RESUMEN

In this paper we revisited the Ziff-Gulari-Barshad model to study its phase transitions and critical exponents through time-dependent Monte Carlo simulations. We use a method proposed recently to locate the nonequilibrium second-order phase transitions and that has been successfully used in systems with defined Hamiltonians and with absorbing states. This method, which is based on optimization of the coefficient of determination of the order parameter, was able to characterize the continuous phase transition of the model, as well as its upper spinodal point, a pseudocritical point located near the discontinuous phase transition. The static critical exponents ß, ν_{∥}, and ν_{⊥}, as well as the dynamic critical exponents θ and z for the continuous transition point, were also estimated and are in excellent agreement with results found in literature.

RESUMEN

The authors study the short-time dynamics of helix-forming polypeptide chains using an all-atom representation of the molecules and an implicit solvation model to approximate the interaction with the surrounding solvent. The results confirm earlier observations that the helix-coil transition in proteins can be described by a set of critical exponents. The high statistics of the simulations allows the authors to determine the exponent values with increased precision and support universality of the helix-coil transition in homopolymers and (helical) proteins.

Asunto(s)

Modelos Químicos , Modelos Moleculares , Péptidos/química , Simulación por Computador , Cinética , Conformación Proteica , Solventes/química

RESUMEN

We study the critical relaxation of the helix-coil transition in all-atom models of polyalanine chains. We show that at the critical temperature the decay of a completely helical conformation can be described by scaling relations that allow us estimating the pertinent critical exponents. The present approach opens a new way for characterizing transitions in proteins and may lead to a better understanding of their folding mechanism. An application of the technique to the 34-residue human parathyroid fragment PTH(1-34) supports universality of the helix-coil transition in homopolymers and (helical) proteins.

Asunto(s)

Modelos Químicos , Modelos Moleculares , Fragmentos de Péptidos/química , Fragmentos de Péptidos/ultraestructura , Péptidos/química , Teriparatido/análogos & derivados , Simulación por Computador , Humanos , Cinética , Movimiento (Física) , Conformación Proteica , Pliegue de Proteína , Teriparatido/química

RESUMEN

We study the early time behavior of the Baxter-Wu model, an Ising model with three-spin interactions on a triangular lattice. Our estimates for the dynamic exponent z are compatible with results recently obtained for two models which belong to the same universality class of the Baxter-Wu model: the two-dimensional four-state Potts model and the Ising model with three-spin interactions in one direction. However, our estimates for the dynamic exponent theta of the Baxter-Wu model are completely different from the values obtained for those models. This discrepancy could be related to the absence of a marginal operator in the Baxter-Wu model.