A theoretical investigation of water–solute interactions: from facial parallel to guest–host structures

Abstract

Encapsulation of small (bio-)organic molecules within water cages is governed by a subtle equilibrium between water-water and water-solute interactions. The competition between the formation of exohedral and endohedral complexes is investigated. The first step prior to a theoretical characterization of interactions involved in such complexes lies in the judicious choice of a level of theory. The β-propiolactone (BPL), a solute for which the micro-hydration was recently characterized by means of high resolution microwave spectroscopy (Angew. Chem. 2015, 127, 993), was selected for the present study, and a calibration step is carried out. It is shown that the dispersion-corrected density functional theory (DFT-D) suitably reproduce the geometric, energetic and spectroscopic features of the BPL:(H 2 O) 1-5 complexes. The experimentally-deduced structures of the BPL:(H 2 O) 4,5 species are fully understood in terms of the maximization of interactions between complementary sites in the MESPs. DFT-D calculations followed by the topological analysis within the Quantum Theory of Atoms in Molecules framework have shown that the solute could efficiently interact with (H 2 O) 6,10 clusters in a similar manner that the (H 2 O) 4,5 clusters do. The interaction of the solute with two larger water clusters is further investigated. The exohedral and endohedral BPL:(H 2 O) 20 isomers are close in energy with each other, whereas the formation of an inclusion complex is energetically more favored than the facial interaction in the case of the BPL:(H 2 O) 24 cluster. The topological analysis suggests that the substantial energetic stability is due to interactions between the solute and almost all oxygen atoms of the water cage.

What is the hydrophobic interaction contribution to the stabilization of micro-hydrated complexes of trimethylamine oxide (TMAO)? A joint DFT-D, QTAIM, and MESP study

“…41 The most stable isomer for the TMAO:(H 2 O) 3 isomer was already identified in the literature: it is composed of three water molecules solely interacting with the TMAO. Such a structure significantly differ to "water segregation" [30][31][32][33][34][35][36][37] The most stable isomer for the TMAO:(H 2 O) 5 complex can be considered as the beginning of encapsulation (Figure 8): if we assimilate, as a first approximation, the TMAO molecule to a sphere centered on the nitrogen atom, about a fourth of this sphere is covered by an incomplete water layer. It is interesting to further notice that the beginnings of this encapsulation follow a spheroid arrangement of water molecules, with a diameter close to 9 Å in the equatorial axis ( Figure 8).…”

“…However, it is interesting to note that TMAO does not lead to segregation of water molecules, unlike other solutes. [30][31][32][33][34][35][36][37] The fact that the most stable TMAO:(H 2 O) 2 and TMAO:(H 2 O) 3 isomers consist of isolated water molecules interacting with the solute rather than slightly perturbed water dimer and water trimer can easily be understood by considering the interaction energies between the TMAO and a single water molecule on the one hand, and between water molecules in the water dimer and water trimer on the other hand. Indeed, the interaction energy between a single water molecule and TMAO is equal to -61.4 kJ.mol -1 (Table 2) Nona2: D0 = -67.9 kJ.mol…”

The molecular electrostatic potential analysis of solutes and water clusters: a straightforward tool to predict the geometry of the most stable micro-hydrated complexes of β-propiolactone and formamide

“…The reliability of the LC-ωPBE/6-311++G(d,p) level of theory with the GD3BJ empirical dispersion correction to correctly describe water-solute interactions was previously pointed out. 73 stable one (denoted Q1') to the less stable one (denoted Q10'). For all the isomers, the energy relative to the global minimum (denoted Δ(E) DFT ) was calculated.…”

Microhydration of a Carbonyl Group: How does the Molecular Electrostatic Potential (MESP) Impact the Formation of (H2O)n:(R2C═O)Complexes?

“…51−53 The convergence options scf = Tight and Int = UltraFine were also used. 11 After full geometry optimization, frequency calculations were carried out to ensure that the obtained geometries indeed correspond to a minimum on the potential energy surface. The "wfn" files needed for topological characterization were generated during this step.…”

“…10 Alternatively, the choice of a larger value of electron isodensity, corresponding to an isosurface closer to the nucleus, allows better understanding of the formation of some noncovalent interactions. 11 Based on the Hellman-Feynman theorem, the MESP can be used as a rule of thumb to look for noncovalent interactions, beyond the so-called "electrostatic interactions": an electrophilic site is characterized by a local maximum on the MESP and a nucleophilic site is characterized by a local minimum on the MESP.…”