On 15 May, William Scott wrote: > Actually, if you want to feel really good, I learned (in the context > of optics) that you can resolve two points separated by a distance x > with a diffraction limit of x/0.7, so this means you can start to see > carbon - carbon atomicity at 2.2 Å.
This is correct, 2.1 to 2.4 angstroms, and it is the resolution at which the density begins to have a small degree of sphericity, although poor. The sphericity is definitely detectable and sometimes very visible at 2 angstroms which is closer to the determination point of what might be called the atomic pseudo-radius. The atomic position is well determined within this constraint. This is the meaning of over-determined, and possibly a good lower boundary of high resolution atomic structure. A key word here is sphericity, not spherical. Truly spherical density requires better resolution than 2 angstroms, but at the lower limit of over-determination, the density begins to approach the spherical, or a rounded balls and sticks cartoon if you like. High resolution would be that level where the actual atomic positions _begin_ to be apparent as the density begins to approach the spherical. It is over-determined because the atomic coordinate is constrained by the data to be roughly centered within the radius of the theoretical sphere that the density is approaching. Beyond this level of resolution, the density begins to loose sphericity again and enter the realm of ultra-high resolution. The density begins to resolve orbitals. It is a remarkable thing to see. I don't have the exact numbers for distinguishing high versus ultra-high resolution, but this should be specified as well. There is also atomic anisotropy to deal with at better than 2 angstroms resolution, so it is a good thing to get these numbers nailed down with the proper terminology. Regards, Michael L. Love Ph.D Department of Biophysics and Biophysical Chemistry School of Medicine Johns Hopkins University 725 N. Wolfe Street Room 608B WBSB Baltimore MD 21205-2185 Interoffice Mail: 608B WBSB, SoM Shipping Dock: 1915 E. Madison St. office: 410-614-2267 lab: 410-614-3179 fax: 410-502-6910 cell: 443-824-3451 http://www.gnu-darwin.org/ > On May 15, 2008, at 10:12 AM, Gloria Borgstahl wrote: > >> To me, it seems legal to use the words "atomic resolution" once we >> are within the carbon-carbon bond length. So I'm agreeing with Dr. >> Scott. >> Otherwise I'll never get to use the words... >> >> ****************************************************************************** >> Gloria Borgstahl >> Eppley Institute for Cancer Research and Allied Diseases >> 987696 Nebraska Medical Center >> 10732A Lied Transplant Center >> Omaha, NE 68198-7696 >> >> http://sbl.unmc.edu >> Office (402) 559-8578 >> FAX (402) 559-3739 >> >> Associate Professor >> Hobbies: Protein Crystallography, Cancer, Biochemistry, DNA >> Metabolism, >> Modulated Crystals, Crystal Perfection, X-ray Topography, >> Interests: ThimbleTack, skateboarding, RAGBRAI, and rollerskating >> ****************************************************************************** >> >> >> >> William Scott <[EMAIL PROTECTED]> >> Sent by: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> >> 05/15/2008 12:09 PM >> Please respond to >> William Scott <[EMAIL PROTECTED]> >> >> >> To >> CCP4BB@JISCMAIL.AC.UK >> cc >> >> Subject >> Re: [ccp4bb] poll: cutoff for "high resolution" >> >> >> >> >> >> >> On May 15, 2008, at 10:01 AM, Ed Pozharski wrote: >> >>> 1.2A (not surprisingly since this is about the length of covalent >>> bond). >> >> A carbon-carbon single bond is about 1.55 Å. -- Michael L. Love Ph.D Department of Biophysics and Biophysical Chemistry School of Medicine Johns Hopkins University 725 N. Wolfe Street Room 608B WBSB Baltimore MD 21205-2185 Interoffice Mail: 608B WBSB, SoM office: 410-614-2267 lab: 410-614-3179 fax: 410-502-6910 cell: 443-824-3451 http://www.gnu-darwin.org/ Visit proclus realm! http://proclus.tripod.com/ -----BEGIN GEEK CODE BLOCK----- Version: 3.1 GMU/S d+@ s: a+ C++++ UBULI++++$ P+ L+++(++++) E--- W++ N- !o K- w--- !O M++@ V-- PS+++ PE Y+ PGP-- t+++(+) 5+++ X+ R tv-(--)@ b !DI D- G e++++ h--- r+++ y++++ ------END GEEK CODE BLOCK------
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