I think if there had been a case of a protein quasicrystal, it would have made
the cover of Nature....
Here are some papers about quasicrystals:
1: Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14267-70.
New perspectives on forbidden symmetries, quasicrystals, and Penrose
tilings.
Steinhardt PJ.
Quasicrystals are solids with quasiperiodic atomic structures and
symmetries forbidden to
ordinary periodic crystals-e.g., 5-fold symmetry axes. A powerful model for
understanding their
structure and properties has been the two-dimensional Penrose tiling. Recently
discovered
properties of Penrose tilings suggest a simple picture of the structure of
quasicrystals and shed
new light on why they form. The results show that quasicrystals can be
constructed from a single
repeating cluster of atoms and that the rigid matching rules of Penrose tilings
can be replaced by
more physically plausible cluster energetics. The new concepts make the
conditions for forming
quasicrystals appear to be closely related to the conditions for forming
periodic crystals.
2: Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14271-8.
Five-fold symmetry in crystalline quasicrystal lattices.
Caspar DL, Fontano E.
Institute of Molecular Biophysics, Florida State University, Tallahassee,
32306-3015, USA.
[EMAIL PROTECTED]
To demonstrate that crystallographic methods can be applied to index and
interpret diffraction
patterns from well-ordered quasicrystals that display non-crystallographic
5-fold symmetry, we have
characterized the properties of a series of periodic two-dimensional lattices
built from pentagons,
called Fibonacci pentilings, which resemble aperiodic Penrose tilings. The
computed diffraction
patterns from periodic pentilings with moderate size unit cells show decagonal
symmetry and are
virtually indistinguishable from that of the infinite aperiodic pentiling. We
identify the vertices
and centers of the pentagons forming the pentiling with the positions of
transition metal atoms
projected on the plane perpendicular to the decagonal axis of quasicrystals
whose structure is
related to crystalline eta phase alloys. The characteristic length scale of the
pentiling lattices,
evident from the Patterson (autocorrelation) function, is approximately tau 2
times the pentagon
edge length, where tau is the golden ratio. Within this distance there are a
finite number of local
atomic motifs whose structure can be crystallographically refined against the
experimentally
measured diffraction data.
Jacob
==============Original message text===============
On Mon, 27 Aug 2007 2:02:36 pm CDT Bart Hazes wrote:
I believe Wayne Hendrickson's lab has had such a case with a 10-fold
symmetric mollusc hemocyanin crystal. This must have been in the early
90's and to my knowlwedge they were never able to solve the structure
even though it diffracted beyond 2 Anstrom.
I'm not sure if this work has been published but you can check the paper
describing a single domain of this protein complex or contact one of its
authors.
Bart
J Mol Biol. 1998 May 15;278(4):855-70.
Crystal structure of a functional unit from Octopus hemocyanin.
Cuff ME, Miller KI, van Holde KE, Hendrickson WA.
Jacob Keller wrote:
> I am still eagerly awaiting a biomacromolecular quasicrystal with a five-fold
> symmetric diffraction
> pattern. It seems that this is entirely possible, if one gets roughly
> Penrose-tile shaped oligomers
> somehow. But wow, how would you solve that thing? I guess one would have to
> modify software from
> the small molecule or matsci folks.
>
> Jacob
>
>
> ==============Original message text===============
> On Mon, 27 Aug 2007 11:19:15 am CDT "George M. Sheldrick" wrote:
>
>
> Some small molecule crystallographers have specialized in solving and
> refining structures that, exactly as you describe it, consist of two (or
> more) interpenetrating, non-commensurable lattices. The usual approach is
> to decribe the crystal in up to six dimensional space. The programs SAINT
> and EVALCCD are able to integrate such diffraction patterns and
> SADABS is able to scale them. However the case in point is probably
> commensurate.
>
> George
>
> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry,
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-2582
>
>
> On Mon, 27 Aug 2007, Jacob Keller wrote:
>
>
>>What a beautiful and interesting diffraction pattern!
>>
>>To me, it seems that there is a blurred set of spots with different cell
>>dimensions, although
>>nearly the same, underlying the ordered diffraction pattern. A possible
>>interpretation occurred to
>>me, that the ordered part of the crystal is supported by a less-ordered
>>lattice of slightly
>>different dimensions, which, because the crystal is a like a layer-cake of
>>2-d crystals, need not
>>be commensurable in the short range with the ordered lattice. The
>>nicely-ordered "cake" part of the
>>crystal you solved, but the "frosting" between is of a different, less
>>ordered nature, giving rise
>>to the diffuse pattern which has slightly different lattice spacing. I would
>>have to see more
>>images to know whether this apparent lattice-spacing phenomenon is
>>consistent, but it at least
>>seems that way to me from the images you put on the web. I would shudder to
>>think of indexing it,
>>however.
>>
>>All the best,
>>
>>Jacob Keller
>>
>>ps I wonder whether a crystal was ever solved which had two interpenetrating,
>>non-commensurable
>>lattices in it. That would be pretty fantastic.
>
>
>
> Jacob,
>
> Some small molecule crystallographers have specialized in solving and
> refining structures that, exactly as you describe it, consist of two
> interpenetrating, non-commensurate lattices. The usual approach is
> to index the diffraction pattern in multiple dimensional space
> ('superspace'). The programs SAINT and EVALCCD are able to integrate
> diffraction patterns in up to six dimensions, SADABS is able to scale
> them and the refinement is almost always performed with Petricek's
> program JANA2000:
>
> http://www-xray.fzu.cz/jana/Jana2000/jana.html > However the case in point is
> probably commensurate.
>
> George
>
> Prof. George M. Sheldrick FRS
> Dept. Structural Chemistry,
> University of Goettingen,
> Tammannstr. 4,
> D37077 Goettingen, Germany
> Tel. +49-551-39-3021 or -3068
> Fax. +49-551-39-2582
> ===========End of original message text===========
>
>
>
> ***********************************
> Jacob Keller
> Northwestern University
> 6541 N. Francisco #3
> Chicago IL 60645
> (847)467-4049
> [EMAIL PROTECTED]
> ***********************************
>
>
--
==============================================================================
Bart Hazes (Assistant Professor)
Dept. of Medical Microbiology & Immunology
University of Alberta
1-15 Medical Sciences Building
Edmonton, Alberta
Canada, T6G 2H7
phone: 1-780-492-0042
fax: 1-780-492-7521
==============================================================================
===========End of original message text===========
***********************************
Jacob Keller
Northwestern University
6541 N. Francisco #3
Chicago IL 60645
(847)467-4049
[EMAIL PROTECTED]
***********************************
