Macrocyclic binding

The preorganised macrocycle binding sites remain effective at all dendrimer generation levels and hence binding is not inhibited by hydrophobic collapse of the dendritic branches. 

Clifford, T., Abushamleh, A. and Busch, D.H. (2002) Factors affecting the threading of axle molecules through macrocycles binding constants for semirotaxane formation, Proc. Natl. Acad. Sci. 99, 4830-4836. 

Receptors for anions vary widely, and are in many instances either the same or modified versions of the ligands that bind transition metal ions [5-20], For example, poly amine macrocycles can bind transition metal ions, while poly ammonium macrocycles bind anions. In many instances the same ligand can bind either a transition metal ion [21-24] or an anion [25-29],... 

Molecular shuttle 154+ consists of a tetracationic cyclophane macrocycle, a linear thread containing two hydroquinol stations and a polyether spacer. The macrocycle binds the stations via n - n and charge-transfer interactions between the electron-poor cyclophane and the electron-rich hydroquinols. As explained above, because both stations are energetically degenerate (they are chemically identical) the macrocyclic unit has no preference for either of them and randomly shuttles between them, in this case at a rate of k = 2360 s 1 in (CDs CO at 34 °C, measured by JH NMR spectroscopy. It was already noted in Stoddart s seminal 1991 paper that including two stations of different binding affinity in the thread could allow a stimuli-induced change of position of the macrocycle in a molecular shuttle. 

The chemical structures of [2]catenane 19 and the related [3]catenane 20 (Fig. 8) were conceived as an extension of their work on molecular shuttles. The larger macrocycle in 19 comprises two fumaramide stations with differing macro cycle binding affinities. In station B (red) the methyl groups on the fumaramide motif cause it to have lower affinity than the standard fumaramide station. The non-methylated fumaramide station (station A, green) is located next to a benzophenone unit. This allows selective, photosensitized isomerization of station A by irradiation at 350 nm. Station B (red) can be photoisomerized by direct irradiation at 254 nm. The third station, a succinic amide ester (station C, orange), is not photoactive and is intermediate in macrocycle binding affinity between the two fu-... 

In a study of chiral dipeptide [2]rotaxanes it was found that the presence of an intrinsically achiral benzylic amide macrocycle near to the chiral center could induce an asymmetric response in the aromatic ring absorption bands [62], This induced circular dichroism (ICD) effect was stronger in apolar solvents (Fig. 9), where intercomponent interactions are maximized, showing a direct relationship to the tightness with which the macrocycle binds the chiral thread. Computer simulations showed that chirality is transmitted from the amino acid asymmetric center on the thread via the achiral macrocycle to the aromatic rings of the achiral C-terminal stopper. 

We have also synthesized a catalyst related to 131 in which the cyclodextrin rings were replaced with synthetic macrocyclic binding groups [196], Also, we have examined catalysts related to 131 in which substrate binding involved metal ion coordination, not hydrophobic binding into cyclodextrins or macrocycles [198]. 

Below we will concentrate our attention only at the main trends of molecular design that were based upon the original concept of macrocyclic binding. From the very beginning, the strategies of numerous investigations in this field were distinctly different. 

A preformed macrocycle binds the open precursor of a second one inside its cavity to form what could be called a pseudorotaxane. The threading step is then followed by connecting the two ends of the pseudorotaxane with each other in a inacrocyclization reaction. 

The macropolycyclic speleand (30 a) combines the [18]-N303 macrocyclic binding subunit with the cyclotriveratrylene shaping component [23]. Its tight intramolecular cavity allows inclusion of the CH3-NH3 ion yielding the speleate [CH3--NH3 c (30 a)] whose structure should be of the type shown schematically by (30 b). 

Figure 29 (a) Schematic drawing showing a generic allosteric, cooperative interaction of the two macrocycles binding first Na+... 

Initial reports by Lehn and coworkers showed that guanidinium-containing macrocycles bind to phosphate (P03" ) in water." Weak association constants were... 

From the data presented, it is clear that the tetrameric macrocycles bind alpha substituted naphthalene derivatives, simple aromatic compounds or 1-amino-adamantane very poorly, a beta substituted... 

Winkler, J., Coutouli Argyropoulou, E., Leppkes, R. and Breslow, R., Artificial transaminase carrying a synthetic macrocyclic binding group, /. Am. Chem. Soc., 1983,105, 7198-7199. 

Complexation/Decomplexation Kinetics. Though most researchers report that diffusion predominates over complexation/decomplexation kinetics in determining traasport rates, reaction kinetics also play a role (37). The rate at which macrocycles bind to cations is determined principally by two factors-- the charge density of the cation and the degree of preorganization inherent in the macrocycle. 

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