The use of gum Arabic as “Green” stabilizer of poly(aniline) nanocomposites: A comprehensive study of spectroscopic, morphological and electrochemical properties

Gum Arabic microgel-based biomimetic waterborne anticorrosive coatings with reinforced water and abrasive resistances

The inadequate water resistance and mechanical properties of waterborne anticorrosive coatings is a serious problem that leads to coating failure. When the bark of acacia trees sustains damage, the liquid Gum Arabic (GA) that oozes from the trunk coagulates at the site of injury to safeguard it, which is called "gummosis" self-protection. Inspired by this, biomimetic GA microgel-based waterborne anticorrosive coatings are designed. Microgel exhibits a crosslinked polymer network structure with a combination of advantageous characteristics derived from both solids and liquids. By encapsulating the liquid corrosion inhibitors (MeBT) within the solid microgel matrix, the coating system is endowed with self-protective capabilities. The as-prepared GAMG-MeBT microgels are introduced into waterborne epoxy (WE) matrix and sprayed onto the surface of Q235 steel. Corrosion studies reveal the 3.0-wt% GAMG-MeBT/WE coating exhibits an impedance modulus value in the low-frequency region (Z0.01Hz) of 1.37 × 109 Ω cm2 after immersing in 3.5-wt% NaCl solution for 60 days, which is nearly two orders of magnitude higher than that of the pure WE coatings. Moreover, the coatings display improved water resistance, enhanced abrasive resistance, and active corrosion protection. This work provides a new approach to solving the failure of WE anticorrosive coatings.

Competitive photooxidation of small colorless organics controlled by oxygen vacancies under visible light

Visible-light photooxidation sensitized by surface attachment of small colorless organics on semiconductor photocatalysts has emerged as an economical method for photocatalytic synthesis or degradation. In particular, heteroatom (X = N and Cl)-containing substrates could undergo either C-N coupling or dechlorination degradation via sensitizing TiO2, but the mechanism in conducting the competitive visible-light sensitized photooxidations is still vague. Herein, the visible-light photooxidation of colorless 4-chlorobenzene-1,2-diamine (o-CAN) on TiO2 was revealed, contributing to selective C-N coupling rather than dechlorination. Oxygen vacancies (OVs) were in situ generated on the TiO2 surface, which could be dominant in weakening the Cl-Ti adsorption of o-CAN and regulating the activation of O2 for selective C-N coupling. The C-N coupling product, functionalized as the sensitizer, further promoted the visible-light photooxidation upon N-Ti and Cl-Ti coordination. This process was then confirmed by on-line mass spectrometric analysis, and the intermediates as well as their kinetics were determined. Thereby, theoretical calculations were employed to verify the roles of OVs in competitive photooxidation and lowering the energy barriers as well. Based on the comprehensive characterizations of both the catalysts and intermediates, this work has provided insights into competitive photooxidations under visible light.

Multivariable analysis of egg white protein-chitosan interaction: Influence of pH, temperature, biopolymers ratio, and ionic concentration

The influence of pH, temperature, biopolymer ratio, total concentration, and ionic concentration on the interaction between egg white protein (EWP) and chitosan (CS) was investigated through turbidity, zeta potential, and state diagram in our research. In addition, phase behavior was observed under various conditions. The turbidity of EWP remained low (turbidity < 0.03) and basically unchanged at a wide range of pH (4.0-8.0), while the turbidity of CS was slightly higher (turbidity < 0.2) after pH 7.0 than before. Moreover, under the same conditions, a sharply rising peak pattern was observed for the complex between EWP and CS. The maximum turbidity value was observed at 55 °C, and the temperature had a mild effect on turbidity. The optimum EWP to CS ratio was found to be 12:1 based on the turbidity curves and state diagrams influenced by different biopolymer mixing ratios. With the enhanced concentrations of total biopolymer, the maximum turbidity rose insignificantly above 0.1%.

Strategic Electrochemical Determination of Nitrate over Polyaniline/Multi-Walled Carbon Nanotubes-Gum Arabic Architecture

Significant agricultural and industrial activities necessitate the regular monitoring of nitrate (NO₃^-) ions levels in feed and groundwater. The current comparative study discloses an innovative user-friendly electrochemical approach for the determination of NO₃^- over polyaniline (PAni)-based modified electrodes. The electrochemical sensors concocted with PAni, multi-walled carbon nanotubes (CNT), and gum arabic (GA). The unique electrode material GA@PAni-CNT was synthesized by facile one-pot catalytic polymerization of aniline (Ani) with FeCl₃/H₂O₂ in the presence of CNT and GA as integral components. As revealed by cyclic voltammetry (CV), the anchoring/retention of NO₃^- followed by reduction is proposed to occur when a GA@PAni-CNT electrode is immersed in phosphate buffer electrolyte containing NO₃^- that eventually results in a significantly higher redox activity of the GA@PAni-CNT electrode upon potential scan. The mechanism of NO₃^- anchoring may be associated with the non-redox transition of leucomeraldine salt (LS) into emeraldine salt (ES) and the generation of nitrite (NO₂^-) ions. As a result, the oxidation current produced by CV for redox transition of ES ↔ pernigraniline (PN) was ~9 times of that obtained with GA@PAni-CNT electrode and phosphate buffer electrolyte, thus achieving indirect NO₃^- voltammetric determination of the GA@PAni-CNT electrode. The prepared GA@PAni-CNT electrode displayed a higher charge transfer ability as compared to that of PAni-CNT and PAni electrodes. The optimum square wave voltammetric (SWV) response resulted in two linear concentration ranges of 1-10 (R² = 0.9995) and 15-50 µM (R² = 0.9988) with a detection limit of 0.42 µM, which is significantly lower. The GA@PAni-CNT electrode demonstrated the best detection, sensitivity, and performance among the investigated electrodes for indirect voltammetric determination of NO₃^- that portrayed the possibility of utilizing GA-stabilized PAni and CNT nanocomposite materials in additional electrochemical sensing applications.

In vitro biocompatibility screening of a colloidal gum Arabic-polyaniline conducting nanocomposite

Although polyaniline (PANI) is a widely investigated conductive polymer for biological applications, studies addressing the biocompatibility of colloidal PANI dispersions are scarcely found in the literature of the area. Therefore, PANI nanoparticles stabilized by the natural polysaccharide gum Arabic (GA) were screened for their biocompatibility. The GA successfully stabilized the colloidal PANI-GA dispersions when exposed to a protein-rich medium, showing compatibility with the biological environment. The results obtained from a series of in vitro assays showed that, after up to 48 h of exposure to a range of PANI-GA concentrations (1-50 μg/mL), both mouse BALB/3T3 fibroblasts and RAW 264.7 macrophages showed no evidence of change in cellular proliferation, viability and metabolic activity. An increase in macrophage granularity poses as evidence of phagocytic uptake of PANI-GA, without resulting activation of this cell type. Additionally, the PANI-GA nanoparticles modulated the cell morphology changes induced on fibroblasts by GA in a concentration-dependent manner. Thus, this unprecedented biocompatibility study of PANI nanoparticles stabilized by a plant gum exudate polysaccharide showed promising results. This simple biomaterial might be further developed into colloidal formulations for biological and biomedical applications, taking advantage of its versatility, biocompatibility, and conductive properties.

Encapsulated Microparticles of (1→6)-β-d-Glucan Containing Extract of Baccharis dracunculifolia: Production and Characterization

β-Glucans are biomacromolecules well known, among other biological activities, for their immunomodulatory potential. Similarly, extracts of Baccharis dracunculifolia also possess biological properties and are used in folk medicine for the treatment of inflammation, ulcers, and hepatic diseases. Microparticles containing (1→6)-β-d-glucan (lasiodiplodan) and B. dracunculifolia extract were produced and characterized. A 23 factorial design was employed to define the conditions of production of microparticles by atomization. Lasiodiplodan associated with maltodextrin and gum arabic was studied as a matrix material. Microparticles of 0.4 μm mean size and high phenolics content (3157.9 μg GAE/g) were obtained under the optimized conditions. The microparticle size ranged from 0.23 to 1.21 µm, and the mathematical model that best represented the release kinetics of the extract was the Korsmeyer-Peppas model. Diffusional exponent (n) values of 0.64 at pH 7.7 and 1.15 at pH 2.61 were found, indicating particles with a non-Fickian or anomalous transport system, and Super Case II transport, respectively. Thermal analysis indicated that the microparticles demonstrated high thermal stability. The X-ray diffraction analyses revealed an amorphous structure, and HPLC-DAD analysis showed microparticles rich in phenolic compounds: caffeic acid, p-coumaric acid, and catechin. The microparticles obtained comprise a new biomaterial with biological potential for applications in different fields.

Preparation and characterization of nanocomposite films based on gum arabic, maltodextrin and polyethylene glycol reinforced with turmeric nanofiber isolated from turmeric spent

Turmeric nanofibers (TNF) were used as reinforcement in the gum arabic (GA), maltodextrin (MDX) and polyethylene glycol (PEG) matrices to enhance the physicochemical properties. The TNF were prepared from turmeric spent by acid hydrolysis accompanied by high pressure homogenization. The thermal and mechanical properties, structure morphology and antimicrobial activities of the prepared nanocomposites were investigated. Differential scanning calorimetry (DSC) data indicate that the addition of TNF significantly increased the onset temperature (T_o), peak temperature (T_p) and conclusion temperature (T_c) of the melting peaks of nanocomposites, but considerably decreased the enthalpy change values. The tensile properties showed that the addition of TNF enhanced mechanical properties due to the formation of networks within the GA, MDX and PEG. The scanning electron microscopy (SEM) images revealed the films of GA-TNF and MDX-TNF show smooth, homogenous surface due to intermolecular hydrogen bonding, and the film of PEG-TNF shows good dispersion of TNF with PEG matrix with rough surface because of strong interfacial adhesion between TNF and PEG and strong hydrogen bonding, which are further confirmed by the FT-IR spectroscopy. XRD results exhibited the disappearances of peaks of TNF indicating the reinforcement of TNF in the prepared nanocomposite matrices. The antibacterial tests show the prepared nanocomposites exhibited excellent antibacterial performance against Bacillus cereus, Escherichia coli, Staphylococcus aureus and Salmonella typhimurium.

Tree gum-based renewable materials: Sustainable applications in nanotechnology, biomedical and environmental fields

The prospective uses of tree gum polysaccharides and their nanostructures in various aspects of food, water, energy, biotechnology, environment and medicine industries, have garnered a great deal of attention recently. In addition to extensive applications of tree gums in food, there are substantial non-food applications of these commercial gums, which have gained widespread attention due to their availability, structural diversity and remarkable properties as 'green' bio-based renewable materials. Tree gums are obtainable as natural polysaccharides from various tree genera possessing exceptional properties, including their renewable, biocompatible, biodegradable, and non-toxic nature and their ability to undergo easy chemical modifications. This review focuses on non-food applications of several important commercially available gums (arabic, karaya, tragacanth, ghatti and kondagogu) for the greener synthesis and stabilization of metal/metal oxide NPs, production of electrospun fibers, environmental bioremediation, bio-catalysis, biosensors, coordination complexes of metal-hydrogels, and for antimicrobial and biomedical applications. Furthermore, polysaccharides acquired from botanical, seaweed, animal, and microbial origins are briefly compared with the characteristics of tree gum exudates.

Improving the water solubility of Monascus pigments under acidic conditions with gum arabic

BACKGROUND

Monascus pigments (Mps) are natural food colorants and their stability in acidic solutions is important for application in the food industry. This study aimed to evaluate the use of gum arabic (GA) as a stabilizer for maintaining the solubility of Mps in an acidic aqueous solution exposed to a high temperature, and to analyze the molecular interactions between GA and Mps.

RESULTS

Mps dispersed (0.2 g kg^-1 ) in deionized water at pH 3.0-4.0 without GA formed precipitates but remained in a stable solution in the presence of GA (1 g kg^-1 ). The significant improvement of Mps water solubility under acidic conditions was attributed to the formation of Mps-GA complexes, as indicated by a sharp increase in the fluorescence intensity. The results on particle size, zeta potential, and transmission electron microscopy further suggested that molecular binding of Mps to GA, electrostatic repulsion, and steric hindrance of GA were contributing factors to preventing the aggregation of Mps in acidic solutions. A mechanistic model was presented for GA-Mps interactions and complex structures.

CONCLUSION

GA was proven to be an effective stabilizer of natural food colorants in acidic solutions. © 2016 Society of Chemical Industry.

Stability of gum arabic-gold nanoparticles in physiological simulated pHs and their selective effect on cell lines

Stable gold nanoparticles coated with gum arabic (GA-AuNPs) exhibit selective effect on B16-F10 cells that could provide a future alternative for melanoma treatment.

Structure and effects of gold nanoparticles in bacterial cellulose–polyaniline conductive membranes

Bacterial cellulose (BC) and poly(aniline) (PANI) composites were successfully synthesized by in situ polymerization of aniline by ammonium persulphate (APS) in the presence and absence of gold nanoparticles.

A tailored biocatalyst achieved by the rational anchoring of imidazole groups on a natural polymer: furnishing a potential artificial nuclease by sustainable materials engineering

Biocatalysts were obtained by anchoring imidazole groups on the biocompatible gum arabic, with catalytic activity in dephosphorylation reactions and cleavage of plasmid DNA.