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
2007-06-19
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) 10681-10688]
• 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.
Fig. 3. Carbohydrate structures:
Sucrose (C12H22O11)
Glucose and Fructose (C6H12O6)
Sucrose
a-D-Glucose
a-D-Fructose
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
Fig. 5. Experimental ATR–IR spectra of 15
mixtures of D–glucose and water.
A,
B,
OH and CH stretch regions
finger print and water deformation region
A
ATR Absorbance
1
ATR Absorbance
0
4300
3800
3300
2800
2300
B
1
0
2150
1650
~
 /cm
1150
–1
650
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
A
ATR Absorbance
1
0
4300
3800
3300
2800
2300
B
ATR Absorbance
1
0
2150
1650
1150
~
 /cm
–1
650
Fig. 7. Integrated intensity of:
D–glucose () and D–fructose () aq. solutions
vs. water concentration relative to pure water
Molar integrated HOH deformation
relative intensity
Molar integrated OH stretch relative
intensity
A) OH stretch band;
B) HOH deformation band.
A
1.5
a
b
1.0
B
a
1.5
b
1.0
20
25
30
35
40
45
Water concentration / mol×L–1
50
55
Factor Analysis of
Spectral Data
S 
e
, n
 
 S
P
, f
 
 MF f , n  R
e
, n
Se, experimental spectra; SP, principal spectra;
MF, multiplying factors; Re, residues

MF f ,n  S

P T
f ,
 
S
P
, f
  S 
–1
P T
f ,
 
 Se
No special algorithm is needed
Operations are done in a spreadsheet
But orthogonalization is needed
 ,n
Fig. 9. Pre-orthogonalization FA – glucose
Three principal factors
a, pure water,
b, 2.541 M,
c, 4.440 M glucose.
A) MFs,
B) experimental spectra,
C) residues (Diff. between calculated and exp. spectra)
A
MFs
1.0
b
a
c
-0.2
0
1
2
3
4
D–Glucose concentration / mol×L
–1
ATR Absorbance
B
1.0
c
b
D ATR Absorbance
0.0
0.02
a
C
0.00
-0.02
3700
2700
~
 /cm
1700
–1
700
Thermodynamic Equilibrium in Aqueous
D–glucose and Hydration Numbers
 m - n  H 2O 2  2  C6 H12O6
nH 2O 

 2  C6 H12O6 mH 2O 


C6 H12O6  m H 2O
2
KG 
C6 H12O6  n H 2O  H 2O 2 
2
mn

 2  C6H12O 6 5H 2O 
 5  2  H 2O 2  2  C6H12O6 2 H 2O  

Principal Factor Matrix before
and after Orthogonalization
Matrix
P
P'
MF '
D–glucose
Water
1
0
0
0
1
0
D–fructose
0
0
1
Water Hydrate Hydrate
I
II
55.341 30.584 15.292
0
1.2434 1.0682
0
1.3033 3.3558
Water
1
0
0
0
1
0
0
0
1
Water Hydrate I Hydrate II
55.309 30.511
0
1.5663
0
1.0046
 P'  P
1

14.119
1.1735
3.8266
MF
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.
A
0.2
molar ATR
absorbance
b
c
a×6
0
4300
3800
3300
2800
molar ATR
absorbance
B
2300
c
0.2
b
a×6
0
2200
1700
~
 /cm
1200
700
C
–1
concentration / mol L
–1
4
a÷15
b+c
c
2
b
0
D
K G ×10
4
0.5
0.0
0
1
2
3
D–Glucose concentration / mol L
4
–1
Fig. 13. IR D–glucose hydrate: C–O region
a, pure water (—–)
2800
b, D–glucose pentahydrate (·····)
c, D–glucose dihydrate (——)
2300
c
a×6
1200
700
Fig. 14. Pre-orthogonalization FA – fructose
Three principal factors:
a, pure water,
b, 2.560 M,
c, 5,009 M fructose.
A) MFs,
B) experimental spectra,
C) residues (Diff. between calculated and exp. spectra)
A
MFs
1.0
b
a
c
-0.2
0
1
2
3
4
D–Fructose concentration / mol L
ATR Absorbance
2.0
5
–1
B
1.0
0.0
D ATR Absorbance
0.02
C
0.00
-0.02
3700
2700
~
 /cm
–1
1700
700
Thermodynamic Equilibrium in Aqueous
D–fructose and Hydration Numbers
KF 
C6 H12O6  5 H 2O
C6 H12O6 1H 2O  H 2O 2 
2

 C6H12O 6  5 H 2O
2  H 2O 2  C6 H12O6 1H 2O 

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.
A
0.2
c
molar ATR
absorbance
b
a×6
0
4300
3800
3300
2800
2300
B
molar ATR
absorbance
c
0.2
b
a×6
0
2200
1700
~
 /cm
1200
C
–1
concentration / mol L
700
–1
b+c
a ÷ 15
3
c
b
0
D
K F ×10
2
1
0
0
1
2
3
4
D–Fructose concentration / mol L
–1
5
Fig.
17. IR D–fructose hydrate: C–O region
a×6
a, pure water (—–)
3300
m
b, D–fructose pentahydrate (·····)
c, D–fructose dihydrate (——)
2800
2300
c
a×6
1200
–1
C
700
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
molar ATR absorbance
A
a+b
0.3
c
b
a
0.0
molar ATR absorbance
B
0.6
a+b
c
0.3
a
b
0.0
1300
1250
1200
1150
1100
~
 /cm
1050
–1
1000
950
900
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) 2679-2689.
Acknowledgements
• NSERC (National Science and Engineering
Research Council of Canada)
• UQTR (Université du Québec à Trois-Rivières)
• ITF Lab, Montréal, QC, Canada