Host-guest complexes cyclophanes

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

Since the seminal work of Cram on cyclophanes and resorci-narenes (1) the host-guest chemistry of container molecules has been extensively investigated and more sophisticated examples with other forms and larger cavities have been reported. Thus a large number of host-guest complexes containing neutral,... 

Unique inclusion behavior in reflection of the induced-fit binding mechanism is observed when an organic stock solution of octopus cyclophane 3 is injected into an aqueous medium containing ANS for the host-guest complexation study [17], A circular dichroism (CD) spectrum does not undergo any change for 3 upon complexation with ANS, indicating that the conformation around l-... 

Similar results have been reported for the host/guest complex formation between a tetracationic cyclophane host [=cyclobis(paraquat-p-phenylene)j and the planar het-eroarene indole. The binding constants Kg, determined in six solvents of different polarities, increase with increasing solvent polarity, being ca. 100-fold greater in water than in acetone [306]. Further examples of solvent-dependent cyclophane/guest complexation reactions can be found in reference [299],... 

Figure 18 Near identity of phenyl -phenyl interactions in a cyclophane-benzene host-guest complex (a) and in crystalline benzene (b) (see Klebe and Diederich [85])...

Crown compounds having cyclophane-skeletons and called crownophanes , are reviewed. They form characteristic host-guest complexes due to their crown-cyclophane hybrid structures. Significant stabilization of complexes is often reported through the ion-dipole, cation-aromatic n-electron and n-n stacking interactions, size-and-shape complementarity, and hydrophobic interaction. 

Another attempt to use the host-guest complexation of simple cyclophanes has been reported by Schneider They take the easily accessible host 7, an analogue of which had been demonstrated by Koga to bind aromatic guest molecules by inclusion into its molecular cavity, and study its rate effects on nucleophilic aliphatic substitutions of ambident anions (NOf, CN, SCN ) on 2-bromomethylnaphthalene 8 and benzylbromide. Similar bimolecular reactions are well known in cyclodextrin chemistry and other artificial host systems . In addition to the rather poor accelerations observed (see Table 3) the product ratio is changed in the case of nitrite favouring attack of the ambident nucleophile via its nitrogen atom. 

Inoue Y, Liu Y, Tong LH, Shen BJ, Jin DS, Calorimetric titration of inclusion complexation with modified y -cyclodextrins. Enthalpy-entropy compensation in host-guest complexation from ionophore to cyclodextrin and cyclophane, J. Am. Chem. Soc. 1993 115 10637-10644. 

Host-guest Complexes with Organic Cations 12.2.1 Cyclophanes... 

Abstract. The inclusion behavior of the octopus cyclophane constructed with a rigid macrocyclic skeleton and eight hydrocarbon chains was studied in aqueous media by means of fluorescence and electronic absorption spectroscopy. Both hydrophobic and electrostatic interactions came into effect in the host-guest complexation process. The cyclophane acted as an effective apoenzyme model for constitution of an artificial vitamin B -dependent holoenzyme by simultaneous incorporation of pyridoxal-5 -phos-phate and a hydrophobic alkylammonium substrate into the host cavity to give the Schiff-base species, showing the substrate selectivity. 

A. An example of a host-guest complex between paraquat and a polyether cyclophane. 

Walliman, P., Mattel, S., Seiler, P. Diederich, F. (1997) New cyclophanes as initiator cores for the construction of dendritic receptors Host-guest complexation in aqueous solutions and structures of solid-state inclusion compounds, Helv. Chim. Acta, 80, 2368-2390. 

Diederich, F. and Dick, K. (1984) A New Water-Soluble Macrocyclic Host of the Cyclophane Type Host-Guest Complexation with Aromatic Guests in Aqueous Solutitm and Acceleration of the Transport of Arenes Through an Aqueous ase , J. Am. C hem. Soc. 106, 8024-8036. 

Figure 3 Examples of structures from MC simulations of host-guest complexes in solution. Some hydrogen bonds are indicated with dashed lines solvent molecules have been deleted for clarity, (a) Complex of chloride ion with Reinhoudt s bis-urea-derivatized p-r-butylcalix[4]arene. (b) Complex of hydroquinone with Diederich s cyclophane including two solvating water molecules, (c) Complex of pyridine and Rebek s acridine diacid, (d) Complex of 9-methyladenine and Zimmerman s tweezer acid...

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