基于混酸回流制备碳点的中和过程

Carbon dots (C dots) are relatively novel carbon nanomaterials that have attracted significant interest due to their unique photoluminescence, good biocompatibility, and stability. The preparation methods of C dots was usually summarized into "top-down" and "bottom-up", and mixed acid reflux is a top-down strategy that can be used to synthesize C dots, during which neutralization is a necessary step that can significantly influence the properties and potential applications of the final product. Previously, this research area mainly focused on tuning the properties of C dots by changing the starting materials and/or varying the reaction conditions; the influence of the reagents used during neutralization has been largely ignored. As the previously reported C dots prepared by mixed acid reflux were obtained from different starting materials under varied conditions, a meaningful comparison is difficult. Herein, yellow-emitting C dots were prepared by mixed acid-refluxing a carbon-rich material derived from fullerene carbon soot. For the same batch of as-prepared C dots, the influences of four reagents, i.e., NaOH, Na₂CO₃, K₂CO₃, and NH₃·H₂O, during neutralization on the structures and photoluminescence of the resulting C dots were investigated in detail. The results of thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy clearly showed that the reagent used during neutralization can affect the degree of dissociation of the acidic functional groups on the C dots. This is further supported by examination of the C dot/surfactant mixtures where subtle changes in the phase behavior were observed. Structural changes of the C dots cause variations in their surface states, ultimately altering the optical characteristics, including UV-vis absorption and fluorescence. Among the treated C dots, the sample prepared with Na₂CO₃ showed the strongest emission under the same excitation wavelength, while that prepared with NH₃·H₂O exhibited a distinct red shift (~8 nm) in the emission curve. The results presented herein provide clear evidence that neutralization reagent selection is important for optimizing the properties of the resulting C dots obtained by mixed acid reflux. In addition, the photoluminescence of the C dots can be influenced by their counterions, providing a novel method for tuning the properties of C dots while explaining their behavior in saline solutions. In short, the basicity of the neutralizing reagent and the type of counterions affect the structure of the C dots surface, which brings different performances. This work reminds researchers that it is necessary to use the type of neutralizing reagent as an experimental condition when preparing C dots in the future.     

蛋白质高效分离两维色谱柱的选择优化

为了构建高效的离子交换/反相二维液相色谱(IEC/RPLC)分离平台系统,提高复杂蛋白质样品的分离效率,对色谱柱进行了评价与筛选。通过对实际人肝蛋白质样品的分离效果的比较,选择确定了TSKgel DEAE-5PW弱阴离子交换色谱柱(WAX)作为第一维色谱分离柱;考察了同一规格的10支代表性反相色谱柱(250 mm×4.6 mm, 5 μm, 30 nm, C4、C8或C18),通过评价其对尿嘧啶、硝基苯、萘和芴的分离性能以及对3种标准蛋白质样品的非特异性吸附、对人肝蛋白质样品的WAX馏分的分离效果,最终确定以Jupiter 300 C4反相色谱柱作为第二维色谱分离柱。对两维色谱柱的选择优化为蛋白质高效分离二维液相色谱平台的搭建提供了可靠基础。     

Dynamics of excited states in nanoscale materials

This tutorial provides a broad perspective on the synthesis, characterization, and size-dependent dynamics of nanoscale materials. Synthetic strategies include bottom-up, top-down, and hybrid strategies in gas and condensed phases. Advances in imaging and structure analysis provide the spatial information to correlate dynamic phenomena to structure in complex nanocomposites. Excited-state dynamics can change with material dimensions due to changes in the properties of the host and due to unique nanoscale phenomena such as plasmon resonance in metals and quantum confinement in semiconductors.     

Uncertainties of gas chromatographic measurement of troublesome pesticide residues in apples employing conventional and mass spectrometric detectors

In recent years the declaration of estimated uncertainty of measurement has become an integral part of analytical results. This study presents the assessment of results generated within the analysis of selected pesticides represented by carbamates, pyrethroides and azoles, residues of which may be found in treated apples. Multiresidue method used for analysis of spiked samples (residues at levels 0.040–0.163 mg/kg) consisted of (i) ethyl acetate extraction, (ii) GPC clean-up and (iii) identification/quantification of residues by GC. Procedures utilizing either conventional (electron-capture, nitrogen–phosphorus) or mass-selective detectors (quadrupole and ion trap analyzer) were evaluated. The results generated through alternative strategies of uncertainty estimation (“bottom-up”, “top-down”) were compared.

Using the “bottom-up” approach uncertainty of extraction which comprises two components—(i) repeatability of extraction and (ii) uncertainty of extraction recovery was shown to represent the main source of combined standard uncertainty (values of uncertainty of extraction for tested pesticides ranged from 4.6% to 21.6%). On the other hand, uncertainties associated with the GC calibration (uncertainties of weighing and diluting standards, uncertainties of purity of standards) were not so important (most of them did not exceed 2%). Combined standard uncertainties associated with the described analytical method ranged for individual compounds from 9.3% to 24.3%. Similar values of combined standard uncertainties were obtained using the alternative “top-down” approach.     

Contour level object detection with top-down information

This paper presents a contour level object detection approach. In contrast to conventional bounding box results, we give out the salient closed contour of the object, which provides a possibility of semantic analysis for the object. We get the salient closed contour with Ratio Contour algorithm. The top-down information needed by salient closed contour extraction is based on the well-known Bag-of-Features methodology. Our top-down information based contour extraction and completion is much more efficient and robust than many related approaches lack of the top-down information. We also propose a novel post-processing framework for object detection. With low threshold and a refined binary classifier, we can get stable high performance. We evaluate our approaches on UIUC cars dataset. We show that our approaches apparently improve the performance of object detections under clutter.     

Comparison of different approaches to estimate the uncertainty of a liquid chromatographic assay

A measurement result cannot be properly interpreted without knowledge about its uncertainty. Several concepts to estimate the uncertainty of a measurement result have been developed. Here, four different approaches for uncertainty estimation are compared on the example of the RP-high-performance liquid chromatography (HPLC) assay for tylosin for veterinary use: the guide to the expression of uncertainty in measurement (GUM) approach, which derives the uncertainty of a measurement result by combining the uncertainties related to the uncertainty sources of the measurement process; the top-down approach, which uses the reproducibility estimate from an inter-laboratory study as uncertainty estimate; an approach recently presented by Barwick and Ellison, which combines precision, trueness and robustness data to obtain an uncertainty estimate of the measurement result and finally a further approach, which directly estimates the measurement uncertainty from a robustness test. The comparison shows that the different approaches lead to comparable uncertainty estimates.     

不同电荷态泛素蛋白离子的193 nm紫外光解离质谱

将193 nm激光与傅里叶变换离子回旋共振(FT-ICR)质谱仪结合, 研究了不同价态的泛素蛋白离子的紫外光解离质谱. 结果表明, 在光解离过程中向分析池内引入适量的碰撞气, 不仅能增加母体离子的裂解率, 也能提高碎片离子的捕获效率. 相对于碰撞辅助解离(CAD)中产生的b和y离子, 紫外光解离(UVPD)方法能够产生更为丰富的不同种类碎片离子. 其中, 对于+11价泛素离子, 蛋白质序列的覆盖率接近80%, 远高于对应的CAD实验结果. 与已往报道不同的是, 裂解覆盖率呈现出较强的电荷相关性. 因此, 如何进一步提高较低电荷态的蛋白离子的解离效率和序列覆盖率还需深入研究.     

自上向下的合成策略:最大程度提高贵金属的原子利用率

因为贵金属的价格比较高,并且很多催化反应主要发生在载体和金属接触的周围原子,所以减少贵金属的粒径对于提高金属原子利用率是非常可取的.原子利用率的最高极限就是形成单原子催化活性中心,然而合成稳定的单原子金属催化剂是一个巨大的挑战,因为单原子金属极易聚合成较大的金属颗粒.尽管存在着很大的困难,合成稳定的单原子金属还是可能的.研究表明,单原子金属容易镶嵌在表面能量最高的活性位上,以降低金属和载体的总能量,使之达到最稳定状态.随着金属的负载量增加,以此单原子金属为"晶种"将形成金属纳米粒子.根据这一原理,我们通过简单热扩散方法在HMO表面把Ag纳米粒子"拆分"成单个的Ag原子,并稳定地镶嵌在由HMO四个氧形成的空穴上(HMO的孔道口),使体系的能量降到最低.我们通过原位X射线衍射(XRD)、扩展X射线吸收精细结构光谱(EXAFS)和电子显微镜照片(TEM)详细证明了这种自上而下的合成过程,并通过X射线吸收近边结构光谱(XANES)、氢气程序升温还原(H2-TPR)、CO吸附实验等表征手段和理论计算说明了诱导这一过程的原因.首先我们合成了具有高比表面积的Hollandite型二氧化锰(HMO)纳米颗粒,并且在上面负载纳米银颗粒.TEM数据表明经过焙烧纳米银颗粒消失,形成单原子分散在HMO表面.原位XRD的结果表明随着焙烧温度的升高,银颗粒的衍射峰强度逐渐降低,最后消失,说明纳米银颗粒随着温度的升高逐渐减少,最后达到银高分散的状态.通过对Ag(111)衍射峰强度进行分析,我们发现当温度低于150 oC时,Ag(111)衍射峰强度基本保持不变,说明银颗粒没有变化.当温度高于150 oC时,Ag(111)衍射峰强度开始减小,并且减小的程度随温度的升高而变大.当温度高于260 oC时,Ag(111)衍射峰消失.为了更好的研究这个过程,我们分别在150,200,350 oC焙烧银颗粒的样品,并测试了它们的EXAFS谱.结果表明随着焙烧温度的升高,银和银之间配位数减小,意味着银颗粒的减小.350 oC焙烧样品的EXAFS谱在银原子散射的0.28–0.30 nm范围内没有吸收峰,说明银原子在HMO表面高度分散.然后我们通过XANES谱和理论计算证明了银和载体表面晶格氧的相互作用导致银的前线轨道的电子重新发生排布,从而诱导了整个自上向下的合成过程.最后活性测试表明,单原子银催化剂在甲醛催化氧化中表现出最好的催化活性,并简单研究了单原子催化氧化甲醛的机理.因此这种合成策略有两个重要的作用:(1)增加催化活性位的数量;(2)单原子催化剂的合成有利于催化反应机理的研究,比如甲醛催化氧化.     

A top-down method for the determination of residue-specific solvent accessibility in proteins

We present a method employing top-down Fourier transform mass spectrometry (FTMS) for the rapid profiling of amino acid side-chain reactivity. The reactivity of side-chain groups can be used to infer residue-specific solvent accessibility and can also be used in the same way as H/D exchange reactions to probe protein structure and interactions. We probed the reactivity of the N-terminal and epsilon-lysine amino groups of ubiquitin by reaction with N-hydroxysuccinimidyl acetate (NHSAc), which specifically acetylates primary amines. Using a hybrid Q-FTMS instrument, we observed several series of multiply acetylated ubiquitin ions that varied with the NHSAc:protein stoichiometry. We isolated and fragmented each member of the series of acetylated ubiquitin ions in the front end of the instrument and measured the fragment ion masses in the FTMS analyzer cell to determine which residue positions were modified. As we increased the NHSAc:protein stoichiometric ratio, identification of the fragments from native protein and protein with successively increasing modification allowed the assignment of the complete order of reactivity of the primary amino groups in ubiquitin (Met 1 approximately Lys 6 approximately Lys 48 approximately Lys 63>Lys 33>Lys 11>Lys 27, Lys 29). These results are in excellent agreement with the reactivity expected from other studies and predicted from the known crystal structure of ubiquitin. The top-down approach eliminates the need for proteolytic digestion, high-performance liquid chromatographic separations and all other chemical steps except the labeling reaction, making it rapid and amenable to automation using small quantities of protein.     

利用原子力显微镜探针的扫帚机理制备胶原蛋白纳米纤维阵列

利用原子力显微镜能够在微观尺度上对样品材料进行操控和加工的特性,发现并考察了一种自上而下的生物大分子纳米纤维阵列的制备方法。将50μg/mL的天然I型鼠尾胶原蛋白溶液在云母晶面上形成胶原蛋白膜层,接着在原子力显微镜的接触模式下,利用探针对溶液中的胶原蛋白膜层施加100~1000 nN的力时,可以将膜层加工成具有特定取向的蛋白纳米纤维阵列。单根纤维的高度约2~5 nm,宽度在150~350 nm之间。根据纳米纤维阵列的结构与探针扫描方式的关系,对探针的制样原理进行了探讨,验证了原子力显微镜接触模式下的“分子扫帚”机理。此制备方法为生产细胞培养器皿、制备高特异性的生物探针,合成新型微纳材料提供了一种可行技术。