There is also one case of a protein structure that I am aware of, where a similar problem has been tackled (the phenomenon is also known as one-dimensional disorder, according to A.J.C. Wilson - yes, the one how invented the plot).
Check: Trame, CB & mcKay, DB (2001). Acta Cryst. D57, 1079-1090. Boaz ----- Original Message ----- From: "George M. Sheldrick" <[EMAIL PROTECTED]> Date: Monday, August 27, 2007 18:49 Subject: Re: [ccp4bb] Strange diffraction images To: CCP4BB@JISCMAIL.AC.UK > 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 > Boaz Shaanan, Ph.D. Dept. of Life Sciences Ben-Gurion University of the Negev Beer-Sheva 84105 Israel Phone: 972-8-647-2220 ; Fax: 646-1710 Skype: boaz.shaanan‎