Hi Charlie, The bending of needles is hard to avoid :) My advice is to investigate different areas of the needle using finely focused beam - in particular focus on the protruding end and on the area inside the loop. The protruding area is particularly good since it has the least solvent attached to it. One of those may work out :) There's an alternative to this and that's using a very large loop so the needle never touches the nylon. The disadvantage of this approach is obviously the large volume of solvent/oil present in the loop, resulting in large background scatter.
As far as systematic absences lost due to special orientation - yes, although if you have a bent loop (similar to the cheater pins from the bygone days) that's not much of an issue. Additionally, precise selection of space group can be always made as the structure's solved :) Artem > Useful summary, Artem. > > Two comments spring to mind. > > - I have had trouble with slight bending of needles when frozen like > this, causing problems with mosaicity. (Presumably due to different > forces acting on the parts of the crystal within and without the loop.) > > - You can have lots of trouble measuring systematic absences in crystals > mounted like this as the unique axis in hexagonal or tetragonal is close > to the rotation axis. > > Cheers, > Charlie > > > Artem Evdokimov wrote: >> Sorry, hit send by accident. Here it is: >> >> http://www.xtals.org/pdfs/needles.pdf >> >> Artem >> >> -----Original Message----- >> From: Artem Evdokimov [mailto:ar...@xtals.org] >> Sent: Monday, October 05, 2009 9:05 PM >> To: 'Tanner, John J.'; 'CCP4BB@JISCMAIL.AC.UK' >> Subject: RE: [ccp4bb] Mounting needle-shaped crystals >> >> Hello felow MO crystallographer, >> >> For all it's worth, a while ago I've compiled a little document which >> describes mounting needles. I've converted it into PDF and posted it >> here: >> >> >> "Nothing is built on stone; all is built on sand, but we must build as >> if >> the sand were stone" >> Jorge Luis Borges >> >> >> -----Original Message----- >> From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of >> Tanner, John J. >> Sent: Monday, October 05, 2009 5:52 PM >> To: CCP4BB@JISCMAIL.AC.UK >> Subject: [ccp4bb] Mounting needle-shaped crystals >> >> Dear CCP4, >> >> I'm looking for advice on mounting thin needles for low temperature data >> collection. Our needles are fairly long (100-200 microns) but only 20 >> microns or less thick. When I pick them up with Hampton loops (0.05-0.1 >> mm >> size), the crystals tend to break as they are moved out of the drop and >> through the liquid-air interface. >> >> I see that Mitegen sells MicroLoops E, which are advertised as working >> well >> for mounting needles. Can anyone recommend them? Can anyone recommend >> Mitegen MicroMeshes or another tool for mounting needles? >> >> Thanks, >> >> Jack Tanner >> >> > > -- > Charlie Bond > Professorial Fellow > University of Western Australia > School of Biomedical, Biomolecular and Chemical Sciences > M310 > 35 Stirling Highway > Crawley WA 6009 > Australia > charles.b...@uwa.edu.au > +61 8 6488 4406 >
