A highly sensitive isotope-coded derivatization method and its application for the mass spectrometric analysis of analytes containing the carboxyl group

A novel isotope labeling reagent d₀-/d₆-2, 4-dimethoxy-6-piperazin-1-yl pyrimidine (DMPP) has been developed for derivatization toward the carboxyl group based on carbodiimide chemistry for mass spectrometry (MS) analysis. The strengths of this derivatization strategy involve fast labeling (15 s), low chemical background and general access to most carboxylic analytes. This has been demonstrated using a series of compounds containing carboxylic acids, including peptides and proteins. To enhance the MS response of the derivatized analytes, the design of DMPP has been based on integration of the theoretical consideration of high gas-phase hydrogenation capacity and hydrophobicity. In addition, the high abundance product ions at m/z 225 and m/z 231 from d₀-/d₆-DMPP labeled carboxylic acids indicate high efficiency of the gas-phase cleavage induced by the labeling reagent. Quantitative determination of these ions can also be used in single reaction monitoring to achieve extremely high sensitivity toward the target analytes. This has subsequently been used to determine trace free fatty acids in human urine. Furthermore, the DMPP labeled peptides also provide additional sequence information in MALDI–MS/MS because of the formation of sequence-related isotope fragment ions. This DMPP-oriented labeling technique is expected to be a promising tool for the MS detection of many varieties of compounds containing carboxyl groups.     

Reduction Removal of Cr(VI) from Wastewater by CO2·- Deriving from Formate Anion Based on Activated Carbon Catalyzed Persulfate

As a strong reducing radical, carbon dioxide anion radical(CO₂^·-) can be generated by initiating sulfate radical(SO₄^·-) in the presence of formate anions(FA) for Cr(VI) reduction. Moreover, activated carbon(AC)-catalyzed persulfate(PS) oxidation is an economically justifiable, environmentally friendly, and easy-to-scale-up method to produce SO₄^·-. The complete removal of Cr(VI) was achieved within 280 min for an initial Cr(VI) concentration of 50 mg/L under the optional condition of c(AC)=1 g/L, [PS]₀=10 mmol/L, [FA]₀=10 mmol/L, T=30℃, and unadjusted pH. When the molar ratio of FA to PS was greater than or equal to 1, the system maintained a strong reduction state. The mechanism investigation confirmed that FA was converted to carboxyl anion radical(CO₂^·-) as the predominant radical for Cr(VI) reduction. This novel system may offer a potential platform technology for Cr(VI) wastewater treatment.     

α-氨基酸在水-乙醇中羟基质子化热力学

α 氨基酸为重要的两性物质 ,其酸碱性质对于维持生物体内的酸碱平衡和蛋白质的生物活性起着十分重要的作用．α 氨基酸在纯水溶剂中的质子化反应热力学性质已进行了广泛的研究［１ -６］,但对球形蛋白来说 ,蛋白亚基间的作用是处在一个大量但不完全由水组成的非水环境中 ,因此 ,研究氨基酸在水 有机物混合溶剂中的质子化热力学性质具有重要意义．但这方面的工作 ,特别是用量热法直接研究溶剂对质子化焓变的影响开展得不多．本文选择乙醇和水组成的混合溶剂模拟蛋白质亚基所处的介质环境 ,利用精密微量流动热量计测定２９８．１５Ｋ时甘氨…     

α-氨基酸在水-乙醇中羧基质子化热力学

Enthalpy changes for the protonation of carboxyl group of four α-amino acids(glycine,L-α-alanine,L-valine and L-serine) were measured in water-ethanol mixtures (10－ 70wt％) at 298.15K using LKB-2277 Bioactivity Monitor.The corresponding entropy and Gibbs energy changes were also calculated.The results show that both enthalpy changes and entropy changes are favorable to the protonation of carboxyl groups of the investigated amino acids in water-ethanol mixtures.However,the influence of the composition of ethanol in the mixed solvents on the enthalpy change and entropy changes is complicated.Both sδ and sδ ,the differences of enthalpy changes and entropy changes in mixed solvents and in pure water respectively,show a minimum approximately at xEtOH=0.1.The effects of side chains on the enthalpy change and entropy changes were also investigated using the proton transfer process between glycine and the other three amino acids.The results demonstrate that the proton transfer processes for alanine and valine are spontaneous but not for serine,which could be interpreted in terms of the electrostatic interaction between amino group and carboxyl group within the molecule and the interaction between carboxyl group and the solvent.     

表面羧基化Fe3O4磁性纳米粒子的快捷制备及表征

亲水性磁性纳米颗粒在生物科学领域有着广泛应用,本研究提出了一种快速对磁性纳米粒子表面进行羧基化的方法. 首先使用氯化铁和氯化亚铁为原料, 以油酸为表面活性剂, 通过共沉淀法制得油酸包覆的亲油性磁性纳米粒子, 然后用高锰酸钾进行原位氧化, 将覆盖在粒子表面的油酸中的C＝C键氧化成-COOH, 从而得到单层羧基功能化的亲水性磁性纳米粒子. 利用透射电镜(TEM)、X射线衍射(XRD)、傅利叶红外光谱仪(FT-IR)、热重分析仪(TGA)、振动样品磁强计(VSM)、Zeta电位分析仪等对其进行表征. 结果表明磁性纳米粒子表面被成功羧基化,粒子的平均直径约为9 nm,饱和磁化值为64.5 emu/g,剩磁和矫顽力近似为零,具有典型的超顺磁性. 羧基化磁性纳米粒子可在pH7-10的水溶液中形成稳定分散的磁流体,保存6周无沉淀出现.     

Transferability of the -COOH...−OOC- dyad Geometry from the gas phase to crystals and proteins

Summary Simple models of the -COO^– ... HOOC- moiety were studied byab initio and semiempirical MNDO/PM3 methods combined with retrieval from the Cambridge Crystallographic Database and Protein Data Bank in order to check transferability of the non-bonded geometry. We found that the gas-phase O ... O distance (252 pm) elongates in crystals and proteins to 256±14 and 262±27 pm, respectively. C-O ... O-C dihedral angles are much more variable, however, energetically excluded values appear only exceptionally in crystals and less frequently in proteins. Most probably due to packing effects -COO^– ... HOOC-conformations, preferred in the gas phase, are poorly populated in crystals     

高Fe_3O_4含量单分散P(St/AA)复合微球的合成与表征

在表面由十一烯酸和油酸共同修饰的Fe3O4磁流体存在下,以苯乙烯(St)和丙烯酸(AA)为共聚单体,用细乳液聚合法,制备了单分散,高Fe3O4含量,且表面带有羧基的超顺磁性高分子复合微球.采用透射电镜(TEM),热重分析(TGA),物性测量系统(PPMS),Zeta电位以及红外光谱等手段对磁性复合微球的各项性能进行表征.结果表明,Fe3O4粒子的表面改性是影响复合微球Fe3O4含量及形貌的关键因素.在优化的实验条件下,可以制得Fe3O4含量高达77wt%,平均粒径为137·9nm,表面羧基密度0·0894mmol/g,比饱和磁化强度为44·7emu/g的单分散超顺磁性高分子复合微球.     

Effect of carboxyl end groups content on the thermal and electrical properties of poly(propylene terephthalate)

Poly(propylene terephthalate) (PPT) samples with different carboxyl terminal groups content were synthesized in bulk and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers under investigation show a good thermal stability, however decreasing with increasing carboxyl terminal groups content. No significant change of the glass transition temperature as well as melting temperature values was found in the samples under investigation; on the contrary, the crystallization rate of PPT was found to be affected by carboxyl terminal groups content, regularly decreasing as the amount of -COOH terminal groups is increased. This trend was interpreted on the basis of the interactions among the terminal groups of the polymeric chains, which determine a decrease in the chain mobility. Direct current (dc) electrical behavior was also investigated. The dc charging/discharging currents and electrical conductivity are studied as a function of temperature, time of applied voltage and amount of -COOH terminal groups. The conductivity values were found to increase as the content of -COOH end groups was increased, due to an increment of amount of ionic charge carriers.     

Magnetic hydrophilic methacrylate-based polymer microspheres for genomic DNA isolation

Carboxyl groups containing magnetic and non-magnetic microspheres were used in solid-phase reversible immobilization (SPRI) of genomic DNA. Magnetic non-porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)--P(HEMA-co-EDMA), poly(glycidyl methacrylate)--PGMA and P(HEMA-co-GMA) microspheres with hydrophilic properties were prepared by dispersion copolymerization of the respective monomers in the presence of colloidal iron oxides. DNA from chicken erythrocytes and DNA isolated from bacterial cells of Bifidobacterium longum was used for testing of adsorption/desorption properties of magnetic microspheres. The occurrence of false negative results in polymerase chain reaction (PCR) caused by the presence of extracellular inhibitors in DNA samples has been solved using SPRI. The P(HEMA-co-EDMA) and P(HEMA-co-GMA) microspheres were used for isolation of DNA from different dairy products followed by PCR identification of Bifidobacterium strains.     

Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin

The effects of water absorption on hydrophilic polymer matrices based on carboxylic functionalized glucose (glucose maleic acid ester vinyl resin) and epoxy resins were studied as a function of curing temperature. The matrix cured at higher temperature shows compact crosslinks due to the higher concentration of ether bonds comparing to the matrix cured at the lower temperature. The polymer matrices cured at different temperatures were immersed in water at room temperature for 1000 h and the thermomechanical properties of the cured polymers were characterized using DMA and TGA. Two types of sorbed water were identified. Type I sorbed water contributed mainly to increasing the weight and to the decrease in T_g due to a plasticizer effect. Type II sorbed water was not removed after heating the polymer to 110 °C for an hour. Type II sorbed water causes changes in the mechanical properties of the polymers cured at different temperatures depending on the crosslinks of the matrix. The cured matrix at the higher temperature has the comparatively tight crosslinks in the network structure and the sorbed water molecule disturbed the polymer network resulting in the degradation of the matrix such as microcracks.