing CV and MB dyes in water, achieving over 73.1 and 74.4 mg g-1 dyes removal.

Efficiency of water treatment with crushed shell of jatobá-do-cerrado (Hymenaea stigonocarpa) fruit to adsorb Cu(II) and Ni(II) ions: experimental and quantum chemical assessment of the complexation process.

The shell surrounding fruits of the jatobá-do-cerrado tree, in its natural state, was modified by the addition of HNO3 and NaOH and used as an adsorbent in the removal of Cu(II) and Ni(II) from aqueous solutions. The untreated (JIN) and chemically modified (JCT) fruit shell samples were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction. Their efficiency as adsorbents in the removal of Cu(II) and Ni(II) ions from aqueous solutions was studied under different conditions of pH (2-9) and it was observed that the optimal pH for Cu (II) adsorption was 5.5 and for Ni (II) it was 6.0. The adsorption isotherms were obtained at different temperatures (298, 308, 318 K) and the qmax values ranged from 33.96 to 41.00 mg g-1. The adsorbents presented higher selectivity toward Cu ions (II). The thermodynamic analysis results suggest that the adsorption process studied is of a physical nature. Supported by quantum mechanical calculations, the interaction sites of the ion-cellulose and ion-lignin complexes were identified, evidencing the central role of water molecules in stabilization of the complexes. The experimental and theorical results indicate that JIN and JCT have good potential for the adsorption of Cu(II) and Ni(II) ions and are thus promising materials for the removal of other metal ions in aqueous systems.

Carboxymethyl chitosan hydrogel formulations enhance the healing process in experimental partial-thickness (second-degree) burn wound healing.

PURPOSE: This study aimed to elaborate a hydrogel constituted by carboxymethyl chitosan (CMC), hyaluronic acid (HA) and silver (Ag) and to evaluate its healing effect on partial-thickness burn wounds experimentally induced in rats. METHODS: CMC was obtained by chitosan reacting with monochloroacetic acid. The carboxymethylation was confirmed by Fourier-transform infrared spectroscopy and hydrogen nuclear magnetic resonance (NMR). Scanning electron microscopy was used to determine the morphologicalcharacteristics of chitosan and CMC. After the experimental burn wound induction, the animals (n = 126) were treated with different CMC formulations, had their occlusive dressings changed daily and were followed through 7, 14 and 30 days. Morphometric, macroscopic and microscopic aspects and collagen quantification were evaluated. RESULTS: Significative wound contraction, granulation tissue formation, inflammatory infiltration and collagen fibers deposit throughout different phases of the healing process were observed in the CMC hydrogels treated groups. CONCLUSIONS: The results showed that, in the initial phase of the healing process, the most adequate product was the CMC/HA/Ag association, while in the other phases the CMC/HA association was the best one to promote the healing of burn wounds.

Carboxymethyl chitosan hydrogel formulations enhance the healing process in experimental partial-thickness (second-degree) burn wound healing

ABSTRACT Purpose This study aimed to elaborate a hydrogel constituted by carboxymethyl chitosan (CMC), hyaluronic acid (HA) and silver (Ag) and to evaluate its healing effect on partial-thickness burn wounds experimentally induced in rats. Methods CMC was obtained by chitosan reacting with monochloroacetic acid. The carboxymethylation was confirmed by Fourier-transform infrared spectroscopy and hydrogen nuclear magnetic resonance (NMR). Scanning electron microscopy was used to determine the morphologicalcharacteristics of chitosan and CMC. After the experimental burn wound induction, the animals (n = 126) were treated with different CMC formulations, had their occlusive dressings changed daily and were followed through 7, 14 and 30 days. Morphometric, macroscopic and microscopic aspects and collagen quantification were evaluated. Results Significative wound contraction, granulation tissue formation, inflammatory infiltration and collagen fibers deposit throughout different phases of the healing process were observed in the CMC hydrogels treated groups. Conclusions The results showed that, in the initial phase of the healing process, the most adequate product was the CMC/HA/Ag association, while in the other phases the CMC/HA association was the best one to promote the healing of burn wounds.

Ab Initio Molecular Dynamics Simulations of Aqueous Glucosamine Solutions: Solvation Structure and Mechanism of Proton Transfer from Water to Amino Group.

Glucosamine is a component of many cellular glycoproteins that constitutes the cartilage, and it has several biological activities, such as anti-inflammatory, antioxidant, antifibrotic, and anticancer, and has been used in arthritis and dermatological treatments. Considering that the biological activities of glucosamine occur mainly in an aqueous environment, it is essential to understand the effects of an aqueous solvent on its geometric and electronic parameters using ab initio molecular dynamics. The Car-Parrinello molecular dynamics results show that the hydroxyl groups form stable hydrogen bonds with the water molecules with intensities ranging from weak (closed-shell interaction) to intermediate (partially covalent interactions). The H bonds formed between the amino group and the water molecule range from weak (closed-shell) to strong (covalent), and it shows an infinity residence time. The natural bonding orbital (NBO) approach was applied to analyze the effects of charge-transfer interactions on the behavior of the hydrogen bonds. The main contribution to stabilizing energies comes from n → σ* hyperconjugation and explains the stability of the H bonds. The energy barrier for the proton transfer from water to the amino group is 0.88 kcal/mol, and the van der Waals complex energy is 0.3 kcal/mol. The low protonation energy barrier shows that glucosamine can be protonated in an aqueous environment at room temperature, which helps to explain many of its biological activities.

Soybean hulls: Optimization of the pulping and bleaching processes and carboxymethyl cellulose synthesis.

Soybean hulls, a co-product generated in high volumes, were used to obtain pulp and CMC. The pulping process was optimized with the aid of 1%, 2%, and 2.5% NaOH solutions at 90 °C for 2 h. A 22 central composite design was used in order to optimize the bleaching process and the CMC synthesis. Volumes of bleaching solution (VS) of between 55 and 65 mL/g at temperatures between 85 and 95 °C and VS of 70 and 75 mL/g at 95 °C were applied in the pulp bleaching process. The factors considered in the carboxymethylation were the chloroacetic acid mass (1.2-2.1 g/g) and the reaction time (192-228 min), at 63 °C. The soybean hulls contain 40.62% of cellulose and have a low lignin content. The pulping process was optimized when 1% NaOH was used at 90 °C/2 h and bleaching process applying VS = 75 mL at 95 °C/4 h. The pulps showed low lignin content (<6%) and the cellulose had a high degree of crystallinity. The SEM, 1H NMR, XRD, FTIR and TGA/DTG analysis results demonstrated that it is possible to synthesize CMC (DS = 1.45) by acetylating the bleached pulp with 2.1 g of chloroacetic acid for 192 min, at 63 °C.

Sorghum straw: Pulping and bleaching process optimization and synthesis of cellulose acetate.

The process employed for the pulping and bleaching of sorghum straw was optimized prior to the synthesis of cellulose acetate. A 22 factorial central composite design was carried out. The variables considered were cooking time (1.5 to 2.5 h) and dilute alkali concentration (0.75 to 1.25%) for the pulping and bleaching time (30 to 35 min) and bleach volume (20 to 25 mL) for the bleaching. The sorghum straw was comprised of 49.43% α-cellulose, 19.18% hemicellulose and 30.42% lignin. The optimum conditions that maximize these processes were 2.5 h and 1.25% (dilute alkali concentration) at 90 °C, and 35 min and 25 mL (bleach volume) at 80 °C, respectively, providing pulps with a low Kappa number (<3) and lignin content, and cellulose with a high degree of crystallinity. The 1H NMR, XRD, FTIR spectroscopy, SEM and thermal analysis demonstrated that it is possible to synthetize cellulose acetate (with 2.62 degrees of substitution) by acetylating bleached pulp for 16 h at 25 °C.

Inhibition of bacterial biofilms by carboxymethyl chitosan combined with silver, zinc and copper salts.

Investigation of the antimicrobial action of carboxymethyl chitosan (CMCh) is among the alternative approaches in the control of pathogenic microorganisms. This study aimed to screen the toxicity using the brine shrimp lethality assay and to investigate the inhibitory activity of carboxymethyl in isolation or in combination with silver nitrate, copper sulfate and zinc sulfate on biofilm formation by Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, Kocuria rhizophila ATCC 9341, Pseudomonas aeruginosa ATCC 9027, Escherichia coli ATCC 25312, and Burkholderia cepacia ATCC 17759. The CMCh was obtained by reacting chitosan with monochloroacetic acid under alkaline conditions, and the occurrence of carboxymethylation was evidenced by FTIR and 1H NMR spectroscopy. The CMCh was combined with metallic salts (AgNO3, CuSO4·5H2O and ZnSO4) to perform the bioassays to screen the toxicity, to determine the minimum inhibitory concentration and the impact of sub-inhibitory concentrations against biofilm formation. Although CMCh did not show inhibitory activity against bacterial growth, it had an interesting level of inhibition of bacterial biofilm. The results suggest that sub-inhibitory concentrations of compounds were effective against biofilm formation.

Optimization of carboxymethyl chitosan synthesis using response surface methodology and desirability function.

In this paper, chitosan was reacted with monochloroacetic acid under alkaline conditions to prepare carboxymethyl chitosan. A 2(3) full-factorial central composite design was applied to evaluate the effect of molar ratio sodium hydroxide (NaOH)/Chitosan (Ch), time and molar ratio monochloroacetic acid (MCA)/Chitosan (Ch) on the reaction yield and on the characteristics of carboxymethyl chitosan such as average degree of substitution (DS¯) and solubility. An optimization strategy based on response surface methodology was used together with the desirability function approach to optimize this process. The occurrence of carboxymethylation was evidenced by FTIR and (1)H NMR spectroscopy. The optimum conditions for carboxymethylation process were found to be 12.4, 10.6h and 5 for molar ratio sodium hydroxide (NaOH)/Chitosan (Ch), time and molar ratio monochloroacetic acid (MCA)/Chitosan (Ch), respectively. Under these optimal conditions, it was possible to obtain carboxymethyl chitosan with DS¯ of 1.86 and solubility of 99.6%. X-ray diffraction and thermogravimetry analysis showed that crystallinity and thermal stability of derivatives was lower than chitosan and decreased with increase of DS¯.

Microwave-assisted carboxymethylation of cellulose extracted from brewer's spent grain.

Cellulose was extracted from brewer's spent grain (BSG) by alkaline and bleaching treatments. The extracted cellulose was used in the preparation of carboxymethyl cellulose (CMC) by reaction with monochloroacetic acid in alkaline medium with the use of a microwave reactor. A full-factorial 2(3) central composite design was applied in order to evaluate how parameters of carboxymethylation process such as reaction time, amount of monochloroacetic acid and reaction temperature affect the average degree of substitution (DS) of the cellulose derivative. An optimization strategy based on response surface methodology has been used for this process. The optimized conditions to yield CMC with the highest DS of 1.46 follow: 5g of monochloroacetic acid per gram of cellulose, reaction time of 7.5min and temperature of 70°C. This work demonstrated the feasibility of a fast and efficient microwave-assisted method to synthesize carboxymethyl cellulose from cellulose isolated of brewer's spent grain.