Modeling of Supramolecular Properties of Molecular Tweezers, Clips, and Bowls

Abstract

The electrostatic potential surface (EPS) is calculated for molecular tweezers, clips, and bowls at different levels of theory (semiempirical AM1, ab initio HF/6-31G*, and density functional theory pBP/DN**). According to these calculations, the molecular electrostatic potential (MEP) on the concave side of the molecular tweezers and clips is suprisingly negative for hydrocarbons. This finding seems to be a general phenomenon in nonconjugated π-electron systems with concave-convex topology and it explains the receptor properties of the molecular tweezers and clips. Analogous calculations performed for the conjugated aromatic molecular bowls show different results. The DFT calculations predict that in these systems the more negative MEP lies on the concave side similar to the findings for the nonconjugated molecular tweezer-and clip-systems, whereas the AM1 calculation leads to the opposite result that the MEP is more negative on convex side of the bowl-systems.

Synthesis and Supramolecular Properties of Trimethylene‐Bridged Clips

“…These findings can be explained by the electrostatic potential surface (EPS) calculated by means of quantum-chemical methods. [38] In agreement with analogous calculations for the molecular tweezers 1 and 2, [20] the EPS of 3 and 4 is calculated with various quantum-chemical methods to be highly negative on their concave faces, whereas the EPS on their convex faces is similar to that of alkyl-substituted arenes (Figure 8). Accord- ing to these quantum-chemical calculations this seems to be a general phenomenon of nonconjugated p systems with convex ± concave topology.…”

“…This high selectivity has been correlated with markedly negative molecular electrostatic potentials calculated for the concave sides of 1 and 2 by using quantum-chemical methods. [19,20] When analogous calculations were performed for the electron-deficient substrates, the complementary nature of their electrostatic potentials to the electrostatic potentials found for the inside of the cavity of 1 or 2 became evident. This suggests that the relatively strong receptor ± substrate binding is predominantly of electrostatic nature.…”

Onion‐Type Complexation Based on Carbon Nanorings and a Buckminsterfullerene

“…Recent theoretical studies have predicted that the anisotropic distribution of p electrons causes a substantial segregation of electrostatic charge between concave and convex p surfaces. [16][17][18][19][20][21] The electrostatically attractive forces as well as dispersion forces would be operative between curved conjugated systems. The drastic decrease in the association constants from the fullerene complexes to the nanoring complexes can be attributed to the decrease in the curvature of the corresponding p systems.…”

Towards the Design of Neutral Molecular Tweezers for Anion Recognition

“…The same type of behavior was observed by the group of Klärner, in which they report no meaningful changes in the differences between the convex versus concave MEP of several NH 2 , OH, and OAc substituted molecular clips. [11] We did not try to evaluate these differences because our main goal was to characterize the interactions of the anion in the concave side of the tweezers and to analyze its potential as a molecular receptor site for anions. However, some changes in the fragments that join the benzene rings in the frame of the tweezers can noticeably alter the MEP sign of the convex side.…”

“…[11] Substituents on the benzene ring of the molecular tweezers alter their binding parameters, but the effect seems to be related to steric rather than electrostatic factors. [9,12] Complexes between these molecular tweezers and electron-rich aromatic, aliphatic, or anionic substrates have not been observed.…”