Characterization of N‐methylated amino acids by GC‐MS after ethyl chloroformate derivatization

Methylation is an essential metabolic process in the biological systems, and it is significant for several biological reactions in living organisms. Methylated compounds are known to be involved in most of the bodily functions, and some of them serve as biomarkers. Theoretically, all α‐amino acids can be methylated, and it is possible to encounter them in most animal/plant samples. But the analytical data, especially the mass spectral data, are available only for a few of the methylated amino acids. Thus, it is essential to generate mass spectral data and to develop mass spectrometry methods for the identification of all possible methylated amino acids for future metabolomic studies. In this study, all N‐methyl and N,N‐dimethyl amino acids were synthesized by the methylation of α‐amino acids and characterized by a GC‐MS method. The methylated amino acids were derivatized with ethyl chloroformate and analyzed by GC‐MS under EI and methane/CI conditions. The EI mass spectra of ethyl chloroformate derivatives of N‐methyl ( 1–18 ) and N,N‐dimethyl amino acids ( 19–35 ) showed abundant [M‐COOC₂H₅]⁺ ions. The fragment ions due to loss of C₂H₄, CO₂, (CO₂ + C₂H₄) from [M‐COOC₂H₅]⁺ were of structure indicative for 1–18 . The EI spectra of 19–35 showed less number of fragment ions when compared with those of 1–18 . The side chain group (R) caused specific fragment ions characteristic to its structure. The methane/CI spectra of the studied compounds showed [M + H]⁺ ions to substantiate their molecular weights. The detected EI fragment ions were characteristic of the structure that made easy identification of the studied compounds, including isomeric/isobaric compounds. Fragmentation patterns of the studied compounds ( 1–35 ) were confirmed by high‐resolution mass spectra data and further substantiated by the data obtained from ¹³C₂‐labeled glycines and N‐ethoxycarbonyl methoxy esters. The method was applied to human plasma samples for the identification of amino acids and methylated amino acids. Copyright © 2016 John Wiley & Sons, Ltd.     

基于结构化光纤Bragg光栅的折射率梯度传感器研究

研究结构化光纤Bragg光栅(FBG)在折射率(RI)呈线性分布的液相介质环境下的响应特性。数值仿真结果表明,结构化FBG的反射谱特性强烈依赖于液相介质折射率(RI)的线性分布函数的某些特征参数,比如液相介质的RI沿FBG轴向的分布梯度、RI在FBG两端的差值等。基于理论仿真结果,建立了结构化FBG在低RI区(1.330～1.360)对液相介质的RI梯度进行测量的线性近似理论模型。通过相关实验研究,证明了理论仿真和分析的合理性及基于结构化FBG的RI梯度传感器在现实应用中的可行性。     

高效液相色谱法考察银杏内酯B与其衍生物的变化规律

通过半制备色谱柱从银杏内酯B(GB)中分离出一种衍生物。高效液相色谱结果显示:该衍生物色谱峰的保留时间是GB的3.0倍左右;紫外光谱结果显示:该衍生物的最大紫外吸收波长为212.1 nm,最大吸光值为2.29×104,大约是GB的最大吸光值的100倍,说明是π→π*电子跃迁的结果,表明其分子结构中存在共轭双键;高效液相色谱-质谱分析结果显示:该衍生物在正离子模式下产生的分子离子峰为m/z 429.1(M+Na)+,负离子模式下产生的分子离子峰为m/z 405.2(M-H)-,与GB的分子离子峰质荷比相差18,且与GB具有相似的解离模式。GB对热稳定,而该衍生物对热相对不稳定。pH对两者的关系影响不大,当pH值逐渐增高时,衍生物的开环速度比GB快。溶剂和温度的综合作用对衍生物的稳定性影响更加显著,GB在聚乙二醇溶液中分别于50 ℃下保存15 h和120 ℃下保存4 h后其中的衍生物峰全部消失;将该溶液于120 ℃下保存4 h后分析,除有主峰GB外,在保留时间为1.2～3.0 min范围还伴随有小峰出现,这说明衍生物处于高能态,GB相对较为稳定,两者共存,且相互转化;在特定条件下衍生物能全部转化为GB。     

Characterization of coal tars by HPLC group type separation and capillary GC of volatiles

Summary Group separation of malthene fractions of tar samples obtained from brown coals of different ranks at two different temperatures (500 and 800°C) was performed by HPLC using amino-cyano bonded phase packing with two eluent systems of different polarities and backflushing technique. Group composition of different tar samples was compared and evaluated. Amount and distribution of volatile compounds in the malthene fractions were determined by capillary gas chromatography on a CP-Sil 5 WCOT column. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

An improvement of the resolution of the identity approximation for the formation of the Coulomb matrix

A straightforward modification of the resolution of the identity (RI) approximation to the Coulomb interaction is described. In the limit of basis sets that are dominated by high angular momentum functions the observed speedups in realistic test systems reach a factor of 2 compared to the standard RI algorithm, and a factor of up to 300 compared to the standard algorithm to form the Coulomb matrix. More moderate savings on the order of 0-20% are obtained for the more commonly used smaller basis sets. A series of test calculations is reported to illustrate the efficiency of the algorithm.     

Auxiliary basis sets for main row atoms and transition metals and their use to approximate Coulomb potentials

We present auxilliary basis sets for the atoms H to At – excluding the Lanthanides – optimized for an efficient treatment of molecular electronic Coulomb interactions. For atoms beyond Kr our approach is based on effective core potentials to describe core electrons. The approximate representation of the electron density in terms of the auxilliary basis has virtually no effect on computed structures and affects the energy by less than 10⁻⁴ a.u. per atom. Efficiency is demonstrated in applications for molecules with up to 300 atoms and 2500 basis functions. Received: 17 December 1996 / Accepted: 8 May 1997     

二元碱度对印尼钒钛矿烧结过程及烧结矿质量的影响

以典型钢铁企业矿石资源为基础,进行不同碱度条件下配加印尼钒钛矿的烧结试验,考察了二元碱度(R=m(Ca O)/m(Si O2))对该矿烧结过程及烧结矿质量的影响.研究表明:当碱度R由1.4逐渐增至2.3时,烧结有效利用系数由1.63 t/(m2·h)降至1.44 t/(m2·h),烧结矿成品率由78.5%降至75.3%;同时,垂直烧结速度有所上升;烧结矿中w(Fe O)不断下降;转鼓指数先下降而后逐渐回升,并在R=1.7时出现最小值.随着碱度的逐渐增加,低温还原粉化性能和还原性逐渐改善,这有利于高炉上部透气性的改善和间接还原的发展.     

RI指数联合超声对孕晚期胎儿肾积水预后预测价值的研究

目的探讨RI指数联合超声对孕晚期胎儿肾积水预后预测的价值.方法选取行超声检查发现的晚孕期肾积水胎儿141例,检测胎儿的肾实质厚度、肾盂前后直径(APD)、肾盂肾盏形态,并给予评分,累计3项指标评分分值;对胎儿行超声检查时测定积水肾脏肾门位置的RI值.将以上检测结果与胎儿出生后1 a内行超声检查和临床诊断结果进行对照研究.结果 141例胎儿共有170只肾积水;出生后1 a内行超声检查和临床诊断显示,非病理性肾积水121只,病理性49只.随着超声评分值增加,病理性肾积水风险越高,其中超声评分≤3分均为非病理性肾积水,评分≥8分均为病理性肾积水.病理性肾积水与非病理性肾积水超声评分之间差异具有显著统计学意义(P0.01).超声评分为5分时,为辨别诊断非病理性肾积水和病理性肾积水的截断值,特异度为88.61%,灵敏度为95.00%.超声评分≤5分的肾积水胎儿的肾动脉RI值在0.60~0.67,而超声评分5分的肾积水胎儿肾动脉RI值在0.70~0.78.结论超声评分法联合RI指数评估胎儿肾积水预后客观准确,具有较高实用价值,超声评分5分为诊断胎儿病理性肾积水的最佳截断值.     

Accelerating Kohn‐Sham response theory using density fitting and the auxiliary‐density‐matrix method

An extension of the formulation of the atomic‐orbital‐based response theory of Larsen et al., JCP 113, 8909 (2000) is presented. This new framework has been implemented in LSDalton and allows for the use of Kohn‐Sham density‐functional theory with approximate treatment of the Coulomb and Exchange contributions to the response equations via the popular resolution‐of‐the‐identity approximation as well as the auxiliary‐density matrix method (ADMM). We present benchmark calculations of ground‐state energies as well as the linear and quadratic response properties: vertical excitation energies, polarizabilities, and hyperpolarizabilities. The quality of these approximations in a range of basis sets is assessed against reference calculations in a large aug‐pcseg‐4 basis. Our results confirm that density fitting of the Coulomb contribution can be used without hesitation for all the studied properties. The ADMM treatment of exchange is shown to yield high accuracy for ground‐state and excitation energies, whereas for polarizabilities and hyperpolarizabilities the performance gain comes at a cost of accuracy. Excitation energies of a tetrameric model consisting of units of the P700 special pigment of photosystem I have been studied to demonstrate the applicability of the code for a large system.     

New Generation of Experiments for the Investigation of Stellar (p, γ) Reaction Rates Using SAMURAI

The future experimental campaign with the SAMURAI setup at RIKEN will explore a wide range of neutron-deficient nuclei with a particular focus on the most critical  (p, γ)  reaction rates relevant to the astrophysical rp-process in type-I X-ray bursts (XRB). Intense radioactive-ion (RI) beams at an energy of a few hundred MeV/nucleon will be deployed to populate proton-unbound states in the nuclei of interest through the Coulomb excitation or nucleon-removal processes. The decay of these states into a proton and a heavy residue will be measured using complete kinematics and the information about timereversal proton-capture process will be obtained. This method will provide the vital experimental data on the resonances, which dominate the stellar (p,γ) reaction rates, as well as on the direct proton-capture process for some other cases. The experimental setup will utilize for the first time the High-Resolution 90?-mode of the SAMURAI spectrometer in combination with the existing detection systems, including custom-designed Si-strip detectors for simultaneous detection and tracking of heavy ions and protons emitted from the target. The details of the experimental method and the utilized apparatus are discussed in this paper.