Determination of selenoamino acids by gas chromatography-mass spectrometry

The application of the recently introduced ethylchloroformate derivatization method for the separation and determination of selenomethionine and selenocystein in selenium-enriched yeast and yeast-free tablets by means of a gas chromatography-mass spectrometry (GC-MS) system has been studied. The efficiency of three methods for the extraction of selenomethionine from the tablets were compared. Total selenium content of the same tablets were measured using inductively coupled plasma (ICP)-MS and it was found that in the selenized yeast tablets about 80% of the total selenium is present as selenomethionine. The results were in agreement with the values in the labels and with the literature. The accuracy of the total selenium analysis was controlled by the analysis of a reference material.     

硒代胱氨酸在银电极上的电化学行为及其定量分析

研究了硒代胱氨酸 (SeCys)于0.03mol/L的硼砂 -NaOH( pH9.5)介质中在银电极上的电化学行为 ;实验发现在 -0.62V和 -0.68V(vsSCE)处存在一对氧化还原峰 ,其峰电流与硒代胱氨酸浓度具有良好的线性关系 ,由此建立了SeCys的电分析化学测定方法, (1)循环伏安法 ,其线性范围为8.6×10 -9～1.1×10 -7mol/L,检出限为4.3×10 -10mol/L, (2)二次微分线性扫描伏安法 ,其线性范围为2.2×10 -10～1.0×10 -8mol/L,检出限为8.6×10-11mol/L;该法应用于中药黄芪中SeCys含量的测定 ,结果令人满意 ;该文还探讨了硒代胱氨酸在上述条件下的电极反应机理     

Novel selenium-containing non-natural diamino acids

The general synthesis of a new class of non-natural diamino acids, 2-amino-3-[(2′-aminoalkyl)seleno]propanoic acids, or Se-(aminoalkyl)selenocysteines, is reported. Under the conditions devised, enantiopure N-Boc-protected β-l-iodoamines, which are readily generated from proteinogenic α-amino acids, were treated with the selenolate anion obtained from NaBH₄ splitting of the Se-Se bond in commercial l-selenocystine. The Se-alkylation products were enantiomerically pure and the reaction is high yielding (92-98%), without any detectable traces of accompanying by-products.     

用离子抑制色谱法分析二（2,2,6,6—四甲基—4—哌啶基）马来酸酯合？…

建立了用离子抑制色谱法分析二（２,２,６,６－四甲基－４－哌啶基）马来酸酯合成反应液的方法。平均回收率为９８．８％,相对标准偏差为０．５６％,测量的平均相对偏差不大于５．０％,方法简单,快速,可用于工艺条件的选择和质量检测。     

Speciation of selenomethionine and selenocystine using online micro-column containing Cu(II) loaded nanometer-sized Al2O3 coupled with ICP-MS detection

A flow injection online speciation procedure by using micro-column packed with Cu(II) loaded nanometer-sized Al₂O₃ coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the separation and determination of selenomethionine (SeMet) and selenocystine (SeCys₂) has been developed. The main factors affecting the separation and preconcentration of SeMet and SeCys₂ including pH value, sample flow rate, eluent concentration, eluent volume and flow rate, and interfering ions have been investigated. It was found that SeCys₂ could be selectively retained by micro-column packed with Cu(II) loaded nanometer-sized Al₂O₃ at pH 4.0, and the retained SeCys₂ could be eluted by 1.0 mol L⁻¹ HNO₃, while SeMet was not retained and passed through the micro-column directly at this pH. Both SeMet and SeCys₂ could be quantitatively adsorbed by the micro-column at pH 9.0, and the retained SeMet and SeCys₂ could be easily eluted with 1.0 mol L⁻¹ HNO₃. The content of SeMet was obtained by subtracting the SeCys₂ from the total content of seleno amino acids. With the enrichment factor of 7.8 and 7.7, the limits of detection (LODs) for SeMet and SeCys₂ were found to be 24 pg Se mL⁻¹ and 21 pg Se mL⁻¹, respectively. The relative standard deviations (RSDs) for SeCys₂ and SeMet with seven replicate determinations of 1.0 ng mL⁻¹ SeMet and SeCys₂, were 2.1% and 1.6%, respectively, the sampling frequency of 8 h⁻¹ was obtained. The proposed method was applied to the speciation of SeMet and SeCys₂ in selenized yeast, human urine and serum with satisfactory results.     

硒代胱氨酸和硒代蛋氨酸电化学检测的比较

对硒代胱氨酸 (SeCys)和硒代蛋氨酸 (SeMet)在银电极上的电化学性质、电极反应机理及检测灵敏度等方面进行比较研究。实验表明 ,两者在pH9.5的硼砂 氢氧化钠介质中 ,于 -0 .62V和 -0 .68V(vs.SCE)处均存在一对氧化还原峰 ,电化学行为相似 ,两者具有良好的线性范围和低检出限 ,SeMet比SeCys具有更高的检测灵敏度。在相同的实验条件下 ,比较了含硫氨基酸与含硒氨基酸的电化学响应 ,含硫氨基酸的检测灵敏度远低于含硒氨基酸     

Study of the lipophilicity of selenium species

In this work the lipophilicity of different selenium species occurring in environmental matrices and food, Se(IV), Se(VI), selenomethionine (Se-Met), selenocystamine (Se-CM), selenocystine (Se-Cyst), and dimethyl diselenide (CH₃)₂Se₂, was investigated in the octanol–water system, using the shaking flask method and detection with inductively coupled plasma–atomic emission spectrometry (ICP–AES), in order to assess their environmental fate and tendency to bioaccumulate. Polarography was also used for the electrochemically active Se species, Se(IV), Se-Cyst, Se-CM and (CH₃)₂Se₂, and the results were compared with those measured by ICP–AES. Furthermore, the influence of pH was studied by determining the logarithm of the distribution coefficient, log D, at three pH values, 5, 7, and 9, as was the impact of the marine environment on the lipophilicity profile of the six investigated Se species. The results were compared with those estimated approximately by use of PrologD software, based on the Ghose-Crippen log P (P: partition coefficient) calculation system, the only system which incorporates values—even though approximate—for the atom type of Se. Finally, from our experimental data an indicative value of the Se–Se fragment for log P prediction, for use in drug design, was estimated.     

硒代胱氨酸修饰银电极及应用研究

介绍了硒代胱氨酸修饰银电极的制备及其电化学特性 ,并将该修饰电极用于痕量金属离子的分析。研究结果表明 ,此修饰电极具有良好的电化学性质和化学、机械和电化学的稳定性 ,在测定Pb2 + 时 ,检出限可达到 1.0× 10 - 11mol·L- 1,线性范围在 2 .0× 10 - 10 ～ 4 .0× 10 - 11mol·L- 1,同时对于其他金属离子 (Cd2 + ,Cu2 + ,Zn2 + )的分析中也获得较满意的结果     

Effect of nitric acid for equal stabilization and sensitivity of different selenium species in electrothermal atomic absorption spectrometry

Determination of selenium by electrothermal atomic absorption spectrometry (ETAAS) is complicated by the presence of different species of this analyte. The presence of different oxidation states (−II, IV and VI) may result in different sensitivities obtained for each species rendering impossible the use of a single species for calibration. These species also exhibit different behaviours regarding thermal stabilities; the temperature program must be provided to conform to this problem. Chemical modifiers are commonly used for thermal stabilization of selenium species. In this study, experiments were carried out to demonstrate the effect of nitric acid in the presence of chemical modifiers. Nickel and palladium + magnesium were selected as the most commonly used chemical modifiers. Using both aqueous and human serum solutions it has been demonstrated that although chemical modifiers provide thermal stabilization of species so that higher ashing temperatures can be used, equal sensitivities cannot be achieved unless nitric acid is also present. Selenite, selenate, selenomethionine and selenocystine were used in experiments. When equal sensitivities for all these species are achieved, determination of total selenium by ETAAS can be performed by using a single species as the standard; selenite was used in this study. Precision was 5.0% or better using peak height signals. There was no significant difference in detection limits (3s) when Ni or Pd + Mg(NO₃)₂ was used as chemical modifier; 37 and 35 pg of selenium were found to be the detection limits for Ni and Pd + Mg(NO₃)₂ chemical modifiers, respectively. For chemical modifications, either 5 μg of Ni or 0.5 μg of Pd and 5 μg of Mg(NO₃)₂ were used; final solutions contained 2.5% HNO₃. In serum analyses, 10 μg of Ni was used in presence of 2.5% HNO₃.     

Electrochemical oxidation of selenocystine and selenomethionine

Electrochemical oxidation of selenocystine (SeCys) and selenomethionine (SeMet), on a gold electrode was studied by cyclic voltammetry (CV), rotating disk electrode technique (RDE) and chronocoulometry (CC). In 0.2 mol/L HAc-NaAc (pH = 3.90) supporting electrolyte, anodic peak I potential of SeCys and SeMet was 810 mV and 638 mV, respectively, and this electrode process was diffused controlled. The electrochemical oxidation process of SeCys, in which six electron-transfers were involved, yielded selenocystine selenoxide. The electrochemical oxidation process of SeMet, in which two electron-transfers were involved, yielded selemethionine selenoxide.