Dear Anna, The reprint:- http://www.sciencedirect.com/science/article/pii/S0020169300822689 has some bearing on your query. Best wishes, John Prof John R Helliwell DSc
On 7 May 2012, at 17:30, anna anna <[email protected]> wrote: > Dear all, > I'd like some suggestions/opinions about the sense of an experiment proposed > by a collaborator expert in saxs. > In few words, he wants to collect SAXS data on a suspension of protein xtals > to investigate "low resolution periodicity" of the xtal (more details below). > The experiment requires a very huge number of xtals to obtain the circles > typical of saxs and it is very time-consuming to me (I know nothing about > saxs, I have only to prepare the sample). I proposed to measure a single > rotating xtal (like in XRD) but he told they don't have a goniometer on saxs > beamline. > Here is my concern: does it make sense to measure many xtals together? Don't > we lose information with respect to single xtal? And, most of all, what can I > see by saxs that I can't see by waxs?? > Sorry for the almost off-topic question but I think that only someone who > knows both the techniques can help me!! > > > Some detail for who is intrigued by my story: > we prepared doped magnetite nanoparticles using ferritin as bioreactor. I > crystallized this spheres filled with metal and solved the structure at 3.7A > but I can see only the protein shell while there is no density inside, even > if I know that the nanoparticles are there. A simple explanation is that the > particles are free to move in the cavity(note that the diameter of the > nanoparticle is shorter then the inner diameter of the protein shell), ie are > disordered, and do not contribute to diffraction, in fact, to my knowledge, > nobody have ever seen the metal core inside ferritin or dps proteins. > However, since they are magnetic particles they must "see" each other through > the protein wall, ie they can't be completely free to move in the cavity. > Maybe, but this is just my opinion, I don't see the particle because the > "period of the particle" in the xtal is different/longer than the period of > the protein shell. > Anyway, we are interested in the relative distance between the magnetic > particles in the xtal to study the effects of magnetostatic interactions in > nanoparticles 3D arrays. We are going to do this by saxs since, they told me, > lower resolution is useful in studying this long range periodicity (the > diameter of ferritin is about 120A) but it seems fool to me using a > suspension of so many xtals to obtain a scattering curve while I could > collect diffraction images from a single xtal!!! I know that saxs is used > when you don't have xtals but if you have xtals, ie your system is ordered, > xtallography is much more powerful!! > > Another question: how can I handle my diffraction data at 3.7A resolution to > "look for" nanoparticles? Should I try a lower symmetry? Maybe the anomalous > signal? Have you any reference for a similar case? > > Thank you very much!! > > anna > > > > >
