I seem to recall a discussion at some Study Weekend where someone reported a needle crystal in which the twin fraction appeared to vary continuously from 0 at one end of the needle to 0.5 at the other! You just had to make sure you picked the right end to collect the data!
-- Ian > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Eleanor Dodson > Sent: 18 April 2007 09:27 > To: Mark Mayer > Cc: [email protected] > Subject: Re: [ccp4bb] twin fraction varies between crystals? > > This is a very common thing - twinning is a sort of > accidental overlap > of crystal fragments and thus will be different for diferent > "crystals". ( Should a twinned object be called a crystal? Discuss) > > More serious - it is probably different for different parts > of the data > collection if your crystal is smaller than the beam - I dont know if > anyone has ever tried to analyse for this. > In our experience smaller is often better.. > Eleanor > > Mark Mayer wrote: > > For cases where people have had merohedral twinning, did > the twin fraction vary substantially > > between individual crystals grown under indentical > conditions? I have no prior experience with > > merohedral twinning, and was surprised to see that the twin > fraction varied substantially as detailed > > below, and that by screening we were able to get untwinned xtals. > > > > The project started with a weak home data set for which the > twin fraction was 0.478, and which > > scaled in both H3 and H32. We just came back from APS with > data sets from another three crystals, > > for which the ML twin fraction, estimated using > phenix.xtriage with scalepack merged intensities as > > input, varied from 0.335, 0.219 and 0.02. The latter is > refining very nicely, in H3 and will not scale in > > H32. > > > > Thanks - Mark > > > > > > > > > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [EMAIL PROTECTED] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
