Synthesis, crystal structures and magnetic properties of a phenoxo-bridged dinuclear Cu(II) complex and a dicyanamide bridged novel molecular rectangle based on it

The phenoxo-bridged dinuclear Cu-II complex [Cu2L2-(NCNCN)(2)] (1) and the dicyanamide-bridged molecular rectangle [Cu4L4{mu(1,5)-(NCNCN)(2)}]center dot(ClO4)(2)(H2O)(2) (2) were synthesized using the tridentate reduced Schiff-base ligand HL {2-[(2-dimethylamino-ethylamino) methyl] phenol}. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 2 was formed through the joining of the phenoxo-bridged dinuclear Cu2O2 cores of 1 via the mu(1,5)-bridging mode of dicyanamide. The structural properties of the Cu2O2 cores in two complexes are significantly different. The geometry of the copper ions is distorted trigonal bipyramid in 1 but is nearly square-pyramidal in 2. These differences have a marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -185.2 and -500.9 cm(-1) for 1 and 2, respectively) differ considerably.

Syntheses, characterization and X-ray crystal structures of a mono- and a penta-nuclear nickel(II) complex with oximato Schiff base ligands

A mononuclear octahedral nickel(II) complex [Ni(HL(1))(2)](SCN)(2) (1) and an unusual penta-nuclear complex [{(NiL(2))(mu-SCN)}(4)Ni(NCS)(2)]center dot 2CH(3)CN (2) where HL(1) = 3-(2-aminoethylimino)butan-2-one oxime and HL(2) = 3-(hydroxyimino)butan-2-ylidene)amino)propylimino)butan-2-one oxime have been prepared and characterized by X-ray crystallography. The mono-condensed ligand, HL(1), was prepared by the 1:1 condensation of the 1,2-diaminoethane with diacetylmonoxime in methanol under high dilution. Complex 1 is found to be a mer isomer and the amine hydrogen atoms are involved in extensive hydrogen bonding with the thiocyanate anions. The dicondensed ligand, HL(2), was prepared by the 1:2 condensation of the 1,3-diaminopropane with diacetylmonoxime in methanol. The central nickel(II) in 2 is coordinated by six nitrogen atoms of six thiocyanate groups, four of which utilize their sulphur atoms to connect four NiL2 moieties to form a penta-nuclear complex and it is unique in the sense that this is the first thiocyanato bridged penta-nuclear nickel(II) compound with Schiff base ligands.

Syntheses, crystal structures and properties of sterically congested heteroleptic complexes of group 10 metal ions with p-tolylsulfonyl dithiocarbimate and 1,2-bis (diphenylphosphino) ethane

Three novel heteroleptic complexes of the type cis- [ML(dppe)] [M = Ni(II), Pd(II), Pt(II); L = p-tolylsulfonyl dithiocarbimate; dppe = 1,2-bis(diphenylphosphino)ethane] have been prepared and characterized. X-ray crystallography revealed the close proximity of one of the ortho phenyl protons of the dppe ligand to the metal in the Ni(II) complex showing existence of the less common C-H center dot center dot center dot Ni anagostic interactions observed for the first time in the dithio-phosphine mixed-ligand systems. The platinum complex showed a strong photoluminescence emission near visible region in CH(2)Cl(2) solution.

Application of hydrogen-bond propensity calculations to an indomethacin–nicotinamide (1:1) co-crystal

The crystal structure of an indomethacin–nicotinamide (1 : 1) cocrystal produced by milling has been determined from laboratory powder X-ray diffraction (PXRD) data. The hydrogen bonding motifs observed in the structure represent one of the most probable of all the possible combinations of donors and acceptors in the constituent molecules.

Chapter 17: X-Ray rheology of liquid crystal polymers

X-ray Rheology is an experimental technique which uses time-ressolved x-ray scattering as probe of the molecular level structural reorganisation which accompanies flow. It provides quantitative information on the direction alignment and on the level of global orientation. This information is very helpful in interpreting the classic rheological data on liquid crystal polymers. In this research we use data obtained from a cellulose derivate which exhibits a thermotropic liquid crystal phase. We show how increased shear rates lead to a rapid rise in the global orientation and we related this to therories of flow in liquid crystal polymers from the literature. We show that the relaxation time is independent of the prior shear rate.

X‑ray crystal structure of rac-[Ru(phen)2dppz]2+ with d(ATGCAT)2 shows enantiomer orientations and water ordering

We report an atomic resolution X-ray crystal structure containing both enantiomers of rac-[Ru(phen)2dppz]2+ with the d-(ATGCAT)2 DNA duplex (phen = phenanthroline; dppz = dipyridophenazine). The first example of any enantiomeric pair crystallized with a DNA duplex shows different orientations of the Λ and Δ binding sites, separated by a clearly defined structured water monolayer. Job plots show that the same species is present in solution. Each enantiomer is bound at a TG/CA step and shows intercalation from the minor groove. One water molecule is directly located on one phenazine N atom in the Δ-enantiomer only.

Crystal design approaches for the synthesis of paracetamol co-crystals

Crystal engineering principles were used to design three new co-crystals of paracetamol. A variety of potential cocrystal formers were initially identified from a search of the Cambridge Structural Database for molecules with complementary hydrogen-bond forming functionalities. Subsequent screening by powder X-ray diffraction of the products of the reaction of this library of molecules with paracetamol led to the discovery of new binary crystalline phases of paracetamol with trans-1,4- diaminocyclohexane (1); trans-1,4-di(4-pyridyl)ethylene (2); and 1,2-bis(4-pyridyl)ethane (3). The co-crystals were characterized by IR spectroscopy, differential scanning calorimetry, and 1H NMR spectroscopy. Single crystal X-ray structure analysis reveals that in all three co-crystals the co-crystal formers (CCF) are hydrogen bonded to the paracetamol molecules through O−H···N interactions. In co-crystals (1) and (2) the CCFs are interleaved between the chains of paracetamol molecules, while in co-crystal (3) there is an additional N−H···N hydrogen bond between the two components. A hierarchy of hydrogen bond formation is observed in which the best donor in the system, the phenolic O−H group of paracetamol, is preferentially hydrogen bonded to the best acceptor, the basic nitrogen atom of the co-crystal former. The geometric aspects of the hydrogen bonds in co-crystals 1−3 are discussed in terms of their electrostatic and charge-transfer components.

Cocrystalline copolyimides of poly(ethylene 2,6-naphthalate)

Copolycondensation of N,N′-bis(2-hydroxyethyl)-biphenyl-3,4,3′,4′-tetracarboxylic diimide (5–25 mol %) with bis(2-hydroxyethyl)-2,6-naphthalate affords a series of cocrystalline, poly(ethylene 2,6-naphthalate) (PEN)-based poly(ester imide)s. The glass transition temperature rises with the level of comonomer, from 118 °C for PEN itself to 148 °C for the 25% diimide copolymer. X-ray powder and fiber diffraction studies show that, when 5 mol % or more of diimide is present, the α-PEN crystal structure is replaced by a new crystalline phase arising from isomorphic substitution of biphenyldiimide for PEN residues in the polymer crystal lattice. This new phase is provisionally identified as monoclinic, C2/m, with two chains per unit cell, a = 10.56, b = 6.74, c = 13.25 Å, and β = 143.0°.

The principles underlying the use of powder diffraction data in solving pharmaceutical crystal structures

Solving pharmaceutical crystal structures from powder diffraction data is discussed in terms of the methodologies that have been applied and the complexity of the structures that have been solved. The principles underlying these methodologies are summarized and representative examples of polymorph, solvate, salt and cocrystal structure solutions are provided, together with examples of some particularly challenging structure determinations.

Controlled dehydration of a ruthenium complex-DNA crystal induces reversible DNA kinking

Hydration-dependent DNA deformation has been known since Rosalind Franklin recognised that the relative humidity of the sample had to be maintained to observe a single conformation in DNA fibre diffraction. We now report for the first time the crystal structure, at the atomic level, of a dehydrated form of a DNA duplex and demonstrate the reversible interconversion to the hydrated form at room temperature. This system, containing d(TCGGCGCCGA) in the presence of Λ-[Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyridophenazine), undergoes a partial transition from an A/B hybrid to the A-DNA conformation, at 84-79% relative humidity. This is accompanied by an increase in kink at the central step from 22° to 51°, with a large movement of the terminal bases forming the intercalation site. This transition is reversible on rehydration. Seven datasets, collected from one crystal at room temperature, show the consequences of dehydration at near-atomic resolution. This result highlights that crystals, traditionally thought of as static systems, are still dynamic and therefore can be the subject of further experimentation.

Perylene as an electron-rich moiety in healable, complementary π–π stacked, supramolecular polymer systems

A two-component, supramolecular polymer blend has been designed using a novel π-electron rich bisperylene- terminated polyether. This polymer is able to self-assemble through electronically complementary π–π stacking interactions with a π-electron-deficient chain-folding polydiimide to afford thermally healable polymer blends. Model compounds were developed to assess the suitability of the deep green complexes formed between perylene residues and chain-folding bis-diimides for use in polymer blends. The polymer blends thus synthesised were elastomeric in nature and demonstrated healable properties as demonstrated by scanning electron microscopy. Healing was observed to occur rapidly at ca. 75 degC, and excellent healing efficiencies were found by tensometric and rheometric analyses. These tuneable, stimuli-responsive, supramolecular polymer blends are compared to related healable blends featuring pyrene-terminated oligomers.

Mesomorphic behaviour in copoly(ester-imide)s of poly(butylene-2,6-naphthalate) (PBN)

Copolycondensation of N,N’-bis(4-hydroxybutyl)-biphenyl-3,4,3',4'-tetracarboxylic diimide at 20 and 25 mol% with bis(4-hydroxybutyl)-2,6-naphthalate produces PBN-based copoly(ester-imide)s that not only crystallise but also form a (smectic) mesophase upon cooling from the melt. Incorporation of 25 mol% imide in PBN causes the glass transition temperature (measured by DSC) to rise from 51 to 74 °C, a significant increase relative to PBN. Furthermore, increased storage- (G'), loss- (G'') and elastic (E) moduli are observed for both copoly(ester-imide)s when compared to PBN itself. Structural analysis of the 20 mol% copolymer by X-ray powder and fibre diffraction, interfaced to computational modelling, suggests a crystal structure related to that of α-PBN, in space group P-1, with cell dimensions a = 4.74, b = 6.38, c = 14.45 Å, α = 106.1, β = 122.1, γ = 97.3°, ρ = 1.37 g cm-3.

Morphology of polymer networks formed in the chiral and non chiral phases of an anti-ferroelectric liquid crystal

We introduced photo-polymer networks into the various liquid crystalline phases of the antiferroelectric liquid crystal AS612 and studied the effects of these networks by measuring the temperature dependence of the Bragg wavelengths selectively reflected. After polymerization, the decrease in Bragg wavelengths with respect to the original values is consistent with a shorter helical pitch due to polymer network shrinkage. Also, by removing the liquid crystalline material, we are able to image the residual polymer network using scanning electron microscopy and polarized light microscopy. The polymer strands are a few microns thick and the networks show both chiral and non-chiral features.

Predicting sizes of hexagonal and gyroid metal nanostructures from liquid crystal templating

We describe a method to predict and control the lattice parameters of hexagonal and gyroid mesoporous materials formed by liquid crystal templating. In the first part, we describe a geometric model with which the lattice parameters of different liquid crystal mesophases can be predicted as a function of their water/surfactant/oil volume fractions, based on certain geometric parameters relating to the constituent surfactant molecules. We demonstrate the application of this model to the lamellar (LR), hexagonal (H1), and gyroid bicontinuous cubic (V1) mesophases formed by the binary Brij-56 (C16EO10)/water system and the ternary Brij-56/hexadecane/water system. In this way, we demonstrate predictable and independent control over the size of the cylinders (with hexadecane) and their spacing (with water). In the second part, we produce mesoporous platinum using as templates hexagonal and gyroid phases with different compositions and show that in each case the symmetry and lattice parameter of the metal nanostructure faithfully replicate those of the liquid crystal template, which is itself in agreement with the model. This demonstrates a rational control over the geometry, size, and spacing of pores in a mesoporous metal.

The crystal structure of the leptospiral hypothetical protein LIC12922 reveals homology with the periplasmic chaperone SurA

Leptospirosis is a world spread zoonosis caused by members of the genus Leptospira. Although leptospires were identified as the causal agent of leptospirosis almost 100 years ago, little is known about their biology, which hinders the development of new treatment and prevention strategies. One of the several aspects of the leptospiral biology not yet elucidated is the process by which outer membrane proteins (OMPs) traverse the periplasm and are inserted into the outer membrane. The crystal structure determination of the conserved hypothetical protein LIC12922 from Leptospira interrogans revealed a two domain protein homologous to the Escherichia coli periplasmic chaperone SurA. The LIC12922 NC-domain is structurally related to the chaperone modules of E. coli SurA and trigger factor, whereas the parvulin domain is devoid of peptidyl prolyl cis-trans isomerase activity. Phylogenetic analyses suggest a relationship between LIC12922 and the chaperones PrsA, PpiD and SurA. Based on our structural and evolutionary analyses, we postulate that LIC12922 is a periplasmic chaperone involved in OMPs biogenesis in Leptospira spp. Since LIC12922 homologs were identified in all spirochetal genomes sequenced to date, this assumption may have implications for the OMPs biogenesis studies not only in leptospires but in the entire Phylum Spirochaetes. (C) 2010 Elsevier Inc. All rights reserved.