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Modeling the mechanisms of protofibril twisting: Molecular-dynamics simulations of simian viral peptide aggregates show that β sheets of 10 to 30 chains form left-handed helical ribbons with saddlelike curvature (see picture). These structures are highly dynamic, with oscillations around an average twist angle of 9-10°, and a pitch of 15-20 nm, depending on β-sheet length. The peptides studied are key to viral entry into host cells.

A new phase in the Si-Al-O-N system has been identified, following syntheses based on the nitridation of silicon/clay mixtures at low temperatures (

The title compound, C10H9N2+·C8H4NO6−·C8H5NO6·2H2O, consists of singly protonated 2,2′-bipyridinium cations, 5-nitroisophthalate anions, 5-nitroisophthalic acid and water mol­ecules of crystallization, linked by N—H⋯O and O—H⋯O hydrogen bonds. The moieties are linked by multiple hydrogen bonds into an undulating sheet structure.

A solvate of 5-fluoro­uracil with di­methylform­amide (DMF), 2C4H3FN2O2·C3H7NO, is reported. It crystallizes in the monoclinic space group P21/n, with two mol­ecules of 5-fluoro­uracil and one mol­ecule of DMF in the asymmetric unit. This solvate exhibits a sheet structure, with the DMF mol­ecules present on both surfaces of the sheet and 5-fluoro­uracil mol­ecules within the sheath of DMF mol­ecules.

The title compound, C5H4N2O4·H2O, a uracil derivative, contains several important functional groups, which give rise to its use in biomedical applications. The crystal structure consists of mol­ecules held together by extensive intermolec­ular hydrogen bonding between neighbouring pyrimidine rings and between the acid groups and water mol­ecules, resulting in a layered sheet structure. The asymmetric unit contains two molecules of the carboxylic acid and two water molecules.

New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by HCH…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phane 8b (di-dihydrochloride salt) adopts a chair-chair conformation, confirming that protonation of the N atoms does not change the conformation.

Solvates of triphenylmethyl potassium have been prepared with three different Lewis bases and their crystal structures determined by X-ray diffraction methods. In [KCPh 3 (PMDTA)] (bd1) (PMDTA  N,N,N′,N″,N″-pentamethyl-diethylenetriamine) discrete molecules are observed whereas the solvates with DIGLYME (MeOCH 2 CH 2 0CH 2 CH 2 OMe) and THF are polymeric in the crystal: [KCPh 3 (DIGLYME)] n ( 32 , zigzag-chain structure) [KCPh 3 (THF)] n (3, sheet structure).

Amyloid fibrils were isolated from heterozygous Met 30 familial amyloidotic polyneuropathy (FAP) patients. A chelating agent, collagenase digestion and defatting agents were used to remove the serum amyloid P-component, collagen and other adherent tissue components from the fibrils. The characteristic birefringence of amyloid fibrils remained after purification. X-ray diffraction experiments were performed before and after the removal of adherent material. The predominant features from the X-ray diffraction pattern, consisting of a series of concentric rings, indicate the presence of a lipid structure in all the samples that had not been previously delipidated. In contrast, defatted fibrils exhibited only two reflections in the 4-30 A region: a sharp reflection corresponding to a 4.76 A spacing and a broad and diffuse one centered at 10.5 A spacing, both characteristic of a β-pleated sheet structure. The low angle pattern, from the purified material, shows one unique reflection at 63 A spacing.Analysis of...

The crystal and molecular structures of diethyl 6-[4-(4′-nitrophenylazo)phenoxy]hexylmalonate (1) as a comonomer in the synthesis of liquid-crystalline polymers and its 2′-nitrophenyl isomer (2) have been determined by X-ray analysis. Both compounds crystallize in space group P1 with two molecules per unit cell and the following lattice parameters. 1: a = 7.995(2), b = 10.699(2), c = 15.021(4) A, a = 95.04(2), β = 96.54(2), γ = 94.72(3)°. 2: a = 8.912(2), b = 9.664(2), c = 16.064(4) A, α = 98.68(2), β = 97.54(1), γ = 105.11(1)°. The structures were solved by direct methods and refined to R (wR) values of 0.082 (0.068) and 0.071 (0.076), respectively. The molecules have an optimum stretched shape excepted one of their two ethoxycarbonyl groups which is perpendicularly oriented to the molecular long axis. The molecular packing in the crystal can be described in terms of a sheet structure in which the sheets are penetrated by the laterally branched ethoxycarbonyl groups of neighboring sheets.

In the title compound, C(5)H(8)N(6)OS(2), the supramolecular architecture is sustained by two N--H...O and three N--H...S hydrogen bonds, and by N.S electrostatic interactions. The hydrogen-bond network generates a sheet structure, which extends in the a and b directions and is one c-cell dimension thick. These extended sheets are then linked across inversion centres in the c direction by N...S electrostatic interactions, thus forming a three-dimensional network. The principal intermolecular dimensions include N(H)...O distances of 2.8393 (17) and 3.0268 (16) A, N(H)...S distances in the range 3.2896 (14)-3.5924 (16) A and N...S distances of 3.0822 (16) A.

Polymeric di­chloro(N,N-di­methyl­ethyl­enedi­amine)­cad­mium­(II), [CdCl2(C4H12N2)]n, has been synthesized and characterized by single-crystal X-ray diffraction. The two-dimensional polymeric sheet structure involves 12-membered zigzag rings formed by chloro bridges.

The title compound, C5H6ClN3O, is essentially planar with a maximum deviation of 0.0256 (11) Å for all non-H atoms. In the crystal, adjacent molecules are linked by a pair of N—H...N hydrogen bonds, forming an inversion dimer with an R22(8) ring motif. The dimers are further linked via N—H...O hydrogen bonds into an undulating sheet structure parallel to the bc plane.

The reactivity of aqueous Fe(II) with aluminum oxide in anoxic solutions was investigated with batch kinetic experiments combined with Fe K edge X-ray absorption spectroscopy measurements to characterize Fe(II) sorption products. Formation of Fe(II)-Al(III)-layered double hydroxides with an octahedral sheet structure similar to nikischerite (NaFe(II)(6) Al(3)(SO(4))(2)(OH)(18) (H(2)O)(12)) was observed within a few hours during sorption at pH 7.5 and aqueous Fe(II) concentrations of 1-3 mM. These Fe(II) phases are composed of brucite-like Fe(II)(OH)(2) sheets with partial substitution of Al(III) for Fe(II), charge balanced by anions coordinated along the basal planes. Their fast rate of formation suggests that these previously unrecognized Fe(II) phases, which are structurally and compositionally similar to green rust, may be an important sink of Fe(II) in suboxic and anoxic geochemical environments, and impact the fate of structurally compatible trace metals, such as Co(II), Ni(II), and Zn(II), as well as redox-reactive species including Cr(VI) and U(VI). Further studies are required to assess the thermodynamics, formation kinetics, and stability of these Fe(II) minerals under field conditions.

Conformational potential energy hypersurfaces (PES) for the N-acetyl-N'-methylamides of all the 20 common amino acids have been analyzed by means of the molecular mechanics method in combination with the programs rose, daisy, cicada and panic. Global and fragmental flexibility f and Φ, conformational softnessf0 as well as flexibility of each conformation found have been computed for each residue. Rank correlation between the flexibility and Boltzmann probability, respectively, and the ability to form α-helix or β-pleated sheet structure in a protein has been evaluated. It has been revealed that the ability to form α-helix or β-pleated sheet correlates better with the conformational flexibility of single residues in the corresponding region than with the Boltzmann distribution of the corresponding single residue conformations in that region.

[5]Trovacenol (4•) prepared according to the sequence (C7H7)V(C5H5) (1•)→ (C7H7)V(C5H4OSiMe3) (5•) → (C7H7)V(C5H4OH) (4•) in the crystal adopts a sheet structure. The sheets consist of parallel chains of hydrogen bonds, graph set C(4), to which the [5]trovacenyl groups are connected, forming double layers. Packing of the trovacene units on both sides of the (···O−H···O−H···)n spines displays a herringbone pattern. In this way O−H···O as well as (C7H7)H···π(C5H5) hydrogen bonding is optimized. This study represents the first full structural characterization of a metallocenol.

The bis(benzimidazol-1-yl)methane molecule of the title compound, C15H12N4·2H2O, displays a trans conformation with a twofold axis running through the methylene C atom. Two adjacent water molecules are bonded to this molecule through O—H...N hydrogen bonds, forming a trimer. Adjacent trimers are connected together via C—H...O interactions, forming a chain running along the b-axis direction. Two such chains are joined together via π–π interactions [centroid–centroid distance = 3.556 (2) Å], forming double chains, which are connected via the water molecules through C—H...O associations, forming a sheet structure. The sheets are stacked on top of each other along the a-axis direction and connected through O—H...O and C—H...O interactions, forming a three-dimensional ABAB layer network structure.

In the crystal structure of the title compound, C6H13N2O+·C7H4NO5−, the isonipecotamide cations and the 5-nitrosalicylate anions form hydrogen-bonded chain substructures through head-to-tail piperidinium–carboxylate N—H...O hydrogen bonds and through centrosymmetric cyclic head-to-head amide–amide hydrogen-bonding associations [graph set R22(8)]. These chains are cross-linked by amide–carboxylate N—H...O and piperidinium–nitro N—H...O associations, giving a sheet structure.

The structure of tetragermanium strontium nonaoxide, SrGe 4 O 9 , comprises two different types of sheet structure stacked alternately along the c axis. One sheet comprises GeO 6 octahedra and SrO 8 polyhedra while the other sheet contains three-membered rings of GeO 4 tetrahedra. In addition, this crystal structure shows a basic unit of the superstructures which are found for PbGe 4 O 9 .

The reaction of silver(I) perchlorate with the semi-rigid ligand 1,4-bis((3,5-dimethylisoxazol-4-yl)methyl) benzene (bisox) in methanol gives a triply-interpenetrated sheet structure, but a structure containing both interpenetrated sheets and Ag-2(bisox)(3) cages is formed on recrystallisation from acetonitrile-diethyl ether. Rearrangement of the cages into sheets occurs on heating under vacuum, a process which involves a solid state change in conformation of the bisox ligands.

Sheet- and column-like cyanide bridged lanthanide−transition metal arrays were synthesized through metathesis reactions between anhydrous LnCl3 (Ln = Eu, Yb) and A2[M(CN)4] (A = K+, NH4+; M = Ni, Pt) in a 1:2 molar ratio in DMF (DMF = N,N-dimethylformamide) solution. Single-crystal X-ray analysis revealed that complexes of formula {K(DMF)7Ln[M(CN)4]2}∞ (Ln = Eu, M = Ni, 1; Ln = Yb, M = Pt, 2) consist of infinite layers of neutral, puckered sheets that contain hexagonal rings of composition {(DMF)10Ln2[M(CN)4]3}6 with interstitial (DMF)4K2[M(CN)4] units located between the layers. The sheet structure is generated through the repeating (DMF)10Ln2[M(CN)4]3 unit with trans cyanide ligands in [M(CN)4]2- serving as bridges. The column-like complex {(NH4)(DMF)4Yb[Pt(CN)4]2}∞, 3, is formed when NH4+ replaces K+. It consists of infinite, negatively charged, square, parallel columns bundled through N−H···NC hydrogen bonds between NH4+ and terminal CN from the columns. Cis cyanide ligands in [Pt(CN)4]2- units serve ...

The asymmetric unit of the title salt, 2NH4+·B10H102−·1.5H2O or (NH4)2B10H10·1.5H2O, (I), contains two B10H102− anions, four NH4+ cations and three water mol­ecules. (I) was converted to the anhydrous compound (NH4)2B10H10, (II), by heating to 343 K and its X-ray powder pattern was obtained. The extended structure of (I) shows two types of hydrogen-bonding interactions (N—H⋯O and O—H⋯O) and two types of dihydrogen-bonding interactions (N—H⋯H—B and O—H⋯H—B). The N—H⋯H—B dihydrogen bonding forms a two-dimensional sheet structure, and hydrogen bonding (N—H⋯O and O—H⋯O) and O—H⋯H—B dihydrogen bonding link the respective sheets to form a three-dimensional polymeric network structure. Compound (II) has been shown to form a polymer with the accompanying loss of H2 at a faster rate than (NH4)2B12H12 and we believe that this is due to the stronger dihydrogen-bonding inter­actions shown in the hydrate (I).

A theoretical analysis is given to the wave characteristics of a textile sheet structure which is proposed as a submerged flexible breakwater. The analysis is based on a two-dimensional linear potential theory. The numerical results have good agreements with experimental observations. It is found that the flexible type structure is much more effective as abreakwater than the non-flexible one.

Based on first-principles methods, we present a self-doping picture in atomically thin boron sheets: this shows that for two-dimensional boron nanostructures, adding or removing boron atoms is essentially equivalent to simply adding or removing electrons from a fixed electronic structure. This picture allows us to propose a general design rule for pure boron nanostructures and explains the occurrence of known stable nanostructures. In addition, self-doping provides a powerful tool for finding stable metal boride nanostructures. We illustrate this last point by showing an unexpectedly stable ${\text{MgB}}_{2}$ sheet structure which is likely the precursor of ${\text{MgB}}_{2}$ nanotubes. Our results are easily generalized to other stoichiometries and other choices of metals.

There are two unique molecules in the asymmetric unit of the title compound, C17H15NO4, which are linked into chains via intermolecular N—H...O and C—H...O interactions; the chains are linked via weak C—H...O interactions, forming a parallel sheet structure. The molecule is approximately planar, with dihedral angles of 19.91 (4) and 11.06 (4)° between the naphthyl ring and the aminomethylene group, and between the aminomethylene unit and the planar part of the dioxane ring, respectively. The dioxane ring adopts a half-boat conformation, with the C atom between the dioxane O atoms 0.595 (8) Å out of the plane through the remaining atoms. The molecule has an intramolecular N—H...O hydrogen bond which stabilizes the planar conformation.

Hydrothermal synthesis in the M/Mo/O (M=Co,Ni) system was investigated. Novel transition metal tetramolybdate dihydrates MMo4O13·2H2O (M=Co,Ni), having an interesting pillared layer structure, were found. The molybdates crystallize in the triclinic system with space group P−1, Z=1 with unit cell parameters of a=5.525(3) A, b=7.058(4) A, c=7.551(5) A, α=90.019(10)°, β=105.230(10)°, γ=90.286(10)° for CoMo4O13·2H2O, and a=5.508(2) A, b=7.017(3) A, c=7.533(3) A, α=90.152(6)°, β=105.216(6)°, γ=90.161(6)° for NiMo4O13·2H2O The structure is composed of two-dimensional molybdenum-oxide (2D Mo-O) sheets pillared with CoO6 octahedra. The 2D Mo-O sheet is made up of infinite straight ribbons built up by corner-sharing of four molybdenum octahedra (two MoO6 and two MoO5OH2) sharing edges. These infinite ribbons are similar to the straight ones in triclinic-K2Mo4O13 having 1D chain structure, but are linked one after another by corner-sharing to form a 2D sheet structure, like the twisted ribbons in BaMo4O13·2H2O (or in orthorhombic-K2Mo4O13) are.

From its very beginning, papermaking has been targeted to produce a homogeneous sheet structure out of large volumes of water containing small amounts of fibre and filler. Fibre concentrations of below 1% are quite common in this context.

Representations of nonlinear nonbijective canonical transformations in quantum mechanics are discussed. Due to the nonbijectivity the classical phase space has a Riemann sheet structure, and a family of partial isometries translating this structure into quantum mechanics is constructed. If a unitary representation is required, a new variable-the ambiguity spin-has to be introduced in order to recover bijectivity following the approach of Moshinsky (1981) and co-workers. The new degree of freedom is analysed in terms of multiboson operators. The application of this formalism to some non-classical states of light is discussed.

A layered structure of the paperboards manufactured from two different consistency levels of pulp slurry was examined by measurement of the fiber orientation in the paper thickness direction. The standard deviation of the probability density distribution function of the fiber orientation in the paperboard made from 3.3% (high consistency) pulp slurry was found to be higher than that from 0.9% (low consistency) slurry. This indicates that the paperboard from a high consistency pulp suspension has rather a felt-like structure. The felt-like sheet structure of the high consistency paperboard was proved to be attributable to the core layer structure. The standard deviation of the fuction in the cross machine direction in all of the paperboards tested was higher than that in the machine direction. This implies the existence of microstriation in the papers which was probably introduced during the drying process.

Crystals of sulfathiazole, 4-amino-N-thiazol-2-ylidenebenzenesulfonamide, C 9 H 9 N 3 O 2 S 2 , formed from boiling water are shown to be a fifth polymorph. The crystal structure contains two independent molecules, which associate through hydrogen bonds and van der Waals interactions to produce a two-dimensional sheet structure.

The crystal structure of 4,4'-bipyridyl, C 10 H 8 N 2 , at 203 K contains two independent, non-planar, molecules whose mean planes subtend an angle of 14.1(8)°. The long axes of the two molecules are oriented at approximately 88° to each other, allowing interaction between the N atoms and phenyl-H atoms on adjacent molecules and thereby giving rise to a sheet structure. The two molecules are primarily differentiated by the dihedral angle between the connected phenyl rings [18.50(12) and 34.85(10)°].

In the title compound, C14H17N2O4P·CH3OH, the planes of the pyridinium-2-ylamino and 2-hydroxyphenyl groups form a dihedral angle of 75.6 (1)°, with the pyridinium NH group and the 2-hydroxyphenyl OH group pointing in opposite directions. Three intramolecular hydrogen bonds are observed. Two phosphonate and two methanol molecules are connected by O—H...O hydrogen bonds as a centrosymmetric dimeric cluster, and interact further with other dimeric clusters via N—H...O, O—H...O and C—H...O hydrogen bonds and C—H...π interactions, resulting in a sheet structure.

The molecule of the title compound, C18H18O2, a symmetrically phenol-substituted divinyl analog, exhibits crystallographically imposed C2 symmetry. The phenolic and divinyl planar groups intersect each other orthogonally, with a dihedral angle of 82.7 (1)°. The structure is stabilized by a short intramolecular C—H...O contact. The molecules are held together by C—H...π interactions, forming a sheet structure parallel to the (201) plane.

We present a sheet structure that rotates the local ray direction through an arbitrary angle around the sheet normal. The sheet structure consists of two parallel Dove-prism sheets, each of which flips one component of the local direction of transmitted light rays. Together, the two sheets rotate transmitted light rays around the sheet normal. We show that the direction under which a point light source is seen is given by a Mobius transform. We illustrate some of the properties with movies calculated by ray-tracing software., Comment: 9 pages, 6 figures

Modeling of three‐dimensional (3-D) thin‐sheet telluric anomalies has been a popular means of estimating the distortions of magnetotelluric (MT) response functions in the vicinity of an upper crustal resistivity inhomogeneity (Kaikkonen, 1986) because structures with an arbitrary 3-D shape in plan view can be simulated with modest computational effort. In the class of thin‐layer problems of this note, the sheet structure overlies an infinitely resistive basement; and anomalous fields are computed in the long‐period or zero‐frequency (dc) limit (e.g., Hermance, 1982). Under the assumption of no vertical current flow into the basement, this 3-D problem reduces to a two‐dimensional (2-D) dc solution across the sheet. Since only the long‐period limit is considered, however, the conclusions that can be drawn about the effects of general 3-D structures are restricted. The purpose of this note is to clarify restrictions on the use of 2-D MT interpretations in 3-D areas based on just thin‐sheet telluric modeling.

A simple model for describing the motion of material in a debris cloud is presented. Motion and distribution of this material are described using three axial velocities, one radial velocity, and the diameter of the projectile. Results of hypervelocity impact tests using copper projectiles and aluminum bumpers are presented. Data from these tests were used to verify several assumptions integral to the development of the model. A method for approximating the pressure-loading history applied to the interior wall of a double sheet structure is also presented.

The molecular structure of the title compound, 2-CH3O—C6H3-1,3-[B(OH)2]2 or C7H10B2O5, features two intramolecular O—H...O hydrogen bonds of different strengths. One of the boronic acid groups is almost coplanar with the aromatic ring, whereas the second is significantly twisted. Molecules are linked by intermolecular O—H...O hydrogen bonds, generating infinite chains cross-linked to form a two-dimensional sheet structure aligned parallel to the (01overline{1}) plane.

The cyanides $M\mathrm{C}\mathrm{N}$, $M=\mathrm{Cu},\mathrm{Ag},\mathrm{Au}$, have experimentally a structure with hexagonally packed, infinite $M\mathrm{C}\mathrm{N}M\mathrm{C}\mathrm{N}$ chains. Following our earlier study for AuCN, we now predict that all three $M\mathrm{C}\mathrm{N}$ could have an alternative ${M}_{3}{\mathrm{C}}_{3}{\mathrm{N}}_{3}$ sheet structure of comparable energy with the known one. The valence isoelectronic systems $M{\mathrm{C}}_{2}$ versus ${M}_{3}{\mathrm{C}}_{6}$, $M=\mathrm{Be}\mathrm{Ba},\mathrm{Zn}\mathrm{Hg}$, are also studied. Now, the known dicarbides have the $\mathrm{Ca}{\mathrm{C}}_{2}$ or $\mathrm{Mg}{\mathrm{C}}_{2}$ chain structures, which are well reproduced. The predicted sheets lie energetically below the chains for $M=\mathrm{Zn}$, Cd, and Hg. All these group-12 systems are experimentally unknown. Indeed, they are clearly endothermic, compared to the elements. For some sheet structures, the densities of states suggest rather small band gaps and even metallic character. When available, the experimental geometries agree well with the calculated ones.

The architecture of the heart remains controversial despite extensive effort and recent advances in imaging techniques. Several opposing and non-mutually compatible models have been proposed to explain cardiac structure, and these models, although limited, have advanced the study and understanding of heart structure, function and development. We describe key areas of similarity and difference, highlight areas of contention and point to the important limitations of these models. Recent research in animal models on the nature, geometry and interaction of cardiac sheet structure allows unification of some seemingly conflicting features of the structural models. Intriguingly, evidence points to significant inter-individual structural variability (within constrained limits) in the canine, leading to the concept of a continuum (or distribution) of cardiac structures. This variability in heart structure partly explains the ongoing debate on myocardial architecture. These developments are used to construct an integrated description of cardiac structure unifying features of fibre, sheet and band architecture that provides a basis for (i) explaining cardiac electromechanics, (ii) computational simulations of cardiac physiology and (iii) designing interventions.

Mesh deformation, which is sometimes referred to as mesh morphing in CAE, is useful for providing various shapes of meshes for CAE tools. This paper proposes a new framework for interactively and consistently deforming assembly models of sheet structure for mechanical parts. This framework is based on a surface-based deformation, which calculates the vertex positions so that the mean curvature normal is preserved at each vertex in a least squares sense. While existing surface-based deformation techniques cannot simultaneously deform assembly mesh models, our method allows us to smoothly deform disconnected meshes by propagating the rotations and translations through disconnected vertices. In addition, we extend our deformation technique to handle non-manifold conditions, because shell structure models may include non-manifold edges. We have applied our method to assembly mesh models of automobile parts. Our experimental results have shown that our method requires almost the same pre-processing time as existing methods and can deform practical assembly models interactively.Copyright © 2007 by ASME

Amyloid refers to a family of abnormal proteins that share a common fibrillar β-pleated sheet structure that gives it unique optical and staining properties. In addition to the fibrillar component, amyloid deposits contain a universal amyloid P component. Detection of amyloid in myocardial tissue with Congo red alone is difficult and tedious. We evaluated …

The topologically unique sheet structure of [Ag(tcm)] [tcm=the tricyanomethanide ion, C(CN)3-] is retained in the derivative [Ag(tcm)(phz)1/2] (phz=phenazine). The sheet structure is composite, consisting of two independent hexagonal grid nets which are corrugated so as to allow one to interpenetrate the other. The Ag+ ion is three-coordinate and provides half the three-connecting nodes of the hexagonal grid net, the others being provided by the tcm central carbon. [Ag(tcm)(phz)1/2] contains essentially the same composite double sheets linked together by phenazine units that bridge between silver centres which thereby become four-coordinate. The topology of [Ag(tcm)(pyz)] (pyz=pyrazine) is very different; in this case the Ag(tcm) component forms a planar, non-corrugated hexagonal grid and each such sheet is connected on both sides to neighbouring sheets by pyrazine bridging ligands whereby the silver becomes five-coordinate and trigonal bipyramidal. Two such 3,5-connected three-dimensional nets then interpenetrate.

Herein we present the first unequivocal evidence of the ability of isotactic N-alkyl acrylamide oligomers to assume self-assembled sheet-like structures that are reminiscent of protein beta-sheets.

Cyanuric acid forms a hydrogen-bonded framework with 2,7-diazapyrene that adopts a threefold interpenetrated two-dimensional sheet structure with an unexpected 44 topology, generated via the supramolecular assembly of dimeric cyanuric acid nodes.

In the title complex, [Cu(BF4)2(C5H5N)2], the Cu(II) ion is in an octa-hedral coordination environment and is surrounded by four pyridine and two tetra-fluoridoborate mol-ecules. The four pyridine mol-ecules are coordinated to the copper ion through their N atoms in the equatorial plane and display a right-handed screw arrangement around the Cu(II) ion. The remaining two trans positions in the octa-hedron are occupied by the BF4 (-) anions, each coordinating weakly through an F atom. The crystal packing shows a two-dimensional sheet structure parallel to the ab plane that is formed by C-H⋯F hydrogen-bonding inter-actions.