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The chemical shift of the anomeric proton is very different in M (4.6-4.7 ppm)
and G (5.05 ppm). We also see resonances for the G-5 proton. In addition,
the shift depends strongly on the sequence.
The peak areas can be determined by the NMR software, and from these
areas all sequence parameters are easily calculated. The next example
shows this in more detail:
The
peaks
denoted A-C correspond to the following protons:
Peak
Chemical shift
(ppm)
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Peak identity
Comment
A
5.05
G-1
All G independent of sequence
B1
4.75
GGM-5
Termination G-block
B2
4.72
MGM-5
Single G
B3
4.70
MG-1
B4
4.67
MM-1
C
4.46
4.44
GGG-5
MGG-5
ü
⎭
GGG-5 + MGG-5 = GG-5
11
Chemical shift depends also on pH. Normally we use pH = ca. 7 (strictly: pD).
A
B1
B2
B3
B4
C
R
2
R
1
Figure 15. Assignment of peaks used for determining
sequence parameters in alginates