Steroid cyclophane

Fig. 3A-C. Space-filling models of artificial receptors, each being capable of providing a large hydrophobic cavity A octopus cyclophane 4 B steroid cyclophane 6 C cage-type cyclophane 8...

Formation of the hybrid assemblies of peptide lipid 9 with the octopus cyclophanes (3 and 4) and the steroid cyclophanes (5 and 6) was also character-... 

Octopus and Steroid Cyclophanes Embedded in Synthetic Bilayer Membranes... 

Each of the hybrid systems, composed of steroid cyclophane 6 and octopus cyclophanes 3 and 4 in combination with lipid 9, also exhibits effective guestbinding in comparison with the cyclophane-free system as reflected in the fluorescence features of ANS and TNS, which are similar to those shown in Fig. 6. On the other hand, the hybrid assembly formed with a steroid derivative, the monomeric analogue of 5 with respect to the steroid fragment, and lipid 9 in a molar ratio of 1 10 does not enhance the fluorescence intensities of the guests to any significant extent. 

The steroid cyclophanes provide less polar microenvironments for ANS and TNS by forming the hybrid assemblies with the peptide lipid. To our surprise, the microenvironment around the ANS molecule incorporated into the hybrid assembly formed with lipid 9 and steroid cyclophane 5 is equivalent to that provided by hexane ( = 0.009). In contrast, the microscopic polarity experienced by TNS in the identical hybrid assembly is as polar as 1-pentanol ( = 0.568). On the other hand, the hybrid assembly formed with lipid 9 and steroid cyclophane 6 binds the TNS molecule in a less polar microenvironment than ANS. Meanwhile, both of the octopus cyclophanes and their hybrid assemblies formed with the peptide lipid incorporate both guest molecules into the comparable binding sites with respect to the microenvironmental polarity. 

The steroid cyclophane also provides a sizable and well-desolvated hydro-phobic cavity in aqueous media in a manner as observed for the octopus cyclophane. The molecular recognition ability of the steroid cyclophane is inferior to that of the octopus cyclophane in aqueous solution due to the structural rigidity of steroid segments of the former host. When the steroid cyclophane is embedded in the bilayer membrane to form a hybrid assembly, however, the steroid cyclophane becomes superior to the octopus cyclophane with respect to functions as an artificial cell-surface receptor, performing marked guest discrimination. 

K. Ariga, Y. Terasaka, D. Sakai, H. Tsuji, J. Kikuchi, Piezoluminescence Based on Molecular Recognition by Dynamic Cavity Array of Steroid Cyclophanes at the Air-Water Interface , J. Am. Chem. Soc., 122, 7835 (2000)... 

As a pioneering model, one kind of molecular machine, steroid cyclophane, was embedded at the air-water interface as a dynamic interface, to demonstrate capture and release of a target guest molecule through macroscopic mechanical motions (Fig. 2.2.9) [23]. The steroid cyclophane machine possesses a cyclic core consisting of a l,6,20,25-tetraaza[6.1.6.1]... 

The fact that the dendritic shell can produce localized microenvironments has been used by Diederich et al. who developed water-soluble dendritic cyclophanes (dendrophanes) as models for globular proteins (Figure 16.13) [5, 170, 171], These dendrimers contain well-defined cyclophane recognition sites as initiator cores for the complexation of small aromatic guests [172-174] and steroids [174-176], Enlargement of the cyclophane core could be used as a tool to complex larger steroid molecules. 

Cyclophanes and Steroids That May Form Inclusion Complexes... 

The cage-type peptide cyclophanes (7 and 8) exhibit discrimination toward steroid hormones, as effected by hydrophobic and n-n interactions. In addition, the chirality-based discrimination between a- and -estradiol as well as between D- and L-amino acids bearing an aromatic moiety is performed on the basis of their capacity of forming efficient hydrogen bonding with the host molecules in aqueous media [41, 43]. 

Fig. 7A-C. Schematic representations for guest-binding modes of hybrid assemblies formed with peptide lipid 9 and octopus (3 and 4) and steroid (5 and 6) cyclophanes a guest molecule is located in the hydrogen-belt domain (A for 11 and 12 each bound to 3 and 4 B for 11 and 12 bound to 6 and 5, respectively) a guest molecule is located in the hydrophobic domain (C for 11 and 12 bound to 5 and 6, respectively)...

Computational studies followed by molecular modeling were performed on a variety of fullerene-porphyrin dyads that contained either flexible polyether or rigid steroid linkers as well as on doubly linked cyclophane-like C60-porphyrin [212]. Not surprisingly those studies confirmed that the attractive van der Waals interactions between porphyrin and C60 units cause these dyads to adopt unusual conformations in order to get together in close proximity. 

Cyclophanes are cyclic hosts made by Unking aromatic rings. Several examples of cyclophanes are depicted in Fig. 2.21. While the cyclophane in (a) is a simple two-dimensional cyclophane, the cyclophane in (b) has four alkyl chains attached. Using a similar molecular design process, a cyclophane with eight alkyl chains can be synthesized and is called an octopus-type cyclophane. The alkyl chains self-assemble in an aqueous phase and form a three-dimensional cavity. Cyclophanes with rigid steroidal walls are called steroid... 

Figure 6.37 (a) small cyclophane core dendrophane for complexation of small aromatic guests such as benzene, (b) large core dendrophane for binding steroids such as testosterone. ... 

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