Dear Jacob,
Our, ie protein, crystals usual diffuse scattering ring involves a
typically 2.8 Angstrom solvent oxygen to oxygen distance.
There must be a 1Angstrom OH diffuse scattering ring but the weakness
of the hydrogen scattering mitigates against that.
The covalent links, to which you refer, are for the ordered atoms and
whose scattering is all scooped up into the Bragg spots.
The ferritin iron core I imagine as being possibly powder pattern
generating as nanoparticles were mentioned; indeed as it turns out
from Anna's diffraction image they are narrow-ish but still diffuse
rings, whose width will allow an estimate of the nanoparticles
diameter. The intensities of these diffuse rings should also allow an
estimate of the number of the iron atoms in the core. And thereby the
number of nanoparticles can be estimated......
All very interesting!
John
On Wed, May 9, 2012 at 3:16 PM, Jacob Keller
<[log in to unmask]> 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
>
> --
> *******************************************
> Jacob Pearson Keller
> Northwestern University
> Medical Scientist Training Program
> email: [log in to unmask]
> *******************************************
--
Professor John R Helliwell DSc
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