Double Helical Chains Research Articles

The helical structure induced by metal–organic complexes: synthesis and characterization of a novel layered vanadate complex containing double helical chains

A novel two-dimensional inorganic–organic hybrid vanadate complex [Co(2,2′-bpy) 2V 3O 8.5] 1 (2,2′-bpy, 2,2′-bipyridine) has been hydrothermally synthesized and characterized by the elemental analyses, XPS spectra, TG analysis, IR spectrum and the single-crystal X-ray diffraction. Crystal data for 1: monoclinic, space group P2 1/c, a=15.612(3) Å, b=14.830(3) Å, c=10.548(2) Å, β=91.90(3)°, V=2440.8(8) Å 3, Z=4, and R 1[ I>2 σ( I)]=0.0367. The title compound consists of an unusual two-dimensional vanadate network grafted with [Co(2,2′-bpy) 2] 2+ complexes. Moreover, compound 1 contains left-handed and right-handed helical chains, which are built up from only vanadium-oxide building blocks and further interconnected to form the double helical chains.

Hydrothermal synthesis and crystal structure of a three-dimensional metal selenite containing double helical chains: Fe 3(H 2O)(SeO 3) 3

A novel three-dimensional (3D) transition metal selenite Fe 3(H 2O)(SeO 3) 3 ( 1) has been hydrothermally synthesized and characterized by the elemental analyses, IR spectrum, TG analysis and the single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P 1 ̄ , with a=8.0916(16) Å, b=8.2089(16) Å, c=8.5679(17) Å, α=69.21(3)°, β=62.74(3)°, γ=67.16(3)°, Z=2, and R 1[ I>2 σ( I)]=0.0379. Compound 1 exhibits an interesting 3D framework formed by {FeO 6} octahedra and {SeO 3} trigonal pyramids via the corner- and/or edge-sharing mode. Furthermore, compound 1 consists of left-handed and right-handed helical chains, which are further entangled to form the double helical chains.

Hydrothermal synthesis and crystal structure of a novel layered vanadate complex containing double helical chains: [{Zn(2,2′-bpy)} 2V 8O 21](2,2′-bpy=2,2′-bipyridine)

A novel organic–inorganic hybrid vanadate complex [{Zn(2,2′-bpy)} 2V 8O 21] 1 (2,2′-bpy=2,2′-bipyridine) was synthesized by the hydrothermal reaction of V 2O 5, ZnCl 2, 2,2′-bpy and water. Its structure was determined by elemental analyses, XPS spectra, TG analysis, IR spectrum and the single-crystal X-ray diffraction. Crystal data for 1: C 20H 16N 4O 21V 8Zn 2, triclinic, space group P−1, a=8.0610(16) A ̊ , b=9.7339(19) Å, c=11.613(2) Å, α=85.63(3)°, β=96.59(3)°, γ=72.13(3)°, Z=1 and R( F)=0.0456. The title compound contains an unusual two-dimensional vanadate network grafted with [Zn(2,2′-bpy)] 2+ complex. Furthermore, the vanadate layer in 1 consists of left-handed and right-handed helical chains, which are built up from {VO 5} square pyramids linked by {VO 4} tetrahedra and further interconnected to form the double helical chains.

Synthesis, crystal structure and non-linear optical properties of the heterobimetallic polymeric compound {[n-Bu4N][W2Ag3S8]}n

The heterobimetallic, polymeric compound has been synthesized by the reaction of (NH4)2WS4 and AgBr with n-Bu4NBr in CH2Cl2 solution under a purified nitrogen atmosphere using standard Schlenk techniques. The crystals were characterized by elemental analysis, IR and single-crystal X-ray crystallography. The polymeric anion has a hanging ladder-like polymeric chain which can also be described as double helical chains bridged by silver atoms. Its non-linear optical properties (NLO) were investigated using Z-scan techniques with an 8 ns pulsed laser at 532 nm, and the cluster also exhibits both strong non-linear optical absorption and an optical self-defocusing effect (effective α2 = 1.11 × 10−10 m W−1, n2 = 3.67 × 10−18 m2 W−1, when measured with a 1.2 × 10−4 mol dm−3 DMF suspension).

Synthesis, crystal structures and magnetic properties of helical double-stranded three-dimensional network [Co(NO 3) 2(bpt) 2·2CH 3OH] n and two-dimensional network [Mn(NCS) 2(bpt) 3·H 2O] n (bpt= N, N′-bis(3-pyridylmethyl)thiourea)

Compounds [Co(NO 3) 2(bpt) 2·2CH 3OH] n ( 1) and [Mn(NCS) 2(bpt) 3·H 2O] n ( 2) (bpt= N, N′-bis(3-pyridylmethyl)thiourea) have been synthesized and characterized structurally. Two bpt ligands coordinate simultaneously to two cobalt(II) centers to generate the double helical one-dimensional chain [Co(NO 3) 2(bpt) 2] n . Intermolecular hydrogen-bonding arising from the interaction of thiourea units of bpt with NO 3 − ions or solvent molecular forms a three-dimensional supramolecule in the solid structure (polymer 1). Bpt ligands (polymer 2) acting as bridges connect to two manganese(II) centers lead to the one-dimensional linear chain [Mn(NCS) 2(bpt) 3] n . The two-dimensional network was formed by O⋯HN, S⋯HO and OH⋯SCN hydrogen bonds. The determination of variable-temperature magnetic susceptibilities (5–300 K) of the two compounds shows that the magnetic behavior obeys the Curie–Weiss law.

A three-dimensional zeolite-like organic-inorganic hybrid material constructed from (CuMo2O8N)n double helical chains linked via [Cu(4,4'-bpy)]n fragments.

The three-dimensional microporous [Cu2Mo2O8(4,4'-bpy)]n.3nH2O 1 contains (CuMo2O8N) double helical chains, which are built up from (CuIIO4N) square pyramids linked by (MoVIO4) tetrahedra and further connected to each other by 4,4'-bpy coordinated (CuIIO5N); the study of the physical properties of 1 demonstrates it is a paramagnetic semiconductor and a zeolite material; the specific channeling cavities in 1 have potential adsorption activities, indicating that 1 might be an attractive functional microporous solid material.

Three Novel Structure Types of Polythiometalates: Syntheses, Structures, and Electrical Properties of {[W4Ag6S16]·[Ca(DEAC)6]}n, {[W2Ag2S8]·[Zn(4,4′-bipy)2(DMF)2(DMSO)2]}n, and {[W2Ag2S8]·[Zn(4,4′-bipy)2(DMSO)4]·(DMSO)}n

Three novel 1-D coordination polythiometalates have been synthesized and characterized by single-crystal X-ray crystallography, and their electrical properties have been studied. Compound {[W4Ag6S16]·[Ca(DEAC)6]}n, 1 crystallizes in the mono- clinic space group P21/n with a=13.769(3), b=11.613(2), c=24.153(5) Å, β=96.31(3)°, V=3838.7(13) Å, and Z=2 with R(wR2)=0.0607(0.1338), the polymeric anions in 1 feature a novel hanging ladder-like polymeric chain which can also be described as double helical chains bridged by silver atoms. Both compounds {[W2Ag2S8]·[Zn(4,4′-bipy)2(DMF)2(DMSO)2]}n 2 and {[W2Ag2S8]·[Zn(4,4′-bipy)2(DMSO)4]·(DMSO)}n 3 are composite polymers which consist of polymeric cations as well as polymeric anions. In 2, two polymeric chains simultaneously exist in the cell unit, one is the zigzag anionic chain, the other is the linear cationic chain. 2 crystallizes in the monoclinic space group C2/c with a=8.996(2) Å, b=21.728(4) Å, c=21.560(4) Å, β=94.00(3)°, V=4204(2) Å3, and Z=8 with R(wR2)=0.0546(0.1556). The difference between 2 and 3 is that the latter has a linear anionic chain and a zigzag cationic chain. X-ray crystallography established the monoclinic space group C2/c with a=28.8896(2), b=11.9395(1), c=16.2341(2) Å, β=122.932(1)°, V=4699.82(8) Å3, and Z=8 with R(wR2)=0.0438(0.1166)·4.50×10−6 S cm−1, respectively. Room temperature conductivities of 1, 2 are 2.92×10−5. Thus, compounds 1 and 2 have semiconductor electrical properties.

Structural aspects of the phase transition in

High-resolution neutron powder diffractometry has been used to characterize the structural phase transition which occurs in at . The change in lattice parameters of the trigonal unit cell as a function of temperature, observed in the range from ambient to , shows that the transition from the polar space group to the non-polar space group is associated with a collapse of the a-dimension, whereas the c-dimension and the cell volume increase monotonically with small changes of slope at the transition temperature. The structure of the lower-temperature phase, previously determined at ambient temperature by single-crystal x-ray diffraction, has been refined at 20, 500 and and the structure of the higher-temperature phase determined from data taken at 535, 560 and . The thermal evolution of the atomic coordinates shows that the deciding role in the transition is provided by a complex movement of the B - O tetrahedron, in which the main component is a rotation around the axis. The transition is continuous and results from structural changes which are displacive but also show order - disorder character. This conclusion is in accordance with the known thermal, optical and dielectric properties of this new multifunction (laser, ferroelectric and non-linear optic) material. In the high-temperature modification, the dynamically disordered double helical chain of B - O tetrahedra has no polarity in the c-direction. This is the main structural reason for the absence of ferroelectric properties above . The lower transition temperature of in the related phase may be understood by comparing the structural aspects of its transition with those of using the Abrahams - Jamieson - Kurtz criteria. The effect of isomorphic substitution for Ge with the smaller Si atoms is equivalent to pressure being applied to the helical B chain and results in a chain which is more tilted in the silicate than in the germanate.

Determination of the nucleosidic structural parameters by means of DNA vibrational markers

Normal mode calculations based on the GF-Wilson method and a reliable force field allow the vibrational markers arising from the deoxyadenosine (dA) and deoxyguanosine (dG) residues in DNA double helical chains (right- and left-handed conformations) to be reproduced. To do this, a fast, optimized code running on a CRAY-2 computer has been performed. The normal modes of these nucleosides have been calculated as a function of their structural parameters, on the basis of a non-redundant set of internal coordinates. This study permits a better understanding of the behaviour of the main nucleosidic markers used experimentally to determine the conformation of an oligonucleotide or polynucleotide in the crystalline phase and in solution. Taking account of the calculated data, we propose a reliable set of values for the nucleosidic structural parameters which are in good agreement with those estimated by other techniques such as X-ray diffraction or nuclear magnetic resonance (NMR) spectroscopy. We have extended this study to follow the evolution of the nucleosidic vibrational markers as a function of the sugar conformation and the glycosidic torsion angle.

Normal coordinate analysis of 2'-deoxythymidine and 2'-deoxyadenosine.

The proposed valence force field allows us to reproduce the vibration modes of 2'-deoxythymidine and 2'-deoxyadenosine. The present calculations are based on the Wilson GF-method and a non-redundant set of symmetrical coordinates. The calculated wavenumbers have been compared to the available Raman and infrared peak positions observed in solid, amorphous or aqueous samples. Moreover, the results obtained with the present force field allow us to assign some of the characteristic vibration modes for the thymidine and adenosine residues involved in DNA double-helical chains.

Complexes métalliques de l'acide rubéanique. I. Synthèse, structure moléculaire et cristalline d'un rubéanate de cuivre(I): CuCl(C2N2S2H4)1,5(H2O)0,45

Abstract CuCl(C2N2S2H4)1.5(H2O)0.45 crystallizes in the orthorhombic system, space group Ccca. The cell parameters are: a = 14.528(3) Å, b = 22.686(4) Å, c = 13.503(3) Å. The crystal structure has been determined using X-ray single crystal techniques and refined by full-matrix least-squares calculations to R = 0.051. The structure is polymeric and consists in double helical chains … Cu SC(NH2)C(NH2)S Cu …, wrapped round the [0 1/4 z] axis. In these chains, the rubeanic acid acts as a bidentate ligand through the two S atoms. The connections between the chains are ensured by a third ligand, showing the same coordination scheme. The metal atom Cu(I) is surrounded by three S atoms and one Cl atom, achieving a near perfect tetrahedron.

The polymeric state of actin in the human erythrocyte cytoskeleton.

Reports on the polymeric state of actin in the red cell have been diverse. We have used phalloidin to stabilize the actin in erythrocyte ghosts prior to extraction in low ionic strength media. A mild proteolytic digestion and Sepharose 4B gel filtration enable an F-actin polymer to be isolated in pure form [1]. Detailed size analysis of this polymer in a range of experiments suggests that actin exists in the erythrocyte principally as a polymer of 100 nm length composed of 30 monomers in a double helical chain 15 monomers long with an estimated molecular weight of 1.3 X 10(6) daltons.

Equilibrium studies on the formaldehyde reaction with native DNA.

Equilibrium analysis of the reaction of formaldehyde with native calf thymus DNA was carried out at temperatures below the thermal transition zone by the spectrophotometric method. The apparent equilibrium constant, Kconf., for the conformational opening and closing reaction of base pairs along the double-helical chain, was measured in various concentrations of formaldehyde, and these values were extrapolated to the zero concentration. The value of KOconf. thus obtained in the absence of the chemical probe was 0.12 in 5 mM 2-(N-morpholino)ethane sulfonic acid buffer (Mes), and 0.003 in 0.15 M NaCl plus 5 mM Mes, pH 7.0, at 50 degrees C. These results make it possible to calculate roughly that 230 base pairs and 7 base pairs are open respectively, at 50 degrees C in the native DNA molecule composed of 2300 base pairs, using Mr = 1.5 x 10(6) for the sample used. This conformational reaction was also characterized by the following thermodynamic parameters: deltaGOconf. = 1.36 kcal - mol-1 (5.68 kJ - mol-1), deltaHOconf. = 36.8 kcal - mol-1 (154 kJ - mol-1), and deltaSOconf. = 110 cal - mol-1 - K-1 (460 J - mol-1 - K-1) in 5 mM Mes, pH 7.0, at 50 degrees C, and the nature of the 'breathing' of base pairs was discussed.

A re-evaluation of x-ray diffraction patterns of DNA.

Concentric circular lines are present on X-ray diffraction patterns of DNA. They cannot be accounted for by the double helix model. It is suggested that they may indicate the presence of double helical side chains.