Hmmm…interesting James!. I don’t usually make a habit of trying to form a class, or losing face because of a point, -or even making a group in space.. But.. Id say it is neither different form nor different habit. -since these are centuries old terms -and still valuable, - from mineralogy that reflect (form) faces that grow preferentially due to packing of molecules within the crystal,- so the crystal may have no different form, or may have. So that term doesn’t define... Likewise crystal habit reflects the growth of crystals sort of above crystal forms, - and again could be the same habit or be different.. Id say -this great example is more like a conformational variant that is non-isomorphous with the previous structure, -you got it right the first time Id say!. I propose that these examples should be termed something different…. a “Holton fractal”. Robert Stroud str...@msg.ucsf.edu 415 987 7535
> On Dec 8, 2020, at 4:56 PM, James Holton <jmhol...@lbl.gov> wrote: > > I have a semantics question, and I know how much this forum loves discussing > semantics. > > We've all experienced non-isomorphism, where two crystals, perhaps even grown > from the same drop, yield different data. Different enough so that merging > them makes your overall data quality worse. I'd say that is a fairly > reasonable definition of non-isomorphism? Most of the time unit cell changes > are telling, but in the end it is the I/sigma and resolution limit that we > care about the most. > > Now, of course, even for non-isomorphous data sets you can usually "solve" > the non-isomorphous data without actually doing molecular replacement. All > you usually need to do is run pointless using the PDB file from the first > crystal as a reference, and it will re-index the data to match the model. > Then you just do a few cycles of rigid body and you're off and running. A > nice side-effect of this is that all your PDB files will line up when you > load them into coot. No worries about indexing ambiguities, space group > assignment, or origin choice. Phaser is a great program, but you don't have > to run it on everything. > > My question is: what about when you DO have to run Phaser to solve that other > crystal from the same drop? What if the space group is the same, the unit > cell is kinda-sorta the same, but the coordinates have moved enough so as to > be outside the radius of convergence of rigid-body refinement? Does that > qualify as a different "crystal form" or different "crystal habit"? Or is it > the same form, and just really non-isomorphous? > > Opinions? > > -James Holton > MAD Scientist > > ######################################################################## > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 > > This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing > list hosted by www.jiscmail.ac.uk, terms & conditions are available at > https://www.jiscmail.ac.uk/policyandsecurity/ ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
