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Hello Jacob,
I do not know the data, but the word 'fibre' sounds close to
'one-dimensional crystal', especially considering the screw axis you
have in DNA, at least within the resolution limits that the pictures
suggest.
Cheers,
Tim
On 05/09/12 18:35, Jacob Keller wrote:
> Well, what about the original DNA fiber diffraction images--no
> microcrystals there, as far as I know, but one can clearly see the
> stacking distances and the phosphate backbone.
>
> JPK
>
> On Wed, May 9, 2012 at 11:03 AM, Tim Gruene
> <[log in to unmask]> wrote:
>
> 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
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