Liquids do exert pressure on small, immersed particles, such as nanotubes[1]. The magnitude of this solvation pressure is closely related to a parameter called the cohesive energy density (CED)[2]. We report the equality of solvation pressure and external pressure in the case of molecular and biological samples.
Raman spectra of chloroform were measured as a function of concentration in various solvents, under hydrostatic pressure applied by a diamond anvil cell and in the vapour phase. It was found that the peak shifts due to solvation pressure matched the shifts obtained by hydrostatic pressure for some vibrational modes of chloroform.
Starch grains were subjected to different solvation pressures by placing them in water-ethanol mixtures. The pressure induced gelation of starch grains was then observed as a function of applied pressure. It was found that the sum of CED and gelation pressure is constant[2]. Here we report data on water-ethanol-glycerol mixtures, again the sum of CED and applied pressure remained constant, except for high glycerol concentration.
Protein unfolding was also studied under external applied pressure. The proteins were immersed in ethanol-water, glycerol-water solutions and a hydrostatic pressure was applied. The unfolding of the protein was recorded using tryptophan fluorescence. Preliminary results suggest a strong correlation between the internal pressure of the solution and the unfolding pressure in the regime of low ethanol-glycerol concentration.
[1] J. R. Wood et al., J. Phys. Chem. B 103 (1999), 10388
[2] N.W.A. van Uden et al., Journal of Physics: Condensed Matter 15 (2003), 1577
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