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 rod.
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