ExCage

Abstract

Cyclophanes, especially those where pyridinium units in conjugation with each other are linked up face-to-face within platforms that are held approximately 7 Å apart by rigid linkers, are capable of forming inclusion complexes with polycyclic aromatic hydrocarbons (PAHs) with high binding affinities as a result of a combination of noncovalent bonding interactions, including face-to-face [π···π] stacking and orthogonal [C-H···π] interactions. Here, we report the template-directed, catalyst-assisted synthesis of a three-fold symmetric, extended pyridinium-based, cage-like host (ExCage(6+)) containing a total of six π-electron-deficient pyridinium units connected in a pairwise fashion by three bridging p-xylylene linkers, displayed in a trigonal (1,3,5) fashion around two opposing and parallel 1,3,5-tris(4-pyridinium)benzene platforms. The association constants (K(a)) of eight complexes have been measured by isothermal titration calorimetry (ITC) in acetonitrile and were found to span the range from 2.82 × 10(3) for naphthalene up to 5.5 × 10(6) M(-1) for perylene. The barriers to decomplexation, which were measured in DMF-d7 for phenanthrene, pyrene, triphenylene, and coronene by dynamic (1)H NMR spectroscopy undergo significant stepwise increases from 11.8 → 13.6 → 15.5 → >18.7 kcal mol(-1), respectively, while complexation experiments using rapid injection (1)H NMR spectroscopy in DMF-d7 at -55 °C revealed the barriers to complexation for pyrene and coronene to be 6.7 and >8 kcal mol(-1), respectively. The kinetic and thermodynamic data reveal that, in the case of ExCage(6+), while the smaller PAHs form complexes faster than the larger ones, the larger PAHs form stronger complexes than the smaller ones. It is also worthy of note that, as the complexes become stronger in the case of the larger and larger PAHs, the Rebek 55% solution formula for molecular recognition in the liquid state becomes less and less relevant.

A Very Highly Efficient Magnetic Nanomaterial for the Removal of PAHs from Aqueous Media

“…The particular chemical characteristics of PAHs, extended aromatic flat systems with a high electronic density, allow them to form supramolecular complexes with complementary receptors, such as graphene and fullerenes . Other candidates are cyclophane‐type receptors, formed by the union of a polycyclic system such as perylene bisimide (PBI), or the extended pyridinium‐based, cage‐like host (ExCage6 +) . Although these receptors are effective, their practical application is discouraged by their high economic cost of preparation.…”

Adsorption of polycyclic aromatic hydrocarbons and inversion barriers of curved conjugated systems inside the molecular cage ExCage6+

“…The study was divided in two parts: (a) since accurate encapsulation constants of PAH are available for ExCage 6+ this is an excellent opportunity to assess the performance of the methodology selected. Thus, in the first part of the study, we calculated the free energy changes for 14 PAH, the nine included in the work by Dale et al, plus five more selected by us to shed light into the interactions between PAH and ExCage 6+ . The set of PAH analyzed is shown in Figure ; (b) in the second part of the work, we investigated the inversion barriers of buckybowls inside ExCage 6+ .…”

Modulating the Binding of Polycyclic Aromatic Hydrocarbons Inside a Hexacationic Cage by Anion–π Interactions

“…The template-directed synthesis [12] of BlueCage·6 PF 6 was achieved by a procedure (Scheme 1) similar to that described [11] for ExCage·6 PF 6 . Treatment of 2,4,6-tris(4-pyridyl)-1,3,5-triazine [14] (TPT) with 10 equiv of 1,4-bis(bromomethyl)benzene in MeCN/CH 2 Cl 2 (1:1) heated at 90 8C for 3 days afforded TPTB in 58 % yield following counterion exchange.…”

“…As a consequence of their electrostatic and redox properties, [8] polycationic macrocycles such as cyclobis(paraquat-p-phenylene) [9] (CBPQT 4+ ) have played a crucial role in establishing the functional aspect (e.g., switching) of MIMs. Recently, we described [10] the evolution (Figure 1) of CBPQT 4+ into its extended homologue Ex n Box 4+ (n = 1-3), which displays high affinities for sequestering polycyclic aromatic hydrocarbons (PAHs), and subsequently to the three-dimensional analogue [11] ExCage 6+ .ExCage 6+ , which possesses averaged D 3h symmetry, is composed (Figure 1) of three pyridinium units that are fused to the central benzenoid rings with 1,3,5-substitution patterns and paired together by three bridging paraxylylene units. As a consequence of its macrobicyclic nature, the larger cavity permits [11] increased orbital overlap between ExCage 6+ and PAHs, thereby leading to higher complexation strengths in solution.…”

“…Recently, we described [10] the evolution (Figure 1) of CBPQT 4+ into its extended homologue Ex n Box 4+ (n = 1-3), which displays high affinities for sequestering polycyclic aromatic hydrocarbons (PAHs), and subsequently to the three-dimensional analogue [11] ExCage 6+ .…”