Aniline-containing guests recognized by α,α’,δ,δ’-tetramethyl-cucurbit[6]uril host

Abstract

The host−guest complexation of symmetrical α,α’,δ,δ’-tetramethyl-cucurbit[6]uril (TMeQ[6]) and cucurbit[7]uril (Q[7]) with a series of aniline-containing guests has been investigated by various experimental techniques including NMR, ITC, and X-ray crystallography. Experimental results indicate that both TMeQ[6] and Q[7] hosts can encapsulate aniline-containing guests to form stable inclusion complexes. However, the oval cavity of TMeQ[6] is more complementary in size and shape to the aromatic ring of the guests than the spherical cavity of Q[7]. Shielding and deshielding effects of the aromatic ring on guests lead to the remarkable chemical shifts of the TMeQ[6] host protons. The rotational restriction of the guests in the oval cavity of TMeQ[6] results in the large negative values of entropy. The X-ray crystal structure of the 1:1 inclusion complex between TMeQ[6] and N,N′-diethyl-benzene-1,4-diamine unambiguously reveals that the aromatic ring of the guest resides in the oval cavity of TMeQ[6].

Symmetrical-Tetramethyl-Cucurbit[6]uril-Driven Movement of Cucurbit[7]uril Gives Rise to Heterowheel [4]Pseudorotaxanes

“…Because the benzimidazolium unit is complemented to the ellipsoidal cavity of TMeQ[6] in shape, the TMeQ[6] cannot rotate freely around the horizontal axis of the 1 4+ axle, and the benzimidazolium group induces two different magnetic fields, one being the shielding zone and the other being the deshielding zone. This phenomenon is in agreement with what we have observed in the inclusion complexes of the host TMeQ[6] with positively charged aniline . The proton signals’ (H1, H2, H5, and H7) separation indicates that two portals of TMeQ[6] are located in different chemical environments.…”

“…This phenomenon is in agreement with what we have observed in the inclusion complexes of the host TMeQ[6] with positively charged aniline. 20 The proton signals' (H1, H2, H5, and H7) separation indicates that two portals of TMeQ[6] are located in different chemical environments.…”

Enabling dual aromaticity in fused nanobelts: evaluation of the magnetic behavior of fused [10]CPP units

“…Such surfaces reveal the shielding/deshielding regions affecting NMR shifts of incoming guest species, useful to perform NMR titrations of the host–guest phenomena in solution, providing knowledge of relevant quantities given by association constants, among other studies. 78–83 The shielding/deshielding regions within the [10]SCPP structure can be rationalized as its inherent anisotropy effect, 21,36,41–44 where a diminished shielding is expected to be experienced by an incoming guest at the neutral counterpart within the [10]CPP moiety, which in turn leads to an enhanced shielding when di- and tetraoxidized counterparts are formed, revealing the expected pattern for plausible NMR titration experiments. 84,85…”

Supramolecular chemistry of substituted cucurbit[n]urils

“…Consequently, Q[n] homologues fail to selectively recognize some guest molecules with special shape. [75][76][77]142,152 Thirdly, in comparison with other macrocyclic hosts, for example the calix[n]arenes, Q[n] homologues are difficult to functionalize. To overcome these shortcomings, significant efforts have been invested on the design and synthesis of substituted Q[n]s.…”

“…However, we recently encountered shielding and deshielding effects induced by a guest. [75][76][77] When the aromatic motif of a guest, such as aniline-containing guests, is located inside of the TMeQ [6] cavity, the ellipsoidal cavity of the TMeQ [6] is complementary in both size and shape to the aromatic group of the guest. As a result, remarkable chemical shifts for the TMeQ [6] host protons were observed (Fig.…”