Nanotechnology Provides a New Perspective on Chemical Thermodynamics

Abstract

A small mechanical device, the atomic force microscope, measuring a force and the distance over which this force is applied, can be used on a single polysaccharide molecule to obtain the Gibbs energy of a conformational change within the polysaccharide. This well-defined conformational change within certain types of polysaccharide molecules is analogous to a chemical reaction with an equilibrium constant, Gibbs energy, enthalpy, and entropy applying to the individual molecule. Normally these thermodynamic properties for a substance would be obtained by measuring a heat of reaction and heat capacity and the measurements would be done on a large collection of molecules. It is now possible, with the new tools of nanotechnology, to do this measurement mechanically and on just one molecule. Single-molecule stretching is a fundamentally different way of measuring thermodynamic properties that links, in a simple and remarkable way, the physics of springs and forces with chemical reactions and equilibria. These concepts can be used in undergraduate physical chemistry courses to fascinate students about new ways of understanding physical chemistry and of measuring thermodynamic properties that arise from the techniques of nanotechnology.