Hi Edward, MicroED as defined by Tamir Gonen does not encompass 2D crystals. This is to keep it separate from 2D electron crystallography in which the data is collected in a very different manner. Personally though, I don't see why you couldn't collect microED style data from a 2D crystal. Less copies of the unit cell means you would get less signal and you might have to bump up your dose per frame, which can cause more radiation damage, but these are (probably) not deal breakers.
For me, the thing that defines microED is the collection of electron diffraction data using the (continuous) rotation method without precession of the electron beam. It requires microcrystals/nanocrystals because if the crystals are too thick, the electron beam cannot penetrate them. The beauty of collecting data in this manner is that this is the same strategy employed by most X-ray crystallographers and therefore the data can be processed with familiar programs (DIALS, XDS, HKL3000, MOSFLM, APEX3, etc). The reality though, is that data processing is not trivial and there is a lot of room for improvement in handling this data. It is the early days for this field and I am hopeful that things will continue to improve. And in the meantime, we are solving lots of small molecule structures that could not easily be solved by X-ray crystallography or NMR. Cheers, Jessica On Sun, Aug 16, 2020 at 8:32 PM Edward A. Berry <ber...@upstate.edu> wrote: > For my own info, > Does microED encompass work with 2D crystals, or only micro-3D crystals? > > On 08/15/2020 10:40 PM, Jessica Bruhn wrote: > > Hi Alex, > > > > Welcome to the field of microED! From a practical standpoint, microED > also suffers from the phase problem, and somewhat moreso compared to X-ray > crystallography because anomalous signal is very limited. It is true that a > TEM microscope operated in imaging mode produces images that contain both > phase and amplitude information, which you correctly infer means that > single particle cryoEM does not suffer from the phase problem. This is why > a map from cryoEM is generally of higher quality than one determined by > X-ray crystallography at the same resolution, because we don't have to > guess at the phases. > > > > In classic microED data collection, we don't actually take advantage of > the phase information that can be measured using imaging mode. We quickly > find our crystals in imaging mode and then flip the switch to diffraction > mode and collect a dataset devoid of phase information. It has been > suggested that we could use imaging mode to get at the phases of the > diffraction patterns, but I am not aware of anyone actually doing this. > Practically speaking, this would add significant additional time to the > data collection and we likely would only be able to reliably use the phases > for the lower resolution range (though, that might not be a deal breaker). > Thankfully though, molecular replacement and ab initio methods for small > molecules work pretty well on these datasets. Plus, most X-ray structures > are solved this way anyways. > > > > There have been efforts to use radiation damage as a means to phase a > small peptide bound to zinc ( > https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7313391/ < > https://urldefense.com/v3/__https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7313391/__;!!GobTDDpD7A!d9GMLVpOCJjYcJ8TK3Sn2QYRR5JPvL8Vb51isRJMME8AssIo499krUEDQ5gHtKOV$>). > And there is some interesting work being done with dynamical scattering as > a way to see differences in Friedel pairs (see Tim Gruene's post here: > https://www.jiscmail.ac.uk/cgi-bin/wa-jisc.exe?A2=CCP4BB;b22eae56.2007 < > https://urldefense.com/v3/__https://www.jiscmail.ac.uk/cgi-bin/wa-jisc.exe?A2=CCP4BB;b22eae56.2007__;!!GobTDDpD7A!d9GMLVpOCJjYcJ8TK3Sn2QYRR5JPvL8Vb51isRJMME8AssIo499krUEDQx24VbXZ$>), > but these methods are not "classic microED" and require completely > different data processing software that is unfamiliar to most X-ray > crystallographers. > > > > For now, we just crank up the cycles in SHELXT/SHELXD or hope for a good > molecular replacement model. > > > > Best of luck, > > Jessica > > > > On Sat, Aug 15, 2020 at 6:03 PM Alex Lee <alexlee198...@gmail.com > <mailto:alexlee198...@gmail.com>> wrote: > > > > Hi, All, > > > > I am new to MicroED (microcrystal electron diffraction). I know that > X-ray crystallography has phase problem, and I think MicroED has phase > problem too (it is diffraction of electron instead of x-ray). However, when > I read the Wikipedia, I could not understand the following description of > MicroED: One of the main difficulties in X-ray crystallography is > determining phases in the diffraction pattern. Because of the complexity of > X-ray lenses, it is difficult to form an image of the crystal being > diffracted, and hence phase information is lost. Fortunately, electron > microscopes can resolve atomic structure in real space and the > crystallographic structure factor phase information can be experimentally > determined from an image's Fourier transform. The Fourier transform of an > atomic resolution image is similar, but different, to a diffraction > pattern—with reciprocal lattice spots reflecting the symmetry and spacing > of a crystal. > > > > Does the above description mean that MicroED, or more broadly > electron crystallogaphy does NOT suffer from phase problem? How about > single particle cryo electron microscopy, it should NOT have phase problem, > right? > > > > Thanks for any input in it. > > > > Best, > > Alex > > > > > > ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ > > > > To unsubscribe from the CCP4BB list, click the following link: > > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 < > https://urldefense.com/v3/__https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1__;!!GobTDDpD7A!d9GMLVpOCJjYcJ8TK3Sn2QYRR5JPvL8Vb51isRJMME8AssIo499krUEDQ8Gjq2MX$ > > > > > > > > > > -- > > Jessica Bruhn, Ph.D > > Principal Scientist > > NanoImaging Services, Inc. > > 4940 Carroll Canyon Road, Suite 115 > > San Diego, CA 92121 > > Phone #: (888) 675-8261 > > www.nanoimagingservices.com < > https://urldefense.com/v3/__http://www.nanoimagingservices.com__;!!GobTDDpD7A!d9GMLVpOCJjYcJ8TK3Sn2QYRR5JPvL8Vb51isRJMME8AssIo499krUEDQ4ha5wnW$ > > > > > > > ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ > > > > To unsubscribe from the CCP4BB list, click the following link: > > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 < > https://urldefense.com/v3/__https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1__;!!GobTDDpD7A!d9GMLVpOCJjYcJ8TK3Sn2QYRR5JPvL8Vb51isRJMME8AssIo499krUEDQ8Gjq2MX$ > > > > > -- Jessica Bruhn, Ph.D Principal Scientist NanoImaging Services, Inc. 4940 Carroll Canyon Road, Suite 115 San Diego, CA 92121 Phone #: (888) 675-8261 www.nanoimagingservices.com ######################################################################## 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/
