A new crystal form of sodium thiosulfate hydrate with the stoichiometry Na2S2O3.2/3H2O is reported.

The synthesis of 1,6-dipyrrol-1-yl-2,4-hexadiene (5) is described. The N-alkylation of pyrrole was catalysed by crown ether and the intermediate acetylene was oxidatively coupled using cuprous chloride and oxygen.

The structure of the protein tumour necrosis factor (TNF) was determined from crystals of space group P3(1)21 which contain six copies of the TNF monomer per crystallographic asymmetric unit [Jones, Stuart & Walker (1989). Nature (London), 338, 225-228]. The nature of these crystals (relatively high crystallographic symmetry coupled with multiple copies of the protein in the asymmetric unit) led to some peculiarly challenging problems at several points in the structure determination. In particular, (1) self-rotation function calculations failed to yield clearly interpretable solutions, (2) the analysis of difference Patterson maps for heavy-atom derivatives required the development of a Patterson search program suite GROPAT. The redundancy in the asymmetric unit allowed refinement of poor-quality isomorphous phases at 4 A resolution and phase extension from 4 to 2.9 A resolution using real-space symmetry averaging and solvent flattening in the absence of any isomorphous phase information. Despite further difficulties caused by structural differences between the six independent copies of the monomer the resultant electron density map was of high quality and proved to be easily interpretable.

The binding of acetazolamide to human carbonic anhydrase II (HCA II) has been investigated by X-ray crystallography. The atomic positions of the enzyme inhibitor complex have been refined at 1.9 Å resolution using the least squares refinement program package PROLSQ. The crystallographic R-factor is 17.6%. The bound inhibitor is clearly resolved in the active site of the enzyme. The acetazolamide amine group is bound as a fourth ligand to the zinc ion, the other three are all histidine residues. In addition to van der Waals' interactions and the previously described binding of the sulphonamide group, the inhibitor forms a hydrogen bond from the carbonyl oxygen of the acetylamido group to the amino group of Gln 92.

The three-dimensional structure of TNF has been determined at 0.29 nm using the technique of X-ray crystallography. Published data on site-directed mutagenesis and antibody binding may now be assessed in the light of the structure, thus the links between structure and function for TNF may be addressed. TNF is a compact trimer composed of three identical subunits of 157 amino acids. The main-chain topology for a single subunit is essentially a beta-sandwich structure formed by two anti-parallel beta-pleated sheets. This mainchain fold corresponds to the 'jelly roll' motif observed in viral coat proteins such as VP1, VP2 and VP3 of rhinovirus, or the hemagglutinin molecule of influenza. TNF is the first non-viral protein to contain this motif. The subunits associate tightly about a threefold axis interacting through a simple edge-to-face packing of the beta-sandwich to form the solid, conical shaped trimer. A large number of the residues conserved between the amino acid sequences of TNF and lymphotoxin lie within the beta-sandwich or at the threefold axis of the trimer. This implies the presence of the same beta-sandwich motif in the lymphotoxin monomer and preservation of the edge-to-face mode of trimeric association. The detailed three dimensional structure for TNF explains a wide range of observations, including data on antibody binding and site directed mutagenesis. The currently available evidence points to a region of biological importance situated at the interface between two subunits on the lower half of the trimer.

AbstractReaction of N‐(α‐acetoxy)4‐pyridylmethyl]‐3,5‐dimethylbenzamide 3 with methyl and ethyl isocyanates afforded 1,3‐dimethyl and 1,3‐diethyl‐4‐(3,5‐dimethylbenzoylamino)‐2‐oxoimidazolidine‐5‐spiro‐4′‐[1′,4′‐dihydro‐1′‐acetyl]pyridine 6a,b, respectively. However, the reaction of 3 with isopropyl, t‐butyl and phenyl isocyanates gave the corresponding N,N′‐diurea and the dimerization compound 8. The structure of 6a was confirmed by crystal X‐ray diffraction analysis.

Tumour necrosis factor is a trimeric molecule, each subunit of which consists of an antiparallel beta-sandwich. Individual subunits from the trimer by a novel edge-to-face packing of beta-sheets. A comparison of the subunit fold with that of other proteins reveals a remarkable similarity to the 'jelly-roll' structural motif characteristic of viral coat proteins.

The preparation, crystal structure and diamagnetism of Cu2(HOBB)2 (OBB)2(ClO4)2·5C2H5OH where HOBB is 2-α-hydroxybenzylbenzimidazole and OBB its deprotonated form are reported. The crystals are triclinic P1 with a = 19.380(4), b = 21.345(6), c = 9.484(3) Å, α = 102.52(2), β = 103.93(2), γ = 105.76(2)°, Z = 2. The structure was refined with 6593 reflections [I⩾2σ(I)] to R = 0.059. The molecule contains bridging OBB and non-bridging HOBB resulting in a geometry around each copper ion that is distorted square pyramidal with apical hydroxyl groups. An interesting feature of the molecule is that both of the apical hydroxyl groups lie on the same side of the plane defined by the Cu2O2core.

Vinylene carbonate [graphic omitted]O reacts at room temperature with [Os2H3(CO)10] to give a good yield of the vinyloxy cluster [Os3H(OCHCH2)(CO)10](1). A similar decarboxylation occurs on reaction with [Os3(CO)10(MeCN)2] to give the formylmethylidene cluster [OS3µ3-CHCHO)(µ-CO)(CO)9](2). The single-crystal X-ray structure of (2) is closely related to those of [Os3(µ-CHR)(µ-CO(CO)10](R = H or SiMe3) with two osmium atoms bridged both by CO and an alkylidene group. In (2) this group is part of a four-electron-donating µ3 bridge. Hydrogenation of (2) or decarbonylation of (1) leads to the formylmethylidene compound [Os3H2(CHCHO)(CO)9](3).

Reaction of 2,2′-diaminobiphenyl with o-phthalaldehyde yielded a number of products including two bi-(14H-dibenzo[4,5:6,7][1,3]diazepino[2,1-a]isoindol-14-ylidene)s, (A) and (B); each was converted on heating into a third isomer (D). The crystal structure of (A), and that of (D), as the solvated trifluoroacetate salt, were determined; (A), previously thought to be the trans-isomer, is in fact the cis-(R,R)/(S,S)-isomer (1a), a racemic compound, and (D) is the meso trans-(R,S)isomer (2b). Compound (B) is considered to be the racemic trans-(R,R)/(S,S)-isomer (2a). The crystal structures of (A) and (D) and the 13C n.m.r. and u.v. spectra of all three isomers are discussed.

AbstractThe title compounds (I) and (III), from which (III) exists as a mixture of the isomers (IIIa) and (IIIb) with dominating (IIIa) (70%), react with CF3COOH to give the protonated cations (II) and (IV).

Calcium performs a unique role in biology, achieving biological effects through highly specific interactions with and modulation of target proteins. It has been proposed that calcium-modulated proteins possess a characteristic, evolutionarily related, binding fold, known as the EF-hand. The high-resolution X-ray structure of alpha-lactalbumin reveals a Ca2+ binding fold that resembles an EF-hand only superficially and presumably has no evolutionary relationship with it. However, there is clear homology with the corresponding loop in c-type lysozyme (the 'parent' molecule of alpha-lactalbumin). This study, at 1.7 A resolution, represents one of the most accurate analyses of a calcium binding protein yet reported.

The new binuclear complex [Pd2(μ-O2CMe)2(C6H5)2(PPh3)2] is formed when [Pd3(O2CMe)6] reacts with PPh3 in methanol. An X-ray crystal structure analysis shows the complex to comprise two square planar palladium(II) atoms bridged by two acetate ligands in a cis fashion. The phosphine and phenyl ligands on each metal atom adopt positions which are mutually trans to the equivalent ligand on the other metal atom, so that the complex has an approximate two-fold axis perpendicular to the plane of the four acetate oxygens. The NMR (1H, 13C and 31P) spectra are reported.

AbstractThe structure of the title compound (I), representative of a new series of powerful, selective, monoquaternary neuromuscular blocking systems, has been determined by X‐ray analysis (space group: P21/n; Z=4).