Carboxymethylcellulose and cellulose xanthate matrices as potential adsorbent material for potentially toxic Cr3+, Cu2+ and Cd2+metal ions: a theoretical study

Theoretical study of the adsorption capacity of potentially toxic Cd2+, Pb2+, and Hg2+ ions in hemicellulose matrices

Hemicellulose is widely available in nature, is a sustainable resource and has a wide range of applications. Among them, adsorption stands out for the removal of potentially toxic ions. Thus, in the study, the adsorption of Cd2+, Pb2+ and Hg2+ ions in two hemicellulose matrices were elucidated through computational simulations using density functional theory. Molecular electrostatic potential and frontier molecular orbitals demonstrated whether the interactions could happen. Four interaction complexes were highlighted due to the interaction energy criteria, ΔEBind, ΔH and ΔG < 0.00 kcal mol-1, that is: Hm1… Pb (1); Hm2… Pb (3); Hm2…Cd (4) and Hm2…Hg (4) and the results show that they occur through physisorption. In structural parameter studies, interaction distances smaller than 3000 Å were identified, which ranged from 2.253 Å to 2.972 Å. From the analysis of the topological parameters of QTAIM, it was possible to characterize the intensities of the interactions, as well as their nature, which were partially covalent or electrostatic in nature. Finally, based on the theoretical results, it can be affirmed that the hemicellulose can interact with Cd2+, Pb2+ and Hg2+ ions, evidencing that this study can support further experimental essays to remove contaminants from effluents.

Theoretical and experimental study of the diastereoisomers (2S) and (2R)-naringenin-6-C-β-D-glucopyranoside obtained from Clitoria guianensis

In this work the diastereoisomers (2S) and (2R)-naringenin-6-C-β-D-glucopyroside, isolated for the first time from Clitoria guianensis, were studied using the density functional theory. The frontier molecular orbitals and structural properties showed that the diastereoisomers exhibit the same energy gap 166.61 kcal mol^-1 and structural properties different, where in the S diastereoisomer, the bond length between the chiral carbon and the phenolic group is greater (difference of 0.0126 Å). The HPLC data showed that the retention time of the S-diastereoisomer (16.7 min) is shorter than that of R, suggesting that the S compound is more polar than R. The HPLC results corroborates with the molecular electrostatic potential which showed that in the S configuration, the electronegative density was more intense overall, particularly in the glucose molecule. The reactivity indices showed that the diastereoisomers are good electrophiles and reactive species. Finally, the absolute configuration of the diastereoisomers were determined using electronic circular dichroism (ECD) spectroscopy and the theoretical spectra were similar to the experimental. METHODS : All calculations of Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) were performed using the program Gaussian 09 and the structures of the diastereoisomers were generated and analyzed using the GaussView program. The optimization and vibrational frequency calculations were performed using the functional CAM-B3LYP and 6-311 +  + G(2d,2p) basis set. Conformational searches were performed for R configuration, by molecular mechanics using the MM + , MMFF, and OPLS05 force fields; the entire molecular mechanics simulation was performed using the Maestro/MacroModel software. The calculations for the simulations of the ECD spectra were performed for the eight lowest energy conformers obtained in the geometric optimization step, and the TDDFT at the CAM-B3LYP/6-311 +  + G(2d,2p) theory level used. The effects of methanol and chloroform were calculated using the SMD implicit solvent model.

Computational study of the interaction of heavy metal ions, Cd(II), Hg(II), and Pb(II) on lignin matrices

Contamination by heavy metal ions, particularly in water resources, is a severe environmental problem. In this study, the interaction of metal ions, namely, Cadmium Cd(II), Mercury Hg(II), and Lead Pb(II), on lignin matrices was investigated based on theoretical calculations. Binding energy (ΔE_Bind) values proved that the Pb(II) interacted better with lignin matrices than Cd(II) or Hg(II), having energy values between -8.4 kcal mol^-1 to -20.2 kcal mol^-1. The Gibbs energy (ΔG) and enthalpy (ΔH) values for Pb(II) were <0, indicating that the process was spontaneous and released heat. However, the lignin matrices studied in this work did not interact efficiently with Cd(II) and Hg(II) ions because almost all ΔE_Bind, ΔG, and ΔH values were positive. The bond length of the interaction proved that the Pb ions yielded the smallest values, ratifying the values for the interaction energy. Analyses based on the quantum theory of atoms in molecules showed that the interactions between Pb(II) and the matrices were partially covalent, whereas the interactions of Cd(II) and Hg(II) were predominantly electrostatic, justifying the positive values of ΔE_Bind, ΔG, and ΔH. The natural bond orbital results showed that the ligand orbitals of the matrix interacted with the lone pair antibonding orbital (LP*) of the metal ions. The theoretical results of the study show the possibility of applying lignin to remove heavy metal ions, especially Pb, and providing information for research related to wastewater treatment.

Interaction of glyphosate in matrices of cellulose and diethylaminoethyl cellulose biopolymers: theoretical viewpoint of the adsorption process

Glyphosate is an herbicide widely used in agricultural activities causing contamination of soils and bodies of water and damage to the biodiversity of ecosystems. In this context, the present study aimed to theoretically study the adsorption potential of the biopolymer cellulose (CE) and its diethylaminoethyl cellulose derivative (DEAEC) with the herbicide glyphosate (GLY). Theoretical calculations were performed using the density functional theory. Molecular electrostatic potential and frontier molecular orbital analyses were performed, which allowed identifying the possible sites of interaction of biopolymers that were in the functional groups -OH and O- of cellulose and in the groups -O- and -NH+(CH2CH3)2 of the DEAEC. Reactivity indices chemical softness and hardness showed that both adsorbents could interact with adsorbate. Simulated IR indicated that the interactions could be evinced in experimental measurements by changes in the bands of glyphosate (ν(P = O), δ(P-O-H), δ(C-N-H)) or in the bands of CE and DEAEC (ν(C-O), ν(C-H), ν(N-H)). The binding energies showed that the GLY interacts more effectively with CE than DEAEC. The ΔH prove that all processes are exothermic and the CE-GLY1 interaction showed value of ΔG < 0. The topological results showed a greater number of interactions with electrostatic nature. The results found in the study show that the theoretical data provides useful information to support the use of biopolymers as matrices for glyphosate adsorption or other contaminants.

Physical and chemical aspects of the interaction of chitosan and cellulose acetate with ions Ca2+ and K+ using DFT methods

Motivated by the use of chitosan (Ch), and cellulose acetate (AC) as organic matrices in several therapeutic drugs, a theoretical study has been elaborated through the density functional theory method (DFT) to investigate the interaction mechanism between two essential ions for the human body Ca²⁺, K⁺ and two organic matrices chitosan (Ch), and cellulose acetate (AC). Many physical and chemical aspects have been carried out after the achievement of structural optimization. This involves structural parameters, molecular electrostatic potential (MEPs), interaction energy, reactivity indexes, frontier molecular orbitals (FMOs), quantum theory atoms in molecules (QTAIM) analysis, and non-covalent interaction (NCI) analysis. The results of FMOs, MEPs, and reactivity index studies have revealed that the site of interaction can be predicted. The calculation of electron interaction energies shows that those ions interact with the matrix of AC and Ch. Concretely, the Ca²⁺ ion interacted efficiently with the AC matrix. The structural analysis results show that the interaction of Ch and ions appear spontaneously (ΔG < 0) while the interaction of AC and ions (ΔG >0) requires more energy to occur. Finally, the QTAIM analysis data indicates that the interactions of AC-ions and Ch-ions are non-covalent presenting an electrostatic character.