Efficient removal of glyphosate from aqueous solutions by adsorption on Mg-Al-layered double oxides: thermodynamic, kinetic, and mechanistic investigation.

Up to 90% of glyphosate was removed in 40 min by a 2:1 MgAl-layered double oxide (LDO) at pH 10, and the adsorption kinetics fitted a pseudo-second-order law. The adsorption isotherms were type L, and the Langmuir model best fitted the experimental data, with q of 158.22 μg/mg at 25 °C.

Study of the stepwise deprotonation reactions of glyphosate and the corresponding pKa values in aqueous solution.

Glyphosate (N-(phosphonomethyl)glycine) (Gph) is a herbicide that is broadly used in several countries. Its application to eliminate weeds may have the undesired effect of diminishing the metallic cations found in the soil (e.g.

Specific rotation of monosaccharides: a global property bringing local information.

Carbohydrates generally occur in several conformations that may differ among themselves by energy values that are smaller than the accuracy of the most sophisticated theoretical methods used to determine them. In addition, the preferential orientations of the hydroxyl groups of these molecules cannot be identified by any experimental technique. Therefore, a method that is able to validate the absolute conformations (i.

Polarimetry as a tool for the study of solutions of chiral solutes.

Optical rotation of aqueous solutions of D-levoglucosan was studied experimentally in the 0.03-4.0 mol L(-1) concentration range and a nonlinear concentration dependence of specific optical rotation (SR) was revealed.

The anomeric effect: the dominance of exchange effects in closed-shell systems.

The origin of the anomeric effect has remained an open question. After Mo demonstrated that hyperconjugation is not responsible for the anomeric effect [Y. Mo, Nature Chem.

Specific rotation as a property to validate monosaccharide conformations.

Specific rotation ([α](D)) values were calculated for the 15 conformations of xylopyranose that are the most stable in the gas phase and in aqueous solution. The effects of different theoretical descriptions and the medium on the geometry of the conformers and the [α](D) values are evaluated. Differences in [α](D) values found for the same conformer in all descriptions used were smaller than those found between any two different conformers in the same description.

Conformational study of methylphosphocholine: a prototype for phospholipid headgroups in membranes.

Phospholipid bilayers constitute the largest structural component of cell membranes, in which choline phospholipids are abundant. In this study, through a theoretical sampling on a methylphosphocholine (MePC) potential energy surface, a set of conformers was selected as a prototype for the membrane phospholipid head. We performed a detailed conformational study of such a prototype, both as an isolated moiety and in a solvated system.

The (alpha-1,6) glycosidic bond of isomaltose: a tricky system for theoretical conformational studies.

Stable conformations of beta-isomaltose (alpha-D-glucopyranosyl-(1-->6)-beta-D-glucose) in gas-phase and aqueous solution are investigated in this study using quantum mechanical calculations. Conformational maps are calculated at HF/6-31G(d,p) level and lower energy structures are sampled in the most stable regions. Entropic and thermal corrections are considered and the Boltzmann population is obtained for conformers that are representative of the 18 most stable regions found on the potential energy surface.

A quantum mechanical strategy to investigate the structure of liquids: the cases of acetonitrile, formamide, and their mixture.

A computational strategy based on quantum mechanical (QM) calculations and continuum solvation models is used to investigate the structure of liquids (either neat liquids or mixtures). The strategy is based on the comparison of calculated and experimental spectroscopic properties (IR-Raman vibrational frequencies and Raman intensities). In particular, neat formamide, neat acetonitrile, and their equimolar mixture are studied comparing isolated and solvated clusters of different nature and size.

The Optical Rotation of Glucose Prototypes: A Local or a Global Property?

In this work, we present a quantum-mechanical study of the optical rotation (OR) of model systems representing glucose prototypes with one and two chiral centers. The ONIOM method is used to evaluate the property and to analyze its local or global character. Different ONIOM partitions are tested and compared to better appreciate differences and similarities between mono- and bichiral prototypes.

A theoretical study of glucose mutarotation in aqueous solution.

In this work the mechanism of glucose mutarotation is investigated in aqueous solution considering the most likely pathways proposed from experimental work. Two mechanisms are studied. The first involves an intramolecular proton transfer as proposed by textbooks of organic chemistry, and the second uses one solvent water molecule to assist proton transfer.

Parametrizing PCM to obtain solvation free energies from group contributions.

A parametrization methodology for evaluating the solvation free energy, using the polarizable continuum model implemented in Gamess software, is presented in a formulation which makes use of a group contribution conception to construct the cavities. The systems studied include alkanes, alcohols, aldehydes and ketones embeded in a continuous medium simulating the water as the solvent. For each family, the CH2, OH, and C=O moieties of atoms are put together in single spheres forming a group.

On the generalized valence bond description of the anomeric and exo-anomeric effects: an ab initio conformational study of 2-methoxytetrahydropyran.

An ab initio conformational study of the alpha- and beta-glycosidic C1-O1 bonds has been carried out on the axial and equatorial forms of 2-methoxytetrahydropyran (2-MTHP) at the HF/6-31G(d,p) and GVB-PP/6-31G(d,p) levels of calculation. Six conformers of 2-MTHP were fully optimized at both levels. The calculations have shown that the conformer containing the (+sc) orientation around the axial C1-O1 bond is the most stable one and is favored over that bearing the (-sc) arrangement about the equatorial C1-O1 bond by 1.

Density functional study of the optical rotation of glucose in aqueous solution.

Optical rotation values were calculated for the eight most abundant structures of glucose in aqueous solution, following the TD-DFT/GIAO approach for the property and the PCM description for the solvent. The results show that all alpha structures give a large positive contribution to the OR property, while the beta structures give both positive and negative contributions. The good agreement of the calculated OR, obtained as a Boltzmann average of the property of the eight conformers, with experimental data proves the validity of the quantum-mechanical approach and of the solvent modelization.

Ab initio conformational maps for disaccharides in gas phase and aqueous solution.

Ab initio conformational maps for beta-lactose in both the gas phase and in aqueous solution have been constructed at the HF/6-31G(d,p) level of calculation. The results of the gas-phase ab initio calculations allow us to conclude that a rigid conformational map is able to predict the regions of the minima in the potential energy surface of beta-lactose, in full agreement with those found in the relaxed conformational map. The solvation effects do not give rise to any new local minimum in the potential energy surface of beta-lactose, but just change the relative Boltzmann populations of the conformers found in the gas-phase calculations.