Quantification of malondialdehyde by HPLC‐FL – application to various biological samples

Malondialdehyde (MDA) is stabile product of lipid peroxidation (LPO), and therefore MDA is frequently used as a biomarker of LPO. To determine MDA level in various biological samples (human plasma, fish liver tissue and cells in culture), we used an HPLC method with fluorescent detection based on 2‐thiobarbituric acid (TBA) assay. The method was validated by the use of spiked pooled plasma samples. In tested concentration range (0.15–3.0 µmol/L) the method was linear (R² = 0.9963), the between‐day variability (coefficient of variations, CVs) was between 4.7 and 7.6%, the within‐day variability CVs was between 2.6 and 6.4% and recovery was between 91.2 and 107.6%. The level of MDA in human plasma (healthy male, non‐smokers, 46.3 ± 4.7 years; N = 38) was 2.2 ± 1.4 µmol/L; that in liver tissue of common carp (Cyprinus carpio; N = 12) was 0.02 ± 0.004 µmol/g tissue, and in cultured cells (human laryngeal carcinoma cells; N = 10) it was 0.18 ± 0.02 nmol/mg proteins. The HPLC‐FL method is rapid, accurate and reliable to follow the extent of LPO in various biological samples, particularly in samples in which a low level of MDA is expected, such as cells in culture. Owing to the rapid analytical process and run time, it can be used for routine analysis of MDA in clinical laboratory. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly Enantioselective Zinc/Amino Alcohol‐Catalyzed Alkynylation of Aldehydes

Meeting the challenge : The zinc/amino alcohol catalyzed enantioselective addition of terminal alkynes to aldehydes is effective with both phenylacetylene and methyl propiolate, leading to chiral secondary propargyl alcohols with very high enantioselectivity (see scheme).

     

Car-Parrinello molecular dynamics study of the rearrangement of the valeramide radical cation

Car-Parrinello molecular dynamics (CPMD) studies of neutral (1) and ionized (1 (+.)) valeramide are performed with the aim of providing a rationalization for the unusual temperature effect on the dissociation pattern of 1(+.) observed in mass spectrometric experiments. According to CPMD simulations of neutral valeramide 1 performed at approximately 500 K, the conformation with the fully relaxed carbon backbone predominates (96 %). Conformational changes involving folding of the carbon backbone into conformers that would allow intramolecular H transfers are predicted not to take place spontaneously at this temperature because of the barrier heights associated with these transitions (3.5 and 6.9 kcal mol(-1)), which cannot be overcome by thermal motion alone. For 1(+.), CPMD simulations performed at approximately 300 K reveal a substantial stability of a conformation in which the carbon backbone is fully relaxed; no reaction is observed even after 7 ps. However, when conformers with already folded carbon-backbones are used as initial geometries in the CPMD simulations, the gamma-hydrogen migration (McLafferty rearrangement resulting in C(3)H(6)) is already completed within 2 ps. For this important process, the free activation energy associated with both a required conformational change and the subsequent H transfer equals 4.5 kcal mol(-1), while for the formally related delta-H shift (which eventually gives rise to the elimination of C(2)H(4)/C(2)H(5.)) it amounts to 7.0 kcal mol(-1). Since the barriers associated with conformational changes are energetically more demanding than those of the corresponding hydrogen transfers, 1(+.) is essentially trapped by conformational barriers and long-lived at approximately 300 K. At elevated temperatures (500 K), the preferred reaction (within 7.3 ps) in the CPMD simulation corresponds to the McLafferty rearrangement. The estimated free activation energy associated with this process amounts to 2.5 kcal mol(-1), while the free activation energy for the delta-H transfer equals 4.4 kcal mol(-1). This relatively small free activation energy for the McLafferty rearrangement might cause dissociation of a substantial fraction of 1(+.) prior to the time-delayed mass selection, which would reduce the C3/C2 ratio in the experiments conducted with metastable ions that have a lifetime in the order of some micros at a source temperature of 500 K.     

Reactions of Polymer‐Supported α‐Selenoaldehydes with Grignard Regents. A Facile Solid‐Phase Stereoselective Synthesis of (E)‐1,2‐Disubstituted Ethenes

Polymer‐supported α‐selenoaldehydes easily obtained by reaction of polymer‐supported 4‐(phenylseleno)morpholine with aldehydes react with Grignard reagents to form polymer‐supported β‐hydroxyalkyl selenides, which were treated with thionyl chloride/triethylamine leading to (E)‐1,2‐disubstituted ethenes in good yields.     

氧气和CS自由基反应势能面的密度泛函理论研究

应用量子化学从头计算和密度泛函理论(DFT)对O_2和CS自由基的反应进行了研 究。在B3LYP/6-311G~(**)水平上计算出了各物种的优化构型、振动频率和零点振 动能(ZPVE)。各物种的总能量由CCSD（T）/6-311G~(**)//B3LYP/6-311G~(**)给出 ，并对总能量进行了零点能校正。计算结果表明：CS自由基中的C端沿着O_2的双键 中线方向进攻，进行加成反应，反应的第一步放出大量的热量(450 kJ/mol)，推动 反应继续进行，从稳定的中间体4(Cs)出发，反应主要通过O的相邻位置的迁移生成 P_1(CO+SO)和P_3(COS+O)；通过S的相邻位置的迁移生成了重要的反应复合物 (complex 1)，进一步离解为产物P_2(CO_2+S)。计算结果可以很好地解释反应机理 。     

Electrochemical Phenylselenoetherification as a Key Step in the Synthesis of (±)‐Curcumene Ether

Two variants of a new pathway for the synthesis of (±)‐curcumene ether are described. The key steps in these procedures are intramolecular cyclizations of 6‐methyl‐2‐(4‐methylphenyl)hept‐6‐en‐2‐ol and 2‐methyl‐6‐(4‐methylphenyl)hept‐6‐en‐2‐ol by means of an electrochemically generated phenylselenyl cation. This synthetic approach provides significantly better yields than the previously reported protocols.     

First electrochemical investigation of organophosphorus pesticide azametiphos and its quantification using electroanalytical approach

ABSTRACT

In this work, the electrochemical behaviour and the subsequent development of an analytical procedure for quantification of pesticide azamethiphos, using boron-doped diamond (BDD) electrode are reported for the first time. It was found that azamethiphos electrochemical behaviour is irreversible oxidation at the potential of around 1.70 V, in 1 M nitric acid (pH 0). Also, it was found that potential of this oxidation was not pH dependent which can be attributed to the no proton involvement in electrochemical reaction on the electrode surface. The square wave voltammetric method was most appropriate for azamethiphos quantification. Under optimised experimental conditions, linear working range from 2 to 100 µM was estimated with the detection limit of 0.45 µM. Negligible effect of the possible interfering compound was observed. The obtained results show that the developed analytical methodology can be an adequate replacement for the, up to date, used methods for detection of organophosphorous pesticide.     

The possibilities of voltammetry in the study reactivity of dissolved organic carbon (DOC) in natural waters

Journal of Solid State Electrochemistry - This paper describes the application of a methodology, which primarily involves low-cost voltammetry, to rapidly track the reactivity (i.e. surfactant...