Vibrational assignments and isomerization rate-constants from time-dependent F.t.-i.r. spectra of sugars
✍ Scribed by Darlene M. Back; Prasad L. Polavarapu
- Publisher
- Elsevier Science
- Year
- 1987
- Tongue
- English
- Weight
- 811 KB
- Volume
- 165
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
Time-dependent F.t.4.r. absorption spectra of cY-D-galactose, er>-fucose, LYn-glucose-Z-d,, a-D-glucose-2-d,, and a-D-glucose-5,6,6-d3 were measured. The spectral changes were interpreted in terms of anomeric isomerization, and possible ~b~tional origins were suggested. The ~tensity changes seen for a-fucose were found to follow a reversibte first-order rate-equation and the rate constants obtained from different vibrational bands were found to be consistent among themselves and in reasonable agreement with those obtained by other techniques. lNTRODUCMON When a pure anomer is dissolved in water, the tautomeric reaction proceeds until an equilibrium is achieved. The structural changes that occur include interconversion among a and /3 anomeric forms and pyranose and furanose ring-forms, These changes will be reflected in the spectra as new bands developing, some initial bands decreasing in intensity, and shifts in some band positions. In order to make use of this potential source for the ~brational-bid assignments of different isomers in solution, which are needed for vibrational circular dichroism inter-pretation2-5, we have recently initiated rg6-s time-dependent F.t.4.r. investigation of simple sugars in aqueous solutions. Earlier articles reported the findings on gl ucose6p7, lyxoses, and sucrosel. We now present the results of studies on galactose, fucose, and isotopomers of glucose. These e~~rnent~ data and the resulting assignments are needed in order to determine the scaling factors for the force constants derived recently9 for glucose by using a molecular-orbital scheme. The timedependent absorption data of fucose are also used to verify whether the rate constants obtained from the absorption intensities of different bands are in agreement among themselves and with those derived from other methods. This verification is errant in order to explain the kinetic isotopic effects. "Fourier-transform Infrared Spectroscopy of Sugars. Part V. For Part IV, see ref. 1.