Living cells can get a lot of chemistry done in some very tight quarters. In fact, if you take the chemical constituents of a cell and try to get them to interact outside of those confines, you will get nothing like the same level of activity.
Cecile Malardier-Jugroot, an associate professor of chemistry and chemical engineering at the Royal Military College of Canada in Kingston, Ont., has spent the past few years weighing the implications of this simple and fundamental observation. By exploring the principle of confinement at the nanometre scale, Malardier-Jugroot is leading a new approach to some major technological challenges.
This work began with a system of biocompatible polymers that can self-assemble to form sheets or tubes resembling biomolecules, with inner cavities on the order of two to three nanometres across. Although the formation of these structures takes place in water, their interior is hydrophobic, much like a cell would be. The structures can serve as a secure repository for tiny amounts of reactants such as nanoparticles of gold or platinum. Here, too, the approach took its inspiration from the arrangement of living cells, which often use a metal centre as a reactive focal point. The effect turned out to be no less dramatic when it was applied in the laboratory. With nanoparticles of platinum(II) chloride (PtCl2) confined in the polymer matrix, for example, their thermokinetic activity soared to five times what it would have been with the effect of confinement alone. “This is the effect of having a hydrophobic molecule confined in a hydrophobic cavity,” says Malardier-Jugroot. “This mimics a biosystem.”
Malardier-Jugroot and her fellow researchers named these cell-like systems nanoreactors, describing their findings in a paper for Chemical Physics Letters, where they also outline some of the surprising qualities that accompanied this innovation. “Usually biosystems are very narrow in their environment range — temperature or pH,” she says. “This system is stable from pH 3 to pH 13. It’s also stable from room temperatures up to 80 C.”
Although the chemical basis of this behaviour has yet to be explained, it represents an environmentally benign and biocompatible means of promoting various types of chemical interactions. Malardier-Jugroot emphasizes the fact that these nanostructures can be fabricated in a controlled setting, which enhances the potential for various applications. She notes that nanoreactors are light sensitive, a feature that could possibly be harnessed to promote other reactions. She is particularly interested in how nanoreactors could improve the efficiency and output of fuel cells. Moreover, if specific molecules can be incorporated into the polymer nanocontainer, these structures could make a highly effective mechanism to deliver drugs to cancerous tumours.
In the meantime, Malardier-Jugroot has been building a network of collaborators who can help her pin down the finer details of how nanoreactors achieve such remarkable results. Her team at RMC specializes in modelling and they have welcomed the analytical expertise of staff at the Canadian Light Source in Saskatoon, the Canadian Centre for Electron Microscopy at McMaster University, NIST Center for Neutron Research in Maryland and a European facility for small angle neutron scattering. “We’re trying to understand what’s happening inside the nanoreactor at the atomic level and explain the effect of confinement on the thermodynamics equilibrium of the reactions,” Malardier-Jugroot says. “It’s been helpful to be able to combine theoretical predictions with experiments at the nanoscale to characterize those interactions.”