Osmotic Pressure Induced Coupling between Cooperativity and Stability of a Helix-Coil Transition

Abstract

Most helix-coil transition theories can be characterized by three parameters: energetic, describing the (free) energy cost of forming a helical state in one repeating unit; entropic, accounting for the decrease of entropy due to formation of the helical state; and geometric, indicating how many repeating units are affected by the formation of one helical state. Depending on their effect on the helix-coil transition, solvents or cosolutes can be classified with respect to their action on these parameters. Solvent interactions that alter the entropic cost of helix formation by their osmotic action can affect both the stability (transition temperature) and the cooperativity (transition interval) of the helix-coil transition. Consistent inclusion of osmotic pressure effects in a description of helix-coil transition, for poly(L-glutamic acid) in solution with polyethylene glycol, can offer an explanation of the experimentally observed linear dependence of transition temperature on osmotic pressure as well as the concurrent changes in the cooperativity of the transition.

Exact solution of a classical short-range spin model with a phase transition in one dimension: The Potts model with invisible states

“…The 1D (1, r) case with nearest-neighbour interactions is equivalent to the ZimmBregg model for the helix-coil transition [30]. The multispin extension of this model possesses a re-entrant phase transition and is in good agreement with experimental observations for polymer transitions [31,32]. The (2, r)-state Potts model without external fields is equivalent to the Blume-Emery-Grifiths (BEG) model [19,33,34] with a temperature dependent external field.…”

Macromolecular Stabilization by Excluded Cosolutes: Mean Field Theory of Crowded Solutions

“…27,93,94 Our approach focuses on the entropic and enthalpic components of the molecular-level solution interactions, and thus allows to account for the temperature dependence of the cosolute effect. However, our mean field theory does not account for correlations between molecules.…”

Statistical mechanics of DNA-nanotube adsorption

“…Instead, a line of naive argumentation could lead to the opposite expectations that the presence of extra free ssDNAs in solution will result in the promotion of ssDNA-ssDNA interactions, which should introduce a destabilizing effect onto the ssDNA-CNT complex because of obvious competition between the two targets for adsorption. In view of our previous studies of the osmotic stress effects onto DNA conformations [17], the reported increase in stability of bound conformations finds its explanation as arising because of the increased osmotic stress due to the increased excluded volume effects (crowding) from the free DNA added. Thus, by providing a Statistical Mechanical Hamiltonian to describe the DNA-CNT interaction, which is at the heart of numerous Nano(Bio)technologies, we open the doors for a better understanding of the principles behind the relevant biotechnologies and suggest a route towards the predictable design of nanodevices.…”

“…Using the abovementioned similarity, we make use of models suggested in the past [16][17][18] and describe the adsorption of DNA on CNT with an energy function (Hamiltonian) that depends on the coarse-grained variables of the system. We do so by adopting the Potts-like spin model [18][19][20] to the problem of DNA-CNT association.…”