THERMODYNAMICS OF HELIX-COIL TRANSITIONS IN AMINO-ACID HOMOPOLYMERS STUDIED BY MULTICANONICAL ALGORITHMS

Thermodynamics of helix-coil transitions in amino-acid homopolymers ar e studied by the multicanonical algorithms. Homopolymers of length 10 are considered for three characteristic amino acids, alanine (helix fo rmer), valine (helix indifferent), and glycine (helix breaker). For al anine other lengths (15 and 20) are also considered in order to examin e the length dependence. From one multicanonical production run with c ompletely random initial conformations, we have obtained various therm odynamic quantities (average helix length, specific heat, etc.) as fun ctions of temperature. The results, though preliminary, suggest that t he helix-coil transition for poly-alanine is second-order, while the n ature of phase transition is not clear for poly-valine and poly-glycin e.