Mitigation of signal suppression caused by the use of trifluoroacetic acid in liquid chromatography mobile phases during liquid chromatography/mass spectrometry analysis via post‐column addition of ammonium hydroxide

A method has been developed to reduce the mass spectrometric ion signal suppression associated with the use of TFA as an additive in LC mobile phases. Through post‐column infusion of diluted NH₄OH solution to LC eluents, the ammonium ion introduced causes the neutral analyte‐TFA ion pair to dissociate which consequently releases the protonated analyte as free ions into the gas phase (through regular electrospray ionization mechanisms). An ion signal improvement from 1.2 to 20 times for a variety of compounds had been achieved through the application of this method. The molar ratios of NH₄OH:TFA which result in a reduction of signal suppression were determined to be between 0.5:1 and 50:1. In addition, it was shown that this NH₄OH infusion method could reduce the level of doubly‐charged species and the product ions formed via in‐source collision. The use of diluted NH₄OH solution is favorable since it is compatible with mass spectrometry analysis, and it is applicable in both positive and negative‐ion generation mode. Copyright © 2012 John Wiley & Sons, Ltd.     

Copper‐catalyzed Clauson–Kass pyrroles synthesis in aqueous media

An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Cyclopalladated ferrocenylimine as an efficient catalyst for the syntheses of diarylmethane derivatives

The cyclopalladated ferrocenylimine adducts Ia , Ib , Ic were evaluated in the Suzuki cross‐coupling reaction of benzyl halides with arylboronic acids. The tricyclohexylphosphine adduct Ia exhibited highly catalytic activity for the coupling of aryl and heteroaryl boronic acids containing various functional groups with benzylic bromides and chlorides (up to 99% yield), furnishing diarylmethane derivatives with low catalyst loading (1 mol%). It is worth noting that catalyst Ia can be reused eight times without losing its catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Interactive Phenomena of a Rotating Arc and a Premixed CH4 Flame

The interactive phenomena between a rotating arc and a premixed methane/air flame have been investigated. The effects of the rotating arc on the flame were observed: both lean and rich flammability limit was extended with the rotating arc on. More interestingly, the opposite interactions, i.e., the effects of the flame on the rotating arc, were also observed: the arc length, angular speed, and electrical characteristics are affected by the flame. An analysis of the optical emission spectra showed that the rotating arc generates chemically active species such as excited N₂ molecules and O and H atoms. An analysis of the gas products indicated that the concentrations of the major gas products such as CO₂, CO, and H₂ were not significantly affected by the rotating arc, although the flammability limit are significantly extended. Unlike these major gas products, minor products like NO_x emissions increased by an order of magnitude in the presence of a rotating arc under certain air/fuel conditions.     

Control the self-assembly of fluorenone-based polycatenars by tuning chain length

Using Suzuki coupling reactions as key steps, a series of fluorenone-based polycatenars, consisting of a central 2,7-diphenyl-9-fluorenone core connected with the 3,4,5-trialkoxybenzoate unit via –COO- linkage at each side have been synthesized. Upon elongation of the terminal alkyl chain, these compounds self-assembled into mesophase sequence of Col_hex/p6mm - Cub_I/$\mathit{Pm}\overline{3}n$ in solid states as well as organogels with interesting morphologies varied from 3D helical fibers to spherical structures in solvents.     

Rotationally resolved state-to-state photoelectron study of zirconium monoxide cation (ZrO+)

Using two-colour visible (Vis)–ultraviolet (UV) photoionisation and pulsed field ionisation–photoelectron (PFI–PE) methods, we have obtained cleanly rotationally resolved photoelectron spectra for ZrO⁺(X ²Δ_3/2,5/2; v⁺ = 0, 1, and 2). The rotation assignment of these state-to-state Vis–UV–PFI–PE spectra has allowed the unambiguous determination of the ground state term symmetry for ZrO⁺(X) to be ²Δ_3/2, and the adiabatic ionisation energy of ⁹⁰Zr¹⁶O, IE(⁹⁰Zr¹⁶O) = 54,948.3(8) cm^?1 [6.81272(10) eV]. The symmetry of the ionic ZrO⁺(X ²Δ_3/2) ground state determined here disagrees with that reported in previous experiments. The rotational and vibrational constants determined in this experiment for the ionic ⁹⁰Zr¹⁶O⁺(X ²Δ_3/2) ground state are: B_e⁺ = 0.4343(8) cm^?1 and α_e⁺ = 0.0019(5) cm^?1, and ω_e⁺ = 991.2(8) cm^?1 and ω_e⁺x_e⁺ = 3.5(8) cm^?1; and those for the ionic ⁹⁰Zr¹⁶O⁺(X ²Δ_5/2) excited spin-orbit state are: B_e⁺ = 0.4357(6) cm^?1 and α_e⁺ = 0.0022(4) cm^?1, and ω_e⁺ = 991.9(8) cm^?1 and ω_e⁺x_e⁺ = 3.6(8) cm^?1, respectively. Based on the latter B_e⁺ value, the equilibrium bond distances are determined to be r_e⁺ = 1.691(2) Å for ⁹⁰Zr¹⁶O⁺(X ²Δ_3/2) and r_e⁺ = 1.688(1) Å for ⁹⁰Zr¹⁶O⁺(X ²Δ_5/2). The IE(ZrO) along with the spectroscopic constants obtained here are valuable for benchmarking the ab initio quantum chemical calculations for energetic and structural predictions of ZrO/ZrO⁺.     

Arylsulfimide Polymers. IV. Prototype Transamidations–A Comparison of the Reactions of Benzamides,Benzimides, Sulfonamides,Sulfonimides, and Saccharins

Transamidation reactions of nonpolymerizing systems involving benzamides, phthalimides, arylsulfonamides, benzenedisulfonamides and -disulfonim-ides, and saccharins are described. The study includes reactions of both N-substituted and unsubstituted amides and imides with anilines and aniline hydrochlorides. An evaluation of the results of these reactions, aimed at establishing the optimum conditions for transamidations in polymerizing systems, is also presented.