Abstract
Self-assembly of macromolecules with ligands is an intricate dynamic process that depends on a wide variety of parameters and forms the basis of many essential biological processes. We elucidate the underlying energetic processes of self-assembly in a model system consisting of amphiphilic core-shell polymers interacting with paramagnetic, amphiphilic ligand molecules from temperature-dependent continuous wave electron paramagnetic resonance (CW EPR) spectroscopy subsequent to spectral simulation. The involved processes as observed from the ligands’ point of view are either based on temperature-dependent association constants (KA,j,k) or dynamic rotational regime interconversion (IC) constants (KIC,j,k). The interconversion process describes a transition from Brownian (b1) towards free (b2) diffusion of ligand. Both processes exhibit non-linear van’t Hoff (lnK vs. T−1) plots in the temperature range of liquid water and we retrieve decisive dynamic information of the system from the energetic fingerprints of ligands on the nanoscale, especially from the temperature-dependent interconversion heat capacity (∆C°P,IC).
Highlights
Thermodynamic profiles of macromolecules are nowadays routinely obtained with calorimetric methods
While differential scanning calorimetry (DSC) directly monitors phase transition temperatures (Tm ) [1] and molar heat capacity changes (∆CP ) [2], isothermal titration calorimetry (ITC) delivers a quantitative account of interactions in solution, such as small molecule binding to macromolecules with their corresponding binding stoichiometry (N), association constants (KA ) and molar enthalpy changes (∆H) [3]
This study offers a general treatise concentrating exclusively on ligand binding thermodynamics while proving an unconventional strategy to advance towards an EPR-based quantification of the physical driving forces of ligand binding to macromolecules
Summary
Thermodynamic profiles of macromolecules are nowadays routinely obtained with calorimetric methods. While differential scanning calorimetry (DSC) directly monitors phase transition temperatures (Tm ) [1] and molar heat capacity changes (∆CP ) [2], isothermal titration calorimetry (ITC) delivers a quantitative account of interactions in solution, such as small molecule binding to macromolecules with their corresponding binding stoichiometry (N), association constants (KA ) and molar enthalpy changes (∆H) [3]. Depending on the macromolecular system the resulting thermodynamic quantities (∆H, ∆S = molar entropy changes, ∆G = molar free energy changes, ∆CP ). The van’t Hoff plot will be linear [4]. The observation of non-linear van’t Hoff plots was first reported by Brandts [5] and several other groups [6,7], subsequently. Several strategies have been developed to extract thermodynamic parameters from curves deviating from linearity
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