Organic Chimeras based on Selenosugars, Steroids, and Fullerenes as Potential Inhibitors of the ß-amyloid Peptide Aggregation.

The aggregation of ß-amyloid peptide (Aß) is associated with neurodegenerative diseases such as Alzheimer's disease (AD). Several therapies aimed at reducing the aggregation of this peptide have emerged as potential strategies for the treatment of AD. This paper describes the design and preparation of new hybrid molecules based on steroids, selenosugars, and [60]fullerene as potential inhibitors of Aß oligomerization. These moieties were selected based on their antioxidant properties and possible areas of interaction with the Aß. Cyclopropanations between C60 and malonates bearing different steroid and selenosugar moieties using the Bingel-Hirsch protocol have enabled the synthesis of functionalized molecular hybrids. The obtained derivatives were characterized by physical and spectroscopic techniques. Theoretical calculations for all the selenium compounds were performed using the density functional theory DFT/B3LYP-D3(BJ)/6-311G(2d,p) predicting the most stable conformations of the synthesized derivatives. Relevant geometrical parameters were investigated to relate the stereochemical behavior and the spectroscopic data obtained. The affinity of the compounds for Aß-peptide was estimated by molecular docking simulation, which predicted an increase in affinity and interactions for Aß for the hybrids containing the C60 core. In addition, parameters such as lipophilicity, polar surface area, and dipole moment were calculated to predict their potential interaction with membrane cells.

A mechanistic study on conversion of carbon dioxide into formic acid promoted by 1-ethyl-2, 3-dimethyl-imidazolium nitrite.

CONTEXT: The conversion of carbon dioxide (CO2) to formic acid (FA) through hydrogenation using 1-ethyl-2,3- dimethyl imidazolium nitrite (EDIN) ionic liquid was studied to understand the catalytic roles within EDIN. CO2 hydrogenation in various solvents has been explored, but achieving high efficiency and selectivity remains challenging due to the thermodynamic stability and kinetic inertness of CO2. This study explored two mechanistic pathways through theoretical calculations, revealing that the nitrite (NO2-) group is the most active site. The oxygen site on nitrite favorably activates H2, while the nitrogen site shows a minor activation barrier of 108.90 kJ/mol. The Gibbs energy variation indicates stable FA formation via EDIN, suggesting effective hydrogen (H2) activation and subsequent CO2 conversion. These insights are crucial for developing improved catalytic sites and processes in ionic liquid catalysts for CO2 hydrogenation. METHODS: Quantum chemical calculations were conducted using the ORCA software package at the Restricted Hartree-Fock (RHF) and density functional theory (DFT) levels. The RHF method, known for its predictive abilities in simpler systems, provided a baseline description of electronic structures. In contrast, DFT was employed for its effectiveness in complex interactions involving significant electron correlation. A valence triple-zeta polarization (def2-TZVPP) basis set was employed for both RHF and DFT, ensuring accurate and correlated calculations. The B3LYP functional was utilized for its rapid convergence and cost-efficiency in larger molecules. Dispersion corrected functionals (DFT-D) addressed significant dispersion forces in ionic liquids, incorporating Grimme's D2, D3, and D4 corrections. Geometry optimizations, kinetics, and thermodynamic calculations were performed in the gas phase. The Nudged Elastic Band Transition State (NEB-TS) approach, combining Climbing Image-NEB (CINEB) and Eigenvector-Following (EF) methods, was used to find the minimum energy path (MEP) between reactants and products. Thermochemical analyses based on vibrational frequency calculations evaluated properties such as Enthalpy, Entropy, and Gibbs energy using ideal gas statistical mechanics.

Expanding chalcogen bonds in thiophenes to interactions with halogens.

Compounds containing the thiophene moiety find several applications in physics and chemistry, such as electrical conduction, which depends on specific conformations to properly exhibiting the desired properties. In turn, chalcogen bonding has found to modulate the conformation of some N-thiophen-2-ylfomamides. Since halogens participate in a kin interaction (halogen bonding) and are abundant in agrochemicals, pharmaceuticals, and materials, we have quantum-chemically explored the interaction between organic halogen and thiophene as a conformational modulator in some model compounds. Although such interaction indeed appears, as demonstrated by atoms in molecules and natural bond orbital analysis, it is inefficient to control the conformational equilibrium. An energy decomposition analysis scheme demonstrated that halomethane and thiophene tend to move away from one another due to a core component (Pauli repulsion and exchange), which is mainly due to a deformation term. Therefore, chalcogen bonds with halogens appear weaker than with other chalcogens.

Chemical modification and doping of poly(p-phenylenes): A theoretical study.

CONTEXT: Conjugated polymers (CPs) have been recognized as promising materials for the manufacture of electronic devices. However, further studies are still needed to enhance the electrical conductivity of these type of organic materials. The two main strategies for achieving this improvement are the doping process and chemical modification of the polymer chain. Therefore, in this article, we conduct a theoretical investigation, employing DFT calculations to evaluate the structural, energetic, and electronic properties of pristine and push-pull-derived poly(p-phenylene) oligomers (PPPs), as well as the analysis at the molecular level of the polymer doping process. As a primary conclusion, we determined that the PPP oligomer substituted with the push-pull group 4-EtN/CNPhNO2 exhibited the smallest HOMO-LUMO gap (Eg) among the studied oligomers. Moreover, we observed that the doping process, whether through electron removal or the introduction of the dopant anion ClO4-, led to a substantial reduction in the Eg of the PPP, indicating an enhancement in the polymer's electrical conductivity. METHODS: DFT calculations were conducted using the PBE0 functional along with the Pople's split valence 6-31G(d,p) basis set, which includes polarization functions on all atoms (B97D/6-31G(d,p)).

Bifunctional iminophosphorane organocatalyst with additional hydrogen bonding: Calculations predict enhanced catalytic performance in a michael addition reaction.

A new iminophosphorane-thiourea superbase was rationally designed and investigated as an organocatalyst for the enantioselective Michael addition reaction of nitromethane to 4-phenylbut-3-en-2-one. Starting from an iminophosphorane-thiourea organocatalyst structure already known, we have used theoretical calculations to determine the structures of transition states involved in the carbon-carbon bond formation step and carried out structural modifications to accelerate the reaction rate and to increase the enantioselectivity. The effective structural modification was adding a rigid hydroxyl group able to make an additional hydrogen bond to the transition state, producing a substantial decrease of the ΔG‡ by 7 kcal mol-1. The enantiomeric excess is predicted to be above of 97% using the reliable M06-2X and ωB97M - V functionals. The determination of the complete reaction mechanism and free energy profile was followed by a detailed microkinetic analysis. The present study points out a new direction for structural modifications on this kind of organocatalyst.

Benzazole-Based ESIPT Fluorophores: Proton Transfer from the Chalcogen Perspective. A Combined Theoretical and Experimental Study.

In this study, we present a comprehensive photophysical investigation of ESIPT-reactive benzazole derivatives in both solution and the solid state. These derivatives incorporate different chalcogen atoms (O, S, and Se) into their structures, and we explore how these variations impact their electronic properties in both ground and excited states. Changes in the UV-Vis absorption and fluorescence emission spectra were analyzed and correlated with the chalcogen atom and solvent polarity. In general, the spectral band of the benzazole derivative containing selenium was redshifted in both the ground and excited states compared to that of its oxygen and sulfur counterparts. Furthermore, we observed that the solvent played a distinctive role in influencing the ESIPT process within these compounds, underscoring once again the significant influence of the chalcogen atom on their photophysical behavior. Theoretical calculations provided a deeper understanding of the molecular dynamics, electronic structures, and photophysical properties of these compounds. These calculations highlighted the effect of chalcogen atoms on the molecular geometry, absorption and emission characteristics, and intramolecular hydrogen bonding, revealing intricate details of the ESIPT mechanism. The integration of experimental and computational data offers a detailed view of the structural and electronic factors governing the photophysical behavior of benzazole derivatives.

Organosulfur and Organoselenium Functionalized Benzimidazo[1,2-a]quinolines: From Experimental and Theoretical Photophysics to All-Solution-Processed OLEDs.

In this study, we present the synthesis of benzimidazo[1,2-a] quinoline-based heterocycles bearing organosulfur and organoselenium moieties through transition-metal-free cascade reactions involving a sequential intermolecular aromatic nucleophilic substitution (SNAr). Both sulfur and selenium derivatives presented absorption maxima located around 355 nm related to spin and symmetry allowing electronic 1π-π* transitions, and fluorescence emission at the violet-blue region (~440 nm) with relatively large Stokes shift. The fluorescence quantum yields were slightly influenced by the chalcogen, with the sulfur derivatives presenting higher values than the selenium analogs. In this sense, the quantum yields for selenium derivatives can probably be affected by the intersystem crossing or even the photoinduced electron transfer process (PET). The compounds were successfully applied in all-solution-processed organic light-emitting diodes (OLEDs), where poly(9-vinylcarbazole) was employed as a dispersive matrix generating single-layer device cells. The obtained electroluminescence spectra are a sum of benzimidazo[1,2-a]quinolines and PVK singlet and/or triplet emissive states, according to their respective energy band gaps. The best diode rendered a luminance of 25.4 cd⋅m-2 with CIE (0.17, 0.14) and current efficiency of 20.2 mcd⋅A-1, a fivefold improvement in comparison to the PVK device that was explained by a 50-fold increase of charge-carriers electrical mobility.

Molecular interaction analysis of the lignans from Piper cubeba in complex with Haemonchus contortus phosphomethyltransferase.

In vitro larvicidal assays carried out previously by our research group with cubebin, dihydrocubebin and hinokinin, lignans extracted from the fruits of Piper cubeba, against Haemonchus contortus larvae showed strong action larvicidal these compounds. Hinokinin was the most active (EC50 = 0.34 µg/mL) with strong action on the cuticle of the larvae as observed by scanning electron microscopy of the L3 stage. Therefore, to understand the mechanism of action of these compounds in silico studies were carried out using the enzyme phosphomethyltransferase of Haemonchus contortus that contain PMT-1 and PMT-2 di-domains responsible for phosphocholine synthesis, which is one of the main lipids in nematodes. This pathway is not found in mammals, so this enzyme is an important biological target for the development of new anthelmintics. Results of molecular docking, molecular dynamic and a density functional theory calculations studies with the three lignans show few interactions with PMT-1. However, hinokinin has important interactions with PMT-2, that can deactivate the enzyme and interrupt the phosphocholine synthesis, which is an essential compound for the development and maintenance of the nematode cuticle and its survive. Therefore, the previous results of the in vitro assay allied with in silico results, now realized; suggest that hinokinin may be a possible selective target for the development of new anthelmintics against Haemonchus contortus since the PMT-2 domain is present in this nematode.

Study of the Counter Cation Effects on the Supramolecular Structure and Electronic Properties of a Dianionic Oxamate-Based {NiII2} Helicate.

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K2(dmso)(H2O)5][Ni2(H2mpba)3]·dmso·2H2O}n (1) and [Ni(H2O)6][Ni2(H2mpba)3]·3CH3OH·4H2O (2) [dmso = dimethyl sulfoxide; CH3OH = methanol; and H4mpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni2(H2mpba)3]2- helicate, hereafter referred to as {NiII2}. SHAPE software calculations indicate that the coordination geometry of all the NiII atoms in 1 and 2 is a distorted octahedron (Oh) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D2d) and distorted octahedron (Oh), respectively. The {NiII2} helicate in 1 is connected by K+ counter cations yielding a 2D coordination network with sql topology. In contrast to 1, the electroneutrality of the triple-stranded [Ni2(H2mpba)3] 2- dinuclear motif in 2 is achieved by a [Ni(H2O)6]2+ complex cation, where the three neighboring {NiII2} units interact in a supramolecular fashion through four R22(10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the NiII/NiI pair being mediated by OH- ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The NiII ions from the helicate and the counter-ion (complex cation) in 2 can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in 1 also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K+ counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations.

Prospects of ZnS and ZnO as smart semiconductor materials in light-activated antimicrobial coatings for mitigation of severe acute respiratory syndrome coronavirus-2 infection.

We carried out theoretical and experimental analyses of ZnO and ZnS nanoparticles as smart semiconductor materials in light-activated antimicrobial coating for application in masks. We used low-cost hydrothermally processable precursors to direct the growth of the coatings on cotton fabric. Both ZnO and ZnS coatings had high reactivities as disinfection agents in photocatalysis reactions for the degradation of a methylene blue dye solution. Also, these coatings showed excellent UV protection properties. For understanding at the molecular level, the broad-spectrum biological activities of the ZnO and ZnS coatings against Fusarium Oxysporum fungi, Escherichia coli bacteria, and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus and their variants, were investigated computationally. Hexagonal Zn6O6 and Zn6S6 clusters were used as models for the simulations through excited- and ground-state calculations. The theoretical findings show that changes in the local chemical environment in these excited systems have a profound impact on their physical and chemical properties and thus, can provide a better understanding to engineer new functional materials in light-activated antimicrobial coatings for the mitigation of SARS-CoV-2 infection.

Electronically excited states of formic acid investigated by theoretical and experimental methods.

Absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements of gas-phase formic acid (HCOOH) in the photon energy range 4.7-10.8 eV (265-115 nm), together with quantum chemical calculations to provide vertical energies and oscillator strengths. The combination of experimental and theoretical methods has allowed a comprehensive assignment of the electronic transitions. The VUV spectrum reveals various vibronic features not previously reported in the literature, notably associated with (3pa'←10a'), (3p'a'←10a'), (3sa'←2a″) and (3pa'←2a″) Rydberg transitions. The assignment of vibrational features in the absorption bands reveal that the C=O stretching, v3'a', the H'-O-C' deformation, v5'a', the C-O stretching, v6'a', and the O=C-O' deformation, v7'a' modes are mainly active. The measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of HCOOH in the upper stratosphere (30-50 km), showing that solar photolysis is an important sink at altitudes above 30 km but not in the troposphere. Potential energy curves for the lowest-lying electronic excited states, as a function of the C=O coordinate, are obtained employing time dependent density functional theory (TD-DFT). These calculations have shown the relevance of internal conversion from Rydberg to valence character governing the nuclear dynamics, yielding clear evidence of the rather complex multidimensional nature of the potential energy surfaces involved.

Atenolol-imprinted polymer: a DFT study.

The purpose of this work was to investigate, via DFT calculations, the molecularly imprinted polymer (MIP) for atenolol (ATL) ß-blocker evaluating distinct functional monomers (FMs), solvents, and cross-linker agents (CLAs). As the main result, we could determine from structural and thermodynamic data the best MIP synthesis protocol as being: p-vinyl benzoic acid (APV) as FM, toluene as solvent, and pentaerythritol triacrylate (PETRA) as CLA. We believe this rational design can be very useful for experimentalists in an attempt to perform an efficient synthesis of a MIP for this important ß-blocker drug.

Capture of Fullerenes in Cages and Rings by Forming Metal-π Bond Arene Interactions.

Nowadays, the task of the selectively capture of fullerene molecules from soot is the subject of several studies. The low solubility of fullerenes represents a drawback when the goal is to purify them and to carry out chemical procedures where they participate. There are different molecules that can act as a kind of cocoon, giving shelter to the fullerene cages in such a way that they can be included in a solution or can be extracted from a mix. In this work, a theoretical study of some known and new proposed organic molecules of this kind is presented. In all cases, the interaction occurs with the help of a metallic atom or ion which plays the role of a bridge, providing a place for a metallocene like interaction to occur. The thermodynamic arguments favoring the formation of this adduct species are addressed as well as the nature of the bond by means QTAIM parameters and frontier molecular orbitals analysis.

Synthesis and Identification of Epoxy Derivatives of 5-Methylhexahydroisoindole-1,3-dione and Biological Evaluation.

Cyclic imides belong to a well-known class of organic compounds with various biological activities, promoting a great interest in compounds with this functional group. Due to the structural complexity of some molecules and their spectra, it is necessary to use several spectrometric methods associated with auxiliary tools, such as the theoretical calculation for the structural elucidation of complex structures. In this work, the synthesis of epoxy derivatives of 5-methylhexahydroisoindole-1,3-diones was carried out in five steps. Diels-Alder reaction of isoprene and maleic anhydride followed by reaction with m-anisidine afforded the amide (2). Esterification of amide (2) with methanol in the presence of sulfuric acid provided the ester (3) that cyclized in situ to give imides 4 and 4-ent. Epoxidation of 4 and 4-ent with meta-chloroperbenzoic acid (MCPBA) afforded 5a and 5b. The diastereomers were separated by silica gel flash column chromatography, and their structures were determined by analyses of the spectrometric methods. Their structures were confirmed by matching the calculated 1H and 13C NMR chemical shifts of (5a and 5b) with the experimental data of the diastereomers using MAE, CP3, and DP4 statistical analyses. Biological assays were carried out to evaluate the potential herbicide activity of the imides. Compounds 5a and 5b inhibited root growth of the weed Bidens pilosa by more than 70% at all the concentrations evaluated.

Experimental and theoretical affinity and catalysis studies between halogenated phenols and peroxidases: Understanding the bioremediation potential.

Halogenated phenols, such as 2,4-dichlorophenol (2,4-DCP) and 4-bromophenol (4-BP) are pollutants generated by a various industrial sectors like chemical, dye, paper bleaching, pharmaceuticals or in an agriculture as pesticides. The use of Horseradish peroxidase (HRP) in the halogenated phenols treatment has already been mentioned, but it is not well understood how the different phenolic substrates can bind in the peroxidase active site nor how these specific interactions can influence in the bioremediation potential. In this work, different removal efficiencies were obtained for phenolic compounds investigated using HRP as catalyst (93.87 and 59.19% to 4BP and 2,4 DCP, respectively). Thus, to rationalize this result based on the interactions of phenols with active center of HRP, we combine computational and experimental methodologies. The theoretical approaches utilized include density functional theory (DFT) calculations, docking simulation and quantum mechanics/molecular mechanics (QM/MM) technique. Michaelis Menten constant (Km) obtained through experimental methodologies were 2.3 and 0.95 mM to 2,4-DCP and 4-BP, respectively, while the specificity constant (Kcat/Km) found was 1.44 mM-1 s-1 and 0.62 mM-1 s-1 for 4-BP and 2,4-DCP, respectively. The experimental parameters appointed to the highest affinity of HRP to 4-BP. According to the molecular docking calculations, both ligands have shown stabilizing intermolecular interaction energies within the HRP active site, however, the 4-BP showed more stabilizing interaction energy (-53.00 kcal mol-1) than 2,4-dichlorophenol (-49.23 kcal mol-1). Besides that, oxidative mechanism of 4-BP and 2,4-DCP was investigated by the hybrid QM/MM approach. This study showed that the lowest activation energy values for transition states investigated were obtained for 4-BP. Therefore, by theoretical approach, the compound 4-BP showed the more stabilizing interaction and activation energy values related to the interaction within the enzyme and the oxidative reaction mechanism, respectively, which corroborates with experimental parameters obtained. The combination between experimental and theoretical approaches was essential to understand how the degradation potential of the HRP enzyme depends on the interactions between substrate and the active center cavity of the enzyme.

Elucidation of the chromatographic enantiomer elution order for praziquantel: An experimental and theoretical assessment.

In this work, we have studied both experimentally and theoretically the praziquantel (PZQ) chiral discrimination. According to the main results, the enantioseparation of PZQ was efficiently optimized by HPLC on the reverse phase from the Chiralpak IB column, which has cellulose tris (3,5-dimethylphenylcarbamate) (CDMPC) as a chiral selector. The thermodynamic and structural parameters obtained via density functional theory (DFT) calculations pointed out the chiral discrimination as well as the enantiomeric elution order of PZQ, thus elucidating the experimental data and validating our proposed method. Finally, the hydrogen bonds and π-π stacking interactions played a key role in the discrimination between the PZQ diastereomeric complexes formed.

Development and validation of an experimental and theoretical method for the chiral discrimination of dinotefuran.

Dinotefuran is a low-cost agrochemical considered a highly toxic product. In this sense, there is a need for its constant environmental, biological, and food control, aiming to ensure its use to humans as well as to preserve biodiversity and ecosystems. In the present work, we developed an experimental and theoretical method for dinotefuran chiral discrimination. According to the main results, the dinotefuran enantioselective separation was efficiently optimized by high-performance liquid chromatography evaluating the influence of different percentage compositions in the mobile phase to improve the resolution of the peaks in the chromatogram. The novelty of this work was the proposition of a reduced molecular model for the chiral selector amylose-Tris-(3,5-dimethylphenylcarbamate) polysaccharide that was able to adequately describe at the molecular level its interaction with the dinotefuran enantiomers. Besides, the thermodynamic and structural parameters obtained via density functional theory calculations pointed out the chiral discrimination as well as the enantiomeric elution order of the analyte studied, confirming the experimental data, thus validating our proposed method. Finally, hydrogen bonds and repulsive interactions played a key role in the discrimination between the diastereomeric complexes, and consequently, for the dinotefuran enantioselective separation.

Disarming Pseudomonas aeruginosa Virulence by the Inhibitory Action of 1,10-Phenanthroline-5,6-Dione-Based Compounds: Elastase B (LasB) as a Chemotherapeutic Target.

Elastase B (lasB) is a multifunctional metalloenzyme secreted by the gram-negative pathogen Pseudomonas aeruginosa, and this enzyme orchestrates several physiopathological events during bacteria-host interplays. LasB is considered to be a potential target for the development of an innovative chemotherapeutic approach, especially against multidrug-resistant strains. Recently, our group showed that 1,10-phenanthroline-5,6-dione (phendione), [Ag(phendione)2]ClO4 (Ag-phendione) and [Cu(phendione)3](ClO4)2.4H2O (Cu-phendione) had anti-P. aeruginosa action against both planktonic- and biofilm-growing cells. In the present work, we have evaluated the effects of these compounds on the (i) interaction with the lasB active site using in silico approaches, (ii) lasB proteolytic activity by using a specific fluorogenic peptide substrate, (iii) lasB gene expression by real time-polymerase chain reaction, (iv) lasB protein secretion by immunoblotting, (v) ability to block the damages induced by lasB on a monolayer of lung epithelial cells, and (vi) survivability of Galleria mellonella larvae after being challenged with purified lasB and lasB-rich bacterial secretions. Molecular docking analyses revealed that phendione and its Ag+ and Cu2+ complexes were able to interact with the amino acids forming the active site of lasB, particularly Cu-phendione which exhibited the most favorable interaction energy parameters. Additionally, the test compounds were effective inhibitors of lasB activity, blocking the in vitro cleavage of the peptide substrate, aminobenzyl-Ala-Gly-Leu-Ala-p-nitrobenzylamide, with Cu-phendione having the best inhibitory action (K i = 90 nM). Treating living bacteria with a sub-inhibitory concentration (½ × MIC value) of the test compounds caused a significant reduction in the expression of the lasB gene as well as its mature protein production/secretion. Further, Ag-phendione and Cu-phendione offered protective action for lung epithelial cells, reducing the A549 monolayer damage by approximately 32 and 42%, respectively. Interestingly, Cu-phendione mitigated the toxic effect of both purified lasB molecules and lasB-containing bacterial secretions in the in vivo model, increasing the survival time of G. mellonella larvae. Collectively, these data reinforce the concept of lasB being a veritable therapeutic target and phendione-based compounds (mainly Cu-phendione) being prospective anti-virulence drugs against P. aeruginosa.

Rotaxane and pseudo-rotaxane molecules from molecular wires. Theoretical description.

Some rotaxane molecules were designed, and their electronic capabilities were studied by means of DFT calculations. The original molecular wire consists of an iron complex that comprises aromatic substituents that constitute linear chains, and this system is complemented by the addition of fullerene C60 unities at both extremes of the chain, which act as the stoppers of the chain. Another modification was to add a link that gives way to the mechanical bond; this link is a square molecule of bis-pyrydyl-pyridinium tetraion. An interesting effect was observed as a result of these modifications; the conductivity of the systems rises with the first substitution and even more with the second in such a way that the original semiconductor material changes to give a conductor one.

Chitosan-iron oxide hybrid composite: mechanism of hexavalent chromium removal by central composite design and theoretical calculations.

In this study, the synthesis of iron oxide stabilized by chitosan was carried out for the application and optimization in the removal process of aqueous Cr(VI) by central composite design (CCD). The calculation of these effects allowed to know, quantitatively, the variables and the interaction between them that could affect the Cr(VI) removal process. It was also verified that the most favorable conditions for chromium removal were the following: pH 5.0, Cr(VI) concentration of 130 mg L-1, adsorbent mass of 5 mg, and Fe(II) content of 45% (w/w) in the CT-Fe beads. The adsorption kinetics performed under these conditions showed that the chitosan/iron hybrid composite is an adsorbent material with high chromium removal capacity (46.12 mg g-1). It was found that all variables were statistically significant. However, it was observed that the variable that most affected Cr(VI) removal was the pH of the solution, followed by the concentration of chromium ions in solution and the interaction between them. Therefore, the studied experimental conditions are efficient in chromium adsorption, besides the operational simplicity coming from statistical design. Theoretical calculations showed that the most stable chitosan was that with Fe(II) in the structure, that is, in the reaction mechanism, there is no competition of Fe(II) with Cr(III, VI) in the available sites of chitosan. Thus, the theoretical calculations show that the proposed Cr(VI) removal is effective.