Modern Polymer Spect..

~~ ~
270 5 Vibrational Sl~ectroscop~~ oj Polypeptides
Table 5-8. Parameters of some observed helical polypeptide structures
Structure
hlrvrlnloleL 1rltrr
~1-Hel1x
q1-Helix
3lo-Hel1~
to-tieli~
R-HKIIX
n” nib hL Yd id cod H-bonde Ref.
3.62 13 1.496 -57.4 -47.5 180 5-1 104
3.62 13 1.496 -70.5 -35.8 180 5-1 106
2.99 10 2.01 -45 -30 176 4- 1 111
-4.00 13 1.325 62.8 54.9 175 541 1 I ?
-4.25 16 1.17 51 74 177 6-1 115
Intevniolec iiliw
Polyglycine I1
Polypioline 11
Polypioline 1’
-3.00 3.10 -76.9 145.3 180
-3.00 3.10 -78.3 148.9 180
3.33 1.90 -83.1 158.0 0
122
128
135
Number of residues/turn, + for right-handed and - for left-handed helices
Number of atoms in hydrogen-bonded ‘ring’.
Unit axial translation, in A.
‘’ Dihedral angle, in degrees.
Hydrogen bonding pattern, N-H-O=C.
Cis peptide groups.
(j
b
Figure 5-6. Structure of a-helix of poly(L-alanine). (a) al-helix; ib) q1-helix. Methyl groups are
represented by large circles. (From 151)
which, though having different p, $, has the same IZ and 11, and is comparably
allowed energetically [ 1061 (and may be present in bacteriorhodopsin [ 1071). These
structures are shown in Figure 5-6, where it can be seen that the plane of the peptide