Letter from Donald L. D. Caspar to Rosalind Franklin
Biophysicist Donald Caspar's recent doctoral research on TMV, using heavy-atom substitution, was of great interest to
Franklin. In this letter he discussed the mathematical analysis of his data, and suggested that he come to work with her in
England later that year.
Item is handwritten.
Number of Image Pages:
2 (138,376 Bytes)
1955-04-09 (April 9, 1955)
Caspar, Donald L. D.
California Institute of Technology. Kerckhoff Laboratories of Biology
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
Reproduced with permission of Donald L. D. Caspar.
Jim tells me he has just written you, but he did not include the copy of the Fourier-Bessel Transform, so I'm sending
it along. The solid curve on the left in the 16 angstrom resolution radial density distribution, calculated from my equatorial
Geiger counter measurement[s?]. The broken curve is the 10 angstrom resolution projection, obtained from photographic estimation
of the intensities of the next four visible equatorial maxima. The reliability of these intensity estimates is not very good,
but the signs and positions are definite, so the general shape of the projection at 10 angstroms resolution should be as plotted.
The radial effective mass distribution is plotted at the right. As soon as I get this written up, I'll send you a copy.
Jim has written about the use of lead binding to determine the signs -- the same method may be used for non-equatorial
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layer lines, since my photographs indicate some modification of the intensities for the 3rd layer line, as well as perhaps
some others. On the equatorial layer line I suspect the occurance [sic] of four small amplitude maxima or minima, which could
not be detected in the angular range covered. The only one expected to be at all appreciable is an amplitude minimum (minus)
on the high angle side of the amplitude maximum at about 20 angstrom spacing (that is the sixth equatorial intensity maximum).
This expected weak reflection appears in the pattern from the lead substituted TMV, since it is in phase with the lead contribution.
You may have detected this weak reflection in your photography.
I'd like to come to England for a few months toward the end of the summer to work with you -- if I can get funds. Yale
may pay for this, since I'll be returning there, and it would be a good idea to see you before planning a research program
there. Geiger counter intensity measurements should be quite useful where large intensity ranges have to be covered, and for
establishing the location of bound metals, so perhaps we could work together to get the cylindrical Fourier-Bessel projection
of the sub unit. I'll be back at Yale for the next two or three weeks, and will write you if this plan is possible.