RESUMEN

Peptides are receiving significant attention in pharmaceutical sciences due to their applications as anti-inflammatory drugs; however, many aspects of their interactions and mechanisms at the molecular level are not well-known. This work explores the molecular structure of two peptides-(i) cysteine (Cys)-asparagine (Asn)-serine (Ser) (CNS) as a molecule in the gas phase and solvated in water in zwitterion form, and (ii) the crystal structure of the dipeptide serine-asparagine (SN), a reliable peptide indication whose experimental cell parameters are well known. A search was performed by means of atomistic calculations based on density functional theory (DFT). These calculations matched the experimental crystal structure of SN, validating the CNS results and useful for assignments of our experimental spectroscopic IR bands. Our calculations also explore the intercalation of CNS into the interlayer space of montmorillonite (MNT). Our quantum mechanical calculations show that the conformations of these peptides change significantly during intercalation into the confined interlayer space of MNT. This intercalation is energetically favorable, indicating that this process can be a useful preparation for therapeutic anti-inflammatory applications and showing high stability and controlled release processes.

Asunto(s)

RESUMEN

Industrial effluents, especially those containing dyes, have become the main cause of contamination of water resources. In this context, Brazilian bentonite/MgO composites, with excellent adsorptive properties, were prepared and investigated for their effectiveness in removing cationic and anionic dyes from aqueous solutions. The new adsorbents were obtained using Brazilian bentonites and MgO using the mechanochemical method followed by heat treatment (at 700 °C for 4 h). Different characterization techniques were used for the chemical, mineralogical, thermal, surface, and morphological analysis of the raw clays and the composites. The experimental adsorption isotherms were quantified under different conditions of initial concentration, contact time, pH, adsorbent dosage, and temperature variation to interpret the adsorption mechanism of the crystal violet (CV) and Congo red (CR) dyes. The modeling results were obtained from the empirical Sips equation and Pseudo Second Order (PSO) kinetics, indicating that the adsorption of molecules is a heterogeneous phenomenon that occurs in a monolayer on the surface (ns > 1), with the adsorption rate determined by chemisorption. The composites showed the best removal efficiency performance compared to the raw bentonites, with an increase of 12% for the CV dye and 46% for the CR dye. In addition, the qmax values obtained were 423.02 mg/g and 479.86 mg/g (AM01). This research underscores the potential of Brazilian bentonite/MgO composites as a promising solution for the removal of cationic and anionic dyes from water, offering hope for future applications in the field of environmental engineering and materials science.

Asunto(s)

RESUMEN

Glucosamine-chitosan synthesized by the Maillard reaction was combined with montmorillonite to obtain a nanohybrid composite to immobilize horseradish peroxidase. The material combines the advantageous properties of clay with those of the chitosan derivative; has improved water solubility and reduced molecular weight and viscosity; involves an eco-friendly synthesis; and exhibits ion exchange capacity, good adhesiveness, and a large specific surface area for enzyme adsorption. The physicochemical characteristics of the composite were analyzed by infrared spectroscopy and X-ray diffraction to determine clay-polycation interactions. The electrochemical response of the different polyphenols to glassy carbon electrodes modified with the composite was evaluated by cyclic voltammetry. The sensitivity and detection limit values obtained with the biosensor toward hydroquinone, chlorogenic acid, catechol, and resorcinol are (1.6 ± 0.2) × 102 µA mM-1 and (74 ± 8) nM; (1.2 ± 0.1) × 102 µA mM-1 and (26 ± 3) nM; (16 ± 2) µA mM-1 and (0.74 ± 0.09) µM; and (3.7± 0.3) µA mM-1 and (3.3 ± 0.2) µM, respectively. The biosensor was applied to quantify polyphenols in pennyroyal and lemon verbena extracts.

Asunto(s)

RESUMEN

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

Asunto(s)

RESUMEN

Aluminosilicates are adsorbents able to bind mycotoxins, and their chemical modification increases their affinity to adsorb low-polarity mycotoxins. To further investigate if the inclusion of salts in bentonite modifies its adsorptive capacity, we studied T-2 toxin adsorption in natural bentonite (NB) and when modified with quaternary ammonium salts differing in polarity and chain length: myristyl trimethyl ammonium bromide (B14), cetyl trimethyl ammonium bromide (B16) and benzyl dimethyl stearyl ammonium chloride (B18). The results showed that quaternary salts made bentonite: displace monovalent (Na+1, K+1) and divalent (Mg+2, Ca+2) ions; reduce its porosity; change its compaction and structure, becoming more crystalline and ordered; and modify the charge balance of sheets. T-2 adsorption was higher in all modified materials compared to NB (p ≤ 0.0001), and B16 (42.96%) better adsorbed T-2 compared to B18 (35.80%; p = 0.0066). B14 (38.40%) showed no differences compared to B16 and B18 (p > 0.05). We described the T-2 adsorption mechanism in B16, in which hydrogen bond interactions, Van der Waals forces and the replacement of the salt by T-2 were found. Our results showed that interaction types due to the inclusion in B16 might be more important than the hydrocarbon chain length to improve the adsorptive capacity of bentonite.

Asunto(s)

RESUMEN

Removal of emerging contaminants, such as antibiotics, from wastewater by adsorption is a simple, low-cost, and high-performance process; however, regeneration and reuse of the exhausted adsorbent are necessary to make the process economically viable. This study aimed to investigate the possibility of electrochemical-based regeneration of clay-type materials. For this, the calcined Verde-lodo (CVL) clay was saturated with the antibiotics ofloxacin (OFL) and ciprofloxacin (CIP) in one-component systems by an adsorption process and then subjected to photo-assisted electrochemical oxidation (0.45 A, 0.05 mol/L NaCl, UV-254 nm, and 60 min), which promotes both pollutant degradation and adsorbent regeneration. The external surface of the CVL clay was investigated by X-ray photoelectron spectroscopy before and after the adsorption process. The influence of regeneration time was evaluated for the CVL clay/OFL and CVL clay/CIP systems, and the results demonstrate high regeneration efficiencies after 1 h of photo-assisted electrochemical oxidation. Clay stability during regeneration was investigated by four successive cycles in different aqueous matrices (ultrapure water, synthetic urine, and river water). The results indicated that the CVL clay is relatively stable under the photo-assisted electrochemical regeneration process. Furthermore, CVL clay was able to remove antibiotics even in the presence of natural interfering agents. The hybrid adsorption/oxidation process applied here demonstrated the electrochemical-based regeneration potential of CVL clay for the treatment of emerging contaminants, since it can be operated quickly (1h of treatment) and with lower consumption of energy (3.93 kWh kg-1) than the traditional method of thermal regeneration (10 kWh kg-1).

Asunto(s)

RESUMEN

Anthocyanins are one of the natural pigments that humanity has employed the most and can substitute synthetic food dyes, which are considered toxic. They are responsible for most purple, blue, and red pigment nuances in tubers, fruits, and flowers. However, they have some limitations in light, pH, oxygen, and temperature conditions. Combining biomolecules and inorganic materials such as clay minerals can help to reverse these limitations. The present work aims to produce materials obtained using cetyltrimethylammonium bromide in bentonite clay for incorporation and photostabilization of anthocyanin dye. Characterizations showed that the organic molecules were intercalated between the clay mineral layers, and the dye was successfully incorporated at a different pH. Visible light-driven photostability tests were performed with 200 h of irradiation, confirming that the organic-inorganic matrices were efficient enough to stabilize the quinoidal base form of anthocyanin. The pigment prepared at pH 10 was three-fold more stable than pH 4, showing that the increase in the synthesis pH promotes more stable colors, probably due to the stronger intermolecular interaction obtained under these conditions. Therefore, organobentonite hybrids allow to stabilize the fragile color coming from the quinoidal base form of anthocyanin dyes.

Asunto(s)

RESUMEN

Edible coating can improve fruits shelf life and, consequently, reduce their waste. Chitosan, which presents a potential for chemical modifications and capacity to form films, can be an alternative for coating due to its biocompatibility, biodegradability, and antimicrobial properties. Chitosan film can be obtained through casting method presenting suitable mechanical properties, such as resistance to traction and elongation, ability to adhere to surfaces and selective permeability to gases, such as O2 and CO2. However, it is highly permeable to water vapor, which can limit its potential coating use. The properties of chitosan films can be improved through the formation of composites by inserting nanoclays as montmorillonite in the polymeric matrix. The objective of this study was to develop and characterize chitosan/montmorillonite nanocomposites for fruit coating aiming for future applications in the field of smart packaging. Nanocomposites were characterized by its microstructure, thermal, mechanical, and physicochemical properties. X-ray diffraction analysis indicated changes in crystallinity with the insertion of montmorillonite. Nanocomposites became more transparent and significantly reduced its water permeability rate with 0.5% w/w montmorillonite addition. Elastic rigidity and tensile strength of the films were improved. Chitosan/montmorillonite nanocomposites demonstrated the potential to improve the storage time of Williams pears.

Asunto(s)

RESUMEN

Capsaicin is the main compound responsible of the hot sense of the chili fruits. This compound has interesting therapeutic properties including anticancer, anti-inflammatory effects, and analgesic. However, its use has several secondary effects, such as skin irritation and allergies. Then, new therapeutic strategies are searched in order to overcome these problems. Montmorillonite has proved to be an excellent excipient for the release of pharmaceutical drugs. In this work, the molecular structure and crystal structure of capsaicin, and the adsorption of this molecule into the interlayer space of montmorillonite have been studied using quantum mechanical calculations based on Density Functional Theory (DFT) level of theory and molecular dynamics simulations. The crystal structure has been predicted with these calculations and the intermolecular interactions have been determined with a higher resolution than the previous experimental data. The adsorption of capsaicin into the confined interlayer space of montmorillonite is energetically favourable with low and high octahedral charge. This adsorption can be monitored by IR spectroscopy observing frequency shifts in some bands during the adsorption. This enhances the use of these clay minerals for capsaicin therapeutic formulations.

Asunto(s)

RESUMEN

Nanocomposite polymer electrolytes (NPEs) were obtained using gellan gum (GG) and 1 to 40 wt.% of montmorillonite (Na+SYN-1) clay. The NPEs were crosslinked with formaldehyde, plasticized with glycerol, and contained LiClO4. The samples were characterized by impedance spectroscopy, thermal analyses (TGA and DSC), UV-vis transmittance and reflectance, X-ray diffraction (XRD), and continuous-wave electron paramagnetic resonance (CW-EPR). The NPEs of GG and 40 wt.% LiClO4 showed the highest conductivity of 2.14 × 10-6 and 3.10 × 10-4 S/cm at 30 and 80 °C, respectively. The samples with 10 wt.% Na+SYN-1 had a conductivity of 1.86 × 10-5 and 3.74 × 10-4 S/cm at 30 and 80 °C, respectively. TGA analyses revealed that the samples are thermally stable up to 190 °C and this did not change with clay addition. The transparency of the samples decreased with the increase in the clay content and at the same time their reflectance increased. Finally, CW-EPR was performed to identify the coordination environment of Cu2+ ions in the GG NPEs. The samples doped with the lowest copper concentration exhibit the typical EPR spectra due to isolated Cu2+ ions in axially distorted sites. At high concentrations, the spectra become isotropic because of dipolar and exchange magnetic effects. In summary, GG/clay NPEs presented good ionic conductivity results, which qualifies them for electrochemical device applications.

Asunto(s)

RESUMEN

The drug delivery systems are an important strategy of pharmaceutical technology to modulate undesirable properties, increasing efficacy, and reducing the side effects of active pharmaceutical ingredients (API). The sustained release is a type of controlled-release system that provides a suitable drug level in the blood through a slow release rate. An interesting alternative to achieve a controlled release is the application of carrier materials such as polymers, cyclodextrins, and clays. Sodium montmorillonite (Na-MMT) is a biocompatible natural clay that allows the insertion of organic compounds in interlamellar space, owing to its high cation exchange capacity and large internal surface area. Bromopride (BPD) is an aminated compound with antiemetic properties classified as class II (low solubility, high permeability) of the Biopharmaceutical Classification System (BCS). Herein, the aim of the study was the development and investigation of a drug delivery system formed by intercalation of BPD with Na-MMT. The results indicate the successful intercalation of this API with the lamellar silicate, meanwhile, there was no evidence of BPD intercalation in organic montmorillonite. The Na-MMT/BPD molecular complex exhibits a sustained release in performed assays. Molecular dynamics simulations suggested that BPD molecules interact with the montmorillonite layer through ion-dipole interactions and also between BPD molecules, forming hydrogen bonds web into montmorillonite interlayer space. The new drug delivery system showed an alternative to achieve the BPD sustained release, which may improve its pharmacological performance in therapeutic applications.

Asunto(s)

RESUMEN

In this work, calcium alginate hydrogels with natural and pillared bentonites (0.5 and 5% w/w) were synthetized in two geometries (disks and beads) and their capacity to adsorb cadmium ion from aqueous media was evaluated. Pillarization effect on bentonite morphology was evidenced by SEM, XRD, LD and BET isotherms. Structure and swelling capacity of hydrogels were determined, showing that hydrogels beads with pillared clays presented the higher ability to retain water. Regarding cadmium adsorption capacity, the effect of pH media (3, 5 and 7), the contact time (0 to 320 min.) and the initial cadmium ion concentration (6 to 42 mg/L) were studied employing hydrogel beads. Regardless bentonite type and concentration, the optimal pH cadmium adsorption was 7, reaching the highest adsorption capacity (93%) for hydrogel with 0.5% natural bentonite. Besides, the equilibrium adsorption time was reached at 120 min for all studied hydrogels and experimental data fitted with a pseudo-second order kinetic model.

Asunto(s)

RESUMEN

The unstable proteins in white wine cause haze in bottles of white wine, degrading its quality. Thaumatins and chitinases are grape pathogenesis-related (PR) proteins that remain stable during vinification but can precipitate at high temperatures after bottling. The white wine protein stabilization process can prevent haze by removing these unstable proteins. Traditionally, bentonite is used to remove these proteins; however, it is labor-intensive, generates wine losses, affects wine quality, and harms the environment. More efficient protein stabilization technologies should be based on a better understanding of the main factors and mechanisms underlying protein precipitation. This review focuses on recent developments regarding the instability and removal of white wine proteins, which could be helpful to design more economical and environmentally friendly protein stabilization methods that better preserve the products´ quality.

Asunto(s)

RESUMEN

This work presents a ceramic monolith with a honeycomb structure obtained from a natural zeolite (clinoptilolite), bentonite, and alumina. The monolith obtained by extrusion had a cell density of 57 CPSI (cells per square inch), an open frontal area of 52% w/w, and a wall thickness of 0.9 mm. The raw materials and the natural zeolite ceramic monolith (NZCM) were characterized by X-ray diffraction, N2 adsorption-desorption at 77 K, CO2 adsorption at 273 K, mercury intrusion-extrusion, axial compression tests, resistance to leaching at acidic and basic pH, and point of zero charge. The NZCM presented an SBET = 31 m2∙g-1, a modal micropore size of 0.44 nm, a porosity of 39%, the compressive stress = 14 MPa, and a pHPZC = 7.5. The NZCM was used as an inexpensive and easy-to-handle adsorbent to remove methylene blue (MB) dye in batch studies of kinetics and adsorption isotherms. From modeling of adsorption kinetic data, the predominant phenomenon in this system was physisorption. The modeling of adsorption isotherm data shows that the material has homogeneous active sites. The adsorption occurs by monolayer formation, finding a maximum capacity removal rate of 27 mg MB per gram of NZCM. Compared to other structured materials, a high capacity for removing MB with the ceramic monolith was obtained along with good mechanical properties and resistance in acidic and alkaline environments.

Asunto(s)

RESUMEN

Contamination of water with arsenic is a major global health problem. The use of adsorbent materials for the removal of As from aqueous systems is a plausible solution to this problem. In this work, the use of commercial bentonites (purified and modified with iron (III)) for the removal of As from water was studied. The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption/desorption isotherms to determine their physicochemical properties. The arsenic removal capacities of adsorbent materials were studied from 1 mg/L solutions of As (III) using the colorimetric technique of molybdenum blue. High adsorption capacity (0.33 mg/g) of As (III) was obtained in aqueous systems after 1 h of treatment with unmodified bentonite. The incorporation of iron improved the removal performance in short times. The obtained results could be the starting point for the development of a low-cost filtration system that contributes to solve the problem of arsenic in water.

Asunto(s)

RESUMEN

Combining coagulants with ballast (natural soil or modified clay) to remove cyanobacteria from the water column is a promising tool to mitigate nuisance blooms. Nevertheless, the possible effects of this technique on different toxin-producing cyanobacteria species have not been thoroughly investigated. This laboratory study evaluated the potential effects of the "Floc and Sink" technique on releasing microcystins (MC) from the precipitated biomass. A combined treatment of polyaluminium chloride (PAC) with lanthanum modified bentonite (LMB) and/or local red soil (LRS) was applied to the bloom material (mainly Dolichospermum circinalis and Microcystis aeruginosa) of a tropical reservoir. Intra and extracellular MC and biomass removal were evaluated. PAC alone was not efficient to remove the biomass, while PAC + LMB + LRS was the most efficient and removed 4.3-7.5 times more biomass than other treatments. Intracellular MC concentrations ranged between 12 and 2.180 µg L-1 independent from the biomass. PAC treatment increased extracellular MC concentrations from 3.5 to 6 times. However, when combined with ballast, extracellular MC was up to 4.2 times lower in the top of the test tubes. Nevertheless, PAC + LRS and PAC + LMB + LRS treatments showed extracellular MC concentration eight times higher than controls in the bottom. Our results showed that Floc and Sink appears to be more promising in removing cyanobacteria and extracellular MC from the water column than a sole coagulant (PAC).

Asunto(s)

RESUMEN

The presence of norfloxacin antibiotic (NFX) in drinking water raises significant scientific concern due to the health and environmental problems that may cause. This study aimed to evaluate the NFX removal: 1) in batch adsorption at different pH values on montmorillonite (M) and montmorillonite-carbon hybrids (M-HC); 2) in continuous columns experiments, to assess the technological application of these hybrids as domestic filters, using one M-HC as adsorbent material ranging from 1% to 5%. Batch experiments showed that adsorption occurred in all the samples, being M the material with the highest adsorption capacity (95% of adsorption for cationic NFX). For the M-HC the adsorption seemed to be not strongly dependent of the pH (20%- 41% of adsorption). The characterization of adsorbents and NFX adsorption products (FTIR, XRD, and zeta potential analysis) disclosed that adsorption occurs at both the external surface and the interlayer space of M. For the M-HC synthesized without activation, the interlayer space seemed to be predominantly responsible; while for the activated M-HC the adsorption occurred at the external surface (its interlayer was destroyed). The column experiments revealed that the best adsorption capacity and highest flow were attained using 1% of adsorbent material in the column packing.

Asunto(s)

RESUMEN

The objective of the present work was to develop biodegradable polymeric films (starch-PBAT) as support for the immobilization of lipases using sodium montmorillonite (MMT) as a reinforcing agent (2% w/w) and itaconic acid (IA - 0.5-1.5% w/w) as a compatibilizing agent. The films were produced through a two steps blow-extrusion. The addition of MMT increased the tensile strength and Tg of the films, while the presence of IA made the films more flexible, reducing their Tg. Lipases from Burkholderia cepacia LTEB11 were immobilized in the films by the adsorption method. The ester yield (% of ethyl oleate synthesis) has shown best results (96%, 6 h) for immobilized enzyme in the MMT film and six cycles of reuse were carried out until a reduction of 50% in the catalytic activity of the enzyme.

Asunto(s)

RESUMEN

Most adsorption and radiolysis experiments related to prebiotic chemistry studies are performed in distilled water or sodium chloride solutions. However, distilled water and sodium chloride solutions do not represent the composition of the primitive seas of Earth. In this work, an artificial seawater with ion abundances Mg2+ > Ca2+ >> Na+ ≈ K+ and SO42- >> Cl- was used, one that is different from the average composition of seawater today. This artificial seawater is named seawater 4.0 Ga, since it better represents the composition of the major constituents of seawater of primitive Earth. The radiolysis of adenine adsorbed onto montmorillonite was studied. The most important result is that adenine is adsorbed onto montmorillonite, when it is dissolved in artificial seawater 4.0 Ga, and the clay protects adenine against gamma radiation decomposition. However, desorption of adenine from montmorillonite was possible only with 0.10 mol L-1 of KOH. This result indicates that adenine was strongly bonded to montmorillonite. Fourier transform infrared spectroscopy showed that NH2 group and electrostatic interactions, between negatively charged montmorillonite and positively charged adenine, are responsible for adsorption of adenine onto montmorillonite. In addition, X-ray diffractograms showed that adenine enters in the interlayer space of montmorillonite.

Asunto(s)

Asunto(s)