1. IR SPECTROSCOPY of GLUCOSE and FRUCTOSE HYDRATES in AQUEOUS SOLUTIONS
Camille CHAPADOS
and Jean-Joseph MAX
Département de chimie–biologie
Université du Québec à Trois-Rivières
Trois-Rivières, QC, Canada G9A 5H7

2. Abstract
The composition of common carbohydrates (sucrose, glucose, fructose, etc.) in aqueous solutions is not known
To remedy this situation we studied previously aqueous sucrose by IR [J. Phys. Chem. A 105, # 47 (2001) ]
Factor analysis was used to obtain the principal spectra and the species abundances
Three species were obtained: 1) pure water; 2) sucrose pentahydrates {5}; and 3) sucrose dihydrates {2}. These are present in the whole solubility range
Here we present a similar study on D–glucose and D–fructose in aqueous solutions
For these we also found three species: water and two hydrates
The biggest spectral differences of the carbohydrate species lie in the C–O stretch region.
For D–glucose we found pentahydrates {5} and dihydrates {2}
For D–fructose we found pentahydrates {5} and monohydrates {1}
As a function of the sugar concentration, the hydrate abundances are non linear but their sum are
The four hydrates are present only in aqueous solutions and are not obtained in the solid state.
We will present the spectra of each carbohydrate hydrates.

3. Fig. 3. Carbohydrate structures: Sucrose (C12H22O11) Glucose and Fructose (C6H12O6)
a-D-Glucose
a-D-Fructose

4. Experimental FTIR ATR (ZnSe cylindrical crystal)
(3.3 internal reflections)
500 scans (2 cm–1 resolution)
Successive addition of the mother solutions to the measured solutions
Continuous circulation of the samples

5. Fig. 5. Experimental ATR–IR spectra of 15 mixtures of D–glucose and water. A, OH and CH stretch regions B, finger print and water deformation region

6. Fig. 6. Experimental ATR–IR spectra of 19 mixtures of D–fructose and water. A, OH and CH stretch regions B, finger print and water deformation region

7. Fig. 7. Integrated intensity of: D–glucose (ª) and D–fructose (Ñ) aq
Fig. 7. Integrated intensity of: D–glucose (ª) and D–fructose (Ñ) aq. solutions vs. water concentration relative to pure water A) OH stretch band; B) HOH deformation band.

8. Factor Analysis of Spectral Data
Se, experimental spectra; SP, principal spectra;
MF, multiplying factors; Re, residues
No special algorithm is needed
Operations are done in a spreadsheet
But orthogonalization is needed

9. Fig. 9. Pre-orthogonalization FA – glucose
Fig. 9. Pre-orthogonalization FA – glucose Three principal factors a, pure water, b, M, c, M glucose. A) MFs, B) experimental spectra, C) residues (Diff. between calculated and exp. spectra)
C) residues obtained from the difference between calculated (S MF × principal spectrum) and experimental spectra

10. Thermodynamic Equilibrium in Aqueous D–glucose and Hydration Numbers

11. Principal Factor Matrix before and after Orthogonalization

12. Fig. 12. Post-orthogonalization FA – glucose
Fig. 12. Post-orthogonalization FA – glucose Three principal factors: a, pure water; b, D–glucose penta– and c, di–hydrates. A) and B) spectra; C) Species concentration; D) Equilibrium constant: KG.

13. Fig. 13. IR D–glucose hydrate: C–O region a, pure water (—–) b, D–glucose pentahydrate (·····) c, D–glucose dihydrate (——)

14. Fig. 14. Pre-orthogonalization FA – fructose
Fig. 14. Pre-orthogonalization FA – fructose Three principal factors: a, pure water, b, M, c, 5,009 M fructose. A) MFs, B) experimental spectra, C) residues (Diff. between calculated and exp. spectra)

15. Thermodynamic Equilibrium in Aqueous D–fructose and Hydration Numbers

16. Fig. 16. Post-orthogonalization FA – fructose
Fig. 16. Post-orthogonalization FA – fructose Three principal factors: a, pure water; b, D–fructose penta– and c, mono–hydrates. A) and B) spectra; C) Species concentration; D) Equilibrium constant: KF.

17. Fig. 17. IR D–fructose hydrate: C–O region a, pure water (—–) b, D–fructose pentahydrate (·····) c, D–fructose dihydrate (——)

18. Fig. 18. IR of C–O & C–C of sugar st. region A, pentahydrates of
Fig. 18. IR of C–O & C–C of sugar st. region A, pentahydrates of (a) D–glucose, (b) D–fructose, and (c) sucrose. B, dihydrates of (a) glucose, (c) and sucrose, and (b) fructose monohydrate

19. Conclusion
In aqueous solutions, glucose has two hydrates: pentahydrate and dihydrate;
This is similar to that of sucrose;
In aqueous solutions, fructose has two hydrates: pentahydrate and monohydrate;
This is different to that of glucose and sucrose;
The reasons lie probably in the rigidity of fructose compared to that of glucose and sucrose;
The hydrates of glucose and fructose in aqueous solutions are different than that in the solid.
Reference: J. Phys. Chem. A 111, # 14 (2007)

20. Acknowledgements NSERC (National Science and Engineering
Research Council of Canada)
UQTR (Université du Québec à Trois-Rivières)
ITF Lab, Montréal, QC, Canada