Dendrimer reversible binding

In particular, rotaxane dendrimers capable of reversible binding of ring and rod components, such as Type II, pseudorotaxane-terminated dendrimers, can be reversibly controlled by external stimuli, such as the solvent composition, temperature, and pH, to change their structure and properties. This has profound implications in diverse applications, for instance in the controlled drug release. A trapped guest molecule within a closed dendrimeric host system can be unleashed in a controlled manner by manipulating these external factors. In the type III-B rotaxane dendrimers, external stimuli can result in perturbations of the interlocked mechanical bonds. This behavior can be gainfully exploited to construct controlled molecular machines. 

These structural characteristics mean that the dendrimer porphyrin can be used to mimic the function of the heme protein - its ability to bind to oxygen. A dendrimer porphyrin with an Fe(II) ion can stably trap oxygen via coordination with imidazole ligands. The oxygen was reversibly trapped within the dendrimer, and it can be released when the oxygen in the surrounding solvent was removed. The dendrimer sphere shields the porphyrin part from the outer environment. Therefore, side effects such as irreversible oxidation of the porphyrin by water and dimerization of the oxygen-bound porphyrins can be suppressed. 

In addition to inhibiting viral binding, dendrimers have been shown to exhibit the ability to disturb the replication of viruses. Amine-terminated PAMAM dendrimers have been reported to interact with transacting response elements RNA, which affected the viral replication.[156] Moreover, viral protease and reverse transcriptase were inhibited by carboxylated fullerene-based dendrimers and sulfonated dendrimers, respectively.[157]... 

Dioxygen binding is one of the natural phenomena that have been pursued by many researchers. The 4th generation dendrimer 1 depicted in Fig. 21 shows the ability to bind and release dioxygen reversibly depending on the atmosphere [100]. It is believed that the crowded dendritic structure avoids formation of porphyrin p-0X0 dimers and consequent auto-oxidation stabilizing the dioxygen complex. 

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