eprintid: 17809
rev_number: 22
userid: 1419
dir: disk0/00/01/78/09
datestamp: 2013-03-20 16:41:06
lastmod: 2021-06-12 23:55:34
status_changed: 2013-03-20 16:41:06
type: article
metadata_visibility: show
item_issues_count: 0
eprint_status: archive
creators_name: Holtz, JSW
creators_name: Li, P
creators_name: Asher, SA
creators_email: 
creators_email: 
creators_email: asher@pitt.edu
creators_id: 
creators_id: 
creators_id: ASHER
title: UV resonance Raman studies of cis-to-trans isomerization of glycyglycine derivatives
ispublished: pub
divisions: sch_as_chemistry
full_text_status: public
abstract: We report kinetic UV resonance Raman measurements of the pH dependence of the activation barrier for the trans-cis isomerization of glycylglycine (Gly-Gly). We determined the charge-state dependence of the trans-cis ground- state energy difference, ΔG, and the trans-cis isomerization activation barrier, E(a). ΔG for zwitterionic Gly-Gly at pH 5.7 (3.0 ± 0.5 kcal/mol) is below that of pH 10.5 anionic Gly-Gly (4.4 ± 0.7 kcal/mol). The measured value of ΔG for cationic Gly-Gly at pH 3.0 (3.6 ± 0.4 kcal/mol) lies between the zwitterion and anion values. The measured trans-to-cis activation barriers of 13.3 ± 1.0, 12.6 ± 0.9, and 13.9 ± 1.1 kcal/mol for the cation, the zwitterion, and the anion, respectively, are identical within experimental error. However, the larger zwitterionic Gly-Gly (13 ± 1.9 s-1) cis-to-trans isomerization rate constant over those of the cation (3 ± 0.4 s-1) and anion (2 ± 0.3 s-1) suggests a ~1 kcal/mol decreased activation barrier. The small differences in energy and activation barriers are somewhat surprising since the zwitterionic form can uniquely form ion pairs, which should impact the trans, the cis, and the activated complex energies.
date: 1999-04-21
date_type: published
publication: Journal of the American Chemical Society
volume: 121
number: 15
pagerange: 3762 - 3766
refereed: TRUE
issn: 0002-7863
id_number: 10.1021/ja984003b
citation:   Holtz, JSW and Li, P and Asher, SA  (1999) UV resonance Raman studies of cis-to-trans isomerization of glycyglycine derivatives.  Journal of the American Chemical Society, 121 (15).  3762 - 3766.  ISSN 0002-7863     
document_url: http://d-scholarship-dev.library.pitt.edu/17809/1/licence.txt