Dimerization of ionized 4‐(methyl mercapto)‐phenol during ESI,APCI and APPI mass spectrometry

A novel ion/molecule reaction was observed to occur under electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo ionization (APPI) conditions, leading to dimerization of ionized 4‐(methyl mercapto)‐phenol followed by fast H^· loss. The reaction is particularly favored during ESI, which suggests that this ion/molecule reaction can occur both in the solution inside the ESI‐charged droplets and in the gas‐phase environment of most other atmospheric pressure ionization techniques. The dimerization reaction is inherent to the electrolytic process during ESI, whereas it is more by ion/molecule chemistry in nature during APCI and APPI. From the tandem mass spectrometry (MS/MS) data, accurate mass measurements, hydrogen/deuterium (H/D) exchange experiments and density functional theory (DFT) calculations, two methyl sulfonium ions appear to be the most likely products of this electrophilic aromatic substitution reaction. The possible occurrence of this unexpected reaction complicates mass spectral data interpretation and can be misleading in terms of structural assignment as reported herein for 4‐(methyl mercapto)‐phenol. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of 5'-Functionalized Indolinospiropyrans with Vinylene Unit as Linker

A protocol for the synthesis of a new family of spiropyran derivatives is described. A 5‐formylated indoline intermediate ( 5 ) was achieved for the first time, which was the key intermediate for constructing the spiropyran derivatives with vinylene linker. Five 5′‐functionalized indolinospiropyrans ( 11 – 15 ) were obtained by utilizing vinylene unit as a linkage between the photochromic spiropyran fragment and the ferrocene or triphenylamine donor.     

Kinetic method for the simultaneous chiral analysis of different amino acids in mixtures

The kinetic method has been extended to enantiomeric excess (ee) determinations on amino acids present in mixtures. Singly charged trimeric clusters [Cu(II)(ref*)(2)(A(m)) - H](+) are readily generated by electrospraying solutions containing Cu(II), a chiral reference ligand (ref*), and the amino acids (analytes A(m), m = 1-3). A trimeric cluster ion for each amino acid is individually mass-selected and then collisionally activated to cause dissociation by competitive loss of either the reference ligand or the analyte. For each analyte in the mixture, as shown from separate experiments, the logarithm of the ratio of the fragment abundances for the complex containing one enantiomer of this analyte expressed relative to that for the fragments of the corresponding complex containing the other enantiomer is linearly related to the enantiomeric composition of the amino acid. Formation and dissociation of each trimeric complex ion are shown to occur independently of the presence of other analytes. Chiral selectivity appears to be an intrinsic property and the chiral selectivity R(chiral(m)) measured from the mixture of analytes is equal to R(chiral) measured for the pure analyte. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, characteristic of the kinetic method, allow the determination of chiral impurities of less than 2% ee in individual compounds present in mixtures by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.     

自由基官能化聚合合成主链桂嘧啶碱基的聚合物

以合成的三种嘧啶衍生物为单体,通过加入能在自由基作用下开环异构的乙烯酮缩醛类进行了酯基封端、酯基嵌入的官能化聚合反应,对所得聚合物的生物降解性进行了一定程度的探查。     

Desulfurization of phosphorothioate oligonucleotides via the sulfur-by-oxygen replacement induced by the hydroxyl radical during negative electrospray ionization mass spectrometry

While the occurrence of desulfurization of phosphorothioate oligonucleotides in solution is well established, this study represents the first attempt to investigate the basis of the unexpected desulfurization via the net sulfur-by-oxygen (S-O) replacement during negative electrospray ionization (ESI). The current work, facilitated by quantitative mass deconvolution, demonstrates that considerable desulfurization can take place even under common negative ESI operating conditions. The extent of desulfurization is dependent on the molar phosphorothioate oligonucleotide-to-hydroxyl radical ratio, which is consistent with the corona discharge-induced origin of the hydroxyl radical leading to the S-O replacement. This hypothesis is supported by the fact that an increase of the high-performance liquid chromatography (HPLC) flow rate and the on-column concentration of a phosphorothioate oligonucleotide, as well as a decrease of the electrospray voltage reduce the degree of desulfurization. Comparative LC-tandem mass spectrometry (MS/MS) sequencing of a phosphorothioate oligonucleotide and its corresponding desulfurization product revealed evidence that the S-O replacement occurs at multiple phosphorothioate internucleotide linkage sites. In practice, the most convenient and effective strategy for minimizing this P?=?O artifact is to increase the LC flow rate and the on-column concentration of phosphorothioate oligonucleotides. Another approach to mitigate possible detrimental effects of the undesired desulfurization is to operate the ESI source at a very low electrospray voltage to diminish the corona discharge; however this will significantly compromise sensitivity when analyzing the low-level P?=?O impurities in phosphorothioate oligonucleotides.     

Clopyralid detection by using a molecularly imprinted electrochemical luminescence sensor based on the “gate-controlled” effect

A new strategy for trace analysis was proposed by preparing a molecularly imprinted polymer (MIP) sensor. The template molecules of clopyralid were determined based on “gate-controlled” electrochemiluminescence (ECL) measurement. A dense polymer film was electropolymerized on an electrode surface to fabricate the MIP–ECL sensor. The process of template elution and rebinding acted as a gate to control the flux of probes, which pass through the cavities and react on the electrode surface. ECL measurement was conducted in the luminol–H₂O₂ system. A linear relationship between ECL intensity and clopyralid concentrations in the range of 1?×?10^?9 mol/L to 8?×?10^?7 mol/L exists, and the detection limit was 3.7?×?10^?10 mol/L. The prepared sensor was used to detect clopyralid in vegetables. Recoveries of 97.9 % to 102.9 % were obtained. The sensor showed highly selective recognition, high sensitivity, good stability, and reproducibility for clopyralid detection.     

Effect of alloying on the stabilities and catalytic properties of Pt–Au bimetallic subnanoclusters: a theoretical investigation

Density functional theory (DFT) has been applied to study the geometrical and electronic structures and the catalytic properties for NO oxidation of pure Pt and PtAu clusters. The calculated results suggest that Pt₁₀ clusters shows the most stable structure among the pure Pt _n (n = 2–13) clusters with the local maximum Δ₂ E value. The doping of Au atoms reduces the stability of the clusters, and Pt₆Au₄ cluster has the most stable structure among Pt_10?n Au _n (n = 1–7) clusters, due to the closest band centers between Pt and Au atoms (0.83 eV) and the obvious s–p resonance peaks near the Fermi level. Pt₆Au₄ cluster displays the strongest activation of O₂ molecules among Pt_10?n Au _n (n = 0–7) clusters, owing to the clear overlap between O 2p and Pt 6 s and Au 6 s near the Fermi level, and the more positive d band center than the others. The interaction between NO and metals changes slightly in NO/Pt_10-nAu_n (n = 2–7) systems, which is weaker than that in NO/Pt₉Au system, as a result of the decreasing resonance peaks of sp hybridization near the Fermi level. Compared to pure Pt₁₀ cluster, the lower energy barriers and larger reaction energies on Pt₆Au₄ cluster suggest a higher catalytic activity of PtAu cluster for the O₂ dissociation and NO oxidation reactions. Our study provides atomic-scale insights into the nature of the interfacial effect that determines NO oxidation on PtAu cluster catalysts.     

Mechanisms for the Ni-mediated oxidation of benzene to phenol by N2O

The gas-phase Ni⁺-mediated benzene oxidation by N₂O on both quartet and doublet potential energy surfaces are surveyed using density functional theory (DFT). Geometries and energies for all relevant intermediates are calculated. The initial N₂O reduction for forming NiO⁺ takes place only via reaction with the excited Ni⁺(⁴F) through the N–O insertion mechanism. The second step of the oxidation can involve two mechanisms: ‘nonradical’ through benzene H migration following the formation of the boat complex of benzene–NiO⁺ or ‘oxygen-insertion’ via rearrangement to an arenium intermediate from the chair-type benzene–NiO⁺ encounter complex. Both mechanisms are energetically available.     

镍催化芳基硼酸与芳基醛的加成反应

发展了一种基于NiCl2(PPh3)2/IPr·HCl催化体系的、芳基硼酸和芳香醛进行加成反应制备二芳基甲醇类化合物的新方法,并取得了较好的催化效果。该方法具有简便,易操作等优点,是过渡金属催化制备二芳基甲醇类化合物的一个重要补充。