Adsorption of CO on a Pt electrode in acidic solution: Ir-acttve and -inactive CO'S adsorbed in the double-layer region

Carbon monoxide adsorbed on a smooth platinum electrode in the double-layer region was investigated in 1 M HClO₄ solution by using in situ polarization modulation IR reflection spectroscopy and an electrochemical oxidation. From the electrochemical oxidation, the adsorbed CO could be distinguished to be comprised of stable and unstable adsorbed CO's. The unstable adsorbed CO constituted about of the adsorbed CO, and corresponded to linearly adsorbed CO, but the band intensity of the linearly adsorbed CO was not proportional to the amount of unstable adsorbed CO. The stable adsorbed CO constituted about ; it was one-site adsorbed, and was an IR-inactive species. It is presumed that the IR-inactive species is adsorbed on two Pt atoms with the C-O axis parallel to the electrode surface and one of the Pt atoms bound to two CO molecules.     

竹红菌素自敏光氧化反应机制的研究

本文对竹红菌素自敏光氧化反应的机制作了较详细的研究,竹红菌素通过自敏光氧化反应生成不稳定的过氧化物,它可以放出¹O₂回到母体化合物,也可以转化为稳定的氧化产物,我们用活泼的单重态氧的接受体捕获到了体系中放出的¹O₂,用吸收光谱的变化证明过氧化物回到了母体化合物。文中还用猝灭实验证实此自敏光氧化反应除涉及¹O₂机制外,还有其它机制起着作用。     

UPLC‐QTOF‐MSE‐based diagnostic product ion filtering to unveil unstable C6‐C2 glucoside conjugates in Forsythia suspensa

Forsythia suspensa contains C₆‐C₂ glucoside conjugates (CCGCs) that are chemically unstable, thereby hindering their isolation and purification. In the present study, ultra‐performance liquid chromatography‐quadrupole time‐of‐flight mass spectrometry (UPLC‐QTOF) was utilized to screen and identify unstable CCGCs in the fruits and leaves of F. suspensa without any tedious isolation and purified process based on independent information acquisition (also called MS^E) and individual MS/MS experiments. Diagnostic product ion filtering (DPIF) was further applied to mine unknown analogs in MS^E high energy levels based on characteristic m/z of key substructures. A modified nomenclature for CCGCs is hereby proposed to facilitate discussions. Possible fragmentation pathways of major types of known CCGCs were proposed and used for deducing their structures. A total of 8 potentially new CCGCs were discovered and initially identified. The accuracy of their identification was further verified by structural elucidation of 3 unstable CCGCs isolated from the fruits of F. suspensa using 1D and 2D‐NMR spectroscopy. The established UPLC‐QTOF‐MS^E‐based DPIF technique facilitates the rapid discovery and direct identification of unstable CCGCs in fruits and leaves of F. suspensa .     

The relationship between end‐group concentrations and stability of spin‐coated thin polymer films investigated by ToF‐SIMS depth profiling

Stable and unstable spin‐coated polymer films were prepared using various solvents and substrates. The relationship between polymer end‐group concentrations and stability of spin‐coated polymer films was revealed by time‐of‐flight secondary ion mass spectrometry depth profiling. A high concentration of bromine end groups at the interface between the polymer and the substrate helped to prevent the dewetting of films. In contrast, the bromine end groups were found to be more evenly distributed in unstable thin films. The extent to which the bromine end groups segregate to the interface depended on the competitive interactions between the polymer, the solvent and the substrate. Stronger polymer–solvent and solvent–substrate interactions prevented the segregation of the bromine end groups to the interface, resulting in unstable polymer films. Copyright © 2013 John Wiley & Sons, Ltd.     

A Method of Correcting for Flow-Rate Fluctuations in Size Exclusion Chromatography Calculations: Applications to Methylene Chloride/Hexafluoroisopropanol Solvent System

Abstract

The mixture of methylene chloride/hexafluoroisopropanol (70/30, v/v) is an excellent polyester solvent, but its low boiling point causes unstable flow when it is used for size exclusion chromatography (SEC). In high-performance SEC experiments, retention time is normally used to measure elution volume; however, unstable flow makes it difficult to calibrate an SEC column set or calculate molecular weight parameters from a chromatogram. We have devised a simple and inexpensive method to compensate for the effect of unstable flow in SEC calculations. A calibration marker injected along with each sample is used to indicate flow-rate variations. The ratio of the sample retention time to the marker retention time is invariant to flow-rate changes and is used in place of retention time as a measure of elution volume in the universal calibration technique. Calibrating a column set and analyzing chromatograms by this method result in a large improvement in the accuracy and precision of calculated molecular weight parameters.     

Complexes of a bio-molecule and a C60 cage

C₆₀ is the most important fullerene cage and glycine is the simplest representative of a backbone unit of a protein. In this paper, the structures and the energies of glycine–C₆₀ complexes were calculated at the B3LYP/6-31G(d) level DFT. It was found that the binding of glycine to C₆₀ generated a slightly unstable complex via its amino nitrogen, a moderately unstable complex via its hydroxyl oxygen, and a very unstable complex via its carbonyl oxygen. This indicates that fullerene cages might be unable to form stable bindings to proteins via their amino nitrogen, hydroxyl oxygen and carbonyl oxygen active sites.     

Atropo-enantioselective reduction of configurationally unstable biaryl lactones with BINAL-H

The atropo-enantioselective reduction of configurationally unstable biaryl lactones with BINAL-H yields axially chiral biaryl alcohols in high enantiomeric ratios of up to 94:6 (er >99.5:0.5 after one crystallization step). Within this two-step reduction process the stereochemically deciding step is the first attack on the lactones and not the reduction of the likewise configurationally unstable biaryl lactol/hydroxy aldehyde intermediates, as evident from the non-stereoselective reduction of the latter under the same conditions.     

Electrochemical interconversion of 1-(p-tolyl)-6-methyl-2,4-diphenylpyrimidinium perchlorate and 1-(p-tolyl)-6-methylene-2,4-diphenylpyrimidine

It is shown that reduction of the 6-methyl-1-(p-tolyl)-2,4-diphenylpyrimidinium cation proceeds in two one-electron stages. In the first stage, an unstable radical is formed, and in the second stage, an unstable anion. As a result of dehydrogenation of the radical, the anhydro base 6-methylene-1-p-tolyl-2,4-diphenyl-6H-pyrimidine is formed. Oxidation of this compound in a single one-electron stage forms an unstable cation radical, the hydrogenation of which leads to the original pyrimidinium cation. Data obtained by cyclic voltametry and electrosynthesis with subsequent identification of the products have shown that, the same as in the reaction with the hydroxide anion, the methyl-substituted pyrimidinium cation acts as a CH-acid.Rostov State University, Rostov-on-Don 344101, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 71–75, January, 1999.     

Periodic orbits in atomic hydrogen exposed to circularly polarised laser light

Exact circular periodic orbits for a hydrogen atom in a strong circularly polarised laser field are derived. A stability analysis shows one orbit to be stable or unstable depending on the laser parameters, whereas the other orbit is always unstable. These orbits are expected to manifest themselves as resonances in laser assistede ^? ?H ⁺ scattering. The binding mechanism for these resonances is provided by the trapping of the quantum mechanical wave function onto the neighbourhood of a classical periodic orbit. This mechanism is analogous to that for a Wannier ridge resonance in a doubly excited two-electron atom.     

Simple model for the instabilities in the aggregation of silica sols in a sol-gel process

A simple kinetic model based on the Prigogine's Brusselator model was used to explain some unstable non-linear oscillations found in the particle size profile of sols in a sol-gel process. These oscillations were explained, in some previous papers, by using the stability criterion from the non-linear irreversible thermodynamics; it is the excess entropy production that characterizes the stability of a system and the occurrence of new structures. In the solgel reaction considered here, one of the steps is auto-catalytic; this fact produces local gradients in the concentration of one of the chemical components, forming a wide variety of new unstable structures. With this model we obtained a relationship for the reaction constants that determines the unstable character of the reaction, and the dependence of the frequency of oscillations on the reactant concentrations. The dependence of the oscillation frequency on water and ethanol concentrations obtained from the experimental data, were well explained by using this model.     

Synthesis and kinetics of Ni(CO)3N2 in liquid krypton; indication of NiN2 bond energy

We have previously shown (ref. 1) that unstable metal carbonyl species can be photochemically generated and examined in low-temperature liquefied rare gases as solvents. In this paper we shall describe experiments in which the transient Ni(CO)₃N₂ is generated by photolysis of Ni(CO)₄ in liquid krypton doped with nitrogen, at 114K. This species is thermally unstable and may be allowed to decay slowly back to Ni(CO)₄. By following the kinetics of this decay as a function of temperature it is possible to establish kinetic and energetic parameters for the reaction.     

A SOLUTION TO THE UPWARD MIGRATION OF AN INTRUSION

The evolution of the upward migration of the magma is a nonlinear and unstable problem in mathematics. It is difficult to solve it. And using the numerical method, the solution is relatively tedious and time-consuming. This paper introduces a method of the instantaneous point source to solve the linear and unstable heat conduction equation during the infinite period of time instead of the solution of the nonlinear and unstable heat conduction equation. The results obtained by this method coincide with those by the numerical method, meaning that this method offers a simple way to solve the nonlinear and unstable heat conduction equation.     

用AFM研究阳极氧化铝的不稳定生长

用原子力显微镜(AFM)研究了多孔阳极氧化铝(AAO)模板的不稳定生长. 结果表明:AAO模板的不稳定生长导致了纳米孔道结构有序度的降低.在H₃PO₄溶液中生长的AAO模板孔道结构稳定性较差;而在H₂C₂O₄溶液中生长的AAO模板稳定性依赖于氧化电压和电流密度,在低电压和电流密度下稳定性较好,高电压和电流密度下稳定性较差. 充分利用这种不稳定生长特性,通过控制AAO模板的阳极氧化条件,可得到具有分枝孔道结构的特殊模板,这为利用模板法制备各种Y形或T形纳米线、管提供了新的发展空间.     

Mössbauer study on the photolysis of pentacarbonyliron isolated in low temperature nitrogen matrix

The UV photolysis of pentacarbonyliron isolated in low temperature nitrogen matrix was studied by the Mössbauer Technique. Besides stable compounds /Fe₂/CO/₉ and Fe₃/CO/₁₂/ unstable species such as Fe/Co/₄ and Fe₂/CO/₈ were produced by UV irradiation. Furthermore, the unstable species were found to react with nitrogen matrix, leading to the formation of Fe/CO/₄N₂. Mössbauer parameters of the products were obtained.     

Stability of radio-metallofullerenes against beta-decay

The effect of β⁻-decay on the stability of metallofullerenes was investigated for three decay chains of¹⁵⁵Sm-¹⁵⁵Eu,¹⁶¹Gd-¹⁶¹Tb and¹⁷⁷Yb-¹⁷⁷Lu. For the former two cases, the metallofullerenes were found stable even after the β⁻-decay while in the case of¹⁷⁷Yb, the metallofullerene became unstable after β⁻-decay. The present results point to the fact that metallofullerenes are stable against ordinary β⁻-decay unstable after β⁻-decay. The present results point to the fact that metallofullerenes are stable against ordinary β⁻-decay recoil energies, but they become unstable if the oxidation state of the metal atom is changed by nuclear transformation.     

Synthesis of SiO2 thin films by sol-gel method using photoirradiation and molecular structure analysis

The SiO₂ thin films were prepared by a process which combines a sol-gel method and photoirradiation. The HF etch rate and microhardness of a film prepared by this process were better than those of a film furnace-fired at same temperature. The Raman and ²⁹Si solid state NMR spectra of film prepared by this process were similar to those of a film furnace-fired at higher temperature. There are many unstable folded non-linear SiO₂ species in the film prepared at low temperature. On treatment at higher temperature, unstable folded non-linear Si-O-Si rearranges to the stable linear Si-O-Si bond. Photoirradiation enhances this structure change. The process provided denser and harder SiO₂ thin films, even at low temperature, than the conventional furnace-firing method did.     

Hydrocarbon Formation in the Catalytic Conversion of Methanol Over Zeolite ZSM-5

The reaction mechanism of methanol conversion to hydrocarbons on HZSM-5 zeolite was studied. From the selectivity plots of products in an integral fixed-bed flow reactor, paraffins were classified as primary and secondary stable products, light olefins as primary unstable products, aromatics as primary and secondary unstable or stable products. The results of the ¹⁴C-labelled methanol reaction indicated that the C₁–C₅ surface intermediates generated by dimethyl ether / methanol equilibrium gave paraffins and olefins at 300°C. The concentration of intermediates and adsorbed methanol on ZSM-5 decreased with increasing temperature. The distribution of radioactivity showed that propylene played an important role in the autocatalysis of the reaction.     

A Versatile Route to Unstable Diazo Compounds via Oxadiazolines and their Use in Aryl–Alkyl Cross‐Coupling Reactions

Coupling of readily available boronic acids and diazo compounds has emerged recently as a powerful metal‐free carbon–carbon bond forming method. However, the difficulty in forming the unstable diazo compound partner in a mild fashion has hitherto limited their general use and the scope of the transformation. Here, we report the application of oxadiazolines as precursors for the generation of an unstable family of diazo compounds using flow UV photolysis and their first use in divergent protodeboronative and oxidative C(sp²)−C(sp³) cross‐coupling processes, with excellent functional‐group tolerance.     

Interaction of solvated electrons with an Mo(V) oxalate complex in a water—ethylene glycol system

The reactivity of metal ions towards e_s^? was studied to identify the stable and unstable reaction products by spectroscopic analysis of the o     

On the reaction of alkylargentates with some 2- alkynenitriles.

Alkylargentates add $\text{trans}$ to the triple bond of 2-alkynenitriles to furnish α -cyanovinylargentates in a high yield. The adducts are configurational unstable at higher temperature.