Channel inclusion compounds

Selenourea [630-10-4] ]5k.e urea and thiomea can form channel inclusion compounds (87) with a variety of hydrocarbons. Though the difference in channel diameter between thiourea and selenourea is small, selenourea seems to be much more selective for the inclusion of certain guest molecules (eg, cis/trans isomers). 

Fig. 3. Channel inclusion compound of deoxycholic acid (6) with acetone. The crystal packing is affected by head-to-tail H-bond-mediated double layers of host molecules (H-bonds as dotted lines, guest molecules shaded) (Adapted from Ref. 13)...

M. D. Hollingsworth, U. Werber-Zwanziger, M. E. Brown, J. D. Chaney, J. C. Huffman, K. D. M. Harris, S. P. Smart, "Spring-loaded at the molecular level relaxation of guest-induced strain in channel inclusion compounds ,/. Am Chem Soc 1999,121, 9732-9733. 

Figure 7.16 Channel inclusion compounds of di-ol 7.13 with either (a) CC14 or (b) the host molecule itself as guests.

Since the major driving force of inclusion is hydrophobic interaction, stabilities of ICs depend strongly on the polarity of the polymer. The more hydrophobic the polymer is, the higher is the affinity of CDs towards it. On the other hand, solubility in water decreases with increasing hydrophobicity of the polymer. Since affinity and solubility have to be compromised, an optimum of polarity of the polymer should exist for complexation by CDs. It is difficult to quantify the binding free energies of CD channel inclusion compounds, since they are insoluble in water. Stabilities of these polymeric ICs can be qualitatively compared by competition experiments. For example, PLLA and PCL were competitively included in a-CD. The IC of PCL was... 

II. Classical Channel Inclusion Compounds of Urea, Thiourea, and Selenourea. 155... 

It. CLASSICAL CHANNEL INCLUSION COMPOUNDS OF UREA, THIOUREA, AND SELENOUREA... 

Table 8. Typical Linkage Modes of Self-Assembled Hydrogen-Bonded Chains and Ribbons of Urea, Thiourea or Selenourea Molecules in Their Pure Crystals and Channel Inclusion Compounds...

A considerable amount of recent work has been directed towards the study of detailed molecular orientations and motions of guest molecules in urea channel inclusion compounds, as well as the generation of crystalline modifications in different space groups, such as P2i2i2i [30a,b] R3c [60] and Pbcn [67], but the principal structural characteristics of the channel-type host lattices remain virtually unaltered. Structural properties of the 1,10-dibromodecane/urea and 1,12-dibro-modecane/urea inclusion compounds have been determined by single-crystal X-ray... 

Host-Guest Hydrogen Bonding in the Channel Inclusion Compound (CH3)3bt CH2)20HNH2C0NHC02iNH2)2C0 (1.14)... 

The examples listed in Table 4 [cf. Sect. 4.1 (3)] are isostructural channel inclusion compounds in which the essential structural element is TMA TMA alone. 

The overall structural formula for all these TMA HjO channel inclusion compounds can be written as... 

It was recognised that the plates were neat TTP and the needles molecular adducts of composition 4 (TTP) - guest. Our own work has confirmed and extended these results we have found three polymorphic forms of TTP (Figs. 13 and 14), have confirmed that only guests with aromatic character participate in the formation of these adducts (see Table 6), and have shown that the needles are all isomorphous channel inclusion compounds. We have also found that tetralin forms an inclusion compound but that decalin and cyclohexane do not. Heteroaromatics are permissible guests (e.g. pyridine and a-picoline) but not aromatic quinones (e.g. p-benzoquinone and 2-methyl-p-benzoquinone). Pyrene is the largest molecule which forms an inclusion compound while perylene and fluoranthene form (what appear to be) ti—7i -charge transfer compounds with TTP. 

Table 5. Summary of crystallographic results for the polymorphs of TTP and its channel inclusion compounds...

Table 6. List of guest molecules used to prepare channel inclusion compounds of TTP, together with details of superstructure periodicity and overall symmetry of the crystals. This information is derived from the nature of the weak intermediate layer lines if these are diffuse then the overall symmetry cannot be determined. The periodidty along the channel axis is given as a multiple (n) of the monoclinic repeat (3.91 A). Results are for crystals at room temperature (25 °C)...

TTP also has two polymorphs but only the motif of stacking found in y-TTP persists into the structure of the channel inclusion compounds. 

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