Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

X-ray crystalography

  1. May 1, 2003 #1
    does anybody know of any current work that is being done to improve x-ray crystalography techniques?
  2. jcsd
  3. May 1, 2003 #2
    No, but Sigourney Weaver narrated the NOVA show about photo 51, an x-ray diffraction photo of the DNA molecule, the first of its kind.
  4. May 1, 2003 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    she was great in The Year of Living Dangerously
    where is Fox? I like imagining places up north
    Schild means forehead in German
    there is a fine touch of whimsey to signing God Save the Empire
    with the silhouette of an ironical English moviedirector
    I will look for something online about the xray DNA picture
    why was it a first-ever?
  5. May 1, 2003 #4
    Am not sure just how recent it has to be considered "current" for your purposes, but some of the methods which have been introduced in the past decade or so (esp. in protein crystallography) have been:

    1.) cryocooling, in which you add in some cryoprotective agents and then do your x-ray data collection in the beam at very low temperatures. This will decrease crystal degradation and reduce the rate at which free radicals will diffuse through the crystal (after all, you are pumping x-ray radiation through the thing).

    2.) lipidic cubic phase crystallization. Mainly for proteins (although I guess you could do this for anything which is somewhat hydrophobic and doesn't crystallize easily with more traditional methods), you put your sample into a lipidic solution with a little bit of water and essentially the hydrophobic packing leads to nucleation which leads to crystal growth.

    3.) Multiwavelength Anomalous Dispersion (MAD) is a method for solving the phase problem by using heavy atoms (similar to MIR) and a spectrum of wavelengths to determine structure. Again, used especially by protein/macromolecular crystallographers. Pioneered by Wayne Hendrickson (now at Columbia Univ.)

    4.) You might want to discuss two somewhat recent developments in structure refinement, namely the usage of the R(free) value and the increasing usage of molecular modeling techniques (simulated annealing, molecular dynamics, and the like) to improve the quality of the final structure.

    I admit most of these have a protein crystallography bias, as that's what I'm most familiar with (such as it is), but hopefully this will give you some ideas.
  6. May 1, 2003 #5


    User Avatar

    Staff: Mentor

    On a side note, how dangerous is it to be in the room with an operating device? I'm doing some HVAC work for U Penn in a room they do x-ray crystallography.
  7. May 1, 2003 #6
    It's probably OK as long as you follow whatever safety guidelines the lab has in place. The x-ray lab at my old university was staffed by full time scientists, so never spent much time there and the x-ray lab at my current school is not particularly relevant to my work, so I don't spend any time there. I would definitely make sure to ask them that they turn off/remove anything that might be dangerous or valuable and for anything you should know about it. I would think it would be fine as long as you do that. I mean, it's not like you're going to be doing any work when they have the beam turned on. Right?
  8. May 1, 2003 #7
    Which technique are you interested in?

    For Debye-Scherrer methods, you typically want to blast a pulverized sample with a white spectrum and hope that you get as many different wavelengths to interact with as many different crystal orientations as possible. It seems logical to assume that the best way to improve such a technique would be to make a broader, flatter x-ray source.

    For rotating-crystal methods, you ideally want a very specific wavelength x-ray to interact with a very specific crystal orienation. So, the best way to improve this method would be to develop a good tunable, narrow-band x-ray source and better stepping motors for turning the crystal.

    For the Laue method, you usually want to hit a stationary crystal with a very white x-ray source, and try to detect all the diffracted rays. This is traditionally done by surrounding the crystal with a spherical shell of film. I suppose the best way to improve this technique would be to improve the whiteness of the x-ray source and perhaps improve the stepping motors as well.

    Last edited by a moderator: May 1, 2003
  9. May 2, 2003 #8
    "why was it a first-ever?"

    Guess it couldn't be the first ever, otherwise it would be photo 1 not 51, but the NOVA show said that she was the first to photograph DNA with x-ray crystallography, and interpret the diffraction pattern by hand. She had to run the x-ray camera for up to 100 hours per frame, which gave her cancer at age 36. Watson & Crick so famous for 'discovery' of DNA used her work without her knowledge to construct their models.

    Fox is north of Fairbanks about 5 miles.
    Last edited by a moderator: May 2, 2003
  10. May 2, 2003 #9
    You should have a look on the web site of the international cristallogarphy union.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook