LC–MS bioanalysis of intact proteins and peptides

Bioanalysis assays that reliably quantify biotherapeutics and biomarkers in biological samples play pivotal roles in drug discovery and development. Liquid chromatography coupled with mass spectrometry (LC–MS), owing to its superior specificity, faster method development and multiplex capability, has evolved as one of the most important platforms for bioanalysis of biotherapeutics, particularly new scaffolds such as half-life extension platforms for proteins and peptides, as well as antibody drug conjugates. Intact LC–MS analysis is orthogonal to bottom-up surrogate peptide approach by providing whole molecule quantitation and high-level sequence and structure information. Here we review the latest development in LC–MS bioanalysis of intact proteins and peptides by summarizing recent publications and discussing the important topics such as the comparison between top-down intact analysis and bottom-up surrogate peptide approach, as well as simultaneous quantitation and catabolite identification. Key bioanalytical issues around intact protein bioanalysis such as sensitivity, data processing strategies, specificity, sample preparation and LC condition are elaborated. For peptides, topics including quantitation of intact peptide vs. digested surrogate peptide, metabolites, sensitivity, LC condition, assay performance, internal standard and sample preparation are discussed.     

Characterization of In Vivo Metabolites of a Potential Anti-obesity Compound,the 3-Methyl-1H-Purine-2,6-Dione Derivative C-11, Employing Ultra-High Performance Liquid Chromatography Coupled with Quadrupole Time-of-Flight Mass Spectrometry

C-11 (2-((7-Ethyl-3-methyl-8-(4-(2-(methyl(pyridin-2-yl)-amino)-ethoxy)phenyl)-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-1-yl)methyl)benzonitrile-one hydrochloride), which is based on the structure of rosiglitazone, was first synthesized in our laboratory and shown to be a promising anti-obesity drug candidate in our previous pharmacological study. Considering the importance of metabolic fate in vivo in the further development of drug candidates during early drug discovery, it is essential to characterize the metabolism of C-11 in vivo. In this work, a method based on ultra-high performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) was successfully developed to investigate the in vivo metabolic profile of C-11 in rats. Rat urine, feces, and plasma samples were collected from male Sprague–Dawley rats after intravenous administration of C-11 in a single dose of 30 mg kg⁻¹ body weight. Besides the parent drug, a total of 25 metabolites (including 18 phase I and 7 phase II metabolites) were detected and tentatively identified by comparing their mass spectrometry profiles with those of C-11. This enabled the metabolic pathways of C-11 to be proposed for the first time. Our results revealed that N-depyridinylation, N-demethylation, hydroxylation, glucuronidation, and sulfate conjugation are the predominant metabolic pathways of C-11 in rats. The present study provides systematic information on the metabolism of C-11 in vivo, which should lead to a better understanding of its safety and mechanism of action.

     

Spectroscopic and time-dependent density functional investigation of the role of structure on the acid-base effects of citrinin detection

A time-dependent density functional theory (TD-DFT) study was carried out on tautomers of the mycotoxin citrinin in the neutral, anionic, and cationic forms to gain insight into the role of chemical structure on detection. Steady-state fluorescence studies of citrinin in micellar aqueous solutions produced unusual results for ionic surfactants and the neutral Triton X-100 enhanced fluorescence emission. Ground-state and time-dependent density functional studies were carried out on five tautomers of citrinin using the B3LYP density functional and the 6-311+G(2df,2p) basis set. The investigation revealed that deprotonation is a major factor governing the shifts in fluorescence excitation and emission maxima. Moreover, the position of the lowest unoccupied molecular orbitals is removed from the fluorophore moiety of citrinin in the dianionic state which is consistent with the diminished fluorescence of the toxin in basic solutions. The ionic characteristics of certain chemosensors can influence the structure and intrinsic spectroscopic properties of citrinin.     

碳纳米管制备蓝光石墨烯量子点及其在柔性有机存储器上的应用

通过化学裁剪法打开碳纳米管获得了粒径一致、性能稳定、具有蓝色荧光的石墨烯量子点。该方法属于化学溶液法，具有成本低廉、工艺简单、条件易控等优势。将该样品与半导体聚合物按一定比例混溶，通过旋涂技术形成基于石墨烯量子点掺杂的聚合物复合薄膜，进而制成柔性存储器。该柔性可弯曲存储器具有低驱动电压、接近10³的ON/OFF 比率、较好的循环次数，较好的重复性和稳定性。该研究结果为柔性有机存储器领域的研究展开了新的方向。     

喹啉-8-甲醛乙酰腙锌/镉配合物的晶体结构及荧光性质

合成并通过单晶X射线衍射、元素分析及红外光谱表征了配合物{[Zn（HL）（H₂O）（SO₄）]·H₂O}_n（1）,[Cd（HL）Cl₂]（2）和[Cd（HL）I₂]（3）的结构（HL为喹啉-8-甲醛乙酰腙）。单晶衍射结果表明,配合物1中,中心Zn（Ⅱ）离子的配位构型为扭曲的八面体,与来自1个中性三齿配体HL的ONN原子供体,1个水分子和2个μ₂桥联的硫酸根配位,从而形成沿b轴方向的一维链。配合物2和3中Cd（Ⅱ）与1个中性三齿配体HL和2个卤素阴离子（2中为氯离子,3中为碘离子）配位,配位构型为扭曲的四方锥。乙腈溶液中,配合物3与配体HL几乎无荧光发射,而配合物1和2分别在428和408 nm处有强荧光。     

NO2在黑碳表面的非均相反应

HONO是大气中OH自由基的重要来源,NO2在黑碳表面可反应生成HONO,因此NO2在黑碳表面的非均相反应引起了人们的关注。目前不同研究小组测量的摄取系数可相差7个数量级,选择不同的摄取系数去评估非均相反应的重要性将得到完全不同的结果。本文在深入分析NO2在黑碳表面反应机理的基础上,从反应体系、黑碳表面性质、反应条件等角度对不同小组测量的摄取系数存在差异的原因进行了分析,为模式中摄取系数的选取提供了依据。     

Synthesis and Characterization of Task‐Specific Ionic Liquids Possessing Two Brönsted Acid Sites

Abstract

Task‐specific ionic liquids possessing two Brönsted acid sites with –COOH, HSO^? ₄, or H₂PO^? ₄ groups have been designed, synthesized, and characterized. Under mild conditions and without any additional organic solvent, the esterification of isopropanol by chloroacetic acid could be carried out in these new task‐specific ionic liquids. In comparison with most of acidic ionic liquids in current use, these ionic liquids are halogen free and more environmentally benign as media and catalysts.     

Preparation and Characterization of Styrene/Butyl Acrylate Emulsifier-Free Latex with 2-Acrylamido-2-Methyl Propane Sulfonic Acid as a Reactive Emulsifier

A kind of emulsifier-free latex (FL) was successfully synthesized from styrene (St) and butyl acrylate (BA) with 2-acrylamido-2-methyl propane sulfonic acid (AMPS) as a reactive emulsifier. The particle size of latex particles, stability against electrolytes, minimum film forming temperature (MFT) and water contact angle (CA) were evaluated and compared with a conventional latex (CL). Test results show that FL has larger particle size, better stability against electrolytes and lower MFT value compared with CL; higher AMPS content leads to smaller particle size and smaller water CA.     

PMAA microgel surface-supported phase transfer catalyst as reusable microreactors for ultra-deep desulfurization

The reusable microreactors, poly(methacrylic acid) (PMAA) microgels surfacely covered with 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM) and K₂{W(=O)(O₂)₂(H₂O)}₂ (W2) complexes, have been synthesized by using an ion exchange reaction between AEM located on PMAA microgels and W2 in aqueous solution. The final composite microspheres and intermediate products are characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectrophotometer, and thermogravimetric analysis, respectively. The results indicated the PMAA/AEM/W2 composite microspheres with surface-wrinkling morphology and core-shell structure. The feasibility of the composite microspheres used as reusable microreactors in catalytic oxidation of dibenzothiophene (DBT) was investigated. Additionally, the effects of some factors, including the amount of the microreactors, temperature, H₂O₂/DBT molar ratio, the loaded amount of AEM, DBT concentration, and recycling times, on the catalytic oxidation were examined. The results demonstrated that the prepared composite microspheres possess high catalytic performance and reusability in the catalytic oxidation of DBT.