Inclusion complexes formed

Fig. 9. An inclusion complex formed between a protonated primary amine and a chiral crown ether.

One of the examples of inclusion complexes formed by intermolecular forces is the C60/PVP complex for the first time described by Yamakoshi et al. (1994). The non-covalent intermolecular nature of forces that stabilizes this complex confirms the fact that fullerene can be quantitatively extracted from its water solution by toluene. 

ELECTROCHEMISTRY OF INCLUSION COMPLEXES FORMED BY CAVITAND-TYPE HOSTS... 

Mechanism of Separation. There are several requirements for chiral recognition. (/) Formation of an inclusion complex between the solute and the cydodextrin cavity is needed (4,10). This has been demonstrated by performing a normal-phase separation, eg, using hexane—isopropanol mobile phase, on a J3-CD column. The enantiomeric solute is then restricted to the outside surface of the cydodextrin cavity because the hydrophobic solvent occupies the interior of the cydodextrin. (2) The inclusion complex formed should provide a rdatively "tight fit" between the hydrophobic species and the cydodextrin cavity. This is evident by the fact that J3-CD exhibits better enantioselectivity for molecules the size of biphenyl or naphthalene than it does for smaller molecules. Smaller compounds are not as rigidly held and appear to be able to move in such a manner that they experience the same average environment. (5) The chiral center, or a substituent attached to the chiral center, must be near to and interact with the mouth of the cydodextrin cavity. When these three requirements are fulfilled the possibility of chiral recognition is favorable. 

In other media like micelles, cyclodextrin, binary solvent mixtures, and proteins (47-55), lifetime distributions are routinely used to model the decay kinetics. In all of these cases the distribution is a result of the (intrinsic or extrinsic) fluorescent probe distributing simultaneously in an ensemble of different local environments. For example, in the case of the cyclodextrin work from our laboratory (53-55), the observed lifetime distribution is a result of an ensemble of 1 1 inclusion complexes forming and coexisting. These complexes are such that the fluorescent probe is located simultaneously in an array of environments (polarities, etc.) in, near, and within the cyclodextrin cavity, which manifest themselves in a distribution of excited-state lifetimes (53-55). In the present study our experimental results argue for a unimodal lifetime distribution for PRODAN in pure CF3H. The question then becomes, how can a lifetime distribution be manifest in a pure solvent ... 

A solution of chiral host and racemic guest compounds in an appropriate solvent is kept at room temperature until inclusion complex crystallizes out. In the complexation, it is necessary to use a solvent which does not form inclusion complex with the host compound. The inclusion complex formed is filtered and purified by recrystallization from solvent, if necessary. Host guest molar ratio is... 

When a mixture of acetophenone 59a (1.0 g, 8.3 mmol), NaBH4 (0.94 g, 24.9 mmol), and water (10 ml) was stirred at room temperature for 2 h, rat-60a was produced. To the water suspension medium of rac-60a was added powdered 8a (3.87 g, 8.3 mmol), and the mixture was stirred for 3 h to give a 2 1 inclusion complex of 8a with (-)-60a.25 Inclusion complex formed was filtered and dried. Heating of the complex in vacuo gave (-)-60a of 95% ee (0.42 g, 85%). From the filtrate left after separation of the inclusion crystals, (+)-60a of 77% ee (0.35 g, 70%) was obtained by extraction with ether. By the same procedure, optically active 60a and 60c-g were prepared (Table 5). Solid state and solvent-free organic reactions have been well established25,263 0. Host-guest inclusion complexation in the solid state has also been reported.260... 

Figure 11 Structures of discrete binuclear inclusion complexes formed by koilands 11 with />-xylene 31 (a), 12 with CH2C12 (b), 14 with CH2C12 (c), 13 with CHC13 (d), 13 with />-xylene 31 (e) and 13 with anisole 32 (f). For the sake of clarity, hydrogen atoms are not represented.

The ability of cyclodextrin to resolve stereoisomers is very readily applied for the separation of diastereomers, such as the cis- and trans-geometric isomers (6,7). Similar to both of the examples presented above, resolution of geometric isomers appears to result from both the level of inclusion complex formed, as well as the level of interaction of the molecule with the 2- and 3-hydroxyl groups of the cyclodextrin. This can be illustrated with the synthetic antiestrogen tamoxifen (Figure 1), which is synthesized in both the cis and trans forms. 

The macrostructure and microstructure of starch lead to the ready formation of inclusion complexes and surface adsorbates.1 Inclusion complexes form by involvement of the inner core of the amylose helix, the intergranular... 

Starch-guest molecule compounds in inclusion complexes are usually nonstoichiometric species. On the other hand, in the case of amylose such compounds are stoichiometric, but their composition is not repeatable. Starch complexes may consist of partly physical mixtures, adsorbates, and true inclusion complexes formed by direct involvement of dipolar interactions, host-guest hydrogen bonds, and/or clathration-like interactions within the starch matrix. 

The kinetics of Eq. 1 corresponds to a first-order process, characterized by a rather low rate constant (kobs = 8.9 x 10 s at 25 °C), whose value increases with increasing temperature. As the inclusion complex forms only when the macrocyclic ligand is fully protonated, on addition of base the adduct dissociates and the exoergonic reaction reverse of Eq. 1 takes place. The thermal reaction provides an example of an electron transfer process which can be switched on/off by a pH change [32],... 

Clathrate An inclusion complex formed when molecules of one kind are trapped in the crystalline network formed by molecules of a different kind. 

In summary, microscopic and thermal observations of PET samples coalesced from their crystalline y-CD-IC suggest crystalline characters and melt-crystallized morphologies that are different from normal samples. After coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion complex formed with host y-CD, PET chains are much more readily crystalliz-able, and, locally, quickly form small, possibly chain-extended crystals. In addition, the noncrystalline regions of coalesced PET exhibit conformational and motional... 

The stoichiometry and association constants of the inclusion complexes formed between BPHTs and CDs were classically calculated by means of the Scatchard and Benesi-Hildebrand methods [101,102]. Assuming a 1 1 stoichiometry ratio, the following equilibrium 1 is established ... 

Fig. 7 Molecular geometry of the inclusion complex formed between 10-MeBPHT and HP-(3-CD (from [18], with permission)...

V-type starch inclusion complex formed using continuous dual feed homogenization potential use as delivery vehicle... 

The photoisomerisation kinetics and other properties of the 1 1 inclusion complexes formed between aromatic derivatives of norbomadiene and P-cyclo-dextrin have been measured." (S)- or (R)-2-Chloropropiophenone affords partially racemised (S)- or (R)-2-phenylpropionic acid respectively by a photo-induced rearrangement via what is probably an ion or radieal intermediate," and (Z)-N-substituted benzoyl-a-dehydrophenylalanines such as (7) are photo-isomerised to 1-azetidine derivatives (8) by a 1,3-acyl migration. Irradiation of 9,9 -bifluorene-9,9 -diol (9) gives a mixture of fluoren-9-one and spiro[9H-fluorene-9,9 (10 -H)-phenanthren]-10 -one (10) whose composition is solvent dependent with the more polar solvents favouring (10). Laser flash photolysis shows the presence of two transients, one of which can be identified with the 9-fluorenyl cation (11), and which originates from photoheterolysis of the diol (9). There is also evidence to support the view that unimolecular rearrange-... 

Solid-state carbon NMR with MAS has been used to study the structure and dynamics of semicrystalline polycaprolactone (PCL) and its inclusion complexes formed with a- and y-cyclodextrins (a- and y-CDs), which are shown to have channel structures occupied by single and two parallel, side-by-side chains, respectively. ... 

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