Stoddart Mechanostereochemistry Group





Stoddart Mechanostereochemistry Group



A great advantage to many of the bistable systems created in the Stoddart labs is that they are switchable only on demand. Despite the obvious utility in molecular electronics, these systems can be anchored to various surfaces and the same controlled switchability can be replicated.1 By utilizing the well-understood complexation between CBPQT4+ and BHEEN, a simple pseudorotaxane system has be created2 at the surface of mesoporous silica nanoparticles (MCM-41), which can act as a valve that opens and closes upon the introduction of an appropriate stimulus such as electrochemical, redox or even light (with the use of photosensitizers).

To take this idea further, we have shown repeated release using a fully reversible system based on a bistable rotaxane after a chemical redox stimulus.3 We can therefore envision trapping guest molecules (i.e. drugs) in the pores of the functionalized MCM-41 and releasing them on demand and only on demand. By using different molecular systems to functionalize the mesoporous silica nanoparticles, the release can also be activated4 using pH control. All the work using mesoporous silica is performed in collaboration with the group of Professor Jeffrey Zink.

Multivalent Aggregation Inhibitor

Self-assembled pseudopolyrotaxanes consisting of lactoside-displaying cyclodextrin (CD) "beads" threaded onto linear polyviologen "strings" have been investigated5 for their ability to inhibit galectin-1-mediated T-cell agglutination. The CDs of the pseudopolyrotaxane are able to spin around the axis of the polymer chain as well as to move back and forth along its backbone to alter the presentation of its ligand. This supramolecular superstructure incorporates all the advantages of polymeric structures, such as the ability to span large distances, along with a distinctively dynamic presentation of its lactoside ligands to afford a neoglycoconjugate that can adjust to the relative stereochemistries of the lectin's binding sites.

The pseudopolyrotaxane exhibited a valency-corrected 10-fold enhancement over native lactose in the agglutination assay, which was greater than the enhancements observed for traditional lactoside-bearing trivalent glycoclusters and a lactoside-bearing chitosan polymer tested using the same assay. The experimental results indicated that supramolecular architectures, such as pseudopolyrotaxanes, provide tools for investigating protein-carbohydrate interactions.

In the course of this research, it was found6 that polyviologens are responsive to the Bradford assay, which is traditionally highly selective for proteins. The response of the pseudopolyrotaxanes to the Bradford assay was dependant on, and thus indicative of, the degree of threading of the CD rings onto the polyelectrolyte. The assay was then used to report on the threading and dethreading of native and lactoside-bearing a-CD rings onto and off of polyviologen chains, a phenomenon which demonstrates the utility of biochemical assays to address problems unique to supramolecular chemistry.


  1. (a) Chia, S. Y.; Cao, J. G.; Stoddart, J. F.; Zink, J. I., "Working Supramolecular Machines Trapped in Glass and Mounted on a Film Surface," Angew. Chem. Int. Ed. 2001, 40, 2447. (b) Saha, S.; Johansson, L. E.; Flood, A. H.; Tseng, H.-R.; Zink, J. I.; Stoddart, J. F. Small 2005, 1, 87-90. (c) Saha, S.; Johansson, L. E.; Flood, A. H.; Tseng, H.-R.; Zink, J. I.; Stoddart, J. F., Chem. Eur. J. 2005, 11, 6846-6858.

  2. Hernandez, R.; Tseng, H.-R.; Wong, J. W.; Stoddart, J. F.; Zink, J. I. J. Am. Chem. Soc. 2004, 126, 3370-3371.

  3. Nguyen, T. D.; Tseng, H.-R.; Celeste, P. C.; Flood, A. H.; Liu, Y.; Stoddart, J. F.; Zink, J. I. Proc. Natl. Acad. Sci. USA 2005, 102, 10029-10034.

  4. (a) Nguyen, T. D.; Leung, K. C.-F.; Liong, M.; Pentecost, C. D.; Stoddart, J. F.; Zink, J. I. Org. Lett. 2006, 8, 3363-3366. (b) Leung, K. C.-F.; Nguyen, T. D.; Stoddart, J. F.; Zink, J. I. Chem. Mater. 2006, ASAP Article.

  5. Nelson, A.; Belitsky, J. M.; Vidal, S.; Joiner, C. S.; Baum, L. G.; Stoddart, J. F. "A Self- Assembled Multivalent Pseudopolyrotaxane for Binding Galectin-1," J. Am. Chem. Soc. 2004, 126, 11914-11922.

  6. Belitsky, J. M.; Nelson, A.; Stoddart, J. F., "Monitoring cyclodextrin-polyviologen pseudopolyrotaxanes with the Bradford Assay," Org. Biomol. Chem. 2006, 4 , 250-256.

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