Host-guest ratio

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Examination of the steric relations in these complexes (cf. Fig. 30) suggests that the more voluminous branched alcohols cannot follow the same principle. Indeed, in the 2-butanol and also in the t-butanol inclusion compound, a different ring system is built (Fig. 17b and type I in Fig. 19). While the short-chain alcohols form twelve-membered H-bond loops, the branched butyl alcohols are embedded into a ten-membered asymmetric loop. The stoichiometry of the asymmetric unit also changes from 1 2 (host guest) ratio to 1 1. The so-built ring system of homodromic H-bonds still contains a mirror-related pair of hosts 1, but comprises only one guest molecule. 

A more deviating stoichiometry is found in the case of the inclusion compound of / with /-propanol 77 >. Here the assistance of two independent host molecules is required and results in a 2 1 stoichiometry. Nevertheless, even this unusual host guest ratio gives rise to a similar H-bond pattern (Fig. 18a and type lib in Fig. 19) as found for the inclusions of 1 with simpler alcohols (cf. Fig. 17a), namely the 12-membered ring system. Now, another interesting fact arises, signalling the flexibility of host 1 in its inclusion behavior. This is the formation of host dimers through H-bonds to ensure clathration. 

Enantioselective photocyclization of 74 occurred efficiently in the inclusion complex with 2a. In particular, the selectivity is very high in the case of 74a. However, control is inefficient in the 1 2 complex 85 composed of 2a and 74c. The host guest ratio probably depends on the packing of the components in the crystal. The packing is... 

The high affinity of ammonium cations for tetra-bridged phosphorus(IV) P=0 cavitands was used to complex bis-ammonium guests. The highly insoluble NjAT-dimethyl-bipyridinium dication [paraquat " ] was readily dissolved in chloroform solution in presence of 12b in a 2 1 host-guest ratio. 

Host Guest Ratio Irradiation time (h) Product ... 

In addition to 1 1 (host-guest) complexes with different structures, a number of complexes with different host-guest ratios exist in equilibrium when aromatic molecules are included into either a- or p-CD. For example, sodium 1-pyrenebutyrate (75)/a or /J-cyclodextrin complexes in solution form equilibrium mixtures of a 1 1 and 2 1 complexes and form 1 1 and 2 2 complexes with y-CD (Figure 39) [247]. 

The solvent inclusion properties of ll-phenyl-6,ll-dihydrodibenzo[A,< ]thiepin-ll-ol 272 were investigated <2004MI44>. DMF and DMSO were both included by host 272 with a host guest ratio of 2 1 however, the presence... 

In a typical resolution procedure, two equivalents of a racemic compound and one equivalent of a chiral host dissolved in an inert solvent (toluene, benzene or hexane) are left to crystallize. The resulting crystalline product is an inclusion compound with a typical host guest ratio of 1 1 or 2 1. The guest compound... 

Table 2 Complexing properties and host guest ratio for 27 and 28 in comparison with 3c (from ref. 48).

In crystalline 7 there is only poor interaction between the parallel chains, and it is this property that results in its special inclusion behaviour. The only guests included are small aromatic hydrocarbons, and these usually give a host guest ratio of 1 1. Incorporation of the guests between the parallel chains increases the OFF and EF attractions within the layers, with concomitant reduction of the Br Br interactions between layers. 

Calculated values of the host/guest ratio. The host/guest ratio determined by NMR. The layer distance measured by PXRD. 

Table 3 Formation of the inclusion compounds of bile acid derivatives with their host-guest ratios. 

Table 7 Lattice parameters, host framework type, host guest ratio, and PCcavity for inclusion compounds of CA.

Guest Space group a (A) b A) c (A) PC ) V (A3) Host frame- work Host guest ratio PCcavity (%)... 

This order indicates that the aG-type host framework is more favorable than the other two trans-types ((TP or aT), and the 1 1 aG type is more favorable than 2 1 aG. In addition, this order agrees with the fact that less-selective enclathrations (entry 1, 12 and 21) were observed when they construct the same host frameworks at the same host-guest ratios in a single-component system. For example, both benzene and toluene can be included in the same 1 1 aG type. In the same way, less-selective enclathrations were also observed in the cases of ethylbenzene vs. n-propylbenzene (1 1 (3P) and n-amylbenzene vs. n-hexylbenzene (2 1 aG). 

Inclusion complexes of Cl-MIT (1) were prepared by crystallization of hosts and 1 from methanol solution. The IR spectra and the content of 1 in these complexes were measured by IR spectrometry and HPLC, respectively. The host-guest ratio of each complex was determined from the content of 1. 

TABLE -11. Melting points and host-guest ratios of selected DBTA complexes... 

The octahedron 24 has a very large internal cavity, capable of enclosing multiple neutral guests [62]. Guests have included carboranes, adamantane, adamantols and 1,3,5-trimethoxybenzene. In all of these cases a host guest ratio of 1 4 is observed with no lower ratios. The hydrophobic cavity that the cage possesses promotes the encapsulation of the above guests in D20 solution. Tri(tert-butyl)benzene was only observed to be encapsulated in a 1 1 ratio. The size of this... 

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