Hi Everyone,
Pavel’s statement is likely a bit of an exaggeration, but he has a valid (yet hard to prove point). The default in CCP4i was (and is?) to use hydrogens only if present in the input file. This is IMO not a safe default. Because there were some reporting errors in the past (http://proteincrystallography.org/ccp4bb/message18808.html) it is hard to tell from the PDB when refinement with hydrogens became hip. Discussions on this BB show that at the use of riding hydrogens is still not fully accepted, especially at low resolution (where they actually help most). Cheers, Robbie From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Pavel Afonine Sent: Monday, March 05, 2012 21:53 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] REFMAC Riding Hydrogens Dear Tim, good catch, thanks; I could craft that phrase more carefully! Although often it may not be quite fair to take phrases out of context: this newsletter article was written in the context of macromolecular refinement. And yes, "recently" may be a broad term -:) All the best, Pavel On Mon, Mar 5, 2012 at 12:45 PM, Tim Gruene <t...@shelx.uni-ac.gwdg.de> wrote: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Pavel, you may want to add to the structures mentioned in [1] one or two organic structures present in the Cambridge Database. "Until recently it was customary to ignore hydrogen atoms throughout the process of crystallographic X-‐ray structure determination." [1] 'recently' as in 1997 [2]? Even though 1997 is probably a poor estimation of the corresponding year... Cheers, Tim [1] "On contribution of hydrogen atoms to X-ray scattering" http://www.phenix-online.org/newsletter/ [2] http://shelx.uni-ac.gwdg.de/SHELX/shelx.pdf On 03/05/2012 09:14 PM, Pavel Afonine wrote: > Hi, > > On Mon, Mar 5, 2012 at 11:52 AM, Matthew Franklin <mfrank...@nysbc.org>wrote: > >> Adding the riding hydrogens generally gives you some improvement in R >> factors even with a good quality (i.e. stereochemically correct) model. >> > > and here are the results of more or less systematic test that prove this: > > see "On contribution of hydrogen atoms to X-ray scattering" > here: > http://www.phenix-online.org/newsletter/ > > Pavel > - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFPVSXkUxlJ7aRr7hoRAm1TAJ9Hyfhkl3yhD5QSKw9I4RSK58m0fACgmlxk YGILzeMam/3gQVmCeh0vQ8k= =3m2J -----END PGP SIGNATURE-----
