Since processing non-merohedrally twinned crystals became routine in small-molecule crystallography, the number of such twins has increased dramatically. The data are often as good as from normal crystals and there is the advantage of getting a higher redundancy and greater completeness by collecting data from two or more crystals in different orientations at the same time! At the moment non-meroderally twinned protein crystals are often thrown away (e.g. because they don't index with programs designed for untwinned crystals) or one tries not to notice that the other components are there. I predict that when MOSFLM, XDS, HKL2000 etc. are able to index and integrate non-merodedral twins, they will suddenly become much more common for macromolecules too. At least there is no problem indexing and integrating merohedral twins, and some refinement programs can handle them, so most of the discussion in this list has been about merohedral twins so far.
George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-2582 On Fri, 31 Aug 2007, Ian Tickle wrote: > > In the past twinned crystals must have been much more frequent than > published twinned structures because the traditional reaction of > crystallographers to twinning has been either to find a way of > inhibiting it or chucking the crystals in the bin and finding a > non-twinned form. But I guess that's changing now with better software > and we're becoming more adventurous - maybe that's why we're hearing > about more twinned crystals now. > > -- Ian > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Jacob Keller > > Sent: 31 August 2007 18:32 > > To: CCP4BB@JISCMAIL.AC.UK > > Subject: How many twinned crystals? > > > > Since I joined this list, I have seen many many issues with > > twinned structures, but have never seen > > any personally. Granted, problems with twinning induce people > > to write to the list, making them > > seem more prominent, but does anyone have an idea what > > percent of crystals are twinned, or know of > > a ref about this? I always thought it was an anomaly, but.... > > > > All the best, > > > > Jacob Keller > > > > > > > > > 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 >
