PGSE NMR diffusion study of the self-association of N-methylacetamide in carbon tetrachloride

✍ Scribed by David G. Regan; Bogdan E. Chapman; Philip W. Kuchel

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 225 KB
• Volume: 40
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1117

✦ Synopsis

Abstract

N‐Methylacetamide (NMA) is known to self‐associate in solution through the formation of hydrogen bonds. This behavior, and the presence in the molecule of an amide bond, make this an interesting model for study since the oligomer can be considered to be a protein analogue. The aims of the present study were to estimate the thermodynamic parameters of the self‐association process, through the measurement of the diffusion coefficient of NMA in carbon tetrachloride (CCl~4~), and to predict the population distribution of oligomers as a function of the concentration of NMA. Diffusion coefficients were measured using pulsed field gradient spin‐echo (PGSE) NMR spectroscopy. A computer model based on the Kirkwood–Riseman theory of macromolecular diffusion and an attenuative model of self‐association were used to fit the experimental data and to derive estimates of the thermodynamic association constants and bond length, and these values were, in turn, used to estimate the oligomer distribution. In addition, the temperature dependence of the diffusion coefficient was measured at three different concentrations in order to calculate the apparent Arrhenius activation energies so as to provide additional insight into the self‐association process. Finally, the concentration dependence of the viscosity of NMA in CCl~4~ was measured to characterize further the hydrodynamic behavior of the polydisperse system. Copyright © 2002 John Wiley & Sons, Ltd.