Review: Graphene-supported coordination complexes and organometallics: properties and applications

Recent advances in the functionalization of graphene (G) and graphene oxide (GO) using classical coordination complexes, as well as σ- and π-organometallic compounds as precursors, are discussed. Graphene can form hybrids via covalent or non-covalent interactions with metal complexes of carboxylates, amines, polypyridine compounds, a host of N,O-containing ligands, porphyrins, phthalocyanines, carbonyls, cyclopentadienyls, pyrene-containing moieties, and other aromatic structures. The hybrid constructs are interesting for applications in catalysis, energy storage, and corrosion inhibition and present interesting possibilities of modulating the electronic structure of graphene.     

Communication: Barium ions and helium nanodroplets: Solvation and desolvation

The solvation of Ba(+) ions created by the photoionization of barium atoms located on the surface of helium nanodroplets has been investigated. The excitation spectra corresponding to the 6p (2)P(1∕2) ← 6s (2)S(1∕2) and 6p (2)P(3∕2) ← 6s (2)S(1∕2) transitions of Ba(+) are found to be identical to those recorded in bulk He II [H. J. Reyher, H. Bauer, C. Huber, R. Mayer, A. Schafer, and A. Winnacker, Phys. Lett. A 115, 238 (1986)], indicating that the ions formed at the surface of the helium droplets become fully solvated by the helium. Time-of-flight mass spectra suggest that following the excitation of the solvated Ba(+) ions, these are being ejected from the helium droplets either as bare Ba(+) ions or as small Ba(+)He(n) (n < 20) complexes.     

Review: Mixed-valent metallodendrimers: design and functions

Various types of mixed-valent metallodendrimers and star-shaped macromolecules containing ferrocenyl, biferrocenyl, or other redox-robust iron groups with rigid or flexible tethers of short and long lengths mostly studied in the authors’ laboratory including the class type in terms of Robin-Day classification and their functions including electrode modification, sensing, and nanoparticle templates are discussed in this mini review.     

Precipitation and determination of tantalum and niobium from homogeneous solution with 3:3' :4' :5:7-pentahydroxyflavanone

3:3,:5:7-Pentahydroxyflavanone in fairly concentrated acidic solution (6-9N) does not precipitate tantalum and niobium ; however, on heating or boiling, in the presence of air, this flavanone is transformed into 3:3':4':5:7-pentahydroxyflavone, which precipitates any tantalum and niobium present in the solution. Under the precipitation conditions, racemisation of the flavanone also takes place. The racemised flavanone which is less soluble than the original d-form may accompany the tantalum and niobium precipitates without affecting the quantitative determination of these elements.

The precipitation of the tantalum and niobium complexes can be controlled by regulating the acidity and the duration of boiling, as well as the concentration of the flavanone. Experimental data and procedures are given for the precipitation and determination from homogeneous solution of tantalum and niobium complexes. Zirconium and molybdenum do not interfere with the determination. Titanium must be absent or present only in minute quantity.

Since the generation of the precipitating reagent, flavone, from the flavanone is comparatively slow, the precipitation of tantalum and niobium is uniform throughout the solution. By this technique, adsorption and co-precipitation of potassium and sulphate ions in the solution are shown to be negligible. This is in contrast to the less effective dropwise addition of the flavone reported by earlier investigators, in which adsorption and co-precipitation were pronounced.

In the present study, tantalum and niobium oxides were fused with potassium bisulphate. There is no necessity using hydrofluoric acid to dissolve these oxides and therefore no polyethylene apparatus is required.     

Paradigms and paradoxes: organic thermochemistry without hydrogen: carbon oxides and nitrides

All organic compounds contain carbon. Most contain hydrogen. This brief study discusses the enthalpy of formation of a collection of organic compounds containing only oxygen or nitrogen accompanying the carbon.     

Diisophorone and related compounds—III: 2,7-Epoxydiisophoranes: production and reduction

Alkaline hydrogen peroxide oxidises diisophor-2(7)-en-1-ol-3-one and its lower homologue to the corresponding 2,7-epoxides. Reduction with LAH or catalytic hydrogenation converts 2,7-epoxydiisophoran-1-ol-3-one into the 1,3-diol, with preservation of the epoxide ring. Reduction by hydrazine (Wharton reaction) cleaves the epoxide ring and affords diisophor-2-ene-l,7-diol. the formulation of which is in accord with its hydrogenation to diisophor-2(7)-en-1-ol of established structure, either directly, or after dehydration to diisophorane-2,7-dien-1-ol.2,7-Epoxydiisophorones lacking the 3-keto-function are accessible in good yield from 1-hydroxy-, 1-acetoxy- and 1-chlorodiisophor-2(7)-ene by the action of peroxy-acids in dichloromethane. Of these, 2,7-epoxydiisophoran-1-ol is isomerized to diisophor-7-ene-1,2-diol by the combined action of LAH and AlCl₃. In the carbon-skeleton of the 2,7-epoxides described, the oxirane ring is likely to project above the plane of the A-B rings, on the side opposite ring C.     

High-temperature behaviour of lithium borates:: Part I: Characterization and thermal stability

Nine compounds, namely Li₃BO₃, -Li₄B₂O₅, β-Li₄B₂O₅, Li₆B₄O₉, -LiBO₂, Li₂B₄O₇, Li₃B₇O₁₂, LiB₃O₅ and Li₂B₈O₁₃ in the Li₂O–B₂O₃ system have been synthesized and characterized. The unit-cell parameters, density and solubility in water at room temperature of all the compounds are reported. The densities of the compounds were found to be in the 1.90–2.50 g cm⁻³ range, while their solubility in water at room temperature was in the 0.91–8.64×10⁻² g cm⁻³ range. Determination of the thermal stability of the compounds by quenching and differential thermal analysis (DTA) showed that only -LiBO₂ and Li₂B₄O₇ retained their original symmetry up to their congruent melting at 1121 and 1188 K, respectively, in air.     

ChemInform Abstract: Warwickites: Electronic Structure and Bonding.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Simulating GTP:Mg and GDP:Mg with a simple force field: A structural and thermodynamic analysis

Di‐ and tri‐phosphate nucleotides are essential cofactors for many proteins, usually in an Mg²⁺‐bound form. Proteins like GTPases often detect the difference between NDP and NTP and respond by changing conformations. To study such complexes, simple, fixed charge force fields have been used, which allow long simulations and precise free energy calculations. The preference for NTP or NDP binding depends on many factors, including ligand structure and Mg²⁺ coordination and the changes they undergo upon binding. Here, we use a simple force field to examine two Mg²⁺ coordination modes for the unbound GDP and GTP: direct, or “Inner Sphere” (IS) coordination by one or more phosphate oxygens and indirect, “Outer Sphere” (OS) coordination involving one or more bridging waters. We compare GTP: and GDP:Mg binding with OS and IS coordination; combining the results with experimental data then indicates that GTP prefers the latter. We also examine different kinds of IS coordination and their sensitivity to a key force field parameter: the optimal Mg:oxygen van der Waals distance R_min. Increasing R_min improves the Mg:oxygen distances, the GTP: and GDP:Mg binding affinities, and the fraction of GTP:Mg with β + γ phosphate coordination, but does not improve or change the GTP/GDP affinity difference, which remains much larger than experiment. It has no effect on the free energy of GDP binding to a GTPase. © 2012 Wiley Periodicals, Inc.     

Sarin and Soman: Structure and Properties

The most stable conformers of sarin (isopropyl methylphosphonoflouridate) and soman (pinacolyl methylphosphonofluoridate) are determined in high-level-correlated calculations with extended Gaussian basis sets. The two molecules are found to have three low-energy conformers each. For both molecules two of the lowest energy conformers have almost the same energies with a very small barrier separating the corresponding minima. The third conformer of sarin is found to lie about 1 kcal/mol above the lowest energy form. For soman the corresponding value is equal to about 4 kcal/mol. The significance of these data for the mechanism of the toxic action of sarin and soman is discussed. According to our investigations sarin and soman are highly similar electronically and differences in their features arise mostly from the size and spatial arrangement of the alkoxy substituent at phosphorus. Also the influence of solvents on the conformations and solvation energies of sarin and soman is investigated.     

Dodecamethoxy- and hexaoxotricyclobutabenzene: synthesis and characterization

We report herein the syntheses of dodecamethoxytricyclobutabenzene (TCBB) 1 and hexaoxo-TCBB 2, a class of molecules with structural and theoretical interest. The preparation is based on the 3-fold [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where the selectively protected 2-iodophloroglucinol derivative served as a synthetic equivalent of benztriyne I, allowing rapid and regioselective annulation of fully functionalized four-membered rings. Structural study on the former compound showed that the C-C bond lengths in the central benzene ring were essentially the same.     

Thiophenium-ylides: Synthesis and reactivity

The reaction of propanedioic acid, 2-diazo-1,3-bis(1,1-dimethylethyl) ester (di-tert-butyl diazomalonate) with a series of cyclopenta[b]thiophenes in the presence of catalytic rhodium acetate was studied. The resulting S—C ylides underwent a rearrangement to form a heterocycle with different topology; thialene, in very low yields. Experimental and spectral data for all compounds are provided.