Julie K. Cope and Dr. Roger G. Harrison, Chemistry
Cavitand [Co412]-8 is a cage-like molecule having an inner cavity with a volume of approximately 1375 Å that traps small organic molecules. The “1” in the chemical formula represents resorc[4]arene, a bowl-shaped molecule1. Two resorc[4]arenes are connected with four cobalt molecules to form the cavitand [Co412]-8. Experiments were conducted in which resorc[4]arene was mixed with a small organic guest, then cobalt was added to connect the cage and trap the organic guests. These experiments were conducted in a calorimeter and the heat of the reaction was measured. From this data one is able to calculate the heat released during encapsulation and to formulate a hypothesis as to the mechanism of binding.
The first calorimetric experiments attempted to determine the concentration of cobalt that would yield an enthalpy of binding which would register on the calorimetric scale. The standard experiment was determined to be approximately 50 injections of 10.00øl(micro liters) of 0.7823g/L cobalt mixture at approximately 6-minute intervals into a solution of 0.100mg resorc[4]arene dissolved in 1.00ml distilled water.
Then experiments were conducted which determined the heat released when the resorc[4]arene was closed without any organic guests present. This data was used as the control (See attachment “cotobowl5-19”).
Next, the heat of dilution was determined. The heat of dilution is like a control; it is the heat that is released when a salt solution is added to resorc[4]arene. To determine the heat of dilution, a solution of KCl was added to 0.100mg resorc[4]arne dissolved in 1.00 ml distilled water. The KCl solution was balanced to be stoichiometrically equivalent to the cobalt solution (See attachment “kcltobowl”).
Lastly, experiments were attempted in which organic guests were trapped by the closing resorc[4]arenes. By subtracting the heat of dilution from the heat released when the organic guests were trapped, a net enthalpy of the reaction could be determined (See attachments “cotoethacetateandbowl5-15” and “cototolueneandbowl5-17” for graphic representation of the cavitand enclosing ethyl acetate and toluene, respectively).
The data obtained will give the ÄH and ÄG of each reaction. Another member of the research group is now determining these thermodynamic values. The fact that the energy released after each injection changes over time gives us valuable clues as to the exact mechanism by which this cavitand and other metal-assembled cavitands trap small organic molecules.