# 2007 International Union of CrystallographyPrinted in Denmark -all rights reserved Radiation 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.

In this paper the anisotropy of anomalous scattering at the Br K-absorption edge in brominated nucleotides is investigated, and it is shown that this effect can give rise to a marked directional dependence of the anomalous signal strength in X-ray diffraction data. This implies that choosing the correct orientation for crystals of such molecules can be a crucial determinant of success or failure when using single-and multiple-wavelength anomalous diffraction (SAD or MAD) methods to solve their structure. In particular, polarized absorption spectra on an oriented crystal of a brominated DNA molecule were measured, and were used to determine the orientation that yields a maximum anomalous signal in the diffraction data. Out of several SAD data sets, only those collected at or near that optimal orientation allowed interpretable electron density maps to be obtained. The findings of this study have implications for instrumental choices in experimental stations at synchrotron beamlines, as well as for the development of data collection strategy programs.

Abstract. X-ray induced anisotropic variations of cell parameters in porcine pancreatic elastase (PPE) were used in a multi-Pawley refinement in order to improve the deconvolution of overlapping peaks occurring in the high-angle region of the powder pattern. The benefit of combining scans is demonstrated by an improvement in the quality of the isomorphous difference Patterson maps used to detect the positions of heavy atoms in a uranyl derivative of PPE.

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A set of Cu-30%Zn,Cu-49%Zn, Cu-65%Zn and Cu-86%Zn (that are in composition range of the phases , ' , and , respectively) have been synthesized by mechanical alloying of the stoichiometric mixtures of pure copper and zinc powders in a planetary mill of high grinding energy by using a ratio weight of the balls/weight of sample (RBS here after) equal to 3.3.The results obtained have shown that the full alloying of the starting mixtures of copper and zinc powders is attained after 3 hours of grinding. The study of the intermediate phases as a function of the grinding time pointed out that the reaction is started with the formation of phases very rich in zinc, like the phase, and continue reacting with copper until the full alloying is achieved. This behavior suggests that the mechanical alloying takes place trough a mechanism that implies the diffusion of copper into the zinc matrix.On the other hand, the grinding under more severe conditions (RBS equal to 13.3) extends considerably the composition range at which phase becomes stabilized. A mechanochemical Cu-Zn binary phase diagram at room temperature is proposed. Recent progress in the solid state coordination and structural chemistry of aromatic disulfonates, as well as the amine interaction properties of crystalline Cd 2+ sulfonate complexes with amines will be presented. [1] Due to the weak coordination strength, most of the metal monosulfonates obtained from aqueous solution are water-coordinated metal sulfonate salts.[2] However, by employing arenedisulfonates, which can provide multiple coordination sites, stable frameworks sustained by sulfonate-metal interactions can be obtained with various dimensionalities. [1] Moreover, due to the flexible coordination modes, the 1,5-naphthalenedisulfonate ligand shows variant coordination modes in complexes obtained from different reaction conditions, resulting in polymorphism.[3] Finally, layered sulfonateand water-coordinated Cd 2+ complexes can selectively uptake amine vapor via solid-state substitution reaction, which is a reversible process at room conditions. [4,5] [1] Cai J., Coord. Chem. Rev., 2004, 248 When the crystal is irradiated with UV or visible light at low temperatures, the averaged molecule in the crystalline lattice reaches the equilibrium state composed of ground and excited states. The structure of the excited molecule in the equilibrium state can be analyzed by X-rays if the occupancy factor of the produced excited molecules exceeds the limiting value (>5%). This method is called equilibrium analysis of excited molecule. Recently we obtained the excited structure of the diplatinum complex with the equilibrium method[1]. The Pt-Pt and Pt-P distances of the diplatinum complex are shortened at the excited state.The same method was applied to the other complex crystals and was successful to observe the structures of the excited molecules. The first example is the (VO)(acac) 2 complex. The unit-cell was expanded at the equilibrium state and the molecular structure indicated that one V=O and...