Pressure perturbation calorimetry of helical peptides.

Pressure perturbation calorimetry quantifies the temperature dependence of a solute's thermal expansion coefficient, providing information about solute-solvent interactions. We tested the idea that pressure perturbation calorimetry can provide information about solvent-accessible surface area by studying peptides with different secondary structures. The peptides comprised two host-guest series: one predominately an alpha-helix, the other predominately a polyproline II helix. In aqueous buffer, we find a correlation between the amount of secondary structure as assessed by circular dichroism spectropolarimetry and the pressure perturbation calorimetry data. We conclude that pressure perturbation calorimetry can provide information about the exposure of polar and nonpolar surface area. Data acquired in a buffered urea solution, however, are not as easily interpreted.