Building Subunits Research Articles

Construction of a new acentric metal–organic framework with isolated tetrahedral {Zn4O} clusters as building subunits

A new noncentrosymmetric Zn(II) compound, namely [Zn4(mbdc)3(μ4-O)(DMA)(H2O)]n·2n(DMA) (1, H2mbdc=isophthalic acid, DMA=N,N′-dimethylacetamide), has been solvothermally synthesized by the combination of H2mbdc and Zn(NO3)2. Single crystal X-ray analysis reveals that compound 1 is a complicated 3D framework based on isolated tetrahedral {Zn4O} clusters as building subunits, which can be simplified into a 6-connected sxb topological network. Second-harmonic generation (SHG) measurements on powder samples reveal that compound 1 exhibits moderate SHG signals approximately 1.67 times that of KDP (KH2PO4). Luminescent investigations show that compound 1 emits intense blue luminescence at room temperature.

Gram-scale synthesis of high-temperature (900 °C) stable anatase TiO2 nanostructures assembled by tunable building subunits for safer lithium ion batteries

Unusually thermal stable anatase TiO2 with high-order structures and controlled grain size were produced for highly reversible lithium ion storage.

Synthesis, structure and luminescent property of a new Zn(II) coordination polymer with isolated tetrahedral {Zn4O} clusters as building subunits

Abstract A new luminescent Zn(II) coordination polymer, namely [Zn4(L)2(μ4-O)(H2O)2(DMF)]n (1 H3L = biphenyl-3,4,5-tricarboxylic acid, DMF = N,N′-dimethyl formamide) has been synthesized by combining the H3L ligand with Zn(II) salts under solvothermal conditions. Single-crystal X-ray diffraction analysis reveals that 1 features μ4-oxygen-bridged tetrahedral {Zn4O} clusters as building subunits, which are further bridged by L3 − ligands into a complicated three-dimensional (3D) architecture. Topological analysis reveals that it can be reduced into a (3, 6)-connected topological network with the schlafli symbol of {4 · 62}2{42 · 69 · 84}. In addition, the luminescent property of 1 was also investigated in the solid state at room temperature.

Employing heterometallic trinuclear cluster as building subunit to construct a new coordination polymer with rare 3D inorganic –Cd–O–Ba– connectivity

A new heterometallic compound, namely [CdBa2(m-BDC)2(DMF)4(NO3)2]n (1 m-H2BDC=isophthalic acid), has been successfully synthesized from m-BDC ligand and corresponding metal salts. Single-crystal X-ray diffraction analysis revealed that 1 is a three-dimensional (3D) framework containing heterometallic trinuclear [CdBa2(COO)4] clusters as building subunits and can be simplified into a 4-connected dia net with the schäfli symbol of 66. Of particular interest is that it also features a rare 3D inorganic connectivity. Moreover, this compound exhibits strong yellow luminescence in the solid state at room temperature.

Alkaline earth metal ion doped Zn(ii)-terephthalates

Alkaline earth metal ion doped Zn(II)-terephthalates, [Zn2Mg(PBDC)3(DMA)2]n (1), [ZnCa(PBDC)2(DMA)2]n (2), [ZnSr(PBDC)2(DMA)2]n (3) and [Zn2Ba(PBDC)3(μ2-O1w)2(DMF)]n·n(DMF) (4) (H2PBDC = terephthalic acid, DMA = N,N′-dimethylacetamide, DMF = N,N′-dimethylformamide), have been solvothermally synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, IR spectra, and thermal analyses. Different secondary building subunits, [Zn2Mg(μ2-COO)3] for 1, [ZnCa(μ2-COO)3] for 2, [ZnSr(μ2-COO)3] for 3, and [Zn2Ba(μ2-COO)4(μ2-O1w)2] for 4, are realized by the introduction of different alkaline earth ions. Compound 1 is a two-dimensional (2D) layer structure with 6-connected hxl topology. Compounds 2 and 3 are isostructural and exhibit a three-dimensional (3D) framework with (3,5)-connected {4.62}{4.66.83} topology owing to their similar secondary building subunits. Compound 4 is a three-dimensional (3D) opened framework with the channels occupied by the disordered lattice DMF molecules and can be simplified into a (3,8)-connected {42.6}2{44.614.78.82} topology. Moreover, the solid-state fluorescence of compounds 1–4 have also been investigated at room temperature.

Mastering the Propagation Through Stacked Perforated Plates: Subwavelength Holes vs. Propagating Holes

More insight on the physics underlying the transmission through subwavelength hole arrays prism by comparing it with propagating hole arrays prism is provided. We show the critical role that the size of the holes plays in this electromagnetic propagation, changing the effective index of refraction from negative (backward wave) to positive values (forward wave) as the hole diameter increases. This causes negative refraction for the zeroth order emerging beam in the cut-off holes prism whereas positive refraction in the non-cut-off holes prism. Furthermore, we revisited from the perspective of superposition principle the explanation of these stacks based on the so-called building sub-units: horizontal rods and vertical wires. Our simple analysis reveals the drawbacks of this earlier interpretation, and reinforces the powerful model founded on a inverse transmission line. Experimental results (co- and cross-polar measurements) performed at the V-band of the millimeter-waves in the Fresnel zone are well supported by numerical analyses. As expected, higher order diffracted outgoing beams are recorded for the classical prism but not for the cut-off holes prism.

Anion Modules: Building Blocks of Supramolecular Assemblies by Combination with π-Conjugated Anion Receptors

Dipyrrolyldiketone boron complexes, as π-conjugated acyclic anion receptors, act as building subunits of various assemblies through noncovalent interactions in the form of receptor-anion complexes. Instead of, or in addition to, the modification of receptor structures, the introduction of anion modules as building blocks for the assemblies was found to be useful in forming various soft materials. Gallic carboxylate derivatives 3-n (n = 16, 18, 20), as tetrabutylammonium (TBA) salts, form receptor-anion-module complexes that can be used to fabricate supramolecular assemblies. Combinations of aliphatic anion modules 3-n and receptors 1a,b along with a TBA cation afforded products with mesophases, which were indicated by differential scanning calorimetry and polarized optical microscopy. X-ray diffraction measurements of the solid states and mesophases of 1a·3-n·TBA and 1b·3-n·TBA revealed highly ordered structures including lamellar structures, which could be modulated by the lengths of the alkyl chains of the modules. Functional materials exhibiting electrical conductivity were fabricated by using combinations of anionic building blocks that form assemblies by themselves and π-conjugated acyclic receptors.

Synthesis and characterization of a novel coordination polymer with isolated tetranuclear lead(II) clusters as building subunits

A novel coordination polymer, [Pb 4(L1) 3( μ 4-O)(H 2O)] n ( 1 H 2L 1 = 5-(pyridine-2-ylmethoxy)-isophthalic acid), was hydrothermally synthesized, which contains μ 4-oxygen-bridged Pb 4O tetrahedral clusters as building subunits. These isolated Pb 4O tetrahedral clusters are combined by the L1 ligands, extending into a two-dimensional (2D) layered motif. Finally, these parallel layers are further linked by intermolecular CH⋯π interactions to form a three-dimensional (3D) stacked supramolecular architecture. Moreover, this polymer exhibits strong photoluminescence at room temperature.

Supramolecular Assemblies Derived from Formyl‐Substituted π‐Conjugated Acyclic Anion Receptors

AbstractWe report on the synthesis and properties of formyl‐substituted dipyrrolyl diketone–BF2 complexes (anion receptors) and their extended derivatives. The formyl‐substituted receptors exhibited efficient anion‐binding behavior and complicated solid‐state hydrogen‐bonding assembly patterns, due to the formyl group's electron‐withdrawing and hydrogen‐bond‐accepting properties. The extended derivatives, prepared by the formation of Schiff bases and their subsequent reduction, behaved as building subunits to provide gel‐like materials in spite of the existence of β‐ethyl substituents. Fairly unspecific spherical particle morphologies were observed for these gel‐like materials by optical microscopy and AFM. The anion‐responsive behavior of the supramolecular assemblies (gelated materials) was also examined.

Synthesis, properties, and solid-state assemblies of β-alkyl-substituted dipyrrolyldiketone BF 2 complexes

In this paper, the synthesis and solid-state structures of β-alkyl-substituted dipyrrolyldiketone BF 2 complexes are discussed; these complexes can function as π-conjugated acyclic anion receptors (“molecular flippers”) and are potential building subunits of anion-responsive π-conjugated oligomers or polymers. Modes of the solid-state assemblies in these complexes determined by performing single-crystal X-ray analysis are found to depend on the lengths of the alkyl chains at the β-positions. A β-methyl-substituted receptor has a highly planar structure, which efficiently forms stacking assemblies in the core π-plane in the solid state, while a β-ethyl-substituted receptor shows no stacking assemblies due to the presence of bulky ethyl moieties, which form only dimeric structures by hydrogen bonding. β-Alkyl-substituted anion receptors can be used not only as monomer units of stimuli-responsive polymeric macromolecules but also as components of solid-state electronic materials.

Polysaccharides from Gracilaria corticata: Sulfation, chemical characterization and anti-HSV activities

In this study, we have analyzed water-extracted polysaccharides of Gracilaria corticata. The water extract (WE), a galactan-containing sub-fraction (F3) and their hyper sulfated derivatives (WES1, WES2, F3S1 and F3S2) had anti-HSV activity with inhibitory concentration 50% (IC 50) from 1.1 to 27.4 μg/ml. Sub-fraction F3, which has a molecular mass of 30 kDa, consists of a backbone of β-(1 → 3) and α-(1 → 4)-linked-galactopyranosyl residues. This linear galactan contained Gal 2Xyl 1, Gal 2AnGal 2, Gal 4 and Me-Gal 3AnGal 2 as oligomeric building subunits. Sulfate group was located at C-4 of (1 → 3)-linked galactopyranosyl residues of the native galactan, and appeared to be very important for the anti-herpetic activity.

Heteroaryl-Substituted C3-Bridged Oligopyrroles: Potential Building Subunits of Anion-Responsive π-Conjugated Oligomers

Acyclic anion receptors (BF 2 complexes of dipyrrolyldiketones) with heteroaryl moieties synthesized by using cross-coupling reactions have unique electronic states, as observed in UV/vis absorption spectra. Among heteroaryl-substituted derivatives, a pyrrolyl-substituted receptor exhibits an extremely high affinity for anions in solution.

Supramolecular Chemistry of Acyclic Oligopyrroles

AbstractAcyclic π‐conjugated oligopyrrole derivatives, though not extensively studied, often have more advantages as anion receptors and metal‐coordination ligands than their cyclic counterparts. This is due to the formation of versatile complexes and supramolecular assemblies, although they do require conformational changes by guest binding. Of the linear oligopyrroles, oligomeric derivatives of dipyrrins bridged by π‐conjugated spacers behave as building subunits and form coordination oligomers and discrete coordination nanorings. In contrast, pyrrole oligomers with hydrogen‐bond‐acceptor site(s) have yielded unique morphologies as supramolecular assemblies and micro‐ and nanometer‐scale structures by means of hydrogen‐bonding interactions. Furthermore, a new class of acyclic anion receptors, namely, BF2 complexes of dipyrrolyl diketones, has been shown to interact with anions by means of the pyrrole NH group and bridging CH interactions. Inversion of the pyrrole rings was found to be essential to capture anions by using these binding sites. Aryl substitution of the receptors as π‐extended derivatives has enabled the formation of assemblies such as supramolecular organogels that can be controlled by the addition of anions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

BF2Complexes of β-Tetraethyl-Substituted Dipyrrolyldiketones as Anion Receptors: Potential Building Subunits for Oligomeric Systems

Synthesis and anion binding properties of BF2 complexes of beta-tetraethyl-substituted dipyrrolyldiketones, with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole alpha-positions, are reported. The substituents at pyrrole rings of these acyclic anion receptors are found to play a key role to control not only the polarization of binding sites (NH and CH) but also the relative stabilities of the preorganized conformations and the degrees of sterical repulsion, both of which notably affect the affinities for anions.

Sulphated polysaccharides from Indian samples of Enteromorpha compressa (Ulvales, Chlorophyta): Isolation and structural features

Heteroglycan and xyloglucan rich fractions were extracted from Indian samples of Enteromorpha compressa in 25% yield by sequential extractions with water and alkali. This heteroglycan is sulfated and has an apparent molecular mass of 55 kDa. Chemical structural analysis of this polysaccharide revealed a branched structure having 1,4- and 1,2,4-linked rhamnose 3-sulphate, 1,4-linked glucose, 1,3- and 1,6- linked galactose, 1,4- and terminally linked glucuronic acid and 1,4-linked xylose partially sulfated on O-2. Chemical and spectroscopic analysis showed that the 4-M KOH extracted hemicellulosic fraction contained an unusual β-(1,4)-linked linear xyloglucan. Enzyme hydrolysis and analysis of the resulting fragments by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) showed that this linear polymer contained partially sulfated Glc 3Xyl 2 or Glc 4Xyl 2 as oligomeric building subunits.

A novel Keggin-type tungstogermanate dimer bearing dinuclear copper-organic coordination ions: {H 8[Cu(phen)(μ 2-CH 3COO) 2Cu(phen)(H 2O)] 2[Ge 2W 23CuO 80]} · 24H 2O

An unprecedented Keggin-type tungstogermanate dimer bearing dinuclear copper-organic coordination ions {H 8[Cu(phen)(μ 2-CH 3COO) 2Cu(phen)(H 2O)] 2[Ge 2W 23CuO 80]} · 24H 2O has been synthesized and characterized by IR, UV, ICP analyses, ESR spectra, element analysis, TG and single crystal X-ray diffraction analysis. The compound is built up from a dimeric heteropolyanion constituted by two corner-shared Keggin-type building subunits and two dinuclear copper-organic coordination cations [Cu(phen)(μ 2-CH 3COO) 2Cu(phen)(H 2O)] 2+, each of which consists two square pyramidal copper-phen ions bridged by two μ 2-acetate ligands.

Polysaccharides from Enteromorpha compressa: Isolation, purification and structural features

Abstract Polysaccharides containing fractions were obtained from the seaweed Enteromorpha compressa by sequential extractions with various solvents. Anion exchange chromatography (AEC) of the oxalate extracted fraction (OSP) yielded rhamnoxylogalactoglucuronan, xyloglucan and glucuronan rich sub-fractions. The heteroglycuronan, which is sulfated, has an apparent molecular mass of 50 ± 20 kDa and is soluble in water. Methylation analysis of the native, desulfated and desulfated reduced heteroglycuronan sulfate suggested that this polymer is branched and contains, inter alia, (1 → 4)- and (1 → 2,4)-linked-rhamnopyranosyl, (1 → 4)-linked xylopyranosyl, and (1 → 4)- and terminally linked glucuronosyl residues. Sulfate groups, when present, are located at C-3 of (1 → 4)-linked rhamnose units and C-2 of (1 → 4)-linked xylose units. Degradation of the xyloglucan rich extract (Ec1OH) by endo-(1 → 4)-β- d -glucanase and analysis of the resulting fragments by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) showed that the E. compressa xyloglucan contains Glc3Xyl1, Glc4, Glc3Xyl2(SO3Na)2, Glc4Xyl2(SO3Na)2 and Glc5Xyl2(SO3Na)2 as major oligomeric building sub-units.

Polysaccharides from Sesamum indicum meal: Isolation and structural features

Defatted Sesamum indicum seed cake was extracted, following two separate sequences, and the effects of extraction medium on yield and composition of the extracts were compared. Polysaccharides extracted sequentially with dilute acid and alkali represented 250 mg/g of defatted meal. The isolated polymers contained arabinan, rhamnogalacturonan I (RG I) and arabinogalactan proteins. Polysaccharides extracted during chlorite treatment and with dilute alkali had a higher proportion of rhamnose, suggesting a more branched variety of polymer. Three extracts, which were further characterized by size exclusion chromatography, gave two overlapping peaks. Structural characterisation of hemicellulosic polysaccharides, isolated with KOH, using specific enzyme hydrolysis, ion exchange chromatography (HPAEC) and matrix assisted laser desorption ionisation-time-of-flight (MALDI-TOF) mass spectroscopy, showed that sesame meal xyloglucan (XG) contained XXXG, XXFG and XXLG, and XLLG (named according to Fry et al., 1993) as the major building sub-units in the ratio of 1:0.9:0.3. Hydrolysis with endo-β-(1 → 4)- d-xylanase and analysis of the xylan derived oligosaccharides showed the presence of monomeric xylose (40%), xylobiose (46%) and acidic xylan oligosaccharides containing 4- O-methyl- d-glucuronic acid residues (14%).

Cell wall polysaccharides of Brassica campestris seed cake: isolation and structural features

Brassica campestris seed cake is an important source of water-soluble polysaccharides. The polysaccharides extracted with acid and dilute alkali represented 270 mg/g of defatted meal. These polymers, which have high amount of neutral sugars are arabinan, rhamnogalacturonan I and arabinogalactan proteins. These polymers have been analyzed by size exclusion chromatography. Two overlapping peaks have been found. Structural characterization of 4 M KOH-soluble hemicellulosic polysaccharides using specific enzyme hydrolysis, ion exchange chromatography (HPAEC) and matrix-assisted laser desorption ionization-time of flight mass spectroscopy showed that mustard meal xyloglucan is of XXXG type and contained XXXG, XXFG, XXLG and XLFG (named according to Fry et al. [Physiol. Plant. 89 (1993) 1]) as the major building sub-units. Hydrolysis with endo-β-(1→4)- d-xylanase and analysis of the xylan derived oligosaccharides showed the presence of xylose (27%), xylobiose (26%) and acidic xylan fragments containing 4- O-methyl- d-glucuronic acid residue (47%).

CdII(bpdc)·H2O]n: A Robust, Thermally Stable Porous Framework through a Combination of a 2-D Grid and a Cadmium Dicarboxylate Cluster Chain (H2bpdc = 2,2‘-Bipyridyl-4,4‘-dicarboxylic Acid)

The synthesis and characterization of a cadmium(II) coordination polymer, [Cd(C(12)H(6)N(2)O(4)) x H(2)O](n)() (1), is reported. A single-crystal X-ray analysis shows that compound 1 presents a non-interpenetrating three-dimensional porous host containing one-dimensional hydrophilic channels, where guest water molecules reside. The strategy in designing the 3-D framework architecture is based on a combination of two building subunits: a porous two-dimensional grid of (4,4) topology and a metal dicarboxylate cluster chain. Both subunits are assembled from the coordination of a cadmium ion with a three-connecting organic modular ligand, 2,2'-bipyridyl-4,4'-dicarboxylic acid (H(2)bpdc). The results of thermogravimetric analysis and powder X-ray diffraction study show that the framework rigidity of compound 1 remains intact upon the removal of guest molecules, and maintains the thermal stability up to 440 degrees C. The second-row transition-metal ions are capable of engaging higher coordination modes (e.g., hepta- and octacoordination) because of their atomic sizes and intrinsic electron configurations. Our results show that the heptacoordinated cadmium center plays an important role in the overall framework rigidity and high thermal stability of compound 1. Crystal data for 1: Cd(C(12)H(6)N(2)O(4)) x H(2)O, triclinic, space group P1 macro, a = 6.7843(5) A, b = 9.3299(7) A, c = 9.4439(7) A, alpha = 104.629(1) degrees, beta = 92.324(1) degrees, gamma = 100.416(1) degrees, Z = 2.