Microsolvation of aminoethanol: a study using DFT combined with QTAIM

Reactivity of Monoethanolamine at the Air-Water Interface and Implications for CO2 Capture

The development of CO2-capture technologies is key to mitigating climate change due to anthropogenic greenhouse gas emissions. These cover a number of technologies designed to reduce the level of CO2 emitted into the atmosphere or to eliminate CO2 from ambient air. In this context, amine-based sorbents in aqueous solutions are broadly used in most advanced separation techniques currently implemented in industrial applications. It has been reported that the gas/liquid interface plays an important role in the early stages of the capture process, but how the interface influences the chemistry is still a matter of debate. With the help of first-principles molecular dynamics simulations, we show that monoethanolamine (MEA), a prototypical sorbent molecule, has a weak affinity for the air-water interface, where in addition it exhibits a lower nucleophilicity compared to bulk solution. The change in reactivity is due to the combination of structural and electronic factors, namely, the shift of the conformational equilibrium and the stabilization of the N-atom lone pair. Based on these results, strategies for improving the efficiency of alkanolamine sorbents are proposed.

What is behind a gas stream scrubbing liquid? Monoethanolamine/water mixtures as seen by dielectric relaxation spectroscopy

High-quality dielectric data for monoethanolamine (MEA)/water mixtures covering the entire miscibility range are presented. For MEA concentrations c1 ≥ 1 M the obtained complex permittivity spectra, covering the frequency range from 0.05 to 89 GHz, are best described by a sum of four Debye relaxations. Modes at ∼3 GHz and ∼10 GHz are solute-specific. Whilst the first can be assigned to MEA aggregates, the second is a composite arising from "free" MEA dipoles with dynamically retarded water hydrating them. The relaxations at ∼18 GHz and ∼200 GHz essentially reflect the cooperative H-bond fluctuations of more-or-less unperturbed "bulk" water, albeit with minor solute contributions. Evaluation of the bulk-water amplitude reveals that in water-rich mixtures (c1 ≤ 3.5 M) Zt = 3.5 ± 0.2 H2O molecules hydrate a MEA molecule. Then Zt drops linearly, reaching zero for neat MEA. Supported by the literature, this concentration dependence suggests that only H2O molecules H-bonded to the NH2 and OH groups of MEA contribute to Zt. At concentrations beyond hydration shell overlap (c1 ≥ 3.5 M) these H-bonds are gradually eliminated, while new interactions with neighboring MEA molecules are formed. From the evaluation of the MEA-specific amplitudes we conclude that for c1 ≥ 2 M, including neat MEA, ∼35% of the solute molecules are in aggregates, where breaking the intermolecular NH⋯O hydrogen bond determines the dynamics.

New equation for calculating total interaction energy in one noncyclic ABC triad and new insights into cooperativity of noncovalent bonds

In this work, a new equation consist of A⋅⋅⋅B, B⋅⋅⋅C, A⋅⋅⋅BC, and AB⋅⋅⋅C interactions is proposed for calculating the total interaction energy of noncyclic ABC triads. New equations are also proposed for calculating the changes in values of A⋅⋅⋅B and B⋅⋅⋅C interactions on the formation of triad from the corresponding dyads. The advantages of equations proposed here in comparison with many-body interaction energy approach are discussed. All proposed equations were tested in F₃ MLi⋅⋅⋅NCH⋅⋅⋅HLH and F₃ MLi⋅⋅⋅HLH⋅⋅⋅HCN (M = C, Si; L = Be, Mg) as well as H₃ N⋅⋅⋅XY⋅⋅⋅HF (X, Y = F, Cl, Br) noncyclic A⋅⋅⋅B⋅⋅⋅C triads. The data show that the total cooperativity of triad correlates well with the sum of the changes in values of A⋅⋅⋅B and B⋅⋅⋅C interactions calculated through new equations proposed here. © 2016 Wiley Periodicals, Inc.

Composition-dependent association behavior in the mixture of isopropanol and trichloromethane: a volumetric, vibration spectroscopic and quantum chemical study

Herein the intermolecular associative behaviors in the binary mixture of isopropanol and trichloromethane have been studied via a combined excess volumetric, vibration spectroscopic and quantum chemical approach.

Interactions of Alkanolamines with Water: Excess Enthalpies and Hydrogen Bonding

We report a transferable force field to describe the interactions of alkanolamines based on the N-C-C-O backbone with water, derived from a comparison with experimental excess enthalpies. This force field is tested on 2-aminoethan-1-ol (MEA), 2-amino-2-methylpropan-1-ol, 2-aminobutan-1-ol (ABU), and 1-aminopropan-2-ol. These alkanolamines are derivatives of MEA obtained by substitution with methyl and ethyl groups on the carbon atoms of the N-C-C-O backbone. A specific cross interaction site corresponding to the hydrogen bond between the hydroxyl group of the alkanolamine and the oxygen atom of water was introduced in order to reproduce quantitatively experimental excess enthalpies. The transferability of this specific site was assessed by predictions on alkanolamines that were not included in the parametrization data set. New data on enthalpy of mixing for ABU with water are reported, since they were not available in the literature. From the molecular simulations, several microscopic quantities of the alkanolamine-water mixtures were analyzed in order to improve our understanding of these systems. The structure of the solvation shells at varying compositions, statistics of hydrogen bonds, conformations, and energy decompositions served as bases for an interpretation of the molecular reasons underlying the behavior of the excess enthalpy. The prominent result is that water-water interactions play a major role in differentiating alkanolamine-water mixtures, which is a manifestation of the hydrophobic effect. Both the structural and energetic effects observed at the molecular level point to phenomena that have strong composition dependence, in particular, the interplay between the intramolecular hydrogen bond in the alkanolamine and the intermolecular hydrogen bonds with water.

Existence of dynamic tautomerism and divalent N(I) character in N-(pyridin-2-yl)thiazol-2-amine

N-(pyridin-2-yl)thiazol-2-amine is a versatile chemical functional unit present in many therapeutically important species. Quantum chemical analysis shows that there are six competitive isomeric structures possible for this class of compounds within a relative energy difference of ∼4 kcal/mol. Some of the isomeric structures possess divalent N(I) character. There appears to be a competition between the thiazole and pyridine groups to accommodate the tautomeric hydrogen, and consequently show electron donating property in the structure with R-N←L representation. Details of electron distribution, tautomeric preferences, protonation energy, and divalent N(I) character, and so on, of this class of compounds are presented in this article. Subsequently, upon protonation, (L→N←L)(⊕) character is clearly evident in these moieties as molecular orbital analysis clearly shows two lone pairs of electrons on the central nitrogen, in this system.