Physical and chemical considerations of damage induced in protein crystals by synchrotron radiation: a radiation chemical perspective

Abstract

Radiation-induced degradation of protein or DNA samples by synchrotron radiation is an inherent problem in X-ray crystallography, especially at the 'brighter' light sources. This short review gives a radiation chemical perspective on some of the physical and chemical processes that need to be considered in understanding potential pathways leading to the gradual degradation of the samples. Under the conditions used for X-ray crystallography at a temperature of <100 K in the presence of cryoprotectant agents, the majority of radiation damage of the protein samples arises from direct ionization of the amino acid residues and their associated water molecules. Some of the chemical processes that may occur at these protein centres, such as bond scission, are discussed. Several approaches are discussed that may reduce radiation damage, using agents known from radiation chemistry to minimize radical-induced degradation of the sample.

Changes of the Molecular Structure in Organic Thin Film Transistors during Operation

“…Preliminary measurements concerned the control of the exposure time to the highly collimated X-ray synchrotron beam generating photoelectrons which may affect the OFET response on one hand, and consequently the parameters extracted, and, on the other hand cause radiation damage to the organic film. [31][32][33] By applying V DS = V GS = -20 V, the source-drain current (I DS ) and the source-gate current (I GS ) were continuously measured (Figure 2a) while X-ray measurements around the 001 reflection were carried out every 40 minutes (/2 and  scan, RC, reported in Figure S5) to monitor the evolution of stacking layer periodicity. The occurrence of the bias stress during the device operation is evidenced by the characteristic decrease of |I DS |, compensated by the photocurrent generated by Xray irradiation (inset in The RC shift to smaller angles can be ascribed to a lattice expansion along the film thickness (i.e.…”

Diffraction data analysis in the presence of radiation damage

“…Localized in real space, the specific changes induced by X-ray radiation are a complex function of radiation chemistry. Each absorbed photon generates hundreds of secondary ionization events at distances much larger than the unit-cell repeat in the crystal, so effectively the changes arising from these secondary events (O'Neill et al, 2002) as well as those arising from the recombination of their products are not localized at the absorption site. Localized changes can be identified by calculating the corresponding electron-density map, which represents the difference between the initial and radiation-exposed states.…”

X-ray absorption by macromolecular crystals: the effects of wavelength and crystal composition on absorbed dose

“…The energy of the photoelectron is dissipated in the crystal, contributing to mechanical disruption of the crystal lattice, thermal heating, ionizations and bond scissions. Although the relative probabilities of these various events is not known, it has been estimated that a single absorbed photon could produce~500 ionization events (O'Neill et al, 2002). The absorbed energy is not uniformly distributed but is deposited in small volumes known as`spurs' (Ravelli & McSweeney, 2000).…”