Diffraction quality crystals are essential for crystallographic studies of protein structure, and the production of poorly diffracting crystals is often regarded as a dead end in the process. Here we show a dramatic improvement of poorly diffracting DsbG crystals allowing high-resolution diffraction data measurement. Before dehydration, the crystals are fragile and the diffraction pattern is streaky, extending to 10 A resolution. After dehydration, there is a spectacular improvement, with the diffraction pattern extending to 2 A resolution. This and other recent results show that dehydration is a simple, rapid, and inexpensive approach to convert poor quality crystals into diffraction quality crystals.

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The synthesis, structural and solid-state 31P cross-polarization magic angle spinning (CP MAS) NMR characterization of cis-bis(dipheny1phosphino)ethylene (dppey) and the copper(1) and gold(1) complexes [M(dppey),]PF, has been carried out. The complexes, which have been shown to exhibit cytotoxic and antitumour activity, belong to the relatively rare class of copper(1) and gold(r) complexes with tetrahedral CUP, and AuP, co-ordination spheres. Crystals of dppey 1 are monoclinic with space group P2Jc and a = 12.861 (8), b = 13.097(2), c = 14.228(8) A, p = 11 6.1 5(3)"; R was 0.047 for 31 17 'observed' reflections. The solid-state CP MAS 31P NMR spectrum consists of an AB multiplet with 6(PA) -24.2, 6(PB) -27.2 and J(P-P) = 126 Hz. Crystals of [Cu(dppey),]PF, 2 are orthorhombic with space group P2,2,2, and a = 14.479( 5), b = 16.703(4), c = 20.891 (4) A; R was 0.046 for 31 38 'observed' reflections. The CUP, co-ordination sphere is regular within the constraints of chelation with Cu-P in the range 2.276(2)-2.289(2) A. The copper atom lies on a pseudo two-fold axis of symmetry bisecting the C=C bonds. Charge-transfer interactions between phenyl rings on each ligand contribute to the stabilization of the structure of the cation. The solid-state 31P NMR spectrum consists of four broad bands ( A V ~ = 300 Hz) centred at 6 8 with J(Cu-P) zz 820 Hz. Distortion of the quartet spacings by quadrupolar interaction with the copper nuclei is minimal. Crystals of [Au(dppey),] PF, 3 are isomorphous with 2 with a = 14.644( 4), b = 16.703( 1), c = 20.699(5) A; R was 0.025 for 3947 'observed' reflections. The Au-P distances lie in the narrow range 2.377(2)-2.388(2) A. Solid-state CP MAS 31P NMR of this complex and the analogous nitrate and chloride complexes at magnetic field strengths of 2.11, 7.05 and 9.40 T reveal splitting of the phosphorus signal into a quartet ascribed to Au-P spin-spin coupling effects with J(Au-P) estimated to be 200 Hz. As for the copper complex, distortion of the quartet spacings is minimal and indicative of a small Ig7Au quadrupolar coupling constant. Solution and solid-state 31P N M R chemical shift parameters are similar, supporting the hypothesis that the tetrahedral bis(che1ated) cations are also stable in solution. Spin-spin coupling to the quadrupolar (lg7Au or 63/65Cu) nuclei was not resolved in the solution spectra, however, due to rapid quadrupolar relaxation.

The crystal structure of 3,5-dinitrosalicylic acid monohydrate (1) and its adducts with 2- aminobenzoic acid (2-aba) [( dnsa )(2-aba)] (2), 3-aminobenzoic acid (3-aba) [( dnsa )(3-aba)] (3), and 4-aminobenzoic acid (4-aba) [( dnsa )(4-aba)2] (4), have been determined and the hydrogen bonding associations in each analysed . The acid (1), which is essentially planar, forms strong hydrogen-bonding network associations involving the carboxylic, nitro and phenolic oxygens as well as the lattice water. In all adducts, protonation of the amino group of the second acid occurs, with subsequent hydrogen bonding via all three alkyl ammonium hydrogens to the carboxylic, nitro and phenolic oxygens of dnsa. With the 1:2 adduct (4), only one of the two 4-aba molecules is protonated, these forming a secondary hydrogen-bonded cyclic dimer. A strong intramolecular hydrogen bond between the phenolic proton and the carboxylate group is found in all adducts.