Host-guest complexes resorcinarenes

Calix[4]resorcinarenes, a subclass of calixarenes, are large cyclic tetramers that have found applications as macrocyclic receptors, host molecules, host-guest complexes, and so on (Botta et al, 2005 Martinez et al., 2000 Leyton et al., 2005 Yonetake et al, 2001). It shonld be noted that the synthesis of calix[4]resorcinarenes was first reported in the late nineteenth century by Bayer based on the concentrated sulfuric acid-catalyzed cyclocondensation of benzaldehyde and resorcinol (Bayer, 1872). These cyclic compounds were synthesized by TSA (Scheme 3.8) (Karami etal.,2012f). 

Analysis of CP kinetics and the parameters obtained are a source of important information about host-guest interactions. From the classic I-S model of cross polarization, it was found that the values of T pH relaxation times for guest and host molecules are considerably different. This suggests that DMF carbons cross-polarize from the DMF protons, not from the remote protons, of calixarene. Moreover, such a result proves that the DMF is located outside the calices and between the calixarene molecules. The simple I-S model is not sufficient to describe the cross-polarization of the complex of tetra (C-undecyl)calix[4]resorcinarene with DMA. The best fit of experimental data was seen when the more advanced I-F-S model of cross polarization was adopted [57]. Analysis of CP kinetic parameters provides important information on molecular mobility (Fig. 19, Table 5). 

Several recent and comprehensive review articles have been published on calixarenes and resorcinarenes, lich cover both the chemistry and the host-guest properties of these macrocycles. The conformational properties of calix[4]arenes and resorcinarenes are particularly well studied and exploited. They can exist in four different conformations (Figure 2) named cone, partial cone, 1,3-alternate, 1,2-alternate which strongly influence their complexation properties. 

C60 and Cyo fullerenes are able to form complexes with resorcinarene [80]. In this case, the host molecule can guest only one fullerene molecule in its inclusion complex structure. The n-n, CH-n and n-n interactions were observed by CPMAS and FTIR analysis data. Chattopadyay and coworkers [81] investigated the ability of C o and Cyo fullerenes to form ICs with a series of crown ethers. They showed that fullerenes can form 1 1 molecular complexes with crown ethers, but two of them, dibenzeno-24-crown-8 and dibenzeno-30-crown-10, are able to form complexes only with C6o fullerene, not with Cjq. 

It took 8 years to publish another structure. In 1976 K. J. Palmer et al. reported two conformers of another resorcin[4] arene derivative, i.e. cis- and trans-C-para-bromophenyl-4,6,10,12,16,18,22,24-0-octaacetylcalix[4]resorcinarene [3]. Than in next 3 years G. D. Andreetti et al. published the first crystal structure of inclusion compound formed by para-ferf-butylcalix[4] arene with toluene [4]. The calixarene molecule was found in cone conformation and the guest molecule could not be located within the host cavity due to its disorder (the molecular complex was located on a crystallographic fourfold axis). The Authors also noticed that the structure undergoes the order-disorder phase transition at 248 K. In 1996 the disorder high temperature phase was resolved with the aid of solid-state NMR data by E. B. Brouwer et al. [5] (unfortunately, the atoms coordinates are not deposited in CSD) and in 1998 the low temperature ordered phase was reported by A. Arduini et al. [6] (Fig. 38.2). The inclusion complex is stabilized by week interaction. The crystal and molecular structure of this... 

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