  Thermodynamics of helix-coil transitions in amino-acid homo-oligomers are
studied by the recently proposed multicanonical algorithms. Homo-oligomers of
length 10 are considered for three characteristic amino acids, alanine (helix
former), valine (helix indifferent), and glycine (helix breaker). For alanine
other lengths (15 and 20) are also considered in order to examine the length
dependence. From one multicanonical production run with completely random
initial conformations, we have obtained the lowest-energy conformations and
various thermodynamic quantities (average helicity, Zimm-Bragg $s$ and $\sigma$
parameters, free energy differences between helix and coil states, etc.) as
functions of temperature. The results confirm the fact that alanine is
helix-forming, valine is helix-indifferent, and glycine is helix-breaking.
