Table of Contents
International Journal of Statistical Mechanics
Volume 2014, Article ID 439891, 11 pages
Research Article

Exact Solution to the Extended Zwanzig Model for Quasi-Sigmoidal Chemically Induced Denaturation Profiles: Specific Heat and Configurational Entropy

1Colegio de Ciencia y Tecnología, Universidad Autónoma de la Ciudad de México-Centro Historico, Fray Servando Teresa de Mier 99, 06080 México, DF, Mexico
2Colegio de Ciencia y Tecnología, Universidad Autónoma de la Ciudad de México-Cuautepec, Avendia la Corona 320 Loma La Palma, 07160 México, DF, Mexico

Received 12 August 2013; Revised 25 November 2013; Accepted 2 December 2013; Published 23 January 2014

Academic Editor: Liao Y. Chen

Copyright © 2014 G. E. Aguilar-Pineda and L. Olivares-Quiroz. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Temperature and chemically induced denaturation comprise two of the most characteristic mechanisms to achieve the passage from the native state to any of the unstructured states in the denatured ensemble in proteins and peptides. In this work we present a full analytical solution for the configurational partition function of a homopolymer chain poly-X in the extended Zwanzig model (EZM) for a quasisigmoidal denaturation profile. This solution is built up from an EZM exact solution in the case where the fraction of native contacts follows exact linear dependence on denaturant’s concentration ; thus an analytical solution for in the case of an exact linear denaturation profile is also provided. A recently established connection between the number of potential nonnative conformations per residue and temperature-independent helical propensity complements the model in order to identify specific proteinogenic poly-X chains, where X represents any of the twenty naturally occurring aminoacid residues. From , equilibrium thermodynamic potentials like entropy and average internal energy and thermodynamic susceptibilities like specific heat are calculated for poly-valine (poly-V) and poly-alanine (poly-A) chains. The influence of the rate at which native contacts denature as function of on thermodynamic stability is also discussed.