Theoretical Studies on the Binding Mode and Reaction Mechanism of TLP Hydrolase kpHIUH

In this work, we have investigated the binding conformations of the substrate in the active site of 5-HIU hydrolase kpHIUH and its catalytic hydrolysis mechanism. Docking calculations revealed that the substrate adopts a conformation in the active site with its molecular plane laying parallel to the binding interface of the protein dimer of kpHIUH, in which His7 and His92 are located adjacent to the hydrolysis site C6 and have hydrogen bond interactions with the lytic water. Based on this binding conformation, density functional theory calculations indicated that the optimal catalytic mechanism consists of two stages: (1) the lytic water molecule is deprotonated by His92 and carries out nucleophilic attack on C6=O of 5-HIU, resulting in an oxyanion intermediate; (2) by accepting a proton transferred from His92, C6–N5 bond is cleaved to completes the catalytic cycle. The roles of His7, His92, Ser108 and Arg49 in the catalytic reaction were revealed and discussed in detail.     

Pure Ion Chromatograms Combined with Advanced Machine Learning Methods Improve Accuracy of Discriminant Models in LC–MS-Based Untargeted Metabolomics

Untargeted metabolomics based on liquid chromatography coupled with mass spectrometry (LC–MS) can detect thousands of features in samples and produce highly complex datasets. The accurate extraction of meaningful features and the building of discriminant models are two crucial steps in the data analysis pipeline of untargeted metabolomics. In this study, pure ion chromatograms were extracted from a liquor dataset and left-sided colon cancer (LCC) dataset by K-means-clustering-based Pure Ion Chromatogram extraction method version 2.0 (KPIC2). Then, the nonlinear low-dimensional embedding by uniform manifold approximation and projection (UMAP) showed the separation of samples from different groups in reduced dimensions. The discriminant models were established by extreme gradient boosting (XGBoost) based on the features extracted by KPIC2. Results showed that features extracted by KPIC2 achieved 100% classification accuracy on the test sets of the liquor dataset and the LCC dataset, which demonstrated the rationality of the XGBoost model based on KPIC2 compared with the results of XCMS (92% and 96% for liquor and LCC datasets respectively). Finally, XGBoost can achieve better performance than the linear method and traditional nonlinear modeling methods on these datasets. UMAP and XGBoost are integrated into KPIC2 package to extend its performance in complex situations, which are not only able to effectively process nonlinear dataset but also can greatly improve the accuracy of data analysis in non-target metabolomics.     

Complexation and redox chemistry of neptunium,plutonium and americium with a hydroxylaminato ligand

There is significant interest in ligands that can stabilize actinide ions in oxidation states that can be exploited to chemically differentiate 5f and 4f elements. Applications range from developing large-scale actinide separation strategies for nuclear industry processing to carrying out analytical studies that support environmental monitoring and remediation efforts. Here, we report syntheses and characterization of Np(iv), Pu(iv) and Am(iii) complexes with N-tert-butyl-N-(pyridin-2-yl)hydroxylaminato, [2-(^tBuNO)py]⁻(interchangeable hereafter with [(^tBuNO)py]⁻), a ligand which was previously found to impart remarkable stability to cerium in the +4 oxidation state. An[(^tBuNO)py]₄ (An = Pu, 1; Np, 2) have been synthesized, characterized by X-ray diffraction, X-ray absorption, ¹H NMR and UV-vis-NIR spectroscopies, and cyclic voltammetry, along with computational modeling and analysis. In the case of Pu, oxidation of Pu(iii) to Pu(iv) was observed upon complexation with the [(^tBuNO)py]⁻ ligand. The Pu complex 1 and Np complex 2 were also isolated directly from Pu(iv) and Np(iv) precursors. Electrochemical measurements indicate that a Pu(iii) species can be accessed upon one-electron reduction of 1 with a large negative reduction potential (E_1/2 = −2.26 V vs. Fc^+/0). Applying oxidation potentials to 1 and 2 resulted in ligand-centered electron transfer reactions, which is different from the previously reported redox chemistry of U^IV[(^tBuNO)py]₄ that revealed a stable U(v) product. Treatment of an anhydrous Am(iii) precursor with the [(^tBuNO)py]⁻ ligand did not result in oxidation to Am(iv). Instead, the dimeric complex [Am^III(μ₂-(^tBuNO)py)((^tBuNO)py)₂]₂ (3) was isolated. Complex 3 is a rare example of a structurally characterized non-aqueous Am-containing molecular complex prepared using inert atmosphere techniques. Predicted redox potentials from density functional theory calculations show a trivalent accessibility trend of U(iii) < Np(iii) < Pu(iii) and that the higher oxidation states of actinides (i.e., +5 for Np and Pu and +4 for Am) are not stabilized by [2-(^tBuNO)py]⁻, in good agreement with experimental observations.

The coordination modes and electronic properties of a strongly coordinating hydroxylaminato ligand with Np, Pu and Am were investigated.Complexes were characterized by a range of experimental and computational techniques.     

软珊瑚Sinularia sp.中次生代谢产物的结构鉴定

细胞毒性;软珊瑚Sinularia sp.中次生代谢产物的结构鉴定     

Ti接枝MCM-41催化剂的结构设计及化学亲和选择性研究

 用二氯化钛茂作为活性物种的来源，利用Si－MCM－41催化剂表面羟基的反应性，得到了Ti接枝MCM－41催化剂的两种结构模型．结构表征结果表明，Ti接枝MCM－41催化剂不仅长程结构好，孔径分布均一，而且催化剂表面活性中心含量高．两种结构模型催化剂上芳烃羟化反应性能表明，Ti接枝MCM－41催化剂表面的亲水／憎水性可以在较宽的范围内调变，从而可实现控制芳烃羟化的化学亲和选择性．另外，研究结果还表明，Ti接枝MCM－41催化剂具有很好的活性稳定性．     

Optical properties of nanocrystalline Y2O3:Eu depending on its odd structure

The structure of nanocrystalline Y2O3:Eu prepared by a combustion reaction was analyzed by XRD and high-resolution electron microscopy. Compared with a large-scale particles, 5-nm Y2O3:Eu particles presented as distorted crystallite and rough surfaces. Luminescent and absorption properties of nano-Y2O3:Eu showed remarkably particle size effects. At Y2O3:Eu particle sizes smaller than 10 nm some new results were observed: (a) a red shift of the charge-transfer-state absorption; (b) new emission bands of Eu3+ in the 5D0 --> 7F2 region; (c) luminescent decay of energy level 5D0 of Eu3+ turning to a two-step exponential; and (d) a pronounced increase in quenching concentration and much lower phonon density compared with those of the bulk material. All these phenomena can be attributed to the effect of the softened lattice and surface state of the nanomaterial. The latter was confirmed by stronger excitation by the host absorption after the surface modification.     

不同剂型药用抑肽酶纯度的胶束电动毛细管测定

 以十六烷基三甲基溴化铵 (CTAB)为阳离子表面活性剂 ,用胶束电动毛细管 (MECC)分别对抑肽酶粉针剂和抑肽酶注射液进行纯度测定。实验中选择了最佳缓冲液 (含 4mmol/LCTAB的 80mmol/LNa2 HPO4 H3 PO4,pH 7 0 0 ) ,考察了进样量与样品中高浓度盐对分离的影响。并对毛细管区带电泳、MECC和高效液相的分离效果加以比较 ,表明MECC的分离效果最佳。     

S-亚基谷胱甘肽对亚油酸过氧化和苯乙烯聚合的抑制作用的研究

研究了S－亚硝基谷胱甘肽（GSNO）对偶氮二异丁腈(AIBN)引发亚油酸过氧化 和苯乙烯聚合的抑制作用。GSNO的抑制作用可能归结为反应中生砀氮氧自由基的抑 制活性。EPR证据表明,含有AIBN和GSNO的DMSO溶液在无氧和50 ℃下,生成了谷胱 甘肽巯基,2－氰基－2－丙基氮氧自由基。