Synthesis of polyfunctionalized acrylates via one-pot reactions of arylamines, methyl propiolate, aromatic aldehydes, and active methylene compounds

An efficient synthetic method for the densely substituted 3-arylaminoacrylates was successfully developed via the one-pot reaction of arylamines, methyl propiolate, aromatic aldehydes, and active methylene compounds such as pivaloylacetonitrile, 1,3-cyclopentanedione, and 4-hydroxycoumarin. The key step of the reaction was believed to involve the formation of a β-enamino ester and a sequential Michael addition to the in situ formed arylidene dicarbonyl compound.     

New Cross-Linking Quinoline and Quinolone Derivatives for Sensitive Fluorescent Labeling

A variety of contemporary analytical platforms, utilized in technical and biological applications, take advantage of labeling the objects of interest with fluorescent tracers-compounds that can be easily and sensitively detected. Here we describe the synthesis of new fluorescent quinoline and quinolone compounds, whose light emission can be conveniently tuned by simple structural modifications. Some of these compounds can be used as sensitizers for lanthanide emission in design of highly sensitive luminescent probes. In addition, we also describe simple efficient derivatization reactions that allow introduction of amine- or click-reactive cross-linking groups into the fluorophores. The reactivity of synthesized compounds was confirmed in reactions with low molecular weight nucleophiles, or alkynes, as well as with click-reactive DNA-oligonucleotide containing synthetically introduced alkyne groups. These reactive derivatives can be used for covalent attachment of the fluorophores to various biomolecules of interest including nucleic acids, proteins, living cells and small cellular metabolites. Obtained compounds are characterized using NMR, steady-state fluorescence spectroscopy as well as UV absorption spectroscopy.     

Enthalpies of formation and isomerization of aromatic hydrocarbons and ethers by G3(MP2)//B3LYP calculations

A computational method for estimation of the gas‐phase enthalpies of formation of aromatic hydrocarbons and ethers has been developed. The method is based on high‐level G3(MP2)//B3LYP calculations, atomization reactions, and structure‐dependent correction terms. By this method, enthalpies of formation Δ_fH_m°(g, 298.15 K) of 86 aromatic compounds were evaluated. The calculated enthalpies of formation raise questions of the reliability of several experimental enthalpies of formation reported in the literature. As an application of the computational enthalpies of formation, reaction enthalpies for several types of isomerization reactions of aromatic compounds were calculated. In cases in which experimental reaction enthalpies were available for comparison, the agreement between the computational and experimental data proved to be excellent. Copyright © 2008 John Wiley & Sons, Ltd.     

Atomic force microscopy investigation of chemically stabilized pericardium tissue

Native and chemically stabilized porcine pericardium tissue was imaged by the contact mode atomic force microscopy (AFM), in air. Chemically stabilized pericardium is used as a tissue-derived biomaterial in various fields of the reconstructive and replacement surgery. Collagen type I is the main component of the fibrous layer of the pericardium tissue. In this study, the surface topography of collagen fibrils in their native state in tissue and after chemical stabilization with different cross-linking reagents: glutaraldehyde (GA), dimethyl suberimidate (DMS) and tannic acid (TA) was investigated. It has been found that chemical stabilization causes considerable changes in the surface topography of collagen fibrils as well as in the spatial organization of the fibrils within the tissue. The observed changes in the D-spacing pattern of the collagen fibril correspond to the formation of intrafibrilar cross-links, whereas formation of interfibrilar cross-links is mainly responsible for the observed tangled spatial arrangement of fibrils and crimp structure of the tissue surface. The crimp structure was distinctly seen for the GA cross-linked tissue. Surface heterogeneity of the cross-linking process was observed for the DMS-stabilized tissue. SDS-PAGE electrophoresis was performed in order to evaluate the stabilization effect of the tissues treated with the cross-linking reagents. It has been found that stabilization with DMS, GA or TA enhances significantly the tissue resistance to SDS/NaCl extraction. The relation between the tissue stability and changes in the topography of the tissue surface was interpreted in terms of different nature of cross-links formed by DMS, GA and TA with collagen.     

Synthesis under Pressure of Potential Precursors of CN x Materials Based on Melamine and Phenolic Resins

The cross-linking under pressure of a mixture of novolak and melamine resins with a weight ratio of 1 has been investigated by means of several techniques, including DSC, TGA, XRD, and IR. Four samples were prepared under varying pressure and temperature. The application of pressure to the reaction vessel favored the formation of a more structured cross-linked resin. The sample cross-linked at both the highest temperature and pressure levels exhibited higher structuring effects than the others. Moreover, this sample exhibited much higher thermal stability than the others. This achievement may allow us to open the pathway toward new precursors of structured CN _x materials.     

Thermal transitions and degradative processes in Fe(III)-tetracarboxyphthalocyanine-grafted poly(N-vinylcarbazole)

The introduction of 2,9,16,23-tetracarboxy-Fe(III)phthalocyanine [Fe(III)tcPc] units onto fractions of poly(N-vinylcarbazole) (PVK) by Friedel-Crafts reaction leads to amorphous PVK-based grafted compounds that show major interchain distances by the wide-angle x-ray scattering (WAXS) technique. Glass transition temperatures of the products are lower than the main glass transition temperature of PVK and are attributed to local movements of the voluminous added groups. Dynamic thermogravimetric experiments show decarboxylation processes within the 250°C-500°C range and little weight loss. The large remaining residue, up to 70% of the sample at 800°C, is suggested to be the consequence of successive cross-linking reactions. The Fourier transform infrared (FTIR) spectrum of the residue is similar to that of the grafted sample before degradation.     

Lattice energy calculation for quantitatively-modeled Perovskite distortion

In case of reactions, it is a necessary condition that the free energy of formation, Δ_fG, of the product is lower than the total free energies of formation of the reactants. The free energy of all reactions and/or all compounds have not been determined in the literature. In this paper, we report the formation, stability, and reactions for all compounds based on their free energies. However, it also seems possible to discuss them based on their lattice energies, because it can be calculated for many compounds if their composition, structure and their lattice parameters are known. Also, we can discuss the formation, stability, etc., for compounds excluding small effects due to temperature and entropy. As a result of the calculations, the lattice energy correlates with the perovskite distortion.     

Chemical and catalytic effects of ion implantation

Energetic particles are used for inducing chemical reactions as well as for modifying the properties of materials with regard to their bulk and surface chemical behavior. The effects are partly caused by radiation damage or phase intermixing, partly by the chemical properties of the individual bombarding particles. In this contribution a survey of relevant applications of these techniques is presented:

1) Chemical reactions of implanted and recoil atoms and their use for syntheses, doping and labeling of compounds.

2) The formation of thin films by decomposing chemical compounds with ion beams.

3) Catalytic effects on substrates treated by sputtering or ion implantation. Recent results with nonmetallic substrates are reviewed. Mainly hydrogenation reactions at a solid/gas interface or redox reactions at an electrified solid/liquid interface are mentioned.

The present status and future prospects of these kinds of investigations will be discussed.     

Selectivity in metal ions mediated C–N bond formation reactions of 8‐aminoquinoline derivatives

Cyclisation reactions via C–N bond formation of 2‐bromo‐N‐(quinolin‐8‐yl)propanamide (I) and 2‐bromo‐N‐(quinolin‐8‐yl)acetamide (II) are facilitated by metal salts such as copper (+2), nickel (+2) perchlorate or nitrate and palladium (+2) acetate. Nickel (+2) perchlorate mediated reaction of I and II resulted in C–N bond formation to give corresponding perchlorate salts of three fused six‐membered heterocyclic rings. The copper (+2) mediated reactions are found to be solvent dependent for I, but independent for II. Copper mediated reaction of II gave cyclised product analogous to the one obtained from reaction of II with nickel (+2) perchlorate in methanol or ethanol. But the reaction of I with copper (+2) perchlorate in methanol gave C–N bonded methoxylated cyclised product. This reaction took place in two steps, cyclisation followed by methoxylation. The source of methoxy group is confirmed to be from methanol by deuterium labelling experiments. Whereas similar copper mediated reaction of I in ethanol led to nucleophilic substitution of bromide ion by ethoxide. The structures of the salts of fused heterocyclic compounds were determined and their fluorescence emissions were studied. The large difference in fluorescence emission of compound V formed from copper mediated reaction in ethanol from the compound VI formed from nickel mediated reaction in methanol or ethanol, this feature can be used to distinguish nickel (+2) and copper (+2) ions. The reaction of II with palladium (+2) acetate resulted in the formation of C–N bond to yield the corresponding heterocycle as bromide salt; without anion exchange. Copyright © 2011 John Wiley & Sons, Ltd.     

Muonium formation in xenon and argon up to 60 atmospheres

Results of muon polarization studies in xenon and argon up to 60 atm are reported. In argon for pressures up to 10 atm, the muon polarization is best explained by an epithermalcharge exchange model. Above this pressure, the decrease inP _D and increase inP _L are ascribed to charge neutralization and spin exchange reactions, respectively, in the radiolysis track. Measurements with Xe/He mixtures with a xenon pressure of 1 atm indicate that the lost polarization in the pure xenon at this pressure is due to inefficient moderation of the muon. As the pressure in pure xenon is increased above 10 atm, we find thatP _L remains roughly constant andP _D begins to increase. The lost fraction may be due to the formation of a XeMu Van der Waals type complex, whileP _D is ascribed to XeMu⁺ formation. This suggests that spur processes appear to be less important in xenon than in argon.     

Influence of the ignition delay time on the explosion parameters of hydrocarbon–air–oxygen mixtures at elevated pressure and temperature

Combustion phenomena change as the conditions in which they are occurring change. Proper understanding and reliable prediction of these phenomena, including important explosion indexes (e.g., flammability limits, explosion pressures), are required for achieving safe and optimal performance of industrial processes and creating new applications. To this end, we investigated the influence of the residence time on aforementioned parameters of n-butane–oxygen mixture and a typical mixture for ethylene oxide production: methane–ethylene–oxygen, focusing on how elevated conditions affect the upper explosion limit and the explosion pressure. Elevated initial conditions (T = 230 °C, P = 4–16 bar) cause pre-ignition reactions to occur in the regime of the low temperature oxidation mechanism (LTOM). These reactions change the mixture composition prior to ignition. For both mixtures investigated, these changes in the initial mixture composition, due to pre-ignition reactions, result in a different explosion pressure. This is significant, because pressure rise is used as the ignition criterion. Consequently, a different classification of the investigated mixtures, as flammable or non-flammable, is possible, depending on the residence time prior to ignition. The experimental results are compared with theoretical calculations performed using detailed reaction kinetic models.     

On some hydrogen bond correlations at high pressures

Structural data from in situ high pressure neutron diffractions studies are analysed to show that the measured lengths of O?H and H---O pairs in hydrogen bonds follow the correlation between them established from 0.1 MPa data on different chemical compounds. In particular, the accepted view in literature that the high pressure data on ice VIII differ from it is not supported. For compounds in which the O?H stretching frequencies red shift under pressure, it is shown that wherever structural data is available, they follow the stretching frequency versus H---O (or O---O) distance correlation. For compounds displaying blue shifts with pressure, an analogy appears to exist with ‘improper’ hydrogen bonds. Another pressure effect expected is the symmetrization of a hydrogen bond with evolution of the double-welled, hydrogen bond potential into a single-well potential. Using the results from some recent ab initio electronic structure studies, we show that the bulk modulus shows a discontinuity at this point and this can be taken as signature for hydrogen bond symmetrization. This is supported by analysing a few available experimental data.     

Crystalline Aluminium Borates with the Mullite Structure: A <Superscript>11</Superscript>B and <Superscript>27</Superscript>Al Solid-State NMR Study

²⁷Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were acquired at 8.45, 14.1 and 16.45 T for a series of aluminium borates with the mullite structure (Al_6−x B _x O₉, where x has nominal values of 1 to 4) augmented with ²⁷Al multiple-quantum MAS NMR spectra at 8.45 T. Even though the ²⁷Al NMR spectra are complex, simulation of the combined set of data produced a relatively well-defined set of parameters (e.g., quadrupolar interaction, isotropic chemical shift, etc.) for each site. The ¹¹B MAS NMR spectra of the same compounds were also acquired at 14.1 T. Linear changes in the X-ray a-, b- and c-cell parameters with composition suggest that these compounds constitute a continuous series. Based on a Rietveld structural refinement of the compound synthesized as Al₄B₂O₉, the resulting site occupancies and relative site distortions allow the identification of particular sites with specific NM resonances. Changes in the ²⁷Al and ¹¹B MAS NMR spectra of the related compounds with x = 1–4 show at the lowest Al contents a greater degree of asymmetry in the Al sites of the octahedral chains. A fairly distorted cross-linking tetrahedral site, which persists throughout the composition range, is accompanied in the lower Al compositions by two 5-fold coordinated Al–O units which are replaced by two more-regular tetrahedral Al–O sites as the Al content increases. In the compounds of lowest Al composition (i.e., highest B content) both the tetrahedral and trigonal cross-linking sites are distinguishable, but as the Al content increases, the BO₄ units progressively disappear. Authors' address: Kenneth J. D. MacKenzie, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand     

Thermal stability and detonation characters of nitro-substituted derivatives of pyrazole

High-energy-density compounds are designed successively by substituting the hydrogen atoms of 1H-pyrazole by the nitro group. The thermal stabilities are explored by the calculations of the heat of formation, bond orders, and bond dissociation energy at the B3PW91/6-311?+?G(d,p) level. To evaluate the potential application as high-energy-density compounds, the molecular density (ρ), explosive heat (Q), the detonation velocity and detonation pressure are evaluated by using the empirical Kamlet-Jacobs equation. Based on our calculations, five molecules (3,4,5-trinitro-1H-pyrazole, 1,4,5-trinitro-1H-pyrazole, 1,3,5-trinitro-1H-pyrazole, 1,3,4-trinitro-1H-pyrazole, 1,3,4,5-tetranitro-1H-pyrazole) reached the balance between the stability and detonation characters and can be regarded as the potential high-energy-density compounds.     

Selected studies of magnetism at high pressure

Summary Most previous studies of magnetism in various compounds under extreme conditions have been conducted over a wide pressure range at room temperature or over a wide range of cryogenic temperatures at pressures below 20 GPa (200 kbar). We present some of the most recent studies of magnetism over an extended range of temperatures and pressures far beyond 20 GPa,i.e. in regions of pressure-temperature (P-T) space where magnetism has been largely unexplored. Recent techniques have permitted investigations of magnetism in selected 3d transition metal compounds in regions ofP-T where physical properties may be drastically modified; related effects have often been seen in selected doping studies at ambient pressures. We present⁵⁷Fe and¹²⁹I M?ssbauer isotope studies covering the range 300–4 K to sub-megabar pressures in compounds such as Sr₂FeO₄, LaFeO₃ and FeI₂, representative of a broad class of 3d transition metal compounds. At ambient pressure the electronic structure of the transition metal atom in these antiferromagnetic insulators extends from 3d ⁴ to 3d ⁶ and has a distinct influence on the pressure evolution of their magnetic properties. M?ssbauer studies of these compounds are considered in conjunction with available structural and electrical transport data at pressure. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Li3N在生成BN反应中的作用

研究了常压高温下Li3N在B4C与含氮化合物生成BN反应中的作用。实验结果表明,在950℃高温下,B4C与Si3N4反应不生成hBN,B4C与NH4Cl反应只生成少量hBN。在该两种原料中加入Li3N后,反应产物中hBN生成量都明显增多。但Li3N本身没有与B4C生成hBN的反应。由此推断,Li3N在上述B4C与含氮化合物生成hBN的反应中表现出了催化作用。此外,在以hBN为原料,以Li3N为催化剂合成出cBN的温度压力区域内,对B4C-Si3N4-Li3N体系所做的高温高压实验没有合成出hBN或cBN。还讨论了在低压条件下原位合成cBN的探索实验中,应如何选择硼源和氮源的问题。     

Towards an easy carbon dioxide reduction in aqueous solution

Abstract

The homogeneous hydrogenation of carbon dioxide into formate anion has been investigated in aqueous solution, using water soluble ruthenium(1I)-phosphine (meta-monosulphonated triphenylphosphine, TPPMS; and 1,3,5-triaza-7-phosphaadamantane, PTA) complexes as catalysts. These reactions take place in amine free medium under mild conditions, bicarbonate anion is more active than carbon dioxide in the reduction. The initial turnover frequenc of the reduction increases with increasing H₂ pressure, as it was observed in situ by C and 'H NMR spectroscopy. High pressure FT-IR were used to find evidence for the formation of the catalytically active ruthenium hydride species.     

Chemical kinetics at high pressure

Abstract

Numerous studies have demonstrated the importance to include pressure as a kinetic parameter in the elucidation of inorganic reaction mechanisms. These studies have specially led to a better understanding and a systematic classification of solvent exchange and ligand substitution reactions of octahedral complexes of transition metal elements. The mechanistic picture for substution reactions on square planar complexes is well established and involves a concurrent bimolecular attack by solvent and the nucleophile on the substrate with a considerable discrimination among different entering groups. The search for factor promoting the conversion of the normal associative mode of activation into a dissociative process has then attracted much attention. Two attempts to induce dissociation, as studied by high-pressure NMR, are presented: one is to prevent the formation by means of sterically hindered ligands, the other one is to promote bond weakening at the leaving group.     

Recent studies on pressure-induced chemical changes in food constituents

Abstract

The application of high hydrostatic pressure is one of the most promising novel minimal processing methods for food preservation. Under optimal process conditions the natural fresh properties of foods are retained. Pressure is an important thermodynamic factor as is temperature. Both pressure and temperature may influence the position of a chemical reaction equilibrium and the reaction rate. Examples of pressure effects on food quality related reactions are presented The effect of pressure on reactions resulting in flavour or colour defects or the formation of undesirable substances and the effect of pressure on the stability of valuable constituents like vitamin A or sulforaphane.     

The Pressure Dependence of Sterically Hindered Organic Reactions of Ketones

The pressure effect is examined in addition reactions of ketones (Knoevenagel reactions, formation of oximes and trichlorocarbinols). The sensitivity to pressure is enhanced with increasing size of the substituting groups of the carbonyl bond making the pressure parameter as a determining factor in sterically hindered reactions.