Submitted to: UJNR Food & Agricultural Panel Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/24/2008
Publication Date: 8/24/2008
Citation: Vermillion, K., Price, N.P. 2008. Applications of Diffusion Ordered Spectroscopy (DOSY-NMR) [abstract]. UJNR Food & Agricultural Panel Meeting. p. 174-175.
Technical Abstract: Diffusion-ordered NMR (DOSY-NMR) is a powerful, but under-utilized, technique for the investigation of mixtures based on translational diffusion rates. DOSY spectra allow for determination by NMR of components that may differ in molecular weight, geometry or complexation. Typical applications could include small sugars and oligiosaccharides, micelle formation and protein bindings. DOSY-NMR experiments may be done on a standard NMR spectrometer equipped with a z-gradient probe. The pulse programs, acquisition macros and processing software needed are considerably different from typical 2D experiments but are available from most instrument manufacturers. DOSY-NMR can be used to rapidly determine micelle formation and behavior. In this paper, we show a series of proton DOSY-NMR spectra of increasing concentration of octyl-b-D-glucopyranoside in D2O. The diffusion constant (as log D) remains constant below the critical micelle concentration (~8 mg/mL) and then increases rapidly during micelle formation. This type of experiment is a convenient, fast way to test for micelle formation and determination of the CMC. The acquisition at each concentration of octyl-b-D-glucopyranoside required only 4 min acquisition time. Further changes to micelle geometry (such as spherical to rods or sheets) are expected to show a similar stepwise change in the diffusion constant. DOSY-NMR can be used for investigating structures with variable molecular weights composed of multiple repeating units, such as monomer ' diamer transitions or soluble polymers. Calibration curves can be used to determine molecular weights of compounds with similar geometry. In this paper, we show a series of Shodex pullulan standards in D2O at 1mg/mL plotted vs. diffusion constant, and there is good linearity of the correlation (log MW vs. log D) over most of the range. This correlation can be used to determine the approximate molecular weight of pullulans produced by different strains of fungi under different conditions. Three pullulans are shown with differing molecular weights and, hence, diffusion constants.