Theoretical study of temperature induced transition and hyper stability of collagen mimics Onkar Prasad a , Leena Sinha b, * , Govind P. Gupta a , Neeraj Misra a , Chaman Mehrotra a , Ramesh C. Agnihotri c , J.N. Lal a a Department of Physics , University of Lucknow, Lucknow 226007, India b Department of Physics , Mahila, P.G. College, Ganga Prasad Marg, Aminabad, Lucknow 226018, India c S.I.E.T., Lucknow, India Received 6 December 2005; received in revised form 6 January 2006; accepted 6 January 2006 Abstract Collagen a polymer, is the nature’s most abundant protein. It has an immense tensile strength and is the main constituent of ligaments, tendons, etc. The present communication interprets the experimental data of thermally induced transition in collagen mimics as reported by Steven K. Holmgren and co-workers. The theoretical transition curves as obtained by the modified Zimm and Bragg model are found to be in good agreement with the experimental data. The order of the values of nucleation parameter and enthalpy changes obtained theoretically, attributes the increase in the degree of the stability of collagen mimics [(Pro–Pro–Gly) 10 h(Pro–Hyp–Gly) 10 h(Pro–Flp–Gly) 10 ]. q 2006 Elsevier Ltd. All rights reserved. Keywords: Collagen; Nucleation parameter; Stability 1. Introduction Collagens constitute a super-family of structural proteins of the extra-cellular matrix. There are hardly few other proteins in the nature with such regularity. The sequence in each chain of the collagen is predominantly repeats of (X– Y–Gly), in a left handed helical chain and these polypeptide chains in turn form a right handed triple helix. The first and the second positions of the repeat are more oftenly occupied by L-proline [Pro] and 4(R)-hydroxy-L-proline [Hyp], respectively. The expression of collagens in all tissues of the living organism has made the collagen a distinct/novel model of great interest from the viewpoint of molecular dynamics of polypeptides and proteins [1–16]. Steven K. Holmgren and co-workers experimentally studied the temperature induced transition in collagen mimics and they found that the stability of (Pro–Flp– Gly) 10 far exceeds the stability of any other known collagen of similar size [17]. The present communication explains the phenomenon of temperature induced transition in the various collagen mimics and their relative thermal stabilities, using the modified Zimm and Bragg model of helix4coil (order4disorder) transition, as reported in our recent publications in this journal [18,19], where the Zimm and Bragg model [20] was modified to explain the temperature induced transition in poly (b-benzyl-L- aspartate) [PBLAsp] [18] and in it’s copolymer as well as pressure induced transition in polystyrene–polybutadiene [PS–PB] [19], a synthetic diblock copolymer. 2. Theory The collagen has been treated here as two phase system. The Zimm and Bragg model for helix4coil (order4disorder) transition [20] has been modified to explain the thermal hyper- stability of the collagen mimics. An expression for degree of order Q is obtained from the grand partition function for entire chain in terms of nucleation parameter. Taking into account the nearest-neighbour interactions, the basic transition matrix M is given below. M Z h r h 1 ss r 1 s Polymer 47 (2006) 1674–1677 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.01.010 * Corresponding author. Tel.: C91 522 238 5148. E-mail addresses: onkarprasad@hotmail.com (O. Prasad), leenasinha@ hotmail.com (L. Sinha).