Guest solubility

This supramoleeular tenant, defined by J.M. Lehn, is classically exhibited by the action of a micelle, whereby surfactant molecules aggregate into a globular motif that is capable of enhancing molecular guests solubilities or acting as nanoscale reactors and transport vehicles, to mention but a few utilities. The micelle architecture, as well as the lipophilic-hydrophilic character, leads logically to the consideration of dendrimers as supramolec-ular components this potential is herein chronicled. 

In fact, studies of guest desorption kinetics [111,138] and of gas transport [97,144,145] on SPS films have shown that the guest solubility can be much higher in the crystalline phase (mainly for low-solute activities) while the solute diffusivity is generally much higher in the amorphous phase. This offers the opportunity to prepare and characterize samples including low-molecular-mass molecules essentially only as guests of the host crystalline phase. 

A carboxylate derivative of a fully aromatic, water-soluble, hyperbranched polyphenylene is considered as a unimolecular micelle due to its ability to complex and solubilize non-polar guest molecules [23]. The carboxylic acid derivative of hyperbranched polyphenylene polymer (HBP) (My,=5750-7077, Mn=3810-3910) consists of 40-60 phenyl units that branch outward from a central point forming a roughly spherical molecule with carboxylates on the outer surface. The free acid form of HBP was suspended in distilled water and dissolved by adding a minimum quantity of NaOH. The solution was adjusted to pH 6.2 with aqueous HCl. Calcium carbonate crystals were growth from supersaturated calcium hydrogencarbonate solution at room temperature. HBP gave... 

In 1994 we published the first chiral dendrimers built from chiral cores and achiral branches [ 1,89], see for instance dendrimer 57 with a core from hydroxy-butanoic acid and diphenyl-acetaldehyde and with twelve nitro-groups at the periphery (Fig. 21). As had already been observed with starburst dendrimers, compound 57 formed stable clathrates with many polar solvent molecules, and it could actually only be isolated and characterized as a complex [2 (57- EtO-Ac (8 H20))]. Because no enantioselective guest-host complex formation could be found, and since compounds of type 57 were poorly soluble, and could thus not be easily handled, we have moved on and developed other systems to investigate how the chirality of the core might be influencing the structure of achiral dendritic elongation units. 

Unlike the crystalline cycloamylose complexes, combining ratios of host to guest in solution are usually 1 1. A notable exception is the interaction of the cycloamyloses with long chain aliphatic carboxylic acids. Solubility plots suggest that as many as four cycloheptaamylose molecules may interact with a single molecule of dodecanoic acid (Schlenk and Sand, 1961). In analogy to the crystalline state, cycloamyloses may form channels in solution in order to accomodate extended chains. 

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