Deep-cavity resorcinarene

An example of this design was recently reported by Atwood and coworkers, who showed that an extended, deep-cavity resorcinarene derivative can completely encapsulate a NMe4+ cation with a Cl" anion positioned by hydrogen bonding at the capsule entrance (see schematic receptor 12). [20]... 

Scheme 4-13 Formation of cylindrical-shaped capsule 54 from deep-cavity resorcinarene 53.

Various other examples have been provided in the literature involving the formation of molecular capsules. However, guest binding by these capsules may not have been studied, or evidence of a template requirement for formation may not have been present. These include urea-based calixarene dimers [50], deep-cavity resorcinarenes [51],... 

Ma S, Rudkevich DM, Rebek J Jr (1998) Deep-Cavity resorcinarenes dimerize through hydrogen... 

The first deep-cavity cavitand to be synthesized was the 2.3-quinoxaline derivative 4 (Fig. 4). This second row of aromatic rings in this cavitand. and related cavitands formed by the condensation of resorcinarenes with 2,3-dichloropyrazines. is conformationally flexible. Thus, they exist in a range of conformers between the vaselike C4v form (shown) and a flat C21 form. These families of compounds were termed velcrands, because in the flat, "kite-like" form, they have a propensity to dimerize.When not binding themselves, these types of cal-itands also bind mono-" or di-substituted"benzene derivatives. 

The NARXs possess four spatially-fixed halogen-bond acceptor sites (the four anions) with deep cavities for guest binding. The resorcinarene skeleton and the strong hydrogen bond interactions from the ammonium ions shield the halide anions, so that in the presence of suitable halogen bond donors, the latter interactions can only form either parallel or perpendicular to the upper rim of the NARXs. 

Fig. 11.24 The sliced side (a) and top (b) view of the XB deep cavity cavitand [((dioxane)2 25 4Br) (I-(CF2)4-I)2] with two 1,4-dioxane molecules and one resorcinarene host within the cavity. The sliced side (c) and top (d) view of the XB deep-cavity cavitand [(CHCl3 25 4Br) (IC6F4l)2]. The halogen-bonded layer with peaks and holes and the packing to show the fitting of the layers for the assemblies [((dioxane)2 26 4Br) (I-(CF2)4-I)2] (e, f) and [(CHCl3 26 4Br) (IC6F4l)2] (g, h) respectively. The different colours portray the different components and layers for clarity [57, 58] (Image reproduced from [57, 58] with permission from The Royal Society of Chemistry and The American Chemical Society)...

Receptor 44 is an artificial esterase featuring a zinc(II)-salophen unit appended to a resorcinarene scaffold [39]. The basic hydrolysis of PNPCC in buffered CH2CI2 containing 0.01 % water (Eq. 26.8) is more than 50 times faster in the presence of the catalyst. The substrate shows a very high affinity for 44. The trimethy-lammonium head is hosted deep in the receptor cavity and the ester function is properly oriented towards the metal electrophile of the catalytic site. 

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