Wide Range Of Structural Types Research Articles

Hydrogen-Mediated Photoelectrocatalysis with Nickel-Modified Poly(Heptazine Imides)

Polymeric carbon nitrides (C3N4) are photochemically active organic semiconductors that can be produced in a wide range of structural types. Here, a poly-(heptazine imide) containing nickel single atoms (Ni-PHI) is employed for photochemical hydrogen production and is compared to the non-nickel-doped semiconductor. Film deposits are formed on a platinum disk electrode (to detect hydrogen) and a coating of the molecularly rigid polymer of intrinsic microporosity PIM-1 is applied to (i) mechanically stabilize the photo-catalyst film without impeding photocatalysis and (ii) assist in the interfacial hydrogen capture/oxygen suppression process. In the presence of hole quenchers such as methanol or ethanol, anodic photocurrents linked to hydrogen production/oxidation are observed. A comparison with an experiment on glassy carbon confirms the formation of interfacial hydrogen as a mediator. The effects of hole quencher concentration are evaluated. The system Pt/Ni-PHI/PIM-1 is employed in a single-compartment photo-fuel cell.Graphical

Vzácné obalové vazby ve sbírkách Knihovny Národního muzea

Rare double-cover bindings in the collections of the National Museum Library Unlike contemporary embossed bindings, Gothic double-cover bindings are mostly undecorated, as priority was given to the binding’s useful function. Covered codexes were stored in a horizontal position and the wide overlaps on the front edge of the back panel were inserted between the front panel and the book block; after the fastening of the clasps, the parchment block was perfectly protected by this “packaging“ against the adverse effects of the surrounding environment. The originally Romanesque type of binding was used for larger format codexes and appeared practically throughout the Middle Ages, until the 16th century. In domestic literature, double-cover binding is wrongly included in the “shape and binding curiosities“ category; abroad, the terminology for describing and determining structural types of bindings with a secondary cover is not clear. During conservation research in the National Museum Library, a total of 45 Gothic double­-cover bindings was found in various states of preservation, from which we can determine a wide range of structural types and several methods of execution. A set of ten double-cover bindings published by Dr. Hamanová was expanded to include bindings from Augustinian monasteries

Extended Condensed Ultraphosphate Frameworks with Monovalent Ions Combine Lithium Mobility with High Computed Electrochemical Stability.

Extended anionic frameworks based on condensation of polyhedral main group non-metal anions offer a wide range of structure types. Despite the widespread chemistry and earth abundance of phosphates and silicates, there are no reports of extended ultraphosphate anions with lithium. We describe the lithium ultraphosphates Li3P5O14 and Li4P6O17 based on extended layers and chains of phosphate, respectively. Li3P5O14 presents a complex structure containing infinite ultraphosphate layers with 12-membered rings that are stacked alternately with lithium polyhedral layers. Two distinct vacant tetrahedral sites were identified at the end of two distinct finite Li6O1626– chains. Li4P6O17 features a new type of loop-branched chain defined by six PO43– tetrahedra. The ionic conductivities and electrochemical properties of Li3P5O14 were examined by impedance spectroscopy combined with DC polarization, NMR spectroscopy, and galvanostatic plating/stripping measurements. The structure of Li3P5O14 enables three-dimensional lithium migration that affords the highest ionic conductivity (8.5(5) × 10–7 S cm–1 at room temperature for bulk), comparable to that of commercialized LiPON glass thin film electrolytes, and lowest activation energy (0.43(7) eV) among all reported ternary Li–P–O phases. Both new lithium ultraphosphates are predicted to have high thermodynamic stability against oxidation, especially Li3P5O14, which is predicted to be stable to 4.8 V, significantly higher than that of LiPON and other solid electrolytes. The condensed phosphate units defining these ultraphosphate structures offer a new route to optimize the interplay of conductivity and electrochemical stability required, for example, in cathode coatings for lithium ion batteries.

Structural diversity in the coordination compounds of cobalt, nickel and copper with N-alkylglycinates: crystallographic and ESR study in the solid state.

Reactions of N-methylglycine (HMeGly), N-ethylglycine-hydrochloride (H2EtGlyCl) and N-propylglycine-hydrochloride (H2PrGlyCl) with cobalt(ii), nickel(ii) and copper(ii) ions in aqueous solutions resulted in ten new coordination compounds [Co(MeGly)2(H2O)2] (1), [{Co(MeGly)2}2(μ-OH)2]·2H2O (1d), [Cu(MeGly)2(H2O)2] (2α), [Co(EtGly)2(H2O)2] (3), [Ni(EtGly)2(H2O)2] (4), [Cu(μ-EtGly)2]n (5p), [Co(PrGly)2(H2O)2] (6), [Ni(PrGly)2(H2O)2] (7), and two polymorphs of [Cu(PrGly)2(H2O)2] (8α and 8β). Compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, thermal analysis and X-band electron spin resonance (ESR) spectroscopy. These studies revealed a wide range of structural types including monomeric, dimeric and polymeric architectures, as well as different polymorphs. In all monomeric compounds, except 2α, and in the coordination polymer 5p hydrogen bonds interconnect the molecules into 2D layers with the alkyl chain pointing outward of the layer. In 2α and in the dimeric compound 1d hydrogen bonds link the molecules into 3D structures. 1d with cobalt(iii), and 4 and 7 with nickel(ii) are ESR silent. The ESR spectra of 1, 3 and 6 are characteristic for paramagnetic high-spin cobalt(ii). The ESR spectra of all copper(ii) coordination compounds show that the unpaired copper electron is located in the dx2−y2 orbital, being in agreement with the elongated octahedral geometry.

Probing Brønsted Acidity of Protonic Zeolites with Variable-Temperature Infrared Spectroscopy

Most industrial applications of zeolites as solid-acid catalysts rely on their high Brønsted acidity, which affects both catalytic activity and selectivity, and hence the convenience to find an accurate experimental technique for measuring the acid strength. The enthalpy change, ΔH0, involved in the hydrogen bonding interaction between a weak base (such as carbon monoxide) and the Brønsted acid [Si(OH)Al] hydroxyl groups should correlate directly with the zeolite acid strength. However, on account of simplicity, the bathochromic shift of the O–H stretching frequency, Δv(OH), is usually measured by IR spectroscopy at a (fixed) low temperature in-stead of ΔH0 and correlated with the acid strength for ranking the zeolite acidity. Herein, the use of variable-temperature IR spectroscopy to determine simultaneously ΔH0 and Δv(OH) is demonstrated, followed by a review of recent experimental results showing that the practice of ranking the acid strength by the corresponding O–H frequency shift probed by a weak base could be misleading; and that can be so much the case of zeolites showing a wide range of structure types.

Applicability of the direct displacement-based design method to steel moment resisting frames with setbacks

While quite extensive research has been undertaken during the last decades to extend the direct displacement-based design (DDBD) method to a wide range of structural types and materials, it is recognized that there are still some areas requiring further study and development. Steel structures and, more specifically, steel moment resisting frames with setbacks are one of these and, therefore, this work aims to investigate the seismic response of such structures designed according to the DDBD procedure currently prescribed for regular frames and to elaborate specific recommendations based on the results obtained. The main aspects to be considered are the adequacy of the displacement profile and higher mode reduction factor to be used, as well as the suitable strength distribution required. In a trial application of the current DDBD procedure, two two-dimensional 12-storey frames with setbacks are designed, and the solutions obtained are used to develop models of the structures, which are then subject to a series of non-linear time-history analyses at increasing levels of intensity, using spectrum-compatible scaled accelerograms. The results obtained are contrasted with those of Karavasilis et al. (J Constr Steel Res 64:644–654, 2008), which were developed for steel frames designed via code methods. It is recognized that the DDBD method can benefit from the expressions developed by these authors, and recommendations for the adjustment of the DDBD higher mode reduction factors are subsequently proposed. The efficacy of the latter is evaluated by the design and verification at a range of diverse intensities of a set of two-dimensional frames of 6, 9 and 12 storeys, and satisfactory outcomes are obtained. These results have been fundamental in revealing the need for future research regarding the influence of the design spectral shapes, ductility demand and P-Delta instability in the dynamic amplification of drifts due to higher mode effects.

Seismic displacement-based design of embedded retaining structures

The paper presents an application of the seismic design method named “Direct Displacement Based Design” (DDBD), first introduced in 1990s in the field of earthquake structural engineering, and gaining due attention in the recent years. The method can be applied to a wide range of structural types, including geotechnical structures. The fundamental philosophy behind DDBD is that structures should be designed to achieve a specified performance level under a certain seismic intensity. In the paper, DDBD is described with considerable discussion on its applicability to flexible earth retaining structures in coarse grained-soils. Particular attention is given to the evaluation of the equivalent damping ratio of the wall/soil system, since it sensibly affects the results of the procedure. A simplification of the design process is proposed in order to provide a seismic demand curve, in terms of active/passive thrust, which is dependent on the system ductility. A numerical example of application of the method is provided in the paper.

Terminology and nomenclature for macromolecular rotaxanes and pseudorotaxanes (IUPAC Recommendations 2012)

This document provides (i) definitions of terms related to macromolecular rotaxanes and macromolecular pseudorotaxanes and (ii) recommendations for naming these macromolecular assemblies. The nomenclature recommendations presented here have been developed by combining the nomenclature rules for the low-molar-mass (low-M) rotaxanes and those for macromolecules (both established in published IUPAC recommendations) in such a way that the developed nomenclature system provides unambiguous names for macromolecular rotaxanes (and pseudorotaxanes), including differentiation among various isomers of these supramolecular assemblies. Application of the nomenclature recommendations is illustrated using examples covering a wide range of structure types of macromolecular rotaxanes and pseudorotaxanes. An Alphabetical Index of Terms and a List of Abbreviations and Prefixes are included.

ChemInform Abstract: Iminophosphanes: Unconventional Compounds of Main Group Elements

The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as exotic in main group chemistry. While the rich chemistry of P-C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry.

Group 12 Dihalides: Structural Predilections from Gases to Solids

Connections between the structures of Group 12 dihalides in their vapor and crystal phases are sought and discussed. The molecular structures of all monomers and dimers (MX(2): M=Zn, Cd, Hg and X=F, Cl, Br, I) were calculated at the density functional B3PW91 and MP2 computational levels. All the monomers are linear, with the mercury dihalide molecules having shorter bonds than their cadmium analogues; the ZnX(2) and CdX(2) structures are similar. The shorter Hg-X distances are traced back to relativistic effects. For the dimers, many possible geometrical arrangements were considered. The zinc and cadmium dihalide dimers have the usual D(2h)-symmetry geometry, whereas the mercury dihalide dimers are loosely-bound units with C(2h) symmetry. The origins of this C(2h) structure are discussed from different points of view, including frontier orbital interactions. The crystals of Group 12 dihalides span a wide range of structure types, from three-dimensional extended solids to molecular crystals. There is an obvious connection between the structures and characteristics of monomers, their dimers, and the crystals they form. The similarities as well as startling differences from the Group 2 dihalides are analyzed.

Main Group Supramolecular Chemistry

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

In-Plane Aromaticity in Double Group Transfer Reactions

The main features of double group transfer reactions have been studied under the density-functional theory framework. It is found that a wide range of structure-types and processes including type II-dyotropic reactions and the Meerwein-Ponndorf-Verley reduction take place via highly synchronous in-plane aromatic transition structures. Actually, the orbital topology of these saddle points is equivalent to that which corresponds to a D2h-symmetric aromatic molecule such as pyrazine.

Characterization of Ionized Maltooligosaccharides by Sodium Cation in MALDI-TOFMS Depending on the Molecular Size

E-mail: sschoi@sejong.ack.rReceived May 1, 2006Key Words : Maltooligosaccharides, Ionization, MALDI-TOFMS, Molecular sizeCarbohydrates are the most abundant and structurallydiverse compounds found in nature. Unlike linear polymerssuch as proteins and nucleic acids, oligo- and polymericcarbohydrates can form branch ed structures because linkageof the constituentm onosaccharidesc an occur at a number ofpositions. With such a wide range of structural types, carbo-hydrate analysis by mass spectrometry can involve a largenumber of techniques with no single method being ideal forall compounds. Electron impact ionization, for example, isonly applicable to the smaller molecules. Matrix-assistedon (MALDI),i on/nizt ioati pser deasor l

Complexes of Ag(i), Hg(i) and Hg(ii) with multidentate pyrazolyl-pyridine ligands: from mononuclear complexes to coordination polymers via helicates, a mesocate, a cage and a catenate

The coordination chemistry of a series of di- and tri-nucleating ligands with Ag(I), Hg(I) and Hg(II) has been investigated. Most of the ligands contain two or three N,N'-bidentate chelating pyrazolyl-pyridine units pendant from a central aromatic spacer; one contains three binding sites (2 + 3 + 2-dentate) in a linear sequence. A series of thirteen complexes has been structurally characterised displaying a wide range of structural types. Bis-bidentate bridging ligands react with Ag(I) to give complexes in which Ag(I) is four-coordinate from two bidentate donors, but the complexes can take the form of one-dimensional coordination polymers, or dinuclear complexes (mesocate or helicate). A tris-bidentate triangular ligand forms a complicated two-dimensional coordination network with Ag(I) in which Ag...Ag contacts, as well as metal-ligand coordination bonds, play a significant role. Three dinuclear Hg(I) complexes were isolated which contain an {Hg2}2+ metal-metal bonded core bound to a single bis-bidentate ligand which can span both metal ions. Also characterised were a series of Hg(II) complexes comprising a simple mononuclear four-coordinate Hg(II) complex, a tetrahedral Hg(II)4 cage which incorporates a counter-ion in its central cavity, a trinuclear double helicate, and a trinuclear catenated structure in which two long ligands have spontaneously formed interlocked metallomacrocyclic rings thanks to cyclometallation of two of the Hg(II) centres.

Efficient methods for finding transition states in chemical reactions: Comparison of improved dimer method and partitioned rational function optimization method

A combination of interpolation methods and local saddle-point search algorithms is probably the most efficient way of finding transition states in chemical reactions. Interpolation methods such as the growing-string method and the nudged-elastic band are able to find an approximation to the minimum-energy pathway and thereby provide a good initial guess for a transition state and imaginary mode connecting both reactant and product states. Since interpolation methods employ usually just a small number of configurations and converge slowly close to the minimum-energy pathway, local methods such as partitioned rational function optimization methods using either exact or approximate Hessians or minimum-mode-following methods such as the dimer or the Lanczos method have to be used to converge to the transition state. A modification to the original dimer method proposed by [Henkelman and Jonnson J. Chem. Phys. 111, 7010 (1999)] is presented, reducing the number of gradient calculations per cycle from six to four gradients or three gradients and one energy, and significantly improves the overall performance of the algorithm on quantum-chemical potential-energy surfaces, where forces are subject to numerical noise. A comparison is made between the dimer methods and the well-established partitioned rational function optimization methods for finding transition states after the use of interpolation methods. Results for 24 different small- to medium-sized chemical reactions covering a wide range of structural types demonstrate that the improved dimer method is an efficient alternative saddle-point search algorithm on medium-sized to large systems and is often even able to find transition states when partitioned rational function optimization methods fail to converge.

Recent developments in the discovery of MCH-1R antagonists for the treatment of obesity – an update

Since the discovery and characterisation of melanin-concentrating hormone (MCH) and its role in the regulation of food intake and energy expenditure, there has been increasing interest in this cyclic peptide. The identification of the MCH-1 receptor (MCH-1R) in 1999 initiated the search for small molecules that could block the effects of MCH and provide novel agents for the treatment of obesity. A large number of companies is now actively pursuing MCH-1R antagonists and a wide range of structural types have been reported. Several compounds have been reported to be efficacious in rodent models of obesity and two compounds have recently entered into human clinical trials.

Stationary phases for thin-layer chromatography.

This paper presents a review of the literature concerning development of the stationary phases for thin-layer chromatography (TLC) in the last ten years. The silica gel remains the most important adsorbent for TLC separation. The kinetic properties of the silica-gel thin layer and the new TLC plates have been presented. Other materials used as stationary phase were alumina, zirconium oxide, Florisil, and ion-exchanger. Chemically new bonded stationary phase development is also discussed. The improvement of the separations of some organic mixtures by impregnation of silica gel, cellulose, or polyamide plates (with transition metal ions and silver salts) and their applications is presented. The impregnation of the thin layer with organic stationary phase and inclusion complexes is another method used for the enhancement of the separation efficiences. Another modality to improve the selectivity in TLC using ion-pairing as reagent of impregnation is described as well. The actual state of chiral separation by TLC is discussed with concrete references to recent advances in chiral stationary phases. The use of nonpolar chemically bonded stationary phases impregnated with transitional metal ions is presented as chiral stationary phases. The cellulose, modified cellulose, chitin, chitosan, and their derivatives are presented and their potential for the analysis of the racemates is discussed. The cyclodextrines and macrocyclic antibiotics were used with very good results for enantiomeric separation by TLC. A new separation approach with molecular imprinting polymers was reported as a chiral stationary phase in TLC. The examples provide a wide range of structural types that can be readily resolved enantiomerically by TLC.

Protein structure comparison using bipartite graph matching and its application to protein structure classification.

A measure of protein structure similarity is calculated from the matching of pairs of secondary structure elements between two proteins. The interaction of each pair was estimated from their axial line segments and combined with other geometric features to produce an optimal discrimination between intrafamily and interfamily relationships. The matching used a fast bipartite graph-matching algorithm that avoids the computational complexity of searching for the full subgraph isomorphism between the two sets of interactions. The main algorithm used was the "stable marriage" algorithm, which works on the ranked "preferences" of one interaction for another. The method takes 1/10 of a second for a typical comparison making it suitable as a fast pre-filter for slower, more exhaustive approaches. An application to protein structure classification is described.

Iron, copper, and cobalt complexes of hydrotris(3-phenylpyrazolyl)borate and dihydrobis(3-phenylpyrazolyl)borate. Synthesis and X-ray crystallographic characterization

The scorpionate ligands containing 3-phenylpyrazole have been identified as possessing intermediate steric bulk, due to the wide range of structural types that have been characterized in complexes of these ligands. In this paper, we report the syntheses and structures of a number of complexes containing hydrotris(3-phenylpyrazol-1-yl)borate and dihydrobis(3-phenylpyrazolyl)borate which further manifest the versatility of these ligands. The syntheses and solid-state structures of Tp PhFe(SCN)(THF) ( I), Tp PhFe(NO 3) 2 ( II), Tp PhCuCl(pz Ph) ( III), Tp PhCu(SCN)(pz Ph) ( IV), Bp Ph 2Co ( V), and Tp PhBp PhCo ( VI) are reported (Tp Ph=hydrotris(3-phenylpyrazolylborate); Bp Ph=dihydrobis(3-phenylpyrazolylborate); pz Ph=3-phenylpyrazole). Compound I displays a trigonal bipyramidal coordination sphere, while III and IV are square-pyramidal. Compound II contains one monodentate and one bidentate nitrate ligand in a distorted octahedral coordination sphere. Compound V is tetrahedral and VI is octahedral with an agostic CoH interaction in the sixth coordination site.

Monomer, dimer, tetramer, polymer: structural diversity in zinc and cadmium complexes of chelate-tethered nucleobases.

A series of ZnII and CdII complexes of adenine and guanine derivatives containing a diamine tether have been isolated from aqueous solutions and characterised by single crystal X-ray analysis. These studies reveal a wide range of structural types including monomeric, dimeric, tetrameric and polymeric architectures. The extended structures arise from the ability of the ligands to bridge metal ions using the chelating tether in conjunction with N7 of the nucleobase. Additional metal-nucleobase co-ordination is generally observed at the N3-site of the adenine derivatives. With CdII, ethylenediamine-N9-ethylguanine forms an inverted G-tetrad type structure.