POLYTECHNIC INSTITUTE OF BROOKLYN
9 9 LIVINGSTON STREET
BROOKLYN 2, NEW YORK
DEPARTMENT OF CHEMISTRY
February 3, 1953
Professor Linus Pauling
Gates and Crellin Laboratories
California Inst. of Technology
Pasadena 4, California
Dear Professor Pauling,
Thank you for your letter of January 29 concerning the form factor for the 7-strand
cable. Under separate cover I am sending you and Professor Corey reprints of the
work of Dr. D. P. Riley and myself which are relevent to this problem.
I do not feel that the equatorial spacings will be markedly altered whether one assumes
7 parallel rods or whether one assumes 6 rods twisted with mild pitch about a central
The difference in your form factor for the equatorial spacings for your seven strand
cable and that for the 7 parallel rods case Riley and I have used, comes about in
the averaging process. We assumed that the 7 rod case can rotate.
In the end, experiments will, of course, prove which model is correct. It is
for that reason that I am planning to do some low angle scattering to obtain equatorial
spacings for wool in the α state. A student of mine is in the process of isolating
the spindles of the cortex of wool since we would like a "pure" wool diagram un-obscured
by the scales and cementing material of the wool fibers.
Incidentally, another student of mine has crystallized insulin which has been iodinated
to the extent of 15% by weight in iodine. This material should be of interest since
the scattering by the iodine exceeds that of the whole protein itself.
As you will see from our nucleic acid work, we considered a helical model, however,
parameters can so be chosen as to fit any date. Hence, we were satisfied to choose
the rod model which, at least, can be discussed more uniquely in terms of our data.
Riley and I found, experimentally, a spacing of 16Ǻ for the unhydrated nucleic acid
molecule but the value is based on an extrapolation of our observed data and hence
may be in error.
Professor Pauling -2- February 3, 1953
I am not at the present time working with the X-ray diffraction of nucleic acid. Curiously
enough, my main interest these days is in the photochemistry of dyes in solution in
an optimistic attempt to explain certain biological phenomena such as vision. My work
may never help to explain these phenomena but the photochemical properties of dyes
in solution are themselves fascinating.