Some limit theorems for negatively associated random variables

Let {X _n , n ≥ 1} be a sequence of negatively associated random variables. The aim of this paper is to establish some limit theorems of negatively associated sequence, which include the L ^p -convergence theorem and Marcinkiewicz–Zygmund strong law of large numbers. Furthermore, we consider the strong law of sums of order statistics, which are sampled from negatively associated random variables.     

Validated UPLC‐MS/MS method for determination of moclobemide in human brain cell supernatant and its application to bidirectional transport study

A simple and sensitive analytical method based on ultraperformance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) has been developed for determination of moclobemide in human brain cell monolayer as an in vitro model of blood–brain barrier. Brucine was employed as the internal standard. Moclobemide and internal standard were extracted from cell supernatant by ethyl acetate after alkalinizing with sodium hydroxide. The UPLC separation was performed on an Acquity UPLC^TM BEH C₁₈ column (50 × 2.1 mm, 1.7 µm, Waters, USA) with a mobile phase consisting of methanol–water (29.5:70.5, v/v); the water in the mobile phase contained 0.05% ammonium acetate and 0.1% formic acid. Detection of the analytes was achieved using positive ion electrospray via multiple reaction monitoring mode. The mass transitions were m/z 269.16 → 182.01 for moclobemide and m/z 395.24 → 324.15 for brucine. The extraction recovery was 83.0–83.4% and the lower limit of quantitation (LLOQ) was 1.0 ng/mL for moclobemide. The method was validated from LLOQ to 1980 ng/mL with a coefficient of determination greater than 0.999. Intra‐ and inter‐day accuracies of the method at three concentrations ranged from 89.1 to 100.9% for moclobemide with precision of 1.1–9.6%. This validated method was successfully applied to bidirectional transport study of moclobemide blood–brain barrier permeability. Copyright © 2013 John Wiley & Sons, Ltd.     

激光剥蚀电感耦合等离子体质谱在涂料重金属分析中的应用

将激光剥蚀进样技术(LA)与ICP-MS检测器联用,并将这一新技术应用在涂料重金属元素的检测上,通过优化LA和ICP-MS参数,并采用双气流校正技术,以13C、103Rh为双内标,有效地改善了信号强度和稳定性,同时对Hg的记忆效应进行研究,最终建立了LA-ICP-MS法测定涂料中Cr、As、Cd、Sn、Sb、Hg、Pb元素的定量分析方法,样品测定结果与湿法消解ICP-OES法基本吻合。     

Catalyst‐Free Protocol for the Synthesis of Quinoxalines and Pyrazines in PEG

A facile and simple catalyst‐free protocol has been developed for the condensation of 1,2‐diketones with aromatic 1,2‐diamines in polyethylene glycol (PEG), providing quinoxaline derivatives in good yields. The important features of the methodology are broad substrates scope, simple workup, catalyst free, environmentally benign, and no requirement for metal catalysts. It is noteworthy that the cyclization reaction of 1,2‐diketones with aliphatic 1,2‐diamines is also conducted smoothly to afford pyrazines in good yields under the standard conditions. In addition, PEG could be recovered easily and was reused without evident loss in activity     

Switchable peptide-equipped protein/cucurbit[7]uril supramolecular assembly for targeted drug delivery

ABSTRACT

Herein, we develop a switchable peptide-equipped protein/cucurbit[7]uril (CB[7]) supramolecular assembly as novel targeted drug vector. Specifically, bovine serum albumin (BSA) is used to interact with CB[7], serving as the core of drug vector. Then, a peptide shield layer is formed on the surface of BSA/CB[7], yielding peptide-equipped supramolecular assembly (Pep@BSA@CB[7]). The equipped peptide shield layer is composed of switchable peptide probes consisting of a polycationic cell-penetrating peptide (CPP) motif, a polyanionic motif and a linking motif, and therefore provides a variety of desirable properties. First, the CPP motif displays excellent cell penetration ability and can facilitate internalisation of the drug vector. Secondly, the polyanionic motif performs intramolecular electrostatic interaction with CPP motif and thereby can reduce non-targeted delivery towards normal cells. Thirdly, the linking motif can be specifically cleaved by matrix metalloproteinases 2 that is up-regulated in tumour microenvironment, thus enabling precise cancer-targeting. As a consequent, Pep@BSA@CB[7] can serve as a promising drug vector that exhibits superior targeting ability and high uptake efficiency towards cancer cells, which may be of great potential in cancer-targeted treatment.     

Theoretical study of the mechanism for the ClOO + NO reaction on the singlet potential energy surface

A detailed quantum chemical study is performed on the mechanism of ClOO + NO reaction at the B3LYP/6-311+G (2d) level of theory combined with CCSD (T) single point energy calculation. The possible product channels for the reaction are obtained and discussed on the basis of the singlet [ClNO₃] potential energy surface. The calculation indicates that the dominant product for the title reaction is ClO + NO₂ by the direct dissociation of the initial adduct, and the formation of the other products is much less likely since they are unfavorable kinetically. A comparison is also made between the title reaction and the analogous reaction of FO₂ + NO to gain a deeper insight into the mechanism of the XO₂ + NO reactions.     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Covalent Organic Frameworks toward Diverse Photocatalytic Aerobic Oxidations

Photoactive two-dimensional covalent organic frameworks (2D-COFs) have become promising heterogenous photocatalysts in visible-light-driven organic transformations. Herein, a visible-light-driven selective aerobic oxidation of various small organic molecules by using 2D-COFs as the photocatalyst was developed. In this protocol, due to the remarkable photocatalytic capability of hydrazone-based 2D-COF-1 on molecular oxygen activation, a wide range of amides, quinolones, heterocyclic compounds, and sulfoxides were obtained with high efficiency and excellent functional group tolerance under very mild reaction conditions. Furthermore, benefiting from the inherent advantage of heterogenous photocatalysis, prominent sustainability and easy photocatalyst recyclability, a drug molecule (modafinil) and an oxidized mustard gas simulant (2-chloroethyl ethyl sulfoxide) were selectively and easily obtained in scale-up reactions. Mechanistic investigations were conducted using radical quenching experiments and in situ ESR spectroscopy, all corroborating the proposed role of 2D-COF-1 in photocatalytic cycle.