Premium
A librational entropy mechanism for elastomers with repeating peptide sequences in helical array
Author(s) -
Urry Dan W.,
Venkatachalam Cherayathumadom M.
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560240711
Subject(s) - pentamer , elastomer , chemical physics , chemistry , intermolecular force , trimer , entropy (arrow of time) , polymer , titin , physics , thermodynamics , molecule , dimer , biochemistry , organic chemistry , medicine , sarcomere , myocyte , endocrinology
A librational entropy mechanism is proposed for the elastomeric polypentapeptide of elastin which derives from the particular properties of a previously described dynamic β‐spiral structure comprised of the repeating pentamer sequence. Using a cutoff energy of 2 kcal/mol residue, it is shown that the number of conformational states accessible to a single pentamer segment without perturbing the rest of the β‐spiral is large in the relaxed state but becomes greatly decreased on extension. With use of the Boltzmann relation, it is seen that the effect of identical repeating units in a dynamic β‐spiral is to linearly increase the entropy as the chain length increases. This occurs in spite of the valyl and prolyl side chains that significantly limit the states of the polymer and the Pro‐Gly sequence which inserts a flexible β‐turn. The aggregated states of the dynamic β‐spiral with their weak hydrophobic intermolecular interactions that occur at high concentrations of chains and at physiologic temperatures are presented as an effective means of avoiding the entanglements that can limit numbers of accessible states for a concentrated random tangle of chains. Thus, a new mechanism is presented for an entropic elastomer which does not require that the relaxed state be totally random.