From GOVENDEM@che.und.ac.za Sat Feb 11 01:38:34 1995 Received: from owl.und.ac.za for GOVENDEM@che.und.ac.za by www.ccl.net (8.6.9/930601.1506) id AAA01862; Sat, 11 Feb 1995 00:42:02 -0500 Received: from Charon1.CC.und.ac.za by owl.und.ac.za with SMTP (PP) id <05264-0@owl.und.ac.za>; Sat, 11 Feb 1995 07:41:59 +0200 Received: From CSD/WORKQUEUE by charon1.cc.und.ac.za via Charon-4.0A-VROOM with IPX id 100.950211074127.320; 11 Feb 95 07:41:56 -0200 Message-ID: From: Magan Govender - PG To: chemistry@ccl.net Date: Sat, 11 Feb 1995 07:41:10 +0200 (SAST) Subject: RE: References X-pmrqc: 1 Priority: normal X-mailer: PMail v3.0 (R1a) Dear netters... A friend of mine requires references regarding Experimental Geometries,IR intensities and vibrational frequencies for the following molecules CFCl3, CH2FCl, CHFCl2,CHFCL and CHClF2. Any help would be greatly appreciated. Many thanks ______________________________________________________________________ M.G. Govender Centre for Theoretical and Computational Chemistry Dept of Chemistry University of Natal King George V Avenue Durban South Africa ______________________________________________________________________ From kamal@univ-orleans.fr Sat Feb 11 10:38:42 1995 Received: from centre.univ-orleans.fr for kamal@univ-orleans.fr by www.ccl.net (8.6.9/930601.1506) id KAA04551; Sat, 11 Feb 1995 10:21:19 -0500 Received: from mailhost.univ-orleans.fr ([193.49.81.2]) by centre.univ-orleans.fr (8.6.9/8.6.9) with SMTP id QAA26760 for ; Sat, 11 Feb 1995 16:26:28 +0100 LD?Resent-Date: Sat, 11 Feb 1995 16:26:28 +0100 Message-Id: <199502111526.QAA26760@centre.univ-orleans.fr> X-Sender: kamal@mailhost.univ-orleans.fr X-Mailer: Windows Eudora Version 1.4.4 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Sat, 11 Feb 1995 16:18:52 +0000 To: CHEMISTRY@ccl.net From: kamal@univ-orleans.fr (Kamal Azzaoui) Subject: chromatography and computational chemistry Dears Netters I would exchange informations with everbody working on computational chemistry applied to chromatographic separations and QSRR studies. contact me regards ******************************************************************** Kamal AZZAOUI LCBA Universite d'Orleans France Tel 38-41-70-42 email : kamal@centre.univ-orleans.fr ******************************************************************** From KOEHLER@IRBM.IT Sat Feb 11 11:38:49 1995 Received: from V1.IRBM.IT for KOEHLER@IRBM.IT by www.ccl.net (8.6.9/930601.1506) id LAA04813; Sat, 11 Feb 1995 11:05:08 -0500 Date: Sat, 11 Feb 1995 16:57:22 +0100 (WET) From: "Konrad, IRBM Chemistry, +39-6-91093606" To: chemistry@ccl.net CC: KOEHLER@IRBM.IT Message-Id: <950211165722.2a93@IRBM.IT> Subject: CCL: CoMFA: charge schemes On 10-FEB-1995, Tudor Oprea wrote in response to Nick Tomkinson's post: > MNDO ESP calculations may be slow in MOPAC, but they correlate well with > 631G* ESP charges - 0.94-0.96 R^2 for charge to charge correlation - > better than STO-3G ESP for the same molecules [these with G92]. The latest version of MOPAC93 includes a new option, PMEP[1,2] which is at least two orders of magnitude faster and more accurate (at reproducing 6-31G* ESPFIT charges) than the old MOPAC ESP charges. [1] Ford, G. P.; Wang, B. A new approach to the rapid semiempirical calculation of molecular electrostatic potential based on the AM1 wave function: Comparison with ab initio HF/6-31G* results. J. Comput. Chem. 1993, 14, 1101-1111. [2] Wang, B.; Ford, G. P. Atomic charges derived from a fast and accurate method for electrostatic potentials based on modified AM1 calculations. J. Comput. Chem. 1994, 15, 200-207. > In CoMFA, the choice of charges does not matter as long as you are consistent > throughout the series: "If you can't be right, be consistent" (David Patterson). > In my experience, MNDO vs MNDO ESP charges have no significant impact on > the sets I studied. Of course, there might be some tricky ones out there 8=) > but for systems where no fancy electronic distribution occurs, MNDO or AM1 > can do the works. ... [rest of message deleted] The source of charges may not matter for systems like steroids or peptides, where most commonly used methods (including Gasteiger-Marsili) give reasonable charges. But in my experience, the source of charges does make a _big_ difference for systems such as aromatic heterocycles. We did a comparison of ESPFIT 6-31G* [3] vs. MNDO Mulliken charges [3] vs. Gasteiger-Marsili [unpublished]. The cross validated R2's were 0.71 vs. 0.65 vs. ~0.40 respectively. [3] Allen, M. S.; La Loggia, A. J.; Dorn, L. J.; Martin, M. J.; Costantino, G.; Hagen, T. J.; Koehler, K. F.; Skolnick, P.; Cook, J. M. Predictive binding of b-carboline inverse agonists and antagonists via the CoMFA/GOLPE approach. J. Med. Chem. 1992, 35, 4001-4010. The use of consistent charges will of course cancel systematic errors in the charges. However, if the errors are random and if the electrostatics (relative to sterics, hydrophobicity, etc.) are an important part of the correlation, then bad charges will produce bad correlations. Ciao, ------------------------------------------------------------------ | Konrad Koehler | Computational Chemistry Group | | internet: koehler@irbm.it | Department of Medicinal Chemistry | | | IRBM | | telephone: +39-6-910-93606 | Via Pontina Km. 30,600 | | fax: +39-6-910-93225 | 00040 Pomezia (Roma) | | | Italy | ------------------------------------------------------------------ From steve@carbo.chem.binghamton.edu Sat Feb 11 21:38:49 1995 Received: from carbo.chem.binghamton.edu for steve@carbo.chem.binghamton.edu by www.ccl.net (8.6.9/930601.1506) id UAA08705; Sat, 11 Feb 1995 20:59:59 -0500 Received: by carbo.chem.binghamton.edu (931110.SGI/931108.SGI.ANONFTP) for chemistry@ccl.net id AA02147; Sat, 11 Feb 95 20:58:30 -0500 Date: Sat, 11 Feb 1995 20:51:24 -0500 (EST) From: Steven Schafer Subject: Q:Crystal Structures To: chemistry@ccl.net Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII I have been looking for the following crystal structures, and have had no success: Methyl-3,6-alpha-D-mannopyranoside Methyl-3,6-beta-D-mannopyranoside Methyl-3,6-beta-D-glucopyranoside Methyl-3,6-beta-D-galactopyranoside Is there a searchable index of crystal structures anywhere? I spent a long time in Chem Abstracts and only found the other two alphas (gluco & galacto). I would also need refrences. I have heard about the Cambridge database, but don't know to much about it. Any help you could give would be greatly appreciated. Steven Schafer S.U.N.Y. Binghamton Chemistry Department http://chemiris.chem.binghamton.edu:8080 Binghamton, New York USA