Volume and Expansivity Changes of Micelle Formation Measured by Pressure Perturbation Calorimetry

Abstract

We present the application of pressure perturbation calorimetry (PPC) as a new method for the volumetric characterization of the micelle formation of surfactants. The evaluation is realized by a global fit of PPC curves at different surfactant concentration ranging, if possible, from below to far above the CMC. It is based on the knowledge of the temperature dependence of the CMC, which can for example be characterized by isothermal titration calorimetry. We demonstrate the new approach for decyl-β-maltopyranoside (DM). It shows a strong volume increase upon micelle formation of 16 ± 2.5 mL/mol (+4%) at 25 °C, and changes with temperature by -0.1 mL/(mol K). The apparent molar expansivity (E(S)) decreases upon micelle formation from 0.44 to 0.31 mL/(mol K) at 25 °C. Surprisingly, the temperature dependence of the expansivity of DM in solution (as compared with that of maltose) does not agree with the principal behavior described for polar (E(S)(T) decreasing) and hydrophobic (E(S)(T) increasing) solutes or moieties before. The results are discussed in terms of changes in hydration of the molecules and internal packing of the micelles and compared with the volumetric effects of transitions of proteins, DNA, lipids, and polymers.

Physicochemical Insights into the Role of Drug Functionality in Fibrillation Inhibition of Bovine Serum Albumin

“…When pressure is applied to protein at different stages of fibrillation, the change in heat (ΔQ) reflects on their volumetric properties in terms of the relative change in volume (ΔV/V) and the thermal expansion coefficient (α). 56,[58][59][60][61][62][63]65,66…”

“…Hydrophilic moieties exhibit more negative α values, whereas the positive values indicate significant hydrophilic content in the structure. 56,[58][59][60][61][62][63]65,66 The negative and positive slopes in the plot of α against temperature have been associated with the exposure of polar and hydrophobic residues of the protein, respectively. 56,[58][59][60][61][62][63]65,66 For example, in the protein with polar side chains such as asparagine, glutamine, serine, histidine, and glutamic acid, α is large and positive at low temperatures and its values decrease with the rise in temperature.…”

“…56,[58][59][60][61][62][63]65,66 The negative and positive slopes in the plot of α against temperature have been associated with the exposure of polar and hydrophobic residues of the protein, respectively. 56,[58][59][60][61][62][63]65,66 For example, in the protein with polar side chains such as asparagine, glutamine, serine, histidine, and glutamic acid, α is large and positive at low temperatures and its values decrease with the rise in temperature. 56,[58][59][60][61][62][63]65,66 Further, the α values for aromatic side chains of tryptophan and phenyl alanine display only a small temperature dependence compared with aliphatic side chains.…”

Molecular determinant of the effects of hydrostatic pressure on protein folding stability

“…Biomacromolecules (proteins, DNA, RNA, lipid membrane) adopt unique three-dimensional structures (native or folded state) that are required for their biological function. The stability of these structures is very important for their function and thus biomacromolecules need to evolve to remain folded under the respective living conditions 4 10 11 12 . Increasing pressure, much like increasing temperature, perturbs the thermodynamic equilibrium between native folded state, N , and denatured unfolded state, U .…”

A study of the relationship between water and anions of the Hofmeister series using pressure perturbation calorimetry

“…From this the thermal expansion coefficient (a) of the solute has been calculated and the hydrogen-bond population of the water at the solute-water interface studied. 18,19 This approach has been applied to a diverse range of solutes including polymers, 16 amino acids, 17 small inorganic and organic molecules, 18 proteins, [16][17][18][19][20][21][22][23][24][25][26][27][28] lipid micelles and bilayers, [29][30][31] and nucleic acids. 32,33 The calculation of the thermal expansion coefficient from PPC data assumed a two-state model for water with a relatively low density and a denser liquid species.…”