May 12, 1952
Professor A. R. Todd, F.R.S.
University Chemical Laboratory
I am glad to have your letter of 6th May. Ava Helen and I are still feeling very disappointed that we could not have our
visit in England. I must say that I am astounded that the State Department should have refused me a passport, after I had
pointed out clearly that the visit to England was to be purely for scientific purposes - especially since the principal reason
for the trip was to take part in the Royal Society discussion meeting. We hope that the present situation will not continue
into the future, and that we shall be able at some future time to visit you.
I am pleased to have you say that you will not allow your new government job to cripple your scientific work (I do not think
that you should call it your ordinary scientific work - it seems to me to be extraordinary).
We are only rather slowly beginning work in the field of nucleic adds and nucleoproteins, but I hope that in another year
or two the work on ordinary proteins will have progressed so far as to justify our turning our attrition largely to nucleoproteins.
Will you send me reprints of your papers on nucleic acids, especially those in which you discuss your new ideas about the
Corey is now in England, and I hope that you will talk with him. I do not know what part of this month he plans to spend in
Cambridge, but I think it very likely that he will come to see you.
Right now we are working hard on the structure of silk fibroin. We have found a structure that, so far as the calculations
have gone yet, accounts essentially perfectly for the observed intensities of x—ray diffraction. If the remaining calculations
give as good results, we shall have, for the first time in the history of proteins, a protein structure which has been tested
by completely detailed comparison of observed and calculated x-ray intensities. Our structure involves alternation of glycine
residues and other residues, principally alanine; we have not taken into consideration the side-chain atoms other than the
There is a faint superstructure, which seems to be due in the main to the presence of occasional serine residues - perhaps
every sixth residue in each polypeptide chain is a serine residue. However, it seems unlikely that the structural basis
of the superstructure, involving these rarer amino acid residues, can be determined without a great deal more work.
I enclose a copy of a statement that I made about my passport, a letter that I sent to President Truman, in an effort to get
the original decision changed, and a statement about my political beliefs that I made last year.
With best regards, also to Alison and the children, I am