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With the potential function for orientation about a single bond
between the a carbon (tetrahedral) and the peptide nitrogen or
peptide carbon. The orientations about the a C-N and aC-C bonds
for the π helix have not ;bet been determined. Calculations of
the X-ray form factor and Pourier transforms for the helix are
now proceeding (with H. J. Grenville-Wells). They will be pub-
lished together with a more precise formulation of the helix
later.
The π helix is certainly under some slight strain and
the a helix represents a lower potential. energy minimum for the
atoms of the bare chain (H. C . CO.NH)n. The π helix can probably
not be ruled out, however, on this basis since the potential
energy function for the protein chain with attached poly functional
(R) groups (F~.C'r1.C0.2dH)n may well be rather different from that
of the bare chain.
REFERENCES
1. M. L. Huggins, THIS JOURNAL, _74, 3963 (1952).
2. L. Pauling and R. B. Corey, ibid., _72, 5349 (1954).
3. L. Pauling and. R. B,+ Corey, ibid., _74, 3964 (1952).
L. Paulin;, R. B. Core, and :. R. Branson, Proc. Nat. Acad.
Sci., 37, 205 (1951).
5. R. B. Corey and J. Donohue, THIS JOURNAL, 72, 2899 (1950).
6. :S. W. *.W1-1 -a~~d R. :3. Baybutt, reported at the -loyal Society
(Lor_don) discussion, „The Structure of Proteins::, in May.,
1952, by J. T. adsall, Nature, 1.70, 53 (1952).
See for example the tetrahedral carbon angles of 113' and
l04° found in the threonine molecule, D. P. Shoeraaker, J.
f"onohue, V. Schomaker, and R. B. Corey, THIS JOURNAL, 72,
2328 (1950).
8. L. Pauling, private communication.
9. L. Pauling and R. B. Corey, Proc. Nat. ,.cad.. 37, 729`
(1951)•
Barbara W. Low
R. B. Baybutt
University Laboratory of Physical Chemistry
Related to Medicine and Public Health
Harvard University, 25 Shattuck
Boston, Massachusetts
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