Related Experiment Videos
Relation between adiabatic and pseudoadiabatic compressibility in ultrasonic velocimetry
1Department of Biochemistry, Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana 61801, USA.
Journal of Theoretical Biology
|July 12, 1995
Summary
Measuring macromolecule compressibility in water is challenging due to heat exchange. This study models heat diffusion, finding small proteins under 10 MHz are near thermal equilibrium, suggesting isothermal conditions for sound velocity measurements.
Area of Science:
- Physical Chemistry
- Biophysics
- Acoustics
Background:
- Adiabatic compressibility measurements of macromolecules in aqueous solution are complicated by unknown heat exchange between the molecule's interior and the bulk solvent.
- Standard methods often yield pseudo-adiabatic compressibility, falling between isothermal and adiabatic values, influenced by experimental conditions.
Purpose of the Study:
- To develop a model for estimating deviations from adiabatic conditions in sound velocity measurements of macromolecules.
- To quantify the impact of heat exchange on compressibility measurements.
Main Methods:
- A theoretical model treating macromolecules as heat-conductive spheres was employed.
- Analytical solutions for temporal and local heat diffusion were derived to analyze heat exchange dynamics.
Main Results:
- Proteins under 100 kDa at sound frequencies below 10 MHz exhibit near-complete thermal equilibrium with the surrounding solvent.
- The model predicts that sound velocity measurements in aqueous protein solutions (T <= 25°C, concentration < 2%) approach isothermal conditions for these proteins.
Conclusions:
- The proposed model provides a framework for understanding and correcting for heat exchange effects in compressibility measurements.
- For specific conditions (small proteins, low frequency, moderate temperature/concentration), sound velocity measurements effectively reflect isothermal compressibility.