G. Nemethy et al., ON THE LEVEL DISTRIBUTION OF PERIODIC AND NONPERIODIC COLLAGEN MODELS, Journal of molecular structure. Theochem, 337(2), 1995, pp. 103-107
The negative factor counting method in its matrix block form is used t
o calculate the total electronic density of states (DOS) of different
collagen models. The computations have been executed for periodic and
non-periodic eight-component collagen models consisting of (glycine, p
roline, hydroxypoline and alanine) together with glutamine, arginine,
leucine and aspartic acid. The Fock and overlap matrices of the whole
systems (containing 1014 amino acid residues) have been built up from
ab initio Hartree-Fock dimer calculations (29 different dimers). In co
nstructing these matrices both for the periodic and non-periodic cases
, the well known sequence regularities of collagen have been taken int
o account. The conformation of the chain has been taken from a collage
n-like model triple helix, Nemethy and Scheraga having determined the
conformation of this triple helix with the aid of empirical potential
energy calculations. The DOS histogram of periodic (Gly-X-Y) triplets
(similar to the previous six-component case) shows only very narrow pe
aks in both the valence band and conduction band regions. As a next st
ep the 20 possible different triplets have been arranged in a (composi
tion restricted) random manner (338 triplets). The DOS histogram shows
in these cases essentially broader allowed energy regions and a much
lower number of very narrow peaks than in the previous six-component c
ase. Therefore we can conclude that if one were able to calculate the
DOS of real collagen (with 20 different amino acid residues), the DOS
histograms, the Anderson localization and the hopping frequencies woul
d be very similar to those in random polypeptides.