ITC analysis of guest binding to a deep-cavity cavitand

Abstract

Using the recommended modifications to isothermal titration calorimetry (ITC) analysis proposed by Turnbull and Daranas (J. Am. Chem. Soc. 2003, 125 14859–14866) and Tellinghuisen (Anal. Biochem. 2008, 373, 395–397), we determine the thermodynamic data for the binding of a series of halogenated guests to deep-cavity cavitand 1. These modifications allowed the accurate determination of the thermodynamic data of systems with c values of between 0.2 and 5; values that are much lower than is often suggested as the lower limit of ITC. The compiled data allowed a more accurate glimpse of the strength of the unusual C–H…X–R hydrogen bonds observed between these hosts and halogenated guests.

Keywords:

• resorcinarene
• deep-cavity cavitand
• isothermal titration calorimetry

Acknowledgements

H.G. and B.C.G. acknowledge the financial support of the NSF (CHE-0718461) and the Post-Katrina Support Fund Initiative (PKSFI, LEQSF (2007-12)-ENH-PKSFI-PRS-04) for the support of this work.

Notes

^1. The host is soluble up to approximately 1 mM (the concentration used for binding constant determination by NMR). However, at this concentration, the ITC data obtained was poor. We suspect that over the time frame of the ITC experiment (which is longer than that of the NMR experiment) some amount of the host precipitated out of solution causing poor fitting of the data.