Subject: Re: CCL:gauche+ convention

From: Jeff Nauss <jnauss/at/accelrys.com>
Date: Thu, 15 Jul 2004 09:35:48 -0700

Rick, 

The web site at http://www.chem.qmw.ac.uk/iupac/misc/noGreek/pnuc1.html 
shows gauche+ as being +60 degrees.  But it does refer to polynucleotide 
conformations.

The basic IUPAC definition for torsion angles at 
http://www.chem.qmul.ac.uk/iupac/stereo/TZ.html only states: "The 
synperiplanar conformation is also known as the syn- or cis-conformation; 
antiperiplanar as anti or trans and synclinal as gauche or skew."  I think 
this is for more general situations and I would interpret this as being 
gauche+ being +60 degrees.  Consequently  -60 degrees (or 300 degrees) is 
gauche -.

Hope this helps,
Jeff
--
Jeffrey L. Nauss, Ph.D.
Lead Training Scientist

Accelrys
9685 Scranton Road
San Diego, CA 92121-1761

Phone: 858-799-5555
Fax: 858-799-5100
E-mail: jnauss/at/accelrys.com
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Rick Venable <rvenable/at/pollux.cber.nih.gov> 
Sent by: "Computational Chemistry List" <chemistry-request/at/ccl.net>
07/14/2004 06:13 PM
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Subject
CCL:gauche+ convention

I've been trying to track down references to the convention used to
define the gauche+ torsion state in degrees, and have noted that two
conventions seem to be in use.  From what I can infer,

gauche+ = +60            IUPAC convention
gauche+ = -60            IUPAC-IUB convention

where the latter is used for biological macromolecules.

Is this correct?  Are there any useful references or web sites which can
elaborate on either or both conventions?  Can anyone shed any light on
the history of this dichotomy?

Regards,

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Rick Venable           29/500
FDA/CBER/OVRR Biophysics Lab
1401 Rockville Pike    HFM-419
Rockville, MD  20852-1448  U.S.A.
(301) 496-1905   Rick_Venable/at/nih.gov
ALT email:  rvenable/at/speakeasy.org
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