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Octreotide, a synthetic somatostatin analogue, is an octapeptide with one disulfide bridge. Crystals of octreotide are orthorhombic, space group P212121, a = 18.458 (5), b = 30.009 (7), c = 39.705 (27) A, with three molecules of octapeptide, one ordered oxalate dianion and 52 water molecules in the asymmetric unit. Complete protonation of the NH2 groups (as assumed in the refinement) would require three oxalate dianions in the asymmetric unit for charge neutrality; a chemical analysis indicated that four are present. In either case they are so disordered that they cannot be distinguished from the water molecules. The 18 951 unique reflections (Rsy m = 0.026) used for structure solution and refinement were recorded with the EMBL imaging-plate scanner using synchrotron radiation. The structure was solved by Patterson interpretation, locating the three disulfide bridges, followed by tangent phase expansion and EFourier recycling. The anisotropic refinement against all F 2 data between 1.04 and 10.0 A resolution by blocked restrained full-matrix least-squares techniques converged to a conventional R index based on F of 0.084 [I > 2a(/) and 10.0 > d > 1.04 A] and wR2, the weighted R-index on F 2, of 0.246 (for all data). One peptide molecule adopts a flat ~-sheet structure; the other two possess different irregular backbone conformations, but are similar to each other. All three molecules have a distorted type II'/3-turn around the o-Trp-Lys region, but exhibit different sidechain conformations. The crystal structure is stabilized by a network of inter-and intramolecular hydrogen bonds.

The crystal structures of three quinoxaline antibioticsechinomycin 2QN, triostin C and the C222~ form of triostin A -have been determined, and the structure of the P212121 form of triostin A has been re-refined against our previously reported data. The molecular conformations are compared with those deduced from NMR data and those reported for two complexes of triostin A with oligonucleotides. Although the depsipeptide ring conformations are basically similar, the effective twofold molecular symmetry is violated by the folding of one of the quinoxaline chromophores in echinomycin 2QN and by a rotation of one of the ester planes with the formation of an intramolecular hydrogen bond in triostin C. In the oligonucleotide complexes of triostin A the chirality of the disulfide bridge is inverted. The alanine NH groups are involved in intermolecular hydrogen bonds in all four structures, and (except in echinomycin 2QN) the stacking of the chromophores in the crystal emulates the intercalation involved in DNA complex formation. In echinomycin 2QN, the antibiotic molecules are hydrogen bonded to form a helix along the crystallographic 65 screw axes, with a channel of disordered solvent running through the middle of the helix. Crystal data: (1), echinomycin 2QN,

The interaction of Cu(II) with the following secondary N-substituted derivatives of di(2-picolyl)amine () are reported: N-cyclohexylmethyl-di(2-picolyl)amine (), N-benzyl-di(2-picolyl)amine (), N-(4-pyridylmethyl)-di(2-picolyl)amine (), N-(4-carboxymethylbenzyl)-di(2-picolyl)amine (), N-(9-anthracen-8-ylmethyl)-di(2-picolyl)amine (), 1,3-bis[di(2-picolyl)aminomethyl]benzene (), 1,4-bis[di(2-picolyl)aminomethyl]benzene () and 2,4,6-tris[di(2-picolyl)amino]triazine (). The solid complexes [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2), Cu()(ClO(4))(2), Cu()(2)(ClO(4))(2), [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O, Cu(2)()(ClO(4))(4), [Cu(2)()(Cl)(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were isolated and X-ray structures of [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2,) [Cu()(2)(ClO(4))(2)(H(2)O)].0.5H(2)O, [Cu(2)()Cl(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were obtained. The series is characterised by a varied range of coordination geometries and lattice architectures which in the case of [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O includes a chain-like structure formed by unusual intermolecular pi-interactions between metal bound perchlorate anions and the aromatic rings of adjacent anthracenyl groups. Variable temperature magnetic susceptibility measurements have been performed for [Cu()(micro-Cl)](2)(PF(6))(2) and [Cu()(micro-Cl)](2)(PF(6))(2).0.5H(2)O over the range 2-300 K. Both compounds show Curie-Weiss behaviour, with the data indicating weak antiferromagnetic interaction between the pairs of copper ions in each complex. Liquid-liquid (H(2)O/CHCl(3)) extraction experiments involving and as extractants showed that, relative to the parent (unsubstituted) dipic ligand , substitution at the secondary amine site in each case resulted in an increase in extraction efficiency towards Cu(II) (as its perchlorate salt); at least in part, this increase may be attributed to the enhanced lipophilicities of the N-substituted derivatives.

The metal complexation properties of the naturally occurring Maillard reaction product isomaltol HL(2) are investigated by measurement of its stability constants with copper(II), zinc(II), and iron(III) using potentiometric pH titrations in water, by structural and magnetic characterization of its crystalline complex, [Cu(L(2))(2)]·8H(2)O, and by density functional theory calculations. Strong complexation is observed to form the bis(isomaltolato)copper(II) complex incorporating copper in a typical (pseudo-)square-planar geometry. In the solid state, extensive intra- and intermolecular hydrogen bonding involving all three oxygen functions per ligand assembles the complexes into ribbons that interact to form two-dimensional arrays; further hydrogen bonds and π interactions between the furan moiety of the anionic ligands and adjacent copper(II) centers connect the complexes in the third dimension, leading to a compact polymeric three-dimensional (3D) arrangement. The latter interactions involving copper(II), which represent an underappreciated aspect of copper(II) chemistry, are compared to similar interactions present in other copper(II) 3D structures showing interactions with benzene molecules; the results indicate that dispersion forces dominate in the π system to chelated copper(II) ion interactions.

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Polymeric melaminium sulfate [(LH2)2(SO4)2]n has been synthesized by reaction of melamine L with sulfuric acid in aqueous solution. The compound was characterized by elemental analysis, 1H NMR, ESI MS and a single crystal X‐ray diffraction analysis. The architecture of the assembly formed is based on hydrogen bonded dimers of diprotonated melaminium cations (LH2)2+ which are linked by a hydrogen bonded network with sulfate ions forming 2D sheets. A 3D polymeric structure results from the presence of mutual hydrogen bonds between sulfate ions and melaminium cations in different sheets. Significant π‐π stacking is also present between the aromatic cations in this supramolecular arrangement.