Assessment of hydrophobic interactions and their contributions through the analysis of the methane dimer

Abstract

Hydrophobic Interactions (HIs) are important in many phenomena of molecular recognition in chemistry and biology. Still, the relevance of HIs is sometimes difficult to evaluate particularly in large systems and intramolecular interactions. We put forward a method to estimate the magnitude and the different contributions of a given HI of the C···C, H-C···H, and H···H type through (i) the analysis of the electron density in the intermolecular region for eleven relative orientations of the methane dimer and (ii) the subsequent decomposition of the corresponding interaction energy in physically significant contributions using Symmetry Adapted Perturbation Theory (SAPT). Strong correlations were found between the topological properties of ρ(r) calculated at intermolecular bond critical points and Eint(SAPT) plus its different contributions with the C···C distance of the considered orientations of (CH4 )2 . These correlations were used to construct Mollier-like diagrams of Eint(SAPT) and its components as a function of the separation between two carbons and the orientation of the groups bonded to these atoms. The ethane dimer and tert-butylcyclohexane are used as representative examples of this new approach. Overall, we anticipate that this new method might prove useful in the study of both intramolecular and intermolecular HIs particularly of those within large systems wherein SAPT or electronic structure calculations are computationally expensive or even prohibitive.

N‐Thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)2 as an Excellent Platform for Studying the Synergy between Hydrogen‐Hydrogen Bonding and Other Families of Non‐Covalent Interactions

“…We have delineated herein that the corresponding contours of deformation densities Δ ρ orb clearly demonstrate that the close contacts C–H⋯H–C leads to a charge migration from the σ(C–H) orbitals and the buildup in the inter‐atomic H⋯H region. From this respect it seems similar to the charge transfer picture noted in dihydrogen molecule, albeit, expectedly quantitatively less pronounced, as originally pointed by Bader in the past stormy discussions . It is found, that the negative values of Δ E orb for C–H⋯H–C stems entirely from lowering in kinetic energy (Figure ).…”

“…Richard Bader was the first who suggested based on his QTAIM theory, entirely contrary to the chemical intuition, that also homopolar dihydrogen interactions C–H ··· H–C can be stabilizing in 1,1′‐biphenyl . It has raised unfinished yet stormy discussion on the nature of homopolar X–H ··· H–X contacts in many systems, particularly when intramolecular contacts are considered . Despite of consensus that intermolecular C–H ··· H–C interactions between bulky hydrocarbon units are in many cases stabilizing mostly due to London dispersion forces,, identification and delineation of true character of homopolar X–H ··· H–X interactions are still very controversial and challenging.…”

Influence of the Homopolar Dihydrogen Bonding CH⋅⋅⋅HC on Coordination Geometry: Experimental and Theoretical Studies

“…Duarte Alaniz et al. analyzed hydrophobic interactions, including H⋅⋅⋅H contacts in saturated hydrocarbons, based on the symmetry‐adapted perturbation theory (SAPT) method 20. Furthermore, more evidence is currently being reported in various fields to show that bulky substituents, containing CH bonds, can bring significant dispersion and, accordingly, can overcome steric repulsion 21.…”

“…[19] Duarte Alaniz et al analyzed hydrophobic interactions,i ncluding H•••H contacts in saturated hydrocarbons, based on the symmetry-adaptedp erturbation theory (SAPT)m ethod. [20] Furthermore, more evidence is currentlyb eing reportedi nv arious fields to show that bulky substituents, containing CÀHb onds, can bring significant dispersion and, accordingly,c an overcomes teric repulsion. [21] These results demonstrate that the nature of CÀH•••HÀCc ontactsi s still the matter of intensived ebate and more studies are needed from both experimental and theoretical schools to understandt he nature of the CÀH•••HÀCi nteraction, as well as to determine the relationship betweent he overall stability of ac ompound andt he existence of weak noncovalent interactions.T his issue is also crucial for general chemistry becausei t can lead to novel interpretations of the stabilitya nd reactivity of molecules.…”

Experimental Insights into the Electronic Nature, Spectral Features, and Role of Entropy in Short CH3···CH3Hydrophobic Interactions

“…10,11 The strength of HI between nonpolar surfaces under the influence of proximally immobilized cations such as ammonium and guanidinium ions is measured using atomic force microscopy. 12 Although there are a few computational studies on methane dimers, n-alkanes, and polyhedranes, 13,14 there is no systematic experimental study of HIs such as the methyl••• methyl (Me•••Me) interactions in the solid state, to the best of our knowledge. In particular, their electronic nature, strength, and modes in the solid state, i.e.…”