Applying Low Field 13C NMR Spectroscopy to Find the Isoelectric Points of Amino Acids

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 12 Issue 4 (2007) pp 282-285

Applying Low Field ¹³C NMR Spectroscopy to Find the Isoelectric Points of Amino Acids

Jun H. Shin^†, Sabrina Song^†, Yoomi Kim^†, and Gopal Subramaniam^‡*

^†Department of Chemistry, Queensborough Community College -CUNY, Bayside, NY 11364; ^‡Department of Chemistry and Biochemistry, Queens College -CUNY, Flushing NY 11367, gopal.subramaniam@qc.cuny.edu
Received May 18, 2007. Accepted June 8, 2007.

Published online: 4 August 2007

Abstract. We describe a cost efficient ¹³C NMR spectroscopy experiment using a low-field NMR instrument and non-deuterated aqueous solutions that can be easily performed at teaching schools where high field instruments are not affordable. The experiment uses the effect of pH on the structure of amino acids, which affects the chemical shifts. By monitoring the changes in the¹³C chemical shifts of the amino acid as a function of pH, we can find the isoelectric points (pI) of alanine, cysteine, glycine, proline, serine, threonine, valine and methionine. Other than the one-time cost of purchasing the instrument, ongoing reagent costs are minimal and comparable to other laboratory experiments. The method complements other biophysical methods to find the pI of amino acids and serves as an introduction to the application of the NMR spectroscopy technique to biological compounds with concepts learned in introductory chemistry courses. This experiment is designed for students who have finished the equivalent of the first two semesters of basic chemistry and it provides hands-on learning to a very fundamental structure determination technique.

Key Words: Laboratories and Demonstrations; general chemistry; 2-year college; high school; organic chemistry; biochemistry; hands-on learning; amino acids; isoelectric point; biophysical chemistry; NMR spectroscopy; instrumental methods; pH titration; 13C NMR spectroscopy; undergraduate research

(*) Corresponding author. (E-mail: gopal.subramaniam@qc.cuny.edu)

Article in PDF format (117 KB) HTML format page numbers updated 9/15/07

Supporting Materials:

An instructor note section detailing the chemicals and equipments, procedure, implementation, pre-lab, and post-lab exercises is available. A simple step-by-step operating procedure for acquiring NMR spectrum adopted for our organic chemistry laboratory is also available. (327 KB)