Chemistry Reference
In-Depth Information
Table 3.1
Assignment of
29
Si resonances for the organically modified trimethoxysilanes
R
Peak assignment δ (ppm)
Structural feature
Phenyl
T
3
0
− 51
RSi(OH)3
T
0
0
− 55
RSi(OMe)3
T
2
1
T
2
1
− 61.1
R(OH)
2
Si
-O-
Si
(OH)
2
R
T
2
1
T
1
2
T
2
1
− 60.9
R(OH)
2
Si
-O-SiR(OH)-O-
Si
(OH)
2
R
T
2
1
T
1
2
T
2
1
− 70.5
R(OH)
2
Si-O-
Si
R(OH)-O-Si(OH)
2
R
Ethyl
T
3
0
− 37.2
R
Si
(OH)
3
T
0
0
− 42.2
R
Si
(OMe)
3
T
2
1
T
2
1
− 46.8
R(OH)
2
Si
-O-
Si
(OH)
2
R
T
0
1
T
0
1
− 50.2
R(OMe)
2
Si
-O-
Si
(OMe)
2
R
T
2
1
T
1
2
T
2
1
− 56.8
R(OH)
2
Si-O-
Si
R(OH)-O-Si(OH)
2
R
Allyl
T
3
0
− 43.3
R
Si
(OH)
3
T
0
0
− 48.0
R
Si
(OMe)
3
T
2
1
T
2
1
− 53.0
R(OH)
2
Si
-O-
Si
(OH)
2
R
T
2
1
T
1
2
T
2
1
− 63.1
R(OH)
2
Si-O-
Si
R(OH)-O-Si(OH)
2
R
On the other hand, the trypsin-mediated hydrolysis of ATMS proceeded rapidly,
with all of the ATMS being consumed within the first 10 h. Unlike the enzyme-
free control experiment in which the
29
Si resonance for ATMS was not visible, it
was clearly seen in the spectra for the trypsin-mediated processes. The only hy-
drolysis product that was evident was allylsilanetriol (− 43.0 ppm). Dimerization
products (− 53.0 ppm) were visible after 7 h. These disiloxanes were difficult to
identify, but given the lack of spectroscopic evidence for the first or second hydro-
lysis products, it is likely that the resonance can be attributed to the fully hydrated
disiloxane, 1,3-diallyl-1,1,3,3-tetrahydroxydisiloxane. Higher order oligomers were
not spectroscopically determinable until after 22 h and resonated at − 63.1 ppm.
Under enzyme-free conditions, there was little evidence to suggest that any hy-
drolysis of PTMS occurred; the only visible resonance was located at − 56.0 ppm
which corresponded to PTMS. An additional resonance appeared at − 51.5 ppm dur-
ing the first hour of spectral acquisition when trypsin was included in the reaction
mixture, corresponding to phenylsilanetriol. The identities of these resonances were
derived from those provided for phentriethoxysilane [
26
] and methyltrimethoxysi-
lane [
25
,
27
]. As with the previous experiments in this series, the first and second
hydrolysis products were not detected.
After 13 h of spectral acquisition, a third and fourth resonance appeared
at − 61.1 ppm and − 70.5 ppm as disiloxane and oligomer formation became
favoured processes. The peak at − 61.1 ppm was assigned as the fully hydroxyl-
ated disiloxane and the peak at − 70.5 ppm as the fully hydroxylated trisiloxane.
However, line broadening may have obscured other resonances. The presence of the
1,3,5-triphenyl-1,1,3,5,5-pentahydroxytrisiloxane oligomer was further confirmed
by the growth of a smaller peak at − 60.9 ppm which we believe to be the end groups
of that oligomer.
