I am trying to think, then, what would the Patterson map of a Fourier-transformed electron density map look like? Would you get the shape/outline of the object, then a sharp drop-off, presumably? Is this used to orient molecules in single-particle FEL diffraction experiments?
JPK On Fri, Jan 13, 2012 at 12:33 PM, Dale Tronrud <[email protected]> wrote: > > > On 01/13/12 09:53, Jacob Keller wrote: >> No, I meant the non-lattice-convoluted pattern--the pattern arising >> from the Fourier-transformed electron density map--which would >> necessarily become more complicated with larger molecular size, as >> there is more information to encode. I think this will manifest in >> what James H called a smaller "grain size." > > I've been thinking about these matters recently and had a nifty > insight about exactly this matter. (While this idea is new to me > I doubt it is new for others.) > > The lower limit to the size of the features in one of these > "scattergrams" is indicated by the scattergram's highest frequency > Fourier component. Its Fourier transform is the Patterson map. > While we usually think of the Patterson map as describing interatomic > vectors, it is also the frequency space for the diffraction pattern. > For a noncrystalline object the highest frequency component corresponds > to the longest Patterson vector or, in other words, the diameter of > the object! The bigger the object, the higher the highest frequency > of the scattergram, and the smaller its features. > > Dale Tronrud > >> >> JPK >> >> On Fri, Jan 13, 2012 at 11:41 AM, Yuri Pompeu <[email protected]> wrote: >>> to echo Tim's question: >>> If by pattern you mean the position of the spots on the film, I dont think >>> they would change based on the complexity of the macromolecule being >>> studied. As far I know it, the position of the spots are dictated by the >>> reciprocal lattice points >>> (therefore the real crystal lattice) (no?) >>> The intensity will, obviously, vary dramatically... >>> ps. Very interesting (cool) images James!!! >> >> >> -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: [email protected] *******************************************
