Self‐assembly of bioelastomeric structures from solutions: Mean‐field critical behavior and Flory–Huggins free energy of interactions

Abstract

Elastic and quasi-elastic light scattering studies were performed on aqueous solutions of poly(Val-Pro-Gly-Gly), a representative synthetic bioelastomer that differs from the previously studied poly(Val-Pro-Gly-Val-Gly) by the deletion of the hydrophobic Val in position four. When the spinodal line was approached from the region of thermodynamic stability, the intensity of light scattered by fluctuations, and the related lifetime and correlation length, were observed to diverge with mean-field critical exponents for both systems. Fitting of the experimental data allowed determining the spinodal and binodal (coexistence) lines that characterize the phase diagrams of the two systems, and it also allowed a quantitative sorting out of the enthalpic and entropic contributions to the Flory-Huggins interaction parameters. The contribution of valine is derived by comparison of the two cases. This can be viewed as sorting out the effect of a modulation of the solute. The same approach may allow sorting out the entropic and enthalpic effect of modulations of the solvent by cosolutes (or by cosolvents). This could be of particular interest in the case of small osmolytes, affording important adaptive roles in nature, at the cost of very limited changes in genetic information. Finally, the suggestion is further supported that statistical fluctuations of anomalous amplitude, such as those occurring in proximity of the spinodal line, have a role in promoting the process of self-assembly of extended supramolecular structures. On the practical side, the present approach appears useful in the design of novel synthetic model systems for bioelastomers.

Lysozyme crystallization rates controlled by anomalous fluctuations

“…In agreement with early suggestions based on experimental evidence [10][11][12][13][14][15][16][17][18], we assume a two-step nucleation process [22,[46][47][48]: first, the generation by fluctuations of (still liquid) transient clusters of high protein concentration and, second, the self-arrangement of the clustered proteins into a nucleus already having an ordered structure. In the present model we take explicitly into account the lifetimes of anomalous fluctuations.…”

“…In fact, subsequent differentiation is due to the energetics of specific and permanent inter-protein contacts in the post-nucleation stage, as distinct from the statistically sampled contacts occurring in the transient subcritical assemblies characterizing the pre-nucleation stage [8,10]. In the past, ample experimental evidence had shown the role of liquid-liquid demixing (LLD) of the solution, as well as that of associated anomalous (critically diverging) fluctuations in initiating aggregation of proteins and other biopolymers [11][12][13][14][15][16][17][18]. More recently, experiments have evidenced a role of actual demixing in promoting protein crystal nucleation [19][20][21].…”

Interacting processes in protein coagulation

“…Here a nucleated or a spinodal demixing occurs, respectively, generating a mesoscopic pattern of higher and lower concentration regions. Similarly to several other known cases of not necessarily peptidic polymers, cross‐linking/coagulation is promoted in demixed high‐concentration regions 6–13. In turn, cross‐linking/coagulation prevents further diffusion of polymers and therefore it freezes‐in or interferes with the demixed pattern 6–9, 14.…”

“…Their critically divergent amplitude and lifetime can be described in terms of mean field critical exponents 15. In San Biagio et al6, they have been used for determining the spinodal line shown in They can be viewed as a transient demixing of longer and longer lifetime and in several systems they have been shown to be as effective as permanent demixing in promoting coagulation 11, 12…”

Elastin: a representative ideal protein elastomer

“…with the curvature of the coexistence line convex to the volume fraction axis (Sciortino et al 1993;Manno et al 2001). Conversely, the usual circumstance for polymers is for the coexistence line to be concave to the volume fraction axis and for the polymer to be insoluble below and soluble above the coexistence line (Flory 1953).…”