Oliéric, V.Ennifar, E.Meents, A.Fleurant, M.Besnard, C.Pattison, P.Schiltz, M.Schulze-Briese, C.Dumas, P.2007-06-192007-06-192007-06-19200710.1107/S0907444907019580https://infoscience.epfl.ch/handle/20.500.14299/8766WOS:00024798110000210905Radiation damage in macromolecular crystals is not suppressed even at 90 K. This is particularly true for covalent bonds involving an anomalous scatterer (such as bromine) at the `peak wavelength'. It is shown that a series of absorption spectra recorded on a brominated RNA faithfully monitor the extent of cleavage. The continuous spectral changes during irradiation preserve an `isosbestic point', each spectrum being a linear combination of `zero' and `infinite' dose spectra. This easily yields a good estimate of the partial occupancy of bromine at any intermediate dose. The considerable effect on the near-edge features in the spectra of the crystal orientation versus the beam polarization has also been examined and found to be in good agreement with a previous study. Any significant influence of the (C-Br bond/beam polarization) angle on the cleavage kinetics of bromine was also searched for, but was not detected. These results will be useful for standard SAD/MAD experiments and for the emerging `radiation-damage-induced phasing' method exploiting both the anomalous signal of an anomalous scatterer and the `isomorphous' signal resulting from its cleavage.radiation damageX-ray absorption spectraanomalous scattererstext::journal::journal article::research article