-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Jacob,
A protein would only scatter but not diffract, the latter - in my understanding - being the result of constructive interference from a regular array of unit cells . A powder pattern is the superposition of many small crystals amongst which you don't observe interference. Tim On 05/09/12 16:16, Jacob Keller wrote: > Dear Crystallographers, > > the "saxs on crystals" thread reminded me of a question I have had > for a while, and never having collected data better than ~1.6 Ang > or so, cannot answer myself from experience: I would think that > there might be powder-like diffraction rings at distances > corresponding to the various covalent bond lengths in proteins > (1.2-1.5 Ang), but have never heard of such. My thinking is that > the protein itself is essentially a powder sample within the unit > cell consisting of many small, randomly-oriented molecules (amino > acids) with their covalent bonds. Do the rings in fact exist, and > if not, why not? Maybe the electron density is not as "atomic," or > discrete, as the nuclei are? I wonder whether generally data > collected to beyond ~1 Ang have an intensity "bump" at those > covalent bond lengths, as I believe is seen in nucleic > acid-containing structures at the base-stacking distance (at the > right orientation)? > > Jacob > - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFPqpVlUxlJ7aRr7hoRAhZqAJ9M49u+cYsX+AhzRlYKOCTX8YCsbQCgzFBi ZV+cZCyQgGLusrnufngyZ5A= =cuQy -----END PGP SIGNATURE-----
