2,4-Dichlorophenoxyacetic Acid in the Gas and Crystal Phases and Its Intercalation in Montmorillonite-An Experimental and Theoretical Study.

Many properties of 2,4-dichlorophenoxyacetic acid (2,4-D) depend on its molecular environment, such as whether it is an isolated molecule, a dimer, or in a crystalline state. The molecular geometry, conformational analysis, and vibrational spectrum of 2,4-D were theoretically calculated using Density Functional Theory (DFT) methods. A new slightly more stable conformer was found, which is different to those previously reported.

Intercalation of the anticancer drug lenalidomide into montmorillonite for bioavailability improvement: a computational study.

Context: Lenalidomide (LEN) is used for the treatment of myeloma blood cancer disease. It has become one of the most efficient drugs to halt this disease. LEN is a low-soluble drug in aqueous media.

Kinetic Study and Reaction Mechanism of the Gas-Phase Thermolysis Reaction of Methyl Derivatives of 1,2,4,5-Tetroxane.

Tetroxane derivatives are interesting drugs for antileishmaniasis and antimalaric treatments. The gas-phase thermal decomposition of 3,6,-dimethyl-1,2,4,5-tetroxane (DMT) and 3,3,6,6,-tetramethyl-1,2,4,5-tetroxane (acetone diperoxide (ACDP)) was studied at 493-543 K by direct gas chromatography by means of a flow reactor. The reaction is produced in the injector chamber at different temperatures.

Effect of Iron Isomorphic Substitution in Mg:Al and Zn:Al-Layered Double-Hydroxide Structures by Means of First Principle Calculations.

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 M:M 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).

Modeling of the adsorption of a protein-fragment on kaolinite with potential antiviral activity.

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.

Compressibility of 2M muscovite-phlogopite series minerals.

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 2M polytype and modeled by the substitution of three Mg cations in the Phl octahedral sites by two Al 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.

Conformational polymorphic changes in the crystal structure of the chiral antiparasitic drug praziquantel and interactions with calcium carbonate.

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.

Molecular modeling and infrared and Raman spectroscopy of the crystal structure of the chiral antiparasitic drug Praziquantel.

Anthelmintic praziquantel (PZQ) and its molecular and crystal lattice structures were studied by means of atomistic calculations based on empirical interatomic potentials and quantum mechanical methods (DFT). This chiral drug presents several crystal polymorphs due to the enantiomers (either R or S) or the racemic crystal, and different molecular conformations. The relative configurations of the carbonyl groups in PZQ define these conformations that produce different polymorphs.

A DFT study of the carboxymethyl-phosphatidylethanolamine formation from glyoxal and phosphatidylethanolamine surface. Comparison with the formation of N(ε)-(carboxymethyl)lysine from glyoxal and L-lysine.

Mechanisms of the generation of carboxymethyl compounds Nε-(carboxymethyl)lysine (CML) and carboxymethyl-phosphatidylethanolamine (CM-PE) from the reactions between glyoxal and L-lysine, and glyoxal and phosphatidylethanolamine (PE) were studied using the DFT method at the PBE/DNP level of theory. In order to study the reaction with PE, a periodic model of the PE surface was built. The starting surface model includes two molecules of PE, a molecule of monohydrated form of glyoxal, and five water molecules as explicit solvent that form a hydrogen bond network, which are involved in the reactions by stabilizing reaction intermediates and transition states and as proton-transfer carriers, important in all steps of reactions.

Theoretical study on the influence of the Mg2+ and Al3+ octahedral cations on the vibrational spectra of the hydroxy groups of dioctahedral 2:1 phyllosilicate models.

The effect on the vibrational spectrum of the hydroxy groups in dioctahedral 2:1 phyllosilicates of the isomorphous cation substitution of Mg(2+) by Al(3+) in the octahedral sheet was investigated at the DFT level. Ortho, meta and para Mg(2+) configurational polymorphs were defined. The theoretical vibration frequencies of OH groups depend significantly on the nature of the cations they are joined with.

Theoretical study of the hydrogen bonding and infrared spectroscopy in the cis-vacant polymorph of dioctahedral 2:1 phyllosilicates.

The spatial geometry and local environment of hydroxyl groups of the cis-vacant (cv) crystal polymorph of dioctahedral 2:1 phyllosilicates are studied by computational methods, doing especial emphasis on the hydrogen bonds and electrostatic interactions of the hydroxyl groups with the neighbor atoms. Different types of phyllosilicates are explored: with only tetrahedral charge, with only octahedral charge, with simultaneous octahedral and tetrahedral substitution, and with different interlayer cation (IC). The effect of these interactions on the spectroscopic properties of these hydroxyl groups is also studied.

A Tuned LRC-DFT Design of Ambipolar Diketopyrrolopyrrole-Containing Quinoidal Molecules Interesting for Molecular Electronics.

This work presents a Density Functional Theory (DFT) study on the charge transport related properties of two quinoidal diketopyrrolopyrrole (DPP) based systems. System A, recently synthesized, shows high efficiency as n-type organic semiconductor material while system B, not synthesized yet, has a linking benzothiadiazole (BT) unit between DPP moieties and would display an ambipolar character. The use of tuned, long-range corrected (LRC) functionals allows one to predict HOMO, LUMO, and charge transport properties for compound A in concordance with those experimentally observed.

Influence of the alkyl and alkoxy side chains on the electronic structure and charge-transport properties of polythiophene derivatives.

Density Functional Theory has been used to study the structural, electronic and charge-transport properties of two regio-regular head-to-tail polythiophene derivatives, i.e. poly(3-hexyl-thiophene), P3HT, and poly(3-oxyhexyl-thiophene), P3OHT.

Exploring the rehydroxylation reaction of pyrophyllite by ab initio molecular dynamics.

We have investigated the process of rehydroxylation of pyrophyllite as a limiting factor to the dehydroxylation upon thermal treatment. Car-Parrinello molecular dynamics simulations based on density functional theory have been used along with the metadynamics algorithm. Two possible rehydroxylation mechanisms reaction have been characterized, related to two possible intermediate structures along the rehydroxylation paths, and both involve the interaction of the apical oxygen atoms.

DFT research on the dehydroxylation reaction of pyrophyllite 2. Characterization of reactants, intermediates, and transition states along the reaction path.

We delineate the dehydroxylation reaction of pyrophyllite in detail by localizing the complete reaction path on the free energy surface obtained previously by Car-Parrinello molecular dynamics and the implemented metadynamics algorithm ( Molina-Montes et al. J. Phys.

Adsorption Mechanism and Structure of the Montmorillonite Complexes with (CH(3))(2)XO (X=C, and S), (CH(3)O)(3)PO, and CH(3)-CN Molecules.

The formation of complexes with different ligands in the interlayer space of montmorillonite saturated in Na(+), Mg(2+), Ca(2+), Co(2+), Cu(2+), Ni(2+), Fe(3+), and Cr(3+) was studied. Acetone, acetonitrile, dimethyl sulfoxide, and trimethylphosphate were used as ligands. The nature of the complexes was studied by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, microcalorimetry, and ab initio quantum mechanical methods.

Adsorption of Water Vapor by Homoionic Montmorillonites. Heats of Adsorption and Desorption.

Adsorption isotherms for water vapor, basal spacing, and immersion heats and water desorption heats of Li+, Na+, Mg2+, Ca2+, Cu2+, and Fe3+ montmorillonite are measured at various relative humidities (r.h.).