1) A binding constant determination for NaCl to crown ether 1 was done by titrating

NaCl into an aqueous solution of the host monitoring chemical shift changes by

HNMR

a) Why would it be important to control ionic strength in this experiment? (Note:

ionic strength is the net concentration of ions in solution.)

b) The researchers repeated the experiment using a concentration of 1 M KCIO4.

However, they found that while binding was observable without KCIO4, no

binding was observed in the presence of KCIO4. Why was the likely problem?

c) When the researchers controlled ionic strength using Me4N* CIO4, they were able

to observe a saturation binding isotherm. However, when they used Me,N* Cl to

control ionic strength, they observed a different binding constant. Give a possible

explanation for this difference.

d) Make a prediction as to whether stronger or weaker binding would be observed

the solution containing Me4N* CIO4 versus the one containing Me4N* Cl. Justify

your answer.