Chemistry Reference
In-Depth Information
31.6
31.2
10 G
30.8
30.4
4.3
5.3
6.3
7.3
pH
(a)
6.9
6.8
6.7
6.6
6.5
6.4
6.3
0
10
20
30
Time (min)
40
50
60
(b)
Figure16.10
(a) The pH dependences of hyperfine splitting, (a
N
) measured as a half of the distance between
thelowandhighfieldcomponentsoftheL-bandEPRspectraoftheATIradicalmeasuredatdifferentmodulation
amplitudes, 0.5G (
). Insert: The EPR spectra of the 0.5mM aqueous solutions of the radical R1
measuredatpH6.1,andmodulationamplitudes0.5G(top)and2G(bottom),showingaboutatwofoldincrease
in signal-to-noiseratio for the spectrum measured at higher modulation. Note that the shift of the low and high
field EPR lines between RH
+
and R forms of the radical of the top EPR spectrum is comparable with the line
width,resultinginsignificantdisturbanceoftheEPRlineshapeandcorrespondingnarrowingofthea
N
titration
curve(
)and2G(
).(b)AcidificationofextracellularmediumoftheratheartlocateddirectlyintheresonatoroftheL-band
EPR spectrometer during 1h of global ischemia. The ATI probe (5mM, 2ml) in 0.9% NaCl (
)orinperfused
buffer(
) wasadministeredtotheheartattheonsetofischemia.
rodents. However, loss in EPR sensitivity at low frequency, aggravated by the necessity of acquisition
of numerous spectral projections with variable strength of field gradients, significantly limits spatial and
temporal resolution of the approach. The application of low field EPR spectral detection at high modulation
amplitude provides a significant improvement in sensitivity, allowing for easy conversion of the “position”
image of the low or high field spectral component (Figure 16.10a) in the “pH map”. Figure 16.11a shows
a 3-D image (1-spectral/2-spatial) of a phantom sample of three capillaries with aqueous solutions of ATI
probe with a good spatial (0.2 mm) and functional (0.2 pH units at pH close to the pK of the radical)
resolution obtained for five minutes acquisition time.
Search WWH ::
Custom Search