This study investigates how bending rigidity governs the thermodynamic pathways of conformational transitions in polymer chains, focusing on the collapse from extended random coils to compact globules and subsequent solidification into ordered phases. Using a coarse-grained model with tunable bending stiffness, we apply a generalized microcanonical inflection-point analysis to identify and classify phase transitions across different energy regimes. The results reveal that while the collapse transition remains resilient to increasing rigidity, the liquid-solid transition undergoes a fundamental transformation.
For flexible polymers (λ = 0), two distinct transitions are observed. The first is a second-order collapse transition characterized by a least-sensitive inflection point in the entropy derivative, corresponding to a sharp drop in the inverse microcanonical temperature. This transition is driven primarily by entropy gain as monomers pack into a denser configuration. The second is a first-order liquid-solid transition, marked by a discontinuity in the first derivative of entropy and accompanied by an independent third-order transition. The resulting solid phase exhibits strong icosahedral symmetry, consistent with the global energy minimum.
As bending stiffness increases (λ = 1), the collapse transition persists with only minor shifts in energy and temperature. However, the liquid-solid transition begins to weaken. The peak in the second derivative of entropy diminishes, and the system no longer exhibits a clear jump in the inverse temperature.PEG10 Antibody Biological Activity Instead, the transition becomes continuous—classified as second-order—indicating a smoother approach to ordering. This suggests that local curvature resistance impedes the formation of sharp structural boundaries required for first-order transitions.
At λ = 2, the liquid-solid transition vanishes entirely. No inflection points are detected in any of the entropy derivatives up to third order, even at very low energies. The system fails to access a unique, highly symmetric ground state. Instead, it settles into a disordered, entangled configuration composed of long, slightly bent segments that minimize curvature. The pair distribution function shows broadened peaks and additional substructures absent in the flexible case, confirming the loss of crystalline order.
Structural analysis confirms this shift. In the flexible chain, the lowest-energy conformation is a perfect icosahedron with uniform nearest-neighbor contacts. For λ = 1, strain develops within the icosahedral framework, distorting bond angles. At λ = 2, the structure completely reorganizes: the chain avoids high-curvature regions by forming extended linear segments that assemble into a coil-like, non-symmetric arrangement.Laropiprant manufacturer Contact maps reveal localized patterns—anti-diagonal streaks indicating hairpin turns and diagonal streaks suggesting helical alignment—reminiscent of protein secondary structures.PMID:34655821
These findings demonstrate that bending rigidity acts as a key regulator of phase stability. While entropy-driven collapse remains robust, mechanical constraints prevent the emergence of long-range order when they outweigh intermonomer attractions. The disappearance of the first-order transition indicates a qualitative change in the thermodynamic landscape: the system transitions from a regime dominated by cooperative ordering to one governed by topological frustration.
The implications extend beyond theoretical interest. In biological systems, such as folded proteins or helical filaments, bending resistance plays a crucial role in determining functional conformations. In synthetic materials, controlling rigidity allows tuning between fluid-like and solid-like behavior without altering chemical composition. This work provides a rigorous framework for predicting phase behavior in finite polymer systems and offers insights for designing responsive materials with programmable self-assembly properties.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
