Stimuli-Responsive Nanostructures

Transformersomes

In 2008 we reported the synthesis of our first metal-organic capsule through self-assembly of commercially available 2-formylpyridine and 4,4'-diaminobiphenyl-2,2'-disulfonic acid with iron(II) in presence of base.[1] The crystal structure of the resulting tetrahedral [Fe4L6] cage (solved in collaboration with Kari Rissanen) demonstrates the utility of subcomponent self-assembly in bringing about a large increase in structural complexity with relative ease; provided that the parameters guiding the self-assembly process are understood. The structure revealed the presence of a hydrophobic central cavity which was shown to accommodate a variety of neutral guests in water via the hydrophobic effect. Guests can be released under acidic conditions followed by reassembly of the capsule upon addition of base, thus providing a reversible way of “unlocking” and “relocking” the host. A striking example of this capsule’s ability to modulate guest reactivity was provided by the isolation of its air-stable complex with ordinarily-pyrophoric white phosphorus (P4), as we reported in Science.[2] The phosphorus could be readily extracted through addition of a competing guest benzene. This cage is also capable of selectively binding and sequestering the potent greenhouse gas SF6 from a mixture of gases, preventing the climatic impact of releasing it into the atmosphere,[3] and has been used as a whole molecule ‘supramolecular protecting group’.[4]

 

1. P. Mal, D. Schultz, K. Beyeh, K. Rissanen, J. R. Nitschke, Angew. Chem. Int. Ed. 2008, 47, 8297–8301.

2. P. Mal, B. Breiner, K. Rissanen and J. R. Nitschke Science 2009, 324, 1697–1699.

3. I. A. Riddell, M. M. J. Smulders, J. K. Clegg and J. R. Nitschke, Chem. Commun. 2010, 47, 457–459.

4. M. M. J. Smulders and J. R. Nitschke, Chem. Sci.2012, 3, 785–788.

Supramolecular ​structural transformations

In 2008 we reported the synthesis of our first metal-organic capsule through self-assembly of commercially available 2-formylpyridine and 4,4'-diaminobiphenyl-2,2'-disulfonic acid with iron(II) in presence of base.[1] The crystal structure of the resulting tetrahedral [Fe4L6] cage (solved in collaboration with Kari Rissanen) demonstrates the utility of subcomponent self-assembly in bringing about a large increase in structural complexity with relative ease; provided that the parameters guiding the self-assembly process are understood. The structure revealed the presence of a hydrophobic central cavity which was shown to accommodate a variety of neutral guests in water via the hydrophobic effect. Guests can be released under acidic conditions followed by reassembly of the capsule upon addition of base, thus providing a reversible way of “unlocking” and “relocking” the host. A striking example of this capsule’s ability to modulate guest reactivity was provided by the isolation of its air-stable complex with ordinarily-pyrophoric white phosphorus (P4), as we reported in Science.[2] The phosphorus could be readily extracted through addition of a competing guest benzene. This cage is also capable of selectively binding and sequestering the potent greenhouse gas SF6 from a mixture of gases, preventing the climatic impact of releasing it into the atmosphere,[3] and has been used as a whole molecule ‘supramolecular protecting group’.[4]

 

1. P. Mal, D. Schultz, K. Beyeh, K. Rissanen, J. R. Nitschke, Angew. Chem. Int. Ed. 2008, 47, 8297–8301.

2. P. Mal, B. Breiner, K. Rissanen and J. R. Nitschke Science 2009, 324, 1697–1699.

3. I. A. Riddell, M. M. J. Smulders, J. K. Clegg and J. R. Nitschke, Chem. Commun. 2010, 47, 457–459.

4. M. M. J. Smulders and J. R. Nitschke, Chem. Sci.2012, 3, 785–788.

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