Transcript Investigation of the efficiency and mechanism of gelation

Investigation of the efficiency and mechanism of
gelation and degelation of three positional
isomers of aminobenzoic acid
Vimon Tantishaiyakul
Prince of Songkla University
25th FAPA CONGRESS 2014
Kota Kinabalu, Sabah, Malaysia, 9-12 October 2014
1
P
S
U
Objectives
• Mechanism/interactions/properties of
supramolecular hydrogels
– low-molecular-weight gelators (LMWGs)
• Model compounds
• melamine (M)
• three positional isomers of aminobenzoic acid (AB)
oAB
mAB
pAB
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Methods
• Differential scanning calorimetry (DSC)
• Viscoelastic measurements
• Fourier transform infrared spectroscopy
(FTIR)
• Hot-stage microscope
• powder X-ray diffraction (PXRD)
• scanning electron microscopy (SEM)
• Computational method
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55.93
73.43
55.56
first heat
83.36
57.65
first heat
50
57.18
37.65
first heat
first cool
57.56
56.11
40
second cool
first cool
first cool
30
0.1 W/g
second cool
Heat flow (endo up)
78.69
second heat
Heat flow (endo up)
second cool
Heat flow (endo up)
80.11
0.4 W/g
0.4 W/g
second heat
second heat
60
70
80
90
30
o
Temperature ( C)
40
50
60
70
80
37.81
90
Temperature (oC)
30
40
50
60
70
o
Temperature ( C)
– energy needed to dissociate the H-bond is endothermic.
•
an endothermic peak
–
•
indicated the transition from the gel to a sol.
an exothermic peak
–
reflects the formation of a gel
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55.93
73.43
55.56
first heat
83.36
57.65
first heat
50
57.18
37.65
first heat
first cool
57.56
56.11
40
second cool
first cool
first cool
30
0.1 W/g
second cool
Heat flow (endo up)
78.69
second heat
Heat flow (endo up)
second cool
Heat flow (endo up)
80.11
0.4 W/g
0.4 W/g
second heat
second heat
60
70
o
Temperature ( C)
80
90
30
40
50
60
70
Temperature (oC)
80
37.81
90
30
40
50
60
70
o
Temperature ( C)
–
–
–
–
All samples were in the gel form at low temperature
All samples became a sol at a higher temperature
All showed the characteristics of a thermo-reversible gel
gel formation temperatures
•
•
oAB/M and pAB/M were comparable
mAB/M was the lowest
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pAB/M : E = 0.00 kcal mol–1
The optimized
structures and
relative energies
(E) of the most
possible
conformation for
each 1:1 AB/M
cluster and the Hbond information
1
2
2
mAB/M : E = 0.87 kcal mol–1
intermolecular Hbond interactions
formed between a
oAB/M : E = 1.66 kcal mol–1
COOH group of
AB and the NH2
group and N atom
of M.
•
•
Interaction between pAB and M
stronger than
1
[1] O..H = 1.96 Å
[2] N..H = 1.68 Å
mAB and M
oAB and M
The E values in order from the lowest to the highest are
pAB/M < mAB/M < oAB/M
The lower E indicated stronger interactions between the M and AB.
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G’ > G”
Gel
10000
•
pAB/M: G’ > G” over
this specified
temperature range
Dynamic modula (Pa)
1000
100
10
1
Beyond 74°C
.1
–
.01
.001
20
30
40
50
60
70
80
Temperature (oC)
Temperature sweep measurements : heating from 25 to 74°C
•
–
some samples could not be
measured
due to the melting of the
samples which turned into nonviscous liquids.
storage moduli (G’) were higher than loss moduli (G”)
–
Indicate the samples were gels
•
•
G’ value :
pAB/M > mAB/M > oAB/M
strength of the gels : pAB/M > mAB/M > oAB/M
•
Computational results (strong interaction) :
pAB/M > mAB/M > oAB/M
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73.43
second heat
0.4 W/g
10000
1000
Heat flow (endo up)
Dynamic modula (Pa)
second cool
100
10
1
G' oAB/M
G' mAB/M
G' pAB/M
0.1
78.69
55.56
first heat
first cool
0.01
56.11
30
0.001
20
30
40
50
60
70
40
50
60
70
80
90
o
80
Temperature ( C)
o
Temperature ( C)
•
consistent with the DSC analysis that showed the melting temperature to be about 80°C
1
1
2
2
[1] O..H = 1.96 Å
O..N = 2.96 Å
O..H-N = 171.14°
[2] N..H = 1.68 Å
N..O = 2.69 Å
N..H-O = 169.60°
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73.43
0.4 W/g
second heat
10000
100
10
1
G' oAB/M
G' mAB/M
G' pAB/M
0.1
second cool
Heat flow (endo up)
Dynamic modula (Pa)
1000
78.69
55.56
first heat
first cool
0.01
56.11
0.001
20
30
40
50
60
70
30
80
40
50
60
70
80
90
Temperature (oC)
Temperature (oC)
• consistent with the DSC analysis that showed the melting
temperature to be about 78°C
1
2
3
1
2
3
[1] O..H = 1.96 Å
O..N = 2.96 Å
O..H-N = 169.49°
[2] N..H = 1.67 Å
N..O = 2.67 Å
N..H-O = 169.71°
[3] O..H = 2.00 Å
O..N = 2.72 Å
O..H-N = 126.66°
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55.93
0.1 W/g
second heat
10000
second cool
Heat flow (endo up)
Dynamic modula (Pa)
1000
100
10
1
G' oAB/M
G' mAB/M
G' pAB/M
0.1
57.18
37.65
first heat
first cool
0.01
0.001
20
30
40
50
FTIR + computational Method
37.81
60
70
80
verify this phenomena
30
40
Temperature (oC)
50
60
70
o
Temperature ( C)
• DSC: mp  55◦C, comparable to rheological measurement
• mAB/M, was a stronger gel than the oAB/M
• mAB/M exhibited a lower degelation temperature than the oAB/M
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M showed NH : 3469, 3419 and 3330
cm−1
•
1650
3127
M 3469
3330
oAB showed NH: 3324 and 3239 cm−1
oAB showed OH: 3100–2400 cm−1
oAB
oAB showed C=O: 1661 cm−1
•
•
•
•
•
3419
1661
3324 3239
3419
1699
3131
1680
3469
oAB/M, NH: 3469 and 3419 cm−1of M
oAB/M, C=O: 1699, 1680 cm-1
1
2
3339
oAB/M
3
4000
3000
2000
1000
-1
Wavenumber (cm )
•
More than one C=O band for the oAB/M was observed
•
Generally, carboxylic acids exits as a dimer and their C=O stretching vibrations
are lower than those of the monomers or the normal C=O of ketone.
•
•
The shift to a higher wavenumber of the C=O bands
probably due to the existence of the acids in their monomer forms and these
C=O groups may instead form weaker H-bonds with M compared to the strong
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H-bonds of the dimers.
M showed NH : 3469, 3419 and 3330
cm−1
•
1650
3127
M 3469
3330
mAB, NH: No peak
mAB, C=O: No peak
•
•
•
•
3419
1622
mAB
1691
3420
mAB/M, NH: 3420, 3344
mAB/M, C=O: 1691 cm-1
• shift to a higher wavenumber
mAB/M 3344
1667
4000
3000
2000
1000
-1
Wavenumber (cm )
•
•
mAB prefers to exist in its zwitterionic form
mAB/M gel, C=O 1691 cm-1 : mAB was changed from its zwitterionic form,
mABz, to the uncharged form when it formed a gel via interacting with M.
•
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3419
1650
3127
M 3469
3330
1622
mAB
3324
1644
mAB/M (mAB, zwitterionic form)
3339
mAB/M gel, warm to
sol at about 60C
Dry, FTIR
C=O at 1691 cm−1
disappeared.
•
•
•
mAB/M
1691
3420
3344
4000
3000
2000
1000
-1
Wavenumber (cm )
•
•
conversion of the mAB from the uncharged form in the gel state to the
zwitterionic form when the mAB/M gel was heated to about 60°C.
This FTIR data strongly supported the phenomena observed by the DSC and
rheological studies.
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mABzw/M:
6.72kcal
kcal
–1
mABzw/M
: EE
= =6.72
molmol
–1
mAB/M:
0.87kcal
kcal
mAB/M
: EE
= =0.87
molmol
-1
[1] O..H = 2.74 Å
O..N = 3.75 Å
O..H-N = 178.37°
1
1
2
-1
[1] O..H = 1.94 Å
O..N = 2.94 Å
O..H-N = 171.14°
[2] N..H = 1.66 Å
N..O = 2.67 Å
N..H-O = 169.78°
• zwitterionic form of mAB (mABz),
• the most possible structure of the 1:1 mABz/M cluster was more
unstable than the 1:1 mAB/M cluster.
• The E value of the mABz/M cluster was higher than that of the
mAB/M by about 6 kcal mol−1.
• an inter-molecular COO−· · ·NH2 H-bond of mABz/M was very weak.
oAB/M : E = 1.66 kcal mol–1
10000
•
Dynamic modula (Pa)
1000
100
10
1
G' oAB/M
G' mAB/M
G' pAB/M
0.1
0.01
0.001
20
30
40
50
60
Temperature (oC)
70
80
weak interaction, low degelation temperature
• The H-bond between the mAB and M decrease
• when the mAB was changed to its zwitterionic
structure,
• causing a lower degelation temperature
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M showed NH : 3469, 3419 and 3330
cm−1
•
1650
3127
M 3469
3330
1667
pAB showed NH: 3461 and 3363 cm−1
3363
−1
pAB showed OH: 3100–2400 cm
3461
pAB showed C=O: 1667 cm−1
pAB
•
•
•
•
•
3419
1693
pAB/M, NH: no peak
pAB/M, C=O: 1693 cm-1
• shift to a higher wavenumber
pAB/M
monomer
4000
3000
2000
1000
-1
wavenumber (cm )
•
•
•
pAB/M, NH: no peak detected
demonstrate the strong H-bonds between the pAB and M
via the NH groups of both the M and pAB with other groups of each compound.
•
•
interactions between the M and AB are sequence of pAB/M>mAB/M, oAB/M.
interactions between M and ABs (FTIR) were in agreement with the rheological
and DSC analyses that showed the same order of gel strength
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Polarizing optical
micrographs
gels
SEM images
Freeze-dried xerogels
• similar features : SEM & polarizing micrographs
• Features of each gel remained almost unchanged on
drying.
• Each gel and xerogel showed different structures.
– different isomers of AB may cause distinct supramolecular
interactions with M and create diverse structures.
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• PXRD xerogels
• All samples show crystalline
peaks.
• PXRD patterns of each xerogel
were different from each other.
M
oAB
oAB/M
• Each xerogel showed
different PXRD patterns
compared to those of the
individual components.
• This indicated that there were
intermolecular interactions
between M and each AB.
mAB
mAB/M
pAB
pAB/M
10
20
30
2 theta
40
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Conclusion
• Thermo-responsive based on low-molecular-weight
gelators (LMWG) M & ABs were successfully generated.
• Gelation efficiency : pAB/M > mAB/M > oAB/M
• Gel properties: DSC, viscoelastic measurements
• Interactions: FTIR, computational method
• Useful to investigate other LMWG systems for
pharmaceutical applications
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Dr. Supaporn Dokmaisrijan
Dr. Namon Hirun
Samon Juntarapet
Acknowledgements
• Thailand Research Fund through the Royal
Golden Jubilee Ph.D. Program through
Grant No PHD/0045/2552
• the Nanotechnology Center (NANOTEC),
NSTDA, Ministry of Science and
Technology, Thailand, through its program
of Center of Excellence Network
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Colloids and Surfaces A: Physicochem. Eng. Aspects 446 (2014) 118–126
PSU At a Glance...
Surat Thani
Hat Yai
Phuket
Trang
Pattani
• 1st University in Southern Thailand, est. 1967
• 5 Campuses
21
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22
55.93
73.43
55.56
first heat
83.36
57.65
first heat
50
57.18
37.65
first heat
first cool
57.56
56.11
40
second cool
first cool
first cool
30
0.1 W/g
second cool
Heat flow (endo up)
78.69
second heat
Heat flow (endo up)
second cool
Heat flow (endo up)
80.11
0.4 W/g
0.4 W/g
second heat
second heat
60
70
o
Temperature ( C)
80
90
30
40
50
60
70
Temperature (oC)
80
37.81
90
30
40
50
60
70
o
Temperature ( C)
– energy needed to dissociate the H-bond is
endothermic.
•
•
an endothermic peak indicated the transition from the
gel to a sol.
an exothermic peak reflects the formation of a gel
23
• All ab initio calculations were performed using the Gaussian03W
program.
• The study began by the full geometry optimization of the M, oAB,
mAB (both in the uncharged, and the zwitterionicforms,) and with
pAB molecules at the MP2/6-311 ++G(2d,2p) calculations.
• The optimized structures of these molecules were further used to
generate the trial structures of the AB/M clusters.
• Since the mole ratio of the AB and M in each AB/M cluster in the
experimental method was 1:1, calculations of the 1:1 AB/Mclusters
were performed
24