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![[Figure 7]](hi2028fig7mag.jpg)
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Figure 7
A test of the hypothesis that X-radiation damage, as monitored by X-ray diffraction, requires the presence of an excess-water phase for expression. Low-angle patterns from DMPC in the Lα phase (reflections are indicated in figure) at 34% w/w water (representing the water-stressed condition) were recorded at 302 K with 0 Mrad (I) and 50 Mrad (II) of X-ray exposure. Very little change in the diffraction pattern is apparent under these conditions of water stress. The sample giving rise to pattern II was subsequently cooled to 283 K, where the Lβ′ phase forms under normal conditions, and the diffraction pattern (III) was recorded by irradiating in the same spot used to collect data for pattern II. Pattern III is what is expected for the extensively radiation-damaged Lβ′ phase in excess water. At 283 K and an overall sample composition of 34% w/w water, this sample is expected to be under conditions of excess water. The pattern shown in IV was recorded by translating the capillary by 0.6 mm in the direction perpendicular to the X-ray beam to expose a region of the sample that had not previously been X-irradiated. Pattern IV is typical of the Lβ′ phase in equilibrium with excess water. Diffraction patterns were collected on the A1 station at CHESS (8 keV, 2 × 1010 photons s−1). Modified from Fig. 7 of Cheng & Caffrey (1996  ). |
![[Figure 7]](hi2028fig7.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
