AN ANALYSIS OF CIRCULAR DICHROISM SPECTRA OF URONIC ACIDS

The circular dichroism spectra of a number of uronic acids with equatorial hydroxyl groups at C-4 were examined and compared with the spectra of uronic acids with axial hydroxyl groups at C-4. In aqueous solution, the derivatives of glucuronic and mannuronic acids exhibited negative circular dichroism bands near 234 mμ and positive bands with maxima near 206 mμ. Only a positive band near 210 mμ was obtained for galacturonic acid and its derivatives. For the glucuronic and mannuronic acid derivatives, it appeared that the true position of the band was obscured because of the overlap of the two bands of opposite sign. Thus, in nonaqueous solvents the negative band was more pronounced and was centered near 225-228 mμ. This increase in magnitude of the negative band was always accompanied by an attendant decrease in the magnitude of the positive band. Differences in the mode of solvation of two distinct structural species of these uronic acids in solution probably account for the presence of two bands. © 1969, American Chemical Society. All rights reserved.