Guests selectivity

Figure 75 Selectivity in the formation of the two hosts. Flat guests select the asymmetric host, whereas...

On the basis of previous observations it was anticipated that the clathrate formation would be more selective in controlling guest selectivities if a functionality which could form hydrogen-bonds with guest species and add this strengthening feature to that... 

The above selectivities are affected by changes in the molar ratio between the guests and between guest and host in the solution mixture. They show, however, consistent trends. Qualitatively similar results of guest selectivity were obtained with N,N -bis(tri-p-tolylmethyl)urea and a number of related hosts47. Additional experiments using ureas substituted with chiral spacers are readily envisioned. 

Guest Selectivity Behavior, Separation of Solvent Mixtures. 58... 

Guest selectivity properties to this extent are out of the ordinary, cf. Ref. 7... 

It should be noted that not all host-guest phane complexes are of the type just described. Indeed, a significant number of lattice inclusion complexes also occur. In these, the host molecules stack such that a channel running between hosts is formed. Guest molecules occupy this channel. As expected, such an arrangement is usually reflected by relatively poor host-guest selectivity. 

Andersson LI, Mandenius CF, Mosbach K. Studies on guest selective molecular recognition on an octadecyl silylated silicon surface using ellipsometry. Tetrahedron Lett 1988 29 5437-5440. 

Measurement of circular dichroism can even permit elucidation of relatively small structural changes. CD spectroscopy is also suitable for the solution of specific application-relevant questions. Studies of the sensor properties of chiral dendrimers make use of the fact that complexation of chiral guest molecules induces changes in the CD bands of the host dendrimers. Thus guest-selective chiroptical effects observed in titration experiments with enantiomeric guest molecules give an indication of the potential of the chiral dendrimer to act as an enantioselective sensor [87]. 

Fig. 8.10 Mode of operation of the quartz micro balance (left schematic). Right A dendrimer as guest-selective host compound (selector) for coating of the quartz crystal oscillator. Red Selector layer green various analyte components...

Some amide derivatives have been reported to form inclusion complex with a wide variety of organic compounds.9 Optically active amide derivatives are expected to include one enantiomer of a racemic guest selectively. According to this idea, some amide derivatives of tartaric acid (11-13) were designed as chiral hosts.10 As will be described in the following section, these amide hosts were found to be useful for resolution of binaphthol (BNO) (14) and related compounds (15,16). 

Hiraoka S, Fujita M, Guest-selected formation of Pd(II)-linked cages from a prototypical dynamic library, J. Am. Chem. Soc., 121 10239-10240, 1999. 

Base-mediated condensation reaction of 2,7-dibromotropone with dithiol afforded the 22-membered 79 and 44-membered products 80 in 62% and 24%, respectively (Scheme 11) <2004H(62)149>. Compound 79 was used as a carrier through a chloroform liquid membrane however, the guest selectivity of 79 was lower than that of the corresponding pentaoxadithiacrown ether 76. 

As emphasized in the text, the importance of a zeolite derives from its function. It is not only important to realize a structure which retains its cavities upon removal of the guest but should also demonstrate reversible absorption and desorption of guests, selectivity in the intake of guest molecules and stability under conditions of a typical reaction. 

Guest-Selected Formation of Cages from a Dynamic Receptor Library. . 22... 

In this section two types of self-assemblies of M3L2 complexes will be described. In one case the self-assembly was occurred only in the presence of a suitable guest molecule (guest-induced fit) and in the other case the type of self-assembly was selected by the guest from a receptor s library (guest-selected cage). 

Guest selectivity in the cyclophane (40) can be controlled by E-Z photoisomerisation of the azo moiety (Shinkai et al.). Aoyama et al. have provided the first example of the photo-regulation of membrane permeability. Pandey et al. have... 

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