How carbo-benzenes fit molecules in their inner core as do biologic ion carriers?

Abstract

The present computational study complements experimental efforts to describe and characterize carbo-benzene derivatives as paradigms of aromatic carbo-mers. A long-lasting issue has been the possibility of the π-electron crown of the C18 carbo-benzene ring to fit metals or any chemical agents in its core. A systematic screening of candidate inclusion complexes was carried out by density functional theory calculations. Mayer bond order, aromaticity indices, and energy decomposition analyses complete the understanding of the strength of the host-guest interaction. The change in steric and electronic properties induced by the guest agent is investigated by means of steric maps. Substitution of H atoms at the carbo-benzene periphery by electron-withdrawing or electron-donating groups is shown to have a determining influence on the stability of the inclusion complex ions: while electronegative substituents enhance the recognition of cations, electropositive substituents do the same for anions. The results confirm the experimental failure hitherto to evidence a carbo-benzene complex. Nevertheless, the affinity of carbo-benzene for the potassium cation appears promising for the design of planar hydrocarbon analogues of biologic ion carriersA.P. thanks the Spanish MINECO for a project CTQ2014-59832-JIN and European Commission for a Career Integration Grant (CIG09-GA-2011-293900

Carbo‐mer of Barrelene: A Rigid 3D‐Carbon‐Expanded Molecular Barrel

“…However, taking the dielectric constant of the DCM solvent into account tends to lower the affinity with the following respective values for those ion insertions: −10.5 (−1.1), 16.6 (24.1) and 27.7 (34.1) kcal/mol. This appraisal of the host‐guest affinity with respect to the free ion and isolated empty cage 1 might, [22] however, be an overestimation. If the ion is placed outside the cage near to the OH group, the outer‐sphere complex NH 4 + ⋅⋅⋅ 1 is only 5.0 (5.4) kcal/mol less stable than NH 4 + @ 1 , while the outer‐sphere complex Cl − ⋅⋅⋅ 1 remains more stable by 24.0 (22.7) kcal/mol than Cl − @ 1 because of H‐bonding with the hydroxyl group.…”

“…The steric map of 1, performed by means of the SambVca package of Cavallo and coworkers (Figure 4), [21] shows that the ionic guest should be of reduced size to fit the size of the carbo-barrelene cavity (of slightly more than 2 Å van der Waals diameter, nearly half the one of the carbo-benzene ring). [22] In particular, the sphere of radius 3.5 Å centered at the cage centroid is highly occupied (%V Bur = 59.9 %). [23] To test the hosting capacity of 1, representative ions of various charge, size and H-bonding ability were inserted into the cavity: in the gas phase, binding energies (and binding free energy at 298.15 K) of NH 4 + , Cl À and Ca 2 + are À 44.5 (À 35.1), 1.0 (8.5) and À 165.7 (À 159.3) kcal/mol, respectively.…”

“…The 3D π‐electron‐rich structure of carbo ‐barrelenes suggests that the 7 Å‐high barrel core could behave as a cage for some ionic species in putative ion@ 1 complexes. The steric map of 1 , performed by means of the SambVca package of Cavallo and coworkers (Figure 4), [21] shows that the ionic guest should be of reduced size to fit the size of the carbo ‐barrelene cavity (of slightly more than 2 Å van der Waals diameter, nearly half the one of the carbo ‐benzene ring) [22] . In particular, the sphere of radius 3.5 Å centered at the cage centroid is highly occupied (% V Bur =59.9 %) [23] …”

MOF Encapsulation of Ru Olefin Metathesis Catalysts to Block Catalyst Decomposition

“…The radius of the sphere around the metal centre was set to 3.5 Å, whereas for the atoms we adopted the Bondi radii scaled by 1.17, and a mesh of 0.1 Å was used to scan the sphere for buried voxels [85]. As reported for the interaction of small molecules with carbo-benzenes [86], the study was extended to higher ranks (i.e., 5.0, 8.0, 10.0, 12.0 and 15.0 Å). The elucidation of the steric maps, together with the total and quadrant %V Bur values, give quantitative and qualitative data to predict the reactivity of the metal catalysts.…”

Aromatic Rings and Aromatic Rods: Nonplanar Character of an Indeno-dehydro[14]annulene

“…31 Calculated NICS(1) values for all the rings, along with NICS(0) values for the 18-and 14-membered macrocycles, are collected in Figure 5, where values for nonsubstituted benzene (C 6 H 6 ) and carbo-benzene (C 18 H 6 ) are given as references (see Supporting Information for other NICS indices). 32 According to any NICS index, the magnetic aromaticity of a C 6 or C 18 ring decreases with substitution: the NICS(1) value of the C 18 macrocycle decreases by 3.1 ppm from the nonsubstituted carbo-benzene (-16.5 ppm) to the substituted derivative 1 (-13.4 ppm). This is parallel to the NICS(1) decrease by at least 2.6 ppm (and up 4.8 ppm) when going from benzene to phenyl substituents of 1 and 12.…”