Base uncaps nanovalve

A simple change in pH is all that's needed to open up a new supramolecular nanovalve created by chemists at UCLA (Org. Lett. 2006, 8, 3363). To construct the nanovalves, the researchers attach naphthalene-containing dialkylammonium tethers to mesoporous silica particles (gray in the graphic shown). After filling the pores with a payload of coumarin 460 (yellow spheres), the system is capped off with large macrocyclic polyethers (red rings), which encircle the tethers by hydrogen-bonding to the dialkylammonium ions (blue). Adding base deprotonates these ions and disrupts the noncovalent interactions between the crown ether and the tether. The crown ether then unthreads from the tether, releasing the pores' payload. Different bases have different rates of release, according to the study. Sterically bulky bases tend to open the nanovalves more slowly than do less bulky counterparts. The UCLA team, led by J. Fraser Stoddart and Jeffrey I. Zink, says nanovalves of this kind could have applications in drug delivery.