Correlation of structure and vibrational spectra of the
zwitterion
L
-alanine in the presence of water: an experimental
and density functional analysis
Michael W. Ellzy
a,
*, James O. Jensen
a
, Hendrik F. Hameka
b
, Jack G. Kay
c
a
US Army Edgewood Research Development and Engineering Center, Aberdeen Proving Grounds, Aberdeen, MD 21010-5423, USA
b
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 10194, USA
c
Department of Chemistry, Drexel University, Philadelphia, PA 19104, USA
Received 17 October 2002; received in revised form 30 December 2002; accepted 10 January 2003
Abstract
Infrared vibrational spectra were collected along with the vibrational circular dichroism (VCD) spectra for the
zwitterions a-
D
-alanine, a-
L
-alanine, a-
D
-mannose and a-
L
-mannose as potassium bromide (KBr) pressed samples.
VCD for
D
- and
L
-alanine dissolved in water was also measured and compared against the spectra resulting from KBr
pressed samples. The experimental data were compared against the ab initio B3LYP/6-31G* optimized geometry. The
zwitterion structure of a-
L
-alanine was stabilized by the addition of water molecules. Computationally, b-
L
-mannose
was studied and resulting expected VCD bands assigned. We present the molecular structures resulting VCD spectra
and infrared vibrational spectra from experimentation as compared with the computed results.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Zwitterion; a-
L
-Alanine; a-
D
-Alanine; a-
L
-Mannose; b-
L
-Mannose; Vibrational circular dichroism; Ab initio; Density
functional field theory; Moller Á
/
Plesset second-order perturbation theory; Becke 3 Lee Young Parr; Gaussian 98
1. Introduction
Ab initio analysis is a useful approach for the
evaluation of biological and chemical compounds.
An important aspect of this computational tech-
nique is the ability to determine structural details
for the analyte under investigation. Extending the
application of ab initio analysis is the ability to
apply vibrational information towards the inter-
pretation of analyte conformation. For chiral
compounds, precise stereo-chemical information
is obtained with the application of vibrational
circular dichroism (VCD) in conjunction with ab
initio analysis. The approach has been applied to
conformational analysis of various carbohydrates
[1] dissolved in carbon disulfide. Our current
interest in VCD is the potential to use the
* Corresponding author. Tel.: '
/
1-410-436-3957; fax: '
/
1-
410-436-1846.
E-mail address: mwellzy@sbccom.apgea.army.mil (M.W.
Ellzy).
Spectrochimica Acta Part A 59 (2003) 2619 Á
/
2633
www.elsevier.com/locate/saa
1386-1425/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S1386-1425(03)00036-2