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The intensive use of antibiotics and especially sulfonamides in the livestock industry is getting an alarming level. The presence of these drugs in wastewaters, rivers and underground waters is increasing considerably in developing countries. At the same time, montmorillonite is a natural, low-cost, non-toxic, biocompatible clay with a high adsorption capacity. It is potentially useful as a nanocarrier to design sulfonamides dosage forms. In this work, the interaction between the drug and the clay mineral has been studied from an experimental and computational atomistic point of view to improve the drug¿s biopharmaceutical profile. The results showed the potential enhancement of the drug solubility due to the correct adsorption of sulfonamides in the clay interlayer space. The molecular interactions of these drugs with the surfaces of clay minerals can be interesting for evaluating their mobility in soils and for preparing composite complexes for optimal use. In this work, the intercalation of sulfonamides, such as sulfathiazole, sulfamethazine, sulfamethoxazole, sulfachloropyridazine and sulfacetamide, into the interlayer space of montmorillonite (MNT) is studied at molecular level by using computational modeling, molecular dynamics and DFT calculations. Most of these intercalations are energetically favourable, where the role of water molecules is critical. In general, the bioavailability of these compounds by intercalation in MNT is bigger than from the crystalline powder. The spectroscopic properties of these systems showed interesting frequency shifts in the bands of the IR spectrum produced during the intercalation in the confined space of MNT. These results predict that the IR spectroscopy as an interesting analytical technique for monitoring the intercalation of drugs in clay minerals.

The intensive use of antibiotics and especially sulfonamides in the livestock industry is getting an alarming level. The presence of these drugs in wastewaters, rivers and underground waters is increasing considerably in developing countries. The molecular interactions of these drugs with the surfaces of clay minerals can be interesting for evaluating their mobility in soils and for preparing composite complexes for optimal use. In this work, the intercalation of antibiotics derivatives of sulfonamides, such as sulfamethazine, sulfamethoxazole, sulfachloropyridazine and sulfacetamide, into the interlayer space of montmorillonite (MNT) is studied at molecular and 3-D periodical crystal structure level by using computational modeling, molecular dynamics and calculations based Density Functional Theory (DFT). Most of these intercalations are energetically favourable, where the role of water molecules is critical. In general, the bioavailability of these compounds by intercalation in MNT is bigger than from the crystalline powder. Spectroscopic properties of these systems showed interesting frequency shifts in the bands of the IR spectrum produced during the intercalation in the confined space of MNT. These results predict that the IR spectroscopy as an interesting analytical technique for monitoring the intercalation of drugs in clay minerals.

The behaviors of aragonite (CaCO), strontianite (SrCO), cerussite (PbCO), and witherite (BaCO) at increasing pressure have been studied up to 6 GPa using density functional theory with plane waves. A parallelism of the orthorhombic carbonates with the closed-packed AsNi structure is considered in our analysis, being the CO32- groups not centered in the interstice of the octahedron. The decomposition of the unit-cell volume into atomic contributions using the Quantum Theory of Atoms in Molecules has allowed the analysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distances, and atomic compressibilities are calculated. The largest compression is on the c crystallographic axis, and the c linear modulus has a linear function with the mineral bulk modulus (K). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) only gives linear functions when K is related either with the CC distances modulus or the modulus of the distances of the C to the faces of the octahedron perpendicular to c. These last distances are the projections of the Metal–Oxygen (MO) distances to the center of the octahedron. K carbonates also show linear functions with the atomic moduli of their cations. However, the whole series show a linear relation with the atomic modulus of C atoms. Therefore, the whole series highlight the importance of the C atoms and their interactions in the mechanism of compression of the orthorhombic carbonate series.

Melatonin is a hormone used for treating several disorders. However, its oral administration is problematic due to the variable absorption and extensive first-pass metabolism. The topical application of this drug does not present these disadvantages and can be used for therapeutic and skin protection purposes. The adsorption and release of melatonin in the montmorillonite clay were investigated experimentally and theoretically. The drug-clay interaction products were prepared and characterized, showing a modified and improved release of melatonin. The crystal structure and spectroscopic properties of the crystal of melatonin and melatonin-water-mineral materials were studied by molecular modeling, finding that the adsorption of this drug is energetically favourable, and the results were consistent with the experimental data. Ab initio molecular dynamics simulations with the metadynamics methodology showed the release of melatonin from the confined interlayer nanospace of montmorillonite to the liquid bulk water with a 20 kcal/mol free energy barrier.

Layered double hydroxides (LDHs) are important components in terrestrial and extra-terrestrial environments. The presence of iron in these minerals provides them a wide potential application in environmental and materials sciences. In this work, the role of Fe in the crystallographic properties of LDHs M2+:M3+ 2:1 with Mg:(Fe,Al), Mg:Fe, Zn:(Fe,Al), and Zn:Fe is investigated by means of quantum mechanical calculations based on the density functional theory (DFT). Several relative proportions of Fe are studied. The cation ordering of these LDHs has been explored, finding useful insights for experimental synthetic paths of these minerals. The a and b cell parameters increase with the iron concentration. Some diffraction lines at high angle decrease in angle and increase in intensity with the increasing iron concentration. All of them agree with the experimental results. The iron substitutions tend to aggregate.

Layered double hydroxides (LDH) are interesting materials due to their high absorption and catalytic properties. Their applications in environment, agriculture and pharmaceutical fields are becoming widely important. The interlayer and intralayer cation ordering on layered double hydroxides of Mg:Al 2:1 and Zn:Al 2:1 are studied by means of different ordering models at Density Functional Theory level. The cation ordering in LDH is interesting for monitoring the synthesis of these solids and for the applications of LDH, however it is difficult to determine experimentally. We have explored several ordering arrangements of the cation distribution in Mg:Al 2:1 and Zn:Al 2:1 LDH and the effect of these cation arrangements on some crystallographic and spectroscopic properties.

This work aimed at studying the potentiality of interactions between kaolinite surfaces and a protein-fragment (350–370 amino acid units) extracted from the glycoprotein E1 in the transmembrane domain (TMD) of hepatitis C virus capsid. A computational work was performed for locating the potential electrostatic interaction sites between kaolinite aluminol and siloxane surfaces and the residues of this protein-fragment ligand, monitoring the possible conformational changes. This hydrated neutralized kaolinite/protein-fragment system was simulated by means of molecular modeling based on atomistic force fields based on empirical interatomic potentials and molecular dynamic (MD) simulations. The MD calculations indicated that the studied protein-fragment interacted with the kaolinite surfaces with an exothermic process and structural distortions were observed, particularly with the hydrophilic aluminol surface by favorable adsorption energy. The viral units isolation or trapping by the adsorption on the kaolinite nanoparticles producing structural distortion of the peptide ligands could lead to the blockage of the entry on the receptor and hence a lack of viral activity would be produced. Therefore, these findings with the proposed insights could be an useful information for the next experimental and development studies in the area of discovering inhibitors of the global challenged hepatitis and other pathogenic viruses based on the phyllosilicate surface activity. These MD studies can be extended to other viruses like the COVID-19 interacting with silicate minerals surfaces.

Perchlorates have been found widespread on the surface of Mars, their origin and degradation pathways are not understood to date yet. We investigate here, from a theoretical point of view, the potential redox processes that take place in the interaction of Martian minerals such as olivine, with anhydrous and hydrated perchlorates. For this theoretical study, we take as mineral substrate the (1 0 0) surface of forsterite and calcium perchlorate salt as adsorbate. Our DFT calculations suggests a reduction pathway to chlorate and chlorite. When the perchlorate has more than 4 water molecules, this mechanism, which does not require high-temperature or high energy sources, results in parallel with the oxidation of the mineral surface, forming magnesium peroxide, MgO, and in the formation of ClO, which through photolysis is known to form ClO-O. Because of the high UV irradiance that reaches the surface of Mars, this may be a source of O on Mars. Our results suggest that this process may be a natural removal pathway for perchlorates from the Martian regolith, which in the presence of atmospheric water for salt hydration, can furthermore lead to the production of oxygen. This mechanism may thus have implications on the present and future habitability of the Martian surface.

Organic peroxides are interesting compounds with a broad range of properties from antimalarial and antimicrobial activities to explosive character. In this work the gas-phase thermolysis reaction mechanism of the 3,6-dimethyl-1,2,4,5-tetroxane (DMT) is studied by DFT calculations, considering axial–axial, axial–equatorial, and equatorial–equatorial position isomers. The critical points of the singlet (S) and triplet (T) potential energy surfaces (PES) are calculated. Three mechanisms are considered: i) S-concerted, ii) S-stepwise, and iii) T-stepwise. The first intermediate of the reaction through S-stepwise-PES is a diradical open structure, o, yielding, as products, two molecules of acetaldehyde and one of O in the S state. The S-stepwise-mechanism gives exothermic reaction energies (Er) in the three position isomers. The S-concerted mechanism yields very high activation energies (Ea) in comparison with those of the S-stepwise mechanism. In the T-stepwise mechanism, a triplet open structure (T-o) is first considered, yielding an Er 12 kcal mol more exothermic than that of the S-mechanisms. The S-o and T-o are similar in structure and energies; therefore, a crossing from the S- to T-PES is produced at the o intermediate as a consequence of a spin–orbit coupling. The highest Ea is the first step after o intermediate, and thus it is considered the rate limiting step. Therefore, the Er at the T-PES is more in agreement with the Er of the exothermic experimental diperoxide products. Ea, Er, and O···O distances are studied as a function of the number of methyl groups and the position isomerization.

Muscovite (Ms) and phlogopite (Phl) belong to the 2:1 dioctahedral and trioctahedral layer silicates, respectively, and are the end members of Ms-Phl series minerals. This series was studied in the 2M1 polytype and modeled by the substitution of three Mg2+ cations in the Phl octahedral sites by two Al3+ and one vacancy, increasing the substitution up to reach the Ms. The series was computationally examined at DFT level as a function of pressure to 9 GPa. Cell parameters as a function of pressure and composition, and bulk moduli as a function of the composition agrees with the existing experimental results. The mixing Gibbs free energy was calculated as a function of composition. From these data, approximated solvi were calculated at increasing pressure. A gap of solubility is found, decreasing the gap of solubility at high pressure.

NiTi alloy has important properties such as shape-memory, super-plasticity, resistance, and biocompatibility, therefore is frequently used in biomedical devices. We studied the oxidized form of this alloy and possible Ni segregation in three possible models for the TiO/NiTi interface: i) the perfect interface; ii) the Ni enriched interface and iii) with oxygen vacancies in the TiO coating. We used DFT + U calculations for TiO, because Hubbard correction encourages localization of the excess electronic charge and improves the DFT results. A standard spin polarized DFT was used for NiTi. We obtained the optimized geometries for each model and computed segregation energy, electronic structure, magnetic moment and bond order for the interface and for Ni segregation. Our calculations indicated that Ti species are present at the interface, while in the bulk of the oxide layer the species is the Ti. Also, the electronic structure show that the metallic character of the alloy is unaffected by the interaction with oxygen. These results are consistent with experimental data from literature. Ni enriched interface containing O vacancies show a strong geometric distortion in the TiO layers. In all cases, Ni segregation is an a thermodynamically unfavorable process, helping to understand the biocompatibility of NiTi alloy.

Titanium dioxide (TiO) is one of the most studied oxides in photocatalysis, due to its electronic structure and its wide variety of applications, such as gas sensors and biomaterials, and especially in methane-reforming catalysis. Titanium dioxide and olivine have been detected both on Mars and our Moon. It has been postulated that on Mars photocatalytic processes may be relevant for atmospheric methane fluctuation, radicals and perchlorate productions etc. However, to date no investigation has been devoted to modelling the properties of TiO adsorbed on olivine surface. The goal of this study is to investigate at atomic level with electronic structure calculations based on the Density Functional Theory (DFT), the atomic interactions that take place during the adsorption processes for formation of a TiO regolith. These models are formed with different titanium oxide films adsorbed on olivine (forsterite) surface, one of the most common minerals in Universe, Earth, Mars, cometary and interstellar dust. We propose three regolith models to simulate the principal phases of titanium oxide (TiO, TiO and TiO). The models show different adsorption processes i.e. physisorption and chemisorption. Our results suggest that the TiO is the most reactive phase and produces a strong exothermic effect. Besides, we have detailed, from a theoretical point of view, the effect that has the adsorption process in the electronic properties such as electronic density of states (DOS) and oxide reduction process (redox). This theoretical study can be important to understand the formation of new materials that can be used as support in the catalytic processes that occur in the Earth, Mars and Moon. Also, it may be important to interpret the present day photochemistry and interaction of regolith and airborne aerosols in the atmosphere on Mars or to define possible catalytic reactions of the volatiles captured on the Moon regolith.

The application of clay minerals in therapeutics is becoming important due to their structural and surface physicochemical properties. 5-aminosalicylic acid (5-ASA) is a very common pharmaceutical drug and is used worldwide. The interactions between the 5-ASA molecule and both the aluminol and siloxane surfaces of kaolinite are studied by means of atomistic calculations using force fields based on empirical interatomic potentials and quantum mechanics calculations based on density functional theory. A conformational analysis of 5-ASA has been performed and the anion of 5-ASA was also studied. The calculated adsorption energy values indicate that 5-ASA is likely to be adsorbed on the kaolinite surfaces with greater affinity to the aluminol surface. Hence, kaolinite may be considered as a promising pharmaceutical carrier of 5-ASA.

Praziquantel is an antiparasitic drug used for decades. Currently, the praziquantel commercial preparation is a racemic mixture, in which only the levo-enantiomer possesses anthelmintic activity. The knowledge of its properties in the solid state and other chemical-physical properties is necessary for improving its efficacy and applications. Drug solid dispersions were prepared with calcium carbonate at 1:5 drug to excipient weight ratio by solvent evaporation method. Then, the modification of the crystal structure of the racemic polymorph of praziquantel in presence of calcium carbonate has been studied by means of several analytical techniques (DSC, TGA, XRD, SEM, FTIR, Raman spectroscopy and chiral liquid chromatography). This study has been completed with atomistic calculations based on empirical interatomic force fields and quantum mechanics methods applied to the crystal structure of praziquantel and of intermolecular interactions. The results evidenced that calcium carbonate provoked a conformational change in the praziquantel molecule yielding the formation of different polymorphs of praziquantel crystal. These alterations were not observed replacing calcium carbonate with colloidal silica as excipient in the solid dispersion.